Yeah I had a feeling these would be anemic out of a barrel under 16" Glad I waited to purchase these. Why aren't these ammo manuf. pushing these heavier loads faster. With a test barrel of 24" at 2775 common sense tells us it will be useless out of a 10.5" barrel. These should be at 3000fps from a 20" barrel. Thanks for the testing though.
Last edited by Stone; 11-22-2015 at 03:08 PM.
they didn't test out of a 16?Originally Posted by Unobtanium
As a general rule of thumb I use 50fps per inch of barrel for guesstimating fps. Not an exact science but gets me in the ball park. So around 2500 on a 16"
They will probably run around 2550-2600 from a 20" barrel, given the powder ATK uses.
Last edited by Unobtanium; 11-22-2015 at 08:09 PM.
I'm not sure what results your going to see with 100-150 fps more in 5.56 pressures. Folks asked for 5.56 pressures for reliability in short barrels. If you want MV, go with the 50-55 gr rounds. If you want more mass, then understand they are going to be slower. The 60 gr offerings are a good compromise.
That's a 300fps loss over other 75 and 77gr stuff. Fail.
Last edited by Unobtanium; 11-26-2015 at 08:05 PM.
but whats its effect on targets...?
About 100 yards less effective range than it could have. Remember, under about 1800fps, it's just a tiny pistol round.
I regressed Speer's data on the 75gr Gold Dot, and achieved a functional BC of 0.4.
I verified this by plugging in 0.222 for their 55gr load, and 0.27 for their 62gr load (this is the 64gr load's published BC).---These are published BC's.
I checked all residual velocities at 300 yards with the calculator. Using the above data, All of the loads were within a dozen FPS of the published data, using published MV.
It seems for all the world that Speer is claiming a 0.4 +- 0.01 BC for their 75gr load. I have not found it published, but the velocity data regressed indicates such, directly.
Feel free to check my work.
http://federalpremium.com/downloads/...sue/index.html
*The 75gr Sciroco II is 0.419, and the GD looks at LEAST as streamlined, with a slightly blunter tip...so maybe it's legit?
Here is a revised chart, using 0.4 as the BC.
Hopefully you are right with that ballistic coefficient. Sometimes dropping velocity in a load will make it more accurate(less bullet stress), and perhaps the 75gr design reduces the case capacity such that case capacity is reduced.I regressed Speer's data on the 75gr Gold Dot, and achieved a functional BC of 0.4.
I verified this by plugging in 0.222 for their 55gr load, and 0.27 for their 62gr load (this is the 64gr load's published BC).---These are published BC's.
I checked all residual velocities at 300 yards with the calculator. Using the above data, All of the loads were within a dozen FPS of the published data, using published MV.
It seems for all the world that Speer is claiming a 0.4 +- 0.01 BC for their 75gr load. I have not found it published, but the velocity data regressed indicates such, directly.
Feel free to check my work.
http://federalpremium.com/downloads/...sue/index.html
*The 75gr Sciroco II is 0.419, and the GD looks at LEAST as streamlined, with a slightly blunter tip...so maybe it's legit?
Here is a revised chart, using 0.4 as the BC.
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