another fire lapping question

[chevyiron420]

If I fire lap my revolver is it likely to enlarge my cyl. throats?

[45sixgun]

Depends on how much you lap I'm sure. I shot 30 rounds through the same cylinder, so 5 per throat, and noticed no enlargement.

[kweidner]

No worries here either and I have pin gages to check.

[dubber123]

I've done quite a few revolvers, and never found any measurable enlargement. In each case, I noticed a worthwhile improvement, either in fouling, accuracy, or both.

[Big Boomer]

chevyiron420: I'm going to assume that you have slugged both the cylinder mouths and bore of your revolver before entertaining the thought of firelapping. The cylinder mouths must be larger than the bore dimensions of the barrel. Otherwise, fire lapping is wasted effort. Once you establish that the cylinder mouths are larger than the bore, then you can proceed to the lapping. In nearly every case where I have fire-lapped a revolver, I had to first open the cylinder mouths. The only exception was a .45 Colt Dan Wesson that already had over-sized cylinder mouths and chambers. 'Tuck (as in Kentuck)

[45sixgun]

According to Veral Smith's book, "Since most revolvers already have cylinder throats which are larger than groove diameter....you probably will not have to perform the above task [enlarging the throats]."

Push a freshly cast and unsized bullet through your bore, then drop it through the throats.

[chevyiron420]

Yeah guy's, the cylinder throats are around .3155 and barrels are around .312. I say around cause I'm working on four different H&R 32 revolvers that all have leading problems. I am still working with load development now, but I'm thinking of fire lapping some or all. The surface finish of the bore, even though like new, is about as smooth as a tar and chip road.

[jandbn]

As 45sixgun mentioned, slug the barrel of each revolver and and drop the slug through the respective revolver's cylinder throats. If the slug falls through all throats in the cylinder, next step is to lap the bore. As has been mentioned in other threads on CB, keep in mind you can put metal back in the bore. In regards to enlarging the cylinder throats, I could not detect a measurable difference in my SS Ruger throats with 96 low pressure/velocity lapping loads sent through the bore to remove the barrel/frame restriction.

[huntrick64]

The other two things that really helped me was to 1.) start with a bullet .001 smaller than the smallest cyl throat and then 2.) load those bullets well with lapping compound. Don't just smear compound on the bullet and load it. Really work it in there by rolling between the two plates. You should be able to wipe it off the bullet and see "solid" grey embedded on all bearing surfaces (will look like a whetstone). If not, roll some more. Usually takes me 3-4 minutes per bullet which is very time consuming.

[44man]

Yeah guy's, the cylinder throats are around .3155 and barrels are around .312. I say around cause I'm working on four different H&R 32 revolvers that all have leading problems. I am still working with load development now, but I'm thinking of fire lapping some or all. The surface finish of the bore, even though like new, is about as smooth as a tar and chip road.

Might not help at all with the smaller throats because you will size down the boolit before it enters the bore. That also degrades the lapping compound.
I would hand lap the throats first. I would lap until a .3125" boolit is a snug push through.