JDI Firearms is the sole US importer of SIG SG55x firearms, including models like the SG550 and SG553. In addition to SIG, JDI imports high-end brands like PGM Precision and Wyssen Defence. JDI Firearms announced in an Instagram post that CSR Precision is the latest brand to join their lineup.

SIG @ TFB:

• TFB Review: The SIG Sauer P320 AXG Legion
• POTD: Concamo with SG 751 SAPR and SG 553 BK .300 Blackout
• SIG SAUER Auctioning Numbers-Matching M17 and M18 for Charity
• POTD: SIG Sauer SG 553R
• Range It, Send It! SIG Sauer Kilo Canyon 10x42mm Rangefinding Binos

ACR stock adapter

These guns are the firearm equivalent of a Rolex, and, much like Rolex, finding a specific model can take a very long time (and a whole lot of money). This extends to parts and accessories as well, and sourcing stocks, handguards, and magazines is a major endeavor.

CSR Precision has answered that demand by creating new stock mounting options for the SIG 55x. Their options include a B&T MBT stock adapter (€209, without the stock), a Picatinny rail adapter (€179), and an ACR adapter (€209, without the stock). 

Those prices are listed on the CSR Precision website so we will have to wait and see what the US prices are. Assuming the current currency exchange rate, that would be about $227. B&T sells the MBT stock for $254, so an adapter and the appropriate stock would be about $481. Factory SIG stocks are going for about $360, so this is not too out of line for a stock for these guns. 

B&T MBT stock adapter

Apart from stocks, CSR Precision also makes accessories like an extended magazine release and an improved charging handle for the 55x family. We don’t yet know which products JDI will import, so keep an eye on their website. 

Improved 55x charging handle

From the manufacturer:

The CSR Precision B&T MBT buttstock adapter will mate the ACR inspired B&T MBT buttstock to your SIG SG550, SG551, SG552, SG553, SG556 or SG522. The telescopic buttstock with cheekriser will give you a lot of additional adjustabilities, so you can configure the rifle to you very own needs.

The hinge has a built in locking mechanism, making sure the stock stays folded when it has to while maintaining all operational features. A stainless steel pivot pin and spring will be provided with the adapter

The adapter will be CNC machined from aerospace grade aluminium and will be mil-spec type III class 2 anodized matte black. 

All images from CSR Precision