Rifle Range

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.

Measured my 22″ heavy 6.8 chamber with a Hornady OAL gauge. Several bullets measured out as follows:

Sierra 115 SMK

2.384″ OAL to lands
2.352″ for full neck engagement

Berger 130 VLD

2.471″ OAL to lands
2.381″ for full neck engagement

Nosler 110 Accubond

2.407″ OAL to lands
2.457″ for full neck engagement

Nosler 130 Ballistic Tip

2.563″ OAL to lands
2.572″ for full neck engagement

Interesting that the Nosler bullet shapes are such that the bullets seat deeper when into the lands than the maximum length for full case neck engagement. In the end I decided on the Berger 130 VLD for range testing. My loads are from Western Powders and I went with Accurate LT-30. They list the following load data

COAL: 2.350″
23.4 to 26.0 charge weight
2158 to 2404 fps

I went with a COAL of 2.38″ and ran loads of 23.9, 25.0, and 25.7 grains. I’m far enough from the lands to expect no significant pressure increase and I have plenty of case space at this loading depth for the given loads. I measured the muzzle velocity at 2300, 2395, and 2475 fps respectively for the three different loads. The 25.7 load charge gave me this 10 shot group at 100 yards:

Not bad at all! I was having some issues with this rifle and factory ammo, and I thought I’d try loading long to see what I could get. The COAL is much longer than mag length, so I had to individually chamber each round. I was shooting a Mega side-charge setup, so I was using it like a single shot, straight-pull, bolt action rifle. Statistics worked as follows:

Mean radius: 0.404 MOA
Extreme spread: 1.21 MOA
Sigma: 0.322 MOA

UPDATE: I inadvertently counted the outlying shot twice. After correcting the statistics look like this:

Definitely very good. On the other hand, the weakness of even a single 10-shot group is apparent in the 95% confidence intervals. Still this rifle with the given hand load is at worst Class 4, and Class 3 is very likely. In this case, the likely P1x for this combination is 0.59 MOA for the estimated Sigma, and at worst about 0.85 MOA. I need to put more rounds down range to get a tighter estimate, but things are looking good.

Solid BACS class 3 rifle with this load. I’m going to load these to PRI magazine length right at 2.30″ and see what I can get next time. Here’s a shot of the rifle from an earlier session, although now it’s wearing a PRS stock and Vortex PST scope:

Ben squinting his way through a nice 105 yard group

For next time, I thought of backing off the powder a bit and load to mag length of 2.300″. You can see the difference below between the 2.38″ and 2.30″ rounds:

I’m especially curious what velocity and accuracy I’ll get with the reduced COAL. The loading manual states 26.0 grains of LT-30 at a COAL of 2.35″ and I only went to 25.7 grains at 2.38″. I think given that at 2.26″ they state 25.1 grains is max safe load, that I can keep this load at 25.7 grains at 2.30″.

I’ve also worked up some 2.300″ loads of Benchmark under 115 Sierra Match King bullets. I want to run this load in my Fulcrum and Recon barrels. Here’s the round compared to a factory Remington 115 BTHP:

Range report this coming weekend.

June 2 2017 Range Time

6.8 SPC Range Time (UPDATED)