Ejection Port Questions

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Ejection Port Questions

Postby Eldon Manning » Fri Jun 29, 2018 9:39 am

I've never been able to get a straight answer out of anyone about this. The most specific answer I've gotten is that the brass is dented on ejection.

What happens when you use a 450BM with a standard size port? Does it jam, will it not eject and stove pipe? What happens?
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Re: Ejection Port Questions

Postby AR Sarge » Sat Jun 30, 2018 10:52 pm

Thanks for posing this question.

I logged on specifically t find this info as I am starting to contemplate either a home build or buying a factory upper. I have a stripped upper but it is from a 300blk and I am curious about the port size.

Eagerly awaiting a knowledge download.....

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Re: Ejection Port Questions

Postby Al in Mi » Sat Jun 30, 2018 11:55 pm

I don't know for sure, but guessing a case would stovepipe.

If Bushey and the custom guys opened the port up, it was needed.

Btw, welcome abord
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Re: Ejection Port Questions

Postby Bmt85 » Sun Jul 01, 2018 10:25 am

Depends on the upper. I just measured the ejection ports on some of my uppers and found that some of them are big enough to fit a 450B case, and some are not. I have 2 uppers purchased from the same manufacturer, but at different times. One that I used in my Tromix build is .5030-.5040" on the unground section, the other is .4990 at one spot and .5005" for most of the opening. So that one will not eject a cartridge without being opened a bit. The one used on my Tromix build probably didn't need to be opened up, but why not do it? It will allow more room for the cartridge to get out of there, and it only takes a few minutes with a dremel. I went the route of only opening the front half of the port, because I figure if the front of the case can get out without an issue, the rest should follow with out much of a problem. Haven't had a problem, so far. Also, when your opening the port, your putting a slight "ramp" to help guide the case out, so as to reduce the chance of it hitting the upper and not ejecting.

So I guess, if you want to try a build without opening up the port, find one with a port at least .5020". You still might run into problems, though.
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Re: Ejection Port Questions

Postby AR Sarge » Sun Jul 01, 2018 11:40 pm

Thanks for the replies. I think if I am going to build one I’ll get an upper with the port enlarged. Seems like cheap insurance to me.
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Re: Ejection Port Questions

Postby plant_one » Mon Jul 02, 2018 2:07 am

AR Sarge wrote:Thanks for the replies. I think if I am going to build one I’ll get an upper with the port enlarged. Seems like cheap insurance to me.


with as common and as relatively cheap parts have gotten these days - you're right on track its not worth the risk.

its not like we're 4 years bacck when you cant find a pistol grip on the shelves anywhere
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Re: Ejection Port Questions

Postby AR Sarge » Tue Jul 03, 2018 9:06 am

Hey plant,

Great point. With parts cheap and available might as well get a dedicated upper.

Then, of course, I’ll still have this unused upper lying about so I’ll have to build someting else. I’d consider a 6.8spc, but you know I’m an avid blackout fan from the early years and it’d seem like being unfaithful!
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