lower reciever compatible with any upper?
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Old 04-02-2012, 03:51 PM   #1
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Default lower reciever compatible with any upper?

can you use your lower receiver with any upper like a 5.56 mid length system and swap out the upper and put a carbine length gas system on the same lower? or do you have to switch out certain components from the lower to conform to the different needs from the new upper?

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Old 04-02-2012, 04:04 PM   #2
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Nope, that's the beauty of the modular system. 5.56 lowers of one brand will fit almost all upper brands. Only a few older Colt models may have a pin size problem, but there's an adapter for it. You shouldn't have a problem though if you use something like a PSA lower on a BCM upper though.

ETA: Carbine length or Mid-length uppers don't affect anything in the lower usually. The buffer size may be the only thing that could be affected, but not usually.

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Old 04-02-2012, 04:11 PM   #3
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wow, i might have to do some lower receiver hunting

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Old 04-02-2012, 04:14 PM   #4
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Originally Posted by Armed-Citizen View Post
wow, i might have to do some lower receiver hunting
What exactly are you trying to do?
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Old 04-02-2012, 04:24 PM   #5
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maybe i didn't appropriately asked my question...my thought is to buy a complete rifle in mid length form and wanted to know if the upper can be changed to a Carb length later so I don't have to buy another complete rifle. also can i use a 308 chambered upper with a lower receiver from a 5.56 rifle? just emphasizing my thought...hope i explained my self clearly

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Old 04-02-2012, 04:37 PM   #6
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You can switch between a 5.56 mid and carbine upper by just swapping uppers.

308 will not fit on your lower unless you have a Colt 901. The Colt 901 is the only lower I know of that can interchange between a standard ar15 and ar10 upper, with the help of a magwell adapter for 5.56 size magazines. Another excpetion is a custome bolt action upper for larger rounds. I seem to remember reading a few years ago about seeing .308, .50 bmg, .300 win mag and .338 single shot bolt action uppers that will bolt to an ar15 lower. Not sure tho. But all these rounds are waaaaay to long to fit in a standard ar15 magazine well.


Here's a short list of ar15 compatible uppers (NOT COMPLETE) 6.8 spc, 5.7, 6.5 grendel, 7.62 x39, .300 blk, much much more.

For simplicity sake, don't mix and match Ar10 and Ar15 receivers and parts.

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Old 04-02-2012, 04:41 PM   #7
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Quote:
Originally Posted by AgentTikki
You can switch between a 5.56 mid and carbine upper by just swapping uppers.

308 will not fit on your lower unless you have a Colt 901. The Colt 901 is the only lower I know of that can interchange between a standard ar15 and ar10 upper, with the help of a magwell adapter for 5.56 size magazines. Another excpetion is a custome bolt action upper for larger rounds. I seem to remember reading a few years ago about seeing .50 bmg and .300 win mag and .338 single shot bolt action uppers that will bolt to an ar15 lower. Not sure tho. But all these rounds are waaaaay to long to fit in a standard ar15 magazine well.

Here's a short list of ar15 compatible uppers (NOT COMPLETE) 6.8 spc, 5.7, 6.5 grendel, 7.62 x39, .300 blk, much much more.

For simplicity sake, don't mix and match Ar10 and Ar15 receivers and parts.
thank you,i feel im getting way more progress from here than my local gun store, so it would be safe to put a 7.62x39upper on a 5.56 lower? if i were to put another upper, it would mostly likely be a carbine length 5.56 upper or a 7.62x39 upper..
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Old 04-02-2012, 04:59 PM   #8
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Originally Posted by Armed-Citizen View Post
thank you,i feel im getting way more progress from here than my local gun store, so it would be safe to put a 7.62x39upper on a 5.56 lower? if i were to put another upper, it would mostly likely be a carbine length 5.56 upper or a 7.62x39 upper..
Mechanically, yes. Depending on which state, you may run into some legal issues. Best bet if you aren't sure might be to purchase a lower that says "multi-cal". With regard to the 901 system, you might have to buy one of their proprietary uppers to make the interchangeability work. Very new platform, so I don't have that info.
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Old 04-02-2012, 05:05 PM   #9
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Tuning plays a role as well. It probably won't make the difference b/w cycling or not but one recoil system or trigger way not be ideal when switching calibers.

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Old 04-02-2012, 05:16 PM   #10
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Quote:
Originally Posted by Armed-Citizen View Post
thank you,i feel im getting way more progress from here than my local gun store, so it would be safe to put a 7.62x39upper on a 5.56 lower? if i were to put another upper, it would mostly likely be a carbine length 5.56 upper or a 7.62x39 upper..
If I were going to be looking at the 7.62X39 I would consider the .300 blk simply because you can still use the .223/5.56 bolt and mags with the .300 blk ammo and it will put you near the ballistics of the 7.62 round and you wont need to buy 2 complete uppers you could just buy a 5.56 complete upper and a .300 blk upper minus the bolt carrier group and save yourself $90and not have to worry about different mags , different bolts etc . simple and easy conversion , Im looking to do this myself on my next build
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