Some Colt/Tavor/UZI magazines ship with strong springs capable of powering our +10 extensions. Others don’t.
This TF custom spring (made for us by Wolff) eliminates that problem.
Details: The standard Colt-pattern spring (as supplied with Brownells’ Colt SMG-pattern 32-round magazine) has the squared-off corners — which we’ve seen cause problems with certain followers at the transition point. Our design is longer and narrower (with round coils instead of square).