The barrels are batch MP tested. I called and inquired about MP testing on their bolts when I got a Stag upper about 1.5 years ago and they told me that all their bolts are MP tested though they dont mark them as such. The guy said that they MP test all of the bolts but they dont get them engraved with the MP as they would have to send them out to have it done which would add cost. He did tell me that they could provide the MP marked bolts if the contract called for it.
Anyhow, that is what I was told. Hope it helps.