Help with subsonic .308 load (keyhole??)

[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

[dclifton]

How far is that? I would shoot it at 5-10 yds to make sure it's not key holing there as well. That's what will be the concern shooting through a suppressor if your getting keyholes at 5yds or so ull prolly get a baffle strike.

You might also swap to a flat based bullet. I read that some were having issues with BT bullets at low velocities

[dclifton]

Another thing is I would just use regular primers and save ur bench rests or magnums will work to but possibly slightly louder from what I saw some were having issues with on other forums

[John Galt]

I would think that a 175 in a 1:12 would be just fine. My subsonic load for my Rem 700 AAC 1:10 is 10.6 of Trailboss behind a 190 SMK and I couldn't be happier with it.
I tried some 220 SMKs with the same load but I "thought" I was seeing a little keyholing so stayed with the 190s.

[TXSTDU]

This was at 100 yards. I am looking for some Hornady 180 soft points as they are slightly shorter and more likely to stabilize.

I just have a lot of 175 SMK. I use these supersonic in my .308 as well as subsonic in my 300BLK

If you think I should try at 10 yards I can load up some more and reshoot. I have always used 100 yards as I figure if it is unstable at 100 than close should be bad as well.

[dclifton]

This was at 100 yards. I am looking for some Hornady 180 soft points as they are slightly shorter and more likely to stabilize.

I just have a lot of 175 SMK. I use these supersonic in my .308 as well as subsonic in my 300BLK

If you think I should try at 10 yards I can load up some more and reshoot. I have always used 100 yards as I figure if it is unstable at 100 than close should be bad as well.

No I agree ur prolly right. But if ur ok with a slight keyhole or u think its stabilizing just check it at 5 to be safe so u do t blow the end out of a 1k$ suppressor lol

And yea from what I've seen a shorter so usually dies better. Not to say it can't be done. I'm looking for some bipullets to start the process myself I've done a lot of reading about it in other forums.

[tbeak]

what is keyholing?

[trjones87]

I would think that a 175 in a 1:12 would be just fine. My subsonic load for my Rem 700 AAC 1:10 is 10.6 of Trailboss behind a 190 SMK and I couldn't be happier with it.
I tried some 220 SMKs with the same load but I "thought" I was seeing a little keyholing so stayed with the 190s.

this is good to know, need to start working on my load 308 for a 1/10

[LWD]

what is keyholing?

When the bullet isn't spinning fast enough to be stabile. Instead, it's wobbling. That will cause it to strike the target not tip first. It's a real problem with subsonic ammo in suppressors because if it's not stable in the suppressor it will destroy the suppressor by striking the internal baffles.

LWD

[dustoffer]

Before I did any more tinkering with the propellant charge, I'd pick the 11.0 gr load and tinker with the OAL. I'd load 3 of the current load, 3 .010 longer, and 3 .010 shorter and try them. Just my experience (but not with subsonic loads) that the OAL which governs bullet jump from the case to the rifling engagement, is the most critical factor. Give it a try and report back to us please. And, that looks to be a ham-slammin' load already.

[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.

[John Galt]

I think you're pretty well there. As far as OAL, I don't normally worry about anything except mag fit as the subsonics don't tend to be shot very far. I'm sure you could wring more accuracy out of it if you wanted.

BTW, I started out with my load at 10.8gr of Trailboss but found that as the weather warmed up, you could hear them starting to go transonic. That's why I backed down to 10.6 and it seems to do well in my rifle.

[tbeak]

When the bullet isn't spinning fast enough to be stabile. Instead, it's wobbling. That will cause it to strike the target not tip first. It's a real problem with subsonic ammo in suppressors because if it's not stable in the suppressor it will destroy the suppressor by striking the internal baffles.

LWD

Well that is what i was thinking but hadnt heard that term before