[Devil Doc]

I have done my own testing, tell us if you know yours. I will post pics at a later date.

 

[kozumasbullitt]

I assumed it was 1-9 but am probably thinking it is not due to this thread.

 

[bigdog2003_99]

mines not 1/9

i'm kinda interested to see your results though doc!

 

[Tommys229]

how do you find out the "true" twist rate? This could explain why some ACR's handle heavier loads better than others

 

[Devil Doc]

You guys weren't curious when it shot a ragged one hole group with 69 grainers??

 

[RufusAZ]

I'm getting more curious.

 

[Devil Doc]

Using a ball bearing cleaning rod and some steri-strips (medical tape) I marked the point when the rifling was engaged then I pushed In the rod for one complete revolution of the tape flag then I marked it. Exactly 1/8 twist, btw I got mine a week ago for $1613.00 taxes and shipping included (new). 1/8 is the best rate ever.

 

[bigdog2003_99]

wow that explains why it seems like everyone can shoot 75 gr through their acr with no problems, i wonder why they mark it 1/9 then

 

[Tommys229]

The real question is do you think his 1/8 is what they all are actually twisted at or is it that he is lucky?

 

[cjt50]

Interesting, I measure mine at 1/8.5, better then 1/9 tho, (Mine is just about a year old) You got me thinking and I measure an old bushy barrel I got back in 1995. It measure out just over 1/9, (1/9.2 if my conversion is correct )

 

[kozumasbullitt]

So the question is, how are these barrels out of spec? BM claims 1/9, one guy 1/8, and another 1/8.5, I would be worried what they used to make these barrels.

 

[cjt50]

So the question is, how are these barrels out of spec? BM claims 1/9, one guy 1/8, and another 1/8.5, I would be worried what they used to make these barrels.

Don't know enough about barrel making to make an educated statement, but maybe there is a tolerance range that is acceptable. Maybe my measurement was a little off and closer to 1/8 or even the other way. ( I will try and remeasure later)

What I can say is I'm very happy with the accuracy my ACR shows with the rounds that I use and hope it continues.

 

[Devil Doc]

I measured mine while in the actual rifling (past the throat portion) remember this two people may get different results and usually do because of "how" we measure........but this tells me I'm on the money.

 

[BoovarBjarki]

I would say it would be pretty hard to have a mass produced chf barrel to be out of spec.

 

[kozumasbullitt]

I would say it would be pretty hard to have a mass produced chf barrel to be out of spec.

I agree so I hope everyone's barrel is 1/8 twist but that begs the question why does BM market 1/9.

 

[goteron]

Nice Devil Doc! I dont know anyone that has tested that. I am going to check mine tonight. Youre going to shake up the interwebs with this discovery!

 

[Devil Doc]

Just wait I have a huge comprehensive test in the works. To answer a previous question about the barrel stamping, it is likely the blanks were stamped 1/9 because the companies native stamping of other barrels in the inventory, not to mention it is less likely to piss off the customer base should they tool up and make them in house. Goteron and other gentlemen keep this info in house for now please.

 

[goteron]

Looking forward to it. Let me know if I can do anything.

 

[Devil Doc]

Thanks, I will be shooting varrying weight reloads. I don't have or purchase 5.56 so those who would feel cheated by not seeing the 5.56 NATO need only donate 100rds which will be spread between three guns (XCR, LWRC, ACR). I'm on the fence about using the 1/9 XCR 12 inch barrel when I have a 16 which is 1/8 for a near apples to apples test.

 

[Alien]

I would say it would be pretty hard to have a mass produced chf barrel to be out of spec.

Agreed. If people looked up how cold hammer forged barrels are made, they'll see why. From what I understand, the barrel's rifling is shaped into the bore around the rifling form by the hammering action of the CHFing process, not by running a rifling tool down it.