My buddy wants to trade me 2 10rd beowulf mags, one from Alexander arms and one from Polymer 80.

I need to know if they work with .223 or 5.56 but neither of us actually has or can find any right now!

Anyone know if they can work with .223 or 5.56 and if so what the capacity would be?

I know that you can put 50 beowulf in a 5.56 mag but I do not know if the opposite is true.

For example, and this is what really worries me, the Alexander Arms page specifically says that their mag will only feed .50 Beowulf.

Tsh77769

I don't have a 10 round magazine unfortunately (wish I did) but I checked to see how many fit in my AA 4 round mag.

I was able to get 11 rounds in comfortably, as in with no effort.  It did take a 12th but it was too tight in my opinion.  I'm not able to check to see if it will actually function in my 5.56 AR right now though so can't help you there.  I suspect that it would function but I can't prove that.  

Considering that a 4 round mag will hold 11, that should give you an idea of what a 10 round would hold.  

IIRC, my 30 round 5.56 mags hold 10 Beowulf rounds so the opposite should apply or be very close.

In my experience while experimenting (I was bored) to see if a 10 round Beowulf mag could be used in a crisis to hold 5.56....

...  It held a lot of rounds and functioned (I don't remember the number) but the last two rounds would eject simultaneously.  

My conclusion was you could use it in a crisis but it wasn't ideal.

I didn't try just stuffing a 5.56 follower into it but that would probably work (better).