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Marco Califo · November 18, 2012, 06:39 PM

Not military, but Accurate's Reloading guide includes a section titled: "<62350Psi Appliocation: Bolt Action Rifles and Semi Auto Weapons rated for the latest NATO/MIL ammunition."

As to the TM being wrong, I am not convinced.

While PSI and CUP move in the same direction, the relationship is not linear, nor "equivalent-able". Otherwise we would have a nice table to show just that. I looked at the http://data.hodgdon.com/cartridge_load.asp and noticed that in the case of 223 and 55 grn bullets, all of the loads they listed for 335, 4895 and Varget (which covered 3 different bullets for each powder) included at least one in CUP and at least one in PSI. My point is that the difference between PSI and CUP at this data point is less than 5%. On the other hand, the difference you are talking about, I think, is the difference between Hodgdon's 50K PSI and CUP loads, and, Accurate's 62.35K PSI, in Accurate's last loading data bracket. I believe a large part of that disparity is due to the longer & heavier 62 gr 855/SS109 and other heavy long bullets they list there, are in fact, loaded to the higher pressures. This is supported by that same TM listing this for M855:
Chamber pressure ..............55,000 psi
Velocity ..............................3025 fps, 78 ft from
muzzle
Conclusion: IMO the TM correctly states pressures in PSI as it printed. Coincidentally, there does not seem to be a significant difference (>5%) between PSI and CUP in 223 with 55 grn bullets using the same powder. However, in other calibers and/or bullet weights that difference may be significant.

November 18, 2012, 06:39 PM	#8
Marco Califo Senior Member Join Date: April 4, 2011 Location: LA (Greater Los Angeles Area) Posts: 2,598	Not military, but Accurate's Reloading guide includes a section titled: "<62350Psi Appliocation: Bolt Action Rifles and Semi Auto Weapons rated for the latest NATO/MIL ammunition." As to the TM being wrong, I am not convinced. While PSI and CUP move in the same direction, the relationship is not linear, nor "equivalent-able". Otherwise we would have a nice table to show just that. I looked at the http://data.hodgdon.com/cartridge_load.asp and noticed that in the case of 223 and 55 grn bullets, all of the loads they listed for 335, 4895 and Varget (which covered 3 different bullets for each powder) included at least one in CUP and at least one in PSI. My point is that the difference between PSI and CUP at this data point is less than 5%. On the other hand, the difference you are talking about, I think, is the difference between Hodgdon's 50K PSI and CUP loads, and, Accurate's 62.35K PSI, in Accurate's last loading data bracket. I believe a large part of that disparity is due to the longer & heavier 62 gr 855/SS109 and other heavy long bullets they list there, are in fact, loaded to the higher pressures. This is supported by that same TM listing this for M855: Chamber pressure ..............55,000 psi Velocity ..............................3025 fps, 78 ft from muzzle Conclusion: IMO the TM correctly states pressures in PSI as it printed. Coincidentally, there does not seem to be a significant difference (>5%) between PSI and CUP in 223 with 55 grn bullets using the same powder. However, in other calibers and/or bullet weights that difference may be significant. __________________ ............