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Old October 1, 2013, 12:06 PM   #1
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Turning down heavy AR barrel

My AR has the Bushmaster "Dissipator" upper, which is too heavy. It has a 16" heavy barrel with mid-length gas system, and a second unused gas block/front sight post. Local smith says if you turn the barrel down between the real gas block and chamber, and between the fake gas block and the real one, the rifle will be made "wildly inaccurate." What do y'all think?

Molwn labe!
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Old October 1, 2013, 01:52 PM   #2
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I make AR barrels fairly often. Turning them down correctly does not harm them at all.

Just take light cuts and don’t heat the barrel up much.

It takes a bit of time, but I have made some super accurate ARs with very light weight barrels on them. I light barrel heats up faster than a heavy one, but for short shot strings they can be every bit as accurate as heavy barrels.

You do need to leave the boss under your “gas block” ( front sight mount) full size if you want to retain that sight, but it will do nothing to harm the accuracy if you remove metal on both sides. Think about the fact that ARs have flash hiders. That’s a “glob of steel” that’s on the end of the barrel where it can vibrate the most, and they don’t harm accuracy.

It is true that such a barrel may make the rifle a bit more finicky about ammo. If I were doing it for myself, I’d go with a free flat tube at the same time. That can solve several issues that may come up with GI handguards and light barrels. Don’t use the sight mount as a sling attachment. Use the F.F. tube instead and accuracy will be as good as it is now.
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Old October 1, 2013, 02:39 PM   #3
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As of now I dont have a AR barrel. But this brings up some interesting questions I have considered. I have a very complete CNC and manual shop at my disposal. I like stuff thats out of the ordinary. I had considered buying a bull barrel and doing some mods such as fluting it on my own. I have also considered some type of cooling fins to increase surface area and help dissipate heat. Let me know how you make out turning your barrel or post up some pictures.
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Old October 3, 2013, 07:28 AM   #4
Bart B.
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Fluting or turning down a finished barrel may change its bore and groove diameters under the flutes or turn-down area. Button rifled barrels' get bigger, hammer forged ones smaller. Cut rifled barrels may not change. It's best to flute or profile barrels before they're rifled. Use an air or star gauge to measure the bore before and afterwords to see the difference.

Any good, well made and stress relieved barrel will not change point of impact as it heats up as long as it's properly fit to a receiver having its face squared up with the chamber axis.
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Last edited by Bart B.; October 3, 2013 at 08:49 AM.
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