300 AAC Blackout Build - Finally!

j8064 · Jun 29, 2014

It's been four months since I ordered one of these DPMS 300 Blackout uppers from Midway. Not top of the line by any definition, but for < $400 on sale at the time I couldn't resist. The shipping confirmation came today. :party29:

http://www.midwayusa.com/product/24...gas-block-a2-flash-hider?cm_vc=ProductFinding

While waiting I gathered "parts":

The pre-SB281 Del-Ton lower and Palmetto parts kit have been on hand for over a year waiting for the right upper.
I picked up a set of case forming & trim dies to make my own 300 AAC cases from all those 223 range cases folks generously leave behind.
With a set of reloading dies, components on hand and many years of reloading experience my bet is I can "roll my own" ammo.
Had a carry handle on hand and picked up a front sight I think will work for starters.

It's not my first "AR build" rodeo. But, this is my first trip down the 300 Blackout trail. Any advice would be greatly appreciated.

:shrug:

iH8DemLibz · Jun 29, 2014

Haaaaappyyyyy traaaaaaiilllssssss toooooooo youuuuuuuuuuu.....

300s are fun.

Enjoy!

HarCo2ANewb · Jun 29, 2014

If you have a .223 AR, mark mags so you don't mix them. Better yet, should probably do it anyway in case someone else uses it at the range.

You can cast subsonic, I haven't done it but there is a plethora of info at CB and over at 300blktalk

115-130gr is a great plinking pill size

IIRC Sierra worked with Rem/AAC to develop the 125 and 220 MatchKings for the .300

Oh, and enjoy

BradMacc82 · Jun 30, 2014

H110 and Lil Gun are great powders for supersonic loads. H110 under a 225gr Hornady Match BTHP also worked pretty well for me in subsonic loading, but of course, YMMV.

Fun round to play around with, and can be quite accurate as well too.

Klunatic · Jun 30, 2014

I second the Lil Gun for supersonic, reloads I use 17.3 gr Lil Gun and SMK 125gr pils for plinking, 17.4 gr lil Gun and Barnes TTSX 130gr for hunting. For subsonic I use Accurate 1680 11.2gr and Hornaday 208 GR BTHP for plinking and 11.0gr with Lehigh Defense ME 194gr pills for hunting.

I also suggest your mark your mags. I also recommend you get a Harbor Freight mini chop saw and this jig to make your own cases from .223, http://www.300blktalk.com/forum/viewtopic.php?f=179&t=80842 . This guy also sell a rubber band that you put on the mags to identify them as .300 BLK.

Lastly, get a suppressor!

shocker998md · Jun 30, 2014

I will be stalking this thread. My psa lower is going to be a pistol build and will use an 8" barrel.

Good luck with the build!

Franklin · Jun 30, 2014

I am not trying to steer you in any other direction but i have been reading up on 300 pistols too and have seen a few articles that say the 8 inch barrels have issues sometimes. They say a 10 is as short as you want it. I cant remember where i found these articles, i know travis haley talked about it in one of his videos. they may have been talking about bullet stability with a can.

shocker998md said:
I will be stalking this thread. My psa lower is going to be a pistol build and will use an 8" barrel.

Good luck with the build!

pwoolford · Jun 30, 2014

I picked up a few boxes of Gemtech's 300 blackout last week at Gun Connection and finally tried it this past weekend suppressed. Damn it is quiet. I think my .177 pellet gun is louder. 10.5 barrel by the way. Fun times!

j8064 · Jul 1, 2014

Based on the tracking number the BBTOH will have my upper here Thursday.

The lower is ready and I have a variety of test rounds built from components I already had on hand.

Paging Mooseman, I need a volunteer to play guinea pig!

:party29:

BradMacc82 · Jul 1, 2014

What are your test loads j8064??

j8064 · Jul 1, 2014

BradMacc82 said:
What are your test loads j8064??

