20 Inch AR Accuracy - The HuntingPA.com Outdoor Community
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post #1 of 12 (permalink) Old 07-21-2016, 02:37 PM Thread Starter
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20 Inch AR Accuracy

I purchased a Palmetto State Armory 20 Inch CHF 1:7 twist premium upper last year and for the life of me I cannot get it to group under 5 inches at 100 yards.

I first got rid of the milspec trigger. Accuracy was still terrible. Then I thought maybe the scope wasn't holding zero (Nikon p223 with BDC reticle) so I sent it back to Nikon to inspect.

I got the scope back and still couldn't group less than 5 inches. I put the scope on another AR and shot a sub 2 inch group of 10 shots at 100 yards. The scope is no longer a concern.

I've only shot 55 grain stuff through it and all of my research indicates that the 1:7 twist should handle it just fine.

Any thoughts on the poor accuracy? Did I just get a lemon?
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post #2 of 12 (permalink) Old 07-21-2016, 03:10 PM
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Re: 20 Inch AR Accuracy

55gr. in a 1:7 twist is said to be borderline.

Twist vs. bullet

“There is Truth in the Old Saying, That if you make yourself a Sheep, the Wolves will eat you.”
Benjamin Franklin, 1773
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post #3 of 12 (permalink) Old 07-21-2016, 03:22 PM
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Re: 20 Inch AR Accuracy

Get a box of each 69 grain and 77 grain OTM, Black Hills or Federal and try it. I would also get some 62 XM855 for plinking. Also, Don't expect match grade results with a chrome lined barrel.
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post #4 of 12 (permalink) Old 07-21-2016, 03:53 PM Thread Starter
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Re: 20 Inch AR Accuracy

I never had any issues with the 55gr out of my 16 inch 1:7 barrels, only the 20 inch barrel. That's why I'm frustrated with how the it's shooting compared to the shorter barrels. I've always been pleased with the groups I get from my other rifles.

I'll try some heavier bullets. Certainly not expecting match grade results, just a little better than I'm doing at 100 yards.

Thanks for the suggestions.
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post #5 of 12 (permalink) Old 07-21-2016, 04:53 PM
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Re: 20 Inch AR Accuracy

Accuracy has nothing to do with barrel length, but it does change the velocity at which the bullet is travelling.

Not all barrels will be the same, but 5" at 100 yards is pretty bad.

I would say you should try different ammo as ammo and barrel combo can vary from rifle to rifle how it will perform.

Take as much of the variables out as you can.

1) Make sure the rings/optics are torqued properly.

2) Get another shooter if you are unsure of your marksmanship to see if they have the same results.

3) Have a good front/rear rest to make sure that you are not pulling the shots.

4) Test out various ammo as not all ammo are created equal. I have always used Hornady V/A max as my standard when it comes to .223/5.56.

Typically, I'd say a 1:7 twist would stabilize a 55gr projectile, but it wouldn't surprise me if it's keyholing. Have you seen any signs of keyholing at 100 yards?
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post #6 of 12 (permalink) Old 07-21-2016, 08:53 PM Thread Starter
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Re: 20 Inch AR Accuracy

I'm shooting from a good Caldwell rest. Even had a friend try it and his group was bad too.

No evidence of keyholing.
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post #7 of 12 (permalink) Old 07-22-2016, 11:31 AM
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Re: 20 Inch AR Accuracy

Is that 5 inches with one particular 55 grain load or different 55 grain loads?
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post #8 of 12 (permalink) Old 07-22-2016, 11:34 AM
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Re: 20 Inch AR Accuracy

BTW have you checked the crown?
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post #9 of 12 (permalink) Old 07-22-2016, 12:19 PM Thread Starter
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Re: 20 Inch AR Accuracy

I've tried several different brands of 55 grain with the same poor results each time.

I've inspected the entire upper and I haven't noticed anything abnormal.

About the only thing I haven't tried yet is shooting a heavier bullet through it.
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post #10 of 12 (permalink) Old 07-22-2016, 03:07 PM
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Re: 20 Inch AR Accuracy

NATO SS109 or M855 usually groups at about 2.5" or less. If you can get some try that as a control.

Is the handguard floated?
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