Barrel Lapping Before/After Grouping?

[oldracer]

In a past issue of Black Powder Cartridge Magazine I read the interesting article on lapping the barrel. I can see why it might be needed if there was rust inside or blue residue, etc. I was curious if anyone has done this and measured accuracy before they lapped the barrel and then again after a good lap job. As the article noted if this is done wrong you can totally screw up the internals and at present I see no need to do either of my rifles. I checked them very closely with my borescope and they are smooth and rust/pit free. I would imagine it would help some in grouping especially for a nationally ranked shooter perhaps?

[btroj]

Most of the people lapping barrels these days are using it to smooth out a factory barrel or to remove tight spots in the bore due to sights dovetails, thread choke, or something like that. I have used fire lapping to smooth the throat of a few revolvers. Worked very well. I did it more to reduce leading than to improve accuracy.
Done wrong it can cause problems, it is changing the barrel dimensions some.
What method of lapping did the article mention? Using a lead lap is a different ball of wax. Never done that.

As for the help in grouping, can't say. I don't know about BPCR but I can say that I don't know any NRA high power shooters who lapped their barrels. I haven't read in Precision Shooting of any bench shooters doing it either. Buy a true premium barrel and have installed by a guy who knows what he is doing and there is little need for lapping.

This is an example of a specific technique being used in one shooting game that may not have applications in other shooting games.

[largom]

I have "Fire-Lapped" dozens of center fire rifle barrels. Accuracy was improved on all of them, which was the reason for the lap in the first place.

Larry

[oldracer]

Thanks for the replies. The article mentioned pouring a lead plug in the end, then cutting off any sprue on top and using a cleaning rod with a screw fitting to move the plug back and forth through the bore, changing lapping compounds as the job progressed. I can see how doing this could really mess up the dimensions inside a barrel and so far I have seen the need to try it since I am not doing any competing. I am getting a new Sharps next week and the first things I'll do is clean out the barrel to get rid of any oils and such and then slug the barrel to see how close it is to my other 45-70s. If there appear to be tight spots when doing the slugging that might suggest a need for lapping but I'll try firing it first.

[btroj]

I would not want to lap with a lead lap. Could easily create a muzzle that is larger than the rest of the bore. That is, in my opinion, best left to experts at the barrel manufacturers.

[stubshaft]

The amount of material that you remove while lapping is predicated on how many strokes you use on a certain area. The removal process is very slight, as anyone who has had to lap a barrel can tell you. It would take a concentrated effort to make the muzzle larger than the rest of the bore.

One of the thigs that lapping can also tell you is where the constrictions are in the bore. Looking through the bore will not tell you that, but pushing a lap through will. There are certain areas on different guns that have minor constrictions. The forcing cone on revolvers (or area where the barrel is screwed in), The area of the forend band on some lever actions (all 8 of my Marlins) have a slight constriction. Getting rid of those restrictive areas will go a long way to increasing accuracy.

[mroliver77]

The only way I would use a lead lap on an assembled gun is if the barrel was pretty nasty. I have lapped two assembled rifles. One was a CVA muzzle loader that a friend found in a dumpster from a rental house that was being redone. It was somewhat rusty inside. I scrubbed till it was no longer effective. I used a worn out bush with the bristles removed. I plugged the barrel a couple inches down with a cleaning patch. I inserted the cleaning rod and brush stub the poured lead around it. Normally you would insert rod fro breech end but breech plug would not move. I pulled the lap almost all the way out and trimmed it up, cut some grooves to help hold compound. I then charged lap with 400grit silicon carbide grit mixxed with oil. It was nasty going for a bit. Lap was recharged a couple times and then was loose. I cleaned barrel and poured a new lap. Same procedure as before. Lapped till loose again. It is the lap that wears the most, not the barrel. Third lap was charged with 600 grit. When it was loose I cleaned and quit. Barrel was shiny but pitted in places. It shoots very well! It outshoots my nice TC Renegade! My nephew camoed it with flat Krylon and it is a spare.

Second gun was a Mauser. It cleaned up some and shot jacketed ok but I replaced barrel later with a purdy takeoff.

My buddy shot some old surplus .45 acp in his Rock Island 1911 and did not clean it. It grew green "hairs" in it quickly and pitted/frosted the barrel. There was some nasty lumps that would not come out with cleaning solutions or brushing. I fire lapped it with the SC grits and powder charges that barely got the boolit out of the barrel. It cleaned up nicely with only minor visual defects in the barrel. It actually shoots great!

I shot up a bunch of that same ammo but cleaned with Windex and the Eds Red. No problems.

[nanuk]

I read where you only need to remelt a lap when changing grits.

when the lap gets loose, hold the rod in one hand, insert a brass rod in the other end and with the lap against the rod, tap the rod a few. this expands the lap. then recharge. saves time and compound.

this won't work for a ML unless it has a removeable breech plug