M29-10 Leading

[JudgeBAC]

Just like the grinch I have puzzled and puzzled until my puzzler is sore over leading in a M29 .44.

The specifics: M29-10 S&W .44 mag. 6" throats .4285 bore .429. The bore has been firelapped as it had some obvious tool marks. Load: 8.5, 9.0, 9.5, and 10 grs. Unique behind Lyman 429421 BHN 14 sized .4305 50/50 lube. CCI mag primers.

Problem: Leading in the forcing cone and about 1-2" into the bore in front of the forcing cone. The remainder of the barrel is squeaky clean i.e. no lead.

Some random thoughts:

1. Maybe the mag primer runs the pressure up and the resultant ignition is too hot melting the base of the bullet?

2. I discovered that my .4305 sizer sizes the boolits slightly out of round. Perhaps gas blow by melting the sides of the boolit?

3. Thread constriction from crush fit of the barrel?

4. Try a .429 boolit or go with a fatter boolit?

Any other thoughts or comments greatly appreciated.

[redneckdan]

Here is my theory....The throats are too small, .0005 under bore diameter. It takes two inches or so for the boolits to bump up and quit leading. Boolit should larger than throat whish should be larger than bore.

[lathesmith]

Judge, I am sorry to say that I do not have the solution for your puzzler...but they say misery loves company, so I wish to tell you I have experienced a very similar scenario in several sixguns I have owned. The closest one currently to your situation is my Ruger SBH Hunter; .432 throats, .430 barrel. In this set-up Lee tumble-lube bullets will lead like crazy; after six shots this gun is throwing slugs randomly, with severe leading in just the barrel throat, and nowhere else. In fact, Lee tumble lube bullets do this in every revolver I have tried them in, though not this severely. Also, hard-cast and/or hard-lubed bullets at less than 1,000 fps will lead the barrel throat so badly as to be unshootable in about a cylinderful.
50/50, on the other hand, is a different story. I still have several load/combinations that will actually shoot fairly well for 100+ rounds, but I still get that mild lead-in-the-barrel-throat-and-nowhere-else thing. I have actually discovered a few light loads that shoot great, with no hint of leading anywhere. I have a favorite load that uses the Lee 200grain RF sized to .429 or.430, running about 750 fps, that is a little dirty but wonderfully accurate with NO leading anywhere. I can substitute a heavier bullet on top of this load, it will usually shoot well, but that old mild-leading-in-the-barrel-throat gremlin shows up again. BTW these same loads shoot from my Ruger 99/44 with no leading whatsoever.
Anyway, if your puzzler solves it, please post--you would really make my day(or week, or month).
lathesmith

[mtgrs737]

Just today I finished honing the throats out to their final diameter of .431" from the factory .4285" I had Cylindersmith ream them but he only goes to .4305" so I did what another member here suggested and used a brass rod and some wet or dry paper to finish the job. I can now push a .431" sized boolit through with my fingers. You throats seem a bit undersized for the barrel groove diameter, I would start there. If your bore is too rough it will lead no matter how you present the bullet to it. Is the leading on all sides of the barrel or on one side only?

[JudgeBAC]

The leading is fairly uniform in the forcing cone area but in the barrel it is not uniform. I can still see some visible tooling marks.

Maybe send the cylinder to Cylindersmith and fire lapp the barrel again? When I firelapped it the first time, I called Tubb first (it was a Tubb kit). The person I spoke to suggested not using the grit #1 bullets but to start with grit #2 and only shoot 5 of those and go from there. Perhaps, I should have started with #1 and shot all of them through grit #5?

[Dale53]

I would NOT fire lap again, yet. I would send my cylinder to Cylindersmith and try it when you get it back. I rather suspect this will do it.

Good luck and let us know how it works out.

Dale53

[JudgeBAC]

Gentlemen: Thank you all for the replies. My cylinder will go to cylindersmith and we will go from there. When it comes back and I get back to the range, I will follow up with a report. Thanks again.

[mtgrs737]

I would send the cylinder to cylindersmith and see how that effected the leading. My guess is that the correctly sized throats will work wonders in reduceing your leading problem. From what you said it sounds like the bullet is entering the forcing cone/barrel undersized enough to deposit lead then slugging up to seal the blow by for the rest of the barrel travel. Go one step at a time to learn what fixes the problem.

