Build Thread 300 BLK Pistol

[jblake00]

I've put together 2, 1 for me and 1 for the wife. I used BA Hanson barrels for both with the optional pinned gas block, and JP captured buffer springs for both. Suppressed and unsuppressed they will eat anything.



10.3" BA barrel with Omega with QD can



8.3" BA barrel with Hybrid direct thread can.

I want to build 1 more, but as a side charger. Gas blowback does happen, and I would like to eliminate the charging handle to limit said blowback.

It's by far my favorite caliber. Goodluck with your build!

 

[Roymil666]

I've put together 2, 1 for me and 1 for the wife. I used BA Hanson barrels for both with the optional pinned gas block, and JP captured buffer springs for both. Suppressed and unsuppressed they will eat anything.

View attachment 677075

10.3" BA barrel with Omega with QD can

View attachment 677076

8.3" BA barrel with Hybrid direct thread can.

I want to build 1 more, but as a side charger. Gas blowback does happen, and I would like to eliminate the charging handle to limit said blowback.

It's by far my favorite caliber. Goodluck with your build!

Those are both bad! What handguard is that on the 8"? Why did you go with a direct thread on one and QD the other?

 

[jblake00]

Those are both bad! What handguard is that on the 8"? Why did you go with a direct thread on one and QD the other?

It's a Geissele hand guard, and I went direct thread because it gets heavy/long on the front end with a QD and the ASR adapter.

 

[Tomahawk67]

Both of my .300Blk rifles have Rosco Purebred barrels (8.3, 10.5), non adjustable gas blocks and Vltor A5h2 buffer systems. I'd say if your'e running a 5.56 gun suppressed and you don't get a barrel with a smaller gas port , then an adjustable gas block or BCG is needed, but with the blackout it's a non issue. With the pistol gas port and short barrels , plus subs, there really isn't that much gas to regulate.

 

[flashpan]

Well I promised to share a 300BLK range report ... this could put some folks to sleep but here goes.
The goal: Develop a handload for only subsonic, suppressed with accuracy of 2 MOA for AR pistol with low cost bullets. No intention of hunting except night coyotes so energy is not important...soft recoil and quiet are priorities.
The pistol: Home built side charge upper, Andersen lower, 71/2" 1:8, SBA3, primary arms 1-6 scope. photo
Testing: April 9, TCGC, 65d, 5mph, all 50 yrds, all suppressed, Magneto Speed 3 chronograph. All 4 shot groups.
6 loads tested...3 handloads, 3 factory loads. Handloads = Fed brass, CCI 450, AA1680 Velocity and Accuracy Results:
I hesitate to share actual charge data!!! PLEASE BE CAREFUL. Loading 300BLK is not like most cartridges...most folks work charges down to a load that functions well...TOO LOW you can stick a bullet in your barrel. DOUBLE CHARGE like a pistol cartridge...disaster!

Round	Bullet	Load	Ave Vel	Accuracy
Handload	208 Amax	11/1680	1033	.46 wow photo
Handload	208 Amax	11.5/1680	1096	.96
Handload	200 Accubond 2nd	11/1680	998	1.9 kehole? photo
Handload	200 Accubond 2nd	11.5/1680	1044	1.2
Handload	200 Berrys Plated	11/1680	874	3.9
Handload	200 Berrys Plated	11.5/1680	934	not measured, poor
Remington	220 FB	Factory	845	3.5"
Herters	200 Open Tip	Factory	1001	.560 wow
Sig	220 Pointed	Factory	997	1.3 3 touch

Notes, Observations, Results

• Testing was time consuming but went well after fitting and adj sensitivity on chronograph (on suppressor)
• All loads functioned well, all shot single shot, bolt lock back on all. Seems maybe overgassed, dirty brass as expected, ejecting to 2 o'clock, but with side charging bolt not sure what that means.
• Several handloads obviously went supersonic...a bit surprised at high velocity from this 7 1/2" barrel.
• Clearly the Amax load exceeds accuracy hopes, will cut back the charge. 1000 fps is prefered. photo
• Do not understand, but looks like accubonds keyhole? Bearing surface could be too long for barrels 1:8 twist?
• Berrys test confirms previous testing with coated and plated bullets, this barrel hates them...I give up after testing 4 diff bullets and two powders. I have shotguns that pattern better. And flaring case mouths and recrimping is a PITA anyway.
• Remington factory velocity surprisingly low...tested before...high ES and SD ...wont group
• Herters WOW ... who knew...maybe forget all this reloading stuff and buy this ammo.

