308 subsonic loads for 1/12 twist

G

GUNENTHUSIAST

American
Full Member
Minuteman
Jan 8, 2010
299
26
SE PA
#1
Hey guys,

I finally got my SWR Omega 30 in today and was trying to work up some subsonic 308 loads for my AW308 26". Today I tried Universal Clays from 14 down to 10 grains in 1 grain increments. I was shooting 175 smks, FGMM primers, and un-modified Lapua cases and the groups were very good, but I was not quite subsonic yet - the 10 grain loads averaged 1240 fps. I'm afraid to go any lower with this powder as the powder volume in the case is very low already. I am planning on getting some trail boss next as it seems to be the favorite around here according to my forum search.
I know a 1/12 twist barrel is not ideal for subsonic loads, but I am looking for any recipes anyone may suggest. As I'm sure must of you know there isn't shit for load data on 308 subsonics out there, especially for a 1/12 barrel. I already have a bunch of 175 smks, a few 155 smks and 155 scenars, but would be willing to try anything.


Thanks in advance!
 
#2
Re: 308 subsonic loads for 1/12 twist

I will be tagging along, as I have an 18" 12 twist. I think most use a 180gr. round nose, or a heavier match bullet, like the 190SMK. But that is from someone who hasn't tried it. JPG
 
#3
Re: 308 subsonic loads for 1/12 twist

i cannot comment from experience, but like silverbuller said alot of loads i have seen have been heavier bullets, even most factory loads are 185+
 
#4
Re: 308 subsonic loads for 1/12 twist

I use 180 gr rn sp over 11 gr of trailboss and get 1050 out of my 5r which is a 24" 11.25:1

video of sub with YHM 762 can

Sexy
044.jpg
 
#5
Re: 308 subsonic loads for 1/12 twist

I just loaded some 180 gr hornady rn in prvi brass using 9.6 gr trail boss and 2.650 coal. I haven't measured group size but at 100 yrds Im keeping them inside a 3" shoot n c. At 60 yrds their on top of each other. I started with 10.6 gr but it wasn't subsonic. I ended up going down to 9.6, but I don't have a chrono yet so I don't know fps. Shot out of a 20" barrel with a 7.62sd can.
 
#6
Re: 308 subsonic loads for 1/12 twist

I'll give you my experience, but understand that all rifles are different in some way and to exercise caution when developing subsonic loads. This is some info I have gathered from 'Hide users and some investigating on my own with a little load development thrown in. Of course, I make no representation of omniscience and your mileage may vary.

This information is all relevant to the .308 Winchester cartridge ONLY.

Scanning several subsonic threads in this forum, we have a great many <span style="font-style: italic">proficient</span> reloaders to seek info from. Without naming names, these users are experienced in reloading, and users who I know and trust. These persons have posted that IMR Trailboss has worked for them using barrels from 22-24 inches with 180 grain projectiles in the following charge weights using either Remington or Winchester <span style="font-style: italic">unmodified</span> brass:

10.5 gr
10.4 gr
10.3 gr
10.2 gr

Every loader had their own primer preference, but all utilized a standard, non-magnum rifle primer.

Next, I took at look at jacketed 180 gr component bullets. What I was looking for was the <span style="font-style: italic">shortest</span> projectile in this weight class. Why? Well, if your bullet happens to experience any yaw upon exiting the barrel and within your expensive .30 caliber suppressor; the shortest bullet will experience less off-axis movement at the bullet base and bullet tip. Shorter is better in this regard, and cheap insurance against a possible baffle strike.

A few quick calls to Sierra and Hornady, which are the rifle bullets I most often use identified the following:

Sierra product number 2170, 180gr RNSP, nominal bullet OAL is 1.095".

Hornady product number 3075, 180gr RNSP, nominal bullet OAL is: 1.070".

These bullets are the shortest 180gr .30 caliber projectiles each manufacturer catalogs. The Hornady is 0.025" shorter, so I selected that bullet to work with.

This bullet is dramatically shorter than the Sierra 175gr HPBT Matchking I use in my standard .308 load which average 1.244" OAL, and I personally do not consider appropriate for subsonic use due to length and boat-tail construction.

My load for match ammunition utilizes Lapua brass, so I selected Remington brass for subsonics. Should my brass become mixed up, it will be easy to segregate cases.

I felt it appropriate to use the highest charge reported to guard against sticking a bullet in the bore. So I primed the Remington cases with CCI's standard large rifle primer, charged the case with 10.5gr IMR Trailboss, and seated the Hornady bullet.

I was quite lucky in load development as this combination rendered around 1055fps consistently out of my 22" barrel. At 100 meters, I am able to use the third mildot below the center crosshair intersection as an aiming point. This load works well in <span style="font-style: italic">MY</span> rifle.

Please make certain you have checked for yaw or instability before attaching your suppressor. Place a target as close as you possibly can to your muzzle without the blast deforming it to check for these issues. I also checked at 10, 20 and 50 meters as that seemed the prudent thing to do.

