If you want to use the side rail then the krink sights will interfere with a lot of optics. Also, the UR is probably set to be gassed from a shorter barrel, so using the full length barrel might be hard on the rear trunnion and bolt carrier.

 

Yes, mine gasses pretty hard. I have quite a bit of impact in the rear, and its not very pleasant to shoot. I have plans to go sbr so I'm not to worried

 

Later URs have a restrictor so they are not over gassed with the full length barrel.

Unfortunately I can't define "later". The other forum was trying to put together a list of which serial numbers had the restrictor but I don't know the status of that.

I do know my UR, purchased in May of 2014, with a prefix of AC 54 does not have the restrictor.

-Bob

 

Wolf heavy recoil spring. But if you're not going to SBR, why bother with a UR? You'll still have a 16" barrel, so why not just get the FR? Unless you want the Krink look. Then you could get a fake suppressor/barrel cover.

 

Honestly? Availability. FR's BNIB are few and far between these days.