Seems there has been a reasonable case made for fire lapping.
From David Tubbs: For your new Krieger barrel you will want to use the Throat Maintenance System system. You will shoot 7 to 10 rounds of this through your barrel then clean good.
Originally Posted by J E Custom
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.
From the Krieger website: Because the lay of the finish is in the direction of the bullet travel, very little is done to the bore during break-in, but the throat is another story. When your barrel is chambered, by necessity there are reamer marks left in the throat that are across the lands, i.e. across the direction of the bullet travel. In a new barrel they are very distinct; much like the teeth on a very fine file. When the bullet is forced into the throat, copper dust is removed from the jacket material and released into the gas which at this temperature and pressure is actually a plasma. The copper dust is vaporized in this plasma and is carried down the barrel. As the gas expands and cools, the copper comes out of suspension and is deposited in the bore. This makes it appear as if the source of the fouling is the bore when it is actually for the most part the new throat. If this copper is allowed to stay in the bore, and subsequent bullets and deposits are fired over it, copper which adheres well to itself, will build up quickly and may be difficult to remove later. So when we break in a barrel, our goal is to get the throat “polished” without allowing copper to build up in the bore. This is the reasoning for the "fire-one-shot-and-clean" procedure.
From the Krieger website: Because the lay of the finish is in the direction of the bullet travel, very little is done to the bore during break-in, but the throat is another story. When your barrel is chambered, by necessity there are reamer marks left in the throat that are across the lands, i.e. across the direction of the bullet travel.
This will never happen if the reamer's been properly sharpened and is sharp to begin with.
But that costs money. Many 'smiths will not do that every third or fourth barrel "finish reamed" after "rough reamed" that leaves the chamber several thousandths under size. Good ones will.
Not many folks know that the best 'smiths use two reamers on a barrel; a rough and a finish. Bad ones won't.
Not many folks know that the best finish with any reamer's done with a floating pilot on it that's exactly the right diameter for the barrel blank. Any undersize pilot will end up with a rough finish when using a finish reamer. And an oversize one will damage the origin of the rifling ahead of the leade.
One mandatory thing to do before fire lapping, if that is a "must" for anyone thinking about it, do not do it if your barrel's groove diameter is already the same as the bullets' diameter. It will shoot less accurate if you fire lap it. Best accuracy happens when bullets are larger than the groove diameter.
Note that even with a slight amout of rough finish on the leade, and somehow it's lapped smooth to a 1 micron finish (good luck getting it that smooth), after a hundred rounds of shooting, it will be eroded away to probably more rough than it started by the normal bore erosion caused by the powder burning. If you must have that really smooth finish, you'll need to fire lap the barrel every hundred rounds or so. A .308 Win. erodes the leade at a rate of about .001" (one thousand microinches) per thousand rounds.
You might want to talk to Krieger directly before you go firelapping one of their barrels. My guess is, the waranty will go right out the muzzle with that first shot. I know using these kits will void warranties on a couple of other brands of barrels, and I'd be surprised if Krieger takes a neutral position on this.
I'd suggest using the fire lapping on any barrel you're considering using for a tomato stake. A that pont, you haven't got anything to lose, and it can't hurt. That's not the case with a brand new barrel.
I use Tubb's TMS for barrel break-in, factory or aftermarket, to rid machining jaggies.
10 shots, break-in complete.
I use a few every few hundred rounds to dress up the leade.
I don't see how there could ever be a warranty on a barrel -once finished. Afterall, much is not the barrel maker's fault(unless he finished it).
I don't know about other recipes & methods of FFing, but I do know correct use of Tubbs will not harm ANY barrel.
I also know that many barrels improve after Tubb FFing. I don't think this is because of lap for fouling, but for tightest bore at the muzzle, and possibly crown corrections. Tubb's abrasion is reduced further & further down the bore, affecting leade most, and muzzle area least.
The finish Tubbs leaves in the bore is not a polish, which is not desired. It actually matches very closely the semi-rough lapped finish provided by the best barrel makers(like Krieger).