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Posted: 8/11/2014 6:37:48 AM EDT
[Last Edit: 8/11/2014 6:43:56 AM EDT by 22_boomer]
Let me explain -- years ago I built a gas operated (DI) AR in 5.7X28 and it shoots great but I wanted to build something that was closer to 22 magnum since I can't find that ammo any place around here. This new AR is manually operated (like the fellows in the UK do) so I don't have to worry about operating a gas system. The cartridges are loaded with 6.5gr of H110, CCI BR-4 primer and the 40gr V-max. I tried 30gr Barnes Varmint Grenades with the same powder charge and primer but they did not shot well. When I went to the 40gr V-max the rifle shot unbelievable. I shot 4 five shot groups that you could cover with a dime -- this is at 50 yrds.
The barrel on the rifle is a heavy fluted Green Mountain barrel designed for 22 magnum so the twist rate is 1:14. I had the barrel shortened, chambered in 5.7X28 and a barrel extension added so it would work in an AR. After I got home from the range I decided to check some of the barrel twist rate programs to see why this rifle shot so well and come to find out the programs say the darn thing shouldn't work at all. I can't be driving the bullets at more than maybe 2000fps, the temperature was 90 degrees and I'm at close to sea level. Do I have some type of freak rifle? Anybody got any ideas as to why the rifle shoots that well with the 40gr V-max bullets?

The picture below is an old picture of the rifle -- I've since added an A1 butt stock and a Magpul pistol grip.
Link Posted: 8/11/2014 6:51:36 AM EDT
1 in 14 is perfect for a 40gr bullet. It's what I use in my Cooper .223 with the same twist barrel. Mine will throw them into one ragged hole @ 100 yards if I do my part.
Link Posted: 8/11/2014 7:02:56 AM EDT
Agreed this is perfect weight for 1:14
Link Posted: 8/11/2014 7:41:59 AM EDT
OK, you guys are familiar with the 1:14 twist but when I input my info my velocity is 2000fps at best. The program doesn't show stability till over 3000fps and I'm not even close. Is it a flaw in the twist program? I know the accuracy is super so there has to be some kind of answer.
Link Posted: 8/11/2014 10:02:30 AM EDT
I've shot plenty of 40-grain V-max bullets at mid-2000s velocities (using light charges of Blue Dot) out of a CZ527 with a 1:12 twist barrel and they have shot fine. I would expect no different using a 1:14 twist. I think your program is a bit screwy.

Link Posted: 8/11/2014 10:45:49 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By wombat25:
I've shot plenty of 40-grain V-max bullets at mid-2000s velocities (using light charges of Blue Dot) out of a CZ527 with a 1:12 twist barrel and they have shot fine. I would expect no different using a 1:14 twist. I think your program is a bit screwy.

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I have to say you guys are right -- the twist program seems a bit off. Thank you all for the replies and I just keep shooting that rifle.
Link Posted: 8/11/2014 12:11:48 PM EDT
Want to have fun, load some 75 gr bullets and see what it does. Side ways at 50 yards!
Link Posted: 8/11/2014 2:28:01 PM EDT
[Last Edit: 8/11/2014 2:29:12 PM EDT by 22_boomer]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By P08:
Want to have fun, load some 75 gr bullets and see what it does. Side ways at 50 yards!
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It makes the strangest looking patterns on your target -- looks like a bunch of boats. I have a 7.62X25 mini-whisper type carbine and I was trying out some 200 grain VLD bullets. The twist in the barrel would handle 168 grain bullets fine but the 200gr bullets were all going sideways. Years ago when I had the barrel made there was a shortage of 1:8 twist .308 barrels so I went with the 1:10. Wrong twist is a bummer.
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