has anyone built a gi caliber 30 ar?seems like it might be doable?

I heard rumors of a few conversions many years back, but nothing recently.   I've always liked the .30 carbine round, and I think it makes a good pdw round.  

Here's where I'll get flamed:
.300 BO killed any chance the .30C would have ever had of going mainstream again,  since it offers the ability to use the same mags and bolt.  When you look at the capabilities of the .30 with modern powders, .300 really doesn't do much that the carbine couldn't, aside from the aforementioned compatibility.

Olympic Arms did one years ago.

Greg

The magazine comparability is the thing that would make the 300blackout a better choice than 30 carbine. Everything else would probably be a wash.

I agree here.  Getting an M1 Carbine magazine to work in an AR would require a lot of work.  I never saw the Oly AR in .30 Carbine, but I would expect them to go the way they did with pistol caliber ARs and adapt the magazines to fit the rifle instead of vice versa (a la Colt-type 9mm ARs).  M1 Carbine magazines aren't exactly everywhere, but they are relatively plentiful (South Korea still makes them), and would be one of the big selling points to a .30 Carbine variant.  But with 300 Blackout using standard magazines, that really does seem to end that.

(On the plus side, that means I only have to load .30 Carbine for my M1....  That simplifies things for me. )

I have been shooting 300 BLK for awhile now, not a lot but enough to learn a bit. If you look at listed loadings for the 300 BLK you will find that you have a lot more flexibility with the 300 over the .30 carbine. I had a M-1 carbine some years back and the BLK is a superior round in my mind.  Just compare the load tables and look at the numbers. That is all that needs said...the 300 wins.  As an aside the .300 works perfectly with normal AR magazines. Oh, and for re-loaders you can easily make your own brass as many of us do so its everywhere.

If you just want a .30 cal. carbine round to fire in an AR and you don't care how much work it is or how much performance you will be giving up then by all means...keep looking until you find someone who would love to take lots of your money to build one for your. If you want a nice .30 caliber round that you can fire in your AR do what thousands have successfully and easily done and just pop a .300 BLK barrel in your AR upper and get on with life.

With the price of .30 carbine, why?  Unless you reload for it....

I think it  would be a fairly simple matter to make standard AR size mags that can feed 30 carbine rounds.  Or, 30 carbine mags are significantly smaller than an AR mag.  It would be fairly easy to make an adapter that fits in a standard AR magwell, the way Colt has done on their 901 for accepting AR15 mags.

Let's start with how M1 Carbine magazines are retained in the M1 Carbine.  There are two bumps on the back of the magazine that the Carbine's magazine catch holds (30 round magazines have a third bump on the side to help with the added weight).  These magazines aren't particularly adaptable the way Colt did with Uzi magazines for their 9mm SMG, and their 901 has a lot more structural flexibility than a stock AR lower does for handling odd magazines.  Both the Colt 9mm SMG and the 901 use the "normal" magazine catch/release for their "other caliber" magazines, but a magazine well adapter for a .30 Carbine magazine would have to be completely different, and the shooter would have to keep that in mind every time he changed mags - or the adapter might wind up falling out, the way STEN magazine adapters do, because the shooter hit the "normal" release button instead of some new, different control.

Yes, it's possible, definitely doable.  But it isn't practical, especially given how darn expensive .30 carbine ammunition is.

30 Carbine ammo is not really that expensive.  The panic drove prices up to about $28 a box.  But it has come down to about $18 to $24 a box.  The thing people forget is that it normally comes in 50 round boxes.  At $18 a box, like the PRVI and Aguila costs, that is only 36 cents a round.  That is cheaper or the same as 5.56 normally runs.

I can't find it for less than $21/box for PPU, $25 for Aguila.  Your prices are less harsh than mine, but it's still not a "cheap and plentiful" enough round to make even the magazine adapter anything but a proof of concept project.  Then there's the bolt - the .30 carbine case head is essentially the same as a .32 ACP, so it would need a completely new bolt.  And the loaded round is about 1.65" long, while the AR is built around a 2.25" long round...  Lots of tweaking would be needed to get this sort of thing to work.

Again, I'm not saying it's impossible. I'm just saying there's no compelling reason for a manufacturer to tool up to do it.

I am not saying it should be done.  I am addressing two things mentioned that are not true.  It wouldn't be that hard to do, and ammo is not that expensive and hard to find.

Widener's has been listing it for $18 and putting it on sale for $17.00, maybe $17.50.  I have seen Aguila for as little as $17.95 at other places in the past couple months.  I was looking because I was going to sell some since I picked up some of the Lake City stuff and I was seeing what the market was going for at the time.

This is a gunbot pull from a few minutes ago.  Several places in stock and many at or below 5.56 prices.

I have to say that you're right on the prices being less than I'd been seeing around here.  And yes, for a one-off, it wouldn't be that hard to get around the numerous technical challenges to make a .30 Carbine AR.  But I don't think there's enough demand for a full-on product development effort.  Custom, yes, but not for a commercial product (which is the angle I was looking at this from all along).