Heavyweight cast bullets is a 300 Blackout

6.5K Views
Last Post 21 March 2016

CBA Member

Scearcy posted this 03 December 2015

Last summer I shot a 300 BLK in several matches. I was careful to limit my bullet selection so that I could keep the base from protruding below the case neck. This limits bullet choice or requires some rigorous work with a bump die. I have observed with some interest that bullet molds dropping 247 gr bullets are increasingly popular for this cartridge. These bullets are usually being used in AR rifles which limit the cartridge OAL. The bases are clearly extending well below the case necks. Are people experiencing the gas cutting / barrel leading problems conventional wisdom associates with this practice?

Attached Files

33 Comments

Order By: Standard | Newest | Votes

Standard Member

onondaga posted this 03 December 2015

http://www.castbulletassoc.org/view_user.php?id=7904>JHS

"Are people experiencing the gas cutting / barrel leading problems conventional wisdom associates with this practice?"

No, bullet fit and alloy selection eliminate gas cutting / barrel leading problems. It is the shooters lacking an understanding and practical knowledge of how to achieve bullet fit and how to select an alloy for a load level that lead up their barrels and shoot all over the place. If you begin to ignore these basics of cast bullet loading, you should expect gas cutting, poor accuracy and barrel leading problems.

It is very easy to ink the bullet of a loaded round then chamber and un-chamber it to see if you have a sliding fit of the bullet into the chamber throat. It is very easy to look up your load pressure and select an alloy strength from equal to 10% higher in psi. This is what is basic and what works. Expect good results when you do that.

The shooters that expect lube to compensate for bullet fit and alloy selection are the shooters that have the worst results. Lube is least important and simple tumble lube is excellent when bullet fit and alloy selection are excellent.

Have you tried the Lee 230 gr AAC bullet mold? #2 Alloy, Un-sized, tumble lubed and a gas check finger placed? That is a super simple setup that slides into the throat and works well. You have to fiddle with LOA for feed, that's all.

Gary

Attached Files

CBA Member

Scearcy posted this 03 December 2015

Hey Gary, Thanks for the response. I will try that bullet. I am also thinking of the Lyman 311365 which will also feed well.

You would not be concerned about having the bottom 3/16” of the bullet exposed below the neck. I have not experienced problems , that I can demonstrate, doing this but I have not done it often.

Attached Files

CBA Member

RicinYakima posted this 03 December 2015

JHS, I'll take a theoretical stab at the bullet base inside the case issue. According the gas laws, the pressure inside a closed vessel should be equal in all directions at 90 degrees to the interior surface. Therefore, the cast bullet should be pressurized in all directions equally. If the alloy fails to have the strength to resist changing shape due to gas turbulence, or some other cause as not fitting the throat out side the case correctly, there may be deformation. Using an alloy of the proper composition and being firmly within the throat seems to negate all the old myths. There has been issues in the past with FMJ bullets that have a very soft lead core. It is possible for the exposed lead core to push outward swelling the rear floating area of the bullet's jacket. This increases the size of the bullet while it is still inside the case. This has caused extreme pressure spikes. Ric

Attached Files

CBA President

John Alexander posted this 04 December 2015

Ric, I liked your theoretical stab right down to the last sentence.

Your description of how the gas pressure is working on the exposed base and sides is right on. Since the pressure on the sides of the bullet are equal to the pressure on the base there will be no tendency for the diameter to expand no matter how high the pressure or how weak the material being pressured.

This isn't just theory, in soil strength testing the compression specimens (in a rubber membrane) are sometimes tested in a chamber that exerts water pressure on the sides to imitate the lateral pressures on the soil at depth under a foundation. Expansion (upset) doesn't happen until the axial (mechanical) pressure exerted by the testing device exceeds the lateral water pressure by an amount that differs depending on the strength of the soil. This is probably more than anybody wants to know but this is another old erroneous CB piece of conventional wisdom that can be killed by hard facts but like like a zombies keeps coming back to life. Folks experiencing problems with CBs or JBs that hung out in the powder space need to look for other explanations than the pressure on the base causing fattening (upset) of the bullet. This just can not happen because the pressure is as you described in your second sentence.

