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?

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madsenshooter posted this 14 January 2020

My first experience with cast bullets was all about basing!  I started my efforts with a Lee single cavity tumble lube 160gr bullet out of a 92/96 Krag that I'd scoped with a Krag Haus mount.  Using bluedot for powder I wasn't doing too bad from the very first experiment maybe 4" groups at 100yds, with unexplained fliers.  I was using a push through sizing die in the beginning, and found some of my fliers in the fact that I wasn't tapping the checks all the way down onto the shank before sizing.  There was also an issue with outtie sprues that wouldn't let the check seat squarely.   Then I won an auction on ebay for a cherry for the MX3-30-AR from the Don Eagan estate, and had Bernie Rowles make me a mold with it.  I couldn't believe my eyes as I watched the first group form from about 70yds!  12 or 13rds, most them touching like I later saw the benchrest shooters at Washtenaw shoot, out of a 125yr old rifle with a $30 scope!  One flyer about an inch out was called as I felt the rifle slip a bit off the rest, which was the bannister of my back porch, about the same time the striker was falling.  Since then I've gathered Eagan molds, both original and some made with the cherries I have, and other Eagan things, like the coin gascheck seaters for several calibers, a tapered 30 caliber size die and a little die that tapers a 30 caliber gascheck shank.  I use that one to restore the taper on a B&M 311169 that someone decided to make larger at the rear.  I think basing is very important!  Just got me a Hoch 314225, any of you have any experience with that bullet?  I'm hoping my Krag will like it!

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JBinMN posted this 14 January 2020

This is an exceptional read, IMO, and I thank all of you for your contributions!

 

JB

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Hamish posted this 10 January 2020

Thank you John.  As I never developed much interest in CBA style shooting and history until well after my IHMSA days where cast was merely a cheaper way to practice and handle the banks of chickens, I'm mildly ignorant of the minutia of these things.

The habit of eliminating the basics as contributing factors is sometimes a help, sometimes it is not.

Though my endeavors will always be the rather pedestrian pursuit of acceptable hunting/plinking accuracy, I do appreciate the forum and its contributions.

 

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John Carlson posted this 10 January 2020

Temperatures in single digitsdepressed, winds occasionally over 40 mphconfused, let's just talk about shooting for a bit longer134

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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Ross Smith posted this 09 January 2020

I never thought this would generate 3 full pages of comments. In the end,let's go shoot.

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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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Ross Smith posted this 09 January 2020

H.    When I see one of my mangled GC's crooked bases bullets that can't stand up on a flat table, it gets recycled. I don't know how that base can be squared up by firing it down a barrel without something else being screwed up. It's the little "mis alignments" that are under question and I agree with your observations, my base pour molds don't deliver nearly as good a base as my nose pour molds. But I don't think we need to be too picky about bullets that are going to be shot at a gong. 

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Hamish posted this 09 January 2020

Perhaps I have missed it, if so, I apologise.

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

 As 45 2.1 has regularly repeated for many years that the errant mal seated check can be counted on to be fully seated before muzzle exit, 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.

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max503 posted this 26 December 2019

OK.  You guys have given me several things to try.  What more could I ask?  

John - thank you for the FS.  I will read that article.  (I don't know what happened to my download.)

I was halfway kidding about trimming those bullets, but I will give both methods a try.  Both the knife and the drill press.  I don't need many.  I'm shooting a bolt action not an AR.

I will be glad to do a write-up if I can get something to work.  That's a deal.

Wish me luck.

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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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Ross Smith posted this 26 December 2019

Al Nelson taught me a little trick of chucking the bullets in a drill press and spinning them on a plate. In my usual "that's too slow" mode I switched to 220 grit sand paper. When a 30 cal bullet leaves a 30 cal "smear", you're done.  Still too much work for plinkers and beer can shooting.

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max503 posted this 26 December 2019

So...……...is there an efficient manner of trueing up bullets with less than stellar bases?

I've got a large handful of Lee 55 grain 22 bullets, and many of them have protruding scars from where the sprue was cut.  

