Curious if anyone out there has some input on what has worked for them in this barrel length?

I can't get to the range with the chronograph for quite some time, but I'm interested in hearing what others have seen with this barrel length. From the data/posts I've seen, most are shooting longer barrels, and I'm wondering how barrel lengths affect the velocity.

Have not done the testing yet, but manufacturer states 70% case fill minimum, and the only published load I've seen for .308/trailboss is 10grs, hoping that there is a margin between 70% and 10grs in case velocity is too high, particularly when not using the bullet in the load data. 70% with a heavy bullet is going to be much more different with a 180gr bullet vs a 150, and that doesn't even factor in flat base vs. boat tail, which one would think would be important if you were approaching a safety threshold.

I'm just doing this for fun, no expectations of the load at all in terms of performance, except being subsonic, so I'm more just interested in velocity results from this barrel length as opposed to accuracy at 100yds.  

Have you tried to put 10gr Trailboss in a 300blk case?

I think you might have read it wrong, 70% case fill without bullet is likely maximum.  Most of my testing with Trail Boss has indicated that velocities at 70% fill or a bit higher are around 50% of the velocities loaded with normal powders.  I have tried Trail Boss in 17 Hornady Hornet, 223, 243,7mm Rem Mag, 30-06.  I have a Bushmaster ORC 308 that I could try Trail Boss in but I doubt the findings would differ much

I put 11gr in my 308 case and it almost filled it - this powder is designed for volume (from what I understand) and a 300BLK with a 200gr bullet offers very little room without being compressed (which I have heard of some folks doing with varied results).

Fill case to base of bullet. 70% of that charge weight is starting.

http://www.imrpowder.com/PDF/Trail-Boss-data.pdf

IIRC, 60 or 65% is normally cited as the minimum safe fill for reduced loads, so I suspect the additional margin may be a result of bullet base design.

Until I can measure some charge weights I won't really know if 70% is 10grs in a 308 case (again, the only charge weight published I'm aware of), or if it is lower. 10 grains seems to be right on the cusp of supersonic, I'd hope for more of a powder weight range if barrel length has a different than expected result.

We load 175gr SMK's subs in .308 using Trailboss. They shoot 1/2" groups out of my Ruger Scout rifle with 16" barrel at 100 yds and they are the quietest subs you will ever shoot. You need a 1-10" twist barrel to ensure bullet stability so you can avoid a baffle strike. They are just ridiculously quiet. My very favorite load to shoot with a suppressor.

he is talking about .308 Winchester I think , not 300 blk

I load 7.7gr titegroup with a 190GR SMK.
Shooting from a 1/10 20" bbl.
1000fps. 1.5" groups at 100yds.

No filler, no primer pocket mods etc.

I've shot at least a thousand
Of these rounds without the first problem.

To me, it's the perfect sub load.
I own and use a chrony.

Eta, this is in 308.
I tried trail boss and it was minute of pie plate at best.

My bad.

You chose the powder load via IMR's instructions?

If I can get some to work, even 50yds is past where I need them to be accurate.

Another 308 load is 208 amax with 15ish gr of 3031 IMR.
I shoot this out of a 700 with a 19" barrel.
I grabbed a couple more pounds of trail boss today also so I can mess with 55 gr 223 subs.

I second this post. 175's and trail boss are stupid quiet. I couldn't believe how quiet they were when I first tried them.

What's the starting point with powder on the 175s? I haven't tried them subsonic. I also load my long range rounds with the 175 so I'll have to be careful not to mix.

Start out at 10 grains and tweek it until you get 1050 FPS

My experience...YMMV

results from last weeks range tests - Outside air temp was 40 degrees

Rem 700 308 16-inch barrel, 1x8 twist

Sierra 180gr RN - 10.3-10.4 gr Trail Boss equals 1040-1060 fps out of my gun (quiet and accurate)
Sierra 180gr RN - 8.8gr Clays equates to 1050fps (quiet....but slightly different sounding than TB, accurate)

Sierra 220gr RN - 12.0gr Trail Boss equates to 1000fps (super quiet, super accurate)

Sierra 168 SMK - 8.2 Clays equates to 1040fps (quiet and fairly accurate)

the 220's are insanely quiet and insanely accurate out of my gun.  Trail Boss cant seem to push them much beyond 1000fps though.  Havent tried Clays yet with the 220s but might give them a try.  Trail Boss is handy, but dirty and (in my experience) will attract moisture if the gun is not cleaned after shooting, leading to corrosion in the bore.  Clays is cleaner, doesnt take near as much powder, but is inherently more dangerous probably so be careful.  At distance (100 yards and beyond), my experience is that flat based round nosed bullets fly better.  SMKs or any other boat tail doesnt seem to be as stable and if you look at your targets you will see indications of slight wobble.  Lapua makes a 200 gr bullet specific for subsonic loads. They are accurate but a bit pricey.  Get yourself a Burris Eliminator scope with the rangefinder and bullet drop compensation built in and program it for 22LR subsonic (standard) loads and your good out to 150+ yards with a standard scope base.  I need to try a 20 MOA (or more) scope base set-up and see if i can get them out to 200 yards and beyond before they drop off the scope's capabilities to compensate.  

good luck, have fun....

ETA - I use Lapua brass and both standard and magnum primers with no noticeable difference.  

thanks for your input Slacker.  I havent tried titegroup but i think i will...

10 grains of Trail Boss with a 180 gr Nosler Ballistic Silvertip is pretty quiet in my Bushmaster ORC 308, 16" 1:10

16" 1-8 barrel
225 Hornady BTHP
11.2 Trailboss
#34 primer, FC case, deburred flash holes
~1000fps

I think you forgot a 1, if not your making the most accurate subs I've ever heard about.

a "good" group accuracy wise and typical for my sub loads is about 2.00 inches at 100 yards for a 5-shot group.  I think the 220 Sierras show promise in my gun, but i havent got the load settled in as of yet.  my 700 is custom built thru and thru and set up specifically for the heavier 308 subsonic loads with a 1x8 twist.  I think it might approach 1 inch groups with the 220's, but time will tell. BTHPs and SMKs just dont cut it for accurate shooting in my gun....gotta go with round nose flat based bullets for the best accuracy.  Consistancy in the extreme spread from shot to shot is also a key component since you're basically dealing with 12+ inches of bullet drop at those distances.  if i could get the ES in my loads down to 5 or even 10fps that would help.  I'm thinking about going to 10-shot groups for measuring purposes.  if someone is getting consistant 1/2 inch groups my hats off to 'em....