I'm looking for a few US 556 parts for my Swiss P553, and was curious if anyone knows a source for the bolt and/or bolt carrier and gas piston?  And gas piston and tube would count as 1 part correct?  Thanks for any leads.

Try Gunbroker and Gatewood Supply. You could also try calling Sig Sauer USA and see if they will sell you the parts you need.

The 553 piston is unique to the 553. There is no US made 553 piston. The gas tube is not on the 922(r) parts list.


922(r) compliance on the 553 requires 7 US parts. The parts applicable to 922(r) on the 553 are:
- Flash hider
- barrel
- fore-end
- gas piston
- receiver
- bolt carrier
- bolt
- charging handle
- trigger casing (lower)
- hammer
- trigger
- sear
- pistol grip
- stock
- magazine body
- magazine follower
- magazine floorplate

So your options to be 922(r) compliant are:

Hammer and sear from Shooting Sight
Trigger from 556
Pistol grip from Hogue
US flash hider (already present)
Cocking handle from 556
And one more. You can use a 556 bolt carrier or swap the stock for a US made stock. Sig sells US made stocks that look like the Swiss stock or you could use an M4 stock adapter.

Very helpful post, thanks.  I would have made the mistake of picking up a 556 patrol piston.

I'm assuming the hammer and sear from a 556 would work also?

If I could find a complete 556 bolt group w/ charging handle that would square me away.  I'll try Sig USA.

Yeah, unfortunately that wouldn't help me with compliance.  But I appreciate the thought!

Strictly out of curiosity, the 552 carrier would work in the 553 correct?  Other than the fact it's not a US part.  Just wondering since you said they're not the same.  

Hey that's my photo....

I posted a comparison of the 552 and 553 operating systems:

SIG 552 and 553 operating system comparison