.204 Ruger AR feed issues

Though unusual (we’ve seen a couple of cases of this) there are some instances of the .204 Ruger cartridge case having a feeding issue in some AR’s. We have done some research on this subject online and some of our own testing. The problem originates with these rifles having been initially developed for the slightly different .223 case.

This image shows the crease below the shoulder caused when a .204 Ruger case is still being held by the bolt and the bullet has hit the chamber wall. Though the case may then be pushed into the chamber the crease doesn’t allow it to seat to full depth. This then can prevent the bolt head from rotating and the firing pin will not fall. Or the case may stay jammed part way into the chamber.

Here is what we’ve found in a forum that describes the problem well:

“I imagine that the problem you are having is that the bolt tries to bend the case over the mouth of the chamber. When this happens, the bolt will nearly stall, and it will leave a crescent-shaped mark or crease on the side of the case. If this is the case, what is happening is that the tip of the bullet is striking the top of the chamber before the rim is free of the magazine. This is a problem that is well known to the builders of .204 uppers. Cutting the chamber mouth differently helps, but the magazine, and how it is held in the lower receiver is key to proper function as well. An upper can work perfectly with a given magazine and lower receiver. Take that same upper and magazine and put it onto a different lower receiver, any you may have nothing but problems. “

.204 Ruger AR rifles may require a .204-specific magazine for proper feed. Depending on your combination of upper, lower and magazine there may feed issues with .204 Ruger ammo in .223 magazines. Simply changing to a different lower can cure the issue too – probably because the magazine is held in a slightly different position relative to the upper. Or making any of these changes may cause the problem. Some shooters have reported that larger capacity magazines are worse in this regard, and that P-mags work best with the .204 Ruger.