Chrono'd Today (Update)

[bamashooter]

CCI AR Tactical 40gr (5-shot avg / rounded numbers)

MV FPS):..............1233 /// Advertised @ 1200 fps
ME (FT. LBs): .......135 /// Advertised @ 128 ft. lbs

CCI Copper (Polymer) 21gr (5-shot avg / rounded numbers)

MV FPS):..............1745 /// Advertised @ 1850 fps
ME (FT. LBs): .......141 /// Advertised @ 160 ft. lbs

Little disappointed w/ the 21gr

16.5" barrel vs unknown test barrel length.

Shouldered the 15-22 vs bench therefore very likely I wasn't parallel to sensors.

 

[Meangene]

Thanks for the help full information.

 

[bamashooter]

You bet. When the weather clears this week, I'll repeat on the bench. I'm pretty sure I was angled from the sensors of the chrono.

 

[bamashooter]

Update:

10 rounds today of 21gr. Bench. Carbine secured true / level / approx 3" above chrono sensors. Very surprised with the results. The 10 rounds were from a "second" box.

Created: 04-09-2019 01:35:00 PM
Description: CCI 21 Gr. Deux
Notes 1: 
Notes 2: 
Distance to Chrono (FT): 12.00
Ballistic Coefficient: 0.920
Bullet Weight (gr): 21.000
Altitude (FT): 750.0
Temp: N/A
BP: N/A

Shots
#     FPS        FT-LBS     PF
10    1607       120.44     33.75     
9     1603       119.84     33.66     
8     1642       125.74     34.48     
7     1567       114.52     32.91     
6     1707       135.89     35.85     
5     1643       125.90     34.50     
4     1594       118.50     33.47     
3     1624       123.00     34.10     
2     1624       123.00     34.10     
1     1595       118.65     33.49
     
Average: 1620.60
StdDev: 38.27
Min: 1567
Max: 1707
Spread: 140
True MV: 1623.00
Shots/sec: 0.12
Group Size (IN): 0.00

If I chrono for the next two weeks, the bullet will do well to dribble out of the barrel. Better quit while I'm ahead.

 

[bamashooter]

Contacted CCI and received a reply today regarding the 1850 fps rating of the 21 gr round. The reply stated they use a SAMMI spec'd, 24 inch barrel and chamber for their figures.

 

[mike campbell]

CCI used another 8" of barrel and likely measured much closer than 12 feet ... so maybe the disparity is not that surprising. I'd be more disappointed in the standard deviation ... +/- 80fps for 95% confidence ain't good.

Dropping the high outlier improves it to +/- 50 fps ... still not good.

However, despite the poor stats, they are not a predictor of accuracy which would be my acid test. Velocity stats are useful when velocity is paramount, such as making a minimum power for competition. Otherwise, they're just a matter of curiosity ... which ain't a bad thing.