Need opinions on barrel leading and chamber pressure

[shafer44]

Ok, so I have a 38-55 hiwall that slugs .382". I am shooting a sized .383" bullet from an Accurate mold that has 3 lube grooves and a crimp groove, the ogive is almost like a pointed bullet, except the nose is flat...very small meplat. My shooting friend has a Hepburn 38-55 that slugs .381". I cast and size the bullets for both of us and size his to .382". We are shooting around 1300 fps, mine with 13gr of Alliant 2400, his 9.5gr Unique. I do not get leading, he does. According to QuickLoads, my 2400 load has 13000 psi chamber pressure, his unique load has 23000 psi pressure. I believe he gets the leading because of the 10000 psi higher pressure, but I am not positive. Can anyone chime in on this? I know normally, we lower our velocities until we quit getting leading, but I think pressure has a lot to do with it also.

[Rcmaveric]

Could be. Whats the alloy? Or your bullets may be fitting the throat better while his bullets are not. Lots of different approached to this. Has he tried a 2400 load or a reducing his load?

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[shafer44]

I am ruling out alloy, since like I said, I cast, he does not. I cast the bullets and run mine thru a .383 sizing die and his thru a .382 push thru NOE bushing after I size and lube them. Anyway, my alloy is basically WW and linotype to be around Lyman #2 alloy. Unique generates a lot more pressure than a lot of powders, I am like I said, just trying to see if someone can tell me if the chamber pressure is the culprit. 2400 is a lot less pressure and I started out around 15gr which was close to 1500 fps and it leaded, I backed off until I was not getting leading. If he uses Unique, he would have to drop his velocity to about 1100 fps. However, in his case, I don't think it is the velocity so much as it is chamber pressure.

[243winxb]

A slower pressure curve of the powder may help. Does it spike quickly (fast pistol powder in rifle size case) or is it a gradual increase (full case of slower powder). Protection of the bullet base can also be a factor, we routinely do this by gas-checking, using lube wads, or fillers.

[shafer44]

My thoughts are that the pressure curves for the two loads both show really steep peaks on a scale of pressure versus inches travel in the barrel. 218447 218446

These pics will expand, but the one on the left is using Alliant 2400..13gr and the second using Unique ...9.5 gr. both are with a 257gr bullet
Both are about 1300 fps, same lube, same alloy, just different powders. The 2400 does not lead, the Unique does.

[303Guy]

I would suggest trying two things - changinging powders and larger boolits. If a larger boolit will chamber in his rifle then why size them smaller?

Have you recovered any of his fired boolits? I'm wondering whether gas erosion is occuring before the boolit can properly seal the bore.

[GhostHawk]

I'm with 303guy.

Why size a thou smaller than yours?

" I cast the bullets and run mine thru a .383 sizing die and his thru a .382 push thru NOE bushing after I size and lube them."

That is my first choice to change.

Clean bore, try shooting 10 sized at .383.

Second thing is use your powder.

That second graph shows a much higher, bigger red spike.
One or the other, or both combined should do the trick.

[shafer44]

Why size a thou smaller? Because his barrel is .001 smaller groove diameter than mine. Try .383, we have already been there, it leads even worse. I know it sounds like the solution is to just load Alliant 2400 like I do for mine, but I am waiting for someone that can definitively tell me that "with lead bullets, sized and lubed, if your chamber pressure is above XXXXX, you are likely to have lead fouling problems" Think about trying to figure out the leading and 2 different powders if all you had to look at was a chronograph and both loads chronoed about the same velocity. No offense, but most of the stuff I have gotten is kind of experience level, try this, try that and I can do that, but there should be some scientific reasoning that someone knows about. We all read stuff that tells us that if you shoot a lead bullet above 15 or 1600 fps, then you should use a gas check. I also do the shake and bake PC for some of my other calibers and people are saying that with PC you do not need a gas check. I size and LUBE my PC bullets that I do use and for the most part do not get leading any more, but if I push the velocity, I do get leading. I also have gotten people saying if you PC, then size bullets to groove diameter, not .001 over like plain lead bullets, yet others say size them .001" over. The 32-20, 32-40, 38-55 and 45-70's that I shoot are all way under 1600 fps, but if I get even close to 1500 fps, I get leading even with PC. And again, sometimes higher velocities with lower pressure powders do not lead. There has to be something out there that tells us to keep pressure under XXXX like the idea of keeping velocities under 15-1600.

