Jim.I would follow Mason's sugestion there are a lot of varribles with the .38-55 bore and twist.
It could be the bullet.A280 grainer should fly,a 250 gr might work better.
I ran into a problem with my High wall when I first got it trying to develope a load for it,I dont care what I tryed for a load it just would not bring a good groop.So I finally put scope bases on it and I loade up some copper jacketed bullets I swage Loaded some with 5744 powder and more with 3f goex and shot the smokless jacketed bullets ,only 25 of those buggers,It was a calm day at 200 yds I shot 20 of that load.They printed about 8"high but all 20 would fit in the 3"Xring of that SRC 200 yd target.
Next I shot the lead bullets again, they were all over that 24" paper keyholed,that rifle never put a slug sideways in the 1000+pluss I have shot before working up a load.
I spent a good hour scrubbing thr bore getting the copper out,shot 10 and looked all looked good,no keyhole and they were in a nice 4"groop the best it ever shot.
I guess Jim what I'm trying to say if that rifle has shot copper jackets clean the bore very good and try it again with no gas checks this time.
Heck it might work. :wink:
Kurt.