The Drop-in AR15 22 Conversion Kits are the easiest and least expensive method of converting your AR15 to a .22 caliber plinker. The kits will range in price from about $160-$250 and take about 30 seconds to install. There is a few down sides to using the drop in kits. The bullet must travel a few inches in an unrifled tube before it reaches the barrel. The barrels on most AR type rifles will typically have a twist rate that is optimized for the 5.56 Nato (.223) with a 1:7″- 1:9″ barrel twist rate and not the 1:16″ that works well with .22 long rifle. There is also a few thousandths of an inch difference in the bullets diameter of .22LR (.222) vs 5.56 Nato (.224). Those differences can lead to less then match grade accuracy in an AR15 but the accuracy is perfectly suited for plinking. If that accuracy is not suitable you can purchase a complete .22 long rifle upper. The cost starts at about double of the drop-in conversion and can go upwards well over $1000. The choice is yours.