Few specific questions re: AR platform

[Skribs]

I just have a few specific questions that I've been wondering for a while, and never really got around to asking. I've looked at the AR platform for when I do get around to getting a rifle, but I haven't actually made the jump to it yet. Most of my experience has been with autoloader handguns.

1) Magazines and wildcat (or accepted, non-.223) cartridges: I've read several times on some cartridges "you can use standard AR magazines, but it will only hold X instead of 30". I find this a bit weird, mainly because I use pistols a lot, and if it fits in the same frame, it often needs magazines specifically for that caliber (i.e. 9mm vs. .40 S&W). So how is it that these rifle magazines work better, and would it work better if there was a magazine built specifically for that cartridge?

2) Adding a folding stock: I've seen a few models on the market of AR-style weapons that do not require the buffer tube, such as certain AR pistols or some of the newer guns that are coming out (many of them I believe look like ARs, but aren't quite exactly ARs). I've also seen the folding stock on the market that will work with a buffer tube, it just won't fire without the stock in place.

What I'm wondering is this: would it be possible (and if so, what would be required) to convert an AR from one that requires a buffer tube to one that does not, for the sake of either turning into a pistol or adding a folding stock?

3) What makes a gun an "AR" vs. "not an AR"? Kind of in-line with #2 above, but there are a lot of newer guns on the market that have similar ergonomics to ARs, albeit with some differences. I'm especially thinking of a lot of the newer 5.56 rifles on the market, such as SCAR, HK 416, SIG 556, etc. How does one determine whether or not such a weapon is close enough to classify as an AR?

 

[holdencm9]

I don't know about 1 or 2, but I'd be interested to hear some responses for #3. Kind of like the "what makes a 1911, a 1911?" thread from awhile back.

I suppose the combination of the gas-operated, rotating bolt operation, with the in-line stock, is most of it, although I don't know if pistol-caliber "AR's" technically have the same internal operations.

Kind of like "what makes a mammal a mammal?" ...no matter what universal mammalian trait you come up with, there is probably a mammal that doesn't have it.

 

[Skribs]

I don't know about 1 or 2, but I'd be interested to hear some responses for #3. Kind of like the "what makes a 1911, a 1911?" thread from awhile back.

I suppose the combination of the gas-operated, rotating bolt operation, with the in-line stock, is most of it, although I don't know if pistol-caliber "AR's" technically have the same internal operations.

Kind of like "what makes a mammal a mammal?" ...no matter what universal mammalian trait you come up with, there is probably a mammal that doesn't have it.

When I post 3 questions, and get 2 "I don't know"s and a "I'd like to see what others say on #3", I feel like I've asked 3 good questions

As to your "what makes a mammal a mammal", it's a combination of traits that make it a mammal as opposed to another vertibrate, although sometimes things get classified as a mammal without that trait (i.e. I think the platypus lays eggs, if I'm not mistaken, and one trait for mammals is live birth). Anyway, getting a bit OT there.

 

[SpentCasing]

1. Most of those calibers that use a modified 223 case are able to use the same mags because dimensionally they still fit.

2. Not sure I follow. Ive never seen a folding stock with a AR that uses the buffer tube and/or DI gas system.

3. Those are piston guns. ARs use DI gas systems.

 

[Skribs]

2. http://www.lawtactical.com/ProductDetails.asp?ProductCode=2012001

What I am asking for is what would be required to convert the AR to something that uses a normal folding stock, i.e. one that will let you fire with the stock folded (like you see on a SCAR or a Sig 556).

3. Yet some ARs are piston ARs, like the POF rifles.

 

[pseudonymity]

For #3, I would say the lower receiver, and to some extent the upper receiver as well. You can change barrels, stocks, grips, etc and it is still AR in my mind. Really I mean AR-15 specifically here, since other ARs are not nearly as standardized.

I would not include DI gas systems or rotating bolt in the category, since .22lr conversion kits use neither and I still consider them AR. Same for piston uppers - still AR to me, but that is really pushing the limit in a way.

Just having a similar manual of arms or accepting parts is not enough to make it AR for me - I do not consider Just Right carbines or M&P15-22s to be ARs.

