Bad point of aim is it the crown?

[wszumera]

Uncle made me a .62 underhammer last year. The front sight is at one side of barrel flat the rear at the opposite side of flat to get it to shoot straight. Barrel looked straight when we got it.

I'm thinking the crown might have issues and I have a lathe. Is a 45 degree angle okay for a crown? Better angles? How deep should it be?

Thanks,

Clutch

 

[LRB]

Your bore may have runout, and not be centered, in which case the bore would need to be centered in your lathe, rather than the barrel itself. There is a better chance that it is bent. If you run a string through the bore, attached at each end to a makeshift bow, hold the bore to some light you will be able to see if it is. If it is bent, the strings shadow down the bore will be broken at the main area of the bend, and you can straighten it. If you are convinced that it is the muzzle, you could use a ball file, running very slowly in a hand held drill, and recut the inner crown. A ball file will self center in the bore regardless if the bore is a tad off with runout. It is acually more accurate than a common lathe in this respect. I always recut the muzzle on any gun I get, modern type, or ML. Who is the barrel maker? Most barrels today are planed after they are drilled, eliminating most runout problems, but there may be some that are not. I would suspect a bent barrel is the cause. Check that first.

 

[tg]

Seems like some barrels used to be prone to runout, they worked best if the run out was top to bottom so the front and rear sight elevations
sovled the problem and did not look as odd as the side to side thing with the sites.

 

[cgm]

If the barrel looks straight and there is no runout, I can point to an experience I had with one of the first longrifles I built.

My rifle consistantly shot low, even at close range. I pulled the barrel and it appeared straight, but it always shot low.

Finally, I found the problem. The barrel was attached with pins and I didn't make slots in the underlugs. The holes in the underlugs were a tiny bit off and pulled the barrel down. It doesn't take much. When I elongated the holes in the underlugs, the gun shot fine.

Check to see if something might be pulling your barrel off. Also, shoot off a bag to sight the gun in. Are you new to flint? Some new shooters will flinch away from the flash and the shot goes to one side.

Clayton

 

[cgm]

My previous post mentioned flinching from flintlocks flash - sort of hard with an under hammer!

Clayton

 

[Bill Hall]

I really don't think it's your crown. A bad crown can cause your shot to consistanly go to one side, but the accuracy would be terrible. If you are getting good groups, write off the crown.

And I doubt that it's bore run-out, or only a run-out problem. I think there would need to be an exceptionally large run-out problem to cause your sights to be on opposite sides of the barrel flat like that. I would hate to think that a barrel that bad would ever make it to public sale. It may still be a factor though.

A crooked barrel, or a barrel that becomes crooked after being installed in the stock makes the most sense to me. From what I know of underhammers, don't they usually have a forearm that is separate from the rest of the stock? If so, maybe you could remove the forearm and shoot it a few times like that. If that doesn't tell the tale, I would remove the barrel and recheck for straightness and ru-out, as it could be a combination of both. It's amazing how the slightest curve in a barrel can be seen with the naked eye while looking down the bore.

Now, if you find that your barrel is crooked after all, maybe someone else can give advice on how to straighten it. I have never done this so won't even pretend I know the best method. :surrender: Good luck, Bill

 

[wszumera]

To close this, we ended up clocking the barrel to fix it. We tried bending it using a laser level stuck to the barrel flat pointed at a target across the yard with my barrel clamped to a bridgeport table.

We used hold down clamps to put some bend into it but every time we let up, the laser was pointing to the same place. We stopped when I was afraid we would pull the top of the tee slots out of the table.

Clutch

 

[jerrywh]

It is impossible to have that much runout. The sights would be no futher to one side than the bore if it was runout. Have you or anybody else ever heated the barrel?? Crowning one is easy . go ahead and do it. That will eliminate that possibility. Make a crowning tool out of brass with a long pilot that fits the bore. Do not use aluminum. Aluminum will score the bore.

 

[rafterob]

It is impossible to have that much runout

Impossible? It is certainly possible but I would hope that no respectable barrel manufacturer would allow one past quality control.I would be tempted to put a laser bore sight in this one to see if it is runout or not.

 

[jerrywh]

If the front sight was on the left side of the barrel flat and the rear sight was on the right side of the barrel flat and the cause was runout the bore would come out of the side of the barrel at some point. Think about it.

 

[shortstring]

I say the bore is not straight. Try this. Sight it in at 25 yds. Now back up to 50 yds, if the barrel isn't straight it will again shoot off, you can move the sights again & now move to 75 yds. Again the impact will be off. At least this has been my experience with such problems. The good news it that it can be straightened.