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Fire Lapping a Barrel

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Unread 05-01-2013, 08:15 AM
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Join Date: Dec 2005
Posts: 2,483
Re: Fire Lapping a Barrel

Originally Posted by Edd View Post
Don't those barrel makers run that same type of abrasive thru the barrel when they make it?
Yes, they use something like a lead or brass lap charged with abrasives to enlarge the tight spots in the very slightly undersize bore up to either their specs or those of the customer. They'll use a precision hole micrometer or air gauge to measure the diameters. When they've got a spread of less than .0001" and are at the desired specs, they do nothing else except mark the ends of the barrel blank where diameters start to flare out a bit. Those ends are cut off or reamed out by the 'smith fitting the barrel to the receiver. I think most high end barrel makers want the bore's finish to be between 10 and 15 microinch for best accuracy. Any smoother and steel tends to wipe off more bullet jacket material for some reason I don't fully understand.

Here's a good article on top-quality barrel making by one of the best:


Note the section on "WHAT MAKES A BARREL ACCURATE"

Softer, non-embedding abrasives, such as JB, can easily "lap" out copper wash as well as power and primer hard fouling. But these do virtually no steel removing from the barrel itself.
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Unread 05-01-2013, 09:29 AM
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Join Date: Feb 2009
Location: Sedalia, MO
Posts: 1,256
Re: Fire Lapping a Barrel


Might also add that yes, the barrel makers do use an abrasive when they do the final lapping on a barrel. An abrasive and a lot of hard earned experience. They're going to take a dim view of a customer trying to "improve" the job that they did at the shop.

Some years back there was a firm that offered an "electropolished" micro finishing treatment on "their" barrels. The original barrels were made for them by Ken Johnson, of K&P barrels, after which they did their micropolishing magic. When the marketer wanted to list them as being made by Ken, he was adamant in keeping his name out of it. As he explained it to me at the time, the barrels were "his" when they left his shop. As soon as someone (even a full-on vendor of a process such as this) does something else to the inside of those barrels, they're no longer "his" and he didn't warranty anything after that. I tried a couple of the barrels that were being marketed by this firm, and despite major claims of enhanced accuracy and greatly increased barrel life, they performed no differently than any other barrels. After hearing such claims for the past 30+ years, yes, I've become pretty jaded.
Kevin Thomas
Lapua USA
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Unread 05-18-2013, 06:37 PM
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Join Date: Aug 2012
Location: Champaign, IL
Posts: 203
Re: Fire Lapping a Barrel

Originally Posted by J E Custom View Post
I personally Never recommend fire lapping is a last resort because it laps the throat and does very
little for the rest of the barrel.

The fact that the barrel shoots good the first couple of shots tells me that you need to do a good
break in.

Do a shoot, and clean after every shot for 20+ rounds and you will start seeing an improvement
on the fouling issue. It takes time and patience but is it worth the effort and improves the entire
bore not just the throat.

As you shoot, you should start to feel the improvement in the bore and the number of patches
to come clean should drop to 1 or 2.

It is not unusual for factory barrels to take more than a custom barrel so don't take a short cut
and start firing 2 or 3 shots and then cleaning. The purpose of the shoot and clean method is to
shoot 1 bullet in a clean bore and let it smooth the barrel out evenly end to end.

Fire lapping enlarges the bore at the throat and reduces bullet fit causing lower pressure and velocity.
hand lapping can do this if it is over done breaking it in only wears the high spots and fills in the
machine marks left from the rifling process.

Some custom barrels are very tight even after lapping because the barrel maker allowed for this
and reamed and rifled the barrel .000001 undersized.

Thanks for your input on fire lapping! I've been wondering about this for the last 6 months.
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Unread 05-18-2013, 06:58 PM
Silver Member
Join Date: Aug 2012
Location: Champaign, IL
Posts: 203
Re: Fire Lapping a Barrel

After reading all of these posts, it appears most of you agree, it's not necessary.

3 weeks ago I ordered a Savage Model 12 LRPV with the dual port. Left port load, right port eject. I had to have it special ordered since it's not listed as a stock item anymore. As much as it costs, I want to insure I do everything I possibly can to insure I wring highest possible accuracy from it. Mine will chambered for the 22-250 with a 1 in 9 twist. Effie in the custom shop at Savage said the expected delivery date was 6-8 weeks. That was a shocker for me, since I expected 6 months or more.
Lord, I'm gonna have over $2400 in this setup by the time I have a base, rings & a scope mounted.

I'm 72 & starting to act like a kid near Christmas time.
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