So I have an extra lower and would like to put together a basic 22LR plinker, that said I am looking for the pros/cons of:

1. Getting a basic assembled 5.56/223 upper and using the CMMG conversion bolt or

2. Build the upper using dedicated 22LR components?

Based on feedback from friends and others here, I would be using the S&W 15-22 mags, not the ones that CMMG uses.

Thanks in advance

You may not get optimal accuracy with a 5.56 upper. The rifling twist is too fast for .22LR.

Is the cost near what a 10/22 goes for?

Maybe you want the AR platform, I understand.

https://sigforum.com/eve/forum...990067694#9990067694 Thread about conversion units vs. dedicated uppers.

You want at least a dedicated upper. Most .22LR ammo is happier with a 1:16 twist, and you're not going to find that in a gun built for 5.56. Rimfire ammo is also filthy, and I wouldn't want to subject a gun with a gas system to that. Heck I wouldn't even put it on one of my center-fire lowers, just because of all the crud that gets down in the trigger group. I like to keep all that filth contained to one gun.

The CMMG conversion kits are top notch, though, and they make a version that will work with a dedicated .22 LR barrel. Mine has been phenomenally reliable, both suppressed and unsupressed.

The M&P mags are a better solution. I have the Black Dog Machine ones, and they don't actuate the bolt catch like you can with an M&P .22 mag and adapter.

I went with a complete dedicated .22 upper from TacSol. It's been great.

I know you asked about building, but I've got one of these that is accurate and fun to shoot:

https://waltherarmsusa.com/wal...cal-rimfire-carbine/

MSRP is $414, I got mine from CDNN for $300 about five years ago.

I have multiples of dedicated 22lr AR uppers. This is the way to go. The conversion bolts are never going to give you anything other than the ability to go "bang". They aren't accurate, they will dirty up your AR something fierce with molten lead. Just stay away.

2 of mine are the old Spikes Tactical versions. Very accurate, very well made. One worked perfectly out of the box, one required some fiddling with the recoil spring to make it work. One is a PSA that I had nothing but issues with at first and then about a couple hundred rounds in it became a sewing machine. It was not accurate was the problem. Like wildly inaccurate. So bad that I called for a label to send it back bad. While waiting I kept shooting it. All of a sudden all the issues went away. Poof. To this day I have no idea what changed.

As for the 15-22 mags they will work, albeit sloppily, in a standard AR magwell. Better solution is the Boonie Packer Better Mag Adapter. 20ish bucks and the mags fit like they should. Way better than using Black Dog Mags which I have a bunch of and am not a fan of.

I have the CMMG conversion kit that I use in a PSA 16” upper with a rifle length gas system actuated by a Timney 667S trigger. I did have to replace the trigger hammer with a AR10 hammer as I was getting some light strikes that I did not get with the Mil-Spec trigger I originally used.

Have put several hundred, closer to a thousand rounds through it. I’m choosy what ammunition that I use mainly Federal Automatch. I do run maybe four or five 5.56 rounds through the rifle to every couple hundred .22’s that go through it. So far so good for the action. I did have some hiccups with the conversion bolt initially but between running it wet and a wear in period not it functions fine.

I use it in the .22 configuration for steel plate shooting at my gun club. 55 yards with iron sights and I’m happy to hear the “ping”.

If I was doing it over again I'd get a complete Tippman firearm.