You need the flat slip ring, you can get them from Brownells.
Nope. It is a common misconception that the original XM177E2s had a Flat Slip-Ring as opposed to the Delta Ring. I thought the same, but did some research and realized that I was wrong. The earlier 1966 XM177E1s with the less reliable 10" barrels had Flat Slip-Rings, but not the later 1967 XM177E2. The E2 was the most widely-adopted version of the carbine, with 510 units issued to MACV SOG to kick-off production which ran until 1975.
The Troy 50th Anniversary Commemorative is bang-on accurate in most respects. They even Grey Cera-Koted the parts that were historically treated with a (wear-prone) "Colt Gray" factory dry-film lube. The Aluminum Buttstock is a 100% accurate reproduction, right down to the (more durable) polymer "Vinyl Acerate" coating and the 2-position Receiver Extension. The 6-Hole Slim Handguards are also an accurate reproduction. Note that even the Castle Nut is the correct "old school" Hole version, instead of the modern Notched style.
The Nickel-Boron bolt is obviously not original, nor was the similar looking Hard Chrome version of the BCL used in the early versions of the AR15/M16. I just use it for easier clean-up after firing. The only other modern concessions are invisible to the naked eye unless you read the fine print stamped on the barrel. I replaced the 12.5" factory Troy Barrel with a correct-length 11.5" barrel with the correct lightweight profile from Doublestar Corporation. The new barrel is a modern 1/9" twist, chrome-lined with a 5.56mm NATO chamber. The Upper Receiver also has M4 style feed ramps for increased reliability.
Aside from the barrel twist, M4 feed ramps, the previously mentioned Ejection Port Door and the Front Swivel Rivet, the Troy Commemorative is an extremely accurate clone right down to the lower Receiver "Government" Markings, "Auto" Selector position, and engraved Auto Sear Pin. Presumably it is these markings which have run afoul of the RCMP, despite the fact that they are entirely cosmetic in nature. The lower receiver wall thickness is industry standard with an additional aluminum bridge across the Receiver where the Auto Sear Pin would normally reside. The Troy factory markings required by US law are found on the underside of the Trigger area. The carbine ships with an amazing array of Reproduction Literature (technical manual, two different user manuals, "Kill Cards", etc), plus a repro SOG Sling and a complete USGI cleaning Kit. Tons of very cool reading there.
