Rifle Headspace Gauge This tool is intended to provide you with the best DIY method to understand your rifle's head space in relation to standards. Using this to set your forming dies appropriately for your rifle will give you the best results. I will include a picture and show the use the next time someone hands me their rifle and wants me to take a look at it. drill a lathe would be best, but optional saw drill bit thread tapCutting oil may help A spent casing from the rifle we will make ammunition for Lightweight oilsuch as 1-2-3 oil, or sewing machine oil. A bore cleaning brushused to clean a rifle bore after shooting) that is not less than the inside of the case you are making this for. Drill a hole through the primer pocket, and use a tap to thread that hole. You want to use the same thread size as is what is on a copper chamber cleaning brush (I guess you could use plastic) the same size as the brass casing itself. Cut the case in half closer to the head/primer area, and then another cut about a quarter of an inch farther along. This will create a quarter of an inch gap for room to play. Thread in the cleaning brush into the head of the case, with the brush to the bullet-side of the casing. Press the remainder of the casing (with the shoulder) onto the wire brush (but leave about a half inch of gap). The gap will allow the shoulder to move when this tool is chambered. Give a light coating of oil to the brass to prevent it from binding to the chamber. You should now be able to chamber this tool, which should force the chamber shoulder to press against the casing shoulder and move it back until the bolt has fully engaged. Quickly (so that the shoulder doesn’t get caught on the chamber) remove the casing. Measure the case head-to-shoulder length, and record this number (I’d suggest a headspace “gauge” tool that has the same angle of your shoulder cut into it that the case can be set into to measure this). Twist the shoulder/neck brass back away from the head a small distance, and repeat steps 6 through 9 a few times to ensure you have accurate results. You now have the head space based on the shoulder position. When you load and test your ammunition, use the same measuring base that you used in step 8 to ensure it is accurate.