308 subsonic

[Code Red]

I have a SR-25 sniper rifle with a 24" 1-10 twist barrel. I use a Lauer Weapons .30 cal suppreser with great results. I use the military M118 173gr ammo. I remove the factory powder and reload them with 45.5gr of Varget for long range shooting. I use Varget for it is almost impervious to temperature with extreme accuracy, 1/4 MOA at 100m. For missions that require silence I reload the M118 with 8gr of Titegroup. This shoots at 1062fps at 28 degrees F and neted 3/4 MOA at 100m. This set up is very quiet and very accurate out to 400m.

[Elkman1]

Artful, you seem to be knowledgable on this matter.
I'm looking for some direction from yourself or any other reader of this posting.

I have a DPMS 308 Long Range Rifle. The barrel is 1 in 10 twist. I have a Gemtech TPRS Sup. I am researching where to start in developing a sub-sonic round for my set-up.

I have read so many opinion in the last few days that my brain hurts. I have done alittle reloading myself but mostly pistol ammo and 22-250's. In my search, there seems to be a consensous that underloading (to much air) or using fillers (cotton fibers) is a bad idea. I did find an article where the auther suggested the use of dacron. (pillow stuffing) and claimed that it incenterated completely without clogging. I'm not sure why someone would like to take a chance and clog the baffles in a Sup...so for safety reasons, I have decided to start out using low volume 308 cases.

I don't know how the receipts will differ between pressures. For example one of my questions would be: Would the pressures be the same if I put 12 grains in an reduced volume case with less air vs. 12 grains in a standard underloaded case with more air. I'm looking for a safe starting point...Bullet weight?, Powder type?, Charge amount?, Standard/Magnum Primer. Any advise....?

And even a more important question, will it even be possible to get this AR-308 to even cycle rounds? If not, are there any safety concerns if I use this rifle as a single shot. Meaning, if there is not enough blow back to cycle the next round, are there any side affects that will cause damage to the gas tube, bolt assembly, etc. if I were to manually feed it one at a time?

[ADRIAN B]

Hi

New to this forum and a novice at reloading subsonic .308 so please forgive the basic questions. Looking to buy a .311 rcbs mould to cast my own and in the UK we are limited to which powders we can purchase. Currently we can purchase easily a french powder called Vectan SR9. Ok for supersonic etc.

Apparently there are 2 weights of bullet moulds you can buy in rcbs 308 you can cast 93gr and 155gr approx, as you can gather I am learning and have more info to gather. The powder charge to be used I believe is in the region of 4grains so I would assume be careful of secondry detonation and I am sure you will have to use a case packer like cotton wool?

I await any knowledge/ advise.

Regards

Adrian

[sniperx]

Have not been back here for a while, but here is where I am at
with the load.

9.2grn Unique, Sierra 180grn round nose, CCI large magnum primers.
Cases fully prepped: trim, full length size, primer pocket uniformed and
flash hole debur. They shoot good. No filler, though I did get some flash
cotton and Pufflon. I have a few loaded that I moly coated and have
"seasoned the barrel" Will be testing them and see what this does for the
spread/speed/etc. I did notice that shooting from an elevated position as
from blind, that the drop is noticeably less Good thing I shot a few from
a similar position prior to dialing for the hunt.








The rounds punched through this hog at around 80 yds, no problem, but
did not hit the spine solid dead center. There were a few fragments near
the exit hole, so I am guessing that the bullet expaned fairly well. (pass through)

[Artful]

Originally Posted by Elkman1

Artful, you seem to be knowledgable on this matter.
I'm looking for some direction from yourself or any other reader of this posting.

I have a DPMS 308 Long Range Rifle. The barrel is 1 in 10 twist. I have a Gemtech TPRS Sup. I am researching where to start in developing a sub-sonic round for my set-up.

I have read so many opinion in the last few days that my brain hurts. I have done alittle reloading myself but mostly pistol ammo and 22-250's. In my search, there seems to be a consensous that underloading (to much air) or using fillers (cotton fibers) is a bad idea. I did find an article where the auther suggested the use of dacron. (pillow stuffing) and claimed that it incenterated completely without clogging. I'm not sure why someone would like to take a chance and clog the baffles in a Sup...so for safety reasons, I have decided to start out using low volume 308 cases.

I don't know how the receipts will differ between pressures. For example one of my questions would be: Would the pressures be the same if I put 12 grains in an reduced volume case with less air vs. 12 grains in a standard underloaded case with more air. I'm looking for a safe starting point...Bullet weight?, Powder type?, Charge amount?, Standard/Magnum Primer. Any advise....?

