How many rounds to lap SS barrel

My new Flattop, SS 4-5/8" Bisley in 44 Special has .431" throats, verified via pin gages. The barrel is .4295" and where the barrel is threaded is .4284" so there is .0011" constriction just ahead of the throat. Barrel measurements taken via Hornady .430" pure lead balls pushed down a clean, oiled barrel and measured via 1" micrometer.

How many lapping compound imbedded bullets would you think it would take to even things out in the SS barrel?

The key is that you can always remove more material but it is very difficult to add more once it's removed. I lapped a similar restriction in a .45 RH with 12 or 18 left over lead reloads, smeared with 400 grit SiC valve lapping compound. I wouldn't swear that the constriction is 100% gone, but there's no leading and a pin gauge falls through the barrel, so I am satisfied.

Go back to pages 11 and 14 of this board and read the bore lapping posts. I think they may be informative and helpful. Furman Garza, the "Furman" mentioned in the posts is Colorado gunsmithing school trained and you can trust what he tells you. He has an article on Gunblast that gives some pointers on fire lapping revolvers. Please keep us informed on the results of your efforts.

jgt,

Thank you for the wonderful info. I have most of the tools; lapping plates for rolling slugs, compound, pin gages, .0001" micrometer, just need more pin gages to drop through the bore to verify what the lead slugs "told" me. Need more slugs to roll and imbed with compound. Loaded up what I had (17) last night to see if sub 2 gr of Bullseye would be enough to get the bullet to exit the bore. If not, i've got lots of properly sized wooden dowels to drive the slug out of the bore if any get stuck. I did this with a 45 Colt some 10 yrs back and it was a shooter though tons of accuracy at 15 yds was too necessary.

Alan

Alan, see my reply to your pin gage question. Stainless takes a LOT longer to lap than blued steel, and if the choke is much more than about a thousandth or a thou and a half, by the time you get that much lapped out of a stainless barrel there is a good chance the rifling in the rest of the barrel can be damaged more than you would like to see.


NICE Moose buddy! I would love a hunt like that with a sixgun!! Supremely jealous now sir!

Ditto on Fermins article.
And in no way shape or form will I ever insert a wooden dowel in a barrel again! Don't ask. Yes, yes I know there are ten bus loads of folks that do it with out any bad results. I was not one of them.
I bought some brass rods for just such occasions. Worse comes to worse, a steel rod wrapped in tape will work with no ill effects.
Jeff

So Doug,

I'm a bit confused by your response. Lap and don't lap?

gssp said:

So Doug,

I'm a bit confused by your response. Lap and don't lap?

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I apologize sir.. Blued steel barrels lap easier and faster than stainless by a long shot. If you have a blued barrel with a fairly moderate choke, it will lap out without ruining the rest of the barrel. If you have to beat the jag through it, it's bad and about 50/50 chance of lapping it out without damaging the rifling in the rest of the barrel but it will definitely soften the edges all the way to the muzzle.

Stainless is a totally different animal and takes about 6x longer to lap out the same amount of choke, so the cut off in the stainless barrel whether to lap or seek rebarreling or Taylor throating is before you have to beat the jag through. If it takes really good arm power to push that jag through, it isn't going to respond to lapping like a blued barrel with the same amount of choke would. Does this make any sense?

Makes sense. It's brand new SS barrel with .0011" of difference between the threaded/choked area and the remainder of the barrel. I did shoot 17 lapped bullets yesterday (all I had left) and i'll remeasure tonight, though with what you're telling me, I shouldn't see much of a difference.

Might take a while before you see much difference but it will come. What you measure is not too much to lap so should be good to go when it gets there.

17 lapping rounds took off .0005", LOL. If my math is correct, I should shoot another 37.4 lapping rounds....

Quite pleased with a new SS Bisley, 4-5/8" 480 Ruger I bought a few months back. First measurements with pin gages put all the cylinder throats at .476 minus .0002". The barrel was another surprise where after about 10 rds of factory Hornady it might have smoothed out the barrel a bit. It was somewhat easy to push an oiled .480" Hornady ball down the barrel with mostly a wooden dowel and hand pressure. Barrel measurements came out between .4751" and .4755". The choke point measurements were exactly the same. Hope it's a shooter!

gssp said:

17 lapping rounds took off .0005", LOL. If my math is correct, I should shoot another 37.4 lapping rounds....

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You might consider sending that cylinder and having the throats sized .4325" and evened out within .0002" and sizing to .432" for this revolver. It would help the lapping effort to start with a .432" as well.

My experience has been to shoot 3-5 shots and measure. Soft round balls and wooden dowels are cheap. Barrels are not.

Steve

Does it shoot OK now?