It’s best to clean polymer AR15 lowers with mild soap and water. Make sure to rinse it off thoroughly and then dry it off before reassembling.
Polymer AR15 lowers are known for being easier to clean than their metal counterparts, but it’s still important to take care when cleaning them. Using harsh chemicals or abrasive materials can damage the finish and render the lower ineffective. Soapy water and a soft cloth should do the trick for most cleaning jobs. If there are any stubborn spots or build-up, you can use a gentle brush or nylon pad to scrub them away. Just be careful not to apply too much pressure, or you could damage the surface finish.
Once you’re finished cleaning, make sure to rinse the lower off with clean water and dry it completely before reassembling. Any moisture that’s left on the lower can cause rust or corrosion, so it’s important to get it as dry as possible. If you’re planning on storing the lower for a long period, you can apply a light coat of oil or silicone grease to help protect it from the elements.