I currently own a 18" SPR mid-length with a PA 1 - 6x x24 scope and a 14.5" mid-length with a Eotech XPS2 with PA magnifier so I feel I am in a fairly good position as far as having both a long range option and a under 100 yard option with my 14.5".

I have been thinking for some time and after much thought and due consideration I believe its time to own a SBR.

Since I would like it purpose built for possibly night time HD .300 Blackout appears to be a better option over the 6.8 SPC which I have read is more suited to longer shots.

I have also gotten into suppressors and would like to put a can on this new SBR build.

OK...questions.  I would just be needing a complete upper as I am registering one of my lowers as a SBR so....who is making the finest, toughest and most reliable .300 Blackout these days.  Second question...I was considering the AAC 12.5" 1/7 or their 9" 1/7.  Or should I be thinking about other length barrels.

Or is AAC not the way to go anymore?  I am seeing quite a few AAC for sale on Gunbroker and some PWS I think.  In any case thanx for the advice and suggestions gentlemen.

There have been crazy deals on the AAC 300 black uppers of late. Like $699 shipped brand new from dealers. They are unbeatable at that price.

With the 300 black cartridge, it was developed around a 9" barrel - anything much longer than that starts to venture into the diminishing returns realm.

I have a 9" AAC 300 black upper myself. Have a little over 800 rounds of 220 grain subs through it thus far. Been flawless, and is crazy accurate.

Haven't taken a new/better pic in ages, but here's my setup:



Sits on one of my KAC SBR lowers.

Very nice rifle.  What suppressor is on it?

Can I take one of my AR' lower receivers, remove the upper on it and register it as a SBR and then put on a AAC 9" .300 Blackout?

I'd register it, then remove the upper when its approve, otherwise its without an upper for too long

But seriously. Yes, the 300blk is drop in for the AR platform. Register your lower, engrave it, wait for several months, and slap that new upper on when the tax stamp comes in.

Another popular method is to build your gun in pistol form, and when the stamp comes back take off the pistol tube and put a rifle buffer tube and stock on.

Depending on ammo and super/sub sonic and if you plan to run suppressed you may find changing out the buffer weight needed, but tweaking and tuning is part of the deal with shorty guns.

What differences would make it be in pistol form?

Also...what info exactly must be engraved on the lower receiver?

You are saying that  Kevin Brittingham, founder of AAC intended it to be a 9" barrel?  What is the benefit if any if I were to go 10.5 or the New 12.5?

I was reading an article in the Truth about Guns comparing the .300 Blackout and the 6.8 SPC and Mr Brittingham stated " And one thing that was nice, but was not a ‘deal killer’, was non-adjustable gas system. Cycle all four ways – subsonic suppressed and unsuppressed, and supersonic suppressed and unsuppressed."

Will this be true regardless of barrel length?

10.5" seems like a nice compromise between 9" and 12.5".

I'm thinking you need to research the legal process for building an SBR. Do you plan to do it as an individual or as a trust? Will your sheriff sign the paper work? Once then you must engrave the manufacturer's name of the SBR on the gun. That manufacturer would be you, either personally or your trust. Then you pay your $200 and wait months for approval.

Why a pistol? well it can have a short barrel but not a stock, so while your approval is pending, you just don't have a stock on it.

Anything bigger than a 9" gets diminishing returns very quickly.Perosnally I went 8.5"

Research up and move over to the armory section of the forum, NFA mistakes are not taken lightly and you don't want to end up in f cell

Thanx for the info.  I already have a NFA trust with two suppressor form 4's currently with the ATF waiting for my Tax Stamps for them.  

I am however unfamiliar with the SBR process so I will need to research a bit what is required as far as which forms are needed.

Now...you talk about diminishing returns past 9".  I assume we are still talking about .300 blackout.  How does increasing barrel past 9" length begin to degrade ...what?  Accuracy?  I would think you would want as much length as you can get without compromising purpose and functionality.

And as far as the purpose and functionality....what are peoples opinions of what the main purpose is of the .300 Blackout in suppressed SBR should be for.

The diminishing returns are that it's designed around the 9" barrel. That means the powder is all burnt in those 9" and you gain little velocity going longer. Accuracy is typically better in a shorter barrel typically speaking due to the fact there is less barrel to impart harmonic deflection on the round. Unlike the 5.56 which was designed for a 20" barrel so going short really hurts velocity.

I think 300blk is very much suited to sbr/suppressed form. It's designed for a short barrel, when talking 16" barrels it makes less sense.

If you have a trust then you'll have to engrave the name of the trust, city and state of the trust on the gun.

Thanx...good info.

Just a quick look on Gunbroker shows of course many AAC in various lengths.  I also see quite a few other mfg's from Noveske to PWS and Aero Precision, CMMG.

Do I go with AAC and don't look back?