Originally Posted By: WebopperIf you jump to page 2, you'll see where he sent his back in and BM said the chamber and headspacing was too tight. They fixed it up for him, and it's all good.
http://www.ar15.com/forums/t_3_16/479900...html&page=1
Don't think I'll let anyone mess with a barrel that shoots like this one
, especially since it has never exhibited any signs of excess pressures w/various factory ammo or handloads. Only pressure signs experienced was w/M193 ball (excessive case head expansion on two cases and one blown primer out of 5 rounds fired).
This particular load is above max. in three different manuals, chronographs 3300 fps 15' from muzzle and, loaded to max. magazine length measures 2.264" COL. yet shows no signs of pressure in MY rifle.
I do appreciate the fact that your post caused me to check one parameter that I had not checked to date and think we may have struck on a possible contributing factor, if not the primary cause of the blown primer.
While checking the COL of my handloads, it occured to me to do the same on the M193. First thing I noticed was that the cannelure was not seated to same depth on the 5 cartridges selected at random.
Case base to ogive measured w/Stoney Point bullet comparator:
My 55 gr. NBT handloads: 2.8585-2.859
M193 Ball:
2.902
2.904
2.908
2.913
2.915
M193 variation of up to +/- .013 (which is obviously not conducive to good accuracy!)
Handload variation of +/- .0005
M193 base to ogive(longest)= 2.915
Handload base to ogive...... = 2.859
Less "bullet jump w/M193.. = 0.056"
That's a lot of difference in free travel, no wonder pressures running a great deal higher in the M193!
Regards,
hm
http://www.ar15.com/forums/t_3_16/479900...html&page=1
Don't think I'll let anyone mess with a barrel that shoots like this one
This particular load is above max. in three different manuals, chronographs 3300 fps 15' from muzzle and, loaded to max. magazine length measures 2.264" COL. yet shows no signs of pressure in MY rifle.
I do appreciate the fact that your post caused me to check one parameter that I had not checked to date and think we may have struck on a possible contributing factor, if not the primary cause of the blown primer.
While checking the COL of my handloads, it occured to me to do the same on the M193. First thing I noticed was that the cannelure was not seated to same depth on the 5 cartridges selected at random.
Case base to ogive measured w/Stoney Point bullet comparator:
My 55 gr. NBT handloads: 2.8585-2.859
M193 Ball:
2.902
2.904
2.908
2.913
2.915
M193 variation of up to +/- .013 (which is obviously not conducive to good accuracy!)
Handload variation of +/- .0005
M193 base to ogive(longest)= 2.915
Handload base to ogive...... = 2.859
Less "bullet jump w/M193.. = 0.056"
That's a lot of difference in free travel, no wonder pressures running a great deal higher in the M193!
Regards,
hm