Re: FN SPR and Mcrees chassis
Flynn, you will still need to remove some minimal metal from your FN action to run AICS or similar mags. Search for the past threads on FN and CDI bottom metal mods to see all the photos and reasons about why. You could wait for the New FN bottom metal and 5/10 round FN mags if you don't wanna remove any metal from your action, but then you'll miss all that great mcrees adjustability...
When i got the itch, I called Mcrees just to ask about FNs and expected a long wait, but they had everything in stock, painted it that same day, and shipped into my hands in just a few days--a great experience, just call em.
Also, look for the thread that shows you how to seat your rounds high in AICS mags for the Claw to feed rounds smoothly--you'll want to see the whole primer and some brass below it.