JoshNC
01-05-14, 13:47
For some time it has been known that the geometry of the Swiss 55x trunion obviates the use of USGI aluminum 30 round mags. The top/front of the mag impinges on the bottom rear of the trunion on the Swiss upper. The US 556 has a clearance cut into the trunion that allows the USGI mag to fit.
P-mags fit, though they are very tight and do not drop free.
I never tried a 20-round USGI mag as I figured it was a no-go based on my experience with the 30-round USGI mag. This past week I noticed that the 20s have a different geometry at the top/front and as a result this area is lower than a 30-round mag. So I tried some factory Colt 20s in a 556 Classic lower on three Swiss 551s and a Swiss 552. They fit perfectly, are not tight at all, and drop free.
Next weekend I head to the range and will check for feed and function.
Sorry, no pics.
P-mags fit, though they are very tight and do not drop free.
I never tried a 20-round USGI mag as I figured it was a no-go based on my experience with the 30-round USGI mag. This past week I noticed that the 20s have a different geometry at the top/front and as a result this area is lower than a 30-round mag. So I tried some factory Colt 20s in a 556 Classic lower on three Swiss 551s and a Swiss 552. They fit perfectly, are not tight at all, and drop free.
Next weekend I head to the range and will check for feed and function.
Sorry, no pics.