HELP .204 AR Problems

5

5Bcoyote

New member
I just finished an AR build in .204 Ruger. I am having problems with proper feeding. It is making a large half moon shaped dent just below the shoulder. I have tried a few different magazines and shortened the COL but nothing seems to work. Has anyone ever experienced this? Any input on how to solve this issue would be greatly appreciated.

YHM Lower, YHM Upper, 24" Shilen drop in barrel
 
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This is the first one I have built. It was with the help from a friend that is a gunsmith. It seems to be somewhat of a common problem with 204 on the AR platform. Some say switching lowers can alleviate the problem. I'm trying to see if there is possibly another solution before I go spend the money on another lower.
 
The upper and the barrel have M4 feed ramps and seem to be properly cut. I have tried Pmags and metal seem to be getting the same result.
 
Will do. I only have been using reloads. I created some dummy rounds to try and work on the feeding problem.

Load:
32 gr. Nosler
2.250 COAL
 
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What magazine are you using? I've heard of the issue your having with certain magazines. I think the lancer magazines were the answer to solving your problem.
 
I know the exact problem you're having. My 204 doesn't do it, but one of my 223AI's does. One of the AI's and the 204 were built with DPMS slick side high rise uppers, and they have always run fine. The one that will hickup once in a while is a regular A3 type. I never could pin-point the issue exactly but I lowered the odds significantly by going thru mags with dummy rounds like you're doing and finding the mag that worked the best. I think it's a round that's right on the edge of running right or not and tolerance stacking a certain way will get you.
 
Ok i would check to see how far you are pushing your shoulders back. To measure this take a fired case and a 9mm Luger or a pistol case that is big enough to slide over the neck and touch the shoulder now measure this with your caliper and remember this measurement. Now size your fired case and take that measurement again. I think for an ad to reliably feed you need to push your shoulder back .005-.007. I had some issues with my 6x6.8 I was only pushing my shoulders back .003 then after a couple of few firings they wouldn't feed. What has happened is my cases were work hardened and were springing back enough that they wouldn't chamber or eject easily, or sometimes wouldn't feed and let the bolt close all the way. I annealed my brass and started pushing shoulder back a let further and haven't had an issue since. Now I don't know if this is your issue or not. How times has the brass been loaded? Has this rifle always gave you these problems or has it started acting up after working for awhile? Also I put a little piece of the fuzzy side of Velcro on the shell deflector on mine to help with it denting cases when they get ejected. Sorry for the long post just giving you my experience in my ad not feeding hope you get it figured out. Good luck post your results when you try something else or get it resolved.
 
Before you get too involved in second guessing your reloading, try a box of factory rounds...If the same problem exists, the problem is mechanical with the weapon....If not, then tear apart your reloading/brass prep procedures....Taking a shotgun approach to a problem seldom finds the real culprit...

My .204 AR was put together by a professional and with the exception of using the polymer mags, any problem has been with my brass prep and that is when they fail to go into battery (headspace) that a die adjustment fixed...Never experienced what you are describing...

Mine is a 'slick side' as well,,,,
 
His problem has nothing to do with shoulder set back or any of that. The rounds aren't even making it all the way into the chamber. They are getting caught cock-eyed when entering the chamber. The base of the case is not sliding up the face of the bolt to be pushed straight in, it's getting caught then the force of the bolt shoves it into the bottom of the chamber entrance and dents a little half moon just below the shoulder. It's an issue with straighter walled cases like the 223 ai and 204.

One thing you can do that won't hurt and might help is radius the end of your ejector rod. That made my lbc feed well whereas before it was getting hung up on chambering. Other that that, and trying different mags I don't know. I was tempted to put slightly more bevel and polish on the bottom edge of the chamber mouth but didn't.
 


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