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Posted: 1/9/2005 10:32:36 AM EDT
I have a 20" skinny profile FN barrel. It's on a DK marked C7 upper. It's marked in front of the FSB.......FNMI MP CHROME BORE.......on top of the barrel right in front of the receiver and under the gas tube it's also marked.......5........ I think it's a 1/7, but no way to tell. Thanks, AIRBORNE!
Link Posted: 1/9/2005 12:56:11 PM EDT
Link Posted: 1/9/2005 12:59:12 PM EDT
Nope, should be 1/12, FN made a batch of M16A1 barrels as their first contract to prove they could make mil-spec barrels.

Link Posted: 1/9/2005 4:38:27 PM EDT
OK, I have a 1/7 and a 1/12 answer. Does the number 5 on top of the barrel  in front of the receiver and directly under the gas tube mean anything? I'm converting most of my rifles to Gov profile 1/7 barrels and will keep this one if it's 1/7. I like the light weight and only need to know the twist so I can use the right ammo. Is 1/7 too fast for 55 grain ammo? AIRBORNE!
Link Posted: 1/9/2005 4:41:19 PM EDT
You might have to run a tight cleaning rod through it and check the twist that way.  A jag with an oversized patch may make it tight enough so that you can see how long it takes to make one full revolution - 7" or 12".
Link Posted: 1/9/2005 5:38:15 PM EDT
[Last Edit: 1/9/2005 5:39:06 PM EDT by sovereign]
You could also look down the bore. It is pretty easy to tell the difference between 1/7 and 1/12. J&T sent me what was supposed to be a new 1/7 FNMI 20" lightweight. Just looking down the bore with a light shining from the chamber side and I could tell immediately that it was 1/12. What a dissappointment. They took it back and credited me though.
Link Posted: 1/9/2005 6:01:01 PM EDT
sovereign wrote:

You could also look down the bore. It is pretty easy to tell the difference between 1/7 and 1/12.

Thanks. That was easy. It's a 1/12. I have other barrels of known twist and when compared it was easy to see the difference. AIRBORNE!
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