Like new ARMS SIR #45-M. Military model, you have to remove the delta ring to fit this system. I currently have this mounted on my Colt M4 and will only remove upon sale.
I read somewhere on this site that a monkey can install a SIR M model and I will support this. Very easy to mount.
I would also trade for a ARMS SIR #58-MOD.
$325.00 Shipped USPS Priority Mail, insured.
The SIR for sale is shown mounted on the right hand rifle in the picture email@example.com