bullet bases

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Ross Smith posted this 10 December 2019

After reading a little by Dr. Mann and Harry Pope about bullet bases it brought back some of my worries about bullet bases. Not just Pope and Mann, but several experts have stated the bullets base to be the most important part. They were even arguing that the small amount of lead displaced by the lands causing small fins on the edge of the bullets base to alter the point of impact. Now these guys were probably concerned about .01" or less which is enough to win some matches. But how does that effect us mortals?

I've often wondered about gas checks that don't go on straight. Not just the really ugly ones but also the ones you need a small square to see the the bullet tip when stood on its base. While I was lube sizing several hundred noe 165gr fp bullets and not really trying for match quality bullets , I was getting quite a few crooked gas checks, some would not even stay on the bullet. So the light bulb flashed on. I sorted out 10 really bad ones, the ones you recycle into the pot. Some of these would not even stand up. Very crooked. Then I got out my small machinist square and sorted thru the bullets to come up with 10 that were very square to the world. These 2 groups were loaded over 20 gr R7(my load my fingers) in 30-06 mixed headstamp cases. I also took 10 30-06 cases loaded the same but with noe xcb bullets, my normal load. The xcb were my control and the other 2 groups were the experiment. The xcb went inot 2" out of a cold barrel. ED's red wiped thru the barrel then shot my 10 good 30-30 fn bullets. 4". I didn't expect much and was actually pleased with 4", after all no load developement. Next came the really bad bullets, 4". No effect, at leasdt in this under funded experiment. So ther goes my excuse for those wild fliers that miss the whole target.

What say you all?

just-one-of-my-quandries

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Tom G posted this 22 December 2019

Guys,

Whether or not you accept and shoot wrinkled or rounded base bullets is a personal thing. The important thing is to not cast them in the first place.

A couple of weeks ago I made a long casting run to replenish my supply of 40 cal bullets that my son and I shoot in Action Pistol practice. Between the two of us we can shoot 200 a week when the weather is nice. Since I load for him too, I try to cast as many good bullets as fast as I can. One thing I try to avoid is casting bullets with rounded bases and or wrinkles. This last run was one of the best casting runs I've had in a long time. I cast 898 bullets in a little over an hour and rejected 38 for visual defects. One of the things I did to get good bullets right off the bat was to pre heat the molds. I started casting good bullets right off the bat because my alloy and molds were right up to casting temperature when I started.

Long ago,I bought two electric hot plates for about 12 bucks apiece. I use them to pre heat my molds. If you start out with a mold that is already up to temperature your chances of casting wrinkles is very low. I found that with six cavity Lee aluminum mouds, if I set the temp. control to about 3/4 scale, it will bring my molds up to casting temp. in about 15 or 20 minutes. When I make my first cast, I have to wait for the sprues to solidify before striking off the sprue plate. If the molds are hot enough they will cast nicely filled out bullets that are a little frosty looking the first cast. While the molds are heating up, I also let the two pots that I use heat up too. After some playing around, I know what temp to set the pots to to get the frosty bullets I'm looking for. If they come out shiny, I up the casting temp or cast faster.

Another reason you can get wrinkled bullets is a contaminated mold cavity. I had a friend who was in the commercial bullet making business. I used to do his tool and die work for him maintaining his automatic casting machines. Whenever he saw a cranky mold, he would pull it and clean it out in an acid bath. Then it would run fine again.I started doing that to my cranky molds and it eliminated the problem in most cases. Cavities can become contaminated from a lot of things but is you are careful to clean them before the start of a casting run, chances are they will run for a couple hundred casting cycles or more before having a problem.

I clean my molds almost every time before I start casting. I use a kitchen cleaner powder that contains oxalic acid. There are two brands that are sold locally here in Southern Michigan. One is called Barkeepers Friend and the other is called Zud. They contain a mild acid that will help eat away the junk that builds up in your mold. I clean them in the kitchen sink using a tooth brush and very hot water. I also clean out and open up any vent lines that look suspicious. The hot water helps the aluminum molds to dry quickly. So, when I start, my molds look like new at the beginning of each casting session. They don't require any seasoning or breaking in after doing the acid clean. They cast good bullets right off the bat when they come off the hot plate.

