Barrel Twist

[Zog]

Are 1/9 Twist Barrels cheaper to build? Why are they still common on 2nd and 3rd Tier Guns?

[Coleslaw]

Colt recommended to the DoD a 1/9 twist barrel as optimum to use both M193 55gr and M855 62gr ammunition. The 1-9 had trouble stabalizing the M856 tracer round due to the length of the projectile, so 1/7 was chosen, to stabalize the tracer round.

My guess is some of the '2nd and 3rd tier guns' figure since you probably won't be shooting too many tracers, the 1/9 will suffice. I presume most shoot 55gr ammo anyway, at least in any quantity.

[Robb Jensen]

Colt recommended to the DoD a 1/9 twist barrel as optimum to use both M193 55gr and M855 62gr ammunition. The 1-9 had trouble stabalizing the M856 tracer round due to the length of the projectile, so 1/7 was chosen, to stabalize the tracer round.

My guess is some of the '2nd and 3rd tier guns' figure since you probably won't be shooting too many tracers, the 1/9 will suffice. I presume most shoot 55gr ammo anyway, at least in any quantity.

Yep. But then when the 73gr Berger, 75gr Hornady and 77gr Sierra bullets became popular people then discovered that 1x9 was most of the time too slow.
1x8 and 1x7 is needed to reliably stabilze these long bullets.

Some 1x9s will stabilize 73gr and 75gr, some really long 24" 1x9 barrels will stabilize the 77grs due to better velocities.

I don't own a barrel with a slower twist rate than 1x8.

[carbinero]

This would be an interesting thing to know.

I still see plenty of posts that 1:7 will blow up anything under 55 grains, so the manufacturers must be wagering the majority buyer is more concerned about that and less about shooting heavies.

[Robb Jensen]

This would be an interesting thing to know.

I still see plenty of posts that 1:7 will blow up anything under 55 grains, so the manufacturers must be wagering the majority buyer is more concerned about that and less about shooting heavies.

I've shot 40 and 45gr ammo with no ill effect out if 1x7 twist barrels.

[carbinero]

yup, outside of very few places other than M4C, there's a lot of noise:signal on this topic. I am not interested in anything which won't throw less than 75 gr. accurately.

[kartoffel]

I've shot 40 and 45gr ammo with no ill effect out if 1x7 twist barrels.

Good to know. I've read hearsay on the internet about 1:7 barrels spinning varmint bullets so fast that they fly apart.

Can't say that I've ever tried 40 or 45 grain through my 1:7 gun, though. Never tried it because I had "assumed" the bullets wouldn't hold together. Might as well try it and see what happens!

[Molon]

I still see plenty of posts that 1:7 will blow up anything under 55 grains, so the manufacturers must be wagering the majority buyer is more concerned about that and less about shooting heavies.

Quality, modern 40 to 55 grain copper jacketed, lead core bullets can shoot superbly from fast twist barrels.


The group pictured below was fired from a 1:7" twist Noveske barrel using 40 grain V-MAX bullets.






The 10-shot group pictured below was fired from a distance of 100 yards from a Noveske barreled AR-15 with a 1:7” twist.





The 3-shot group pictured below was fired from the same 1:7” twist barrel for the Internet Commandos in our viewing audience.







The next 10-shot group pictured was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.





Here's another example of just how well a 1:7" twist barrel can shoot light weight bullets. While the group pictured below was fired from a distance of only 50 yards, it's a 10-shot group fired from a chrome lined, NATO chambered Colt barrel with a 1:7" twist using 52 grain Sierra MatchKings.








A 14.5" Colt M4A1 SOCOM barrel,with its NATO chamber, chrome lining and 1:7" twist can shoot quality 55 grain bullets quite well.

[carbinero]

Thinking of that majority buyer who doesn't stray across Molon's magnificent posts, Sportsman's Warehouse often seems to have 45-ish grain available, but almost never 75-77. Occasionally I'll see 62 gr hunting ammo, marketed presumably toward coyote or small deer hunters. Those who think Bushmaster is a great alternative to Colt will typically think 1:9 is the better choice. It's a pervasive fallacy fostered by effective marketing.

[Zog]

Makes sense. I wonder how the cost of ammo (heavy/light) plays into it.