And even a more important question, will it even be possible to get this AR-308 to even cycle rounds? If not, are there any safety concerns if I use this rifle as a single shot. Meaning, if there is not enough blow back to cycle the next round, are there any side affects that will cause damage to the gas tube, bolt assembly, etc. if I were to manually feed it one at a time?

Well, I'm no expert and like you am researching what I can, but from what I've read with 1:10 twist rate your going to be limited to shorter bullets (180's probably - start out loading higher then speed of sound and work your way backwards as each barrel has it's own frictional coeffecient. You might want to start off without the supressor to make sure the load is stable (not gyrating) giving nice round holes in the target at 10 feet and 100 yards.

I have seen the reports of .308 case with reduced volume (either home made - JD Jones route with expoxy or machined from brass) and the same powder charge in lower volume contain will equate to higher pressure...

RifleShooter Jan/Feb 06 issue and some of the other people Debo for example are experimenting with .308 are using bulkier powders in unreduced volume cases Hodgdon's Trail Boss seems to giving good results.

As to Auto Rifle function with subsonic - possible in AR10 I don't have any experience with that platform - I do know it it possible with similar gas system in AR15 but it depends upon many things...Gas port size - location on the barrel - gas pressure at the port - length of barrel beyond the port - pressure curve of load used - ad nasium...

If you use a slower burning powder which keep up the pressure curve and you have enough barrel length after the port (of course your suppressor should help with back pressure) it may be possible to have semi auto function - my first test if I were you would to be buy a commerical 180 or 200 subsonic load - take my can off and shoot to make sure it was stable if it was stable and functioning the action I would put the suppressor back on and see how it functioned. Then I would take a round apart and see what kind of powder (stick, ball etc) and how much it was loaded with so I could have some kind of idea to reverse engineer

As to single shot function see if someone makes an adjustable gas tube or block or if a gunsmith offers a modification to your existing gas block. If you fire sub power loads the only down side I could see would be partial unlock of bolt with maybe some gas leakage into the action from tube/barrel (IE more clean up)

As for fillers w/ suppressors I don't think I would want to use any with my cans - I have used fillers in fireforming cases and such but not with subsonic loads.

[Code Red]

Originally Posted by Elkman1

Artful, you seem to be knowledgable on this matter.
I'm looking for some direction from yourself or any other reader of this posting.

I have a DPMS 308 Long Range Rifle. The barrel is 1 in 10 twist. I have a Gemtech TPRS Sup. I am researching where to start in developing a sub-sonic round for my set-up.

I have read so many opinion in the last few days that my brain hurts. I have done alittle reloading myself but mostly pistol ammo and 22-250's. In my search, there seems to be a consensous that underloading (to much air) or using fillers (cotton fibers) is a bad idea. I did find an article where the auther suggested the use of dacron. (pillow stuffing) and claimed that it incenterated completely without clogging. I'm not sure why someone would like to take a chance and clog the baffles in a Sup...so for safety reasons, I have decided to start out using low volume 308 cases.

I don't know how the receipts will differ between pressures. For example one of my questions would be: Would the pressures be the same if I put 12 grains in an reduced volume case with less air vs. 12 grains in a standard underloaded case with more air. I'm looking for a safe starting point...Bullet weight?, Powder type?, Charge amount?, Standard/Magnum Primer. Any advise....?

And even a more important question, will it even be possible to get this AR-308 to even cycle rounds? If not, are there any safety concerns if I use this rifle as a single shot. Meaning, if there is not enough blow back to cycle the next round, are there any side affects that will cause damage to the gas tube, bolt assembly, etc. if I were to manually feed it one at a time?

Hey Elkman,
I hop that some of this may be helpfull for you. Artful is correct that if you don't have a modified gas system the bolt will not fully cycle, it will partly open, needing a lot more cleaning. I get between 15-20 rounds before I notice the bullets wont chamber as nice. If you send your upper to www.medeshafirearms.com they can instal an external bolt handle on your bolt carrier. This makes chambering your rounds a lot easyer than the T-handle. I had this done to my SR-25 just for subsonic ammo. I think it cost around $110. As far as a place to start for a load, I called Hodgdon (913-362-9455) they said to use 8gr Clays with 168gr Sierra Match and Magnum primers, no filler and Winchester Brass. I didn't have any Clays at the time but I did have a lot of Titegroup so I tried that with 8gr and it worked very well. I got some Clays and tried it, I found that I could not get the same accuracy with the Clays versus the Titegroup but the Clays was a bit more quiet. I found that useing 8gr of Titegroup with 173gr Military Match projectiles will produce sub MOA at 100m. I shot 20rds through my chrony today with a low of 1028fps and a high of 1062fps and an average of 1052fps. Temp was 48 degrees, humidity 40%, elevation 802ft.
I also spoke with a rep from Lapua, (630-350-1116) for a good projectile for sub loads. They have a 200gr FMJBT product code (B416) that they make specific for sub loads. They said that in a 1x10 barrel if you load them with the base of the bullet forward that they will stabalize. I bought some of them but have not tried this yet. I will post as soon as I do, should be next week some time.