Using two 6 or 5 cavity moulds alternately at the same time, I can soon outrun a Lyman 20 lb. bottom pour pot. What I do is pre melt more alloy in a Lee 20 lb. dipper pot and ladle it into the Lyman pot if it gets below half full. Again, you have to play around with the pot temp. controls to get them both at the same temp. By throwing the sprues into the Lyman pot, I can make a pretty Long casting run with this method. This method and using a consistent casting rate will keep the bullets from wrinkling or making rounded bases.

If I need to stop to make an adjustment to a mold or the pot, I put the molds back on the hot plate till I'm ready to go again and they resume casting good bullets right off the start..

Having your lead nice and clean makes a big difference. I usually flux it twice as a minimum. Marvelux is a great product. It not only fluxes well but it encapsulates the dross to keep it from getting into the air you breathe. If you look at the color of it before you skim it off, you can see how dirty it is. When you flux to the point that it stays fairly clean, you have some nice clean lead. Also, I'm very careful when I lube the sprue plate pivot and alignment pins to not let lube gravitate into the mold cavities. If that happens, you have to stop and clean it or accept bad looking bullets.

As an inveterate experimenter with cast bullets, I recently acquired a Ransom Rest. It cost me $400 plus two bags of shot to sweeten up the deal. I feel confident enough using it to work up loads for my pistols and revolvers. When I get through with it, I may sell it to another experimenter. After a casting run for my 9MM FN Browning Hi Power, I saved the bullets that had visual flaws. Once I find an accuracy load for the good bullets, I plan to shoot the rejects and compare them with visually good bullets for accracy. When I do, I'll report the findings to this group.

In the meantime, I'll continue to re melt defective and wrinkled bullets as it only takes a few seconds to re melt them and they have a 99% chance of coming out just fine on the next casting. One nice thing about casting bullets is that you have zero scrap if you do this.

Life's too short to shoot wrinkled bullets !!!

Tom Gray

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Ken Campbell Iowa posted this 12 December 2019

about " square " bases ... back when i was trying to get my sporter rifles under 2 moa with cast, ..... having tortured my way through Mann's book a couple times ... and read a few articles on Pope and even got to,play with a Pope 32-40 muzzle starter system ( with Pope mold ) , remembering the trouble he took to have a fitted bullet and his comments on bases ...

having determined that the first rule ( bullet snug in the throat ) was to be obeyed first thing ...

i fantasized that the base was the magic key to the last 1 moa ... so i dedicated ~800 rounds of pretty good castings with and without lathe collet turning the bases .. the idea was that would be the only difference in fit and basic form ..... Joeb is right, :: 800 ain't enough ... but there was a strong hint that better bases shoot better ... normalized bases gave me the only 10 shot groups under 1 moa with sporter rifles. but the magic trick failed to turn my pretty good castings into under-1.5 moa consistently ... btw, i used commercial all Taracorp Magnum alloy, not hardened. great stuff.

interesting that half the bases were turned 90 degrees flat ... and half were turned with a large bevel base ... both shot the same ... yes, all used the old lyman checks ... even the bevel based ones ... you would think those would distort unevenly and groups would enlarge... but they didn't seem to be worse.

also through those guns with the same starter castings, i made several swagers ... mainly to square the base y checks .. and they also showed slight improvement .. but of course the whole bullet was re-formed during the swaging, so several variables were changed.

the above was through factory sporter barrels, even 2 moa cast groups required some load development, and a bit of luck. those factory sporters would shoot under 1 moa with mj bullets.

and yes lathe turning bases is tedious ... but you can try different cuts on different bullets. the squisher tool is a better answer once you determine what works.

*************

so today for my plinking level loads, i cast scrap, obey rule 1 ( snug in the throat ) and visibly check and remelt any terrible base castings ... the nose is much less critical ... no gas check and about 1100-1300 fps... i expect a max of 3 moa for plinking and can usually get there ... eventually .

if i were shooting group competition, i would definitely normalize the bases.

ken

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Dale53 posted this 12 December 2019

Due to vision problems, I no longer compete in cast bullet matches. However, since it is relatively easy to produce near perfect bullets, why would I want to cast imperfect ones? When using gas checks, I simply used a gas check seater to make sure they were seated perfectly. Easy-peasy!

