As you can see, if you have a 1in9 twist 338 barrel shooting subsonics in winter, you might get some unstable bullets (keyholes), with the Lapua Scenar or Berger Hybrid. I did all the above for you, because you want a minimum stability of 1.500. 510s are cool but screw that projectile cost. Hawk Precision Bullets 300gr SP = 1.445" stability= 2.494(1in9), = 3.156(1in8) What are realistic distances for subsonic rifle rounds like the. Using worst case temperature of 0F, 1050 fps. Use the following bullet lengths for the calculator above. The higher you are away from the ocean (sea level), the more bullet stability you get. Worst case bullet stability is temperature of 0F at sea level, and 100F at sea is much better stability. (free JBM Miller Stability Calculator online) However, that is overkill and a 1 in 8 twist is sufficient for the long 300 grain bullets in 338, at 1050 fps, no matter whether you choose 338 Spectre, 338 Whisper, or 338 Federal. I had the barrel made with a 1 in 7 twist to be safe for the 300 grain bullets. To get good supersonic performance along with subsonic in 338, then you would want either the 338 Whisper or 338 Federal.Įdited to add on 4/13: I built my 338 Federal subsonic bolt rifle some years ago, when the Miller Stability Calculator was not available widely yet. The question is, do you want to use this solely for subsonic? If so, then the 338 Spectre may be best to use on an AR-15 platform or a bolt rifle.
The 338 Federal is made to use with the DPMS 308 or AR-10 platform. The 338 Spectre is made to use with the AR-15 platform. It also has slightly more H2O capacity for the brass than either 338 Spectre or 338 Whisper.ģ38 Federal, 57.5gr capacity, 2.800" COALģ38 Whisper, 43.0gr capacity, 2.650" COALģ38 Spectre, 28.8gr capacity, 2.310" COAL Making 338 Federal brass is simple too, just run 308 brass through the die and expand it and resize in one step. I could also build a new upper for my DPMS 308B or just get a 338 Federal barrel for it and have a semi-auto subsonic rifle. I have been using the 338 Federal for a number of years as a subsonic platform, using a bolt rifle (1in7 twist barrel).
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