Subsonic Load Development

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BJK
Silent But Deadly
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Re: Subsonic Load Development

Post by BJK »

Too funny!
Markball14300
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Joined: Thu Feb 04, 2021 2:23 pm
Location: Milwaukee, WI

Re: Subsonic Load Development

Post by Markball14300 »

So, I was finally able to get out this past weekend and test. It was slightly disappointing but not in the way I was expecting. I got better function in my rifle than I expected but my chronograph data is all messed up.

300 Blackout, 8” Barrel, DI, unsuppressed, 0.106” gas port
220gr Sierra SMK, Rem 7 ½, 2.24” OAL, 0.002” neck tension, No crimp, VV N105
Shooting Chrony Beta Master
7.4gr (136/2001/2021) All FTE, No BHO – Geissele Super 42 Spring / H1 Buffer
7.6gr (137.3/135.2/2043) All FTF, partial feeds, No BHO – NEMO 300 Spring / H1 Buffer
7.8gr (152.0/135.6/138.9) All Cycled, No BHO – NEMO 300 Spring / H1 Buffer
8.0gr (46.31/44.43/629) All Cycled, No BHO – NEMO 300 Spring / H1 Buffer
8.2gr (47.9 /44.3/47.0) All Cycled, No BHO – NEMO 300 Spring / H1 Buffer

My numbers make no sense, even if it was inadvertently switching to m/s those are still too low for what I should be getting. The unit is rated for 30-7000f/s and I haven’t had an issue before.

All bullets were stabilized and made good holes at 50yds. Interestingly POI was similar to Winchester 300BLK 200gr Subsonic and it read 2011 (why, i dont know) across the chrony. Which indicates to me that they were similar velocities.

Before & after recording I shot several 22LR Federal Automatch across the chrony and all shots registered 1130-1150 which is what I would expect.
I am hoping my form 1 will be approved in the next couple weeks. So I think I will hold off testing anymore until I get my suppressor setup. Based off function I think I will load some up at 7.8gr and play with seating depth. I was also able to find some N120 so I will do a workup with that as well.

Now I just have to decide if I need to get a new chrony before that as well. Any recommendations?
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dellet
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Re: Subsonic Load Development

Post by dellet »

For your crazy Chrono readings I would guess either shooting too close to the unit, low batteries, lighting, in that order.

Since the super rounds read correctly, I think the muzzle blast may have been triggering the unit by getting there before the bullet. I generally set up an optical unit at 5 yard minimum.
300 Blackout, not just for sub-sonics.
Markball14300
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Posts: 7
Joined: Thu Feb 04, 2021 2:23 pm
Location: Milwaukee, WI

Re: Subsonic Load Development

Post by Markball14300 »

I didn't even think of muzzle blast having more of an impact when shooting subs. I had it set up at 10ft like I normally do, but with subs I see how the blast could have more of a potential to interfere with readings. Especially since I had a blast can deflecting it all forward. I will try it again farther out next time. Thanks for the input.
Markball14300
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Posts: 7
Joined: Thu Feb 04, 2021 2:23 pm
Location: Milwaukee, WI

Re: Subsonic Load Development

Post by Markball14300 »

So it’s been a long time and I wanted to update this project. Had alot trouble with the website where it would not let me post.

I moved my chronograph farther back and no more issues.

Going through a couple more load progressions I narrowed it down to two loads. A 7.8gr VV N105 and a 10.1gr VV120 both pushing a 220gr SMK @ 2.22 COAL, Rem 7 1/2 primers.

The VV120 had previously shown full function with BHO with a H1/super 42 buffer/spring combo unsuppressed @ 900fps.

I finished my form 1 suppressor and same results with a small increase in speed to 930fps. I also switched out to a JP SCS more on that below.

The VV105 had previously had no BHO and some FTFeed unsuppressed with a H1/NEMO buffer/spring combo and velocities of 1000fps. Suppressed velocity stayed consistent at 1000fps with full function using JP SCS.

Because my son uses this for whitetail and I wanted to switch back and for easily for super/subs I was trying to find the right spring buffer combo for reliability that I would have to swap. Part of my previous load work ups were testing different combinations. Basically I had carbine, h1, h2 buffers and carbine, NEMO ( light) , and super 42 spring. I could not get consistent results. Broke down for the standard JP Silent capture spring system. Needless to say I am impressed. I had full function with every load I tried suppressed ( haven’t tried any subs unsuppressed, now that I have the suppressor it will live on this rifle).

Overall I felt like the N105 was smoother and quieter. Without a meter it’s hard to say but it’s somewhere between my nitro piston pellet gun (900fps) and my 10/22 firing standard velocity rounds 1050fps).

Thank you all for the help along the way.

Now to start working up a supers load to mimic Barnes 110TAC-X for hunting as well as a 194gr Lehigh Defense sub load. Both of which already have a lot of posts on here.
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