Subsonic Load Development

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Markball14300
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Subsonic Load Development

Post by Markball14300 » Fri Feb 05, 2021 1:38 pm

Been lurking around for a couple years appreciate all the information shared and experience. I have only been reloading 10 years and mainly been rifle calibers, I have also worked up some pistol loads as well. I do have experience loading for what I will call simple wildcats (6x45mm, 250-3000AI) that are pretty easy to extrapolate loads for off published data. My new endeavor is a 300BLK AR SBR with an 8” barrel with 1:8” twist with a pistol length gas system, H1 buffer with a Geissele Super 42 spring, that I want to work up a subsonic load with N105 & 220gr SMKs. I plan to test for cycling / bullet stability unsuppressed and my goal would be for full function suppressed. It fully functions currently with factory Winchester 200gr Open Tip Subsonic Whitebox unsuppressed, I have not run them across a chrony though.

My question is what is the proper way to work up a subs load. I know I need to start mid work down to the min, but also that seating depth will play a large role in velocity / pressure. I see that N105 follows closely with No.9 as a guide but lowered by 0.5 - 0.7gr and the Hornady manual is good guide. Knowing that my velocity will be lower than listed 225gr BTHP No.9 @ 9.1gr = 1200fps 16” barrel (also a max load for No.9). The BTHP bullet is 0.069” longer than the SMK so I should be at a lower pressure at a given COAL.

Should I start by trying to do a descending powder load or should I target midweight load and vary seating depth? For example my two thoughts either loading up 4 rounds each of 8.5, 8.2, 8.0, 7.7, 7.5 and test velocity, bullet stability, cycle, and BHO. My other thought is should I start with a mid grain load like 8 grs and vary the depth from 2.25 down to 2.15 in 0.02 increments and do the same tests?

Am I on the right track, am I overlooking anything?

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dellet
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Re: Subsonic Load Development

Post by dellet » Fri Feb 05, 2021 2:13 pm

What's the max load in Hornady for N105?
Do not exceed that. N105 is one of a handful of powders that you can exceed safe pressures below 1200 fps.
300 Blackout, not just for sub-sonics.

Markball14300
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Re: Subsonic Load Development

Post by Markball14300 » Fri Feb 05, 2021 2:24 pm

Dellet I guess that is what I am asking because Hornady doesn't list N105 but they do list No.9. Sierra doesn't list N105 over 150gr bullets. VV doesn't list N105 for over 125gr. I know you have done a lot of work with No 9 as well as as the VV powders.

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dellet
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Re: Subsonic Load Development

Post by dellet » Fri Feb 05, 2021 2:43 pm

What edition of Hornady do you have?

Pretty sure #9 has it, will confirm tonight unless someone can access it and post it.

Because pressure is more important factor than, function, start low and work up. I use 7.8/7.9 for most 190 grain bullets. That's probably a safe spot. There is a good chance you will not have full function without the suppressor, but as long as it cycles, the can will probably give it enogh pressure to lock back.

I will look at some numbers tonight.
300 Blackout, not just for sub-sonics.

Markball14300
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Re: Subsonic Load Development

Post by Markball14300 » Fri Feb 05, 2021 3:02 pm

I have Hornady 10th. Thank you.

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offsidewing
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Re: Subsonic Load Development

Post by offsidewing » Fri Feb 05, 2021 9:35 pm

There is no N105 data for 180gr + subs in Hornady 9th, Lymans 50th, VV 2019 manual, or VV website.

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dellet
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Re: Subsonic Load Development

Post by dellet » Sun Feb 07, 2021 6:49 pm

Looked through old notes and could not find the inspiration for using N105 for subs. Probably old whisper data and Quickload.

Most likely somewhere in the 8-8.5 grain range, depending on seating depth, is where the load will end up, with pressures in the mid to high 40,000 psi range. Maxing our around 9 grains for pressure.

Sorry for the delay. Look forward to results.
300 Blackout, not just for sub-sonics.

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Re: Subsonic Load Development

Post by Markball14300 » Mon Feb 08, 2021 12:15 pm

You know what availability for components has been lately. I have been looking for anything local that is usable for 300 subs, and N105 seems to be it around me. All my other powder is too fast or too slow. I found multiple posts from 2016-2018 by yourself, Certifiable, Rebel, 2ManyToys that showed success using N105 for subs

Here is my thought process. I am going to start long at 2.25” and load up some at 8.2, 8.0, 7.8, 7.6, 7.4gr. Once I find the lowest weight that will cycle I will vary the seating depth by 0.02” to dial in the velocity.

Seems like most people find a load 7.2 - 8grs @ 2.10-2.20” COAL that cycles suppressed in a short barrel. Works going to be busy the next two weekends so I’ll get to shoot last weekend of the month, I’ll update with what I find.

