I’m looking at the 300 blk and will probably go with a 16" but my go smaller and go suppressed. If I go with a 16" is it better to go with a carbine or midlength gas system? Also, if I decide to use a suppressor on a 16" will that make a difference in the gas system I choose?
Thanks.
Also, what is the preferred twist rate?
Midlength gas will not work at all.
Your choices are carbine or pistol. Either one works fine, as long as the maker picked the correct has port size.
1/8… Think of it as 1/7 for 5.56.
Why will the mid-length gas not work with the 300? Does the pressure drop off too much?
Yes. Carbine is the longest gas that works.
If I run a pistol gas system can I shoot both super and sub sonic?
I have couple of blanks. Who would you recomend to do the rest of the work on the 300?
Yes, provided you pick the right gas port size.
I am not sure who to recommend if you don’t have drawings for the barrel you want.
Larger bore for the gas to expand into, with a smaller charge of faster burning powder.
I tried rifle length gas on a 20 inch barrel, and it did not work, even supersonic with a suppressor and a carbine buffer and with the gas port at 0.125.
So stick to carbine gas for barrels over 16 inches, carbine or pistol gas for barrels that are 16 inches, and pistol gas only for barrels in the 7.5 to 14.5 range.
I have been following the development of the blackout for a while now. This is the first time I have seen a choice of pistol or carbine for a 16" barrel. Coming from you I am sure it is correct. That is great news. Does that mean I can initally set up my 16" as a pistol length then if I decide to cut it down to 11" I am still good to go?
Yes, but you will have to enlarge the gas port if you cut it - which is simple to do.
Just note - my statement was not an endorsement of every 300 BLK 16" barrel with a pistol length gas system. There are certainly bad ones for sale. I meant that I know how to make a 16 inch barrel with a pistol length gas system which would be fine.
I still prefer carbine, just as I prefer mid-length gas on 16 inch 5.56mm rifles because it delays unlocking and has lower gas port erosion. I generally believe that the further you can move out the gas system and still remain within spec on cyclic rate, the better.
I am building a 300blk with a 10" noveske barrel pistol gas… what would be the best buffer to use with this barrel? It will be run 100% unsuppressed
H buffer.
Wouldn’t an A5 run even better ?
I like the A5 concept, but I am into the CTR or SOPMOD stock.
a5 tube springs & buffer with STR stock body. Best of both worlds!
Are you saying the tube is compatible with normal stocks? I thought it only worked with the Vltor stock.
Of course it is; that’s the beauty of it. It’s just that the CTR won’t collapse completely to position 0. the STR should collapse to position 0, I’ll tell you after X-MAS. 
I don’t know how it’ll affect sub unsuppressed but for shooting supers unsuppressed it’s very smooth. I’ll do comparative test with some buddies in 2 weeks to compare my A5 with their C, H and H2 setup on my 110gr vmax handloads/Noveske 10".
You can use the A5 or rifle system, we test with a rifle system not just carbine.
Vltor makes two receiver extensions, one for longer stocks like the Emod and ACS to collapse all the way and one for standard length stocks that stop about 3/4" from fully collapsed.