.300 Blk Barrel Swap?

[Danny46]

I've been accumulating parts for a build; my intention was to build a .300 blk out for hunting/home defense with a threaded barrel for suppressor. I currently have a 5.56 AR which is set up for more the short range stuff I am looking to do with the .300 and recently came to the conclusion that I would like to build something for longer distances since I already have an AR built for short distances. Figured the best course of action would be to change my existing AR to a .300 and continue on with my in-progress build in the 5.56 platform.

That being said, I have never done built an AR from scratch and am curious to what goes into making a rifle .300 compatible? Is it as simple as a barrel swap? Will I need a new hand guard or make an modifications to the existing upper?

[motoman]

I'd just buy a complete .300BLk upper and call it done. How far of a distance are you wanting to shoot? The .300Blk was designed to run in short barrels and performs best within 300yds or closer. The only thing you're changing is the barrel as it uses the same bolt carrier group as the 5.56/.223.

[bird_dog0347]

So long as the gas system length (tube length) is the same it's just a barrel swap from 5.56 to .300blk and all you need is the upper vice block and an armorers wrench.

[YALE]

An adjustable gas block wouldn't hurt.

[Cobraman]

Not to thread hijack, but what all is involved in reloading 300blk and what is the cost? I might be interested in swapping barrels or selling my upper to buy a 300blk upper.

[motoman]

Not to thread hijack, but what all is involved in reloading 300blk and what is the cost? I might be interested in swapping barrels or selling my upper to buy a 300blk upper.

It's .223 brass that's trimmed down significantly and the neck is opened up to accept a .30cal projectile. CJ would have to answer the cost of reloading but I know it's more expensive because your smallest projectile is twice that of a 55gr .223 round. Subsonic projectiles can actually crunch the powder.

[bird_dog0347]

I'm also planning to eventually get a .300 upper and reload for it, but I want to start reloading 5.56 first so I always have ammo on hand.

[lilvega]

That being said, I have never done built an AR from scratch and am curious to what goes into making a rifle .300 compatible? Is it as simple as a barrel swap? Will I need a new hand guard or make an modifications to the existing upper?

There may be some disagreement with this....butttt..

Yes and no to the above question.
You can just swap the barrel. However, if your 5.56 bolt has been used, it will be worn in with your 5.56 barrel. It is best to use a new BCG. By the time you buy a bbl and BCG, you are nearing the cost of a complete upper. I built 2 complete uppers for mine so I can use one lower and just pin out and use whichever upper I want. 10 second swap and I have 2 guns.

[lilvega]

Not to thread hijack, but what all is involved in reloading 300blk and what is the cost? I might be interested in swapping barrels or selling my upper to buy a 300blk upper.

I am reloading mine for about 50 cents each. However I bought 600 rds of annealed and formed brass to start with. Then reloading that over and over.
A1680 powder is insanely priced right now. H110 is hard to find too but I have a reliable source for $33/lb. Also using some IMR 4227.

I do have a little saw for trimming the cases and have a full length sizing die so I will make my own brass once I accumulate 1k or so in empties.

[Cobraman]

So with my new bushy m4 all I'd need was to sell the .223 barrel and buy a .300blk barrel?

[Pokulski-Blatz]

So with my new bushy m4 all I'd need was to sell the .223 barrel and buy a .300blk barrel?

Pretty much, but it wouldn't really be worth it on your rifle.

[lilvega]

So with my new bushy m4 all I'd need was to sell the .223 barrel and buy a .300blk barrel?

yep.

If you want a long barrel:

http://www.midwayusa.com/product/680713/cmmg-barrel-ar-15-300-aac-blackout-1-in-7-twist-16-carbine-gas-port-wasp-melonite-finished-chrome-moly-matte-pre-ban

Short like mine:

http://www.midwayusa.com/product/798163/cmmg-barrel-ar-15-pistol-300-aac-blackout-1-in-7-twist-85-pistol-gas-port-wasp-melonite-finished-chrome-moly-matte-pre-ban

**I see they discontinued the 8.5". Glad I got mine 3 months ago

[Danny46]

There may be some disagreement with this....butttt..

Yes and no to the above question.
You can just swap the barrel. However, if your 5.56 bolt has been used, it will be worn in with your 5.56 barrel. It is best to use a new BCG. By the time you buy a bbl and BCG, you are nearing the cost of a complete upper. I built 2 complete uppers for mine so I can use one lower and just pin out and use whichever upper I want. 10 second swap and I have 2 guns.

Good point. Since I was planning to buy a brand new BCG for the build anyway that wouldnt be to much of an issue, would probably just swap the the Barrel and BCG from the current rifle to the build rifle.

And yeah I know I could just buy the complete upper and call it done, however I wanted to do this build as a project sort of thing and put it together myself and do it as cheaply as possible. Basically just waiting till certain parts go on sale, etc. If it wasn't for that then yes, I would just buy a complete .300 upper.

[lilvega]

Cobraman - Or a whole new upper for not much more.

http://www.gunbroker.com/Auction/ViewItem.aspx?Item=389568800

[Danny46]

I'd just buy a complete .300BLk upper and call it done. How far of a distance are you wanting to shoot? The .300Blk was designed to run in short barrels and performs best within 300yds or closer. The only thing you're changing is the barrel as it uses the same bolt carrier group as the 5.56/.223.

It would be close range. Hog hunting/ home defense, etc. Thats why I am wanting to do the switch. In my mind I was going to do my new rifle with free floating barrel etc then realized it was dumb to have a rifle set up for distance with the .300. My current rifle is set up more for what would ideally be a .300