Barrel length and bullets

Twist rate effects stabilization. Barrel length doesn't matter. The longer barrel will get you a little more velocity, and a quieter report. Less muzzle blast because more powder is burned in the barrel. Of course the blast isn't exactly the same as if we were 7mm Mag, but I would go with the longer barrel if it doesn't get in the way. I'm more of an M-16 fan than an M-4 fan for the afore mentioned reasons.

I'd get the American at 21.875 inches. Moves the bang farther away, I had a couple of 20 inch rifles and they were noticeably louder than longer barrels.

Why 21 7/8"? Not an even length in inches or centimeters. The Houston Warehouse Tests concluded 21 3/4" was best.

Barrel length does affect velocity, and velocity affects stability. It’s naive to ignore this. What I can stabilize in a 1:9” 26” Savage is very different than what I can stabilize in a 1:9” 16” M4gery, and still different than what I can stabilize in a 1:7” 9.5” SBR.

Data is all out there for different barrel lengths, and it’s easy enough to run the Berger calculator to give you an idea of whether you’ll stabilize or not.

Yes, but the OP says "I’m planning to use this rifle as a M193 range gun with a possible varmit application should it arise."
I doubt the length/velocity of a 9 twist barrel makes a whole lot of difference in the stability of a 55 grain bullet.

With 223/5.56 you gain very little speed when you go over 20". You lose almost nothing until you go below 18". Even at 16" speeds aren't that bad.

Keep in mind that it is very common to see 20-50 fps difference (sometimes much more) between different barrels of the same length so you often get numbers that may not make sense. Like the 18' barrel shooting faster than a 20" barrel. Stuff like this happens all the time. That is why it is best to find data where someone used the same barrel and measured speeds as it was cut shorter.

These are numbers from 16", 18" and 20" barrels shooting 60 gr ammo in my rifles.

16" 2820 fps
18" 2950 fps
20" 2920 fps


Barrel length doesn't make any difference other than speeds. The bullets will either stabilize or not based on twist.

I think an 8 twist is the most versatile and will shoot pretty much anything from 50-75 gr ammo. A 9 twist might be a little better with loads under 50 gr, and will probably be fine with anything in the 60's. Above about 70 gr it may, or may not work. Sometimes rifles shoot better than they are supposed to with certain loads so you just have to try and see what happens.

Here is one link. Just google "barrel length and velocity" and you find enough to keep you busy reading all day.

http://www.sadefensejournal.com/wp/?p=1093

Varminterror said:

Barrel length does affect velocity, and velocity affects stability. It’s naive to ignore this. What I can stabilize in a 1:9” 26” Savage is very different than what I can stabilize in a 1:9” 16” M4gery, and still different than what I can stabilize in a 1:7” 9.5” SBR.

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jmr40 said:

Barrel length doesn't make any difference other than speeds. The bullets will either stabilize or not based on twist.

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But as Varminterror pointed out, barrel length affects velocity which affects bullet stability for any given twist rate. Not only that, temperature affects bullet stability so your short barrel might be ok at 75F but not ok at 0F.

I highly doubt that the target will notice the 100fps drop from 20" down to 16".... As far as stabilizing bullets goes, a 7.5" barrel will stabilize a bullet.

In practically all barrels, the rate of twist is constant.

Stabilization depends on bullet RPMs.

RPMs are linearly proportional to muzzle velocity. A higher muzzle velocity creates more RPMs.

So barrel length does affect stabilization. In a few cases, the effect might be important.

Jim Watson said:

I doubt the length/velocity of a 9 twist barrel makes a whole lot of difference in the stability of a 55 grain bullet.

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But he didn't say ONLY 55grn bullets...

ExAgoradzo said:

Does that 3.5” ‘make a difference’? I’m thinking a ‘giant step down in FPS’, or the stabilizing of medium sized bullets when/if I go up from the 55grs?

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If he goes up from 55grn, he might find issues. As I mentioned above, I can stabilize the SUPER LONG 75 A-max in a 26" 1:9", whereas I can't in a 1:9" Bushmaster M4gery - which does OK at 100-200yrds with the 77SMK, but the wheels come off at 300-400, whereas that 26" throws them tight to 800... A 1:9", even in a 16" carbine, should do fine up to the 69SMK (and I'm thinking the 73 ELD, but haven't tested it enough to say for certain), so there's a lot of room to "go up from the 55grs" before they give up, but there is a limit, well within the ceiling for common bullet weights for 223/5.56.

And to @Jackal's comment below - I'd say: I have a 1:9" 11.5" barrel which can't stabilize the 77SMK... My 1:7" 9.5" does just fine... So yes, 7.5" barrel will stabilize a bullet if the velocity, bullet weight, bullet length, and barrel twist all align to produce sufficient spin to stabilize... But that's a pretty generic statement to make. Will a 1:9" 7.5" barrel stabilize the 90 VLD? Not in my experience. No free lunches.

Jackal said:

As far as stabilizing bullets goes, a 7.5" barrel will stabilize a bullet.

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Jim Watson said:

I'd get the American at 21.875 inches. Moves the bang farther away, I had a couple of 20 inch rifles and they were noticeably louder than longer barrels.

Why 21 7/8"? Not an even length in inches or centimeters. The Houston Warehouse Tests concluded 21 3/4" was best.

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In Louisiana that is called lagniappe. A little more can’t hurt.