My 1:7" barrel hates heavy stuff

[Tim]

Until this Bren 2ms, I've never had a .223/5.56 that actually LIKES bulk 55gr M193 better than the 69-77grain stuff. Like 1.5 MOA w/55s and 2-3MOA with the heavier stuff. Every .223 I've owned from 10.3" SBR through 18" heavy barreled DMR set ups have liked 69-77gr better.

The Bren has a 14.1" w/1:7 twist that should be stabilizing the heavies without any trouble.

Anybody else run across this?

 

[ronn47]

Until this Bren 2ms, I've never had a .223/5.56 that actually LIKES bulk 55gr M193 better than the 69-77grain stuff. Like 1.5 MOA w/55s and 2-3MOA with the heavier stuff. Every .223 I've owned from 10.3" SBR through 18" heavy barreled DMR set ups have liked 69-77gr better.

The Bren has a 14.1" w/1:7 twist that should be stabilizing the heavies without any trouble.

Anybody else run across this?

Have you verified the 1:7 twist?

 

[Tim]

Have you verified the 1:7 twist?

hmm....no. It's stamped 1:7 and is a factory gun so I never even thought about that being an issue. I'll test it out.

 

[Supermatch]

You're not the first person I've heard who suggested the Bren 2 carbines were more accurate with cheap 55 gr. I wonder if its just unhappy in a certain node that's correlating to the much lower velocities of the heavier grain bullets.

 

[Cole_McD]

Nutty. I don't think I've ever seen a rifle not shoot quality 77s well. How many different loads have you tried? Any difference between 5.56 loadings and 223 loadings?

 

[Tim]

Nutty. I don't think I've ever seen a rifle not shoot quality 77s well. How many different loads have you tried? Any difference between 5.56 loadings and 223 loadings?

3 loads...

Defender 69gr
AAC 75gr
Defender 77gr SMK

 

[Slacker]

Any weirdness with the spent brass ?
Rims chewed up, bulges etc
I'd definitely check the twist rate.

 

[Tim]

Any weirdness with the spent brass ?
Rims chewed up, bulges etc
I'd definitely check the twist rate.

Nope. Brass looks good.

 

[JBoyette]

I have a theory.

Projectiles need 2 full rotations to be accurate.

If we take the 14.1" barrel length, the way this is measured is from a closed bolt to the edge of the crown.

A .223 brass is 1.75" long. Free bore is 0.062" So that gives us 1.812" of no rifling in the 14.1" barrel.

That means you have 12.228" of rifling. Divide this by 1/7 equals 1.75 rotations of the bullet before it exits the barrel.

Its my theory, and I am sticking to it. LOL

John

 

[Tim]

I have a theory.

Projectiles need 2 full rotations to be accurate.

If we take the 14.1" barrel length, the way this is measured is from a closed bolt to the edge of the crown.

A .223 brass is 1.75" long. Free bore is 0.062" So that gives us 1.812" of no rifling in the 14.1" barrel.

That means you have 12.228" of rifling. Divide this by 1/7 equals 1.75 rotations of the bullet before it exits the barrel.

Its my theory, and I am sticking to it. LOL

John

I like the thought process, but that doesn't explain how I get great accuracy from the same loads in 10.3" and 11.5" barrels.

 

[USMC6094]

Gun is going to like what it likes.....

My eleven hundred dollar Sig P226 Mk25 likes cheap Winchester White Box, it clover leafs it.

The guns told you what it likes, it's only a matter of you listening......

 

[Trevillian]

Until this Bren 2ms, I've never had a .223/5.56 that actually LIKES bulk 55gr M193 better than the 69-77grain stuff. Like 1.5 MOA w/55s and 2-3MOA with the heavier stuff. Every .223 I've owned from 10.3" SBR through 18" heavy barreled DMR set ups have liked 69-77gr better.

The Bren has a 14.1" w/1:7 twist that should be stabilizing the heavies without any trouble.

Anybody else run across this?

Yep. My first 1:7 barrel actually. Built up as a heavy "precision" with 18" barrel. Best factory loads over 60g were 3moa. Best I could do with several varieties of heavy handloads just under 2 moa.

I have a 50g vmax recipe that is 1/2" moa out of a few 1:9 twist rifles and my plinking 55g reloads are 1 moa out of my mine and a few friends 1:9 and 1:7 16" barrels. So I probably got a little hubris creep🙄😁

That thing spun the vmaxs out to 4moa (expected) and my plinker 55g would stay around 2moa. Closest I came to 1 moa was flippin federal bulk pack 55g stuff when I was thinking the barrel needed a break in. My loads generally doing well in a variety of rifles hurt my feelings with this one.

It has sat in the safe for a while now. Never have put in the effort to find a load for "it" but I should. It's probably got potential when I find what she likes.

 

[CZfool68]

Guns are like women. Don’t try to figure it out, just do what it likes.

 

[Tim]

The guns told you what it likes, it's only a matter of you listening......

Guns are like women. Don’t try to figure it out, just do what it likes.

I get it. My only concern is bucking the wind (minor issue) and helping RO’s see/hear hits at distance more reliably. Those gongs ring a lot louder with 50% more lead on target!