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Posted: 10/8/2012 4:43:33 AM EDT
Shot with a friend of mine over the weekend, who was using 62 gr FMJBT Arsmcor bullet at 600 yards (I realize it's not an optimum bullet for 600 yards, but this was all he had).  His load was 24.4 grains of Varget.  The guys in the target pits said that the bullet was not supersonic when it hit the target.  Said there was no sonic crack when it came through the target, and every shot of his sounded like a berm shot.  But it was still making round holes in the target, no evidence of any keyholing at all.

It took 3 shots to get him on paper, and a couple more to dial-in the correct elevation.  On his second string of 10 rounds, he did surprisingly well (shot an 88-1X).  Watching the trace, his shots were definitely arcing a bit higher than the others.  Can anyone look at the numbers, and tell me if that round should be supersonic at 600?  We verified his powder scale with a round that I had, by breaking it down and weighing the powder and the bullet, and it read about .1 gr lower than my scale.  Thanks for the help!
Link Posted: 10/8/2012 4:59:28 AM EDT
Need more info.  Muzzle velocity?  Atmospheric conditions?  A measured BC would be nice as well.

Guessing the MV @ 2900fps and using the likely optimistic BC of .307 on the Midway website, the bullet *should* still be supersonic at 600.  However, I don't put much stock in that BC and based on the poor reputation of those bullets with regard to consistency, I wouldn't be surprised if they were wobbling enough to affect drag and decrease the effective BC even more.  As such, wouldn't amaze me if they performed somewhat worse than the modeling would indicate based on the (limited) information.
Link Posted: 10/8/2012 5:16:32 AM EDT
Don't know what the MV is, and like you, the only thing I could find was the BC of 0.307.  Temperature was about 50 degrees, overcast, and humid (southern Ohio).  We realize they weren't match bullets, but I do have to say I was pretty impressed with how he was shooting them!

Thanks!
Link Posted: 10/8/2012 5:18:21 AM EDT
I agree. More info is needed but, unless that is a light load that bullet "should" still be super-sonic at 600. A bullet looses it "forward" velocity a lot quicker than it's rotational velocity. The rotational velocity is what keeps it accurate. It is said however that when a bullet goes from super-sonic to sub-sonic there can be a un-stabilizing effect. I see this a lot from guys who compete with cast bullets in service rifles. They always want the bullet to still be super-sonic at target distance.
Link Posted: 10/8/2012 8:01:15 AM EDT
With the limited information provided I would say a 62g projectile would still be supersonic at 600 yards. The posted MV of the factory ammo is 3050 fps. JBM shows the bullet goes trans-sonic at 800 yards with generic variables entered.
Specs:
Caliber: .223
Grain Weight: 62
Bullet Type: FMJ
Velocity: 3050 Muzzle
2586 @ 100 yds.
2131 @ 200 yds.
1742 @ 300 yds.
Energy: 1136 Muzzle
804 @ 100 yds.
555 @ 200 yds.
371 @ 300 yds.
Rounds per Box: 20
Link Posted: 10/8/2012 10:44:08 AM EDT
At 2700 fps, answer is yes. Tool yourself.

http://m.hornady.com/ballistics-resource/ballistics-calculator
Link Posted: 10/8/2012 5:30:38 PM EDT
What others have said:

Chrono it and find out......
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