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Old November 18, 2012, 07:00 PM   #9
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 3,063
Quote:
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.
FWIW:

SAAMI standards are
52,000 CUP for all four bullet weights (53, 55, 60, and 65gr)
corresponding to their same 55,000 psi standard for the same four bullets.

(See SAAMI Stds page 14 & 19)

NOTE ALSO that SAAMI and C.I.P./NATO (not CUP) give you different pressure numbers for the same cartridge tested side-by-side:

Under C.I.P. proof test standards a drilled case is used and the piezo measuring device (transducer) will be positioned at a distance of 25 millimetres (0.98 in) from the breech face when the length of the cartridge case permits that, including limits. When the length of the cartridge case is too short, pressure measurement will take place at a cartridge specific defined shorter distance from the breech face depending on the dimensions of the case.

Under SAAMI proof test procedures, for bottlenecked cases the centre of the transducer is located 0.175 inches (4.4 mm) behind the shoulder of the case for large diameter (0.250 inches (6.4 mm)) transducers and 0.150 inches (3.8 mm) for small diameter (0.194 inches (4.9 mm)) transducers. For straight cases the centre of the transducer is located one-half of the transducer diameter plus 0.005 inches (0.13 mm) behind the base of the seated bullet. Small transducers are used when the case diameter at the point of measurement is less than 0.35 inches (8.9 mm).

The difference in the location of the pressure measurement gives different results than the SAAMI standard.


See Proof Test Differences

BOTTOM LINE: Don't sweat attaining "NATO" pressures and ballistics. You're already there.

Last edited by mehavey; November 18, 2012 at 07:16 PM.
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