220 gr subsonic from an 8.25" SBR........

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rb288
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Location: Grovertown, Indiana

Re: 220 gr subsonic from an 8.25" SBR........

Post by rb288 »

dellet wrote: Wed Aug 04, 2021 10:40 am
rb288 wrote: Wed Aug 04, 2021 9:06 am Ok, did some further testing.
13.0, 13.2, and 13.4 grains of CFEBLK
11.0, 11.2, 11.4 grains of H119.
8.5" sbr through a specwar 30 suppressor with a Gemtech adjustable bcg.
The bullet was a Berry's 220 grain spire point.
5 shot groups.

The CFEBLK loads got me to 1022 to 1140 fps with 1 inch groups at 25 yards with no pressure signs and full function.
The H110 loads got me to 1028 to 1085 fps with 1 inch groups at 25 yards.
But while the H110 loads functioned, there were a few FTE in each load and the bolt never locked back on the final shot.

CFEBLK at 13.2 grains and 1068 fps was the best group at <1 inch at 25 yds.
I am going to work around that load.
I would not rule out the H110 load yet. It might take some work, but in the end, if you can get it to function, it will be quieter, cleaner and probably more accurate than the CFE.

If this is a new assembly, I would not even begin any serious sub sonic load development until it has at least 200 rounds down range, 500 even better. The actions loosen up that much and when tight can cause reliability issues.

If you have room, move the bullet out, increase the COL, then add .1 grain of powder. This will keep the velocity about the same while adding gas to help carrier movement. It won't take that much from where you are now, to locking back on empty mag.
No, I haven't given up on the H110, yet.
It was actually a bit more accurate.
And the velocities were more consistent, SDs of 5.6 to 15.6 compared to the CFEBLK of 24.3 to 38.4.
So, I'll work a bit on tweaking it to get a bit more gas so it will lock back properly.
I may have been on the losing side, but, I'm not convinced it was the wrong side.
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dellet
Silent But Deadly
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Re: 220 gr subsonic from an 8.25" SBR........

Post by dellet »

rb288 wrote: Wed Aug 04, 2021 12:00 pm
No, I haven't given up on the H110, yet.
It was actually a bit more accurate.
And the velocities were more consistent, SDs of 5.6 to 15.6 compared to the CFEBLK of 24.3 to 38.4.
So, I'll work a bit on tweaking it to get a bit more gas so it will lock back properly.
Absolutely no reason not to have full function with H110 and a bullet over 200 grains. Unless there is a mechanical or gas system problem with the gun. I think it will be worth the effort.

I'm not a fan of CFE BLK and subs.
viewtopic.php?f=141&t=100097
300 Blackout, not just for sub-sonics.
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Gallo Pazzesco
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Re: 220 gr subsonic from an 8.25" SBR........

Post by Gallo Pazzesco »

Really great thread. Subscribed and watched.
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