Difference in Barrel twist

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[ARCHIVED THREAD] - Difference in Barrel twist

Posted: 3/23/2002 6:59:55 PM EDT

I am looking to buy my first Ar15. I am considering either a Bushmaster, or Colt. From what I have read both are fine weapons. The main differences I can find are the barrel twist. The Colt has a 1 in 7 and the Bushmaster a 1 in 9. What are the advantages, dissadvantages and how, if any would accuracy be improved. The weapon will be used for short to medium distances, never more that 300 M.

Thanks for your help,
Dwayne

Posted: 3/23/2002 7:16:25 PM EDT

[#1]

1 in 14 40-50grn bullet:
lightweight frangible,"varmint"-type bullets down to the lighter weight FMJ
1 in 12 45-55 grn bullet:
Medium-weight bullets, typically FMJ but including soft points. Probably the fastest twist useable with .22 rimfire conversion units
1 in 9 50-69 grn. bullets:
Considered by many to be the most versatile twist. Adherents maintain 1 in 9 will stabilize "anything"
1 in 8 62-80 gr. bullets:
Perhaps the most common match barrel twist
1 in 7 80 grm. bullet and up:
"SS-109"-type bullets, the so-called "greentip" FMJs. Also heavier match bullets of 90 grns. and up. The AR-15 Complete Owners Guide

GIB

Posted: 3/23/2002 8:29:29 PM EDT

[#2]

GIB, has all the right data.

As he points out, the 1:9 twist will be the most versatile and probably about a 62 grn bullet is optimum for this twist.
Obviously the 1:7 will better stabilize heavier bullets but few of us seem to shoot heavy bullets.

The thing you might remember is to match your bullet weight to your barrel twist to insure better accuracy.

Now go get yourself an ArmaLite M15A4 that will come with a flattop and a 1:9 twist barrel !!

Posted: 3/24/2002 10:01:25 AM EDT

[#3]

Quoted:

1 in 9 50-69 grn. bullets:
Considered by many to be the most versatile twist. Adherents maintain 1 in 9 will stabilize "anything"

ArmaLite makes their M15's (.223's) with a 1:9 twist barrel and I went to their site and checked their Technical Notes for recommended bullet weight with their 1:9 twist barrel.

Per the site the 1:9 twist will stabilize bullet weights from 40 grn - 69 grn.

Much of the surplus ammo is 55 grn and the 1:9 will shoot this weight fine.
However, should you move toward the rifle with the 1:9 twist I still believe the 62 grn bullet weight is optimal for the times you're doing some serious shooting for accuracy.

Posted: 3/24/2002 10:07:14 AM EDT

[#4]

Note that you will have a difficult time finding a new colt rifle with chrome lined barrel and chamber.

I'm not even sure that they make postbans with chrome lining.

Posted: 3/24/2002 10:21:35 AM EDT

[#5]

markm your right they don't make post ban with 1/7 , all the post bans are 1/9 . I got lucky last year and got a milspec upper with 1/7 . Unfortunately colt milled off the lug and removed the flash suppersor before that sold them. You can post ban by the date stamped on the barrel behind the front sight , preban has no date stamped on them .

Posted: 3/24/2002 4:30:22 PM EDT

[#6]

My MT6551 is 1:7, I bought it in '99
GIB

Posted: 3/25/2002 6:26:20 AM EDT

[#7]

FWIW.

I have used a 1:9 for bullet weights from 52 to 75 grains with no problem. I have also used the 1:8/1:7.7 with 52 to 80 grain bullets with excellent accuracy.

HTH....SRM

[ARCHIVED THREAD] - Difference in Barrel twist

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