Curious if Chad can expound on comment from ammo sale classified. If anyone else is loading sub 300 blk in both 16" and shorter than 11" like I am please share your wealth of knowledge. I just started on subsonic and hadn't thought about my 10.5" barrel having slower velocities. Makes sense. For now read more and load less is my m.o.

SBR load is subsonic load, that is hotter and faster load to reach 1050 fps in the 11" and shorter SBR barrels. Normal subsonic loads designed for 16" barrels will run 850 to 950 fps in SBR barrels. This load will up the speeds to normal 1040-1050 fps in 11" barrels for more energy on target, less bullet drop, and more complete powder burn.

LOL! Sure. It's pretty simple, really. This SBR load was created by accident, honestly. I made a run of some 300 blk out 208 A-max ammo, and the powder charge was too high for that lot of powder I use. I sold some of it to a local buddy of mine and shipped some to a customer who bought it online. This out of town customer called me and told me he was getting the sonic "crack", and that it was a little too hot and supersonic. (I later shot it in my rifle and it was running 1150 fps.) I called up my local buddy and he had also already shot it in his 11" SBR, and it chronographed 1050 fps in his 11". He loved it! So, I had the out of town customer ship me his hot ammo, and I sent him his full order of the normal 16" subsonic load. The SBR load was created!!

The main issue with an SBR, or short barrel rifle, is the velocity loss compared to a standard barrel, which is normally 16" in a 300 blk out. When running normal subsonic ammo (most factory stuff), it is already running 980 to 1020 fps in a 16" barrel. Shoot this ammo in an SBR, and it will be running 850 to 900 fps, if that. To get back some of this velocity, you can load it hotter for the SBR and still stay under the supersonic speeds, about 1100 fps. When you load it hotter, it does 2 things. 1- It increases the powder charge to get more pressure to the gas port to help aid in cycling the bolt. 2- the hotter load makes the load more efficient for a more complete powder burn.

With a cycling sub, you are only getting about 80%-85% powder burn anyway. So, it needs all the help it can get. This is why cycling subsonics are a dirtier round than a standard load. I use powders that give a cleaner burn. Most use AA1680 as their go-to subsonic powder. 1680 will work, but it's very dirty as a subsonic round. I don't use this powder for this reason.

So what powder you do recommend then Chad? If you don't mind me asking.

Honestly, if you go to the Hodgdon website and look up 300 blk out with the 208 A-max and 220 SMK, there are 6 powders listed you can use. If you use this Hodgdon data and look at a burn rate chart, you can piggy back other mfg powders in the same burn rate. This is what I did. I use about 4 different powders, depending on what I have available. But I mainly use about 2 for the cycling subs that will meter well in a progressive press. I can't release my loads and what I use, for obvious reasons. But there is ample reload data for the 300 blk out with cycling subs. I stick to the Hodgdon, IMR and Alliant powders for 95% of the ammo I load.

http://www.hodgdonreloading.com/data/rifle

Thanks for the tip !!!

Chad, thanks for the insight. I was out of pocket for a few days. I will heed your advice, make small batches until I'm satisfied. My SBR has a Silencerco Omega and havent run it yet. Looking forward to dependable cycling and loading an effective hunting round. Luckily the 208 amax is my choice for bullet already and have some.

Don't forget, 300blk was designed to be fired from a 9" barrel. The cartridge is nearly literally a 30 caliber pistol round that fires rifle bullets. In actuality, barrels longer than 9" gain a little more velocity, but severely diminishing returns.

Anything over 200grs should sub cycle pretty reliably. My go to sub powder is H4198.