450 barrels

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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450 barrels

Postby Bagel51 » Sun Oct 15, 2017 5:47 pm

Hello all. I have a couple questions. In planning on building a 450bm build. Most of my questions are about the barrel. I'm looking at a 22-26" barrel but I'm having issues with twist rates. I've seen 1-16. 1-24. I don't know which one I should go with. And am I going to gain anything by going over a 20 barrel? I don't reload so I'll be using factory ammo.

Next question. Rifle length gas or mid length
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Re: 450 barrels

Postby Hoot » Sun Oct 15, 2017 7:41 pm

Welcome aboard OM.

If you never intend to reload, the longer barrel will net you more velocity but is not absolutely necessary as the factory rounds are plenty lethal even at reduced velocity. If your hunting scenario places you within 100 yds, any barrel will suffice. Since the bullets shed velocity as the range increases, the additional velocity afforded by a longer barrel might and that's a big might, help extend the killing range a little. I have two 20 inchers. they are plenty long for my needs and I'm a big proponent for rifles with rifle length barrels, not pop-guns. As for the gas system. I have had all three, carbine, mid and rifle length systems. By far, the mid-length system is the best choice IMHO. Regarding twist rate. With the factory ammo, anything from 1:16 and slower will deliver them point first. I don't hunt with 300gr or heavier bullets, so I'm fond of the 1:24 twist, such as the Bushmaster factory AR uppers come with.

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In Theory, there is no difference between theory and practice. In Practice, there is.
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Re: 450 barrels

Postby Al in Mi » Mon Oct 16, 2017 4:29 am

I've had both 16 and 20" Bushmaster factory uppers, and if my memory serves me correctly, there was like 100-125fps diff in velocity between the two with factory ammo, I chose to stay with 16" for the handiness and never regretted the choice.

If I were to build one I'd probably split the barrel length and go with Gryphon's 18" barrel and call it about perfect. My buds gun just pile drives everything it's been fed so far.

MGM did a test with their Encore barrel on velocity vs barrel length with the 450B last year, I can't find it at the moment, but was eye opening.
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Re: 450 barrels

Postby Bagel51 » Mon Oct 16, 2017 6:52 am

Is this the article? Either way it's a good article.

https://matchgrademachine.com/velocity- ... bushmaster
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Re: 450 barrels

Postby Al in Mi » Mon Oct 16, 2017 8:34 am

Bagel51 wrote:Is this the article? Either way it's a good article.

https://matchgrademachine.com/velocity- ... bushmaster


yep, looks like it.

things may be different is a gas operated gun but there still plenty of punch.
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Re: 450 barrels

Postby Bagel51 » Mon Oct 16, 2017 1:28 pm

So based off those numbers I'm Leaning towards 22". But what it doesn't say is what the twist rate was for these tests. Not sure if twist would matter for these tests
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Re: 450 barrels

Postby Al in Mi » Mon Oct 16, 2017 1:35 pm

their standard barrels are 16t
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