Anyone come up with a action Cycling Subsonic Load yet

[txgunner00]

Man, it's been a while since I've messed with this project. My daughter as gotten into smallbore precision shooting so my gun project time and money as been adsorbed by that. Wouldn't trade it for a thing though.

Keep us posted on your results.

[Azcampman]

Let's revive this thread, I've scoured through your data a bunch, and I think I've found a good bullet to stand in for that 160 rn. Good looking hp, well see where this takes us.

[Dogue]

Mind sharing? My first can is sitting in solitary confinement at the moment but if I could play the quiet game with it later that would be great.

[Warlock]

I don't have quickload but maybe someone can check out how a 6.5 heavy would work with CFEBLK?

[Azcampman]

I went to blackbird bullets and got a some152 gr hp thats the largest he can make right now, loading those up as we speak

[mtnlvr]

I went to blackbird bullets and got a some152 gr hp thats the largest he can make right now, loading those up as we speak

How did your loads work out?

[Silverjay]

Anyone else try WC857? Seems to run 123 class and cycle with a suppressor. Slightly compressed and low pressure. ????*??

[grendelnubi]

Only testing I have done using my 12.7 suppressed pistol with carbine length gas system was with Trail boss which was quiet but would not unlock bolt. I tried some 1680 which would unlock the bolt but not cycle. I have seen a utube video of someone using 8208 which would cycle but negates using a suppressor, it was almost as loud as supersonic loads.

[Burl Finkelstein]

I found a load that works well in my suppressed Bolt gun It is Howa mini action. Runing thru an Omega 300 suppressor.
Even factory full power ammo is not very loud..
However, it is like a daisy BB gun (or quieter) using this load; 140 grain Hornady HPBT bullet on top of 9.5 gains of IMR 4227 with a CCI 400 sm rifle primer. !0 grains has a supersonic crack 9.5 is probably yielding about 1050 fps.

[mtnlvr]

I've got an AR cycling subsonic 6.5 Grendel load. It works well out of my 12" PSA with Superlative Arms adjustable gas block and H2 buffer. I did a lot of digging around and landed on this. It was not my development so I don't fully understand some of the reasons for doing some of the things. And here's the usual disclaimer...use at your own risk...do your own research...work up (technically down) your own load.

You'll want to make sure you have sufficient clearance in your chamber for the heavier walled AK brass to expand and release the bullet.
I started with new 7.62x39 brass sized for the Grendel, enlarged the flash holes to 9/64", and primed with large rifle magnum primers. Charged 5 rds each at 15, 14, 13.5 and 13 grains of IMR 8208 Xbr. Set the Hornady 160 gr RN at 2.220" COAL, no crimp.

I started with the chronograph, unsuppressed, with the heavier charges first, at 50 yds and a big piece of cardboard watching for any keyholing and making sure I had impacts. At 13 grn I had keyholing, 13.5 was possibly a little unstable, 14 and 15 grn looked good. The 14 grn load I settled on ran 1024 fps. I then ran some rounds suppressed (Ultra 7 30 cal) and tuned the gas block till full function and last round hold open was achieved. My unsuppressed supersonic loads and my suppressed subsonic loads both run at 1.5 turns open...suppressed supersonics run 1 turn open.

[Klem]

mtnlv,

Running that solution through QL shows 48% case full and 70% powder burnt at the muzzle. Estimated MV is 1056fps. A suppressor will increase cycling pressure as it does in Blackout and widening the primer holes is a good idea. Never done this myself but hear it's good for ensuring consistent powder burn in low pressure cartridges.

JBM Stability calculator show that bullet in a 1:8-twist stable at 1050fps.

I would have thought leaving that gas block fully open would work best at low pressures. Is it a carbine or pistol length gas barrel?

The AK cases will be a different volume than dedicated Grendel but 50% case full is risky.

[mtnlvr]

It's a carbine length gas system. I figure the drilled flash hole and magnum primers would make up for the marginal case fill. My barrel does seem a little slower than other 12" Grendels that I've hear about so QL seems pretty close.

[Klem]

mtn,

When you think about it, Blackout barrels have almost 30% more volume for the same length than Grendel (28.8%). This means gases have more space to expand and are quicker to lower in pressure. As the bigger diameter 30cal bullet heads down the barrel pressures in Blackout drop rapidly, and so pistol length gas systems have become the norm. When Blackout was first released it was all carbine length gas. That's about the only benefit Grendel has over Blackout in your project. Excess case volume is the big worry however.

Be careful of flashover. If there is only 50% of case space taken by either H4198 or 8208 loads it means when you fire horizontally (normal) the powder is not a column. If it is instead a larger surface area then the primer spit ignites more powder than normal, generating a spike of pressure. Larger primer holes and magnum primers will not help - probably make it worse.

Crunching the numbers, Benchmark is another powder that will likely work in your situation. Around 13 grains, but still only 46% case full.

[JASmith]

I haven't tried subsonic loads in my Grendel, but did a quick search on Trailboss for subsonic loads.

The Hodgdon site has a nice table of subsonic loads for this and other powders. While the Grendel does not appear to be listed, the .223, .243 Win and Blackout are, along wth other popular cartridges.

https://hodgdon.com/wp-content/uploads/2020/07/subsonic-data-final.pdf

This suggests that a load work up for the Grendel might work with this powder.

I think one can extract at least peak pressure at the gas port location using QuickLoad. Doing so with Trailboss and with loads known to operate the action might give a clue on your chances of making it work.

And, yes, this would be a way to check the effects of different gas port locations as Klem suggested.