My 300blk

[dsmjon]

Here's what got me to hop on the latest fadwagon of the 300 Blackout.
She started life from a Green Mountain minigun barrel.... Lopped off the chamber, reamed out room for the 300 Blackout case. Spent today on the lathe, cut the bbl profile, gas block deck, cut gas port, cut muzzle threads, recrowned the bbl, headspaced and fitted the bbl extension.

Now.. it's a 300 Blackout bbl that only cost $35.

Worked up a few loads, 19.0 grains of Hogdon H110 under a Barnes #30811 (110gr TAC-TX FB). Have a mag full worth ready to go, fitting the bbl to a spare upper tonight. Hopefully tomorrow I'll get time to go play with it, then teardown and paint!!







Many thanks to my buddy D.S. for the expertise, education, and my "first hit on the crackpipe" (which is playing on a metal lathe).

[HodakaGA]

Want to build me one? Looks like my wait might be a long one for my DSA upper to show up, or to find a decent priced bare barrel in stock somewhere.

[andremajic]

Good Job. I like to turn the section where the gas block fits a little oversized, then use finer grits of sandpaper until it's the final dimension. Then, use a nylon tipped hammer to "press fit" the gas block, until it butts up on the shoulder.

I'd rather it fit tightly than have to rely on little 8-40 set screws doing the job. Another thing to do is after test firing it for function, take the gas block off, find the little marks the set screws have made, and "dimple" the marks with a drill to allow those set screws to positively index the barrel.

You'll be hooked on this new caliber.

Andy.

[danielk]

What size hole did you use for the gas port? I just finish my 300 blkout build too. You'll love this round!!

[andremajic]

I used the minimum size .086 on my last two because I plan on putting a can on when my form 1 comes back.

If you don't ever plan on suppressing it, you can go anywhere from .096 to .105 and it'll function fine. When I did my 16" barrels for supersonic I picked a halfway point between those I think it was .097 or so and it worked great.

If you do plan on shooting subsonic with a suppressor, you will have to start at the minimum size .086" and slowly test fire and alter it until it cycles reliably. Remember, it's a lot harder to replace metal when it's gone.

Or you could just drill it out full size and put an adjustable gas block on it.

Andy.

[HotGuns]

You do realize that for subsonic 220 grainers it needs to be a 1 in 8 twist right?

Otherwise, it wont stabilize the heavier bullets.

[andremajic]

You do realize that for subsonic 220 grainers it needs to be a 1 in 8 twist right?

Otherwise, it wont stabilize the heavier bullets.

But that would only matter if he's buying Sierra matchking 220 gr. jwords...

I have been using 170 grain cast WW boolits with GC for subsonic with 7 grains h110 and it's a pretty reliable subsonic cartridge. ( I think it's the 311041 but I'll have to check. Approx 1" at 50 meters with the magnification of a standard ACOG scope.) Bolt action, as the subsonic doesn't have enough OOMPH to cycle the action. LC brass, Federal SR primers.

I'm also using a 1/10 twist barrel, so just realize that the greenhill formula is a good rule-of-thumb and not an end-all be-all. You can get subsonic velicities with other, less expensive rounds and not be limited. It just runs into how much time you have to experiment and customize your loads at the range.

This is a casting forum, where people are encouraged to save money and roll their own, and I couldn't possibly imagine spending my hard earned money on a box of 220gr. sierra matchkings.

Andy.

[dsmjon]

You do realize that for subsonic 220 grainers it needs to be a 1 in 8 twist right?

Otherwise, it wont stabilize the heavier bullets.

Tumbling bullets make bigger holes.

Sent from my DROID RAZR using Tapatalk 2

[HotGuns]

This is a casting forum, where people are encouraged to save money and roll their own, and I couldn't possibly imagine spending my hard earned money on a box of 220gr. sierra matchkings.

Yep... its a casting forum alright. Although you couldnt possibly imagine spending your hard earned money on a box of 220 grainers, that is what made the Whisper/Fireball /Blackout work so well.

Cast bullets can work pretty well in the Blackout, I simply posted that reminder so that anyone attempting to use heavier bullets in anything more than a 1/8 twist can expect accuracy to complelety suck.

I've been experimenting with the Whisper concept since the mid 80's. I have tried hundreds of loads, experimenting with primers,powder and most bullet weights available for the .30. I currently own an AR in .300 Blackout, an AR in .300 Fireball, a Contender in .300 Whisper from the custom shop with a 1 in 10 twist and I built a .300 Whisper in a Remington 700. I've killed deer,coyotes and several other critters with them. I build several Blackouts a week.

When it comes to watching heavy bullets go sideways on a sheet of paper, I'm no newb. I know what works and what dosent. Although the Greenhill formula is by no means the end all of all fornulas, its pretty danged close when it comes to subsonic 30 cals.

As a manufacturer of suppressors and one that deals with them everyday, the LAST thing you want to see is an unstable bullet trash out the suppressor that you jumped through hoops for and waited 6 months to get because the twist wasnt right.

Yes, I know that a 1 in 10 twist can work. Just dont get to heavy with the bullets(cast or not) with it if you are shooting suppressed.

[Idaho Sharpshooter]

Just buy an adjustable gas block. Mine is a fine one from JP Enterprises. Retail is $65.

Rich