Thread: Baikal single shot rebarrel - Anyone done this?

Originally Posted by SixtyTen

I should make it clear im not a lapping expert. I have done a lot of research and reading about the subject, but have lapped less than 10 barrels so far, so take everything I say with a grain of salt.

What grit are you lapping to?
On a barrel that is not bad, I will lap with 320 and nothing else, If a barrel needs a fair bit of helping, I start with 220, and then just do a finish run with 320. Make sure to clean the barrel well between grits and cast a brand new lap.
I have read in multiple places that you dont want to go much finer than 320 as it actually increases the friction on the surface and can lead to very bad copper (or lead) fouling. I have not verified this myself, and its only been forum chat that suggests this, nothing from any real experts.
I made my own compound by buying silicone carbide powder if various grits from Rotorua lapidary Supplies. I then mixed up a batch for each grit with grease and with oil. I have found that grease is better than oil for barrel lapping. Any new grease will work.

I thought cut rifled barrels shouldn't open up when the OD is machined?
I have come across this idea myself. I believe they do open up a little with diameter changes as it can be felt with a slug. I have not checked my factory lapped Krieger (Which I believe are cut rifling) but I have come across it on a couple of other cut barrels that were known to be consistent before profiling/muzzle threading. I didnt lap either of these barrels and they both shot just fine.

Bill Calfees book has some information on the subject and he has documented that any change in the outside diameter of a barrel blank will result in a change in the bore size. This goes for receiver threads, barrel contouring, dovetails for sights and muzzle threading.
His book is appallingly bad and I struggled though it thinking there might be some information on the actual mechanics and tools involved in lapping. There isnt. Most of the book is him telling ego stroking stories that have nothing to do with improving rifles. There are a few tidbits here and there, but the good stuff could be covered in less than 5 pages, and its something like 200 pages long. That said, he is a proven gunsmith that has consistently turned out championship winning rimfire benchrest guns, so he cant be completely full of shit.

What I've read suggests that you normally lap before cutting the barrel to length, because the lap tends to bell the muzzle end where it exits and reverses. How are you avoiding this?
I dont extend the lap out the muzzle at all. I butt the muzzle up against something hard to stop the lap from extending out. I only push it out when I need to add more lapping compound. This will stop any bell-mouthing.

Considered it for my problematic grey birch barrel to remove the bore constriction, but preheating the barrel before casting the lap would have been an issue with the carbon fibre wrap.
The Pre-heat is probably only 150c. The carbon on your barrel should handle that just fine for a while. If it doesnt, then the manufacturer is using a type of resin that has no business being on a rifle.
You can sometimes get away with a lower temp pre-head, but the lap wont fill out as well. This can be fixed to a degree by a couple of good bumpings, just make sure you have the lap and barrel greased before you bump it, or you might get it stuck (dont ask me how I found this out)

Hope this helps.

That's great info, thanks for taking the time to lay it out. I presume you haven't seen an issue with lengthening the chamber throat during lapping either?

I'll have to give it a try one of these days. The Grey Birch barrel is long gone though - I took the refund while it was on offer. If the pre-heat is only 150C I expect you're right that the carbon wrap would have taken it - then again that particular barrel already had several features that had 'no business being on a rifle.' I have no idea what resin they would have used.