Semi-auto Subsonic Load Development Without Suppressor

[elmshoots]

So the consensus seems to be that subsonic load development should be initiated without a suppressor attached to ensure stability and avoid costly mishaps. Based on other threads, it appears that the suppressor will add somewhere between 5 to 30 fps or more. So if loads are developed to try and hit say the 1000 fps mark, that should in theory provide a reasonable buffer to stay below the 1050 fps mark suppressed.

I realize that various bullet and powder combinations will in the end dictate actual functionality, but working in an AR platform (10.5”, 1:8, pistol gas, adj. block) is it reasonable to expect that a 900 to 1000 fps load may be able to reasonably cycle the bolt carrier group? (Or a better question may be; if loads can be made to cycle without a suppressor, will they be likely to naturally function without issue once suppressed)?

I would assume the gas block should be wide open for sub development, and that the advantage in the AGB will allow whatever adjustments necessary to get the subs to run to then allow a choke down of gas to allow supers to work as well.

I guess the next logical question is, will a loads developed without the suppressor have the same nodes and hold the same accuracy once suppressed? I realize POI may shift, but will the developed load hold accuracy, or is it necessary to get a stable load over a given load range, and then build the load suppressed within that range to achieve accuracy and function?

[bangbangping]

My theory: Run a few through at the lowest expected velocity to check for stability. Then do load development in the configuration you expect to shoot. Don't complicate things.

For the AGB, yes, you probably want it open (to start) for sub work. After you find something that works, you may be able to shut it down a bit. I've played with half a dozen barrels of various lengths and haven't found one yet that needed the AGB wide open to cycle supers.

[elmshoots]

Isa ingineer – I am not sure I know how not to complicate things.

Probably should have stated from the get-go; I don’t have the suppressor yet. Was wondering if it was really necessary for load development. Sounds like it is. Just spent $$$ on a chrono so that set me further back on the suppressor + tax, but I will get there eventually. (Hey – at this rate, maybe they’ll be tax free by the time I get there).

So, lowest expected velocity to check for stability. Since subs appear to be a start high and work down proposition, what should the target be for the lower end of velocity; 800-850 fps? Lower?
I would assume the same is true, whatever is stable without a suppressor is going to be faster / more stable with one attached.
Is there some rule of thumb on what max grain a 10.5" 1:8 should be able to stabilize

I didn’t imagine supers would ever need to be run wide open. I kind of expect subs may want a lighter buffer / spring and accordingly supers would then want to be choked way down to avoid over gas. (On my Creedmoor I never could get the bolt to fail to lock back, so I need to increase the buffer and maybe the spring – that too in progress). Wondering if getting the subs to run right in the 300 BLK will have the same effect on moving to supers. Would be ideal if it was just a gas block setting rather than a buffer / spring change to work between the two.

[dpete]

My theory: Run a few through at the lowest expected velocity to check for stability. Then do load development in the configuration you expect to shoot. Don't complicate things.

^^ This right here. I'm sure you are itching to start load development for subs a soon as possible, but you'll be better off waiting with it until you have the suppressor. As bang said, make up a few of each possible load to check for stability and also fps, then once stability is established attach your suppressor and do the true load work. 1050 fps is an arbitrary speed of sound number established for semi consistancy. You can go under it and be sure to be subsonic, or push it as a limit and maybe be super under some conditions. I have 3 sub loads for my 8" BLK sbr AR15 225 gr, 220 gr, and 200 gr, and each one is in the 970-980 fps range for best accuracy out of that barrel. My 110 gr mousefart loads for my RARR 300 BLK are right there too and just as accurate. Find the subsonic speed your barrel likes, don't force it to use a load because you want that speed to work.

[dellet]

Everything already said applies, but is misleading. It’s based on experience, and what most people find enjoyable. But it’s certainly not the only way to do things.

Shooting suppressed subs is clearly fun, but shooting subs without a suppressor has a lot to offer. The skills needed to develop a load, and shoot random distances, do not need a suppressor and if you wait until you have one, think of all the time lost you could have been learning something.

Developing a load. Then adding the suppressor really does not change the load, and if anything, in my experience when it does change, it’s for the better, not worse. Smaller groups.

Unless you’re shooting in places with large temperature changes, and by that I mean over 100 degrees winter to summer, develop your most accurate load below 1050 fps and stop worrying about what happens when you add the suppressor.

The system and rifle was designed to have full function without a suppressor. So if you’re having problems, it’s your fault. As long as the rifle is built to spec. Powder choice plays a role as doe bullet weight. Pistol gas, use a standard spring. FA carrier and an H2 buffer.

A load that is not quite perfect, cycles every time, but may not lock back on empty reliably, should improve when the suppressor is added. The added back pressure is helpful.

There are so many variables to your question that confusion will surely result, but there is absolutely no reason to not start load development now. It will only get easier and better once the rifle is suppressed. But the knowledge gained by doing it “the wrong way” will be irreplaceable. You will gain much more knowledge of what it takes to make the system work.

All the rest like adjustable gas blocks, buffer weights, springs can be left for later if you want to fine tune things. But the system was designed to work all 4 ways, subs and supers, suppresses or not. If your rifle will not operate that way, there is something wrong. Either rifle or ammunition.

Don’t over think a simple system.

[elmshoots]

Thanks everybody for weighing in.

So, I have some typical 300 blackout powders (A1680, IMR 4227, W296, N120) available for a start point. (Maybe some H4198, N110 and N105 in the future). I’m going to start by working up some 110 gr. (Vmax and TAC-TX) supers, but I also have a couple hundred 190 gr. Sub-X available as well. I thought I would go ahead and load up some of the Sub-X just to see if/how they might run/function in my gun. I’m also about to order up some 200 gr. Maker REX as they seem well received and they have a non-expanding in that weight at a little more than half the price of the expanding version, so that seems a really good option.

The 205 gr. Gorillas look to be an appealing sub option, but at buck and a quarter each that is a hard swallow. I wonder how different the Hornady 208 gr. BTHP or ELDs would match up for development / plinking (however, neither of those are exactly cheap themselves).

The other performance/LD-Practice pairing I have been considering is the Maker 220 gr. REX with Barry’s 220 gr. plated, but I need to dig deeper into any suppressed subsonic cast plated bullet considerations.

In that same vein, while not in my normal range of consideration, that Acme 265 gr. DS looked very interesting too, but I would probably need to look into an expander die and what have you as I am not at all familiar with cast / coated / plated loading techniques.

[popper]

Plated is like jacketed but don't use a hard crimp, the 'jacket' is thin. For cast, I shoot 185gr ranch dog style for 30/30, good to 1800 fps. Use some pistol powder and go sub. Look at 10mm loads and work up. 7gr hp38 or equal should just be sub with 190 gr.