The big black rivet at the bottom of the new ones is used to secure a plastic internal block to the base plate whereas the older ones I bought didn't have them. My old ones without the block works on a closed bolt with 10 rounds.
Rivet is not the problem, the block is. However, to take the mag apart you will have to take out the rivet. There is no "long-ass rivet", the rivet simply holds a plastic block to the base plate and prevents the plate from being removed. If the block is made shorter or removed, the mag works as it should, just like the older ones.
Not sure about Tar-21 but they do drop free from my X-95
It's an ugly rivet, I'm removing it just on looks alone
Any discounts if buying 10 or more?