AR calibers, and BCG's

[camper4lyfe]

I had myself pretty immersed in AR15's and the different bits while I was building mine, but I've since backed off since I finished buying the parts 4 years ago. I'm not starting to think about new uppers for different functions. I currently have an 18" 1:8 twist barrel, and it's HEAVY. The whole gun is right around the 10 lb mark. It'll be fine for bench shooting, and some hunting that doesn't require a long walk in the woods. But that's about it. I'm currently thinking about 2 more uppers, something closer to a standard 16" carbine to get the weight down for possible home defense and general plinking. Possibly also a dedicated .22LR upper (or just a conversion for fun). I also am looking to go up in caliber to something I feel more comfortable hunting with.

This brings me to my question: What's the largest "standard" caliber that the 15 can handle? I feel like it's the 300blk or the 6.8, right? Going up to .308 would require an AR10 (not a completely forgone option either, but farther down the pipeline).

Secondly, what calibers can be used with the standard 5.56/.223 BCG? Can it be used for everything, or do the different calibers require a different bolt?

[Cgrutt]

Great post! I'm sure Mek will chime in. I'm certainly no expert but believe you're spot on. .308 better suited for AR10 platform. 6.8SPC fine for AR15. As far as the BCG is concerned, I believe the only part that may need to be changed out is the bolt itself, which has to match the barrel on the upper.

[WARFAB]

Possibly also a dedicated .22LR upper (or just a conversion for fun).

Reasons to go with a dedicated .22 upper instead of a conversion kit:

1) .223/5.56 land/groove diameters and twist rate aren't correct for .22 rimfire. It might shoot, but performance will be poor.

2) .22 rimfire ammunition is very dirty ammunition and will clog up your gas system, which could lead to reliability issues when you want to shoot .223/5.56

[camper4lyfe]

Reasons to go with a dedicated .22 upper instead of a conversion kit:

1) .223/5.56 land/groove diameters and twist rate aren't correct for .22 rimfire. It might shoot, but performance will be poor.

2) .22 rimfire ammunition is very dirty ammunition and will clog up your gas system, which could lead to reliability issues when you want to shoot .223/5.56

Good points. I hadn't thought of that.

[Cgrutt]

Sorry missed this in OP, but believe you may need dedicated lower for 22LR as I'm not sure if a rimfire cartridge would have enough energy to compress a standard spring to fully cycle action of standard AR15 lower. For that matter, would a standard firing pin fire a rimfire cartridge? And, don't you also need to modify magazine well to accommodate a 22LR magazine?

[camper4lyfe]

Sorry missed this in OP, but believe you may need dedicated lower for 22LR as I'm not sure if a rimfire cartridge would have enough energy to compress a standard spring to fully cycle action of standard AR15 lower. For that matter, would a standard firing pin fire a rimfire cartridge? And, don't you also need to modify magazine well to accommodate a 22LR magazine?

That's another good question. I remember seeing drop in .22LR "bcg's", but I do wonder how they reset the trigger.

ETA: Apparently there is enough inertia from the round that it does reset the trigger. If not, maybe some minimags would work better.

[big flash]

Do you know what profile the 18" barrel you have is, and what kind of handgaurd do you have? That seems pretty heavy, and i'm guessing that maybe if you went with a clean lightweight modern handguard you can shave some weight and not need an entirely separate upper? unless all that weight is in the barrel i guess.

[WARFAB]

Sorry missed this in OP, but believe you may need dedicated lower for 22LR as I'm not sure if a rimfire cartridge would have enough energy to compress a standard spring to fully cycle action of standard AR15 lower.

The rimfire "conversion" BCGs contain the blowback recoil springs so that all the movement is in the special BCG. The buffer and buffer spring never move. With a dedicated rimfire upper you use a standard lower, but you replace the buffer and buffer spring with a plastic insert that has a lighter spring. Most dedicated rimfire uppers come with the appropriate buffer spring parts.

[Cgrutt]

The rimfire "conversion" BCGs contain the blowback recoil springs so that all the movement is in the special BCG. The buffer and buffer spring never move. With a dedicated rimfire upper you use a standard lower, but you replace the buffer and buffer spring with a plastic insert that has a slighter spring. Most dedicated rimfire uppers come with the recoil spring parts.

Ah, got it, thanks.

[camper4lyfe]

Do you know what profile the 18" barrel you have is, and what kind of handgaurd do you have? That seems pretty heavy, and i'm guessing that maybe if you went with a clean lightweight modern handguard you can shave some weight and not need an entirely separate upper? unless all that weight is in the barrel i guess.

It's a stainless heavy contour barrel with an extended rifle length (to cover the rifle length gas block) free float. The free float doesn't weigh a whole lot. The barrel is definitely where the weight is.

[camper4lyfe]

The rimfire "conversion" BCGs contain the blowback recoil springs so that all the movement is in the special BCG. The buffer and buffer spring never move. With a dedicated rimfire upper you use a standard lower, but you replace the buffer and buffer spring with a plastic insert that has a lighter spring. Most dedicated rimfire uppers come with the appropriate buffer spring parts.

And looking further into it, the .22 conversion, and possibly the dedicated upper, could pose an issue with the magazine itself. The conversions come with a 27 round mag. Maybe 10 round mags exist, but it may be a long shot to find one.

[WARFAB]

I've got a Bushmaster .22 upper. Pretty sure it's a 10 round magazine, but I'm not sure Bushmaster is selling them anymore.

[camper4lyfe]

I'll do some looking. I'm not in a huge rush, just have a bit of the bug that my budget can't handle right now, so only in the preliminary planning stages.

[Meketrefe]

A 223 chromed barrel will handle 22LR just fine. the CCMG is a good conversion but it will not be as accurate as an nice 22LR firearm.
In terms of the caliber for hunting you can go simple or complicated.
Simple is the 6.8SPC II. Awesome power. Forget about the whisper/blackout or 7.62x39 those are anemic cartriges especially the whisper
that is nothing but a +P+ 30 carbine.
Or if you don't mind reloading the 6x45 is amazing in accuracy or a 30 herret AR version using 6.8 cases if you think you need 30 caliber bullets.
You also have the 6.5 LBC/grendel but wtih the simplicity of the 6.8 it is hard to choose.
Or lets build you a 35 AR gunner!!! lol
All the above use the same carrier although the 6.8 and grendel need different bolts.

[Cgrutt]

So I was right?