Blown primers with H110?

[pomofo]

I seemed to have to some trouble today with some handloads loaded with H110. I started off with 110 grain VMax seated to an OAL of 2.050", and with 17.9 grains of H110, 1 of the 3 cases ejected with the primer blown out (found it in the bottom of my brasskeeper.) Since the other 2 cases didn't show any pressure signs, I dismissed it as a fluke, and fired 3 rounds with 18.2 grains of H110. Same thing, 1 of the 3 cases blew the primer. So, I put that aside and started with the 125 Sierras, loaded to 2.050", and when I hit 17.8 grains of H110 I got the same thing, 1 of 3 cases blew the primer. Then I tried the Lapua HPCE 100 grain on top of 17.6 & 17.9 grains, and that did just fine, go figure.

Relevant data:
Model1Sales upper
16" barrel
Carbine-length gas system

Brass: 221 Fireball, virgin, necked up with Redding dies
Primer: CCI 41 (to prevent slamfires)
Powder: H110
Temperature: about 70, indoor climate controlled range

These powder levels are WAY below max, Hornady lists a max of 20.4 grains for the 110 VMax, and Sierra lists 19.0 for the 125 SPT. I run all my loads through Quickload too, and each of these showed up at around 41000PSI. I know H110 has a reputation for being temperature and density sensitive, but it was indoors and these loads filled 87-92% of the case. The only thing I can think is that maybe the pressure was still too high while the bolt was unlocking? There's no really noticeable bulging of the case head, I'll have to measure the expansion, but the primer pockets are all so loose that I can just drop the blown primer into the pocket.

Should I chalk this up as a fluke and keep going? Or try different powders, like AA9 or AA1680?