What causes leading inside of cylinder throats?

[Macchina]

I have an SP101 that is leading up. I have dipped into bullet sizing and it looks like I'm doing it right, but let's check that. I'm shooting hardcast 158 grain LSWC which measure .358" diameter. The box simply says "hardcast", I'm going to call in the morning to see just how hard they actually are. My cylinder throats measure a few ten-thousandths over .358" (an actual bullet slides in like a dowel pin in a slip-fit hole).

I'm shooting the bullet over 4 grains of W321, standard primers, in a .38 special case. A load I've heard thousands of times works great with cast bullets.
The leading occurs immediately after the bullet leaves the case and doesn't stop until a 1/2" after the forcing cone. The leading in the cylinders appears to cover about 50% of the walls in streaks and splotches.

 

[rcmodel]

Hard bullet + light load + bevel base bullet = Leading.

Your charge is too light, or your bullets are too hard to bump up under pressure and seal off.

So you are getting gas cutting past the bullets melting lead off the sides.

For that sort of load, BNH 12 alloy is plenty hard enough.

rc

 

[Macchina]

That is what I thought. Can you suggest a 38 load for something harder (18).

 

[Walkalong]

The bullet is too small for the throats, the pressure is too light to bump the too hard bullet up to seal the throats, and gas cutting results.

Load the 18 BHN bullets in .357 Mag and buy some 12 BHN bullets for .38 Spl. As rcmodel posted, a flat base bullet is better, but not as readily available.

Super Grex (Discontinued), or wax gas checks will eliminate leading with that bullet gun combo, but are more trouble to load.

 

[ltcboy]

I have an SP101 that is leading up.

I have exactly the same problem with the same exact pistol. I have a 2" SS .357mag SP101. I thought that this would be the easiest gun to clean. It took me over 2 hours to do so and it was a chore. It sucked. I used a bronze scouring pad wrapped around an undersized brush chucked into a drill. Lead remover was an absolute joke. I do not have this issue at all with my Colt King Cobra. That is a 6" SS model. Same loads, same everything, the Ruger takes the cake for the leading. The second time I took it out, I did run some regular copper jacketed bullets thru. It seemed to help and it was easier to clean.


MIke

 

[Walkalong]

If the throats in your SP101 are undersized compared to the groove diameter, it will lead, period. The only good news if that is the case is you can get the throats reamed out a hair over groove diameter.

 

[Anmut]

Chore Boy (pure) copper scrubber on an undersized cleaning brush does the trick on my S&W. I've shoot a ton of non-gas-checked Elmer K style through my revolver with an 8" barrel and, while it does lead up, it's nothing that a few minutes with my Chore Boy copper brush doesn't get out.

Before finding that trick I spent a lot of time with different solvents! None of them get lead out like Chore Boy On A Stick!

 

[Macchina]

I have slugged my barrel and as best as I can tell (5 land-groove rifling) I have a .356 groove diameter. A .358" diameter bullet should seal right up.

Aren't cylinder throats supposed to be right at your bullet size but bigger than the bore? Because that is what I have...

 

[918v]

The way it works is this:

The bullet weighs a million times more than the gas particles pushing on it. Before the bullet goes through the cylinder throat and enters the barrel, these super fast gas particles overtake it by getting around the bullet through the .0002" of gap. This causes gas cutting of the bullet and the deposit of lead ahead of the bullet in the throat and the forcing cone.

The way to stop it is to use a soft bullet that obturates at the instant of ignition. This way the .0002" gap is eliminated, the system is sealed, and all the gas stays behind the bullet.

Save hard bullets for high pressure rounds.

Use soft bullets for low pressure rounds.

There is no need for anything harder than wheelweight alloy in anything short of a .454 Cassull.

 

[Macchina]

I called the company that cast the bullets and he said they were around 17 Brinell.
Are these way to hard to shoot from a .38 special?
Are these too hard to shoot from a .357 Magnum? If so, then why would they be made?

 

[rcmodel]

Yes they are too hard for a .38 SPl.

No they are not too hard for a full power .357 Mag load.

