Gaujo
UZI Talk Supporter
I would absolutely heed Mr. Lage's warnings regarding his products, as well as general knowledge of the MAC platform, as he has more than proven his expertise.
I wanted to extrapolate on coil cutting; do not do this. Coil cutting does not alter the spring's poundage, but rather shortens the overall length and weakens the integrity of the spring as a whole. It is a dangerous practice that should not be done in any firearm, let alone straight blowback or API operating systems.
Even if you did this on a stock MAC you would increase the bolt thrust by reducing the bolt's dwell time against positive spring pressure; this can lead to a runaway gun or hammer the rear of the receiver to the point of cracking. Reducing spring weight can be achieved by using smaller coils, or in the more practical case, removing material from the outside of the existing spring using something like a belt sander.
I've seen more than a few firearms ( mostly 1911's and Hi-Power camming systems) damaged or cracked due to users cutting coils
Coil cutting is widely considered the primary tuning method for cyclic rate for these guns. Sanding a spring does not seem like a reliable way to reduce it's overall strength as you would not be removing material uniformly from the round wire. It would seem acid would be best, but in both cases it would be very hard to do that just right. Less coils actually seems the most reliable way to reduce spring strength as long as you have sufficient spring compression distance left not to be close to bottoming out.