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toallmy
03-27-2019, 11:02 AM
I am a newbie in cast rifle shooting , I have only served a couple years of what I think is going to be a life sentence .
I keep running into issues when switching between jacket / cast shooting , or even my lower velocity / higher velocity cast loads . I have noticed this over the few rifles I have been shooting cast boolits out of .
Horizontal point of impact difference between the lower velocity / higher velocity just keeps popping up and it's mind boggling . I must be over looking something - I expect a slower moving projectiles to drop more at a set range . But why do I experience the horizontal shift in impact points .
This first became a problem with my trusty 30-30 . I mounted a side mount scope on it to do some load work up .
I worked up a nice light fun load with unique , then a decent higher velocity load but they print groups at different places on target horizontally several inches at a hundred yards . Just between 50-100 yards I am having up to 6 inch shifting groups horizontally . I finally just removed the scope installed a peep sight and set up at 50 yards with the light loads , for fun .
The Sunday past I took my new 7x57 project out to do a little shooting at a 100 yards planing on going out to 250 yards , just trying to do a little tinkering with the best load so far . I have worked out a 3 inch shooting cast load that's moving along pretty good with a little 7mm Thor cast boolit over 42 grains of imr 4831 holding 3 inches constantly at a 100 . But when I missed the little index cards completely I was stumped until I remembered sighting in for a jacket load the past range trip . Shore enough a 5 shot cluster just to the left of the index card slightly lower but definitely to the left a few inches . I fired a group with a jacket load just to confirm the sights were not shifting the group printing on target .
So it's apparent velocity changes shift impact points quite a bit left / right even at 50-100 yards . [smilie=b:

popper
03-27-2019, 12:03 PM
3 normal problems. First, high fps loads have different recoil so your body/shoulder acts different. Second, bullets travel in a helical path to the target. That path depends on gyro stability which is different for fps and the bullet. If it is a path problem, changes of 10 yds will shift same load to a different point.
3rd is barrel harmonics - look that one up but normally (so I've heard) horz is low load, vert is high load. Pick a point in between. A problem with cast is how well the boolit holds to the rifling which is #2.
I noticed a problem with my 30/30, heavy boolits go to the right a bunch. Then I noticed that these were engraving a lot and cycling some dummies, unevenly! Loaded singly, the long OAL caused the boolit to chamber off-center. Semi-circle lead jam against the bore.
My FTX load with LeverE @ 2100 fps, about the same with H4895. I seat with the case mouth below the crimp groove and FCD just to remove the bell. Very accurate in my Marlin.