Simisdim does a review of the MP7 to MP5 HPA Adapter from Airtac and a gameplay video. Here is what Airtac's description of this product... "This MP5 HPA adapter represents the culmination of months of work to produce, from scratch, a shortened magazine for the Toyko Marui GBB MP7. This leads to an ultra lightweight magazine setup, that is both more enjoyable and economical than buying the gas mags.

A donor mag is required for feed lips, exhaust valve, gas route and valve knocker."