The problem with First Strikes is you can't tube feed them. The nose gets stuck in the "skirt" of the next one.
And even if that didn't happen somehow, instead of a simple ramp for the balls to roll up, you then need an "elevator", a mechanism to raise the round from the feed tube to the breech.
And if you're going to tube feed, the rounds would have to be fed "sideways"- side by side rather than nose-to-tail. This means the round would have to be both elevated and rotated.
Say you had the rounds stacked nose-up. You'd have to have a mechanism that could accept the round from the magazine, and lift and twist it up 'til it's pointing forward at the breech.
It's not an impossible mechanism, of course- I have drawings that might be workable with a little research- but it would potentially double the cost of the gun, necessarily make it up to 2" longer at the receiver, and would require a rectangular lower feed tube, not a round one.
No, First Strikes are better fed from a proper magazine. It's possible I could make an FS/mag capable receiver for this marker, but that's going to have to come after I've developed the marker itself.