I'm going to be getting a BM M4gery when the AWB sunsets. Originally I wanted to get a 1:7 barrel, but is it really worth the extra trouble, time, and expense? Convince me one way or the other. Here are a couple questions:

Does a 1:7 loose performance compared to 1:9 when shooting 55 gr xm193 (which is what I shoot 90% of the time)?

Does the 1:7 wear down the rifling faster?

Does it tear apart bullets lighter than 55 gr?

How much performance is lost when shooting 62 gr m855 out of a 1:9 compared to 1:7?

Can a 1:9 adequately shoot m856 tracers compared to the 1:7?

Can a 1:9 barrel shoot the heavier rounds that are better for very long range shooting?

Thanks for your input.

I'm curious of this too.  I may be picking up a LMT upper soon, and i shoot 99.9% of hte time Q3131A.

the 1:7 should handle the xm193 just as well as the 1:9.  I wouldn't dump a 1:9 barrel in favor of a 1:7 in your case, but I wouldn't not buy a 1:7 either.

I also shoot only xm193, and I am about to buy a 1:7 barrel for my 9/14 celebration rifle.

BTW, there's discussion of this same topic here

www.ar15.com/forums/topic.html?b=3&f=12&t=198300

Quoted: I'm going to be getting a BM M4gery when the AWB sunsets. Originally I wanted to get a 1:7 barrel, but is it really worth the extra trouble, time, and expense? Convince me one way or the other. Here are a couple questions: Does a 1:7 loose performance compared to 1:9 when shooting 55 gr xm193 (which is what I shoot 90% of the time)?  No Does the 1:7 wear down the rifling faster? No Does it tear apart bullets lighter than 55 gr? Only problem I've heard about is with very light (40gr?) varmint bullets which were spun so fast the jacket separated How much performance is lost when shooting 62 gr m855 out of a 1:9 compared to 1:7? None - all else being equal Can a 1:9 adequately shoot m856 tracers compared to the 1:7?  No personal experience Can a 1:9 barrel shoot the heavier rounds that are better for very long range shooting?  I have had trouble with 14.5" and 16" 1:9 barrels and 75gr bullets.  Others have reported no problems.  Y would need to test in your barrel with your load, temp, altitude, etc. to be sure Thanks for your input.

I carry Hornady 75gr TAP ammo for defense and use a 1:7 16" barrel, so call me biased in favor of the 1:7.

The 1:7 does everything a 1:9 will do and is more accurate (for me) with the 75gr TAP ammo.  After thousands of rounds of XM193 out of the 1:7, I can report that it works just fine.

HTH

I am also interested.

A 1:7 is better for heavey ammo and long distance shooting, but the 1:9 is as good for ammo up to 62 grains, even for long distance shooting.
But this is only my personal experiance.

I believe that for anything except a dedicated target/varmint gun, its the only way to go.

In another thread someone mentioned that they were shooting 77 gr rounds in a 14.5" 1:9 and had no problems out to 600 yards, even with heavy wind. Even if this is not the case for everyone, would this suggest that a 1:9 would be able to shoot the heavy self defense bullets for close to medium range without any problem?

Nuclear, some do, some don't might as well try yours and see.

If I'm not mistaken, the 1:9 is a more versatile twist than 1:7.  Someone will list the ammo and barrel guru site that states this.

Quoted: If I'm not mistaken, the 1:9 is a more versatile twist than 1:7.  Someone will list the ammo and barrel guru site that states this.

I disagree. Almost all .223/5.56 ammo is 55 grains or heavier, and these work fine in 1/7, whereas the useful long range and anti personnel rounds are 75-77gr and NEED a 1/7 barrel to work their magic.

sigh ...

I have very good experience with 1:7 as I have with 1:8 or 1:9.

The 1:7 will shoot very well with 52 too around 90 grains bullets. But if you have low quality bullets it seems that group size will be bigger than with a 1:9 twist.

If you have a very long barrel and high velocity you risk to have ball / jacket separation with the 1:7. This occurred in my test with the Sierra 69 grains MK at around 930 m/s or 3050 ft/sek.

The tracer M856 are on the stabilisation limit with 1:7. In very cold environment they even require 1:6,5. They will normally not work in a 1:9 barrel.

A big plus with the 1:7 barrel:

You can shoot almost any factory ammunition on the market, not matter which bullet. It seems that the bullet is very stable, even small obstacles on the way (grass, reeds) will not throw them as much out of direction as it would be done with a 1:9 twist. Even if the 1:9 is capable to stabilise a 77 grains bullet in normal air condition, they will not be stabilised any more when things getting tough (bad wetter, very cold).

Greetings from Germany

It's pretty simple. If you are going to buy a new barrel (or rifle) get a 1/7 if you can get it in the length & contour you desire. This will give you the best probabilty of being able to use the widest range of bullet weights which are relevant to the AR platform's intended use. If you already have a 1/9, don't be afraid to try the heavier bullets. There's a better than 50/50 chance that they will perform satisfactorily from your barrel.

Luck,

SD

I thought it was worth it because I wanted to build an A2 as close to the real thing as possible without going NFA.

That meant a 1:7, government profile, chrome-lined barrel with A2 flash hider.

I like it a lot.

No loss of accuracy with M193(55gr) just change in point of impact, about 2 inches vertically.