308 subsonic

[Artful]

Originally Posted by rumlover

I'm aready using LRM primers. The problem biggest was accuracy. once I got to 12 gr (TB) I seemed to max out in vel with an average of 980ish. The range went anywhere from 860-1040. This created a pie plate group, generally vertical in nature. It filled up the cases with the 240s so I wouldn't think there would be an issue of powder placement at ignition.

I tried 15 gr of Greendot and pierced a primer.

I noticed Trailboss and Greendot are supposed to be similar burning rates but they don't have same volume - sounds like a slower powder is required

10.5 gr in a 16" krieger got me 1050 behind a 220 RNSP, but the powder had to seated against the primer. This did create excellent accuracy, but I missed 3 deer last year because the rifle was generally pointed down (treestand) and the powder was against the bullet.

First are you using a suppressor? If NOT then a bit of gun cotton or polyester fiberfill will hold the powder in place against the primer. problem solved.! If you are then your like me looking for a solution still

Also, I've been getting the first shot to dump on every string. Consequently, as I was shooting those loads Friday, I would wait 15-20 min between shots. Shooting 200 Speer Spitzers, 12.0 TB, WIN LRM primers, Rem Cases, 10" Encore, 1/8; I averaged 960fps with a range of 946-974. By allowing the bore to return to ambient temp (33deg) I had a better representation of actual velocities that I would find in the field and lowered the range of velocities.
Do you lube the barrel before the first shot?

I'd like to try another powder. Based on the posts I've found AA#9 or IMR SC4957 (I think that's the right powder, I'll have to check my notes). I looked up the IMR powder and it was specifically formulated for reduced velocity loads. I also came across some Accurate 2215 (?) at Gander MT which said it was also formulated for low volume loads and a hig tolerance to powder position at ignition.
I'm trying varous powders that others have suggested to me Unique, BlueDot and 2400 and some AA5744 as Trailboss was designed for cast bullet loads and the factory said they didn't recommend it with jacketed I've sort of given up on it unless I try a heavier bullet load as others in rifles seem to be doing better with it. Obviously in shorter pistol barrel your still having issues.

Any idea what length barrel it would take to get TB to push a 240 at 1050? I don't have another 1/8 twist barrel to test with, just the 10". With a little extrapolation, I was figuring each inch would gain 7fps, but I'm not certain.

The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length.
For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

The 43rd edition of the Lyman reloading Handbook gave examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26" down to 22" with the following results:

The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.

For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24" down to 20" with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.

The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types.

good link
http://www.loadammo.com/Topics/October05.htm

The table below lists the velocity change for different barrel lengths for several popular calibers. under 308 they had

.308 Win. 150grain loaded with 40.5 of 4895 giving 2,531 in 24" barrel
Difference in Velocity for a 2" change in barrel Length in fps
22 to 20" chg of 40 fps per inch
24 to 22" chg of 36 fps per inch
26 to 24" chg of 32 fps per inch
28 to 26" chg of 28 fps per inch

Note that the greater velocity increase, per inch of barrel length, generally occurs in the shortest barrel length. As the barrel is lengthened the velocity increase, per inch of barrel length, decreases. It appears as we shorten/Lengthen the interval the per inch change increases by 4 fps per inch, so extrapolating this as
44 fps per inch change from 20" to 18"
48 fps per inch change from 18" to 16"
52 fps per inch change from 16" to 14"
56 fps per inch change from 14" to 12"
60 fps per inch change from 12" to 10"

Now all this is with Full power 308 ammo not subsonic loading which will have way shorter change per inch due to lower pressure loads. So you may be right only way to know for sure is take a long 308 barrel and using subsonic ammo and cut it back an increament at a time.


If I don't get it worked out in the next month, I'll order a 16" whisper upper. I would assume someone has found an accurate 240 load for that.
Yep, it's much easier with smaller case. I just want standard 308/762 case that I can reload a bunch for that does what the $2 a shot comerically reloaded rounds do.

Let me know if you want links to any of the information I have found.

[rumlover]

I shoot a thundertrap on the 16" krieger and a 762sd on the 10" pistol so fillers won't be the solution unless there is something that will easily dissolve the residue in the can. The 308 expense is what I'm looking for. I have heard of some folks buying 223 brass and reforming it with a die, then fire forming it in the chamber as a cheap way to get into the 300. I don't have any interest in another expensive speciality caliber. The 50 alaskan I got is about as much as I'm willing to spend per round as I would like to be able to afford to shoot a lot. I chose it because the straight walled case will last about 12-14 reloadings v/s the 7-8 necked cases in 50 cal and the brass is half the cost and readily available.

Any idea what's the shortest length of 300 Whisper barrel I'd have to have to get a 240 SMK to 1100?

I'm going to order some of the IMR SR4759 and AA#9 to see what I can come up with for the 308. I'm also going to return to Gander Mt to buy the Accurate 2415 (or somethig close to that) that was labeled specifically for low volume loads. As for the unique, I loaded 5 rounds of 14 gr behind the 240's tonight for the pistol. I'll post results when I get back from our lease in tejas and Lousyana...hopefully with some subload results form hogs.

[rumlover]

Almost forgot, what/how are you lubing the barrel? I'd like to test it out.

