I can , The chrono is to close . He is getting muzzle blast readings
That is kind of like his conclusion that its the caliber of bullets though, just a guess at this point; however, even more counter intuitive, to me. Seems more like jumping to conclusions vs drawing one from the information we have. How is it that the 45 acp using a faster burning powder messes up the reading when slower burning powders in the .223 and 30-30 do not? It's not that he cannot chronograph anything, he is doing fine with .223 and 30-30, only having problems with the plated 45 bullets. That is a clue to me.
I am not discounting the guess as impossible, just doesn't sound rational that a small volume of faster burning powder would cause problems when larger volumes of slower burning powders do not, so I wouldn't conclude that without further information.
The chronograph sensing things other than the bullet is of concern, why I have speculated it could be the plating, that being one difference between the Jacketed rounds that work and the plated ones that do not and I have seen them cause issues.
If one can contain the other debris that exit the muzzle, a chronograph can be use just a few feet from the muzzle with no problems.
Like this suppressed rifle.
Or my "Don't bother Mrs. Morris" rig.
If the plating is coming off the 45 acp bullets on the way down range, the distance to get correct readings may be further away than normal.
Page 5 of the manual for the OP's chronograph does state 10-15 feet or at least one full arrow length away, for them.
https://www.btibrands.com/wp-content/uploads/2016/05/1061293-BPC-G2-instructions-rev-A-PROOF.pdf