Summary: I am happy with the build and now very close to a go to load with 208 AMAX at 1000 fps. Pleasantly surprised at how well this generic short barrel shoots these jacketed bullets. Rather not try another barrel to find accuracy with coated or plated...not sure anyone has found 2-3 MOA with costed/plated. Missed one goal for a low cost bullet.
I hope someone finds this useful. I got hooked on 300BLK this first time I shot a suppressed round. I'll put the finishing touches on the AMAX load and go find the first coyote ... maybe in the country near you? But you will never hear it.

 

[jblake00]

Nice work! I havent seen or tried Herters before.

 

[RainMan_PNW]

Here's my current pair (in the middle), along with their cousins...


Aside from the MPX on the right, all three of the MCX's have been built from parts accumulated over the past year and a half. The 300's are a 9" pistol with SBA3 and a 6.75" SBR "hybrid" (Aero AR Form1 lower). That one also has my Form1 30cal can on it that uses Dead Air KeyMo mount and Sandman end caps.

I need to start figuring out loads next.

The 556 will be getting an FDE SBA3 this week when it shows up in the mail. That Sig brace is OK on the MPX, but sucks for the larger MCX. And length of pull on the SBA3 with the folding knuckle is actually longer than the "Kate Moss" thin stock.

ETA: I've also got a DMR length FDE suppressor handguard for running the can on either of the other MCX's, and a short 6" slim handguard for the grey upper when it doesn't have the can. That's one thing about the MCX that I love... handguard changes are stupid fast and easy (as are barrel changes...though I'd rather just have another upper)

 

[flashpan]

Well you can definitely make it rain bullets with that nice collection!

 

[Roymil666]

Here's my current pair (in the middle), along with their cousins...

View attachment 682844
Aside from the MPX on the right, all three of the MCX's have been built from parts accumulated over the past year and a half. The 300's are a 9" pistol with SBA3 and a 6.75" SBR "hybrid" (Aero AR Form1 lower). That one also has my Form1 30cal can on it that uses Dead Air KeyMo mount and Sandman end caps.

I need to start figuring out loads next.

The 556 will be getting an FDE SBA3 this week when it shows up in the mail. That Sig brace is OK on the MPX, but sucks for the larger MCX. And length of pull on the SBA3 with the folding knuckle is actually longer than the "Kate Moss" thin stock.

Those are some bad builds! What solvent trap did you use to start the form 1? Are you running a low-powered variable on that fde .300?

 

[RainMan_PNW]

Those are some bad builds! What solvent trap did you use to start the form 1? Are you running a low-powered variable on that fde .300?

The optics (left to right) are:
Leupold Mk6 1-6 TMR-D
Sig Tango6 1-6 300BLK BDC
Primary Arms 1x Prism "Cyclops"
Sig Romeo4T

I'm thinking of putting the Romeo4T on the grey 300 upper and getting a different red dot for the MPX. No reason to have a LVPO on either of them, since they're really meant for <50yds for me.

The Form1s are a both combination of a lot of time and effort... neither started as an actual kit. And neither ended up cheaper in the long run compared to just buying a manufactured can - it was more about the learning experience.

The 30cal started as an SDTA titanium "D-cell" tube 1.5" OD x 7.5" long. All other parts were sourced individually... I had a guy custom build me the end-cap adapter for the Sandman caps and the adapter on the other end to use the now-standard Omega/Dead Air/etc. threads (I built this before any of that stuff was standardized). It's got 8 baffles built from 60-degree skirted cone cups, with progressive bore diameters and skirt lengths. 5 are Ti and 3 are SS (blast + 2 more). If I were to do it again, there are a lot of things I would do different... And some I'd do the same. But this thread isn't about building a can, so I don't want to hijack.

 

[Roymil666]

Is anybody running a particular BCG for a suppressed .300? I was planning on going with the BCM m16 but primaryarms.com has a geissele on sale for $109 today. As long as they are MPI and HPT is there much of a difference? They are made of the same steels.

