Grendel mags?

[LRRPF52]

If you dont have grendel mags what are the best 556 mags to use, even with just 3-4 rounds in them I heard they will work? I have aluminum 20 and 30 rounders, steel 20 and 30s, and even some thermold 20 and 30s. What is weird is I found the thermolds could hold the most grendel rounds, some of my very old mil spec 20 round aluminum mags would actually start to split down the spine once you put 4 or 5 grendel rounds in them.

I ask cause I got the gun built and have ammo, but the mags are on order, and I would like to sight it in and function test (albiet with 556 mags ), without having to shoot it like a single shot.

I would suggest single-loading until your Grendel mags arrive. There's no reason to introduce known products that don't really work, unless you just want to mag-feed 3 rounds at a time, which might be ok for shooting 3rd groups.