These comments can be taken as confrontational. That is not intended at all. What I would like to do is to simply encourage anyone who is casting bullets to set high standards for themselves, and often with a change in attitude, comes near perfection!

The act of positive thinking...

FWIW

Dale53

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Tom G posted this 11 December 2019

Ross,

Out of square bullet base will definitely cause fliers. But not fliers that will miss the target. About 6 or 8 yrs. ago I decided to find a good cast bullet load that would shoot in my AR-15 house and bug-out gun. I shot hard water dropped bullets and had a load that shot an average of 1.25" at a hundred yards. I tested it against a load made up of jacketed FMJ bullet that were just blasting quality and fairly cheap. The cast load beat out the jacketed load. by a small amount.

Later, my brother decided to work up a cast load for his AR and eventually sent me some bullets he had cast and shot in his gun. I shot them in my gun and got unexplained fliers. They maybe doubled or tripled the group size. They were in the range of 4 inch groups. I got to looking at his bullets and when sitting them up on their bases, I could see the gas checks were on slightly crooked. They definitely caused fliers.

Perhaps your groups are so large at 4" that the fliers don't make them any larger than the groups without fliers. Maybe if you worked up a load that was accurate, you would see the difference. Following Dr, Mann's lead, you might try taking the crooked gas check bullets and orienting them in the chamber so that the out of squareness was in the same direction for all the bullets. Maybe they would shoot to a group!! Seems to me that Mann did the same type test with plain base bullets.

When I was shooting CBA benchrest, I always bumped my bullets in a bump press. This was for two reasons. First to make the bullet the exact same shape as the tapered chamber throat in the gun and make the rear driving band a couple of tenths larger so I would have slight interferance fit when I chambered them. This also formed the gas check flat and square on the bullet. Having a friend who was a tool and die maker, I had him take a couple to work with him and measure the base squareness on an optical comparator. He reported back that the samples that I had bumped were "dead nuts Square". These bullets would routinely shoot around a half inch at 2500 fps. Knowing that the edge of the gas check was a critical factor to accuracy, I bumped them just hard enough to flatten the base but not remove the round edge of the gas check. These were tapered bullets seated into a tapered throat.

My bump press was adjustable for the amount of bump and had an ejector built into it. The bump die was made from the same throater reamer that I used to throat the chamber throat in the gun. I purposely designed the throater to make a .309 throat diameter into a half degree per side taper on the lands. Thus the bullet fit the throat like a morse taper. It also sealed in the back end to stop any gas from flowing past the bullet and damaging the bullet or knocking the lube off the bullet. Bumped bullets were .3093" into a .3090" throat. and were seated way long with just the base of the bullet in the case neck. This allowed the bullets to be oriented straight to the rifling because the chamber throat held the bullet straight and hot the case neck.

One of my deceased prairie dog shooting buddies was a retired scientific type. His I Q was measured over 165. At one time he worked on and off a bunch of government projects. One was to develop a nuculear artilliary shell. The shell had a nuclear warhead and had a rocket motor attached to the base of the projectile. The rocket motor was timed to fire off near the top of the trajectory curve and propel it about 5 times further than normal. This shell had serious accuracy problems. As a result they determined that the edge of the base of the shell was being eroded by the rocket blast. The fix was to implant a ceramic ring to form the edge of the base of the bullet and hold up to the heat generated by the rocket blast. It shot accurately when they did that.

Tom G.

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Shopdog posted this 14 December 2019

It only matters,if it matters.

If the load and rig are in tune,and you have better than average,very clean bases, along with a good "driver" you may not see much gain in obsessing over it. But go outside "normal" for cast boundaries and it can turn a load around. I mill bases on a BP in fixturing that does 5 bullets at a time,in.... and with less effort than it takes to write this post. Again,depending on the rig/load/tune.... it can turn a 1 moa load into bugholes. My work is centered around killing varmints. 3 and 5 shot,DAILY.....rain or shine ragged hole groups at starting JB velocity is what I not only strive for but,honestly is what it takes in the field if you really want to "get after it". I'm not into reans of statistical data which is why I don't post more. Good luck with your project.

