Terrible leading headache........

[Ackley]

First off,I'm new to the forum,but been a shooter for 50 years.I posted this over on the shooters forum,but somebody said I might get more help by posting it here.

I've got a 57 Smith mountain gun in .41 mag that has been giving me fits with leading.I've shot BHN from 12 thru 22.I've shot .410 and .411 diameter bullets.Plain base and gas checks.Fast powders thru 2400.My chamber throats measure .411.The leading I'm getting is right in front of the forcing cone,and naturally,the more times it's shot,the further up the barrel leading continues.I was getting some gas cutting with Unique,so I switched to 2400 and that's when the leading started in front of the forcing cone.I've shot orange magic,blue high velocity and even black powder lube.Nothing has helped.

Honestly,I don't even know where to turn now.Anybody got any ideas.This pistol shoots jacketed like a house a fire and accuracy is super with lead too......for just a few shots.Any replies would be greatly appreciated.

[sqlbullet]

If your throats are .411, I would want .412" bullets. I would guess the bullets are enough smallish that you are getting hot gas past the base of the bullet, heating the lead.

[BABore]

Please slug the bbl and tell us what you get. Also pay particular attention as the slug passes through the bbl thread area. It sounds like you got a boolit fit problem due to the relationship of the throats versus groove size. It could also be bbl thread constrictions sizing your boolit down. That's hard to pin down from just words. Something where you need to see the position of the initial leading yourself. The slugging should tell you.

[454PB]

The fact that even gas checked boolits lead is unusual. I've never seen that happen under normal circumstances, so I would bet on a barrel constriction just forwards of the forcing cone.

[dubber123]

Please slug the bbl and tell us what you get. Also pay particular attention as the slug passes through the bbl thread area. It sounds like you got a boolit fit problem due to the relationship of the throats versus groove size. It could also be bbl thread constrictions sizing your boolit down. That's hard to pin down from just words. Something where you need to see the position of the initial leading yourself. The slugging should tell you.

After slugging 5 S&W's recently, I would lay my bet on the barrel having a thread restriction. 4 out of 5 S&W's I slugged had one. My 6" Mod 14 was the first I did, that one leaded in the same spot yours does, even with 800 fps. .38 loads. After firelapping the restriction out, absolutely no leading. I shot 3-400 rounds without cleaning, no lead. Accuracy noticeably improved also.

[Ackley]

Thanks everybody !!!! It sounds like the thread restriction is the most likely cause.I had wondered if it was tight in this area and I JB'd it hard in that area only,but no help.This gun has somewhere around 2,000 rounds down the barrel

[BABore]

To verify the thread constrictions precisely, you really need to slug the bbl a couple of time. Yes, you can feel constrictions with a tightly fit patch on a cleaning rod, but feel don't equal a micrometer. I would suggest you get a manual from Beartooth Boolits and a lapping kit at the same time. It gives very detailed instructions on the hows and whys.

Revolvers ar hard to slug properly because you can only access the bbl from one end. Driving a soft, hollow egg sinker through, from muzzle to breech is no problem. This slug will likely get sized down by the thread constrictions which is what your looking for. The tough part is pounding a egg sinker just below flush with the muzzle, then getting it back out the way it came.

You can use several short rods that fit the frame window and put them in one after the other from the breech. With the last one sticking out the breech a ways, you rig up a jack plate and push the slug out. Complicated and requires more tools. Another way is to insert a 2 inch nail, with a decent head, into the egg sinker. Drilling the sinker out if needed. The nail's head should be big enough to not want to pull through the sinker, yet small enough to not scratch the bore. Start the nail embedded sinker into the muzzle nail head first. Drive it below flush with a wood or plastic dowel that has been drilled out to slide over the nail shank. When below flush, hold the end of the nail with two pairs of pliers and bend the end over at a right angle. Clamp on a pair of Vise Grip below the bend and tap on the vise grips to get the slug back out. Sounds alot more complicated than it is. Just be careful.

Comparing the two slugs, full pass and muzzle only, will show you what's going on. Fire lapping with a 12-13 bhn boolits, embedded with 320 grit Clover lapping compound, At air gun velocities will remove the constriction. It usually take about 20-30 round, cleaning completely every 5. A final hand lapping is done with a tight fitting bore brush wrapped with cloth and coated with compound. After a new gun break-in, you'll be back in business.

It takes about 2-3 hours to properly fire lap a gun and the Beartooth kit runs about $40 including the manual.

[9.3X62AL]

That last post of BABore's needs sticky-ing. For real.

I concur with the "thread constriction" diagnosis.

[dubber123]

BABore is the one that helped me with my first foray into firelapping, and I am a believer now for sure. I was too cheap to buy the kit, but the directions are the same.

[44man]

Babore comes through again. You can't measure a restriction by pushing a slug all the way through the barrel. You CAN NOT GO BY FEEL! You need two measurements and a good mike, not calipers.
The problem is going to be 5 lands and grooves that are hard to measure. Many here will tell you how to measure.
Yes, make Babores post a "sticky."

[Three44s]

I bought the Beartooth Bullets book a few years ago and count it as a very good and economical resource:


http://www.beartoothbullets.com/bulletselect/index.htm


The author, Marshal Stanton also writes tech articles on that web site and you may wad around there and find (as I recall) some even tread upon the very item you may be having trouble with ....... it will get you running sooner.

Three 44s