Quoted: I could be wrong also, but I was always under the impression that the front of the collar lines up to that step in the barrel making it the right distance from the muzzle.
|
You're right, but that location is wrong. The OPS inc. collar shelf on the inside-front of the collar interfaces with a corresponding shelf on the barrel, but there is also a 20 degree taper aft of that shelf on the barrel a corresponding 20 degree taper on the inside of the collar, so there is complete contact between the collar and the barrel. It is not just secured by that shelf.
That step in the photo above is just a transition, not the OPS inc collar shelf. The OPS inc shelf is further back and a bit taller.
Unfortunately, as the photo above illustrates, "SPR" has come to mean simply an 18" stainless steel barrel. If you want true SPR spec with the OPS inc shelf and taper, you need to specify that and usually special order it. This barrel really isn't an SPR barrel.