[Artful]

I've tried some spray on lubes (one-shot case lube for example).
CRC lube, CLP, usually just wet a patch and pull thru the barrel. then run a dry patch afterwards - use the wet patch to rub the bullet. Someone suggest animal fat (bear grease/bacon fat) but I haven't tried that, yet

[rumlover]

I remember reading about the bear fat back in the last 90's when I first started looking for sub loads. I never gave it much thought, but will try lubing the barrel, minus the bear fat.
.

[zebby001]

JF or anyone,
I am a newbee to the suppresion world... I have an DPMS 308 (16" with 1x10) and have a supressor from aroura tactical... For somone that dont reload, is there somewhere that I can buy subsonic amo that will cycle...
I have read lots of your post on the 300 whisper-ishes and am now thinking that I am way over my head...

Thanks for any help that can be offered...
Zebbby001

[Artful]

You can get .308 subsonic ammo but I have never heard of it cycling semi-auto's -

TTI -
http://www.impactguns.com/store/TTI-308-1003.html
TTI 308 SUBS 170G 20/BX
Price: $19.99
Manufacturer: TTI
Manufacturer Item #: 308-1003
Impact Item #: TTI-308-1003
Out of stock: Ships in 2-3 Weeks. Accepting orders

http://www.gunrunner.com/308T.html
Engle Ballistic Research .308 Thumper (TM)
Subsonic Match Ammunition
7.62 x 51mm (500 rounds, 25 boxes of 20 per case)

1 box, $25.20

2-5 boxes, $23.40

6-9 boxes, $21.60

10-16 boxes, $20.00

17-24 boxes, $19.00

25 boxes or case, $450.00 or $18".00 per box

10 cases +, $427.50 Per case (5% discount)

Recommended 18" or 20" heavy barrel, suppressed, 1:10" twist, no porting
Warning! Do not fire any subsonic rifle caliber ammunition in H&K firearms or any firearm which has a fluted chamber, This type of chamber prevents cartridge case obturation, allowing propellant gasses to escape out the breech, and possibly sticking a projectile in the bore. Subsequent firing with a bore so obstructed can cause serious injury or death.
All ammunition is manufactured to strict tolerances from new components.
Be sure to include photo copy of your FFL or driver's license
Minimum age: 18 years for rifle ammo, 21 years for pistol ammo.

http://www.midwayusa.com/eproductpag...404&t=11082005
Lapua Subsonic Ammunition 308 Winchester 200 Grain Full Metal Jacket Box of 20
Attention!
You must be 18 or older to order ammunition. Ammunition must ship UPS ground. For safety reasons, we cannot accept returns on Ammunition. Make sure you use the correct ammunition in your gun. Check your local laws before ordering.
Technical Specifications & Use
Average Customer Rating: Not Rated.
Package Size
Application Charts & Information
Product #: 998404
Manufacturer #: 4317340
Our Price: $36.99
Status: Available
Should Ship Next Business Day
99% of Orders Placed by 4:00 p.m. CT
(Monday-Friday, Except Holidays) Ship Same Day

Oh, and BLACKHILLS makes subsonic loads but won't sell to
mere mortals but I have seen it used in reviews by the likes
of AL PAULSON and other LEO testers.

[zebby001]

Artful,

Thanks for you help... I have been watching alot of vidios and reading alot and it seems that most everyone is loading there own and
getting it to cycle through there AR's...

Guess I will just start buying and trying...
Thanks...
ZBY

[rumlover]

Anyone tried AA 9 for the 308? I've been google-ing to find something on this powder but have only found stuff for the 300 Fireball.

I got some SR 4759 today and will load up some 240, 220, and 200 SMKs tonight. I'm going to start at 20 gr and work down to 14 or so. If anyone has tried this powder for heavy subs, please share what you found.

[rumlover]

SR 4759 was the tickett.

10" Encore Pistol, 308, 1/8 twist
53deg, drizzle, 15mph wind @ 270 deg

240 smk:(each load was roughly around half the case capacity, then the 240's took up a lot of what was leftover)

18 gr got me 1257, 1256, 1246, 1223, and 1237

Went straight to 14 gr which got me 989, 992, 967, 981 and 1005

Then went to the 16 gr which got me 1098, 1104, 1101, 1094, and 1103

I didn't shoot for accuracy for the first two loads and was more focused on getting the few rounds I had over the crony eyes. When I got to the 16 gr loads, I started shooting for a group and put all within a half dollar from 50 yards. Keep in mind, this is a pistol off a bench, I thought that was damn good. I cleaned with CLP between each shot and let the barrel cool. I also didn't bump the powder against the pirmer.

I also loaded some 200 SMKs with 12.2 gr of Trailboss. While the 200 is not what I bought the barrel for, I had all this TB sitting around and wanted to use it for something. While I missed the 1050fps mark, the average of 10 shots was 964 with a range of 956 to 974 and all shots were touching at 50.

Next up for the 240 SMK will be 50 rounds of 15.5gr sr4759 to shoot for groups, compare powder position, and devolop range cards. I'm also going to try 14 gr behind a 220 rnsp in the 16", 1/10 krieger.

I pulled some 240s out of the berm. Totally deformed in the soft mud. I'll email pics if anyone wants them.