Revolver firelapping prep


September 1, 2012, 04:21 AM
Okay I am pretty sure I am going to just get this over with and firelap my revolver. I plan to write what I am going to do and if you guys got any pointers it'd be appreciated.

I reamed the throats on this gun that where undersized and it reduced leading quite a bit. Still leads though and the location of it indicates I got a constriction, I felt it when slugging the bore last time too. So I got the lapping compound that I've heard is the best, Clover 320 grit, it will break down into finer grit as it travels down the barrel and help give that proper tapered profile.

I cast my own wadcutter bullets so I got a choice of a 220gr hollow base or 250gr solid wadcutter. I am thinking I will use a pure lead alloy with some tin mixed in, no antimony or other stuff. A load of about 3.5 grains of Vihtavuori tin star should yield about 600fps out of my barrel.

I will then seat these flush or almost flush with the case and fire them. Every cylinder I will take apart and clean the gun , what is best here to get rid of the abrasive grit and such. Will I need sacrificial brass brushes that I use once and discard? Or can I get it out with just patches and ballistol (or something else)?

After cleaning I will slug it, maybe the hollowbase WC bullets will be well suited for this task? If there is no constriction I will stop, if not repeat the above steps for another cylinder. After I am happy that the constriction is gone I plan to do this for the finishing touch, advice was given to me earlier:

320 or 400 grit Clover lapping compound is all you need. One special property of the abrasive used in Clover is that it breaks down into a finer grit as it abraids the steel. One bit of technique that most miss is to give the fully lapped bbl a good cleaning, then coat up a bob and give the bbl 100 back and forth strokes as rapidily as you can. I use an old bore brush wrapped with a long, continuous strip of cotton taken from a pair of old skivvies. Make it a snug fit and then coat it with the same lapping compound. Once done, clean it again and tell me it isn't smooth. All those strokes break down the grit to super fine. You almost can't see the rifling it's so shiny and freak out

I am also considering reaming the forcing cone to 11 degrees since I shoot primarly lead SWCs and WCs in this gun. Not sure if I should do that after or before firelapping?

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September 1, 2012, 12:19 PM
Seems to me you need to hand lap the constriction.
Not fire lap the whole barrel.

Fire lapping will just wear the whole barrel slightly bigger, but the constriction will still be there.

I'd drill & tap some wadcutter bullets so you can screw them on a cleaning rod, and just lap the constriction using the bullet as a lap. Change bullets as they wear down.


September 1, 2012, 01:51 PM
I'm with rc' on this. Deal with the restriction first.

Instead of a bullet I'd suggest casting up a few lead or Cerrosafe laps with an 8-32 screw cast into place. Unlike a bullet which will ride only on the lands these cast laps should work on both the lands and grooves.

You'll also want to make up two or three such laps. You will want to polish the area once it's sized. And that will require a fresh lap that doesn't have any of the coarser 320 grit embedded in it. You'll likely want a lap with 500 or 600 for initial polishing followed by the third such lap charged with jeweller's rouge or JB bore paste (same thing from the looks of the colour) for the final polishing.

The issue I see is that there will be SOME cutting as you move the laps into position to find the tight spot. And that is why I suggest making the laps up with a screw embedded in place. That way you can run a cleaning rod down the bore and screw the lap into place in the frame opening. With this setup any cutting done by the charged lap as it's pulled forward to the restriction will occur at the rear part of the barrel where it will not have much effect on the all important crown and last inch of the bore. It'll promote that tapered bore that you're after.

You will need to work the lap back and forth quite a bit over a rather small distance which needs to remain constant. This suggests to me that it would be worth the time to make up a frame from wood to clamp the gun in place and to control the cleaning rod strokes both to avoid making contact at the muzzle crown and to allow adding travel stops so you don't wander in the bore. But maybe that's just me and my OCD over such things..... :D

Because you're using a soft lap the grit won't embed into the steel. So patches with solvent will be fine for cleaning the bore and allow running the slug tester down the bore with a little oil on it.

September 1, 2012, 06:24 PM
You can fire lap it as you described. Just use a soft alloy and a very light load. Your suggested 600fps load is fine. But be sure to verify each round exits the barrel. I recommend shooting at a very close target so you can see each hole.

When the prepared bullets hit the constricted area they will be squeezed down. After they move past the constriction they will just lightly touch the remainder of the barrel. I've fire lapped several revolvers and it works. The constricted area is abraded but the rest of the barrel is just sort of polished. I did not detect any tapering in the barrel. But I was using NECO's fire lapping kit not Clover 320 polishing compound.

I cleaned the cylinders after each 6 rounds using Gun Scrubber, bushes and patches with Hoppes #9. Ballistol should be fine. I reused the brushes after hosing them down with Gun Scrubber.

I checked the progress using Hornady .454 lead balls and a micrometer. After cleaning the barrel I would drive lubbed lead balls down the barrel and measure them. You can tell you're making progress as the driven balls will no longer meet a lot of resistance at the choke point.

You did not identify the revolver to be fire lapped. I found my Ruger Vaqueros to have the hardest barrels. I had to shoot more than a dozen rounds with the largest gritted bullets to get the constrictions to open up close to the size I wanted. The remaining rounds using finer and finer grits also required more rounds than expected. My Uberti revolvers took far few rounds; I assume from this their steel is softer than Ruger's.

I had no need to do any polishing as the use of the finer grits in the NECO kit did that automatically.

Two bits of advice. 1) Get some sample targets before you do your fire lapping. You'll need them to do before and after comparisons. 2) Expect to spend at least two hours per gun. The first one will take longer as you will be learning as you go.

Good luck.

September 1, 2012, 10:40 PM
So what's the/your "accuracy" (or lack of) like to warrant firelapping a revolver. and the leading

September 1, 2012, 10:56 PM
I have a DW 357SM and some of the barrels of the set had rough rifling, one actually snagged the patches, so I got a kit from LBT that was compound and pure lead slugs for checking progress, also very detailed instructions. You really want enough power to drive the bullet out of the barrel. I tested after every 10 shots until I had a smooth, even push through. Accuracy improved so dramatically that I ended up doing all my guns, even the B/p ones. You use pure lead slugs and roll on the compound between 2 steel plates or glass plates, I used some left over ceramic tiles that were very smooth, til well imbeded. Don't size the slugs or the cases and don't reuse the cases after using for the process. Good luck. The bores on all my guns clean up so much easier and accuracy has improved on all of them.

September 2, 2012, 12:25 AM
I like the Amway grit.

.44 Associate
September 4, 2012, 11:12 PM
I use Clover 320 in general. For a severe constriction I will use six or twelve rounds with 280 grit. You have to be careful, as that really cuts fast, but it's better than loading and firing 200 rounds of 320.

I use wheelweight metal. It's cheap and has essentially no "spring" so does not expand after the constriction, causing "full barrel" lapping.

Make sure your bullets are unlubricated. You probably already new this, but I've talked with people who didn't - and it doesn't work.

I have no experience with Vihtavouri powder for fire lapping. Trail Boss is my current favorite for the purpose. If you chronograph, please let us know your results with VV.

You are correct that you should clean the gun after every six rounds, especially for the first few cylinders full. Lapping loads tend to lead for the first 12-16 rounds, in my experience. Do whatever you have to to strip that lead out, or you won't get any lapping effect at all.

Good luck!

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