 

[JustinJ]

1. Sometimes magazines of a different caliber will work but not tend to be less than reliable.

2. Para Ordinance has an AR in which the recoil spring is in front of the carrier and i think above the barrel. It somehow attaches where a standard gas key goes as i understand. Due to this the gun does not require a standard buffer tube and can accept a folding stock. Rock River also makes a piston AR but it is an even greater departure from the standard AR configuration.

3. There are few bigger wastes of time than to argue semantics.

 

[holdencm9]

They are 3 good questions.

Ha, I was even going to use the example of the platypus...it seems to defy all rules of thumb.

I guess if we are to go with the "combination of traits" of an AR we can start with the basics, all of which there are exceptions to the rule:

Light-weight
5.56x45mm
Magazine-fed
Semi-automatic
Gas-operated
Air-cooled
Rotating-lock bolt in a bolt-carrier
Modular
2 pins make it come apart

Other things like FA and dust cover clearly don't make an AR, an AR. Nor do the materials since they make them out of anything nowadays.

 

[Skribs]

I guess the question on #2 is, if I start from a "normal" AR, how much would I have to change in order to get it to work like the RRA or Para Ordnance ARs?

 

[JustinJ]

I guess the question on #2 is, if I start from a "normal" AR, how much would I have to change in order to get it to work like the RRA or Para Ordnance ARs?

To my knowledge none of the needed parts can be purchased independently. So you will have to purchase at least a complete upper.

 

[Skribs]

So if I wanted something in a non-5.56-caliber or a different barrel length, I would need to start with one of their uppers and update it from there?

 

[Skribs]

So if I wanted something in a non-5.56-caliber or a different barrel length, I would need to start with one of their uppers and update it from there?

Or would this be impossible because different gas systems would be involved for different cartridges? Like I said, most of my firearm knowledge comes from handguns, which are not gas-operated, and I don't know a whole lot about the internals. Essentially I'm trying to figure out how to get a rifle with AR-style controls in a non-standard caliber with a folding stock.

 

[holdencm9]

I would think that at least half the problem is the BCG. Even if you figure out a way to move the spring & buffer from the stock, and put it elsewhere (in front or along the side somehow), the standard BCG pretty much sits flush with the rear of the upper receiver. There would be no place for it to move, in order to cycle. Ya know? Hence why you probably have to start with an upper specifically designed for a folding stock.

Or would this be impossible because different gas systems would be involved for different cartridges? Like I said, most of my firearm knowledge comes from handguns, which are not gas-operated, and I don't know a whole lot about the internals. Essentially I'm trying to figure out how to get a rifle with AR-style controls in a non-standard caliber with a folding stock.

It would be tough, because although simple (bullet shoots out, gas goes through a tube back into the receiver to push the BCG back) they can be finnicky. You hear of people having jams with AR's because they don't have the right size gas port for the stock length, or heavy-enough BCG, or buffer. Basically it is a matter of fine-tuning, size and location of gas hole (which dictates how much pressure is built up) and mass/resistance of the bolt and spring. Too little gas and it will short stroke and too much and the cyclic rate will be so fast you may have other issues.

 

[Skylerbone]

Skribs, there are a number of kits available to convert a DI AR to a piston system. If you want a visual of differences between the two, the pistol versions make things obvious. Head over to RRA's site and look at the DI and piston versions. One looks like a giant handgun, the other looks like a giant handgun with a broomhandle added.

A link to a conversion kit: http://www.brownells.com/.aspx/pid=30934/Product/AR-15-M16-GAS-PISTON-CONVERSION-KIT

 

[Ramone]

Me, I?

*I* think it's not an AR15 if it is not Direct Impingement System- and that does mean that .22 conversions and Pistol Caliber Blowback operated rifles are not really "AR"s in my book (though I do kinda give them honorable mention).

Piston Operated ARs, IMO, are not ARs ( they are still 'Gas Operated', just not DI)- not that there's anything wrong with a Piston Rifle, they are just not really ARs IMO.

Of course, if one wants a _True_ AR with a Piston and a folding stock, there is always the AR-18/ AR-180!