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John Carlson posted this 10 January 2020

Temperatures in single digits, winds occasionally over 40 mph, let's just talk about shooting for a bit longer

John Carlson. CBA Director of Military Competition.

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Squid Boy posted this 11 December 2019

I use a lot of M198 duplex ammo and even some experimental quad bullet stuff while in the Army. Both had angles built into the last bullet in the stack. I believe the angle was 4% and it opened that last bullet so as to hit about 10 inches off center. It seemed like a good idea but the individual bullets were pretty light and easily deflected. I would say your results are unusual and there could be other factors at play. My experience is the better the base, the better the shooting. Thanks, Squid Boy

"Squid Pro Quo"

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RicinYakima posted this 11 December 2019

John wrote; "I have also found bases skewed up to 2 degrees (easily seen) increased my groups from average of .96" to 1.28". 1.28" not good to win many CBA matches but still good enough for any practical use."

And that is the crux of the issue, for me. When I am prepping for a 120 round match I make about 200 bullets. When all finished the VISUAL best 120 go into the match boxes, but the others are foulers (well barrel warmers) and sighters. Foulers go into the dirt, but the sighters will almost always go into the group so are used for sight changes.

Making bullets for the 30/40 for walks in the sage brush to shoot varmints, vermin and rock buffaloes, don't get much of an inspection, because it is hit or miss. Part of the adventure is having bullets I made myself to shoot, but another is making the "best" that it is possible to make. John has convinced me that much of the OCD things I do for match bullets is just to make me feel good, and is seldom seen on the targets.

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max503 posted this 13 December 2019

I've often wondered if the pressure of firing would seat a crooked gas check.

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45 2.1 posted this 13 December 2019

I've often wondered if the pressure of firing would seat a crooked gas check.

Indeed it does. Tests involving intentionally crooked seated Hornady gas checks show a raised portion of lead above the gas check on the part that isn't fully seated on the bullet shank. All recovered bullets in the tests showed this and all gas checks were flat on the bullet base.

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Tom Acheson posted this 13 December 2019

Unless I missed it, this discussion is focused on bullets that will eventually have gas checks applied to them.

The guys who shoot Black Powder Cartridge Rifles, typically use single cavity molds for large—dia. and weight—-bullets. These are plain base bullets, the match rules exclude the use of gas checks. The first step of bullet quality evaluation is squareness of the base. You can see it after swinging the spruce plate over and before you open the mold halves. Mold fill-out can be immediately seen. If there is any “roundness” to the edge of the base, the bullet is rejected.

Has there been extensive testing to explore the benefits of square vs. unsquare plain base bullets? Maybe but so far I’ve not seen reports of this kind.

Admiitedly the muzzle velocity of these rounds are quite a bit slower than the benchrest match loads being discussed here.

It would be interesting to see what the CBA match shooters in the PBB (Plain Base Bullet) Gun category/class think about the need for absolute square bases. Since they cannot use gas checks, they need to limit their muzzle velocity. Is an absolutely square base a must for accuracy?

Tom Gray got me hooked on the use of a bump die/press (back in 1997) and everything I’ve loaded over the years since for CBA match use, has been cycled through a bump die. I agree with the benefits of bumping that Tom outlines here.

Tom

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joeb33050 posted this 22 December 2019

hoch filed base big.jpg To see if damaged bases affected accuracy, I took a box of 18 Hoch bullets for the 32/35 Maynard, and made one file pass across the bases at about 45 degrees. This filed a flat defect on the bases, readily seen.

2/23/05 12/IMR 4227, Rem 2 1/2, breech seated, multiple cases, Model 1882 Maynard No. 16 in 32/35, Iron Sights, Hot and plenty of mirage. 100 yards, 5-shot group with perfect base bullets, then 5-shot group with damaged base bullets-alternating for 3 groups each.
Group Sizes:
Perfect bases: 2.15", 2.20", 2.675" Avg. 2.342".
Damaged Bases: 1.2", 2.975", 2.025" Avg. 2.067"
On a good day, with one case and going carefully, this rifle has made many groups under an inch, probably averaging about 1 1/2 inches. The Irons are harder to see than ever.

