DIYguy Posted August 28, 2018 Share Posted August 28, 2018 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? Quote Link to post Share on other sites
DIYguy Posted August 28, 2018 Author Share Posted August 28, 2018 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? Quote Link to post Share on other sites
12glocks Posted August 28, 2018 Share Posted August 28, 2018 I usually loose about 40-45 FPS per inch of barrel but that is solely limited to 16" and 18" comparisons. Quote Link to post Share on other sites
TonytheTiger Posted August 28, 2018 Share Posted August 28, 2018 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. Quote Link to post Share on other sites
Garmil Posted August 28, 2018 Share Posted August 28, 2018 Yeah don't expect to get exactly what it's rated for even with matching barrel length. Quote Link to post Share on other sites
atbarr Posted August 29, 2018 Share Posted August 29, 2018 Do you know for sure what powder Hornady used? Quote Link to post Share on other sites
Stuey Posted August 29, 2018 Share Posted August 29, 2018 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.Sent from my iPad using Tapatalk Quote Link to post Share on other sites
atbarr Posted August 29, 2018 Share Posted August 29, 2018 Yes, so very hard to compare results. Quote Link to post Share on other sites
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