SBH Leading

[mattd]

My SBH 44mag has always leaded. Always in the first 2 inches of the barrel. Had some initial success with powder coating, but it will still lead.

Back to measuring for the umpteenth time. As of today, a pure lead slug pushed 2 inches into the muzzle measures .4300 across all lands. A pure lead slug pushed all the way through measures .4300 across 4 lands (2 measurements), and .4298 across the others.

That slug drops thru all throats with no pushing.

My .430 sizer sizes .4302-3. Those need a light push to go thru the throats. .431 sized bullet will not go through throats.

Pretty obvious I need throats opened up to get .001 over bore size?

The only other thought is that it is a well loved gun. It shows some forcing cone erosion, and has a bit of flame cutting. I've never pushed light bullets hard, and rarely shoot full power mag loads with 240g+ bullets, but a previous owner must have. Could these cause leading? Making it not a good candidate for throat work?

[stubshaft]

Definitely go with opening the throats slightly. You may also consider shooting some fire lapping bullets to smooth out the forcing cone too.

[BK7saum]

My first thought was a bit of thread choke, but there doesn't appear to be much at all.

[BK7saum]

To be honest, I am surprised that you are getting leading. Even though your bullets aren't a full 0.001" oversize, they still start out larger than the groove dimension.

What is your alloy and hardness?

[mattd]

To be honest, I am surprised that you are getting leading. Even though your bullets aren't a full 0.001" oversize, they still start out larger than the groove dimension.

What is your alloy and hardness?

Same here. That’s why I’m wondering if something else is up.

I’ve tried em all. Diff ratios of WW and Lino, WW and pure. Hardball and pure. Air cooled, water dropped. Diff lubes. Powder coat. Diff common bullets, gas checked and plain based.

[Silvercreek Farmer]

Send your cylinder to Doug for throat honing.

https://castboolits.gunloads.com/mem...?29606-DougGuy

[Elpatoloco]

I use RCBS 44-240-SWC in all 4 of my SBH, sided to .430.

Its a GC mould and shoots so well, I never tried anything else. No leading

[Bazoo]

Well, my first instinct is that your expander is too small and thus swaging the bullet base down. If you have tried gas checked bullets and it didn’t help, then that isn’t the case as gas checked bullets don’t swage on the base.

So my next thought is maybe a forcing cone issue. Rough as a cob? Or perhaps cut way too deep?

Your description is of measurements of the bore, but how does it feel? You get the slug in the bore, does it get loose and then real tight again at the threads. You can have a bore that has a tight spot at the threads, then get open, and then tight at the muzzle again. And the two tight spots be close to the same. I haven’t experienced it but I have read about that.

Maybe rough cylinder throats? Or the leade from chambers into the throats are rough and are abrading the bullets?

Just brainstorming.

[Messy bear]

Could I just ask if it’s detrimental leading? What I mean is sometimes there is antimony wash or just a trace of leading. I don’t worry about it especially if accuracy is good. In fact I don’t have many combinations that don’t leave a trace on lands or muzzle.

[Cosmic_Charlie]

if powder coated boolits lead then you have some serious gas cutting happening. Perhaps try a 20/1 alloy with a medium charge to help insure obturation. You may have a really rough forcing cone, get a look at it with a dental mirror.

[243winxb]

Add linotype to get a BHN 15. Size to .430" Measure bullets after sizing. Different alloys spring back differently.
Apply a coating of Lee liquid Alox.

Clean gun barrel well. Test. Real leading changes accuracy. After 50 rounds, look for a lube star on the muzzle. All lubes should make a Lube Star

Use a slower burn rate powder.

[DougGuy]

Hone throats to .4315" and size to .431" any obturation you get will be to the good side and boolits would leave the cylinder at actual throat diameter.

You can rent the forcing cone cutter kit from 4D rentals and they have a really well done video showing how to install and use the tool. Same tooling I use with good results.

2 things.. When you first start using the cutter, since it's cutting only the rifling, it will feel as if you are hogging the whole barrel into being a 45, this is normal but as soon as it smoothes out is when you need to stop and look cause it cuts QUICK. You want the new cut to reach the top of the lands but without making the overall diameter back at the fire ring any bigger than factory if you can help it.

