Converting 5.56 AR15 to 300 Blackout

[Mighty Mouse]

Is it as easy as just swapping the barrel?

I have an AR Stoner kit gun that I put together years ago as a cheap truck gun and have barely ever used. I have a hankering to experiment with 300 Blackout and figured that converting this 5.56 AR Stoner might my cheapest option if it's truly as easy as swapping the barrel. Do I also need a new gas block and/or gas tube? Should I get an adjustable gas block? I will be putting a suppressor on the 300 Blackout FWIW. Photo below of the conversion candidate for reference.

 

[Pescetism]

Yes, it's usually just as easy as swapping a barrel. You may want/need to switch buffers and/or buffer springs but not a requirement in my experience. I'm a fan of adjustable gas blocks, suppressor or not, but again not always a requirement.

 

[flyfisher117]

You will need to have your new barrel cut/drilled for the front sight pins or you will need to replace the front sight for a different gas block. If you replace it just double check that what ever you get is compatible with the front cap that holds the handguard on.

I have adjustable gas blocks but don’t prefer them. They all carbon lock at some point. Subsonic 300 is dirty. That being said the SLR gas blocks I currently have were some of the easiest to get the carbon cleaned out and have them operating again.

If it were me I’d just build another upper. Barrel + $50 blem BCM upper + a basic $60-$120 handguard and you are in business. You can take the BCG and charging handle out of that upper.

 

[The Harbor Master]

You will need to have your new barrel cut/drilled for the front sight pins or you will need to replace the front sight for a different gas block. If you replace it just double check that what ever you get is compatible with the front cap that holds the handguard on.

I have adjustable gas blocks but don’t prefer them. They all carbon lock at some point. Subsonic 300 is dirty. That being said the SLR gas blocks I currently have were some of the easiest to get the carbon cleaned out and have them operating again.

If it were me I’d just build another upper. Barrel + $50 blem BCM upper + a basic $60-$120 handguard and you are in business. You can take the BCG and charging handle out of that upper.

In the past I've been told that swapping carriers is a non- issue, but the bolt itself "wears" to that receiver/lugs, and should not be swapped after heavy use... or at the least be double checked for headspace in the new upper. Not sure if that's true?

 

[Mighty Mouse]

Thoughts on a carbine length vs pistol length gas tube? I'm planning on a 16" barrel with suppressor shooting mostly subsonic ammo but sometimes supers.

 

[waspocrew]

I agree with the recommendation to just go with another upper. You can buy one for fairly cheap and not have to go through the hassle of building, but if you like to tinker, build away.

Thoughts on a carbine length vs pistol length gas tube? I'm planning on a 16" barrel with suppressor shooting mostly subsonic ammo but sometimes supers.

I have pistol length on both my 10.5" and 16" uppers. They work great with subs and supers.

As for gas block, if you're going to primarily shoot subsonic, then go with a standard block. Adjustable blocks only restrict gas, they won't allow you to have more gas than you would with a standard block. You might be a little gassy with supers and a suppressor, but there are other ways around that.

 

[Morell6097]

In the past I've been told that swapping carriers is a non- issue, but the bolt itself "wears" to that receiver/lugs, and should not be swapped after heavy use... or at the least be double checked for headspace in the new upper. Not sure if that's true?

It’s a safe practice to fallow but you’ll really only see that in pretty high round counts

 

[Mighty Mouse]

If it were me I’d just build another upper. Barrel + $50 blem BCM upper + a basic $60-$120 handguard and you are in business. You can take the BCG and charging handle out of that upper.

I agree with the recommendation to just go with another upper. You can buy one for fairly cheap and not have to go through the hassle of building, but if you like to tinker, build away.

I'm liking this plan to buy or build a complete upper.

Thanks for the tip on the BCM blem upper receiver. That looks like a great option for a cheapskate like me.

 

[flyfisher117]

In the past I've been told that swapping carriers is a non- issue, but the bolt itself "wears" to that receiver/lugs, and should not be swapped after heavy use... or at the least be double checked for headspace in the new upper. Not sure if that's true?

I’ve heard that but never really looked into it a ton. I don’t really swap bolts around but I have on a couple and never seen any issues. If this current upper he has is barely shot I wouldn’t sweat it.

I verify headspace on all of my upper builds though. Just makes me feel warm and fuzzy.

I'm liking this plan to buy or build a complete upper.

Thanks for the tip on the BCM blem upper receiver. That looks like a great option for a cheapskate like me.

I love the BCM Blems. I’ve used 5 or 6 of them at this point. One had a scratch on its side. One the finish looked a little thin. The rest all looked great. This most recent batch were both flawless.