For 308 magazines:
From L to R are:
Magpul 20rd - Knight's (KAC) 20rd - Early KAC 20rd - DPMS 20rd
Tha Magpul is shortest and will take a 2.825" round reliably
Both Knight mags will reliably take 2.860", maybe 2.875" (don't have one to try)
The DPMS will relaibly take 2.835"
The difference between the KAC mags and the DPMS is evident. The KAC mags have about 1/8" overlap at the front which is stitch-welded down the front. Thus there is only 1 thickness of metal at the front, so since both bodies are made from approx. .032" metal, there's about a .032" difference in internal dimension (since external dimensions are VERY close.
If you want 10rd limit, Magpul is about it. Otherwise you'll have to butcher up DPMS or KAC mags to permanently (Ban state compliant) limit them to 10rds.