I want to chime in here with support for a metal 15-22 lower, but for different reasons.

I recently purchased a 15-22. I purchased a slide-fire stock. I purchased a timney trigger replacement.

I have been very happy with my rapid mag dumps ever since.

During installation of the timney trigger I overtightened the screws which hold the trigger in place within the lower. Now I can see noticeable bulges on the underside of the lower near the trigger where those screws have now permanently warped the polymer lower.

I cannot imagine that this is good for the integrity of the lower. I imagine that the trigger screws can continue to press against the polymer and loosen up the more I shoot. I would not be surprised if at some point the lower starts to crack in this location.

Had the lower been made from a quality piece of metal, I feel that it would have been much more difficult for me to over-tighten the trigger screws. I would have felt more of a stop. Instead, the screws felt like they needed to be continuously torqued down, but instead they were just pushing out soft, cheap, ****** polymer.

Immediately after my modification the 15-22 performed wonderfully with the trigger and slide-fire stock. I had no issues and could dump all 10 of my magazines one after the other. As time has gone on, I have started to experience the trigger not resetting. There will be an unspent cartridge in the chamber, but the trigger will not release the hammer as it has not been reset. I then have to pull the charging handle. This strips the live round and feeds another round while resetting the trigger. I plan on doing some more testing, as this could be related to a dirty rifle or a operator error with the way I am applying forward pressure for the slidefire stock. It just seems weird that I would have digressed from obviously perfect operating handling resulting in perfect magazine dumps to sloppy operator error resulting in the trigger not being reset.

Now since a lower is registered, I imagine that it might be very difficult to find a replacement part. Unless the replacement part is an entirely new rifle. I imagine that Smith & Wesson will not service/replace my lower as I have caused the damage as a result of my modification of the rifle. Let me know if you think they might help.

I would happily replace my **** polymer lower with an aluminum lower if it were available for the 15-22. Aluminum is not that heavy and is much more solid.