The VFC SCAR-H mags will work out-of-the-box. Everything else would require a mod to either the magazine or the H's magwell. The magwell has a guide rail that runs along the back of the magwell which prevents non-VFC mags from working cleanly.
The Magpul SR25 mags work in an H. The two options to get them to fit are:
1) dremel a groove along the backside of the SR25 mag, so the magwell's rail will slot into it and, therefore, allow the mag to sit
2) remove the magwell rail and add a piece of velcro to help take out any slop encountered
I went with option (2) on my SSR. The magwell rail was removed with a dremel sander, and tidied up with a small file. My SR25 mags seated fine, but was a little sloppy, so a piece of velcro (hook side) was added along the backside of the magwell to tighten that up.
Note that the SR25 mags also needs a little mod on magazine catch so the H's magcatch will lock it in properly - that just requires a little squaring off of the upper-right corner of the magazine's catch. If you don't square that corner, the mag can be pulled out without depressing the mag release - which might lead to accidentally losing mags in the field.
VFC SCAR-L - VFC SCAR SSR - KJW Hi-Capa 5.1 - CAW M79
The Three Sisters - WE G39 E/K/C
Originally Posted by kalnaren
Stalker stays where he is.
His BB's fly across the country to hit their target.