What 320gr Load?
Cylinder lengths:
629 Mtn Gun Cylinder Length: 1.705”
M69 L Frame Cylinder Length: 1.670”
Remember, chambers are not recessed for case rims, therefore OAL can be longer than cyl within reason.
I've shot 325gr Bearthooth Bullets WLNGC with Hodgden Data in the M69.
For info purposes only -- NOT A RECOMMENDATION, but here are some 300+ loads I chroned in my M69
300gr WFNPB 1.651" OAL - LBT type - source unknown.
20.0gr H110.
Fed 155 (Mag)
New Top Brass (Scharch.com).
1,102 fps avg, 37 fps ES
310gr RNFPGC DC 1.605" OAL (top crimp grove) - LEE mold.
20.0gr H110.
Fed 155 (Mag)
New Top Brass (Scharch.com).
1,141 fps avg, 23 fps ES
325gr WLNGC 1.711" OAL - Beartooth Bullets.
22.0gr H110.
Fed 155 (Mag)
New Top Brass (Scharch.com).
1,182 fps avg, 13 fps ES (3 shots only)
Load Data for REFERENCE ONLY -- NOT A RECOMMENDATION.
Here's a picture of various loads POI with the SAME POA (middle of center diamond). Two shot groups to minimize recoil induced fatigue. Shot rested at 25 yards.
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FWIW,
Paul