Appreciate the information. Here is one of the old posts I found.

viewtopic.php?f=128&t=98869&hilit=n105+dellet

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Re: Subsonic Load Development

Post by DaedalusX » Mon Feb 08, 2021 8:43 pm

I absolutely love N105 with my new Defiance anTI 12.5" bolt gun. It's quickly becoming my favorite bolt gun powder for heavy subs as I'm getting better accuracy and velocity spread than Tinstar.

My 2 baseline loads are:

208 Amax: 2.25 coal - 7.3 N105 - 1035 FPS SD 3.8 (7 shot group)
190 SubX: 2.09 coal - 7.3 N105 - No chrono but same drop to 135 yrs so I expect 1020-1040 fps range

I also shoot 225 BTHP and 220 ELD-X and they do about 1020 fps @ 7.3 gr but usually shoot 0.5 mil higher than the 190-208 bullets.

That being said I doubt N105 would cycle an AR unless you have a suppressor, low weight BCG and JP Silent Captured spring. You could try a CAR buffer but then it doesn't really solve the problem and it'll suck if you shoot super sonic. Even N110 with heavy subs is quite finicky.

I think to be able to cycle an AR you'll need something like at least 8.5-9.0 gr and then you'll be in the supersonic 1100fps+ range. And then you'll have 2 MAJOR problems.
1) To be able to be close to subsonic, you'll need to use a long heavier bullet (225 BTHP, SMK 240, etc). And being coal limited because of the AR15 magazine you'll probably have to load them at 2.25-2.26". This won't work because at 9.0gr you're already in a 95% fill and you'll be 100% in the danger zone (60K+ PSI according to Quickload). Even at 8.5gr, 225 BTHP and 2.26" you're at 55K PSI. It's a recipe to get in trouble and you're not even close to the magic 1050FPS to be subsonic all year.

My suggestion would be to get a good chrono and work up from 7.2-8.0 and tune the rifle to the load (AGB, Low mass BCG, JP silent with tuning weights, etc) but I'd forget about N105 cycling unsuppressed. Also when you're on the edge, it's likely you won't get last round bolt open as the gun barely has enough energy to cycle and then as soon as it's a little bit dirty it'll short stroke.

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Re: Subsonic Load Development

Post by dellet » Tue Feb 09, 2021 2:02 am

DaedalusX wrote:
Mon Feb 08, 2021 8:43 pm
I absolutely love N105 with my new Defiance anTI 12.5" bolt gun. It's quickly becoming my favorite bolt gun powder for heavy subs as I'm getting better accuracy and velocity spread than Tinstar.

My 2 baseline loads are:

208 Amax: 2.25 coal - 7.3 N105 - 1035 FPS SD 3.8 (7 shot group)
190 SubX: 2.09 coal - 7.3 N105 - No chrono but same drop to 135 yrs so I expect 1020-1040 fps range

I also shoot 225 BTHP and 220 ELD-X and they do about 1020 fps @ 7.3 gr but usually shoot 0.5 mil higher than the 190-208 bullets.

That being said I doubt N105 would cycle an AR unless you have a suppressor, low weight BCG and JP Silent Captured spring. You could try a CAR buffer but then it doesn't really solve the problem and it'll suck if you shoot super sonic. Even N110 with heavy subs is quite finicky.

I think to be able to cycle an AR you'll need something like at least 8.5-9.0 gr and then you'll be in the supersonic 1100fps+ range. And then you'll have 2 MAJOR problems.
1) To be able to be close to subsonic, you'll need to use a long heavier bullet (225 BTHP, SMK 240, etc). And being coal limited because of the AR15 magazine you'll probably have to load them at 2.25-2.26". This won't work because at 9.0gr you're already in a 95% fill and you'll be 100% in the danger zone (60K+ PSI according to Quickload). Even at 8.5gr, 225 BTHP and 2.26" you're at 55K PSI. It's a recipe to get in trouble and you're not even close to the magic 1050FPS to be subsonic all year.

My suggestion would be to get a good chrono and work up from 7.2-8.0 and tune the rifle to the load (AGB, Low mass BCG, JP silent with tuning weights, etc) but I'd forget about N105 cycling unsuppressed. Also when you're on the edge, it's likely you won't get last round bolt open as the gun barely has enough energy to cycle and then as soon as it's a little bit dirty it'll short stroke.
If I understand you correctly, my standard load of 7.8 grains under either a 190 Nosler or 194 Lehigh using a standard spring, H2 buffer, FA LMT Enhanced carrier will not work and I should stop using it?

Or can I carry on for another couple thousand rounds?

I do like the JP spring with lighter weights and heaviest spring, it just seems faster with follow up shots that way. 1020 fps has no crack at -20 here at home, so would really like to keep this load.
300 Blackout, not just for sub-sonics.

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