Ideal 5.56 wieght for short barrelled M4

[C-grunt]

I was wondering what you all thought would be the ideal wieght for a 5.56/.223 out of a short M4 like the police use or maybe an AR pistol. With the standard length rifles, I believe the heavier bullets (77grn) to be the best rounds. But would a barrel length of only about 10 inches hinder this relatively slow .223. I would think that a lighter, higher velocity round would be better in the short barrels. What do you all think

 

[browningguy]

Well I voted, but it would depend on your use. My .223 is mostly a small varmit gun to be honest, and it likes the 45 gr. Winchester load.

 

[DMK]

I'm assuming you want this SBR for self defense:

Personally, I think that under 14" is too short for 5.56. This round relies heavily on velocity to fragment the bullet and cause incapacitating damage.

A 10" barrel is going to severely limit your effective range to conversation distance.

That said, I'd use the Black Hills 77gr. mk262 round if I could get it. It's loaded hotter than commercial stuff. If I couldn't get that, I'd try to get some of that LEO only 5.56 TAP stuff Hornady has (it's hotter than the regular TAP). Failing that (and you probably aren't going to find anybody to sell you either of those rounds), I'd get some 75gr. Hornady OTM bullets and load up some hot rounds myself.

 

[FunGunner]

Not so much how long the barrel is (only giving up like 40-60 fps a inch) but the twist rate. Longer the bullet, the higher the twist rate should be to stablize the bullets spin.

I'd say for 60-70 grains of bullet 7-8:1 twist, for 50-60 grains of bullet the 8-9: twist, and for sub 50 grains 9:1.

Just remember higher the twist rate for the heaver bullets you might see a bit more barrel ware than with a lower one with lighter bullets. That and a tighter twist on a lighter bullet could cause it to start to break apart due to too much spin.

Just my .02 bits

 

[Bartholomew Roberts]

But would a barrel length of only about 10 inches hinder this relatively slow .223. I would think that a lighter, higher velocity round would be better in the short barrels.

Here are the problems with a lighter, higher velocity round. If you use a varmint type round like a Nosler Ballistic Tip, you will get fragmentation; but penetration will be shallower due to reduced velocity and the light weight of the round. If you use FMJ, you will get penetration but because the round is shorter it requires a higher velocity (2500-2700fps) to fragment after yawing (if it yaws).

The heavier rounds start out slower; but they yaw and fragment more consistently and at lower velocities (around 2200fps). Overall they are more effective than the lighter rounds. Note also that the latest NDIA conference discusses a new ball powder that can generate 100fps more velocity for the 77gr load while maintaining the same chamber and port pressures.

 

[ocabj]

According to testing done by Ammo Oracle, the Nosler 77gr BTHP bullets have the best terminal performance followed by 75gr Hornady BTHP and Sierra 77gr BTHP.

My personal handload recipe for a real-life load with 77gr Sierra MK is 25.3gr Hodgdon Varget, Winchester SR primer, and LC brass. That gets me 2785 fps out of an 18" SPR barrel. That velocity is on par with published velocity data for MK 262 ammo out of an 18" barrel.

 

[rangerruck]

get the keltec, piston driven, 223 pistol. better, without the recoil buffer sticking out like a sore thumb.

 

[Still 2 Many Choices!?]

It depends on the use...

Everyone above has given great advice...I use the light stuff in my M4gery, M193 equivalents. I think it works the best out to 150 yards or so. The heavier stuff would fragment at lower velocities, but my 1/9 twist barrel probably wouldn't stabilize it. If needed, I just say shoot the SOB twice! I also have a 10" AR pistol that is my PDW/Home defense gun. It shoots the 55gr, M193 spec stuff just fine, and at the ranges I would intend to use it, it should fragment just fine. I also keep a mag loaded with 55 gr Soft points, that I have found feed reliably. I am sure they would do a number on anything,"soft", out to 100yds or more, even out of the pistol's 10" barrel...

 

[Bartholomew Roberts]

The heavier stuff would fragment at lower velocities, but my 1/9 twist barrel probably wouldn't stabilize it.

Even the worst 1/9 barrel I've seen would shoot 5-6" groups at 100yds with the heavier ammo. Admittedly, that is pretty disappointing for match ammo but it would still get the job done as self-defense ammo. The 55gr Ballistic Tips are impressive providing you don't need a lot of penetration and get that ideal frontal shot (like a silhouette target). However, if there is a lot of meat in the way (quartering shot on a pig) or an intermediate barrier it becomes a lot less effective.