Hello, have a couple questions for those who have used stuff like this or just know a ton about it.  I am going to be starting a project building an extremely quiet upper for my AR (for use w/ a can and NV) and have narrowed it down to either purchasing a 300fireball upper or a 6.8 upper.  First of all, does anyone make subsonics for 6.8mm SPC?  If so, are they worth anything, where can i find them and how expensive are they?  Also, how large of a bullet will a 1 in 9.5 twist 6.8 barrel stabilize (do not want a baffle strike on an expensive can)?  
Also, is 300fireball ammo widely available?  Where can i get them?  Also who makes the best uppers for this caliber?  I am looking at a model 1 sales upper for a reasonable price, does anyone have any experience w/ these?
Please feel free to offer any suggestions or bits of advice, i am just getting into this stuff and would really like to have all of my ducks in a row before i go writing checks.  Thanks very much.

.338 SPECTRE

Quoted: Quoted: .338 SPECTRE Can't get one of those from Model1Sales.

Nope, and I can't imagine anyone wanting to.  

I hear you, I would much rather spend the money and know it is going to work properly. Or in the event I have problems, I know I'll be taken care of.  


The .338 I got from Marty has been flawless from the begining.

Ok, getting some mal sentiment about model1sales.  Are they "not so good" uppers?  I have never bought from them or anything, but i see on their website that they make 300fireball uppers.  Any input on model1sales would be helpful, i do not want to spend money on something that will not work?  I take it a carbine gas system probably won't cycle the action due to insufficient gas pressure in the tube?  Who makes a good 300fireball upper w/ all of the correct specs?  Thanks so much for the input so far, probably saved me lots of time and money, keep it coming!

I bought my 300 fireball from model 1 and it was 1:8 and I put an adjustable gas tube on it and have had no problems.  What can I say?  Works fine for me.  I also have a couple thousand round 5.56 barrel from them that is still at least as accurate as I am.
You really need to get into reloading if you want to get the most out of any of these rounds in my opinion.  Besides, you can make whisper/fireball/300/221 plinker ammo rather cheap if you like shooting a lot.

Edit:  now let me caviat that with I just recently got the barrel and only fired a couple dozen rounds I made up with what I had in the shop.  I also am in CA  and can't play with cans, so I just made some subsonics to try for the novelty and ran them with the gas off. They are relatively quiet.  Then I ran supersonics with no cycling problems. I have yet to explore the full spectrum of loads available.  I also contacted Randall when I was looking at the round and just got impatient so bought from model 1.  And you can take anything Marty says to the bank. I have bugged him frequently with 458 stuff.  

Quoted: You would be suprised how good the super cheap stuff sells. If Model 1 was selling $400 338 spectre uppers, people would snap them up, 1:10" twist barrels, carbine gas systems and all...

Arrgh [Marty having a fit]

Don't even give them any ideas!!!!  Bad Randall, no cookie for you!

For dedicated subsonic work, there are a few options but if PROPERLY executed, none are cheap.

There is 300-221, or 300 Whisper, using 221 Fireball brass and standard 223 bolts and mags.  Requires special gas system and proper fast twist barrels

There is 30 HRT which can sometimes be used to salvage an improper 300 Whisper barrel, as long as the twist is proper.  These use 30 Herret dies, 6.8 SPC brass and mags.

There is 338 Spectre, which takes the 300 Whisper and ups the energy 25% and the bullet diameter 10%.  Requires custom barrels, 6.8 bolts and mags.  Factory loaded ammo well below the CorBon price of 300 Whisper is available but the guy building the 338 is a flake

Then there is 7.62 x 25 with 180-220 gr loads in a pistol length barrel.  Uses 223 mags, brass is cheap, bolt requires a little touch up but can still be used for 223 work, factory loaded ammo is being worked on.  Also requires proper twist.  Can be used to shoot dirt cheap surplus once the mag well adapter are done (if they ever get done, every small arms machine shop between Houston and LA is swamped it seems)