10-19-2021, 10:39 PM
Anything that works for 300' will also suffice for you at 15,000. Since a cartridge generates its own O2 for deflagration, 15,000 should still work although I have not shot at those heights.
So, Hornady has a 6.5mm fmj, 123 grs, BC 0.420 (G1)... even currently available!
I didn't see any other fmj's on ammoseek currently, so will use this one for examples.
Running some ballistics numbers, at 300 msl, this 123 gr fmj starting at MV of 2375 would drop to 1385 fps and 524 fp-KE at 600 yards. My BC calculator goes up to elev 10,000 and for that, 600 yds increases from 1385 fps to 1805 fps/ 890 ke.
Looking upwards to your 1500/600 yds desires:
At MV of xxx, 600 yds velocity of yyy:
MV 2550 fps, 600 yds 1503
2500 fps, 1469
2450, 1435
2400, 1401
So. Now I have some real world MV data from my 16" barrel, using a few 120 and 123 loads, magnetospeed (elev 324):
Factory Hdy 123 sst: 2432, sd-13
Factory Hdy-black (this was an older lot, might not be this for newer lots): 2432, sd-12
Factory Federal 120 fusion 120: 2429
Hand load, AR comp and cii450 primer, 2442.
The shortest civilian barrel being 16", it would appear that properly loaded 123 fmj's loaded similarly to these would meet or slightly exceed your minimum requirements. I have not shot any 14.5" barrels, and haven't as much data for my (once-upon-a-time) 12.7" barrel, but 16 certainly is a recommendation. Longer obviously if you like. More barrel, more MV.
To get to the 2475-2500 MV level you would probably need 20" barrel, of course note also that most of the faster Grendel powders are ball-type so fairly temp-sensitive (thinking hi-altitude here). AR comp and 8208 xbr are the more insensitive ones typically used.
The 2450-2475 starting MV is achievable from an 18" barrel.
2400-2450, as mentioned, from a 16".
Others more experienced than I might also weigh in.
This should be some of what you're asking about...
So, Hornady has a 6.5mm fmj, 123 grs, BC 0.420 (G1)... even currently available!
I didn't see any other fmj's on ammoseek currently, so will use this one for examples.
Running some ballistics numbers, at 300 msl, this 123 gr fmj starting at MV of 2375 would drop to 1385 fps and 524 fp-KE at 600 yards. My BC calculator goes up to elev 10,000 and for that, 600 yds increases from 1385 fps to 1805 fps/ 890 ke.
Looking upwards to your 1500/600 yds desires:
At MV of xxx, 600 yds velocity of yyy:
MV 2550 fps, 600 yds 1503
2500 fps, 1469
2450, 1435
2400, 1401
So. Now I have some real world MV data from my 16" barrel, using a few 120 and 123 loads, magnetospeed (elev 324):
Factory Hdy 123 sst: 2432, sd-13
Factory Hdy-black (this was an older lot, might not be this for newer lots): 2432, sd-12
Factory Federal 120 fusion 120: 2429
Hand load, AR comp and cii450 primer, 2442.
The shortest civilian barrel being 16", it would appear that properly loaded 123 fmj's loaded similarly to these would meet or slightly exceed your minimum requirements. I have not shot any 14.5" barrels, and haven't as much data for my (once-upon-a-time) 12.7" barrel, but 16 certainly is a recommendation. Longer obviously if you like. More barrel, more MV.
To get to the 2475-2500 MV level you would probably need 20" barrel, of course note also that most of the faster Grendel powders are ball-type so fairly temp-sensitive (thinking hi-altitude here). AR comp and 8208 xbr are the more insensitive ones typically used.
The 2450-2475 starting MV is achievable from an 18" barrel.
2400-2450, as mentioned, from a 16".
Others more experienced than I might also weigh in.
This should be some of what you're asking about...
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