Home Forums Hunting & Shooting Custom Rifles & Wildcats 280AI twist?

1/9...1/8.5....1/8?

Will probably be spending most of the time with 162's but I see the 175 eldx has a recommendation for 8.5.

Mines a 9 twist, if I built another it would be an 8 or 8.5.

I have a couple 7 Mashburns, one an 8-twist and one a 9-twist. I live and mostly shoot above 6000 ft elevation.

If you are going to shoot 160/162s exclusively any of the twists you mentioned would work. If you want to try heavies and you live at lower elevation and shoot when it’s cold I would get the 8-twist.

Mine is 8. Can't think of a reason I'd go slower on a hunting rifle.

8

Looks like it will be an 8. Thanks all.

I went with a 1-9" on my F-class rifle and it shoots 180 grain bergers great, I have not tried any heavier than that, I am at about 600 feet ASL so no gain from elevation. I just purchased a Brux 7mm blank for a hunting rifle 21-inch barrel and spec'ed a 1-8.5" to be on the safe side and I wanted to be able to shoot monos.

^^^^^This

What contour are you going with?

Mine is a 9 twist and handles 140-160 grain bullets great. I have not tried anything heavier so I'm not implying it won't. If I was considering a 170 grain and plus, I would go with a faster twist, as it would only help the cause.

I am shooting the 175g Nosler LRAB with 9T, 500 feet elevation with IMR 7828 and fed 210's, bug holes abound.

Wanting a KS (ish) contour. I see that Bartlein is willing to do that with a stainless so that's the most likely right now. Will try to talk to them Monday about a KS or slightly heavier with an 8 twist..

I think I'll be fine with anything 9 twist or faster. If something close in contour comes along with a 9 or faster twist I might jump on it.

I am at 9T with 162s and shoot 1 hole at 200 yards.

The motivation to go from 9T to 8T with the 175 ELD-x or longer bullets is to go from marginally stable to super-stable, and consequently maximize the bullet's BC, not to go from unstable to stable. Check your stability here and make sure the SG is at least 1.5 for the densest air you'll shoot in:

https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

You lose about 3% of the BC value for every 0.1 drop in SG below 1.5.

I have a 1-10 and a 1-9, next one will be 1-8 so you should start there. 1-10 up to 160s, 1-9 up to 180s, 1-8 190s and above but better stability with the 175-180s.

Keep us posted on the rest of the build.

I'll try to remember to update. Plan is:

1/8 KS (maybe slightly larger) contour to 24". May end up at 22" but I plan on running it at 24" for a while. Could go with a 8.5 or 8.3, etc if something is in stock.
Defiance anTi long action with rail
Going to give a Manners EH6 a try to start with...hoping to like it, if not then maybe an AG composites or Bansner/HTS/LAW/whateveryouwannacallit. Can switch out an Edge with a 700 as a last resort. ADL or BDL depending on stock.
Likely a triggertech
Seekins or APA rings
Nightforce NXS 2.5-10x32 HV 600 with zero stopped elevation dial

I just picked up a Defiance action and am thinking a build in the ball park of yours. I think I’m doing the 280 AI but read the thread with the 6.5 06 AI build and it’s making me pause.

My Brux barreled 7RM is 8 twist. The 280 AI is pretty close to a 7RM and if I was building one, it'd be an 8.

DF

I had Melvin Forbes rebarrel a LH Forbes in 280 AI he said to go 1-9 so that's what I did hoping rifle shows up soon.