20" barrel .308 muzzle velocity question

jackjacker

jackjacker

New member
I shoot a Savage Model 10 Precision Carbine in .308 with a 20" barrel. I've chronoed 175gr FGMM, 168gr FGMM, M118LR and my average velocities were 2658, 2703 and 2651 respectively. I use a ProChrono chronograph at 10 feet from the muzzle. I was expecting to get lower muzzle velocities than those on the box because of my shorter barrel. My POIs at different distances seem to be consistent with the ballistics data from JBM ballistics plugging in the above velocities.

My questions are these: Is the ProChrono an accurate instrument? Has anyone had similar velocities with a shorter barrel ( I understand .308 cartridge is very efficient)? And, third, does it even matter considering my dope seems to be on? My only concern would be calculating an accurate terminal energy value.
 
You won't find a whole lot of difference in velocity in a 20" barrel than you would in say a 22" barrel and so on, the 308 isn't one of the calibers that need long barrels. So I would say your chronograph is probably fine. Do you have any hornady factory loads with the published velocity on them? They are generally fairly well on the money +/- a bit here and there.
 
Originally Posted By: jackjacker
My questions are these: Is the ProChrono an accurate instrument? Has anyone had similar velocities with a shorter barrel ( I understand .308 cartridge is very efficient)? And, third, does it even matter considering my dope seems to be on? My only concern would be calculating an accurate terminal energy value.
your chrono seems to be accurate, i have similar velocity runnin 175SMK's in my 308, (efficient) not really, kind of a slow heavy round, but its accurate and works great, if you want efficient in wind especially, look into the 6.5's they have about 40% less wind drift than the 308...
and regarding your velocity, if it matters... depends on if your gonna be killing in different conditions, yes it matters, because unless you keep your powder temp and atmospheric conditions consistent, you velocity wont be... in short, record everything, you owe it to yourself and the target your shooting especially if its LR.
 
Why so worried about terminal energy? It's just an arbitrary number... There are much more important things to worry about.
 
Great responses, guys! Thanks!!
@BigKev- I've tried hornady and get similarly high velocities.
Skinney, makes a good point about conditions. It's usually been 90 -95 degrees when I've chronoed. Thanks again.
 
I have a Chrony (alpha) and ran some Federal 168 gr match rounds thru my Remington LTR, 20" bbl. Avg vel was 2501 fps. I also loaded some rounds with Varget and Sierra 168 gr bullets, starting with 42 1/2 grs up to 44 grs. Avg vel was low end 2347 fps up to 2439 fps, not quite up to par with the Federal match loads, but VERY accurate. Your Federal match at about 200 fps higher than my findings, sounds HIGH. It might be right, could be difference in bbl, or temps?
 
jbm dope could be wrong ..the dope depends on ur conditions too now.. im pushing 165sst over 41.5 grains of imr 4064 at roughtly 2600 in a 20in barrel
 
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