"What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v
Armalite had a very good pressure curve graphic posted on their tech notes. This is a variation (63-grains being close to legacy M855 Green Tip):
If you have a projectile that enters the rifling at an non optimal angle due to a less than concentric chamber, muzzle velocity won’t be affected but downrange performance of that ever so slightly deformed round with an ever so slight oblong movement to its spiral rotation will show degraded accuracy and probably velocity.
Black River Tactical
BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
BRT Bolt Carrier Groups M4A1, M16 CHROME
BRT Covert Comps 5.56, 6X, 7.62
Full auto-mag dumps.....
They aren't getting higher velocities at 100 m, that 30 to 40 fps is well within the SD of that ammo.
The big take-away of that article is:
1) Cyclic rate (suppressed/unsuppressed):
--carbine: 944/864 rpm
--mid: 881/737 rpm
2) MRBF:
Ambient
--carbine: 836.1 (65 malfunctions)
--mid: 1993.8 (30 malfunctions)
The two are related, BTW.
Black River Tactical
BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
BRT Bolt Carrier Groups M4A1, M16 CHROME
BRT Covert Comps 5.56, 6X, 7.62
Do you have any links to a credible ballistician that can confirm the phenomenon you describe? I’d like to see confirmation of this often repeated theory.
From what I’ve read, the bullet will continue forward from the point which it reaches stability; not returning to a central and consistent point along the rotational axis; ie making a consistent point of impact and thus small group. Typically the smaller groups are often related to shooter performance and buckling down.
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Sadly no, just memory of a Guns and Ammo article from years ago.
In a report from Picatinny, 15 new M4A1 were tested for something else, but the cyclic rates were given.
W1-1: 822
W1-2: 859
W1-3: 794
W2-1: 804
W2-2: 735
W2-3: 832
W3-1: 820
W3-2: 781
W3-3: 747
W4-1: 712
W4-2: 656
W4-3: 773
W5-1: 754
W5-2: 788
W5-3: 806
Average: 788
Another report gives the average cyclic rate for ten M16A3s as 686.
The specification requirement for M4A1 Carbines is "...700 to 1025 rounds per minute when firing M855..."
So, the given cyclic rates seems reasonable.
Last edited by lysander; 07-10-18 at 20:25.
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