I have a 14.5" M4, is there a chart anywhere or a rule of thumb regarding minimum velocity ?
For example, in my testing with PPU 75gr match ammunition I average 2368 fps.
Is a 14.5" barrel long enough to not be concerned about velocities impact on the effectiveness of an otherwise effective bullet under 200 yards ?
There is no, can be no, will be no effective rule of thumb.Originally Posted by dcsys
If you want to know, ask who makes the bullet what it's effective velocity range is.
Depends on whether you're asking about the bullet's minimum expansion velocity or minimum velocity where more damage occurs due to larger temporary and permanent cavities in tissue. If it's the former, ask the ammo manufacturer. If it's the latter, I've heard velocity floors of between 2,000 and 2,200 fps. iSnipe calculates your combination hitting 2,200fps at about 80yds and 2,000fps at about 180yds. Hope that helps.
I know each bullet performance and design is different and I think I've seen "minimum expansion velocity" specs on Mfg websites.
But OTM bullets may not expand, so it would really be "minimum effective velocity" and I don't recall them listing it.
The results of most tests are at near maximum velocity, I think I have seen some references to suggested minimum velocity for a specific round, but not often.
So I was hoping someone might have a link to a chart with general guidelines like: 77gr OTM yaws at 1900 fps but usually will not fragment below 2200 fps.
That bullet is best for shooting paper at any distance.
Any rifle bullet that yaws and fragments has by definition first hyper-expanded.
Facts matter...Feelings Can Lie
Wrong. The 75 grain PPU projectile makes for a decent "poor man's" TAP.
Prvi Partizan 75 grain OTM
Thanks to the efforts of the esteemed Dr. G.K. Roberts, we now have some excellent information on the terminal ballistic properties of the Prvi Partizan 75 grain OTM load.
Privi Partizan 75 gr OTM
Velocity: 2468 fps from a 16" 1:7” twist barrel
penetration in bare ballistic gel: 12.6"
neck length: 0.8”
maximum temporary cavity: 3.2” at a depth of 4.7”
recovered diameter: 0.36”
recovered length: 0.15”
recovered weight: 30.1gr
The same lot of Prvi Partizan 75 grain OTM ammunition that Dr. Roberts used in testing had a nearly identical velocity when I chronographed it from a 16" Colt barrel.
atmospheric conditions:
Average temperature- 83 degrees F
Humidity - 64%
Barometric pressure – 30.04
Elevation- 960 feet above sea level
....
That's how I think of it, however I'm curious what the lower limit velocity wise rounds like this become ineffective, is the lower velocity out of a 14.5" anywhere near that point, or is it not an issue till you get to 11.5" barrels.
As I understand it, there is a point at which they will not fragment, is there also a point where a bullet that normally reliably yaws, will no longer even yaw ?
By the way, I appreciate all your replies, I have read many of your previous posts, have found them very informative and have contributed to my interest in this subject.
I moved to BB loads in my 14.5 carbines. Mainly the 5.56mm 50 TSX by BH
The last case I bought of black hills 75gr blue cost me 400.00 so its been a long time since I bought heavy fragmenting loads
Good data here thanks to Doc and Molon.
#RESIST
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