I have looked through the forum and could not find anything on this. I have been looking for an AR and have been reading about barrel twists for a 77 grain bullet. I noticed that most barrels right now are 1/9 would they be able to properly stabilize the heavier bullets or do you need the 1/7 twist?
barrel twist
- Thread starter twig_40
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There are some small inaccuracies in the ammo oracle as it relates to 1:7 stabilising 55gr
Basically 1:7 will do anything that a 1:9 will do and more.
No reason to get a 1:9
For the really lightweight 40gr bullets -- its more a function of the thin bullet jacket being damaged by the rifling than any perceived "over stabilization"
Basically 1:7 will do anything that a 1:9 will do and more.
No reason to get a 1:9
For the really lightweight 40gr bullets -- its more a function of the thin bullet jacket being damaged by the rifling than any perceived "over stabilization"
Alex Robinson has said a lately on arf.com that they had made some 1:8 SBR bbl's for the XCR but went back to 1:9 after they found that the 77grn shot the same but 55grn shot better out of the 1:9. Probably a lot of variables involved though.
The "myth" that 1/7 cannot shoot 55gr is completely BS - Something the commerical AR manufacturer try to justify their 1/9 barrels.
First of all, US army testing back in the early 80's, during the design of M16A2, showed that the 1/7 barrel of M16A2 is actually slightly more accurate with M193 than the SS109 supplied by FN for testing within 300 yards. The article was published in World Fighting Firearms in 1983, IIRC.
The stupid myth that 1/9 is better for 55gr bullets....is a myth that is created by people like Bushmaster to justify their cost cutting 1/9 Habr. It is a valid execuse if one intends to shoot 40gr hp all day long. However, certain manufacturers need to show that they are improvements over the "milspec", instead of a comproise for certain section of the civilian market
Think of this, if the "button" used for rifling could turn 20% less for each barrel blank, that's a tooling saving of 20% in the long run.
First of all, US army testing back in the early 80's, during the design of M16A2, showed that the 1/7 barrel of M16A2 is actually slightly more accurate with M193 than the SS109 supplied by FN for testing within 300 yards. The article was published in World Fighting Firearms in 1983, IIRC.
The stupid myth that 1/9 is better for 55gr bullets....is a myth that is created by people like Bushmaster to justify their cost cutting 1/9 Habr. It is a valid execuse if one intends to shoot 40gr hp all day long. However, certain manufacturers need to show that they are improvements over the "milspec", instead of a comproise for certain section of the civilian market
Think of this, if the "button" used for rifling could turn 20% less for each barrel blank, that's a tooling saving of 20% in the long run.
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The reason I am asking is I intend to send a LOT of gophers to meet their maker. And was intending on doing it with a 16" A4. 44 grn is too light, I have never used them. But was interested in using the 77 grn. So with what is available right now (55grn-62-65) either 1/9 or 1/7 is o.k. Just so I have this right, the 1/7 is more versatile?