Ohaus 45-405 bullets, 434.5 +/-.5 grains, Darr lubed, 21.5 grains SR4759, Dacron wad, WLP primers, breech seated, 100 yards, five shot groups, C. Sharps 45/70 Model 1875, 30X STS, Muzzle Clamp/Anti-Cant device.

45 405 filed base.jpg

A set of bullets had the bases filed at a 45-degree angle for about half the thickness of the base band. Shot 3/2/05 to see the effect of damaged bases. Windy enough to blow empty plastic ammo boxes off the bench, 70 degrees, bright sun, plenty of mirage. Alternating perfect and damaged bases.

Group sizes:

Perfect bases: 2.1", 4.3", 2.05", 3" Avg. = 2.863"

Damaged bases: 3.35", 2.675", 3.95", 2.9" Avg. 3.219"

I thought there might be lead in the barrel, couldn't find any. I read through the notebook on this rifle last night. Many 10 shot 200-yard groups under 4", many 100 yard 5-shot groups under 2", some under 1", one measured .693"-all with this load. I've used the Wolf No-Grease-Groove bullet almost exclusively in this rifle since 1993. I don't know why I'm shooting such big groups in this damaged bullet testing-but here it is.

Maybe these damaged bases caused the larger groups.

3/23/05, nice and windy, with gusts, varying from bright sun to rain showers. About 84 degrees with excellent high humidity. Martini 30/30 bench rifle, Lyman 20X STS, Wolf No-Grease-Groove 213 grain bullets with two coats of Lee Liquid Alox, 12.5/AA#9, Remington 2 1/2 primers. One hundred yards, five-shot groups, one sighter, shoot two groups, clean.

Good bases 1.1", 1.6", 1.825" Average 1.508"

Filed bases, 45 degree at the edge 1.325", 1.65", 1.075" Average 1.35"

As an aside, I also tested 311299's from a "Beagled" mold, these averaged 1.069" for four groups with the same load.

The Wolf NGG bullet has always shot adequately if not as well as other bullets in this rifle, but sometimes leads about a foot up the barrel-hence the cleaning.

This is the third test.

It starts to look like we can say that damage to the edges of bullet bases doesn't radically affect accuracy.

3/22/06 308403, Darr Lubed, Rem 2 1/2 primers, one case, 7/Unique, 30WCF M54 Winchester, 30X STS, Sandbag bench rest (Hoppes). 85 degrees, very windy, clouds then clear, very hot in the sun. 100-yard five shot groups. 26 bullets had the bases filed at a 45-degree angle to make a defect about half way up the base band. Fired about 6 sighters and stopped. Next relay (15-minute relays) fired 1 fouler, 5 filed base, 5 good bases. Next relay fired 1 fouler, 5 good bases, 5 filed bases. And so on, alternating the first group shot between filed bases and good bases.

Filed Bases 2 .375", .825", 2.4", 2.5", 2.4" Average 2.1"

Good bases 3.3", 2.55", 2.3", 2.2", 2.3" Average 2.53"

There are a lot of bullets tipping. Maybe need more powder or Dacron; I've used 7.5 grains/Unique and Dacron in the past.

This bullet generally shoots into about 1.5" averages at 100 yards. Maybe the wind, which will stop in July, when it gets REAL hot.

Again, I don't think that filed/damaged bases shoot better than good bases, the .825" group is a fluke.

3/29/06 308403, Darr with some beeswax lubed, WLP primers, 7.2/Unique weighed/dribbled, Dacron wad tamped down on powder, 30WCF M54 Winchester, 30X STS, Muzzle clamp/anti-cant device, flat bench rest. 79 degrees, slightly windy, clouds then clear, 100-yard five shot groups. 26 bullets had the bases filed at a 45-degree angle to make a defect about half way up the base band. Fired 6 sighters and stopped. Next relay (15-minute relays) fired 1 fouler, 5 filed base, 5 good base. Next relay fired 1 fouler, 5 good base, 5 filed base. And so on, alternating the first group shot between filed bases and good bases.

