My 11 twist loves the 40 BIBS but negatory on the Lapua brass. It sucks compared to plain jane Remington range brass in
MY no turn rifle. I'm at 23.7 with N133 have gone higher but accuracy fell off. I tried the 205m and BR4s, negligible difference in the two. I'm jumping them .010. Next best bullet is the 39BKs. Have to drag out the magnetospeed SD card but IIRC, velocity was in the neighborhood of 3650.
Just checked, velocity average five shots was 3636, 24" barrel. You will knock the snot out of those PDs for sure.
Humble experienced some chronograph issues: first, he shot the MagnetoSpeed bayonet!

Besides HIM, who could do THAT?!!?

I suspect that the velocities registered are close to 200 FPS short of reality - local pal, Mike, runs his Pracs at about 0.2 Gr. less than your charge weight, and his reliable Oehler says just short of 3700 FPS at about 15'. Mike advise that if he goes over 23.6, with his [N-133]Lot, groups open - similar to you experience. Humble fired all of these groups @ 0.010" off just touching.
So, I believe Humble's second chronograph (don't know brand) produced bogus, though consistent velocities. It cost HIM $176 to replace the bayonet - WOW, I'd have thought they'd have had an IDIOT warranty - then, he was afraid he'd shoot it again!

Thank goodness, my idiocy has not reached that low level yet!

BTW, compared to both Mike's and my Oehlers, my MagnetoSpeed runs very close to, "right on"!
Am I out of touch, and, that next 0.6 Gr. of n-133 produces almost 200 FPS??!!??

I haven't seen that via my .204R, or, 20BR barrels. I did,with the 20 Cals., learn, the "hard way", about increasing in 0.5 Gr. intervals!
In the end, I'm betting that even HIS velocities are anemic, the prairie dogs won't know the DIFF!

RG