John

Attached Files

CBA Member

RicinYakima posted this 04 December 2015

John,

The part I left out, for brevity's sake, is that the ammo was loaded so that the jacket bullets were jammed into the throat upon bolt lock-up. Even thought the case released the bullet, the required energy to start the bullet engraving into the rifling was higher than the strength of the jacket. So there are three bad things happening: 1, the bullet has not free run, but jammed into the barrel; 2, the jacket is made of thin/weak material that was less than US specification; 3, a pure lead core was used that turned to plastic goo when hit with excessive pressure. At least that was the story I got, and believed!

Attached Files

CBA President

John Alexander posted this 04 December 2015

Ric, Although both the core and jacket may have been weak the pressure, as you note would have been pressing on the sides of the bullet with the same pressure ("equal in all directions and at 90 degrees” to the surface) as on the base thus no way to upset.

You just can't cause a cylinder to shorten and upset in a closed pressure vessel no matter the pressure or the strength of the material.

Looking at it another way a person might think that the pressure on the sides of the cylinder (bullet) would cause the diameter to reduce and cause elongation. That can't happen either -- the equal pressure on the base would prevent it.

John

Attached Files

CBA Member

RicinYakima posted this 04 December 2015

I see, that would be correct.

Attached Files

CBA Member

Scearcy posted this 04 December 2015

Ric, John, Gary If I had known this would be such an interesting discussion I would have asked the question sooner. I am on old physicist myself so fortunately for me I can follow and learn.

Setting pressure aside (no pun) , how about the effect of exposing the bullet alloy directly to the heat and flame of the powder burn. I know we do this with plain base bullets but only up to a point before they fail (or are they failing because of pressure on the base as it exits the case not heat and flame). A full pressure 300 BLK load with a 200 gr bullet should reach 1400-1600 fps.

Attached Files

CBA President

John Alexander posted this 04 December 2015

JHS, That is an interesting and probably important (whether we know it or not) question for CB shooters and one that won't be answered by basic physics. It seems to me that we have to catch more bullets (shot with a variety of pressures and other factors) without damaging them too much if we want to know the answer. We have spent more than a century trying to reason through what is really happening to CBs when fired and the results are mostly BS. We need more testing if we want to learn more.

mtngun has recently reported in this forum the results and pictures of catching pistol bullets in a vertical water tank which gives some information on the question. When his tank thaws out in the spring I hope he will give us more of his results.

Merrill Martin published tons of pictures of CB fired into a Mann type bullet catcher. My memory isn't good enough to say more than I remember some pictures of plain bases with clear dents from powder grains but evidence of melting. Will have to review those great experiments. John

Attached Files

CBA Member

Scearcy posted this 04 December 2015

John If we can ignore any ill effects from seating the base of a bullet well below the neck of a case, it opens many possibilities for rifles that have not been throated. I know you shoot long bullets in your 223 Hunter rifle. I am at the cabin and dont have match results in front of me so may I ask if you seat the base of the bullet well below the neck. Clearly you are getting good results with whatever technique you are using.

Now I need to take a handgun and a chain saw and go get some fire wood. The wolves up here don't know they are “endangered” and they are losing their fear of humans. Jim

Attached Files

CBA Member

RicinYakima posted this 04 December 2015

JHS,

Heat transfer rates for lead is almost the same as for carbon steel, 17.2 and 17, much less than cartridge brass, 69.4. That heat transfer rate is so low, that I don't think it is an issue. The heat of the combustion is transferred so slowly that the bullet is within the bore first. Otherwise wise we would have barrel issue from the heat of shooting 22RF's semi-auto. The pictures I have seen seem to show that physical damage to the base of the bullet is limited to pounding from un-ignited powder grains striking the base (from primer blast?). And that only on plain base bullets, not gas-checked.

