The reason for that ten round only mag adapter was for a VERY specific market - Canada. Canada only allows magazines greater than 5 rounds for pistols. Apparently some AR based pistols are legal, (or were until recently), in Canada, they could use ten round magazines. Using this very specific adapter allowed someone who owned a 7.62x39mm AR pistol in Canada to legally use those same ten round magazines in his CZ858 rifle...until recently when the RCMP decided retroactively all vz-58 rifles are now suddenly illegal. If Wolverine would change the design to work in the 5.56mm rifles ad work with most AR magazines, it would sell well here in the US - one reason I sold my 5.56mm vz-58 was that I really couldn't trust the adapter 100% due to it's construction. Great rifle, but a work in progress.