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On 11/15/2018 at 8:40 AM, Wiedzmin said:

have question about 12.7x99 AP M2 cartridge  WWII time books gives muzzle velocity for AP M2 - 895 m/s for 45in barrel, modern days firing tables and manuals gives 856 m/s for 45in barrel, which is correct, or both correct but 1st for WWII and 2nd for modern dayes cartridges ?

 

Too big a difference to be instrumental vs. muzzle velocity. Likely 895 m/s is a misprint. I am not sure any M2 AP has been made since WWII.

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5 minutes ago, Sturgeon said:

 

Oh. Yes. Thanks for reminding me. It appears the velocity discrepancy is due to barrel length. The 895 m/s figure is for the 45in barrel of the M2 ground variant, while the 865 m/s figure is for the 36in barrel of the aircraft variant (AN/M2 and AN/M3).

FT.50-H-2 3  - infantry firing table for 45in + i have US specs on AP M2 cartridge which gives 853m/s IIRC 

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1 minute ago, Wiedzmin said:

FT.50-H-2 3  - infantry firing table for 45in + i have US specs on AP M2 cartridge which gives 853m/s IIRC 

 

I can't tell you exactly why one source or another has a given set of numbers. Sometimes they are just wrong, especially field manuals.

For the record, FM-23-65 gives the muzzle velocity as 2,930 ft/s.

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