Upgrade kit to give match trigger performance with tighter and smoother pull, and a glass sharp break. Competition trigger performance on a combat rifle. Fits all SIG rifles in the 55x series, including the 550, 551, 553, 556 classic, 556R, and the latest 556XI revisions. It also fits the 751. I *think* it will also fit older 510, 543 and 547, though has not actually been done yet.
New hammer, sear, and sear spring. All parts are ‘drop-in’ with zero modifications.
– A true 2-stage trigger. ‘Pre-first stage slack’ in original trigger is eliminated.
– Exceptional butter smooth trigger pull with no gritty feel or break-in needed. Hammer and sear are pre-polished for smoothness, and hard coated for low friction and durability.
– Reliable performance, even in dirty conditions. Grease is optional. Hammer and sear have an advanced low friction surface coating that does not need lubrication, which might attract dirt.
– Hammer and sear are machined from plate tool steel (not cast), and full depth heat treated. High quality steel holds sharp sear edges that will ‘break like glass’.
– Smoother feeding. Low friction coating on hammer reduces hangup with bolt carrier. Latest XI modifications are included to make the ‘hammer hang-up’ issue disappear.
– Long life. Sear edges are oversized, reducing load, for years of match grade performance.
– Installation by gunsmith or armorer is recommended to adjust second stage sear engagement (pressure plunger behind trigger), but should take 20 minutes or less.
– Compatible with entire line of 55x rifles, including 556, 556R, 556XI, and 551-A1, 550, 551, 553, 751.
– Made in the USA. Sear and Hammer count as 2 parts towards 922R compliance.
NOTE CHANGES TO THE POSTED INSTRUCTIONS. This Gen II design is 556XI compatible:
1. It no longer includes the hammer spring. Instead the SIG hammer spring is re-used.
2. It no longer includes the teflon spacer.
3. The sear spring is now used IN ADDITION TO the SIG sear spring.
The included instructions have been modified to reflect these changes, however the posted pdf guide and the website pictures have not been updated yet, so there might be some differences versus what is presented.