The Kynshot Spacer Weight was designed in cooperation with Blitzkrieg Components and can be used with PCC hydraulic buffers, and AR hydraulic buffers to add mass in front of the buffer. The Spacer Weight also adds .75" in length to the buffer system, and adds 2.5 ounces of weight, which is designed for a close fit buffer tube while preventing tilting of the buffer during cycling. If you want to use this weight and have your bolt cycle the full distance and stop behind the bolt catch, you will need to use an AR-10/A5 length buffer tube since they are .75" longer on the inside. The most optimal set up for most 8-16" barreled guns is to run this PCC Buffer weight in front of an RB5015HD buffer with a .308 carbine buffer spring in an AR10/A5 buffer tube for full bolt stroke. If your bolt has a weight pinned into the rear of it, Kynshot recommend leaving that in place to retain full mass of your bolt.