204 case damage caused by failure to feed.

S

sanddude

New member
AR15 204 Stag upper with M4 feed ramps and Rock River Arms Lower

I'm having some case damage and failure to feed issues. I have tried aluminum 5 and 10 and stainless 20 round cp mags, 20 round P-Mag. The P-Mag was the only one that did not have feeding problems but caused some case damage. Here is the photo my wife took to show the damage that the cases were getting. I'm open to all input on how to solve my issue and why you think it could be happining. /ubbthreads/images/graemlins/confused1.gif
Thanks /ubbthreads/images/graemlins/cool.gif
img_3785-1.jpg
 
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Could use a closer/larger picture.
Looks like a large semi-circular dent? Strange. While you're taking pics, shoot one of the barrel extension, inside the upper receiver.
 
Wow!! I have never seen that kind of case damage in any rifle. The location is just odd. It looks as if you may have somthing lodged in the chamber to cause that. I would think if it was hanging up that it would certainly effect extraction and cycling. Maybe our resident gunsmith pro's can identify that problem for you.
 
looks like a faulty chamber to me. A friend of mine had a .223 rem in mod 700 that turned some out like that but only after firing. Remington replaced the gun.

Dave
 
The half round dents are caused by the case being started in the chamber and the rear of the case not coming up to centerline as the bolt head is pushing it forward. The cure could be as simple as cleaning the chamber or an anti-tilt magazine follower like MagPul makes.
 
These shells are among the first 20 rounds shot through this brand new gun, that I might add is cleaned after every shot to my wife amazement. I will also say that I have had the same results with the next 40 rounds while I was trying different mags....From aluminum CP, to the 20 SS CP and the 20 P-Mags...Tried them all!
 
I would call Stag and ask [beeep]. And/Or you could send the upper to a good gunsmith and have it checked out. I have fired over 1/2 a million rnds through ARs and never have seen that......... Looks like those cases are shot. Did you buy that through Midsouth?

Good luck buddy, Keep us posted on how this turns out.
 
I agree it looks like the cartridge is not lining up with the chamber. Are your magazines seated completely? I know if I don't think to whack the magazine a bit it won't seat in all the way.
 
Dan is correct. It has been my experience that MANY things can cause this same situation with the .204 in an AR.

1) The mouth of the chamber has to be cut differently than a .223 chamber in order for it to work correctly. If the chamber-mouth on a .204 is cut just like a .223, you will get this same situation ALL the time. All that being said, being it's a commercial barrel, I would think that they have the chamber-mouth down.

2) Magazines can make a huge difference. I have tried different magazines and followers, and where I normally use Magpul anti-tilt followers, I have found that when you have a .204 upper with problems, the Magpul follower made the situation worse.

3) The lower receiver: I have had many times where a .204 upper will work great with one lower, and not so well with another. It has to do with how and where the magazine is held in the mag-well. Some people have issues with Olympic Arms lowers because their mag-well run to the tight side and some mags don't drop-free. This happens to be a real plus with the .204. I have yet to have any feed/function problems with a .204 and an Olympic lower. There are lowers that are quite notorious for mag-well geometry that may give you issues with a .204 upper.

4) COL can be an issue as well. I have found some combinations that cause this issue, where other loads work fine. When the bullet was seated just a little deeper and the COL shortened by .015", the problems disappeared. As the cartridge is pushed by the bolt into the chamber, the tip of the bullet strikes the top of the chamber-wall. With the rim of the case still held by the magazine lip, the bolt goes on to "bend" the case around the chamber-mouth, and you end up with marks on your cases just like these pictures.
 
I have tried both a stag and a rra lower
with the same results /ubbthreads/images/graemlins/shocked.gif /ubbthreads/images/graemlins/frown.gif
thanks
All that being said, being it's a commercial barrel, I would think that they have the chamber-mouth down

I never said it was a commercial barrel /ubbthreads/images/graemlins/crazy.gif
 
Quote:


I never said it was a commercial barrel /ubbthreads/images/graemlins/crazy.gif



Ooops! I guess I didn't read well enough. If the barrel was produced by even a good smith that has not done .204 barrels, the chamber-mouth may be the problem.
 
Quote:
I never said it was a commercial barrel /ubbthreads/images/graemlins/crazy.gif



So let me get this right... you have an upper with M4 cuts and a barrel that doesn't have them? That combination in the .223 or 5.56mm barrels has been known to cause bullet tip lodgings against the barrel at the chamber opening, jamming the bullets in or even bending the case. I would guess that the smaller diameter of the .204 bullet is probably allowing the bullet to pass right up pass the edge but in the time it takes it to start getting there, the bolt is driving the case forward quick enough to jam the case before it can level out into the chamber.

Just a guess.... /ubbthreads/images/graemlins/confused1.gif
 
I'm still working out some cycling issues on my 204 that I put together, but my cases look different from yours. I original put an oly non-adjustable pneumatic buffer in, it is very stiff and causes my AR to SHORT CYCLE, it cycles enough to eject the fired case, but not enough to catch the base of the next case in the mag, therefore jamming and denting the cases length wise, With a standard spring and buffer it works flawlessly! but then you have to deal with spring noise, I'm going to try my oly adjustable buffer next since it seems alot weaker than the non-adjustable, and see how that works next. In my opinion it looks like your cases are folding due to some sort of chambering problem.

Good Luck,
John
 


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