The other thing, I don't use the brass lap with lapping compound as all this does is re-install grooves that you just cut out, I use the brass lap with a small piece of well worn fine scotchbrite, 5/8" x 1 1/4" poke a hole in the middle and thread it onto the rod, tighten the lap against it and push it into the bore, press against the end of it really hard and turn it a few quarter turns holding force against it, it will do a wonderful job of polishing.

SBH after recutting forcing cone. Note that this pic was taken after using the 11° cutter, but before using the scotchbrite to polish afterwards.

Back to measuring for the umpteenth time. As of today, a pure lead slug pushed 2 inches into the muzzle measures .4300 across all lands. A pure lead slug pushed all the way through measures .4300 across 4 lands (2 measurements), and .4298 across the others.

That slug drops thru all throats with no pushing.

My .430 sizer sizes .4302-3. Those need a light push to go thru the throats. .431 sized bullet will not go through throats.

Pretty obvious I need throats opened up to get .001 over bore size?

The only other thought is that it is a well loved gun. It shows some forcing cone erosion, and has a bit of flame cutting. I've never pushed light bullets hard, and rarely shoot full power mag loads with 240g+ bullets, but a previous owner must have. Could these cause leading? Making it not a good candidate for throat work?

If your barrel has a strongly impressed "lawyer warning" in the side, those impressions leave raised bumps inside the rifling, they squeeze the barrel down. This would explain why two of the grooves mic smaller.

I wouldn't worry bout the flame cutting unless it is so severe that it keeps on cutting and even increases the rate of damage because a larger b/c gap is letting more burning gas escape. I would think recutting the forcing cone and addressing throat and boolit diameters to .4315" / .431" would reduce the amount of gas escaping because now you have a more effective seal.

[243winxb]

Without tin in the alloy- From my Old Lyman cast bullet manual-

While antimony is used to harden the bullet, the mixture of tin is critical, for while antimony mixes with lead in its molten state, it will not remain mixed when it solidifies. If tin were not added, we would have pure antimony crystals surrounded by pure lead. A bullet of this type , while it feels hard , would certainly lead the bore and eliminate all potential for accuracy.. In a lead-tin-antimony mixture, the antimony crystals will be present just the same, but they will be imbedded in a lead-tin mixutre. As the bullet cools the tin will form around the antimony-lead keeping your bullets from leading the bore.

[mattd]

So my next thought is maybe a forcing cone issue. Rough as a cob? Or perhaps cut way too deep?

Your description is of measurements of the bore, but how does it feel? You get the slug in the bore, does it get loose and then real tight again at the threads. You can have a bore that has a tight spot at the threads, then get open, and then tight at the muzzle again. And the two tight spots be close to the same. I haven’t experienced it but I have read about that.

Maybe rough cylinder throats? Or the leade from chambers into the throats are rough and are abrading the bullets?

FC seems smooth to me. Same w cyl throats. I don’t have much of a frame of reference. Slug seemed to push thru barrel consistently.

Could I just ask if it’s detrimental leading? What I mean is sometimes there is antimony wash or just a trace of leading. I don’t worry about it especially if accuracy is good. In fact I don’t have many combinations that don’t leave a trace on lands or muzzle.

I choreboy’d it clean and within 20 shots it went from 2 inches at 15y to 5 inches. You wouldn’t call it a trace of leading. Had to be choreboy’d again.

[mattd]

This is a 429244 in the FC. Not sure if that tells you anything.

[243winxb]

Are you using a gas check when loading. May have something to do with leading, if not? I use flat base bullets.

Brownells - you normally do not want to have the internal di-
ameter of the rear-most portion of the chamfered area to be over .020" larger
than the diameter of the bullet of the cartridge that is being used. In other
words, in a .38 Special revolver, which utilizes a bullet that is normally .356"
to .358" in diameter, the maximum diameter of the chamfer should be
.376" to .378".

[jaguarxk120]

What cast bullet and what lube are you using?

[mattd]

Used nearly all. 429421, 429244, lee 310, lee 200, commercial bullets.

Same w lube. 50/50, C red, mix of c red and 50/50, liquid alox. Just powder coating now.

[jaguarxk120]

Ruger barrels are hammer forged and are very smooth inside.
Could it be there is some jacket material left in some of the grooves?
I have always had good luck with the 429421 bullet and 50/50 alox/bees wax lube.

[mattd]

I have considered that it’s not “clean”. Despite working a chore boy brush back and forth hundreds of times. Dry and soaked.

Maybe there’s still layering of deposits. Been thinking about diy foul out / electrolysis.