Leading Problem

B

Bottom Gun

New member
Can someone give me a clue as to why one revolver will lead up while another won’t?
I have two Model 629’s, one with a 6” barrel, the other with a 3” barrel.
I can shoot the same load (a 240 gr SWC with 9.5 gr Unique) in both guns and the 3” will lead up considerably while the 6” bore stays bright and clean with hardly a trace. The leading in the 3” bore is uniform and consistent.
This isn’t a hot load, in fact it only chronographs 890 fps out of the 3”. The slugs are from Bullet Meister and appear to be fairly hard alloy.
I’m baffled by this.
Anyone have any thoughts about why this happens or better yet, what I can do about it?
I wonder if moly coating the slugs would help?
 
If the 3" 629 is relatively new, that can make a difference. 300 or so jacketed rounds can smooth out a bore a bit, making it more amenable to cast bullets.
 
Or fire lap it.That will stop the leading

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beemerb
We have a criminal jury system which is superior to any in the world;
and its efficiency is only marred by the difficulty of finding twelve men
every day who don't know anything and can't read.
-Mark Twain
 
Hmmm, I had the same problem with Unique. Severe leading in 3 different .44's w/a similar charge. Dropping down a full grain did a little better, but still not great. I switched over to 2400 for loads over 1000fps, and had zero leading. Go figure! Upping the velocity and a switch to a "cooler burning"-ie.slower-powder worked wonders.

Also as stated, the 3" may need some barrel smoothing. In the last 2 years, I've used 5 new S&* products from .22 through .357 and all of them had rough bores. Since you are a handloader, I would give serious thought to loading a few hundred rounds of semi hot jacketed shells and using them to lap the barrel.
 
Since it is the same load we can dismiss alloy and bullet base obturation from the issue. S&W barrels usually have a very good finish so I doubt you have a rough barrel. My guess is that the cylinder throat and groove dimensions are to blame. These are rarely identical from gun to gun.

As an illustration of this, I just recently slugged two rifles of the same manufacture and chambering and groove diameter was off .0025 from one to the other.
 
Fire lapping is system in which you use different grit compounds imbedded in your bullets.These are fired and polish the barrel.You start with a courser grit and get finer as you go.
Brownells and a number of other people sell the kits.Friend has a colt that leaded very badly and after fire lapping the amount of leading decreased by 90+ percent.

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beemerb
We have a criminal jury system which is superior to any in the world;
and its efficiency is only marred by the difficulty of finding twelve men
every day who don't know anything and can't read.
-Mark Twain

[This message has been edited by beemerb (edited July 08, 2000).]
 
Nuther thought. Friend with .41 mag had severe leading problem. Timing spot on, cone was good. He found that the cylinder was undersized at the front ( forward of the case mouth), he honed the holes till fresh bullet would just thumb press through. No more leading problems.

We figgured that the bullet was getting squeezed a bit much, causing a lead feather at the base and allowing hot gasses to get past it in the bore.

Sam....follow me, I know a shortcut.
 
Bottom Gun. I think C.R. Sam has the answer to your query. Take some of your bullets and slide them through the cylinder. As long as you can push them through with some tightness, you should be OK. Try this with both guns. If the bullets just drop through on the 3 inch, them you need a bullet sized slightly larger, or maybe a gas checked bullet might help.
Another thing to check out; after the bullet slides through the cylinder under slight pressure again, mike the bullet to check out the size. Then slug the bore of the offending pistol. If they are different by any great amount (remember, we are talking in thousandths of an inch here) that could be the source of your problem.
While S&W is pretty good on this aspect, Colt single actions in .45 LC are not. With .452 inch bores and .455 to .457 inch cylinder throats, shooting lead bullets in them can be a challenge. I have 3 and I've had to size to .454 to get any kind of accuracy.
Paul B.
 
Newer guns lead more. Try some JB bore paste on it, and that should reduce leading by alot. Personally, I only shoot jacketed or plated in my S&W wheelguns because I hate to have to clean the stinking lead from everything on the gun!
 
Thanks for the help, Guys, I appreciate the advice.
Perhaps, as Bob C says, it may need to be shot more to smooth it out.
This 3” was made by S&W for Lew Horton. I bought it used and it doesn’t appear to have been fired much whereas my 6” has had thousands of rounds through it.

I have a jar of JB paste sitting around somewhere. I’ll try it and see if it makes a difference. I wonder if you can use this JB paste to fire lap a bore? Has anyone ever tried using it like that?

One thing I never did was to check the bore for copper fouling. Could it be possible that the previous owner ran a lot of jacketed ammo through the gun, picked up some copper fouling, and never cleaned it out? Would this contribute to leading?

Paul & Sam: I’ll measure the cylinder too. How close should the cylinder diameter be to the bore diameter?

RAE: I had never considered changing powder, but If the barrel doesn’t smooth out, then I’ll try some 2400 or something.

Thanks again for the help.

-Ken
 
Bottom Gun. If memory serves, the cylinder throat should be about .001 to .002 larger than bore diameter. My Colt Single Action Army's are about .457 with a bore of .452. I have to size bullets to .454 to get any kind of accuracy from them. I size my .44 caliber bullets to .431 and they seem to work our fairly well in my .44's. (Mags and Spls.) Just going to a slightly larger diameter bullet might cure your leading problem, but that is just a guess.
I have heard that yes, you can firelap with JB's, but I haven't tried it. Midway has a kit for about $25.00, but I wasn't too well pleased with it. Had a hard time cleaning the grit from the chamber of the rifle I was working on.
Then again, some guns just don't like lead bullets. I have a SAECO mold for the Keith 240 gr. SWC in .44. My 629 leads like hell with that bullet, and I have to use a gas checked bullet in that gun, but my 624 loves that bullet, and won't shoot worth a darn with the gas checked bullet. Doe this come under the category of, "Are we having fun yet?"
Paul B.
 
Paul,

Thanks for the info.
I wondered about the grit from that lapping compound. How many rounds do they recommend you fire using the compound?

When I have a little time to spend in front of my Dillon, I’m going to coat some SWC’s with JB paste and try lapping with them. I’ll let you know how it works.

Bottom Gun
 
You sure it's lead? Could be soot from a short barrel not completely burning the powder. Unique is not really a bulky, slow powder, but 9.5 gr. is only cranking about 1100 fps -- maybe a little faster with a lead bullet.

It's possible the load is not developing the back pressure necessary to cleanly burn the powder. Most of the time lead bullets generate slightly less back pressure than jacketed. You need the resistence and pressure to cleanly burn the powder.

The solution is not to increase the charge for the short barrel. The solution is to use a faster burning powder. That's the theory anyway.
 
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