Im getting ready to hand lapp my first barrel. For those that have done this is there any thing I should watch out for? How fine a grit do most of you use on the last lapp? Thanks, H.H.

Do not lap a barrel that is chambered and crowned. It will trash the barrel. Use lead with some tin in it, that will help make casting the lap easiar. Linotype works well. I know that is not conventional wisdom but, it works better for me. Get the barrel and rod very hot before you pour. Use some kind of guide to keep from rubbing the rod in the bore. Use a stop to keep the lap from coming out the other end. Grit sizes? Anything smaller than 220 isn't going to remove much. I wouldn't go any finer than 600 to finish. To put choke in my muzzleloader barrels I use 120 then 220 then finish with 320. Speaking of chokes, if this is a larger bore gun that will shoot cast bullets, a choke or taper to the muzzle is good. Non imbeding grit?.......... I always used clover valve griding compound, never messed with the other. .

I am in disagreement with almost everybody on this. I don't feel that the lapping of a chambered barrel is bad. In fact I am beginning to believe it is often a good idea.
Quite often, when the chamber is reamed, the throater portion of the reamer may displace metal on the approach to the lands rather than cutting cleanly. When this happens, a lead slug pushed through will indicate a tight spot right at the throat. Well, it's not really a tight spot as far as bore and groove dimensions are concerned but a widening of the lands due to displacement during reaming. Lapping can correct this.
Concerns about enlarging the barrel at the muzzle are not unfounded but you want to try and enlarge a bore sometime by lapping. Bring a lunch because you will be at it for a while! If some care is taken there is little chance of damaging the barrel at the muzzle. Nonetheless, I prefer to recut the crown. It can't hurt. Actually it can hurt but we'll assume it's going to be done right!
I base my contention that lapping a chambered barrel is beneficial on my experience with having lapped a LOT of barrels which were already chambered. The barrels always performed better after lapping. They never performed worse.
I use 400 or 500 grit Clover compound. This breaks down in use to where the grit is much finer. There is very little dimensional change within the barrel but a significant improvement in finish and uniformity.
When using the lap, perceived tight spots may be just that. Or they may be a variation in land width. What seems to be a tight spot may also be a kink in the bore.This would show up especially if the lap is quite long.
I have had some success lapping gain twist barrels provided the gain is not overly radical and the lap is not too long.
Back to the throat business. Lothar Walther Co. actually recommends polishing the throat of their stainless barrels because this material does not cut as cleanly as other makes. Rather than polishing, I think lapping is the way to go. This is not a long process but just enough to remove burrs from the throat.
Ultimately lapping is not a means of correcting serious dimensional shortcomings but a means of achieving desired surface finish and improving uniformity. In the case of a chambered barrel it is a means of producing a better throat which reduces the chance of fouling and reduces the chance of a microscopic burr from the throat damaging the barrel further down.
The "Quickie" Lap:
Sometimes it can work just as well to, rather than casting a lead lap, simply use very fine steel wool charged with fine abrasive. The steel wool is wrapped around a jag to be a tight fit in the barrel. The purpose in this case is, again, the removal of microscopic burrs or torn edges on the lands. It works. Especially with lead bullet barrels.
I can't say that it is not possible to ruin a good barrel by lapping. In fact there are people who should never try to use any product which can cut. Even if the cutting is only microscopic. I can say that a good and careful workman can often improve even an already good barrel by lapping. Regards, Bill.

Thanks Bill and Scot. I poured the lapp plug about four inches from the muzzle. The lapp plug is about three to four inches long. It slides the full length of the bore with no tight spots with out any compound. I havent used any compound yet. Should I still lapp it since it moves so freely? I was under the impression that usually you find tight spots in a barrel, is this often the case? Thanks, H.H.

I have done this quite a bit to my own firearms. I got my info from various barrel makers. At different times they are willing to share more information. A light lube down the length of the barrel is important before lapping and when you reverse the lap you tend to enlarge the bore more in that location. A tight feel may just be a lack of lube. I charge the lap in the middle. The reason being is its harder to start a charged lap. I chamfer the lap after casting and starting at the breech its all the way out and try not to ding the crown by letting the lap rod drop as it exits. unscrew the lap and go back through. Its funny but its seems no matter how careless I have gotten with the factory barrels they all shot and clean better especially if recrowned. I always remove the barrel from the rifle.

"I use 400 or 500 grit Clover compound.......... This is not a long process but just enough to remove burrs from the throat..........Ultimately lapping is not a means of correcting serious dimensional shortcomings but a means of achieving desired surface finish and improving uniformity..........I can say that a good and careful workman can often improve even an already good barrel by lapping. Regards, Bill.

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I can't disagree with any of that. We are comparing apples and oranges. Usually, when I lap a barrel I am removing all tool marks and usually putting a choke in it. Most of the ones I did were the cheapo Numrich 45-70 barrels. Several had nasty imperfections in the bore. If you want to put a final polish on a barrel with fine abrasive I don't see a problem either.

The only logistical problem is getting the grit on the lap so that it will get at the throat. Normally you need to get it back indexed the way it came out. I usually stick it out the muzzle partway to charge it. That make it a problem to get the part near the breech. If you are carefull I guess you could take it out the breech end and put a bit of grit on it and carefuly re-insert it.

I did once do a Marlin 45-70 lever gun for a friend. It was not at all uniform when I started. It was when I was done. I took it easy on the muzzle. He had a tight spot at the muzzle when I finished. It shot better when I finished, especially with cast bullets.

For the guy doing it the first time, carefull is the key. Don't force it. Charge it with the tiniest amount of grit at first. Otherwise it will stick. Do use lots of oil. I would also set the barrel in the vice so that the lap can not fully exit the muzzle. Put the muzzle against the wall or a block of wood. Do not concentrate on the muzzle. A little taper or choke is not a bad thing. Don't grab a cleaning rod, pour some lead, and go to scrubbing. Use a guide, ball bearing handle, and think about what is happening. If you I think you will do OK.

I no longer try to keep the lap in the same position as cast. In fact, I index the lap one groove every few strokes. The idea here is to improve uniformity of groove dimensions.
I also started lapping on large caliber lead bullet and ML barrels. I went with info gleaned from The Muzzleloading Caplock Rifle by Ned Roberts. My intent at that time was to do like Billinghurst, Warner, and others and produce the choked bore as they did. It did make a nicer shooting muzzle loader. A different intent and similar process. Regards, Bill.