[Shuz]

JudgeBAC--I've had the same problem with a couple of my 629's. .429minus throats and not sure of bbl dimension. The interesting thing I've found, has been that .430 or .431 429421 boolits of Bhn 11 to 14, and 17g of WC820 or 18g of 2400 don't lead at all! Here's how I deal with the the leading problem when using medium burners like Unique or Green Dot. I shoot 5 to 7 loads of 17g of WC820 or 18g of 2400 and a 240g gas checked boolit like a Saeco 449 once I've finished shooting the mid range loads. Cleans the leading right out and without any effort. I will say that the leading I experience with powders like Unique and Green Dot is very minor as long as my charges are 7.5 to 8.5g and the boolits are .430 or .431. Someday, I may have my .429 minus throats opened up, but I can sure live with what I have now since I mostly shoot 2400 and WC820.--Shuz

[JudgeBAC]

OK, had the throats opened up and the leading is not quite as bad but it is now primarily in the portion of the barrel that is threaded into the frame i.e. the forcing cone is not bad but just ahead where I assume the barrel threads would start, I am still experiencing leading.

Is this perhaps the crush fit problem?

[mtgrs737]

What are the throats now measuring and what are you sizing to, also what bullet lube are you using? If you haven't sized the boolits to at least throat diameter then they will be small enough that they may not slug up to fill the throats or barrel in time to seal the powder gases back.

[JudgeBAC]

Throats measure .430, bullet sized to .4305 and bullet lube is lars white 50/50.

[mtgrs737]

Judge,

I am thinking thread constriction, and maybe too fast of a load for the speed of the powder you are using, I would try a slower powder to see how that affected the leading and also change out the mag primer with the unique load. I have painted on Lee Liquid Alox on the front driving band of the boolit to see if it is leading. Change one thing at a time to see if the load itself could be causing the problem. Be sure and keep us updated on your progress so we can learn too!

[Shuz]

Throats measure .430, bullet sized to .4305 and bullet lube is lars white 50/50.

Judge--Try 18g of 2400 and a std LP primer and see if the leading "goes away".

[Crass Whackwords]

I can now push a .431" sized boolit through with my fingers.

If you can push a 0.431" bullet through with finger pressure, then the throat is not 0.431", but more likely 0.4315" or even larger.

[44man]

If you can push a 0.431" bullet through with finger pressure, then the throat is not 0.431", but more likely 0.4315" or even larger.

It's OK. Harder boolit, better lube, slower powder. Sometimes anything with Alox will not work at the upper velocities.
Then two slugs must be made. One in the front of the barrel and one pushed all the way through to see if there is a thread restriction.
I doubt there is one because leading should not start at the tightest spot but after where the boolit is then too small and gas can leak around it.
My take is that if the throats are over bore size where they should be, the soft lead is being deformed at the forcing cone a lot before it enters the bore. Harden the boolits. Fast powder is worse on soft boolits too. Back off on the peak pressure point to extend it down the bore instead of in the cylinder.
I don't think 14 BHN is hard enough for a magnum. Water drop to 22 BHN.
And last of all, a magnum primer is NOT needed with ANY powder in the .44. Boolit bases do not melt but soft lead can turn to putty when slammed into the forcing cone too fast. Lead can even squirt out of the cylinder gap.
I have cleaned hundreds of .38's from the police force after soft wad cutters were used. Lead would coat the OUTSIDE of cylinders and parts of the frames where it could touch. The stuff shot out like grease from the gap.
Obturate????? Is there something wrong with that theory?
I grit my teeth when anyone says to soften boolits!

[JudgeBAC]

"Back off on the peak pressure point to extend it down the bore instead of in the cylinder."

.44 man: help me out here, please elaborate further. I like your theory but I'm not sure I fully understand the above quoted statement.

[MtGun44]

With proper diameter, lube and 18-20 gr 2400 air cooled wwts or 10 gr
Unique it does zero lead in my multiple S&W 29s and 629s.

Switch to 50/50 lube and .432 diam and try again.


Bill

[44man]

"Back off on the peak pressure point to extend it down the bore instead of in the cylinder."

.44 man: help me out here, please elaborate further. I like your theory but I'm not sure I fully understand the above quoted statement.

I PM'd you.

[runfiverun]

he said use a slower powder.
smiths sometimes have a tight spot under the frame.
pretty common problem.