[243winxb]

Lee has a lead hardness tester with this chart. More pressure requires a harder alloy.

[243winxb]

And then we have this for your entertainment. :grin:

The formula used to calculate the pressure required for solid base bullets is:

https://en.m.wikipedia.org/wiki/Obturation

And
Plastic deformation-This whole relationship centers around the elastic limit for the alloy you are using and what the elastic limit is. the elastic limit is the point at which stresses can occur to an object and it will return to it's relative shape. Once you have reached the deformation stage it no longer returns to relative shape. this is a very simplified version of this topic as it pertains to engineering mechanics of materials.
This is meant to be a guide and to keep you within safe/acceptable limits for pressure and alloy for your purposes. Obturated bullets do not mean that the shape has went through plastic deformation, just that it has expanded and stayed within the elastic limits of the alloy.
The formula does not take into account other factors that aide in reducing friction and thus combined forces on the cast slug.

[shafer44]

I appreciate the chart and formula, I am aware of them and have referred to them before. They do not hold true for me, really either. I played with lead hardness with bullets for my rifle (another caliber) and lowered my lead hardness to make sure that they obturated....they leaded the barrel worse. I do have a Cabin Tree lead hardness tester. My alloy is 14+ bhn, and by the pressure required to obturate the bullet at this hardness, in my gun with 13000, it should not be happening, yet I do not get leading in my rifle with the 2400 powder. I really don't understand some of the things that happen with cast bullets some times.

[243winxb]

I think obturation is only useful if there is a tight spot in the middle of the barrel. As long as bullet diameter is .0005" to .001" larger then groove diameter, all is well.

I bought some Rotometal's linotype to test with. Its been online many times that an alloy thats to hard will lead , when shooting target loads in 38/357, 45 acp and 44 magnum. It did not lead.

I tested with water dropped bullets from the molds and oven heat treated water cooled bullets using magnum lead shot. Still no leading that had any effect on accuracy. Barrels looked bad, but cleaned easly.

If diameter is correct, using a good lube like 50/50, the harder the alloy, the better. This helps avoid bullet skidding and slumping with full power loading.

I still shoot cast in handguns a lot.

In the past , i cast for 30 caliber, a T/C Contender.in 30-30 , rifles in 30-06, 30-30, 308, using the same Lyman gas checked 173 gr bullet. Slow IMR 4895 was my powder of choice for top velocity.

A cast bullet cant be to hard IMO. Many others will not agree.

https://www.thehighroad.org/index.php?media/castbullets.494/full

[hornady308]

I cast for a couple of 38-55 rifles (and a 375 Win Contender) and use 10gr Unique on a regular basis with no leading, but I am generally using a much softer alloy of 50/50 acww/pb. I have also used straight acww's and everything has worked well. I wonder if you wouldn't have success with his rifle at a lower bhn.

[Larry Gibson]

"I am waiting for someone that can definitively tell me that "with lead bullets, sized and lubed, if your chamber pressure is above XXXXX, you are likely to have lead fouling problems" "

I measure pressures of numerous cartridges in numerous firearms though the 38-55. I would not hazard to speculate to answer "definitely". I have found that the Lee chart and the "formula" can be basic guides but are not hard and fast rules. There are variables at play.

What I have not see, perhaps I missed it, is what lube you are using?

[243winxb]

Has to be a powder type or pressure problem. Load friends rifle with the 2400 to see.

Without tin, cast bullets will lead? Works for me.

[shafer44]

11 oz beeswax, 6 oz Crisco, 2 oz Vaseline or canola oil. This is a modification of WWW, I add a little more beeswax to stiffen it up a bit.