I received three versions of Tom's 1301 bolt release shroud; the original fully covered design (orange), the high wall open top (black), and the tapered side open top (black). I promptly installed each one and tried to induce the dreaded multiple-shells-on-the carrier malfunction.
Orange - I was able to create the malfunction by lifting on the forward side of the bolt release.
Black high wall - I was unable to create the malfunction by pressing on the rearward side of the bolt release or by lifting on the forward side.
Black tapered side - Same as above.
It seems counter intuitive to me that the orange shroud (round hole bottom) allowed the bolt release to pivot enough to create the malfunction and the black shroud (slotted bottom) did not. That being said, I found a combination that works, so I guess I'm not that concerned.
I left the black tapered side shroud installed on the gun.
Thanks a lot Tom!