What? He said a 516, not a 551 or 556. The 516, is a standard piston AR-15 and nothing proprietary like the 556/551 AK-47 like operating system.
The 516 is good to go for carrier tilt. If you haven't seen it, do a google search on "Sig Sauer lawsuit with LWRC" and read up. Sig stole their bold carrier design from LWRC who is one of the best in the business for piston driven ARs. They have since settled their lawsuit, but the bolt carrier is still very similar and has many of the same benefits as the LWRC one does.
The sig is close to half the cost of the LWRC as well, so you are making out well.
Quoted:
From playing with them in the store I could see that the swiss-style Sigs would be ones that you would never have to worry about tilt. They do it differently than an AR-style piston and their design shouldn't have tilt