 

[Roymil666]

What weight buffer are you guys running for suppressed .300?

 

[flashpan]

Good question ... I need to take mine out and weigh it...will let you know. Your question makes me wonder if I can go heavier because mine locks back on every sub/sup load I've tried. Maybe it would shoot even softer with more weight.

 

[Tomahawk67]

What weight buffer are you guys running for suppressed .300?

Vltor A5H2 in both my 8.3" and 10.5" 300blk's

 

[Roymil666]

Ok. Apologies in advance for rehashing and old thread but I figured I'd give an update on the build. As well as ask for input again.

Aero M4E1 "don't tread" receiver set.
Midwest Industries suppressor series 12" rail
BA 9" premium 300blk barrel
Superlative Adjustable Gas block
JP Silent H2
Geissele SD-C trigger
Raptor SD C.H.
CMMG Rip-brace

So now my issue. I had the receivers and handguard custom cerakoted. Barrel is 9", handguard is actually 12.625" but the Witt Machine SME Muzzle Device is only 3.75" overall. So fully assembled my MD stops inside the handguard a good 1/2" shy. My gemtech direct thread is in jail for who knows how long. I'm half contemplating buying a "display model" to use as a barrel extension while I wait. Anyone with a better idea? Seems as though most of the blast directors are shy of 4".

 

[Tomahawk67]

Ok. Apologies in advance for rehashing and old thread but I figured I'd give an update on the build. As well as ask for input again.

Aero M4E1 "don't tread" receiver set.
Midwest Industries suppressor series 12" rail
BA 9" premium 300blk barrel
Superlative Adjustable Gas block
JP Silent H2
Geissele SD-C trigger
Raptor SD C.H.
CMMG Rip-brace

So now my issue. I had the receivers and handguard custom cerakoted. Barrel is 9", handguard is actually 12.625" but the Witt Machine SME Muzzle Device is only 3.75" overall. So fully assembled my MD stops inside the handguard a good 1/2" shy. My gemtech direct thread is in jail for who knows how long. I'm half contemplating buying a "display model" to use as a barrel extension while I wait. Anyone with a better idea? Seems as though most of the blast directors are shy of 4".

5" long 5/8-24

KAK INDUSTRY SLIM EXTENDED 5/8-24 "FLASH CAN"

KAK INDUSTRY SLIM EXTENDED 5/8-24 "FLASH CAN".Bore will clear up to and including 45 and 458 projectiles.THE BORE WILL ALLOW A 45 CAL TO PASS THROUGH THIS IS A SOLID 6061 ALUMINUM DEVICE THAT IS DESIGNED TO DIRECT MUZZLE GASES AND THE MUZZLE FLASH FORWARD.THREADED 5/8-24 FOR BLK , 308 OR SIMILAR...

www.kakindustry.com

 

[jbett98]

Take a look at Rainer Arms barrel offerings. Local company and easy to deal with.
My first SBR and also my first AR build. Works perfectly.

 

[Roymil666]

5" long 5/8-24

KAK INDUSTRY SLIM EXTENDED 5/8-24 "FLASH CAN"

KAK INDUSTRY SLIM EXTENDED 5/8-24 "FLASH CAN".Bore will clear up to and including 45 and 458 projectiles.THE BORE WILL ALLOW A 45 CAL TO PASS THROUGH THIS IS A SOLID 6061 ALUMINUM DEVICE THAT IS DESIGNED TO DIRECT MUZZLE GASES AND THE MUZZLE FLASH FORWARD.THREADED 5/8-24 FOR BLK , 308 OR SIMILAR...

www.kakindustry.com

I think I saw that earlier but wasn't sure how well KAK stuff holds up. Such a spendy top tier build already.

 

[Geardo]

I think I saw that earlier but wasn't sure how well KAK stuff holds up. Such a spendy top tier build already.

Its just a place holder, so need to spend a ton of money. An aluminum muzzle device on a shorty rifle barrel gives me a little bit of pucker if you are shooting Supers.

 

[Roymil666]

I was also contemplating building a new shroud for the sme. Looks like a simple 1" I.D. ss tube with what looks like NPT on one end. Only problem would be doing the internal threading. Machinist at work says that can be a pain.