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I'm trying to work up a load to duplicate the SSA Barnes 70gr TSX loading, which should be the equivalent of the "browntip". I use once fired cases, FL sized and trimmed. I did not turn neck, clean primer hole, etc. Powder dropped by hand on a scale, so it is pretty accurate.
- Is a 30fps stdev within expectations? The one chrono result from ARFCOM of the SSA load suggested 15fps stdev from a 16" barrel, and 21fps 20" barrel.
- How should I go about tightening the muzzle vel spread? I will keep dropping powder via a scale for the "production" rounds.
About the load
H335
CCI No.41
LC 09 case
COAL 2.258"
Light-ish crimp. I noted where the crimp die started to move the case mouth, and turned it 1/4 turn tighter.
About the gun
Colt 6920
16" chrome lined barrel
5.56 chamber
"Book" data
Barnes data shows max 23gr powder, velocity ~2640 from 16" barrel (data in 20", I guesstimated the 16" number). Nosler data for their 69gr shows max 24gr powder, velocity ~2760 from 16" barrel (data in 20", again guesstimated). The SSA load chronoed to be 2788fps.
3 shot chrono results
23gr
Average 2675fps
Stdev 31fps
23.5gr
Average 2751fps
Stdev 29fps
- Is a 30fps stdev within expectations? The one chrono result from ARFCOM of the SSA load suggested 15fps stdev from a 16" barrel, and 21fps 20" barrel.
- How should I go about tightening the muzzle vel spread? I will keep dropping powder via a scale for the "production" rounds.
About the load
H335
CCI No.41
LC 09 case
COAL 2.258"
Light-ish crimp. I noted where the crimp die started to move the case mouth, and turned it 1/4 turn tighter.
About the gun
Colt 6920
16" chrome lined barrel
5.56 chamber
"Book" data
Barnes data shows max 23gr powder, velocity ~2640 from 16" barrel (data in 20", I guesstimated the 16" number). Nosler data for their 69gr shows max 24gr powder, velocity ~2760 from 16" barrel (data in 20", again guesstimated). The SSA load chronoed to be 2788fps.
3 shot chrono results
23gr
Average 2675fps
Stdev 31fps
23.5gr
Average 2751fps
Stdev 29fps
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