I recently had the opportunity to shoot 3 different Rock River Arms LAR8s with different barrel lengths.(16 inch CM, 20 inch SS bull, 26 inch SS Bull)
Rifles were like new with round counts between 3 and 333.
All shots fired flawlessly from a 5 round magazine.
5 shots were fired with each of 3 loads from each rifle
(41 degrees F, Chrono at 10ft)
Winds were EXTREMELY erratic creating obvious grouping issues. Despite this, all 9 of the 5 shot groups averaged 1.1 inches at 100yds. (many groups had 4/5 shots around .5)
Loads were as follows-
168 HPBT (bought as "BH factory new" but pulled down to reveal fired brass and 41.7gr of extruded powder w/a gold primer)
16 ave vel 2310 ES 88
20 ave vel 2416 ES 31
26 ave vel 2558 ES 39
155 Amax (Lapua brass, 45.6gr Varget, CCIBR2)
16 ave vel 2563 ES 10
20 ave vel 2644 ES 42
26 ave vel 2788 ES 58
175 HPBT Black Hills Factory (Red Box)
16 ave vel 2437 ES 141
20 ave vel 2465 ES 123
26 ave vel 2615 ES 103
<span style="font-weight: bold">Velocity loss per inch of barrel length was as follows</span>-
<span style="text-decoration: underline">26 vs 20 inch barrel</span>
Average of 24fps (24 with 168s, 24 with 155s and 25 with 175s)
<span style="text-decoration: underline">20 vs 16 inch</span>
Average of 18fps (27 with 168s, 20 with 155s, 7 with 175s)
<span style="text-decoration: underline">26 vs 16 inch</span>
Average of 22fps (25 with 168s, 22 with 155s, 18 with 175s)
The ES were extremely high.
The 155 Amax load was chronographed over the summer in the 26 inch barrel and showed ES about half of what was experienced this time.
A larger sample size is obviously needed for more meaningful data!
Rifles were like new with round counts between 3 and 333.
All shots fired flawlessly from a 5 round magazine.
5 shots were fired with each of 3 loads from each rifle
(41 degrees F, Chrono at 10ft)
Winds were EXTREMELY erratic creating obvious grouping issues. Despite this, all 9 of the 5 shot groups averaged 1.1 inches at 100yds. (many groups had 4/5 shots around .5)
Loads were as follows-
168 HPBT (bought as "BH factory new" but pulled down to reveal fired brass and 41.7gr of extruded powder w/a gold primer)
16 ave vel 2310 ES 88
20 ave vel 2416 ES 31
26 ave vel 2558 ES 39
155 Amax (Lapua brass, 45.6gr Varget, CCIBR2)
16 ave vel 2563 ES 10
20 ave vel 2644 ES 42
26 ave vel 2788 ES 58
175 HPBT Black Hills Factory (Red Box)
16 ave vel 2437 ES 141
20 ave vel 2465 ES 123
26 ave vel 2615 ES 103
<span style="font-weight: bold">Velocity loss per inch of barrel length was as follows</span>-
<span style="text-decoration: underline">26 vs 20 inch barrel</span>
Average of 24fps (24 with 168s, 24 with 155s and 25 with 175s)
<span style="text-decoration: underline">20 vs 16 inch</span>
Average of 18fps (27 with 168s, 20 with 155s, 7 with 175s)
<span style="text-decoration: underline">26 vs 16 inch</span>
Average of 22fps (25 with 168s, 22 with 155s, 18 with 175s)
The ES were extremely high.
The 155 Amax load was chronographed over the summer in the 26 inch barrel and showed ES about half of what was experienced this time.
A larger sample size is obviously needed for more meaningful data!
