There are a couple of threads on this and some doubts voiced on why anyone wants
or has a need / use for them. First, my discussion is not about conversion units as
my experience with them has been hit or miss. I own one of the early units from 70s
which is the original Achison unit and its problematic, a plinker novelty item at best.
Specifically: AR upper units made as 22 LR, not a conversion unit in a upper: My search
ended up with a Tactical Solutions upper with Black Dog mags. The unit has over 10K shot
through it now and it will do 1 inch at 100 yds from the rest. TS makes a dedicated match
grade upper and it flat works.
Training: I have this TS upper on a dedicated M4 lower and the weapon is a dead ringer for
my LMT M4 carbine. Side by side, weight, feel , sights, etc: they are exactly alike. The TS
carbine allows me to do single and multiple shot scenarios, tactical drills with the intent of my
getting the first shot fired where it needs to plant. I run a hour of such drills and then run
a half hour with the LMT in 5.56 which finishes off the day of training.
I am not at all happy with the skill degradation I experience between range drills but I know its my
mounting age. I fight it but it is there nonetheless. The TS 22LR M4 allows me to sort out my
failings and get focused before I expend expensive 5.56 ammo in the LMT M4. The TS M4 in 22LR is a serious
training weapon and that is its purpose.
Now I don't know if cheaper options like a 22LR conversion unit as sold by Spikes and others are trustworthy
and worth a hoot. I think most who buy conversion units do it for plinking and they may suffice for that purpose.
They do send that 22LR down your 5.56 barrel and you don't get the accuracy of a 22LR barrel as on the Tactical
Solutions dedicated / made as a 22LR shooting upper unit. I don't (personal opinion) much take comfort with
a lead bullet crapping up my 5.56 barrel and lead residue landing in the gas system. So accuracy and leading/fouling
is a thing that is not a issue with the Tactical Solutions approach, it is a potential problem for the 22LR conversion units.
A dedicated M4 in 22 LR serves my needs. It may not serve yours. Depends on the mission / purpose you have in mind.
There are Look A Like Replica 22LR weapons out there for plinkers and then there are purpose built 22LR quality built clones
that are high quality and are accurate and seriously built for the long haul of hard training use.
M4: I want the real thing (semi auto) and I have several. I have the TS M4 trainer and am very pleased with its performance / quality.
1911: I use the Colt Ace for the same training purposes before I do my training drills with 1911 in 45 acp. I also use a 9mm
1911 as a trainer before I move up to 45acp 1911 in training. Since casting 9mm bullets, its as cheap to shoot 9mm as 22LR so the
9mm 1911 sees more training use these days.
Food for thought: If you train seriously, a 22LR trainer may be beneficial to your needs.