Hornady Match 75gr 223 velocity

[DIYguy]

The data on the boxes of the Hornady 75gr 223 BTHP Match rounds states muzzle velocity of 2790. Using an 18" barrel with 1:7 twist and the MagnetoSpeed V3 chrono I keep getting readings of 2581 to 2677 fps. I haven't seen specs stating what length barrel was used for the 2790 rate. I would NOT think and extra 2" of barrel would drop velocity 125 to 200 fps. Temps were between 58 to 70 degrees during different test.

Any thoughts?

[DIYguy]

Found it....24" test barrel

I believe there is a formula for velocity variable per inch of barrel. Anyone know that formula to see what 2790 @ 24" equals at 18" barrel?

[12glocks]

I usually loose about 40-45 FPS per inch of barrel but that is solely limited to 16" and 18" comparisons.

 

[TonytheTiger]

Formulas aren't worth much. I've had 14.5's as fast as 18's and 24's barely faster than 20's. Every barrel is different, some are fast, some are slow.

[Garmil]

Yeah don't expect to get exactly what it's rated for even with matching barrel length.

[atbarr]

Do you know for sure what powder Hornady used?

[Stuey]

Do you know for sure what powder Hornady used?

The powder is proprietary to Hornady. In the past they used a powder close to H4350. Now they have changed to a new blend that they will not disclose.


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[atbarr]

Yes, so very hard to compare results.