Barrel leading

[dashootist]

Just got a new S&W Mdl-14. There was very noticeable lead buildup around the first 1/4" of the barrel near the forcing cone, after shooting only about 50 rounds of target 38spl handload of 3.5gr Unique and 158gr cast lead SWC bullet from Bulletworks. I thought only hot load cause leading. Why is my light load causing so much leading?

 

[Waywatcher]

There are lots of variables, but honestly I don't like Unique, it leads my gun. Someone will probably come along saying it's not the Unique powders fault, but the simple fact of the matter is that when I stopped using Unique I stopped getting nasty leading. I have had great luck with Trail Boss.

Here are some variables you need to nail down:
What size bullet?
What hardness of bullet?
What are your chamber throat sizes?
What is your bore size?
Is there a constriction where the bore meets the frame?

My first guess would be too hard of a bullet.
My second guess is too small of a bullet.

But I don't like Unique, at least with lead.

 

[Walkalong]

Leading in the first part of the barrel means the alloy is too hard for the pressure (causing gas cutting), or the bullets are too small AND the pressure is not enough to obturate the bullet and seal the throats, or your throats are undersized for your bore.

Powder selection has very little to do with leading.

What BHN are the bullets?

 

[dashootist]

Bulletworks.com shows "Hardcast Premium Lead Bullets". No BHN shown. But alot of the action shooters here use them happily.

 

[prickett]

Just got a new S&W Mdl-14. There was very noticeable lead buildup around the first 1/4" of the barrel near the forcing cone, after shooting only about 50 rounds of target 38spl handload of 3.5gr Unique and 158gr cast lead SWC bullet from Bulletworks. I thought only hot load cause leading. Why is my light load causing so much leading?

Slug your barrel to determine its inner diameter. Your bullets should be .001 or .002 greater than that diameter.

 

[Steve C]

At low pressure and low velocity a hard bullet leads badly. Walkalong explained it pretty well. Most casters cast their bullets pretty hard since it produces a nice looking bullet but as mentioned, too hard a bullet will lead at the beginning of the bore as the bullet isn't sealing properly. If you cast your own or special order you can up the bullet diameter and this will usually fix the problem. For .38 spl loads I only use softer swagged from Speer and Hornady or soft "target" cast bullets from MBC. You can probably take your same bullets and load them to 1,200 fps in a .357 mag and get little to no leading.

Leading at the muzzle end is usually a bullet being pushed too hard or running out of lube before exiting the barrel.

 

[Arkansas Paul]

I've used Unique in my .45 Colt Blackhawk for a wide variety of loads. I've loaded everything from light plinking rounds to Ruger Only stuff and never had any leading. All loads were with 255 grain LSW with a BHN of 18 from Missouri Bullets.

 

[GP100man]

Get ya some of the hornady swaged soft lead bullets & try em at those pressures .

 

[918v]

Boolit too hard. Pressure is too low. Poor seal = gas leaking and leading.

 

[noylj]

Unique has been successfully used with lead bullets for over 100 years.
Re: leading in revolver—
You have to know the throat diameters of your cylinder—you will want bullet diameter to be no more than 0.0005" smaller than the smallest throat diameter. You should be able to just barely push a bullet through the throat.
Is the forcing cone smooth or rough. This is the surface that the bullet crashes into and goes into a plastic-flow situation. If it is rough, it will initiate leading.
You have to know the groove-to-groove diameter of your barrel. Your bullet should be somewhere around 0.001-0.004" larger than the groove diameter for best accuracy.
Cast bullet revolver accuracy is more dependent on throat-bullet fit than any other factor, assuming other good loading practices. The reason is that undersized lead bullets are subject to gas cutting, which will positively ruin their accuracy potential. Most of the gas cutting takes place while the bullet is in the throat. When it hits the forcing cone, it will obturate if it is large enough.
You may very well find that your bullets shoot better with no
sizing at all. My bullet lubrisizer was retired about 20+ years ago.
In a revolver the throats are the areas in each cylinder chamber
immediately ahead of the portion of the chamber where the brass case rests and into which the bullet projects. If the bullet is sized so that it is a gentle force fit in the throat, all else
being equal, your accuracy potential will increase greatly.
Two factors come into play here to improve potential accuracy:
a) the bullet axis is more nearly coaxial with the barrel axis.
b) gas cutting, which will positively RUIN accuracy, is virtually
eliminated.
I have never seen any observable pressure increases when using bullets up to .006" over groove diameter and I have seen no increase in accuracy using sized bullets.

 

[dashootist]

You have to know the throat diameters of your cylinder—you will want bullet diameter to be no more than 0.0005" smaller than the smallest throat diameter. You should be able to just barely push a bullet through the throat.

I was able to push a .358" dewc thru the throats of 5 out of 6 cylinder. I could not push the bullet thru that one cylinder even with light tapping of a hammer. What do I do to enlarge the throat?

 

[fecmech]

Your load of 3.5 Unique is just barely getting out of the barrel, 600 fps maybe. Kick it up to about 4.5 grs and see if the leading goes away, you are gas cutting.

 

[dashootist]

Yes, I did try 4.6gr Unique (Reloading manual shows 4.7gr) with 158 lead SWC on my other revolver, an L frame, this week. The result was even worse than the light load. Very severe leading this time. On my L frame I couldn't even pass a .356" Jac hardball thru the throats, any of them. So here's a summary of my throat diameter...

Revolver 1: K frame
(gentle tap)
.358" DEWC passed thru all cylinder throats except one
.356" Jacketed hardball passed thru all cylinder throats

Revolver 2: L frame
(gentle tap)
.358" DEWC passed thru none of the cylinder throats
.356" Jacketed hardball passed thru none of the cylinder throats

 

[fecmech]

I would suggest you slug both barrels, particularly #2. If it won't pass .356 bullets in the throats and you have a larger than .356 groove dia. (which you should in a .357 revolver) you will lead no matter what you do. To shoot lead with no problems your throats need to be larger than your groove, the reverse is not good for lead.

 

[dashootist]

I just slugged one cylinder on each revolver.

K frame: .3575" throat dia (smallest)
L frame: .3565" throat dia (random)

I also slugged the barrels with egg sinkers. But I couldn't get a good measurement because there are five groves in each barrel. The grooves are not opposite each other. What do I do now?

 

[fecmech]

You could take your slugs to a machine shop where someone would have a mic with a "V" anvil. What I do is not super precise but pretty close. I rotate the slug so that I catch the edge of the groove (with the mic) I'm leaving and the edge I'm coming up on. You have to be very careful not to crush the soft edge with the mic.