It would be nice to use them instead of melting them.

What if I laid them in a vee block and trimmed the scar with a box cutter knife?

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Ross Smith posted this 25 December 2019

Me again. My really crooked GC's happen when I use my lube sizer and are pretty well  swaged into that offset. If I pull a gc to check the base, it too has been skewed and gouged. I doubt that firing the cartridge will cure all that. I still stand by my statement that crooked gc's are ok for plinking. I never would suggest them or other flaws for comp or just striving for your own best accuracy. I am also really impressed with the knowledge and thought coming from this post. Can't say that enough.

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Tom G posted this 24 December 2019

Squid Boy,  Glad that worked for you.  If a mold still won't work right after the Zud treatment, try heating it up to drive any remaining oil out of the pores.  Do this till you get no more oil and then zud again. 

Angled bases.

My test with the bullets with the gas checks on crooked showed fliers that probably doubled the group size.  When I shot bullets that had square bases, they grouped in the normal size with no fliers.  Kind of tells me that crooked gas checks don't square up and that they do cause fliers. And they definately cause fliers.   

Dr. Mann's Experiments

I dug out my hardcopy of Dr. Franklin Manns book called The Bullets flight   The ballistics of small arms.  On June 11, 1903 they did test # 131.  It was shot through a new Pope barrel that they noted had guilt edge accuracy in a V rest. . Shooting took place in the evening under favorable shooting conditions. (no wind).  In this test, they shot bullets with the swaged bases. 

They swaged the bases at two different oblique angles. One group had a base angle of of what they describes as .012" and the other group was .006".oblique.   They shot a control  group with good bullets that was .61".  They also clocked the bullets in the barrel so that they would emit from the muzzle with the oblique side at 12, 3, 6 and 9 O"clock at the muzzle. 

They noted that only one shot in 8 hit within the circle around the group made by the control group. They showed a photo ot the group that resulted from the oblque angle bases bullets shot into the same aiming point as the control group.  of the eight shots with the 12 and 6 thou. oblique bases , it shot a hollow group with two hits in each of the 4 quadrants. Each of them shot into a predictable and repeatable spot on the target according to the way the bullet oblique base emitted from the barrel. 

The only unexplained anomoly was the the ..006 bullets shot into a slightly smaller group than the ones with the larger .012" bases. The oblique bullets shot into a group a little more than twice the size of regular bullets. 

My impressions. 

.006" obliqueness on say a 32 caliber bullet is not very big.  Yet it had a big effect on where the bullets struck the target. 

Please note that these bullets had bases that were swaged slightly oblique. Not filed oblique. Thus, as in Joe's test, if I understand it correctly, they were not unbalanced from taking material from one side more than the other. Therefore , only one variable was tested at this time. Notably, only oblique bases on bullets that weighed the same and were left in balance. 

Also, there was no evidence that they were repaired in any way by the pressure exerted equally on all of the bullet base upon combustion. 

Thought I'd pass that on for you guys who don't have access to this book.  

 

Tom Gray. 

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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 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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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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45 2.1 posted this 24 December 2019

It has been represented to me that the "plastic" base of the bullet is not from heat, but pressure. Both actually... The pressure exceeds the strength of the alloy, not to be confused with hardness. Strength? Which particular strength (compressive, shear, torsional and has nothing to do with tension). Alloy? air cooled or heat treated... there is a BIG difference in how each condition acts with the same alloy... Yes, gas pressure is perpendicular to the base. That's in a static condition or fully engraved in the barrel... otherwise think of a pool ball bouncing on the pool tables bumpers... that's a pure dynamic condition... With the same alloy and same pressure, a gas checked bullet forms the plastic state the same, That's too big a statement and needs some qualifying. Alloy and it's treatment (air or heat treated) vary widely with static hardness let alone when it reaches it's yield point in a moving dynamic condition. Everyone is delving into areas where you need to talk to a materials engineer!..........................

 

This is a lot more complicated than most all here believe. I spent my professional career dealing with materials and how they fail under load, but I really don't expect you to believe what I've just written............................................

 

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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 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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