If you have a Norinco made gun, the new(er) model that only comes with the 5 round mag appears to have a push and pull mechanism on the mag release. First you push the mag release toward the mag, which unlocks it from the receiver, then you pull back on the mag release lever and it will fulcrum out the mag another half inch or so. If you have one of the older style M305 rifles that came with the 20/5 round mags, then it's a little more difficult to get the 5/5 round mags out, as there's no fulcrum mechanism on the mag release.
Other than that, well, you're only allowed 5 rounds anyway, so it doesn't matter much to me; other than the fact that the ergonomics of the rifle do appear to be based on the 20 rd magazine.