Fire Lapping

[Rex]

Anyone fire lap a revolver? How about valve grinding compound, would that do the trick? I have a S&W 686 that is a barrel leader. Speed, bullet size makes no difference. There is a rifleing at about 7 o'clock that always builds the first lump of lead. Maybe it is tight there or something else.
I can use gas checks and get by.
Your thoughts would be appreciated.
Rex

 

[Brad]

Valve lapping compound is too coarse.
Get Clover brand silicon carbide in grease in 320 grit. Use very soft bullets and just enough powder to get them out of the barrel.
First thing I would check is the throats. My wife’s revolver had tight throats and it leaded. I reamed the throats to .358, cleaned up the forcing come a bit, and it doesn’t lead. No firelapping was done.

 

[Rex]

Thanks Brad. My throats are tight, around .357.

 

[Pistolero]

Fire lapping is appropriate for a very rough bore or a thread restriction in a revolver.
IMO, removing the barrel and resetting it properly is a better solution if the issue
is thread choke. But you have to have the proper tools or a gunsmith to do it properly.
Depending on the groove diameter of the barrel, .357 throats can be pretty OK.

Bill

 

[Hawk]

I have fire lapped all of my S&W revolvers.
SS and blued alike. Improved accuracy on every single gun.
Be prepared, the SS revolvers take a lot of lapping.
I bought my lapping compound from Veral Smith.
Follow Brads directions. Hard bullets have "spring back" and you don't want that.
Well worth the exercise, in my humble opinion.

 

[Rick]

The only reason to slug the bore of a revolver is to make sure the groove diameter is not larger than the throats. Heed Brad's advice and do some careful measuring. Bottom line is that revolver throats are the worlds best bullet sizer. Doesn't matter what size you put in the case when they come out of the throats they will be throat diameter. If your groove diameter is larger than "ANY" of the throats it'll lead.

Thread restriction is a possibility but before altering a bore I would look at all of the throats first.

 

[fiver]

yes.

this is the one time I would start measuring stuff before I decided on a course of action.
do you want to lap your cylinder throats to fix a tight spot in the barrel?
is it a tight spot in the barrel?
or is it just the first place where the barrel is actually full diameter.
full diameter versus the cylinder throats?
know what your fixin.

 

[Brad]

What size bullets are you using? Will the bullets push thru the cylinder throats with a push from you pinky?
Rick is right, cylinder throats are an excellent bullet sizer. You can shoot a .358 bullet with .357 throats but the bore will only see a .357 bullet. The lead that can be shaved off might end up in the forcing cone as it is blown forward by powder gasses.

Shove a slightly oversized bullet thru each throat and measure them. The smallest of them tells you the max size to make your bullets.
How do those measurements compare to a bore slug? If they are a small amount, maybe .001, larger then all is good. If the throats measure smaller than the bore then you have a problem.

I have a feeling your throats are a bit small for the bore. Even .001 makes a difference. My wife’s 686 shoots far better after I opened the throats. Her revolver also had a horribly rough forcing cone. I turned a brass lap at the proper angle for the forcing cone and used it to polish the cone. Made a huge difference.

 

[Brad]

Revolver leading

Restriction happens to all of them if they overtighten the barrel. Extremely common. Bill

www.artfulbullet.com

Here is a thread where I showed the difference in the forcing cone.

 

[Bret4207]

IME fire lapping can help. But remember you need to determine where the problem is in the forst place and that a little often goes a looong ways.

 

[Rex]

Guess I can accomplish the same objective by using my 358156 bullet with GC, It kinda limits my choice if bullets but maybe that isn't a bad thing either.

 

[Pistolero]

Firelapping is a good tool, but at this point, I would think that you need to know if the problem is a .358 groove
diameter with .357 throats or a rough spot in the barrel. The rough spot in the barrel can be smoothed up nicely
with fire lapping. But if the throats need to be opened up (after slugging the barrel to see if the groove diam is
larger) then fire lapping isn't the solution. And, it could be frame thread restriction, very common in
S&W revolvers and best handled by unscrewing the bbl and resetting it without the massive over torquing
that the factory often uses.

Bill

 

[358156 hp]

You can buy lapping compound in finer grits than the standard 240 grit popular in automotive machine shops. I use 2-3 different grits, depending on what I'm trying to accomplish, usually 320, then 400, followed by 600. Lap in stages, don't try to do everything at one sitting or you'll err to one side of the other. Needing more lapping is good, lapping too much is obviously bad.

My first lapping generally runs with six coarse, 12 medium, and 12 fine grit. I swap the bore with Eds Red between shots, followed by a dry patch. Since you can't control the amount of residual compound in the bores, I make sure every lapping shot is in a clean bore. And any leading you may encounter from lapping bullets must be removed before the next shot. To be honest, I roll my lapping bullets between steel plates for full coverage, so I haven't experienced any leading from lapping bullets, but have heard enough testimonials from others who have. The cylinder chamber & throat need cleaning too, since the will "lap" as well, just at a rate of 1 to 6 with the bore. I number my chambers with a marker to make certain each cylinder gets the exact same lapping bullet count.

After you run your course for the session, clean and slug the barrel again to check your progress. It is important to know your starting point so you can evaluate your progress. You may want to up the count on coarse compound bullets for the second trip. With stainless, it's almost guaranteed. With Ruger stainless (Terhune Anticorro, a proprietary alloy), you will definitely want to double or even triple the number of coarse compound bullets on the second trip, it's really abrasion resistant!

Eventually you will see the polishing action taking place from the forcing cone forward, don't try to polish the entire length of the bore, you'll likely end up with an oversized bore at the entry. Just lap enough to achieve your immediate goal. The bore will be tapered minutely from forcing cone to muzzle, that's what we're really after. My Super Redhawk took a ton of lapping, and when It was done less than half of the bore showed any change at all. I hated to leave it like that, but it was all that was needed to make it perform, and I had recently replaced a Ruger P90 barrel for a guy who had overdone his lapping, wanting the barrel to be polished smooth & shiney full length. A .454 round ball literally rattled in the bore.