have a couple AR lowers siting around so figured I'd build up a suppressed pistol for now and then SBR it if I like it. 300 BLK seems to by far be the most common pistol kits or uppers I see. But someone told me the 338 is a better option. They didn't specify why though. Any thoughts here?

Here's a crazy idea..how about you just use 5.56 like St. Stoner intended and give up the bullshit calibers for the AR?

Please ignore the comment above, I'm sure it was meant for GD or something and this guy just accidently clicked the wrong thread.

Which caliber really depends on your intended use. I've got SBRs in 556, 300, and am working on a 6.5 right now. They each have specific uses, pros and cons, and roles.

For cheap shooting at the range, 10.5"-11.5" 556 is the winner. You can have a build knocked out for under $1000, stamp included, and the ammo is dirt cheap.

For suppressed awesomeness and hunting at shorter ranges (max range of 250ish yards, depending on ammo), 8.5"-9" 300 is a blast. The rifle is cheap to build, likely within the same price range as 556. The ammo will cost more though. Plinking ammo is down to about $0.50 a round right now for range ammo, and you could reload for cheaper, but long days blasting away will put some hurt on the wallet, with 556 being nearly half the cost per round. (comparing wolf gold 223 @ $0.27 CPR to S&B 124 Gn 300 @ $0.51 CPR). With subsonic loads, these rifles are crazy quiet and a real blast to shoot, and some would argue capable of hunting even subsonic to traditional pistol ranges.

The last option is a 12ish" 6.5 Grendel. This would likely be the more expensive route to build up front, but, wolf steel 6.5 ammo is about $0.27 CPR for range ammo, and should have hunting power out to around 400 yards with good hunting loads. It is going to suppress about as good as 556, and nobody is doing subsonic loads that I know of with a whole bunch of success. So if you want crazy quiet subsonic suppressed fun, look at 300 BLK.

Personally, i'd likely avoid the 338 Spectre for a while. Ammo costs will be higher, parts costs will be higher, and, from what I've seen, there just isn't a ton of support out there for it. Its more of a wildcat cartridge, which is super cool, but not my preference. If this concept interests you, i'd likely suggest going up to its bigger brother, the 458 SOCOM.

The above are solely my opinions, and i'd suggest you do a LOT of leg work with your end goals in mind before committing. Or just build them all...

I think I may take that approach :) Today is last day of SilencerCo's $200 store credit deal so I think I'll go ahead and build out a pistol 300 BLK. I have 3 other AR lowers sitting around and wouldn't mind building up others.

I do think I'll do some hunting use but also some hog pest control,  nothing more than about 200 yards. May do some plinking. Normally I prefer straight up pistols for plinking though.

Is every single '17er a fucking retard?

.338 is only a better option in the sense that it has more energy (heavier bullet, same velocity). In every other way, .300 is better (cheaper, more available, factory ammo, etc.)

556 for cheap plinking and 300 for suppressed or hunting. Build them both.

338 is a great subsonic round, not so much for supers. I really enjoy shooting hogs with 300 gr SMK's.

Thanks All. Got a Sico Hybrid and now looking for a good 8.5" 300 Blackout upper & pistol buffer kit hopefully at a decent price. I already have a lower with the trigger/safety/mag release parts kit installed.

I'd go 300BLK, I think finding ammo for 338 Spectre will be harder and more expensive. While 300BLK really gained a lot of popularity and has become more mainstream. I can find 300BLK in a store which is important to me.

SBR ammo usually has a good supply of 338 Spectre.
They have 300 gr SMK's for $19.99 right now.

The benefit to the 338 is the high BC.
only sheds about 20 fps at 100 yards.

projectile is 1-3/4" in length and starts to tumble at about 2 inches of penetration which makes it very effective.

It is my favorite subsonic round.

Depends on the intended use obviously, but I have built SBR's in 5.56, 9mm, 300blk, and now 6.5 Grendel. All suppressed.

5.56 SBR is great for mid range coyotes
300blk is good at being quiet
9mm is great for cheap plinking

6.5 Grendel is the ultimate in my eyes. You have option of cheap steel case ammo, not much (if any) louder than a suppressed 5.56, but may more powerful. Much more effective at further distances, and can still be pretty compact with a 12" barrel.

My NV rifle is a 12" 5.56, and it's perfect for what I do, which is shoot coyotes at a max of 200yds. But if I had intentions of shooting hogs or other bigger critters, I would definitely go 6.5 Grendel. I've built 3 300blk rifles with friends, and I've never felt the urge to build my own, subsonic isn't too important to me, and that's all it does great in my eyes. If I'm shooting supers, might as well be shooting a Grendel, which is better suited to the task.