As part of the development of the 7mm SAW cartridge, we tested several different powders for suitability. We also started the test barrel at a length of 31 inches, and performed a cut-down test to determine the amount of velocity loss that could be expected with various barrel lengths. The test barrel is a Krieger 5R stainless 1-8.5″ twist, .277″bore/.284″ groove. All loads shown were tested using formed Lapua .308 Palma brass. Hopefully you find this information helpful as you gather data for your next rifle!
Maximum overall lengths for various bullets
Short throat, .045″ Freebore. This chamber would be necessary for shooters using standard AICS .308 magazines, Magpul AICS pattern PMAGS, the HS Precision DBM system, or standard length internal magazine boxes). These overall lengths were measured after barrel break in as well. In an unfired chamber, the lengths would be approximately .005″-.010″ shorter than listed.
162 Hornady ELD-M: 2.850”
180 Berger Hybrid: 2.915”
168 Berger Hunting VLD: 2.840”/1.414” measured bullet length
183 Sierra Match King: 2.988”/1.603 measured bullet length
171 Barnes Match Burner: 2.835”/1.410 measured bullet length
Long throat, .150″ freebore. This chamber is recommended for running the 162 ELD or 168 Berger VLD in the AI A/W magazine, Alpha Mags, Accurate Mags without binder plate, and 3.000″ internal magazine boxes.
183 SMK: 3.090”
180 Hybrid: 3.020”
162 ELD: 2.955”
168 Berger VLD: 2.945”
All four listed bullets would seat with bearing surface above the neck/shoulder junction in this throat length.
Powder Test, Hodgdon Varget
Break in Load
162 ELD-M, 2.830”OAL
39.0grs Varget
Fed 205M
2733FPS/11.5SD
.5” at 100 yards, all sub MOA during break in
162 ELD-M, 2.840 OAL, Federal 205M Primer
40.0: 2806FPS
40.5: 2832FPS
41.0: 2852FPS
41.5: 2886FPS
42.0: 2879fps
42.5: 2889FPS
43.0: 2913FPS
43.5: 2937fps
44.0: 2989FPS, MAX PRESSURE. Bolt lift still easy, but substantial primer flow back and small eject swipe.
Powder Test, IMR 4451
162ELD-M, 2.840”OAL, Fed 205M primer
45.5: 2865FPS
46.0: 2859FPS
46.5: 2908FPS easy extraction, but max case fill at this throat length
IMR 4955 powder
162 ELD-M, 2.850”
Fed 205M Primer
46.0: 2827/27ES, 2.5” vertical at 200
IMR7828SSC powder
162 ELD-M, 2.850”
Fed 205M Primer
46.0: 2725/26ES, 3” vertical at 200
H4350 powder
162 ELD-M 2.850”OAL
Fed 205 M primer
45.5: 2878/20ES, 1.5” vertical at 200
46.0: 2901FPS
46.5: 2924FPS
47.0: 2951FPS
47.4: 2948FPS
All shots from 46.0 to 47.4 were within .5MOA vertical at 200
Re-shot 47.0 at 100 yards, sub .5 MOA accuracy, 2933FPS/38ES
183gr Sierra MatchKing/H4350 powder, 2.978” OAL
44.5: 2670FPS
45.0: 2694FPS, primer looks great
46.0: 2751FPS, primer looks the same at 45.0
46.7: 2782FPS, max load, compression causes issues seating to 2.180”
All loads after this point were tested on chamber with .150” Freebore.
183gr Sierra Match King, 3.090”
46.0grs H4350, Fed 205M
2773/8.1SD
.5MOA 4 shot group, 3 rounds in bug hole and one slightly right
BARREL LENGTH CUTDOWN TEST
Test Load:
162 ELD-M, 2.945”OAL
43.3grs Hodgdon Varget
Fed 205M
Lapua 2x fired brass
Barrel length
31”: 2941FPS/6.8SD
30”: 2916FPS/3.3SD
28”: 2915FPS/7.7SD
26”: 2911FPS/11.6SD
Test notes
a. Even with rough crown, all barrel lengths shot sub MOA at 100 yards. 26” and 28” were the most accurate, both producing almost bughole groups.
b. The 26” barrel test was done again using brand new brass, to find the amount of velocity drop off, if any, between brand new and fired brass. The new brass loads produced a velocity of 2874FPS/8.4SD, with accuracy almost equal to the 2x fired cases. After final load development for this barrel was completed, the new vs. fired brass test was conducted again, with both new and fired brass producing groups in the sub .2″ range(.150″ for fired brass, .197″ for new).