I recently bought a new (to me) M11-A1 that came with E2 grips installed (plus the original two piece grips). The previous owner said he did not change out the mainspring assembly when he installed the E2 grips. I had always thought that all P series guns with two piece grips had the longer mainspring seat and that you had to buy the E2 grip kit including the new mainspring strut and seat in order to install the E2 grip. Well I was wrong. Apparently, sometime in the not too distant past, Sig started using the short seat assembly in all of its P series guns including those with two piece grips. I would assume that this was done to accommodate the E2 grips without additional parts although you still cannot buy just the E2 grip without the parts kit. Some articles speculate that it was a parts shortage that caused the gradual change. Here is a good article on the evolution of the Sig mainspring assemblies: https://www.realgunreviews.com...inspring-assemblies/

When I had my M11-A1 and put the E2 grip on, I never swapped out the original main spring assembly for the E2 one. It still worked, but you could feel there is some rubbing internally against the grip. Suggest you use the correct part for the correct grip.

quote:

Some articles speculate that it was a parts shortage that caused the gradual change.

This makes zero sense.

The E2 grip is sold as a single part https://www.sigsauer.com/sig-s...picker?location=grip