John is correct in that we need more (some, any?) work on collecting bullets. Without that were are just speculating, and that doesn't mean much. Mann's book shows lots of targets, lots of the sides of bullets, but almost no bases. If his daughter had not thrown away all of his last years of work, maybe we would know more now.

Attached Files

CBA Member

Scearcy posted this 04 December 2015

Ric GOOD STUFF! Much food for thought. Jim

Attached Files

CBA Regional Director

Tom Acheson posted this 04 December 2015

Pressure knows no direction. It flows/moves from an area of high pressure to an area of low pressure. The pressure it exerts on surfaces that it is in contact with as it moves to the low pressure area, is uniform on all surfaces.

What might be at work here is the age old caution that the exposed gas check might become loosened and separated and then stop part way down the barrel while the bullet continues on its way out the bore. Then the next bullet would ram into the gas check...supposedly ringing the chamber/barrel or worse.

And...the practice of using a wad at the base of the bullet is usually cautioned by saying this should only be done in straight wall cases so that the wad is always supported and kept in place under and up against the bullet base on the inside sidewall of the case.

FWIW

Tom

Attached Files

Standard Member

norm posted this 04 December 2015

The time a bullet base is exposed to heat and flame is very short. I doubt if there is any melting of the lead alloy in that short time. Pressure might deform the base.

Attached Files

Standard Member

onondaga posted this 04 December 2015

http://castbulletassoc.org/view_user.php?id=7904>JHS Your concern about heat damaging exposed bullet bases during firing is a common misunderstanding because it just seems so likely that damage would happen.

A couple things that should convince you otherwise are time lapse and heat resistance of bullet lube.

The time bullets are exposed to the combustion of powder is in milliseconds and is so short there is no time to heat soak bullets and damage them. Bullets get hotter from air friction in flight than they do from powder flash in milliseconds.

An old Lee Manufacturing video about the heat resistance of Lee Liquid Alox is also very convincing. I can't locate a link, perhaps you have seen it or another can provide a link. The video shows the time it takes a torch to damage a bullet lubed with Lee Liquid Alox and the bullet melts without damaging the lube. It is specifically graphic to your concern.

It takes a lot of seconds with the torch to start melting the bullet. Bullet in the barrel time, in comparison, is negligible. Bullets don't melt in the barrel the way you have been erroneously led to believe.

Will someone provide a link to that old Lee video for http://castbulletassoc.org/view_user.php?id=7904>JHS ? That old video convinced me many years ago.

Gary

Attached Files

Standard Member

onondaga posted this 04 December 2015

http://castbulletassoc.org/view_user.php?id=7904>JHS

I'll also give you an example of a product designed to prevent the problem you are concerned with.

My .500 S&W Mag Handi-rifle shoots a plain based 340 grain #2 alloy cast bullet at 1700 fps. The bullets are not sized and are only tumble lubed. I had concerns about bullet damage from powder burn so I use BPI Original ballistic filler. The maker of the product claims the BPI acts as a quasi gas check and extends the power range of your bullet alloy similarly to the effects of a gas check as the filler protects the bullet base from flame.

I don't understand if the BPI actually prevents any bullet melting, because I don't think there could be any bullet melting anyway. However, in my rifle application the BPI makes a difference, a huge difference , in group size on paper. Shooting loads compressed slightly with BPI, the groups are consistently under 1” at 50 yards. Without the BPI and the same load, groups are 3” at 50 yards.

I suspect, but can't prove, no flame touches the bullets at all when sufficient BPI filler is compressed between the charge and bullet. BPI is a high heat resistant plastic particulate ballistic filler also marketed as a filler for buckshot loads to help buckshot retain it's shape on firing.

I also use this filler with remarkable accuracy increase in light load level cast 30-06 loads with heavy bullets and slow powder. And I use BPI in all of my .458 Win Mag loads with cast bullets.

