Cycle Rate Increase. What causes it and how to reduce it DIY

We got a lot of requests to make a video demonstrating rapid fire ramp up in RPM on autoloading firearms. The question is, why does my AR increase in rate of fire when shooting fully automatic? Great question, some say that it’s because as the magazine is emptied there is less friction pushing up on the bottom of the bolt carrier so the bolt carrier can cycle faster hmm plausible Hookes law of elasticity, some say it’s something in the buffer system others says its the adjustable gas system. These may all be factors but they are very minimal to the real problem. First let’s get something straight, this problem is related to gas impingement operating AR’s not piston operated. In gas impingement the gas flows from your barrel through a tube directly back into the bolt carrier which gets pushed open directly by the gas. Here’s the scenario. When you're shooting you may notice a slight increase in RPM Rounds per minute, but this is more noticeable on mag dump number 2 and even more so on mag number 3. So what is primarily causing this ramp up in RPM? Well if we look closely at the gas tube near the gas block while shooting and then we listen closely we will notice that as the gas tube starts glowing red from heat we can hear the RPM start to increase at the same time. What is happening here is the heat buildup from the gas is overcoming the ability of the gas tube to dissipate it away. It starts turning red near the gas block first because that is the closest to the source of the gas coming from the small port in the barrel. Another point is gas tubes are made of stainless steel and SS’s have a low thermal conductivity (which is the speed ability of the metal to transfer heat) so they quickly are overwhelmed by the hot gas. So, what does this mean? THis means that when you start shooting the gas tube is able to transfer a lot of heat out of the gas used to cycle the action which keeps the RPM consistent but as soon as the gas tube can no longer transfer heat fast enough the gas used to cycle the action starts getting hotter and hotter, now the volume of gas for each shot is the same but the temperature is getting hotter each shot so you will have higher pressure pushing on the bolt carrier and you will get an increase in RPM. So how can we reduce this problem? When working on a submission for SOCOM about 6-7 years back for the Suppressed Upper Receiver Group. The SURG had to meet requirements and one of them was to lower the RPM in Full auto fire. One simple trick I used was to wrap copper wire around the gas tube near the gas block, Copper wire has very high thermal conductivity so it will draw a lot of heat away from the gas tube. I found that 10 ga copper wire wrapped around the gas tube about 2-3 inches in length kept the RPM much lower. On average for 90 rounds of full auto it reduced the RPM about 15% which is definitely noticeable. Quick DIY instructions, you will want to find 6 inches of 12-10 ga bare copper wire and with your gas block and gas tube removed wrap the copper wire around the gas tube starting at the gas block. Wrap it around for about 2-3 inches then reinstall your gas tube and gas block and start benefitting. I hope this all makes sense and even if you don’t have full auto having that copper wrap on the gas tube keeps your action cooler and is beneficial overall. One Last thing if you don’t want to tackle this DIY project wrapping the copper wire reach out to [email protected]