Anyone come up with a action Cycling Subsonic Load yet

[txgunner00]

I would think you could get a mid length to run. I'm chasing other possibilities in mine. I'm not giving up yet.

[txgunner00]

I tried some 8208 tonight. I was able to run 3 consecutive rounds from a magazine with a 14 grain charge. I just need to get to the range and run them over a chronograph.

[Grimmy]

I have ran reloader 7 in my 300aac and it is very quiet. Don't know what that would be in the Grendel as far as case load density but it is really quiet. My load was 10.3 grains. Like stated start high and reduce!!! Also remember what is quiet on a cool day may go trans sonic on a warm to hot day. My target velocity is between 1000fps to 1025fps max. Up here in Pa we have a large temp swing and I want a loading that works in any temp I encounter. L had loads go super sonic just from setting in the chamber and absorbing heat from previous fired rounds.

[txgunner00]

FINALLY!!! I have a sub sonic load that cycles my action. Data is below.

20" Satern barrel, AR-15 carrier, 3.0 OZ buffer, gas port diameter .098"

Powder: IMR 8208
Case: IMI 7.62x39, necked down but NOT fire formed.
Primer: Rem 9 1/2
Bullet: 160 Hornady RN
COL: 2.220

Charges: 5 shot strings

14.5 gr, 1187 avg, 36 ES, 13 SD
14.0 gr, 1129 avg, 55 ES, 23 SD
13.5 gr, 1079 avg, 56 ES, 26 SD

All 5 shot strings were fired from a magazine, cycled properly and locked back on the last round. Temperature was 90 deg. (in March ) so the speed of sound was around 1150 fps. I still intend to do some more testing and fine tuning but these results are encouraging.

Cases were only slightly sooty and I'm hoping magnum LR primers will help with this. Most of the soot blow by could be due to the fact these are not fire formed cases so I'll load some rounds with FF cases to test this theory. I'm using non-fire formed cases specifically for the purposes of increasing load density and fire forming the cases for full power loads.

More to follow as I can get to it...

[txgunner00]

I have ran reloader 7 in my 300aac and it is very quiet. Don't know what that would be in the Grendel as far as case load density but it is really quiet. My load was 10.3 grains. Like stated start high and reduce!!! Also remember what is quiet on a cool day may go trans sonic on a warm to hot day. My target velocity is between 1000fps to 1025fps max. Up here in Pa we have a large temp swing and I want a loading that works in any temp I encounter. L had loads go super sonic just from setting in the chamber and absorbing heat from previous fired rounds.

If your loads are breaking over on a hot day it's probably due to the powder burning faster, not the atmospheric conditions the bullet is traveling through. Here's a link that helped me to understand more on the speed of sound. It also has a speed of sound calculator.

http://www.sengpielaudio.com/calculator-speedsound.htm

The higher the temperature is, the higher the speed of sound threshold is. As I understand it, an object can travel faster on hot day and not create a sonic boom than it can on a cold day. You might consider trying a powder that's less sensitive to temperature swings.

[txgunner00]

Here's a pic of the brass from the 8208 loads.

sub sonic brass.jpg

13.5 gr charge on top, 14.5 gr charge on bottom. Not too bad in terms of soot, at least not nearly as bad as some of the other powders I've tried.

You can also see how they form. The corners are not nice and sharp they do square up a bit more when they are full length re-sized. I measured the internal capacity and compared to full power fire formed brass and difference is nearly immeasurable.

[Variable]

Is that with the can on? My factory supersonic loads look way worse than that with the can on. Your brass looks really clean to me!

[txgunner00]

No- unfortunately I only have a .223 can now. My brass fired suppressed is much dirtier than this also. One of my main concerns with the cleanliness of the case was to get an indication of how well of a seal it was making. I had some of my earlier test loads that came out with unburnt powder stuck to the neck and shoulder. That was a PITA to get out of my chamber.

[Rapier]

[txgunner00]

Nice work.

I've been thinking about terminal effectiveness of these rounds and the fact that your bullets are on the borderline of stability may help you. I don't think these bullets will expand much at SS velocities but they may tumble. That would be much more effective as a 1"+ bullet turned sideways will create a heck if a would channel.

I have also considered a duplex load with a slow burning powder but I'm afraid based on my previous experiences with US869 in a SS load that many of the grains will not burn. This could cause the same problems in a gas system as an inert filler would.

[Variable]

I'd look to "Trailboss" for any kind of duplex load.... That'll get your volume up, and without too much extra pressure.

[sneaky one]

TX.,, are you shooting those 160's -as-is , no swaging or tweaks.-at the .268 diam.? Also, have you recovered any-by h2o jugs-to see the marks,, and expansion -if any on the unit? Would be a nice pic to see,, as my package of those 160's are missing-I was set to load some, and was curious as what to expect. Great work-between you and Rapier BTW.

[txgunner00]

I'd look to "Trailboss" for any kind of duplex load.... That'll get your volume up, and without too much extra pressure.

I have considered TB but I'm not really keen on duplex loads in general. Too many variables, especially in a gas gun. For me at the moment, extreme spreads of 50 or less are OK for my intended use of these loads. As long as they stay within a 3" group at 100 I'm good for now. Maybe one day I'll venture down the duplex load road.

[txgunner00]

TX.,, are you shooting those 160's -as-is , no swaging or tweaks.-at the .268 diam.? Also, have you recovered any-by h2o jugs-to see the marks,, and expansion -if any on the unit? Would be a nice pic to see,, as my package of those 160's are missing-I was set to load some, and was curious as what to expect. Great work-between you and Rapier BTW.

Thanks. I'm using .264 projectiles, Rapier is using the .268s. I have not had the opportunity to shoot water jugs yet but that is in the plan. I'm going to try to work it in next weekend.

[sneaky one]

Thanks TX.