My buddy and I are planning an SBR AR build in 300 Blackout. Planning on always using subsonic with this upper, because there are plenty of other guns if more power is needed. I think 300 yards maximum should be doable, perhaps 200 on deer. Short and light was the thought process behind the gun so I was thinking 8" barrel, but Seekins recommended 12" as they said it would be more accurate. I'm not as familiar with ARs as bolt guns, where barrel length and accuracy aren't necessarily related, but wasn't sure if this was a different case in ARs.

Here was what I thought would make a great quiet and handy short range deer gun:

Seekins 8" upper: $1300 around 4lbs with suppressor adapter
Mag Tactical magnesium lower: $120 6oz
Palmetto State Armory lower kit with Geissele trigger: $220 11oz
ACE ultralight stock+folding stock adapter: $80+$80 5oz, maybe 1lb with buffer and spring and adapter:
Bushnell SMRS 1-6.5x scope: $1100 18oz
Aero Precision ultralight scope mount: $90, 3oz
-------------------------------
$2990 7.3lbs


Thanks for any help!

i don't really think you need to spend that kind of money..  a quality blk upper should run you around 650 or less with a bolt and handle and FF rail.  the 8-9 inch barrels are accurate and shorter as well.  if your only running subs you don't need the length

Barrel length has nothing to do with accuracy.

Go shorter. I did a 10.3 on my 300 BLK SBR first. 8 is better.

I suggest buying a Noveske or AAC upper and skip the MAG Tac lower for that matter, just risking too much with an SBR time loss wise. Go with a heavier stock, you will find weight imbalance issues with a suppressor attacked that will make the weapon nose heavy.

I would purchase an LMT Defender lower with SOPMOD stock if I were in your situation.

Shorter is better if you are going to reload.  then you will be able to customize and optimize the load.  $2900 seems steep to me to me but I am cheap.

300 yds is really optimistic for hunting. At that distance drop begins to be measured in feet not inches.  don't get me wrong with the proper bullet design it could still take down a white tail, you just better know your dope and range estimation down to the foot better then Carlos Hathcock.

I have the 10.5" Noveske upper.  I never worried about reliability, which is a concern in a suppressed gas-operated weapon.





As others have said, being a dedicated subsonic, barrel length is immaterial (except for weight and manuverability) - the only difference is velocity, and thus, your dope at longer ranges.





I put a Magpul UBR (a pretty heavy stock) on mine.  It balances out the 762-SDN-6 that hangs off the front.



ETA - Hunting with subs, I think 100 yards is a more realistic effective range - even for a thin-skinned game animal.  But I don't have any practical experience, since I don't hunt with mine.


 

Go with the 8" given the choices, you see so many 8" and 8.2" because there is really decreasing return on performance after that.  You see a lot of 9" because there is complete powder burnout of subsonc rounds at that length.  It really only makes since to have 8-9" barrels in 300blk if the focus is on subsonic loads.

https://www.youtube.com/watch?v=C_KNGRtgg5Y&list=UUknEBdpmKz9UNXXixoC97cw
this video chronos some of the difference between the 8.2 and the 9.0 pretty much the same and sub and supersonics seem to do great in both

8".  Shortest overall package with a suppressor.

i would be less concerned with overall weight than I would with balance.

cans add a lot of weight.......at the very front of the rifle.  exception would be a subsonics-only 9mm can, or a titanium .30-cal can.

over a pound at the front of the barrel, though, yields serious balance changes.  if it's a hunting rig, i'd go with balance over smallest weight every day of the week.

light as a feather

A titanium YHM suppressor will be used.  Will the balance with the ultralight stock still be an issue?

not nearly as much as it would be with the SS version...which I have

should be fine.  worst case, toss a vertical grip up front.  


i did a 10.2" barrel.  given the choice, shorter means less weight further out.  if you're not trying for fastest velocity, just go with 8" and pew like a ninja.  

so i'm the buddy that tyler is trying to help out - this is my first a r15 and I truly appreciate everyone's input.  i have a YHM titanium can that weighs 15 oz.  one other question is any recommendations on hand loads to try?
thx again!

and also any other 8" uppers that might be alternatives to the seekins pro series 8" that we are contemplating getting?

I built my own upper with a Noveske 8.2" barrel for under a grand.


(click for parts list)

edit: It has a SB15 brace now, which is 1000x than a bare buffer tube.

My 8" .300blk.  Decided to put it on a bit of a diet and get some handguards that don't hold heat...
I'll be making a dissipator-ish front sight barrel mount, so ignore the lack of front sight.

is that a YHM titanium suppressor - did you use an adjustable gas block - just got response from Glen Seekins who though that might be a good idea
thx

Yep, there's a Seekins low profile adjustable block under there

I tune it to juuust lock back on subsonics unsuppressed and it will cycle everything.

OP, I used to wonder the same thing about barrel length until it dawned on me - why not slowly build both an 8" and a 12"? Best of both worlds, ballistically.

That's what I decided to do, while keeping an eye on cost as well.  I started out building two pistols and then decided to SBR the short one.

This is what I did.

Spikes Blem Upper
Spikes NiB BCG
Spikes 7" BAR rail
Noveske 8" Barrel
YHM QD Flash Hider
Magpul BUIS
PA Micro Red Dot

Right about 1000 in the upper. Runs on everything I feed it and sounds like a pellet gun with 220 gr subs and the can.

I think this would save you a lot of money:
CMMG pistol 8"

Add this for a dedicated subsonic gun:
Thunderbeast 30PSS

Two tax stamps included and I saved you $700.