Question: Can any upper go with any lower?

[WestttyWest]

Hey guys, I'm a bit of a noob, and am attempting to build an AR-15. What I want to know is, can any upper attatch to any lower? Thanks for your patience in advance.

[nate76239]

Pretty much the multi cal AR15 lower marked .223-5.56 also work for 6.8,7.62x39, 6.5 Grendel, .300 black and the uppers are just about all the same except 9mm can be different. The .308 AR types are a separate thing with several variations. There were some older Colt models that had larger pins but if you're buying brand new stuff it's not likely you will see one.

[davidb]

If you're going with milspec then yes, all uppers should fit all lowers

[WestttyWest]

okay sweet, thanks guys

[softballcrazy831]

If you're going with milspec then yes, all uppers should fit all lowers

Will the lower say milspec?


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[j15w]

Nope, but lowers are all pretty much the same. Most will just say "Cal Multi", which means it can shoot .223 and 5.56.

[elx144]

Like everyone above said, yes. One other thing to think about is the buffer tube. M4 buffer tubes come in commercial or milspec. They aren't compatible, commercial is a larger diameter. I'd recommend buying a complete kit with the tube/spring/buffer/stock.

[davidb]

Will the lower say milspec?


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Noy sure depends on manufacturer and how they market it I suppose, but all forged milspec lowers look the same, just with different rollmarks, anything like an aero precision, Anderson, PSA, spikes etc.

[L84CABO]

Whatcha buildin...WHATCHA BUILDIN!?

We are a curious bunch!

[gixxnrocket]

Yes and no. (Assuming ar15) A featureless lower will not be legal with a featured upper. I believe the gun must be 30" collapsed so 14.5" barrel will need a long enough muzzle device and it must be pinned. Anything shorter would fall into the sbr or pistol category depending on the configuration of the lower. Be sure to download the "CA Semiauto Ban(AW) ID Flowchart" at the very top left.

Physically, the lowers are cut about the same. Some manufacturer's upper and lower mate up with a tighter fit, if your ocd.

[WestttyWest]

Whatcha buildin...WHATCHA BUILDIN!?

We are a curious bunch!

I have no idea yet! lol. I was wondering if everything was interchangable. Mixing and matching, etc...

But I do dream on building my own badass personal AR. Just gotta figure out what and how

[WestttyWest]

Yes and no. (Assuming ar15) A featureless lower will not be legal with a featured upper. I believe the gun must be 30" collapsed so 14.5" barrel will need a long enough muzzle device and it must be pinned. Anything shorter would fall into the sbr or pistol category depending on the configuration of the lower. Be sure to download the "CA Semiauto Ban(AW) ID Flowchart" at the very top left.

Physically, the lowers are cut about the same. Some manufacturer's upper and lower mate up with a tighter fit, if your ocd.

When you say lowers are cut about the same, its all cookie cutter then? And the same with all milspec?

[wpage]

Keep life simple and leave them the same...

[CALI-gula]

Black Uppers do not go with FDE lowers.

That's just not even fashionable. Totally vulgar and brashly tacky. Like white socks with sandals.

.

[gixxnrocket]

In regards to the cut. Civilian cut lowers are all the same. The difference you will see is is material and finish. There lowers do not take much force from recoil. So material is not a really big issue IMO. However plastic lowers can fatigue where the buffer tube mates the lower. By tuning down the gas system and balancing the recoil spring and buffer, this problem can be mitigated.

Unless you have access to or make a milspec trigger pocket, you probably won't see a true "milspec lower".

Tuning and customization aside, any ar15 lower will mount to any ar15 upper receiver.

Most stuff is at least milspec on the market. There is a lot that is better. In the parts market mil-spec has become so standardized it almost not even a selling point.