I used H110 for all because I had some. The test rounds are supersonic and based on Hodgdon data: http://www.hodgdonreloading.com/

Test bullets are milspec 150 gr M80 and 150 gr M2 (I use them in my Garand loads) plus some 180gr Sierra Spitzers. For sh*ts and giggles I loaded a few 110 gr RN FMJ I use in my M1 carbine to see if they'll feed and a few 155 gr gas checked CB's.

We'll see how they work out.

:fingerscrossed:

BradMacc82 · Jul 1, 2014

The 110gr RN, may give issues - depending on OAL and how hard your pushing them.

I did the same thing when first loading for the caliber a few moons ago. YMMV, but for me they didn't perform well. If it's the Hornady 110gr RN, don't be surprised if you have difficulty getting the BCG fully into battery after firing a round and find a ring of copper in the chamber after inspection.

Don't think the RN's were meant to be pushed on too hard.

j8064 · Jul 1, 2014

BradMacc82 said:
The 110gr RN, may give issues - depending on OAL and how hard your pushing them.

I did the same thing when first loading for the caliber a few moons ago. YMMV, but for me they didn't perform well. If it's the Hornady 110gr RN, don't be surprised if you have difficulty getting the BCG fully into battery after firing a round and find a ring of copper in the chamber after inspection.

Don't think the RN's were meant to be pushed on too hard.

That was my thinking too. I only built 10 rounds with the HDY 110's. If they don't work, pulling the bullets will be a simple matter. I expect decent performance from the 150's and 180's. The CB's were kind of an experiment. It'll be interesting to see if they feed and cycle. I drive them pretty hard in my .308 bolt rifles with GC's. Never had a leading issue. We'll see.

BradMacc82 · Jul 1, 2014

The 150's should do well for you.

My bread & butter was the Hornady 110gr Vmax and the 225gr Match. Both were easily MOA capable and very consistent using H110. Heard a lot of good things about the Nosler 125's, but wound up selling both uppers off before I could try those boolits.

Fun round to play mad scientist with, you should have a good deal of fun experimenting with that caliber.

teratos · Jul 1, 2014

HarCo2ANewb said:
If you have a .223 AR, mark mags so you don't mix them.

Why mark the mags? I thought the mags were interchangeable?

j8064 · Jul 1, 2014

teratos said:
Why mark the mags? I thought the mags were interchangeable?

They are. I assume it's so some dumba** in a moment of CRS doesn't pick up a mag pre-loaded with .223/5.56 and pop it into a 300 AAC rifle. That wouldn't end well. :sad20:

HarCo2ANewb · Jul 1, 2014

j8064 said:
They are. I assume it's so some dumba** in a moment of CRS doesn't pick up a mag pre-loaded with .223/5.56 and pop it into a 300 AAC rifle. That wouldn't end well.

This, precisely because they are interchangeable

j8064 · Jul 1, 2014

HarCo2ANewb said:
This, precisely because they are interchangeable

True. We are human (well most of us...) and mistakes happen. I learned that lesson almost 20 years ago when my son mistakenly loaded a 30-30 cartridge in a .303 Enfield.

That fire-formed case stays on my reloading bench as a reminder.

Praeger · Jul 2, 2014

j8064 said:
Originally Posted by HarCo2ANewb View Post
If you have a .223 AR, mark mags so you don't mix them.

Why mark the mags? I thought the mags were interchangeable?

j8064 said:

They are. I assume it's so some dumba** in a moment of CRS doesn't pick up a mag pre-loaded with .223/5.56 and pop it into a 300 AAC rifle. That wouldn't end well.

Click to expand...

Actually, it's the other way around. I don't think a .223 would chamber in 300 BLK (at least not go into battery - too long). However, a 300 BLK would chamber in a .223 and that would be a .308 going down a .223 barrel.

j8064 · Jul 2, 2014

Praeger said:
Actually, it's the other way around. I don't think a .223 would chamber in 300 BLK (at least not go into battery - too long). However, a 300 BLK would chamber in a .223 and that would be a .308 going down a .223 barrel.

Either way no good could come of it. There is a big visual difference between the rounds. Awareness of exactly what you are chambering in a firearm is always the best practice.

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