Rifle Range

I finally got to test some 95 SMK hand loads. I used Winchester small rifle primers, new Federal brass, and Winchester 760 powder starting at 26.0 grains and working up to 27.5 grains. The rifle has a 24″ 1:6.5″ twist Bison Armory heavy barrel and an Elite Iron muzzle brake but I left off the silencer and shot unsupressed for the testing.

I only shot a single 5-shot group at each charge and got the following average velocities with standard deviation below 13 for all and extreme spread no greater than 27:

26.0: 2430 fps

26.5: 2510 fps

27.0: 2555 fps

27.5: did not measure, estimate 2600 fps

I shot the first three loads at 100 yards and shot a near 1/2″ group with the 26.5 grain load:

 

 

 

 

 

 

 

 

 

 

 

 

 

2510 fps at the muzzle with a G1 BC of 0.60 results in 1318 fps at 1000 yards and 1168 fps at 1200 yards. The speed of sound is around 1130 fps and this load stays above that to 1250 yards according to the G1 BC and available data. The load is definitely a 1000 yard performer in terms of velocity. Hopefully I will get to shoot it at 1000 yards this summer. Pushing to 2550 or even 2600 fps seems reasonable, though accuracy wasn’t quite as good as I pushed the bullet faster. Single 5-shot groups are not sufficient to make a firm determination but more testing is in order.

I am thinking that Federal’s 90 SMK accuracy troubles may result from loads that are just too hot. I wonder if they’re pushing the bullets too hard to get the mythical 1300 yard supersonic performance but sacrificing accuracy. Seems like a lousy trade to me when solid 1000+ yard performance from a 75 to 95 grain bullets is great performance from any AR-15 rifle.

 

 

 

Took 4 rifles to the range on Friday:

18″ 308 Fulcrum

18″ 223 Fulcrum

18″ 6.8 Recon

22″ 6.8 Heavy

Except for the 223, all shooting was with hand loads. Today’s post relays the results of 20 rounds of 308. The rifle was wearing a Vortex PST, decent but nothing fancy.

18″ 308 Fulcrum Results

My version of the 168 SMK FGMM

Load 1:

168 SMK over 42 grains of H4895
Federal cases, CCI large rifle primers
OAL 2.80″
MV 2577fps

Result: 10 shot group at 100 yards

Sigma = 0.249MOA (0.183 to 0.358 – 95% confidence)
Extreme Spread = 0.82 MOA
P1-0.5 = 91.8% (72 to 99% – 95% confidence)
P1-1.0 = 100% (99 to 100% – 95% confidence)

Pretty good. Indicates high probability that 7/10 shots are expected to be within 0.5MOA of true point of aim, and 10/10 shots should be within 1.0MOA of target. For an auto loader this is great.

Load 2:

168 SMK over 43 grains of H4895
Federal cases, CCI large rifle primers
OAL 2.80″
MV 2611fps

Note: First shot was 2″ below the center of the rest of the group. I’m calling this an outlier, but I don’t like it.

Result: 9 shot group at 100 yards

Sigma = 0.389MOA (0.281 to 0.547 – 95% confidence)
Extreme Spread = 1.69 MOA
P1-0.5 = 66.9% (35.2 to 86% – 95% confidence)
P1-1.0 = 97.7% (79.5 to 100% – 95% confidence)

Not as good as the last group, and my shooting ability is an uncertain factor. Still, this data indicates high probability that 3.5/10 shots are expected to be within 0.5MOA of true point of aim, and 8/10 shots should be within 1.0MOA of target. So the question is: did my shooting fall apart and produce this less precise group, did the additional 1 grain of gunpowder cause the degradation, some combination of the two, or something else?

For fun we can combine the two groups by overlaying at the “center of mass” of each group

There is clearly a cluster in the middle and then two outliers. I’ll never know the cause but this is interesting. To get more insight, separating the groups by coloring them differently shows the contribution to the blob above from each (ignore the numbers, they’re for a single group):

The 17 rounds clustered in the middle imply something… the rifle is clearly capable of excellent accuracy for an auto-loading weapon. Did those two shots come from bad shooting? Bad loading? Fatigue? Are they truly representative of the weapon itself?

Possible I wasn’t as careful with the second batch of 10 rounds as I was with the first while charging the cases or seating the bullets. Or I was tired as this was later in the day after shooting the other rifles. And what was with that shot that was 2″ low? Clearly, more range time is warranted.

I’ll get to those other rifles in the next post.