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Lapping A Rifle Barrel
By Reid Coffield
(left) This French Berthier
Model 1916/1927 probably
saw use during World War I and has a less than perfect bore. Its bore can be improved by lapping using a lead slug.
(center) Coffield uses a hot air gun to heat the barrel prior to casting the lap in the bore.
(right) Make sure you have a very sturdy rod for the lap. Coffield uses an old surplus M14 steel cleaning rod.
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If someone suggested you rub the inside of your rifle barrel with sand, would you do it? That's a pretty stupid question, right? Of course you wouldn't.
From day one, we're taught to treat the bore with TLC. We're admonished by every gun expert, self-proclaimed and otherwise, to be extra careful and never allow the slightest amount of wear or smallest bit of abrasive to make even the tiniest scratch inside the barrel.
The rifle bore is one of those mysterious and sacred areas we can only approach with care and by following the specific instructions of experts. After all, if we do anything wrong, we'll ruin the barrel, or so we're told. But like so much popular wisdom, that's not always true.
Over the years, I've developed an interest in older military bolt-action rifles. One of the things I've discovered is if I can afford the rifle, it's probably not in the best shape. In fact, it's pretty safe to say it'll be darn rough! That's okay with me; I'd much rather have a rifle that saw use than a mint-condition example that was never issued.
The problem with these old rifles is compounded by the fact that most military ammo used up through the end of World War II had corrosive primers. If you're standing in mud with somebody shooting at you, you seldom have the time or inclination to go through all the machinations necessary to thoroughly clean your rifle after firing corrosive ammo. Consequently, many--if not most--of these old warhorses have pretty rough bores with pitting ranging from light to "oh my gosh."
(left) A simple Lee melting pot is ideal for preparing the lead.
(center) A small, coarse, flat file is used to cut grooves around the lap (top), and the
abrasive paste is applied sparingly to the lap
(right) Clover lapping compound is a grease-based silicone carbide abrasive available at many auto parts stores.
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If I just wanted to hang these old rifles on the wall, the bore condition wouldn't matter all that much. But for me, part of the romance of these rifles is taking them to the range and firing them. It's one thing to read about 'em, but I want to know what it feels like, how it sounds, and even its aroma after firing.
The problems with a rough bore are that it hurts accuracy and leads to excessive fouling. The pits actually rip metal from the bullet as it passes down the bore. If nothing else, this roughness makes cleaning a real chore.
One way to deal with a bad barrel is to smooth the bore and remove, or at least lessen, the effects of the pitting. That's were the sand comes in.
The only way to smooth the bore is to go over it with an abrasive such as silicone carbide, which is basically like super-fine sand. There are two ways of getting the abrasive into the bore. The quickest is to coat a bullet with abrasive and fire it through the bore. This is called fire lapping and has become quite popular in the last few years. The other method, which I prefer, is a more traditional lapping technique using a lead slug, abrasive, and a sturdy rod. Now keep in mind that I'm talking about rifles with barrels just one step away from being used as tomato stakes. I'm not talking about super-nice commercial barrels or wringing sub-minute-of-angle accuracy from them. If you've got a barrel like that, go see a good gunsmith. I'm dealing with ratty old barrels, and any improvement I make is a net gain.
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