300 blk subsonic - first attempt fail, suggestions?

[LariatBob]

Greetings, all.

So I tried my first subsonic blackout load.
16" barrel

Accubond 200 grain bullet.
Loaded 10 gr. of 4227.
First shot at the range went pffft, lots of smoke at ejection port.
Bullet did not make it out of the barrel. About 3" short.
Took rifle home, drove bullet out with dowel. Did not take much effort.

Thinking that somehow I screwed up and did not put powder in the case I returned to the range a week later. Shot 10 rounds of 125 grain bullets with no issues.
Loaded a single round of the 200 grain loads. Shot very mildly and quietly. Opened the reciever and verified bullet had left the barrel.
Was shooting at 50 yards. No hit on target.
Loaded another round and pffft. Squib again, almost made it out. Again, easy to drive out so bullet did not appear to be binding in bore. Nice consistant rifling marks on bullet.

Unloaded remaining 8 rounds, all had the 10 grains of 4227.
I load using a Chargemaster so I watch each load carefully.

Any thoughts on increasing powder charge? Maybe start by upping it to 12 grains 4227?
Maybe more?

I have been reloading for 30 years but have always used the data in the manuals so I don't know the best way to find the right load.
I am also a bit concerned about over pressure using the 200 grain bullet but as I said it doesn't appear to have too much drag.

Suggestions and advice would be appreciated.

Thanks!

[bobbyfairbanks]

I believe your under charged. Do a ladder your at ten gr. I would go up to 10.5 and then start moving by .2 or .3 increments

[Hoser]

For subs and the 300 Whisper/Blackout and many other subs always I start high and work down.

Most of my first tries come in around 1200-1300 fps. From there I come down till I am subsonic. From there I tweak for accuracy while maintaining below the 1050-1075 threshold.

[LariatBob]

Great. Thank you both. Back to the bench.....