Filed Bases 2.55", 2.2", 1.5", 2.525", 2.85" Average 2.325"

Good bases 1.125", 1.325", 2.3", 1.275", 1.8" Average 1.565"

Most of the bullets are still tipping.

Finally, the damaged base bullets shoot larger groups than the good bases.

4/5/06 308403, Darr with some beeswax lubed, WLP primers, 8.0/Unique weighed/dribbled, Dacron wad tamped down on powder, 30WCF M54 Winchester, 30X STS, Muzzle clamp/anti-cant device, flat bench rest. 84 degrees, quite windy, clear, 100-yard five shot groups. 27 bullets had the bases filed at a 45-degree angle to make a defect about half way up the base band. Fired about 6 sighters and stopped. Next relay (15-minute relays) fired 1 fouler, 5 filed base, 5 good base, cleaned barrel with 2 patches and MM oil. Next relay fired 1 fouler, 5 good base, 5 filed base, cleaned barrel. And so on, alternating the first group shot between filed bases and good bases.

Filed Bases 2.2", 3.7", 1.95", 1.525", 1.275" Average 2.17"

Good bases 1.7", 2.0", 2.6", 1.825", 1.675" Average 1.96"

Maybe half of the bullets are still tipping.

Those shot 4/5/06 were from a lot that weighed 170.6 to 170.9 grains. I just filed the base of one out of that lot. It started at 170.8 grains. After filing it weighed 170.5 grains. The filing lost .3 grains.

4/12/06 308403 lubed with Darr + some beeswax. 11/AA#9, WLP primer, CF Ventures soft gas check, Martini 30/30 bench gun, 30X STS, muzzle clamp/anti-cant device, flat bench rest. Five shot 100-yard groups, 1 sighter and 2 groups per 15-minute relay. Bases on some bullets filed at ~45-degree angle ~ half way up the base band. It was 82 degrees and windy. How windy was it? My Gatorade plastic bottle cap blew off the bench, my gun case blew open (it was slightly open) and a set of sky screens with holder and tripod blew over twice. I have little experience with this bullet in this gun.

Six of 25 shots with both good and filed bases were tipping.

Good bases 2.725", 1.175", .625", 1.45", 1.7" Avg 1.535"

Filed bases 3.125, 2.675, 1.45", 3.45", 1.025” Avg. 2.345"

Summary to date

FILED GOOD

BASES BASES

3/22/06 2.1" 2.53"

3/29/06 2.325" 1.565"

4/5/06 2.17" 1.96"

4/12/06 2.345" 1.535"

Damaged Bullets, Distinction and Difference

After looking at forty groups fired, half with filed-base bullets and the other half with "good" = unfiled-base bullets, I've been assailed by a conclusion, to wit: Not all bullets with damaged = filed bases fly wildly to the target. The probability that any given bullet will land out of the group is greater shooting bullets with damaged bases.

I first thought that this was a distinction without a difference-it's starting to look like bullets with damaged bases make bigger groups than bullets with good bases. But I think that I see a difference.

All our bullets would go through the same hole, we think, if not for the differences that creep in amongst our loads. Differences in brass or bullet or powder or primer or bore condition or weather or any of the dozens of variables. These differences, some or most of us suspect, yield shots outside the group. And my assumption, shared, I think with others, is that if we assembled and shot a set of loads, all with a given difference, the groups would be larger than if that difference were not present. And we suspect that that is true because the differences make the bullets fly out of the group.

Now all bullets with damaged bases do not fly out of the group, some of them fly into very nice groups and others fly into nice four-shot groups with a flyer, or three shot groups with two flyers, or....

Since the filed-base groups look to be larger, probably bullets with damaged bases make larger groups on average than do bullets with good bases. Think of two normal-looking overlapping distributions.

This is where I get stuck. A bullet with a forty-five-degree filed surface for about half of the height of the base band should fly to a different place than an unfiled bullet. And with no specific orientation of the bullet with the bore, these filed-base bullets should make a "big" group. There are any number of folks who can explain why these bullets should make these big groups. They do make bigger groups, on average, I think. But, why are some filed-base groups smaller than good base groups? Why doesn't every filed-base bullet fly out of the group? Why is this a probabilistic process? If damaged bullet bases cause the bullet to fly out of the group, why doesn't every damaged base bullet fly out of the group?

