Apparently there are different Grendel bolts now (somebody just HAD to fuck with it!) so be sure you have the right one. I'm not familiar with this particular carrier, I usually just use JP Ent. full mass --there isn't a better carrier IMO and their bolts are pretty nice too. Think they come in Grendel now. But if one bolt works then any other based on the milspec design should too.
Anyway, I got my bolts from AA way back when Obama was fucking with prices, and there's a different bolt for the Grendel and Beowulf too, I think it's just the extractor, but they are separate.
I do know having the right bolt in there matters. I had the wrong bolt in one a long time ago, I forget all the specifics, but basically it just didn't work right, constant malfunctions one after the other. And if you have the wrong extractor in one, it'll malfunction too.