04-04-2020, 07:31 PM
if i recall the berger reloading manual has some loads listed for the 140s. Lyman published a book on accuracy reloading, which had an article from Dave Emory, the head ballistician at Hornady for many a year. if i recall he recommended a gyro factor of 2 or above. a Grendel won't get there with 140s. 130s is about max. that is with a 1-8 twist. if you want to go 1-7 or so you should be good to go. notice the 300 BLK has a 1-7 twist due to the fact that it's trying to fling 220-230 @<1100 fps. of course long heavy bullets can be shot with gyro <2 but the article was about accuracy, and long range accuracy. notice the 300PRC has, if i recall, a 1-8 spec'd twist to deal with those 220-230 match bullets. it's the length of the bullet vs it's diameter that is the primary driver for what twist rate you need for the bullet for best accuracy. you gotta reach a certain rpm. but twist rate affects that to a much higher degree than velocity. you gotta add a LOT of fps to get to the same rpm as a 1" change in twist rates. so at 3000 fps or so it takes a 8" twist in the 300PRC but at <1100 fps in the 300BLK it takes a 1-7" twist for those same long for caliber bullets. so a 1" twist change makes up for 2000 fps difference in this example.
Hornady's online ballistics 4DOF and Bergers twist rate calculator will give you gyro numbers. the heavy for caliber vld type bullets will retain more velocity at very long distances, in general, but keeping the gyro at 2.0 or higher at launch may give you tighter groups. a miss with a faster bullet is less effective than a hit with a slower bullet.... just saying.... my tightest groups in 308 and 30-06 with 1-10 twists for both have been with 190gr. SMKs. i've tried the 220-230s since there's published load data, primarily in the 30-06 but the tighter groups were with the 190s. when i went to the Hornady 4DOF calculator... hmmm... 190s with a 1-10 twist.. gyro ~2. 225s with a 1-10 twist, gyro < 1.3 if i recall.... hmmm.... tightest group in my 308 was with 190s. so with my Grendel 1-8 twist i'm shooting up to the 130s but have decided not to pursue the heavier bullets. my very limited experience and what i've read seem to indicate that i'll expect tighter groups at 130gr. and below. ymmv of course since each barrel is unique. and if your rifle shoots under 1 MOA it's very difficult to get enough statistical data at close ranges. shoot >= 300yards on calm days, for groups. and at least 5 groups of 5 to start to see statistical differences. and if all your trying to do is to hit a 1/2m gong @ 400m then it probably won't matter at all what bullet you use...
-tdbru
-tdbru
Hornady's online ballistics 4DOF and Bergers twist rate calculator will give you gyro numbers. the heavy for caliber vld type bullets will retain more velocity at very long distances, in general, but keeping the gyro at 2.0 or higher at launch may give you tighter groups. a miss with a faster bullet is less effective than a hit with a slower bullet.... just saying.... my tightest groups in 308 and 30-06 with 1-10 twists for both have been with 190gr. SMKs. i've tried the 220-230s since there's published load data, primarily in the 30-06 but the tighter groups were with the 190s. when i went to the Hornady 4DOF calculator... hmmm... 190s with a 1-10 twist.. gyro ~2. 225s with a 1-10 twist, gyro < 1.3 if i recall.... hmmm.... tightest group in my 308 was with 190s. so with my Grendel 1-8 twist i'm shooting up to the 130s but have decided not to pursue the heavier bullets. my very limited experience and what i've read seem to indicate that i'll expect tighter groups at 130gr. and below. ymmv of course since each barrel is unique. and if your rifle shoots under 1 MOA it's very difficult to get enough statistical data at close ranges. shoot >= 300yards on calm days, for groups. and at least 5 groups of 5 to start to see statistical differences. and if all your trying to do is to hit a 1/2m gong @ 400m then it probably won't matter at all what bullet you use...
-tdbru
-tdbru