A cartridge without a primer doesn't go off, and it doesn't go off every single time. There's no business about it doesn't go off 96% of the time, it doesn't go off.

If damaged bases cause bullets to fly erratically, then every bullet should fly erratically. Every bullet.

Perfect loads make one hole.

Real-world loads make groups with the greatest density of the shots in the center, and reduced numbers of shots as the distance from the center increases. Dense in the middle, density decreasing as the distance from the center increases.

Loads with an intentional defect oriented randomly should make groups that look like a doughnut, with maximum density at some distance from the center, diminishing both toward and away from the center. I don't think that they do.

So, I'll make a bunch of filed-base bullets and fire them at one aiming point. Maybe thirty or so. And I'll fire a set of good-base bullets at another aiming point.

I'm thinking that if I don't get a doughnuty looking group from the filed base bullets that maybe we need to re-think some of those explanations.

4/26/2006 M54 Winchester 30WCF, 30X STS, 12/AA#9, WLP primers, CF Ventures Soft Gas Check, 308403 lubed Darr + beeswax, muzzle clamp/anti-cant device and flat bench rest. 65 bullets had 45 degree filed bases to about half the height of the base band. A set of 18 cases had file marks put on the base and rim for orienting. A fouler was shot before each set of shots, at the center dot. Bullets were put in the cases with the filed bullet marks at 12, 3, 6 and 9 o'clock, four shots, and the cartridge was put in the chamber with the case base/rim mark at 12 o'clock. Then as precisely as I could put the bullet in the case and then the cartridge in the gun, bullets/filed bases were oriented each shot.

Four with filed bases, four perfect bullets, then four with filed bases and four perfect bullets; with a sighter comes to 17 shots per fifteen-minute relay. 64 shots each with filed and perfect bases were made. All shot at 100 yards.

The weather varied from sunny to rain, still to very windy. In the still sunny conditions, there was a lot of mirage, and biting horseflies about the size of robins. Lots of "damn"s and slapping body parts.

The damaged base group is 3 9/16" high by 4 11/16" wide, with no discernable pattern. The perfect base group is 2 7/8" wide by 2 1/2" high with the center shot out and outliers ~evenly distributed.

It is clear from the target that bullets with damaged bases do not shoot wildly, that many of the bullets cluster into a small group, and that the group/distribution is not doughnut shaped. This suggests that the mechanism decreasing accuracy is not one that operates every shot, but is probabilistic in nature.

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Squid Boy posted this 23 December 2019

Excuse me for getting a little off topic but I read Tom's post and the part about cleaning your mold with Zud or Bar Keepers Friend really hit me. I have an old Lee 45-405HB mold that defied everything I could do to make it cast a bullet without some sort of defect on one side. There was some sort of black stuff in that cavity that would not give up. However, five minutes with Bar Keepers Friend was all it took and the mold looks like new. I just finished casting 20 as a test and the weirdness is gone. Just wanted to comment. Thanks Tom and Merry Christmas to all. Squid

"Squid Pro Quo"

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RicinYakima posted this 23 December 2019

David,

It has been represented to me that the "plastic" base of the bullet is not from heat, but pressure. The pressure exceeds the strength of the alloy, not to be confused with hardness. Yes, gas pressure is perpendicular to the base. With the same alloy and same pressure, a gas checked bullet forms the plastic state the same, but has a physical piston to drive it. The shank of above the gas check is just as soft with or without the gas check. That is why I don't worry about little lumps or divots under the gas check, it is all the consistence of bubble gum at the beginning of the bore.

FWIW, Ric

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mashburn posted this 24 December 2019

Hello RicinYakima,

First of all gas takes the shape and volume of its container. If a gas checked bullet becomes elastic as much as a plain base bullet does, there is another problem with that theory that you gave. In order to square the gas check up on a bullet, the pressure would have to be higher on the high side of the gas check. In reality, I think the gas pressure would be deflected toward the lower side of the bullet base and actually increase the angled base and GC. This thread is getting a way to complicated for my brain, but there sure has been a lot of good information to think about and experiment with. When the posts about flyers were put on this thread I wanted to carry that out but I didn't want to take away from the original subject of the discussion. If I don't forget it I'm going to start a post dealing with flyers.

