Help with subsonic .308 load

[TXSTDU]

Gun: Remington SPS Tactical .308 1:12 twist

Load: Case: FGMM 1x Sized and trimmed
Primer: CCI Benchrest
Bullet: 175 SMK
Powder: Trailboss
COAL: 2.790


I started with 11.0 grn and worked down to 9.5. I loaded 3 of each charge in .5 grn increments. I know that this bullet is marginally stable in the JBM calculator, but I have a lot on hand and decided to give them a shot. I have attached the group of 11.0 grn and 10.5 grn. These gave me the best results and I think my load will be somewhere in between. My only concern is in the 10.5 group do yall think the hole with the arrow is a key hole or just the was the paper tore.


***Note: I did push the back of the paper in to get a better look at the holes and the paper was unsupported (Just clipped to the chicken wire)


10.5grn Trailboss

11.0 Trailboss

 

[jwp6114]

i wouldnt shoot 175's that slow out of a 12twist, a 10 twist works well but i could never get the accuracy i wanted...

 

[TXSTDU]

Ok since it has been bugging me, I loaded up 3 of each charge and headed back out back to shoot. Also this time I placed my target on a plywood back.

Here is what I learned.

11.0 grn: I have no crono but to me 11.0 grns sounds supersonic. Great grouping and no key hole at either range

10.5 grn: Sounds to be subsonic. At 100 yards a slight keyhole to the 12 o'clock. I think this is due to the round falling back to the ground and not a stability issue. No keyhole at 20 yards.

10.0 grn: Basically the same as the 10.5 load but a much larger spread.

I am relatively new to subsonic loading. How does the 10.5 load look to start tweaking? I want to make sure all is ok before I send one through my can. I know that this is not a large number of rounds for a test sample, I am just trying to be conservative on components if this isn't going to work out.

 

[xdeano]

I had the 175g SMK out of an 11.25twist going 1087fps with 9.7grn trailboss and CCI200 primers. Super accurate.

xdeano\'

 

[jwp6114]

were you shooting all of these at 100 yds? prety crapy grouping... what kind of accuracy are you looking for?

 

[TXSTDU]

I was not worried about grouping at this point. The low shot was that way on purpose, I wanted to see what it was doing at 20 yards. All I am worried about at this point in the load development is stability. If it won't stabilize then I wont proceed with this bullet. I will worry about the grouping later.

 

[redbullitt]

I have messed with a lot of subs in 308. Number one... the 300 whisper will do what you want easier and BETTER if you want a reason for another gun lol.

With that said, you are on the right track with trail boss, but Id switch projectiles. That 12 twist will limit you IMHO. You know that flat nosed 150 grain 30-30 bullet sierra makes? That shot incredibly well in all of my 308 sub loads AND it will be much easier to stabilize than that long SMK. I would not trust that 175. The 170 flat nose is worth a try too, but I always had better luck with the 150s.

The problem (unless you can stabilize 220s or 240s) is that you will be fighting case fill, even with trail boss. Tough to work around in the 308 case, especially with shorter lighter bullets. Dont chase the lands with the short stumpy bullets either. Realistically try for groups between 1 and 2 MOA. Plenty usable for any practical application if it is consistent. I would suggest a chronograph as well. You need to find something with good consistency, not necessarily just best grouping.

Some people like to load the SMKS backwards... I have tried it, and it does work if you are in a pinch, but I have always had better luck with flat noses or round noses in 308 subs.

 

[cruizer]

Out of my sps tactical I shoot
180gr flat base round nose
11.1 gr trail boss
Cci250

 

[Airborne Falcon]

I've always asked, why the need for a subsonic x51 load? What is the purpose?

 

[TXSTDU]

I am going to look for some of the round nose Hornady 180s to try. I was just wishing that I could bulk buy 175 SMK and use the super/subsonic on the .308 and also use in my 300BLK.

 

[TXSTDU]

Also I realize the 1:12 thing is limiting but when I bought the gun I had no intentions of a can and being able to spin heavy bullets isn't worth a barrel change right now.

 

[sic65stang]

TX, All of those loads IMO could go through a can without a problem. On my track to a sub load I found that most bullets I tried would have a slight offset to it like your original post with the arrow. I attributed this to the possibility that the round was not tumbling, but rather starting to wobble or yaw the rear of the bullet. It may not be right, but in my mind it makes sense.

I have not had any luck getting any boat tail bullet to subsonic speeds without it tumbling or having really poor accuracy, like your pics. IMO you will struggle with these bullets. As you said you will be getting some 180 RN Hornadys, that is where you will end your search. Those bullets shot awesome for me subsonic.

Now you are shooting these rounds and assuming they are subsonic by the noise, you really need to get a chronograph. I have had a supersonic load that sounded quiet, that I would have assumed to be subsonic, but it wasnt. Borrow a buddies and just guess how fast your rounds are going then shoot them, I bet you will be surprised.

Good luck

 

[saw1]

Outlaw State Bullets L.L.C. has 2-1000 lots of pulled 175gr Mk. $320 per thousand. I hear they are looking for some shooters with 12 twist .308 win to test a subsonic 169 gr hollow point hunting bullet.

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