Hi all, I've got a muzzleloader barrel that's a little rough that I'd like to lap. What is the grit recommendation for lapping a barrel. I've got JB Paste that I could use as a final polish, but was looking for a recommendation for something slightly more aggressive. Also, when using a lead slug, what is the recommended slug size in relation to land dia.?
Thanks in advance for your replies.

600-800grit NON-EMBEDDING compound. I use the stuff that comes with the ring lapping kits.

Please forgive my ignorance... define in this instance what non-embedding means.

quote:

Originally posted by brianbo:
Please forgive my ignorance... define in this instance what non-embedding means.

Silicon carbide lapping compounds work by continually breaking down into finer and finer sharp edged particles. On softer steels, aluminum, brass, etc...this can allow these tiny sharpened particles to become imbedded into the material where they are a bitch to clean out.

Most barrels are made from hard enough steel where this won’t be a problem...but if you are worried about it use either aluminum oxide or garnet based compounds. They all cost about the same and they all are readily available.

the silicone carbide based stuff will find it's way into the pores etc and will continue to provide abrasive results which is not what you want. You want the compound to be cleaned out completely when finished. The automotive valve grinding compounds etc are all silicone carbide where ring/barrel lapping compounds are non-embedding for that reason.

The lead slug is cast in the barrel on the end of a rod. It is not turned or fitted. It is cast to fit exactly minus shrinkage.

The non-imbedding compounds sound good in thory. I have not seen it to be a factor in actual practice. If the grit imbedding in the steel was a problem, wouldn't we see something on the outside of parts that we hand polish with silicone carbide paper. I have never seen or detected any grit imbeded in parts I hand polished. I personally think it is more a thoeretical possibility than something that really happens. My biggest problem is blisters on my hands from pushing the rod. So, I will use the most agressive cutting compounds I can get.


So, I'll buck the conventional wisdom on this one. I have done several muzzleloaders and cast bullet barrels. On muzzleloaders it is very desireable to have a choke. This will allow you to start short the bullet or ball then ram it down the barrel easily. It also seems to help acuracy.

To do this you need to remove some barrel steel. You are not going to do much with JB or 600 grit. I start with 120 grit valve grinding compound. Yes, 120! I use an aloyed lead slug cast to the bore with a hole drilled in the middle. The hole gets a taperd wood screw to expand the slug as it wears. You will scrub for several casts with the 120 before you make much progress. Once you do have the barrel uniform and choked skip down to finer grits. I go to 180, 220, then 320. That is it, 320 is plenaty fine. You can polish with steel wool and JB if you want.

It take a lot of lapping to remove the tool marks from a rough barrel. I am talking Numrich $50 barrels here. I would never lap a good barrel. If you want all tool marks gone you have to get pretty brutal with them. The above routine usually involves a dozen, or more, laps and half a day's work. Even so I probably remove a thousandth or less.

A good project is to get a 45 cal cartridge barrel and lap a choke in it. Leave about 5" tight at the muzzle. Chuck the barrel in your lathe and turn a lube size die out of the of muzzle end. Cut off the size die and crown the barrel. Now breech up the barrel. Install it on your rifle. You can now lube and size 45 cal. cartridge bullets for your muzzleloader. They will drop in the barrel and slide down the bore. No starter is necessary. They shoot great. You have basically made a Whitworth with the mechanically fit bullet.

If you have good quality barrel and just want to make it really sparkle, then I would just Flitz or JB it with steel wool.