Thanks for your response, it gave me more to think about. It's getting on toward 2 AM and about time for me to stop. I'm a night owl and I can come up with lots of ideas in the wee hours.

Mashburn

David a. Cogburn

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RicinYakima posted this 24 December 2019

" but I really don't expect you to believe what I've just written............................................"

Of course I believe what you wrote above.

"This is a lot more complicated than most all here believe. "

Especially that statement.

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John Alexander posted this 24 December 2019

Trying to envision what goes on inside a case when things pop is pretty hard although fun to think about. That doesn't mean that we can't make some progress understanding, or partially understanding it.

For instance Max and Ric wonder if the gas pressure doesn't sometime seat a crooked gas check. It can, and 45.2 has observe it which isn't surprising.

Gas does take the shape of its container but only if it has to. it is happier changing the shape of its container and if it has enough pressure -- it will as in forming sharp shouldered cases from factory brass, or blowing up a perfectly good rifle. It's true that it isn't static pressure and it is rushing around in some sort of a turbulent firestorm but it is still probably pushing pretty much perpendicular to the surface at any point because there is little way for a gas to get a grip on a smooth surface and push other than perpendicular. Gas will deform its container most where it is weakest (the unsupported shoulder area in an AI chamber) and if the high side of a crooked gas check is the weakest it will be pushed until seated more firmly. If we could only depend on it working every time which if may, or may not.

John

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Squid Boy posted this 24 December 2019

I agree with John about the gas altering the container to a point. I think that the case being the weakest will be forced to conform to the shape of the much more resistant chamber. However, the bullet base is another part of the container and while plastic under high enough pressures I tend to agree with Dr. Mann's finding that oblique bases do not repair from the action of gas pressure and they remain defective. I believe that is because the pressure is applied in all directions equally even with a pressure wave front hitting the base. I think the unsupported part of a crooked gas check is subject to move until it contacts the bullet base. I am also speculating about these things from some limited observations but it is certainly an interesting topic. Squid Boy

"Squid Pro Quo"

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John Alexander posted this 26 December 2019

Max,

Why not try it? I have already given my opinion about it fixing your peachbasket groups but I have been wrong a lot.

I have a suggestion for you to consider after you have tried a few reloaded as you have been. Set aside 100 of those bullets. Trim off the bumps in a vee block as you suggested. Save this 100 bullets until you get your groups averaging 1.5" or smaller for five shot groups and then run a comparison test as I described in TFS #257.

If you would do that and publish the results in the forum and in TFS. It would make interesting reading and add to our knowledge of what works and what doesn't.

John

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John Alexander posted this 09 January 2020

Hamish wrote:

"I do not remember ever seeing discussion regarding the inherent accuracy differential between nose pour versus base pour.

I cannot help but wonder about this question as it seems to me that with base pour, relatively perfect bases can only occur somewhat regularly.

Whereas, with the nose pour, if good fill out is repeatable, then the base is necessarily square and "perfect" every time."

=================

You have recited the seemingly logical reason why nose pour molds should produce superior accuracy. This belief has been around for well over a hundred years. However, like a lot of superficially logical theories that are also "just common sense", it apparently isn't true at least at the level of accuracy we have been able to achieve with cast bullets [aggregates (averages) of 5-shot groups of about 0.5 moa.]

This theory has been disproved by the actual results in supervised shoulder to shoulder CBA competitions over forty years. Nose pour molds have gone from being considered necessary by most serious shooters to comprising less than ten percent usage at CBA national tournaments. If bases good enough to win matches were hard to achieve with base pour molds they wouldn't have become the overwhelming choice.

There seems to be a lot of evidence that both the need for absolutely perfect bases and our belief in what we call common sense are both vastly overrated and actual competition and/or well designed scientific tests are both superior for finding out what is true and what is just what we have been told.

John

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