AR Build - What Barrel Length For M855

[Code3GT]

Planning out my AR build. Going to go with a stripped lower and complete upper as this will be my first build. I was looking at ammo prices and it seems M855 is cheaper than M193. 16" barrel enough to get the 855 downrange effectively? Sorry if this is a dumb question, again, new to building, only used to what the air force gave me

 

[taliv]

m855 is not normally cheaper than m193. where'd you find it?

 

[Hoppy590]

M855 is about 10-20% more expensive per case as far as iv seen

 

[Float Pilot]

Some of us do tend to stumble into more M855 than the older stuff. His location and military history status will give you a hint why.


While doing some active duty time, I compared M-193 to M855 from a :

20 inch barreled M16A2 (1 in 7 twist) issue rifle using two chronographs at 20 ft.

M-193 Ball = 3,140 fps Chrony
3,126 fps Ohler 33

M-855 ball + = 3,080 fps Chrony
3,050 Ohler 33

14.5 inch M-4 carbine (Issue) 1 in 7 twist

M-193 Ball = 3,055 fps average between 2 chronographs

M-855 ball+ = 2,852 fps average

11.5 inch Bushmaster (my old patrol car trunk gun) 1 in 9 twist.

M-193 ball = 2,710 fps Chrony

M-855 Ball+ = 2,600 fps average

Since 2,700 is considered the minimal impact velocity for a producing a serious wound channel, The 11.5 inch barrel does not cut the mustard unless you are within a few feet of your target.

The 14.5 inch M-4 barrels also leave much to be desired for terminal effect after 100 meters.

 

[Dienekes]

As far as effective fragmentation goes, I figure my M4gery (16" barrel) is about a 120 yard weapon with the M193 round or my handloaded 55 gr FMJBT equivalent. With military M855 that drops to about 90 yards--and I have trouble getting full velocity in my M855 type handloads, using the same bullet, with AA2520 which is the powder I use.

Upshot is that I use the slightly reduced velocity of my M855 type load for practice only out to 100 yard as it prints closely enough to M193; but I would avoid it for serious social work.

There is absolutely no doubt that anytime you shorten the 5.56 barrel under 20" you are giving up a lot in stopping power. So it depends on what you have in mind.