Subsonic 150 gr. bullets

[Garrett]

I've seen a few people ask about subsonic lightweight bullets, but I've never seen anyone post any results. So I came up with my own and tried them out today.

I'm shooting through a 10" Contender barrel from SSK (sorry - can't say if this will cycle in an AR15). I used new brass formed from Rem. .221 Fireball cases. I bought the brass from Reed's Ammo, and I trimmed to 1.350".

I used Sierra 150 gr. Flat Nose bullets from the Pro-Hunter series - the ones designed for a .30-30. Bullets were seated to 1.900" OAL.

Fed # 100 primers.

Outside temperature was around 37 degrees F.

I was expecting some low velocities, as I was using about the same powder charge with a 220 gr. bullet, seated about the same depth inside the case. Surprisingly, they were pretty close to the velocity I was looking for.

What I came up with was:

7.5 gr. AA#9 = 968.7 ave.
8.1 gr. AA#9 = 1083.0 ave, but the high was 1138
8.6 gr. AA#9 = 1126.3 ave.
9.0 gr. AA#9 = 1145.8 ave.

So I suspect the optimal load with be a little over 7.5. The next one up had 6 out of 10 rounds going over 1050 fps. Even if the speed of sound is above that on a given day, it will start getting into the transonic range.

Standard deviation was higher than I like - in the 20s to 40s. But that doesn't really tell us that much when we have such a low sample. Other powders may be a little more consistent.

It looked like it had good accuracy potential. I had a target up at 25 yds. while shooting over the chrono, but wasn't trying very hard. That, and the wind kept pushing the target stand around. Even so, I ended up with one ragged hole about the size of a quarter (40 rounds). At 25 yds. that isn't very impressive, but it's a start.

Temperatures in the mid-30s aren't all that bad, but the wind was making it feel pretty cold. I'd started with the intention of shooting some groups at 100 yds after shooting the chrono, but before I was done I was rushing just to get finished.

Incidentally, I was also trying out some of the Sierra 220 gr. RNSP. I had bought 10 lbs of the "seconds" at the Sierra factory last summer. The optimal load was with 9.0 gr. AA#9 seated at 2.285 OAL for an average of 1038.4 fps. Again, there seems to be good accuracy potential.

I may have to make another trip to the factory this spring and see if they have any 240 SMKs in the "seconds" bin.

[Quarterbore]

Interesting... My AR-15 pistol has a 10-inch BOLT ACTION upper with a 1:8 twist and these loads should make for a fun plinking round. I will have to see if I can get some time to try to reproduce your results in that setup and my YHM 7.62 supressor on the AR-15 pistol.

[Garrett]

I forgot to note that the AA#9 left what looked like small unburned granules in the barrel. Not sure if it wasn't getting a complete burn, or what the issue was. The 220 gr. loads did not leave this behind. I wonder if I need to go to a slightly faster powder to get a more complete burn. I'm also curious if the unburned stuff would tend to sandblast silencer baffles. Something to consider.

Seating the bullet deeper may increase the pressure somewhat, but there is only so much length to play with on these lightweight bullets. The powder load would have to be dropped in this instance as the higher pressures would produce higher velocities, too.

[Garrett]

I'm going to try and play with this powder a little more. But half of the reason I used this powder is because it is supposed to be equivalent to WC820. I can get this for $78 per 8 lb jug, vs. the $100 for commercial AA#9.

[Pitt300]

Out of my M1S upper w16" barrel:
Rem 150g PSPs, w/8.3g H110, Win .223 brass, WSR primer & COAL 2.138" on 66* day gave me 1058-1077 fps range w/avg @ 1066.6 & 0.648" group @ 100 yards.
I adjusted scope +13" up from my regular 125g supersonic POI & they were all in the bullseye.
W/7.62 SD VERY quiet & VERY accurate!