The difference in pressure is about 20,000 PSI.

rc

 

[Macchina]

In reference to the "then why would they be made" comment, I was referring to 918v's claim about hard bullets only needed for the .454 Cassull... a 65 kpsi cartridge...

 

[ArchAngelCD]

I have slugged my barrel and as best as I can tell (5 land-groove rifling) I have a .356 groove diameter. A .358" diameter bullet should seal right up.

Aren't cylinder throats supposed to be right at your bullet size but bigger than the bore? Because that is what I have...

Those bullets would seal right up if they were much softer. A hardnedd of 17 BHN is very hard and a charge of only 4.0gr W231 will not cause them to seal. That is my favorite .38 Special load and I never use a bullet over 12 BHN with that load. That load does not lead my barrels.

I called the company that cast the bullets and he said they were around 17 Brinell.
Are these way to hard to shoot from a .38 special?
Are these too hard to shoot from a .357 Magnum? If so, then why would they be made?

Yes, use those bullets for .357 Magnum loads and you will see much better results and little to no leading. They are too hard for light pressure .38 Special loads...

 

[Jesse Heywood]

In reference to the "then why would they be made" comment, I was referring to 918v's claim about hard bullets only needed for the .454 Cassull... a 65 kpsi cartridge...

The hardcast alloy needed for the Cassull is in the range of 20-22 BHN. Your 17 BHN's aren't that hard.

 

[Arkansas Paul]

A hardnedd of 17 BHN is very hard and a charge of only 4.0gr W231 will not cause them to seal. That is my favorite .38 Special load and I never use a bullet over 12 BHN with that load.

I use that load a lot myself, and it is a very soft shooting load. A BHN of 17-18 is way too hard. I use a 50/50 mixture of clip on and stick on wheel weights and it works just fine. My alloy is probably about 8-10 BHN.

 

[USSR]

I never use a bullet with a BHN higher than 11 for any of my loads, and that includes the .357 Magnum. There is simply no need for the ultra-hard bullets that the commercial casters are pawning off, although they do resist being damaged during shipping. Elmer Keith's original .44 Magnum loads consisting of a 16/1 alloy bullet, never had a BHN greater than 11.

Don

 

[Arkansas Paul]

^ Yep.
A proper fit and good lube is just as important if not moreso than a hard bullet.

 

[Walkalong]

It wasn't that long ago that soft was lead, or lead with some tin, and hard was lead alloyed with antimony as well, but it still wasn't all that hard compared to some bullets sold today.

 

[Macchina]

Wondering if I could shoot these 17 BHN bullets in .38 +P, I used the ideal hardness equation:

Ideal hardness in BHN = Pressure / 1,920
Maximum BHN = Pressure / 1,422

20,000 PSI / 1,920 = 10.4 BHN
20,000 PSI / 1,422 = 14.1 BHN

...crap

 

[rcmodel]

Mr. Elmer Keith invented the 1,500 FPS 240 grain .44 Magnum with 16-to-1 lead/tin, which has a BNH of only 11.

.22 Long-Rifle rim-fire HS ammo uses soft swaged lead bullets at 1,200 FPS+ with a BNH of around BNH 5.0.

The reason they don't lead is because, they are soft enough to slug up and fit any bore size and seal off the gas from melting them.

Hard cast bullets are the spawn of the devil, invented by commercial casters who find a very hard alloy is easier to cast with fewer rejects on high speed casting machines.

As are bevel-bast cast bullets which fall out of automated casting machine molds much better then flat base bullets which seal better.

But nobody ever said anything about them being easier to shoot at high (or low) speed without leading though!

rc

 

[Stormin.40]

I almost started a new thread about this very load with commercial cast bullets. It seems I get leading, not in the cylinder throats, but the forcing cone with a charge of 4.0gr W231 but when using 4.4gr W231 I do not get the leading as much.

This thread answered what was going to be my question. I believe my bullets are too hard for the 4.0 but good at 4.4 so I will stick with that.

I plan to use these same bullets in my SW 586 as well on top of A2400, I plan to start at 12gr and work up to 13.5gr.