.375 Ruger load work up question

[akmac]

Hello all, today I was working up a load for an upcoming moose hunt. I'm using a Mihec 375-275 purchased from a group buy about two years ago. With my lead the bullets weigh in at 273gr including gas check. I am using 34gr of H4198 and a dacron filler. The load has proven to be very accurate with no pressure signs. I forgot my chronograph so I don't have the speed but the book estimate is around 1900fps.

I noted that the shots were all 6" high at 50 yards but when I loaded my 270gr jacketed rounds they only shooting an inch high. I made sure to shoot the same each time and not let the barrel rest on anything.

I found it strange the lead would group so high, any ideas as to why?

[RobS]

Possible: Jacketed bullet moving faster.............less time in barrel so bullet exits before muzzle lifts. Cast boolit load there is more dwell time (longer in the barrel) allowing the muzzle to lift more upon boolit exit from the barrel.

[GooseGestapo]

Barrel harmonics. The barrel vibrates like a tuning fork when fired. The large difference in pressure, velocity, and barrel friction produces a significantly different vibration pattern with the bullet exiting the barrel at a different point in the cycle.

A number of years back, the U.S. Team got badly shellacked by the British team in the Wimbledon long range matches. The British were shooting a modified Enfield action that had a lot of flex and whip. Coincidentally, the whip caused ammo velocity fluxuations to be self compensated at 1,100/1,200 yards yielding significantly better grouping.

This explains why some loads perform better in some guns than others...

[akmac]

Thanks for the replies. This intrigued me because logically you would expect a slower bullet to impact lower, not higher.