I just installed my Fulton Armory barrel with pre-installed barrel extension into my SI Defense upper with a DPMS bolt.  I did my function checks and they're GTG.  I did not check the head space as I don't have the gauges here with me to do so.  My problem is I tried to manually ride a live round forward and the round went into the barrel fine but the bolt did not lock up behind it.  The only way I can get the bolt to lock up and grab the round is letting the bolt slam forward.  It ejects the round fine as well when I do this method.  The action is pretty stiff and tight as well is that just because its new springs etc...  I'm going to have the head space checked before I actually fire it but I think I may have some issues due not being able to ride a live round forward like you can on the AR15 platform.  Thoughts?

Many .308win ARs are tight and you can't ride the BCG. Mine is.  Don't force the round it can get stuck.

You have to let the bolt slam home in any AR type rifle.

When I do the go/no go gauges they require you to "ride" the bolt forward and tell you not to slam it forward.  How did you guys go about doing this check if you cant ride a 308 AR bolt forward?

However, you say this is a newly built rifle - are you trying this on a brand new BCG with no lube on it?  The thing needs to be wet.  Even more so than an AR-15.

Yeah it's new and tight.  I'll lube her up some more and see what happens.

The bolt-to-carrier fit is gonna be tight anyway, until you get a few rounds through it.  It'll loosen up some.  With what you're describing, I wouldn't worry too much about it yet.  Shoot that sucker and enjoy it, it'll be fine.

That may be, but a round is not a gage.  You don't want to damage the gage.

When you use the gauges you need to remove the extractor and the ejector to get a accurate reading.  Some gauges have a cut out for the extractor.  When you are chambering a round you are running the extractor over the rim and that can cause a lot of friction, stopping the bolt from fully locking unless extra force is applied.