Firelapping usually either improves accuracy or leaves it alone. It always reduces fouling and makes cleaning easier if the bore was not previously hand-lapped. Hand lapping is what the custom barrel makers do at their factory, but then you are buying a barrel that costs several hundred dollars without installation to get that extra attention. Volume commercial makers can't afford the extra cost. Firelapping carefully takes me a half a day to finish, and I'm guessing they won't want to add that kind of labor, either.
Every once in a while you hear of accuracy being reduced by firelapping, probably due to excessive lapping. The problem is, I never almost never know what the shooter did exactly that might have messed it up? How hard were the lapping bullets? Did he clean and slug the bore with a pure lead slug every 5 rounds to check progress? Did he watch the muzzle to see when the lapping had cleaned it up that far down the tube? Did he use a coarse abrasive, like 220 grit, on a .22 barrel (.22's have shallower rifling and 320 grit is about as coarse as anything going down them should be; Neco recommends 400 grit). How warm a load did he use?
I don't think a borescope can really tell you when the throat has had enough. You need a throat wear gauge. It's too easy for reflections off that smoothed surface to disguise changes of a few thousandths. I can't spot that by eye alone without something to compare to.
The bore taper seems to help with lead bullets and doesn't hurt with jacketed bullets. I can't say that it will necessarily shoot any better than a straight bore with jacketed bullets, as many benchrest rifles are straight, so it's obviously not a requirement. It sure doesn't hurt, though. I have one of the BlackStar barrels on my AR with 7.5" twist. Those were made with a half thousandth taper to the muzzle through electro-polishing. Mine shoots like a house on fire. Sorry their not doing business now.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Patron Member