The filler would be harmless in your 300 BLK loads and may take you where you desire with accuracy for that cartridge with cast bullets and no gas check. BPI original is available direct from the maker and MidwayUSA as well as other suppliers. BPI original: http://www.ballisticproducts.com/BPI-Original-Design-Buffer-500cc/productinfo/BUFFER/>http://www.ballisticproducts.com/BPI-Original-Design-Buffer-500cc/productinfo/BUFFER/

The BPI meters well from my Lyman 55 powder measure or with Lee scoops. When powder plus BPI equals 106% compressed load and the volume of the BPI is greater than bullet diameter in length within the load, BPI offers a quasi Gas Check benefit for plain based cast bullets,.

Gary

Attached Files

Standard Member

onondaga posted this 04 December 2015

http://castbulletassoc.org/view_user.php?id=7904>JHS

http://www.midwayusa.com/product/938614/lee-2-cavity-bullet-mold-tl309-230-5r-30-caliber-309-diameter-230-grain-300-aac-blackout-tumble-lube-5-ogive-radius>http://www.midwayusa.com/product/938614/lee-2-cavity-bullet-mold-tl309-230-5r-30-caliber-309-diameter-230-grain-300-aac-blackout-tumble-lube-5-ogive-radius

The bullet drops at 225 grains for me in certified #2 alloy and drops large enough that I can size/check at .312” for X39 or .310” for 30-06. The mold is however. not for beginners! You will have to be an excellent bullet caster at casting hot to get this very long mold to cast well and fill out well. Beginners will be infuriated with this mold if they don't cast hot enough. I cast this one with outboard precision PID temp control at 750 F. for #2 alloy and cast fast at 3 drops a minute.....or, the results are brutal.

Attached Files

CBA President

John Alexander posted this 04 December 2015

JHS wrote: John If we can ignore any ill effects from seating the base of a bullet well below the neck of a case, it opens many possibilities for rifles that have not been throated. I know you shoot long bullets in your 223 Hunter rifle. I am at the cabin and dont have match results in front of me so may I ask if you seat the base of the bullet well below the neck. Clearly you are getting good results with whatever technique you are using.

Now I need to take a handgun and a chain saw and go get some fire wood. The wolves up here don't know they are “endangered” and they are losing their fear of humans. JimJim,

Hope the wolves didn't get you while after that firewood.

Actually I designed the long bullets I use to be mostly in the throat and bore when chambered with only the gas check in the case. Long nose and very short band and groove section. This gives maximum chambered length for alignment. If I can get someone to make another mold it will have even more nose and less band because I only lube the tiny gap ahead of the gas check.

Long answer to say my loads don't cast any light on the question at hand. But it seems to me that we have collectively cast some pretty serious doubt that there is a problem. However, nobody should expect that this phantom “problem” won't keep on reappearing by serious writers who smoke a pipe and grunt a lot.

John

Attached Files

CBA Member

Scearcy posted this 05 December 2015

Well said. Experts with little if any actual experience have always been sort of a pet peeve. THAT HAS NOT BEEN A PROBLEM ON THIS THREAD. Its always a pleasure to hear from folks with real knowledge.

Attached Files

CBA Member

Brodie posted this 05 December 2015

JHS, I'm with you on experienceless experts. They are the reason I seldom read gun mags anymore. Along this line of thought: Does anyone know of a documented case of a gas check being left in the barrel and causing a ringing or bursting of said barrel?

I have always heard that the above is the reason that checks should not be loaded below the case neck. But, a little thin bit of brass is not a plug of mud or dirt in the barrel. Wouldn't the compressed air ahead of the bullet (as it rushes up the barrel) blow the gas check out?

So, are there any known and documented cases of this being the cause of the bursting, bulging, or ringing of a rifle barrel? Brodie

B.E.Brickey

Attached Files

Show More Posts