Difference of 5.56 and Multi-Caliber Lower?
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Old 11-14-2012, 11:29 PM   #1
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Default Difference of 5.56 and Multi-Caliber Lower?

Is there truely, differences between the standard Mil-Spec 5.56/223 Lowers dimensions, compared to Lowers that say MULTI Caliber, or is this just a fancy marketing twist on words?
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Old 11-14-2012, 11:33 PM   #2
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Is there truely, differences between the standard Mil-Spec 5.56/223 Lowers dimensions, compared to Lowers that say MULTI Caliber, or is this just a fancy marketing twist on words?
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as long as it says milspec your good. with so many different caliber options for stripped lowers these days i think the manufacturers caught on.. it would be strange to have a 5.56 marked lower with a .300blk upper.. hence the multi dealio.. really it doesnt matter much just kinda is what it is thing.
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Old 11-14-2012, 11:37 PM   #3
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What the lower has marked on it doesn't really matter. There are pressure differences between .223 and 5.56 NATO rounds, and the chamber for the NATO round is a bit more generous in the leade.

So what is important is what the barrel is chambered for. I have seen people shoot 5.56 in a .223 chambered rifle with no problems, and I have seen people shoot them and have blown primers other high pressure signs like flattened primers and ejector marks on the case heads. So, it is not just marketing when people recommend not shooting 5.56 in a rifle that has a barrel with a .223 chamber. But again as far as the marking on the lower goes it could say it was chambered for 40 megawatt plasma rounds, and as long as it is built to original specs it can accept any of the uppers designed to fit a standard AR15.

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Old 11-15-2012, 04:29 AM   #4
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Thanks, this is what I thought. I do have an AR that does say 223-5.56, so I know it can shoot both rounds without problems, and I know about the higher charge of 5.56 and not firing rounds in a dedicated 223 chamber as it can be unsafe, but seeing the Lowers that say Multi-Caliber made me wonder, if they were special, and were needed, if doing something other than a 223/5.56(or another configuration within this parimeter) build. Not including, having to use AR-10 variations, which is another animal.
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Old 11-15-2012, 09:36 AM   #5
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The milspec lowers are all basically the same. other than the caliber marking, there is basically no difference between a 5.56, and a multi cal lower. It's the upper that changes with the caliber.

There MAY be a legal issue though. I think I may have read that if the receiver is marked 5.56, you can only shoot 5.56/.223 out of it legally, but if it says multi, your good to go on everything. I think I read that here on FTF, but it's been awhile. It may be worth looking into.

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Old 11-16-2012, 03:37 PM   #6
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The milspec lowers are all basically the same. other than the caliber marking, there is basically no difference between a 5.56, and a multi cal lower. It's the upper that changes with the caliber.

There MAY be a legal issue though. I think I may have read that if the receiver is marked 5.56, you can only shoot 5.56/.223 out of it legally, but if it says multi, your good to go on everything. I think I read that here on FTF, but it's been awhile. It may be worth looking into.
I know of no legal issues with the lower markings. That is not saying there isn't in some county or state (Seeing as now anyone and everyone can make what ever law they want) doesn't have a little known law that says if you have an evil assult rifle and it is marked different than it is chambered you are in violation and you will be beaten with a lead pipe and locked away as a future mass murder.

The only problem I could see is that if you sold say your 300 blakout rifle and the lower says 556 and some numbnut tried to chamber a 556 and then charged another blowing the thing up in his face.

You just never know in this new world order world anymore. More and more dumb people are allowed to live because of safety warnings and helmets.

So I would say if you want to make a nonstandard caliber (IE not 556 or 223) ar and there is an OFF change you would sell it (Why would you ever sell a gun?) then you might want to get a multical lower.

If you find a multical marked lower that is $30 or 40 cheaper than a 556 marked then hey go for it.
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Old 11-16-2012, 04:39 PM   #7
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Originally Posted by texaswoodworker View Post
The milspec lowers are all basically the same. other than the caliber marking, there is basically no difference between a 5.56, and a multi cal lower. It's the upper that changes with the caliber.

There MAY be a legal issue though. I think I may have read that if the receiver is marked 5.56, you can only shoot 5.56/.223 out of it legally, but if it says multi, your good to go on everything. I think I read that here on FTF, but it's been awhile. It may be worth looking into.
Yeah, I think there are a couple states law that says you can only shoot what caliber is marked on the receiver, or some such stupid crap.
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Old 11-16-2012, 05:43 PM   #8
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I know of no legal issues with the lower markings. That is not saying there isn't in some county or state (Seeing as now anyone and everyone can make what ever law they want) doesn't have a little known law that says if you have an evil assult rifle and it is marked different than it is chambered you are in violation and you will be beaten with a lead pipe and locked away as a future mass murder.

The only problem I could see is that if you sold say your 300 blakout rifle and the lower says 556 and some numbnut tried to chamber a 556 and then charged another blowing the thing up in his face.

You just never know in this new world order world anymore. More and more dumb people are allowed to live because of safety warnings and helmets.

So I would say if you want to make a nonstandard caliber (IE not 556 or 223) ar and there is an OFF change you would sell it (Why would you ever sell a gun?) then you might want to get a multical lower.

If you find a multical marked lower that is $30 or 40 cheaper than a 556 marked then hey go for it.
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Originally Posted by fsted2a View Post
Yeah, I think there are a couple states law that says you can only shoot what caliber is marked on the receiver, or some such stupid crap.
Yeah, I thought someone has a law like that, I just wasn't sure it if it was a federal issue. I guess not.
Personally, I just prefer to get multi cal lowers so that if I do decide to get another upper and swap them, I don't have a .300 blackout or a 6.5 Grendel that says 5.56 on the side. That's just a personal preference though.
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