Once again I hope that this is helpfull.

[Code Red]

I finaly got some of the Lapua B416s loaded and went to the range today. Over all length with the base of the bullet loaded forward is 2.474"
Temp was 42 deg. humidity 60% elevation 802ft. I loaded 14 bullets to start so I could find out what works.
Starting point was 9.4gr tite group. 1st shot was 1200fps 2nd shot 1188fps. 9.2gr, 1st 1166fps 2nd 1128
9gr, 1st 1089fps 2nd 1103,
8.8gr, 1st 1083fps 2nd 1074
8.6gr, 1st 1019fps 2nd 1025
8.4gr, 1st 1035fps 2nd 996
8.2gr, 1st 986.9fps 2nd 989

Suprisingly none of these showed signs of tumbling at 25yrds. All punched a clean hole through a 1/4" particle board.
The only problem that I ran into was the fact that with the flat base of the bullet forward I had to single load each round. They would not feed from the mag. I think that if I opened up the feed ramps than they might feed.
Any suggestions on this would be wonderfull.
I am going to load more up with 8.4, 8.5, and 8.6gr and go back to the range to get more data. I will load up 15 of each to get a good spread. Will post more when I get this done.
Any suggestions would be great.

[RWBlue]

bump, so I don't loose this thread

[js1050]

great info, I can't wait to start developing subsonic .308 loads.

[Artful]

I've wanted to load some subsonic ammo for my .308's
I started with the Evil Black Rifles HK91 and FAL my buddy brought his PTR91 (hk91 clone) and we had some rounds to try out. These loads are not recommended and is only for information purposes. This is our day...

All ammo loaded in Remington 308 case's w/ 163 grain Flat Base spirepoint pulled military surplus bullets fired by CCI 250 magnum primers.

Weather 82 deg F - sunny, not much breeze... AAC Cyclone can

12 grains of Trailboss
my HK fired 1096 fps and 1061 fps in clean barre and oiled barrel then put
Hornady Oneshot Case sizing lube on bullet let dry - velocity 696.6!

My Bud's PTR91 fired in clean and oiled barrel 1093 fps and 1071 fps and 986.8 fps
then tried one with OneShot Hornaday case lube on the bullet 636.6 fps - tried another without OneShot on it 1024 fps

11.5 grains of Trailboss
My HK91 962.6 fps and 1016 fps
PRT91 994.9 fps and 829.7 fps
my FAL w/ 21" barrel 845.6 fps and 915.3 fps added OneShot 781.5 fps and 811 fps

cleaned and re-lubed barrels w/ CRC Power Lube
11 grains of TrailBoss
My HK91 785.1 fps and 726.8 fps
PTR 91 940.1 fps and 824.4 fps
FAL 856.4 fps first shot, 657.6 fps second shot, 567.0 fps third shot and 726.1 fps final shot

10.5 grains of Trail Boss
My HK91 636.7 fps and 762.5 fps
PTR91 691.8 fps and 769 fps
cleaned and lubed barrel on FAL w/ CRC Power Lube
FAL 793.7 fps 758.9 fps nice bullet holes figured I'll put the can on to see what it sounds like - 514.8 fps bullet perfect KEYHOLE in target - tried to shoot another and bullet lodged in the barrel yes did get it out - pulling all the lighter powder charges

Now keep in mind these where all individually weighed powder charges
so they are as listed to with accuracy of the balance beam scale.

Conclusions:
redo test with slightly higher powder charges and only 2 ten's change in powder charge -
That lubing the barrel doesn't keep you from sticking a bullet -
That shooting the bullets with Hornady OneShot case lube significantly slows the bullets down.
That somehow at very low velocity the addition of the suppressor caused the bullet velocity to be further retarded in the FAL - something I haven't seen with full power ammo.