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Posted: 11/23/2017 3:33:42 AM EDT
[Last Edit: 1/29/2018 10:51:16 PM EDT by HighpowerRifleBrony]
According to Douglas, a premium button rifled barrel maker, "NOTE: Our twists are at the whole inch (i.e. 9,10,11, etc.) and tolerance is plus or minus 1/2"."

My technique:

- Use a straight edge and mark a witness line along the length of the rod. Mark the top-middle of the rod guide. (black or silver Sharpie)
- Tighten a worn, but snug, ~1.5" long .22cal bronze bore brush into a one-piece rod.
- Start the brush with the line on the rod facing straight down. Insert until the brush begins to rotate and the line comes up to top dead center.
- Make a horizontal mark on the rod just behind the guide.
- Push rod until the witness lines are together again.
- Make another horizontal mark on the rod just behind the guide.
- Remove rod and measure between the two horizontal marks. This is the distance for one revolution, I.E. 9:1.

If the brush loosens, or the rod binds in it's rotation, or something just doesn't feel right, restart.
View Quote
Please list brand and model, and indicate if it's cut rifled with an asterisk.

Current Arfcommer measurements:

1:6.5"
- CLE NM 6.45*

1:7"
- 7.25
- Core15 7.60

1:8"
- Lilja Recon 7.70
- DPMS NM 8.19
- RRA NM 8.43
- DPMS NM 7.81
- RRA NM 8.06

1:9"

- S&W 9.75
- CMMG 9.75
Link Posted: 11/24/2017 10:26:44 AM EDT
Bump
Link Posted: 11/24/2017 12:22:23 PM EDT
[Last Edit: 11/24/2017 12:24:38 PM EDT by VASCAR2]
I’ve got a 1:9 twist 20” Colt H-Bar, never measured the twist rate but it won’t shoot 75 or 77 grain bullets accuurately enough for me. My 20” Colt H-Bar shoots hand loaded 69 grain SMK very accurately. I have only seen one 1:9 twist barrel shoot 75 grain A-Max accurately but that was at only about 50 yards. I suspect the accuracy of the 75 grain A-Max would deteriorate by 200 yards.

I’ll be surprised if you achieve decent accuracy with 75-77 grain bullets unless you shoot at high elevation. I normally shoot around 350’ ASL and I leave my 75-77 grain bullets for my 1:7 twist barrels. Can’t hurt to try and please post your results. I do agree there are manufacturing tolerances and not all 1:9 twist barrels are exactly 1:9. I just have never been around on that would shoot the heavier 75-77 grain bullets.
Link Posted: 11/24/2017 4:06:20 PM EDT
I'll try and remember to measure some barrels this weekend (all 1/7 but it should give you an idea).
Link Posted: 11/25/2017 11:45:45 PM EDT
I measured up a few barrels that are supposed to be 1/7". I got anywhere between 1/6.75" and 1/7.25" with the cleaning rod with brass brush and Mk 1 eyeball.
Link Posted: 11/26/2017 2:38:24 AM EDT
[Last Edit: 11/26/2017 2:44:45 AM EDT by HighpowerRifleBrony]
*brainfart*

I forgot about the brush.

Thanks for helping.
Link Posted: 11/26/2017 5:19:40 AM EDT
I'm still getting 1:9.75 with the brush.
Link Posted: 11/26/2017 9:05:32 AM EDT
[Last Edit: 11/26/2017 9:06:45 AM EDT by glock24]
I always heard +/- 0.5" too.

This is why I prefer cut-rifling whenever possible.
Link Posted: 11/26/2017 9:07:07 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By glock24:
I always heard +/- 0.5" too.

This is why I prefer cut-rifling whenever possible.
View Quote
How many brands of cut rifled blanks are turned into drop-in barrels? I can name Krieger and Bartlein.
Link Posted: 11/26/2017 10:13:33 PM EDT
[Last Edit: 11/26/2017 11:08:45 PM EDT by EVR]
Alas...my swiveling rod has a kink in the handle and now it won't swivel...
Link Posted: 12/1/2017 12:14:07 AM EDT
I measured my 1:7 at 1:7.6.
Link Posted: 12/8/2017 8:30:50 PM EDT
According to Faxon during a Q&A with Inrange, it's something like +/- 0.01"
Link Posted: 12/9/2017 10:14:59 AM EDT
[Last Edit: 12/9/2017 10:15:51 AM EDT by MS556]
Good observations, OP.

Just checked two barrels out of curiosity.

A CMMG 1:9 measured slower at 1:9.75. Helps explain why it will not shoot 77SMK well, and other 1:9 barrels do.

My Lilja match grade Recce 1:8 measured 1:7.70. That seems optimal to me.

Always good to know actual twist.
Link Posted: 12/9/2017 4:02:13 PM EDT
[Last Edit: 1/28/2018 5:44:52 AM EDT by HighpowerRifleBrony]
Regarding my technique, I'm open to more accurate ways, but we should use the same method.
Link Posted: 12/18/2017 2:57:35 AM EDT
Added two 1:8s and a 1:6.5.
Link Posted: 12/18/2017 5:02:28 AM EDT
I would start the brush with the line on the rod facing straight down. Insert until the brush begins to rotate and the line comes up to top dead center, then mark the rod. Continue to push the brush until you get 1 full revolution, mark the rod, remove and measure.

This should ensure that even with a 1:7 twist barrel that you insert at least 3.5" into the rifling before you start to measure, ensuring the brush has full engagement and does not skid.
Link Posted: 12/18/2017 5:40:46 AM EDT
I must've been vague, or completely omitted that. Will add, thanks.
Link Posted: 1/16/2018 6:18:27 AM EDT
New year bump.
Link Posted: 1/29/2018 10:52:35 PM EDT
Added a couple newer DPMS and RRA NM measurements.
Link Posted: 1/30/2018 1:53:27 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By HighpowerRifleBrony:

How many brands of cut rifled blanks are turned into drop-in barrels? I can name Krieger and Bartlein.
View Quote
Rock Creek I believe is cut rifled and you can get drop-in AR barrels made with their blanks.
Link Posted: 2/1/2018 8:55:15 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By RJeff21:

Rock Creek I believe is cut rifled and you can get drop-in AR barrels made with their blanks.
View Quote
Rock Creek makes far more button rifled barrels than cut, and at a significantly cheaper price point. I would guess any drop-in AR barrel from them is button.
Link Posted: 2/1/2018 8:56:07 AM EDT
Great thread OP, I was always skeptical of the actual twist rates. I'll try to measure some tonight.
Link Posted: 2/1/2018 10:32:31 AM EDT
It's a very neat idea to check, but I'd be just as suspicious of tolerance in the home-testing method than in the factory work.
Link Posted: 2/1/2018 11:14:03 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By EVR:
It's a very neat idea to check, but I'd be just as suspicious of tolerance in the home-testing method than in the factory work.
View Quote
Probably not precise to the hundreth, but accurate enough to determine if the twist is rather bang on, or slow or fast. Just another tool in load testing.
Link Posted: 2/1/2018 11:48:13 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By HighpowerRifleBrony:

Probably not precise to the hundreth, but accurate enough to determine if the twist is rather bang on, or slow or fast. Just another tool in load testing.
View Quote
Yeah, it is interesting, but without a better method that the old cleaning rod job, not something I'd put a lot of trust in.

Now sure, if the gun is marked 1/7 and the home-brew measurement comes in at a consistent 1/10, THAT would be good data for sure and certainly worth a call to the manufacturer!!
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