My other recommendation would be to always start high and work low in powder weights to guard against the possibility of sticking a bullet in the bore.

As I stated above, all rifles are different, so please use caution when developing subsonic loads. Your experience will vary with barrel length and rate of twist, so try your loads without the suppressor attached to confirm results <span style="font-style: italic">BEFORE</span> attaching your suppressor.

I hope this information will be helpful in this regard.
 
#7
Re: 308 subsonic loads for 1/12 twist

After trying numerous powders, bullets, and oals I settled on the standard 10-11 grains of Trailboss with 175 to 180 grain bullets. Most commonly I use 175 SMKs at about 1050. The only unique thing I do, is use large pistol primers. Trailboss has no issue igniting due to position in the case, as it nearly fills it. A slightly higher powder charge, and the pistol primer has given me more consistant velocity. This way, more of the propellant effect is derived from the powder than the primer, with the powder delivering a more consistant and uniform velocity.
 
#8
Re: 308 subsonic loads for 1/12 twist

Thanks a bunch for the replies so far! A lot of very useful information.
Have you guys found it necessary to lube your bullets at all?
One thing I noticed is not one of you guys have 1/12 twist barrels, so while the 180 grain bullets work well for you, they might tumble for me and damage my supressor because the 1/12 barrel cannot stabilize them.
Any thoughts on this?
I would really like to hear from some of the guys with the 1/12 barrels.

Thanks again!
 
#10
Re: 308 subsonic loads for 1/12 twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GUNENTHUSIAST</div><div class="ubbcode-body">Thanks a bunch for the replies so far! A lot of very useful information.
Have you guys found it necessary to lube your bullets at all?
One thing I noticed is not one of you guys have 1/12 twist barrels, so while the 180 grain bullets work well for you, they might tumble for me and damage my supressor because the 1/12 barrel cannot stabilize them.
Any thoughts on this?
I would really like to hear from some of the guys with the 1/12 barrels.

Thanks again! </div></div>

I used to shoot 180gr Sierra's Pro-hunters all the time from a 12 twist with 10.4 grs of trailboss never been a issue. Just load some up and shoot them w/o the can on, if it's a good round hole at 100yds shoot them with the can. Even with the can off you can tell when they are over the SOS with just you hearing, very easy.

I now only shoot my home made cast 187 gr bullets, way cheaper, and still kills hogs an deer just as good (maybe better)as the Sierra's did.
 
#12
Re: 308 subsonic loads for 1/12 twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GUNENTHUSIAST</div><div class="ubbcode-body">Thanks a bunch for the replies so far! A lot of very useful information.
Have you guys found it necessary to lube your bullets at all?
One thing I noticed is not one of you guys have 1/12 twist barrels, so while the 180 grain bullets work well for you, they might tumble for me and damage my supressor because the 1/12 barrel cannot stabilize them. O
Any thoughts on this?
I would really like to hear from some of the guys with the 1/12 barrels.

Thanks again! </div></div>

Never used lube.

I shot paper at 10 feet, 10 yards, 50 yards, and 100 yards to check for key holeing and never seen any with my 11.0 gr TB load.

TB is dirty, don' t leave it in your barrel it'll rust.
 
#15
Re: 308 subsonic loads for 1/12 twist

after doing lots of research on shooting subsonic for the 308 I found that most people, depending on their altitude, use 10-11 grains of Trail Boss. Trail Boss is very flaky so it will take some time to get used to in a Powder Measure. I personally shoot 180 Hornady SP with 10.5 grains of Trail Boss at just around 1050fps. It is very quiet in my Gemtech HVT. In fact, some guys at the range asked me what kind of air rifle I was shooting as they have never seen one like that before.
 
#16
Re: 308 subsonic loads for 1/12 twist

I tried all sorts of round nose and flat nose bullets based on experiences shared here on the hide. Nothing produced accuracy that was worth a damn.

I tried some 175SMK's and stuck with them. Way more accurate than anything else I'd tried.

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#17
Re: 308 subsonic loads for 1/12 twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GUNENTHUSIAST</div><div class="ubbcode-body">Hey guys,

As I'm sure must of you know there isn't shit for load data on 308 subsonics out there, especially for a 1/12 barrel.
Thanks in advance!</div></div>

hodgdon.com

has load data in there for titegroup and clays subsonic. isnt alot of data but it is there
 
#18
Re: 308 subsonic loads for 1/12 twist

I'm in the middle of testing for this atm. Did velocity the other day in my 22" DTA SRS that is 1-11". Temp was 50 F. 2300 feet of elevation.

2nd fired Winchester brass
Rem 9 1/2 Primers
180 grain RN Sierra
Trail Boss

Charge Velocity
8.6 853
9.1 927
9.6 961
10.1 969
10.6 1016
11.1 1028
11.6 1072
12.1 1111

All holes were nice and round and about 24" low, and as someone else said DIRTY. Gonna roll up 11 grains for accuracy test. Keep us updated.
 
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