trouble sighting in knight disc rifle

[east bay ed]

A friend of mine called me last night. He is having trouble getting his Knight Disc sighted in. He put a burris scope on it and now he can't get it to shoot 3 shots together. He can get two shot to group then the third will be off by a couple inches. This is the same gun and load that he has used for a couple of years with great success. He even changed to a different scope and found basically the same problem.
I told him I would look at the mount and rings. If the charge and bullet are the same as he has always used the only change would be the scope, or the mount & rings.
Does anyone else have any ideas?

[shortbox11]

sounds to me like fouling ,,, clean the barrel after the second shot and see what happens.

[rzdrmh]

same powder from previous years?

bp subs go bad quick.

[east bay ed]

he is using black powder so no issue there. I asked him about fouling he said he was cleaning the barrel with a rag after each shot and that didn't seem to make a difference.

[jrbarber]

my guess is that he wont get to a 3rd shot on an animal anyway with a mzldr... i mean chances are that if the first 2 shots thru a clean gun are grouping he shouldnt need a third shot..not that its not a concern - other than that is he using loctite on his mounts?

[Anderson]

If he's cleaning the same between shots and everything is tight, my next thought would be barrel temp.