Tried modifying a 12 round SGM magazine I picked up today using the information I found in the forums. Couldn't find step by step instructions for the SGM mag mod for iz-433 so I just muddled my way through with what I could find. This post helped out a great deal so I'm gonna add a little to it.
First I cut off the front lug with a utility knife (all the posts I've seen seem to agree on this step).
Then I filed down the front lip of the magazine where the lug was until it was close to flush with the rest of the magazine body (many of the posts mentioned straightening the front of t