Mega AR15 Compatibility

[Marine24]

I have a Mega 300 Blackout but just can't connect with the round. It worked well on a pig hunt in Florida but looking to either replace it with a 14.5" 5.56 barrel or build a complete new upper in 5.56.

I know there are compatibility issues with Maten line, similar to most billet 308 AR upper and lowers, but assume Mega's AR15 billet lowers are milspec and compatible with any milspec AR15 upper. I don't see the qualification listed on their website, but wanted to confirm with those that have mixed Mega lowers with another manufacturer's upper.

If I go the new upper route, probably just build me a Mega upper anyway but like the options.

[ray1970]

Call me cheap or lazy, but I'd just stick a 5.56 barrel on it and call it done.

[Marine24]

That would make the most sense. I'm not much for swapping uppers and typically end up building dedicated lowers.

Still curious on how interchangeable billet AR15 uppers are.


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[yz9890]

I have a forged Mega lower that fits at least Noveske, PSA, and BCM uppers. Not sure about billet but don't know why they'd be different.

[Great-Kazoo]

That would make the most sense. I'm not much for swapping uppers and typically end up building dedicated lowers.

Still curious on how interchangeable billet AR15 uppers are.


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Outside of cosmetic issues (finish color match) and the lines matching another mfg lower or upper. A lower is a lower etc. There may be some wobble between the two since the same mfg didn't do them. BUT.. IMO unless the upper & lower were sold as a matched set, there will always be some variances how the fit & look. As Ray said, replace the bbl with a 5.56 one and call it good.

As for Mil Spec.

https://www.americanrifleman.org/articles/2010/3/18/the-milspec-definition/


This one is interesting as it mentions Mega

https://thearmsguide.com/7701/ar-15-isnt-mil-spec-thats-ok/

Here’s an example of what I mean: my MEGA Megalithic billet upper receiver, MEGA billet lower receiver and FailZero bolt carrier group (BCG) technically do not meet military specifications. Instead of being forged aluminum, my MEGA receivers are billet aluminum. Instead of being parkerized, my FailZero bolt carrier group is finished in nickel boron plating.

A billet receiver and nickel boron plating is not mil-spec. However, all of the components I mentioned have dimensions and tolerances that are per mil-spec.

[Marine24]

Good point. Fit is relative particularly with billet receivers and the artistic license some manufacturers take in their design. Functionally may work but aesthetics might be something different.

Barrel swap it is. Now shifting to the hunt.


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[ray1970]

You could always keep it all Mega if you wanted.

https://www.aimsurplus.com/product.aspx?item=XMTTMA55616&name=MEGA+ARMS+16%22+Stainless+5.56+AR+Barrel&groupid=6477

[Marine24]

Possible. I'm pretty impressed with the 300 Blackout Mega barrel accuracy.

Was looking at a LaRue Stealth as well, but a number of good choices.


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[KS63]

You going to sell that Mega Blackout barrel?

[Marine24]

Hadn't thought that far yet, but probably.