Blown out primers Hornady 150 FMJBT & Lil Gun

[Tone72885]

Thanks for the responses. The lil gun powder is older. Top line is 1060208, bottom line 95. It's been sealed up til I opened it for these reloads. Perhaps that's causing the issue. We are in Alaska and yesterday it was about 20 degrees at the range, so perhaps that contributed. After looking at all the data in the books and forum posts on 150 FMJBT and Lil Gun, I figured with a 2.065 OAL and 15.7 grains, that would put us at a good starting point. Was very surprised to see ~2050 MV on the lab radar. The brass being used is stamped S&B. Again, thanks for all the input. First time messing with the 300 blackout. Been reloading for over 15 years and have never seen this. As someone pointed out, to get that ~2050 MV, I would need 17+ grains of lil gun. I've torn down 5 rounds to double check powder and all are correct. I'm thinking of dropping the charge down to 14.5-14.7 and see where that gets us. I have also picked up a pound of 1680, anyone have some good recipes using it? Thanks

[20X11]

20 degrees is an issue for Lil Gun... very unstable and unpredictable at those temps. Not a good powder choice for Alaska IMHO.
I'm in Colorado and stopped using Lil Gun a few years ago due to its temperature (low temp) sensitivity. In warm weather it is one of the best performers, but in the cold, fagettaboutit.

[Asclepius]

Hello. I read the OPs post last night and was inspired to test this problem, as I just finished a load workup using Lil' Gun and I live in a cold climate.

Workup completed in December. Temps were around freezing then.
125 grain Hornady SST
18.5 grain Lil' Gun purchased recently
CCI 400 (non-magnun)
COl 2.1"
MV 2,098 fps
ES 43 fps

No previous problems with this load, however I did note in December that my MVs were higher than the Hornady recipe should produce for a 10.5" barrel.

Today I placed a couple magazines into the freezer at -5 deg f. AR "firearm" left outside in 30 degree snowing weather to get cold. Coldest temp I've measured at home was -20, so I don't believe this test to be outside of reality for my situation. Shots chronographed and velocities recorded with a cell phone to speed up the process so that no cartridge spent a long enough time in the chamber to warm up.

I was in double feed city. Primers popped out of a number of shells. Case heads extruded into the ejector and extractor recesses of the bolt. MV increased by 139 fps, and ES increased by 67 fps.

I do not understand these results, as I was of the understanding that velocity and pressure directly correlated with temperature. I appreciate the OP alerting me to this situation with Lil' Gun.

[Asclepius]

[20X11]

I do not understand these results, as I was of the understanding that velocity and pressure directly correlated with temperature. I appreciate the OP alerting me to this situation with Lil' Gun.

Lil Gun problem is there is an inverse correlation with temperature to stability. Lil Gun causes pressure variances at LOW temperatures.

[7.62x51]

This might be a tad late, and may not apply to your problem, but...

I had the same issue with a blown out primer recently and it was not a pressure issue but a loose primer pocket issue. I formed some cases using .223 brass with crimped primers and had to ream the pockets in order to seat new primers. I was a little concerned that reaming might have left the pockets too loose, but gave them a try anyway and did have one out of about 100 blow a primer. Didn't damage anything, learned my lesson and won't do that again.

[cdl]

Wow. Cast the camber. Looks like the throat wasn't cut.

[plant.one]

Wow. Cast the camber. Looks like the throat wasn't cut.

based on what? i dont see how you u can extrapolate a bad chamber out of the blue like that...

especially when the powder in question is known to be cold sensitive and causes pressure spikes at the temp the OP was having issues with...

[Sig220]

I picked up some Lil Gun powder and did not like it. Never had a blown primer, but it would randomly (or I thought)run too hot.

I also noticed it got my barrel hotter then any other powder.

Anyways, it sits and gathers dust. I may deem it a summer powder for plinkers, but that's about it. My go to powders in 300BO are the 296/110 and the 300-MP. Even they have their particular likes/dislikes!

[cdl]

based on what? i dont see how you u can extrapolate a bad chamber out of the blue like that...

I've seen it before. Pretty easy to cast and then you know. Just don't fill it into the barrel extension. The lands will be square.

Blaming it on the cold is pretty lame... Heard that one before too...