We have been asked to review .22 conversion kits for the AR15 for quite some time. This is not really a review as much as an overview of what they are. We felt that comparing a conversion to a true .22 LR upper receiver was the only way to truly show you the right decision and that review will be coming up shortly.
I know .22 LR is no easier to come by than 5.56 right now but at $25 for 550 rounds it makes the conversion kit a pretty desirable item to have. The .22 LR is not a very clean round, in fact, it’s filthy. The conversion kit is blowback operated versus the direct impingement gas system that your AR15 uses. This presents a couple of issues.
Issues with using a conversion
The first issue is that you will clog up your gas tube if you put a considerable amount of ..22 LR through your standard AR15, so be prepared to really clean your rifle to keep it functioning properly. The other consideration is that you are putting a round meant for a barrel with a smaller internal diameter than your AR15. The 5.56 bullet diameter is .224 inches whereas a 22 LR is .222. This is a minimal difference and does not create a huge issue but your barrel should be cleaned after a few hundred rounds and the diameter difference can affect accuracy.
While most 5.56 rifles have a twist between 1/7 and 1/9, your average .22 LR has a twist rate of 1/16 (Barrel Rifling = 1/X (X = The length of barrel needed to cause the projectile to complete 1 full rotation)). As a general rule, the heavier the projectile the more spin is required to maintain accuracy. If you spin a light projectile too quickly it is going to be less accurate. This will all come into play during our comparison but it is something to consider before buying a conversion kit. Some people will say twist is more importantly related to bullet length which is a notable point… in this case we are talking about .22 LR ammunition for plinking so I think weight may be a better point of reference.
Reliability is going to be of great importance to most people when considering a conversion kit. If you have ever shot a .22 LR semi-automatic rifle or handgun it is a similar experience. I have put around 500 rounds through my Head Down Products PV13 with the conversion kit installed and have had maybe 10 or so malfunctions where the round would load but not fully seat. This is cleared by pulling the charging handle back and turning the gun sideways until the round falls out, then you move on with your life.
All in all I think that these kits are a must for anyone looking to run thousands of rounds through their AR15 for training purposes. You still use your same trigger (I have a Geissele performance trigger and have had no issues), same optic and everything that you would normally use with less recoil at $0.04 a round as opposed to the going rate of 5.56 which is anywhere from $0.90 to $0.60 a round. I love this kit so far and see no issues that would prevent me from recommending it to anyone. We will be comparing the accuracy and reliability to a full .22 upper using the same conversion kit shortly. Stay tuned and please post up any questions.