Not sure which is better.

Which is more reliable?

Thanks

You can get a M&P15 for cheaper than a 22LR Upper. It is super reliable (I don't think I ever had a misfire/ejection/feeding problem not related to a dud ammo). I had a Spikes 22LR upper and sold it. It was reliable for me, but I know the person I sold it to had some issues with it. I think they were minor though.

cheaper is relative.

 

My lower has about $400 worth of non mil-spec stuff in/on it. Replicating that on one of the plastic 22lr ar lookalikes is hard if not impossible, and pricey. You also have to replicate any optics.

 

The cheapest thing is a CMMG insert on your gun. Gets you the same upper configuration, optics, trigger, etc for about $200. However, although they have gotten better, they still have issues, and they aren't the most accurate things.

 

A good dedicated upper isn't cheap, but it saves you having to replicate the lower. My nordic NC-22 has been flawless so far.

I don't know of any upper that will lock the bolt to the rear on an empty mag (it will rest on the follower). Dedicated .22 rifles will be less finnicky about ammo.

 

M&P15-22 are plentiful used. I sold my ST-22 and went with that.

 

EDIT: S&W isn't the only choice either. Ruger's SR22 rifle is a tarted up 10/22 which gets good reviews and Sig has the 522. I only say that because the market for tactical 22's is flush with choices which makes everything cheaper.

Get both. I have a m&p 15-22 and it feeds.everything and 0 issues (knock on wood)