5.56 velocity, barrel length, and distance

[Jerik1m4]

I hope this isn't a stupid question, or already answered 6 times over. I tried a search and couldn't find anything.

From the little research I've done it seems like 2500fps is the threshold for reliable penetration and expansion for quite a few 5.56 bullets.

My main question is with shorter barreled rifles you lose velocity right? but roughly how much do you lose over distance every 100yds?

how short would be too short if you wanted reliable ballistics out to say 300yds if you are running shorter than a 14.5'' barrel.

I know newer ammo like MK262 and MK318 may change this, if you were using stuff like this or 75GR tap T2 or m855 what would be the most ideal barrel length for general purpose rifle?

[WillBrink]

I hope this isn't a stupid question, or already answered 6 times over. I tried a search and couldn't find anything.

It's around here some place. Mods, doc, etc will direct you and or correct me. ;)


From the little research I've done it seems like 2500fps is the threshold for reliable penetration and expansion for quite a few 5.56 bullets.

I believe that's more an issue of yaw and fragmentation of standard mil rnds such as the M855 with some modern loads performing as designed below those velocities. If you see docs post on 5.56 duty loads, you will find advice in terms of loads that performed well out of various length ARs with good terminal ballistics. But, see docs 5.56 Duty Load sticky above where he gives advice on loads and states:

"Short barreled 5.56 mm weapons, such as the Colt Commando, Mk18 CQBR, HK416, HK53, HK G36C, etc… offer advantages in confined spaces. With SBR’s it is best to stick with the barrier blind loads recommended above, although the heavy OTM's suggested for long distance shooting will also work. SBR's can run into rotational velocity issues with some loads, so it is generally best to select faster 1/7 twist barrels whenever possible. Remember, with SBR’s, effective engagement distances are significantly reduced compared to the longer barreled carbines"


My main question is with shorter barreled rifles you lose velocity right? but roughly how much do you lose over distance every 100yds?

how short would be too short if you wanted reliable ballistics out to say 300yds if you are running shorter than a 14.5'' barrel.

I know newer ammo like MK262 and MK318 may change this, if you were using stuff like this or 75GR tap T2 or m855 what would be the most ideal barrel length for general purpose rifle?

I don't have the tables for that info. Info I have in front me lists 16" will give muzzle velocity of 2920 ft/sec using M855 with 1:7 twist, and down to 2600 ft/sec for 10.3" barrel.

Someone here will probably have a link or info that gives X barrel firing Y rnd has acceptable terminal ballistics out to X distance, and so forth.