05-13-2011, 11:35 PM
Stan,
Reference #49 -- That is pretty cool. It looks like you ran the match for the 20 - inch barrel.
Referring to post #32 and the threshold and objective there:
[INDENT]Threshold:[INDENT]Equal or better the vertex and wind drift of the 7.62X51 M80 at 1000 metres when using a 20-inch barrel.[/INDENT][/INDENT]
[INDENT]Objective:[INDENT]Equal or better the vertex and wind drift of the 20-inch barrel 7.62X51 M80 at 1000 metres when using a 14-inch barrel.[/INDENT][/INDENT]
We can be reasonably sure that when both cartridges have a 14-inch barrel, the trajectories will match about as well -- they will, of course, have larger vertex and drift values. The rub comes when we set the somewhat greater challenge of getting 20-inch performance from a 14-inch tube. I. e., we would require that the 110 gr 6.5 have a 2650 ft/sec muzzle velocity from the shorter barrel.
The velocity estimator suggests that we lose about 150 ft/sec going down to 14 inches from 20. That's equivalent to requiring about 2800 ft/sec muzzle velocity for the 6.5 you posited.
That added velocity is not completely unreasonable if the parent cartridge gets 2650 from the longer barrel using standard propellants and we switch to the blended (e. g. Superformance) propellants -- provided they really work as advertised!!
Also, I like this variant of the objective requirement because it is more tangible than an arbitrary change in vertex and drift values. They, of course, will improve with a cartridge meeting the objective statement, but not necessarily by the numbers I pulled out of the air as place holders.
Cheers!
Joe
Reference #49 -- That is pretty cool. It looks like you ran the match for the 20 - inch barrel.
Referring to post #32 and the threshold and objective there:
[INDENT]Threshold:[INDENT]Equal or better the vertex and wind drift of the 7.62X51 M80 at 1000 metres when using a 20-inch barrel.[/INDENT][/INDENT]
[INDENT]Objective:[INDENT]Equal or better the vertex and wind drift of the 20-inch barrel 7.62X51 M80 at 1000 metres when using a 14-inch barrel.[/INDENT][/INDENT]
We can be reasonably sure that when both cartridges have a 14-inch barrel, the trajectories will match about as well -- they will, of course, have larger vertex and drift values. The rub comes when we set the somewhat greater challenge of getting 20-inch performance from a 14-inch tube. I. e., we would require that the 110 gr 6.5 have a 2650 ft/sec muzzle velocity from the shorter barrel.
The velocity estimator suggests that we lose about 150 ft/sec going down to 14 inches from 20. That's equivalent to requiring about 2800 ft/sec muzzle velocity for the 6.5 you posited.
That added velocity is not completely unreasonable if the parent cartridge gets 2650 from the longer barrel using standard propellants and we switch to the blended (e. g. Superformance) propellants -- provided they really work as advertised!!
Also, I like this variant of the objective requirement because it is more tangible than an arbitrary change in vertex and drift values. They, of course, will improve with a cartridge meeting the objective statement, but not necessarily by the numbers I pulled out of the air as place holders.
Cheers!
Joe