I just received my DPMS AP4 and went out back and fired 40 rds through the barrel cleaning after each shot. As I examined the brass there was a sharp indentation on each empty. The edges of the shell deflector are very sharp. I went back to the safe and checked my MP15 and saw that the edges are somewhat rounded. I was thinking of taking the sharp corners off the AP4 deflector.  I wanted to ask if anyone else has made this modification? I do not want to mess anything up on my rifle.

I also noticed the bolt looked just like it did when I started after the 40 rds. I cleaned and lubed everything with Mobil 1 before I started. Of course, 40 rds is not a real teat but still I was pleased.

I will mount the scope tonight and sight in tomorrow. THe lake is full of turtles and I plan to decrease their population.

Thanks, Malcolm

Where is the indentation that you are concerned about on the empty cases?

Here is a photo. Some strikes are light b ut the heavy ones have a pretty good dent i n them from the sharp edges of the deflector.
Thanks, Malcolm
http://i137.photobucket.com/albums/q225/revrun4/20120403_2.jpg

I was just going to post a similar thread in regards to this as I'm having the same problem with my build.  My case markings on the body are almost identical to yours and at the rim edge I have 2 marks very visible––looking closer your cases have the marks on the rim also.  One thing I noticed while breaking my barrel in is the cases were landing out in front of me to the right while usually they end up just behind you.  Where were your cases landing?   Maybe the you should edit the title to say ejection issues???  Pics for comparison...

The cases––


Where the brass is beating the deflectors edge––

My DPMS does it also. Some people put mole skin on it. I ignore it sizing takes 90 percent of it out anyway. My rifle also does not do it as bad now that it has a few thousand rounds through it. It has a nice rounded shiny edge.

AL

I'm guessing your brass also ejects in the 1 - 2 o'clock area. My brass gets the same dents and I know that it needs a heavier buffer. If i was you, I would try an H or even H2 buffer and see how the case damage changes.

Very close, actually about 3 o'clock. I am new to the AR-10 thing, what is an H or H2 buffer and where do I get one (edit:just found them, will the M4 style work for the LR308?). I have read about the adjustable gas blocks too. Many thanks, malcolm

No, the M4 type will not work. You can get a heavier .308 buffer from Slash. You could also put a piece of self adhesive velcro (loop side) on the deflector. That should soften up the dings without having to take any metal off or cut into the anodizing. Realistically, the dents are not an issue, but yeah they bother me too.

Hmmmm, gonna go check my 308 AP4...

~WTS

or try an adjustable gas block.

gpu

I am looking at the JP adjustable gas block. I also want the the Magpul ACS stock so I will have to research the right buffer. I did read last night that the wrong choice could ruin your whole day. Malcolm

After reading several other threads on other forums I ordered the JP adjustable block today. While I was at it I ordered a new trigger and Limbsaver recoil pad too. Recoil never bothered me when I was young but age and arthritis almost demand a recoil pad.
Thanks for all the input and I still may change buffers too.
Malcolm

Is it possible to add more weight to the factory rifle buffer?  Looking for a cheaper solution then Slash's buffer but not finding much for the .308.  Found an adjustable gas tube at Midway USA that might be a better option than the adjustable gas block.  My barrel/handguard combination does not have much room for anything much bigger.  Link to the adjustable tube-

Adjustable Gas tube

If you go up to 0:30 in this video there is slow motion video of the ejection sequence on an M16A1.  Even with no case deflector, an A1 style rifle can produce the same case dings, and if you watch the video it should be obvious how they happen.  Changing the tension on the ejector and/or extractor is the best way to alter the exact position and angle of the case when it hits the rear of the ejection port.

Out of curiosity I have experimented with some of the hypothetical fixes to this occurrence and found most to be ineffective.  I was not able to alleviate this occurrence in an upper that produced it reliably by altering the buffer weight or configuration, or even changing from a carbine to a rifle length buffer system.  I also experimented with adding spacers at the back of the buffer tube to limit the bolt travel, without making a notable change in the case dings.  Changing to a different BCG though did.

Interesting video.  My M16 upper (void of a brass deflector) which has a M4 barrel I turned down to .625 ejects nicely and I'm left handed.  Those cases should be enroute to my neck but they go to the side without any case damage.  When I look at that carbine length system and my mid and rifle length systems I don't have any case damage with nice ejection which to me is out of my head/neck area as I'm a lefty and cases landing in the same spot.

 As you stated "Changing the tension on the ejector and/or extractor" seems in my mind a viable solution to this problem.  A little less tension would let the case eject a little sooner??  I will search for information on this but if you have some knowledge regarding this subject enlightening us a little would be greatly appreciated.

 I look at the price of the good adjustable gas blocks, the buffers, the buffer springs, and the tubes and a guy could have a nice start on another project.  This does not sit well with me as this is by far my most expensive build and I would like to "protect my brass"

Adjustable gas block will fix that. I have one on my DPMS pattern 308.

If your extractor has an insert, you could try removing it, or a different (lighter) spring, but don't F with the extractor claw.   A too strong ejector spring combined with high bolt velocity is probably the culprit.  The adjustable gas block will take care of the velocity.  That may be enough.

Try this:  Coat the face of the deflector with something that will transfer onto the case.  I recommend Dykem.  Manually and quickly extract cases from the chamber (this is to test whether the ejector by itself is causing the strike) and see if they are still hitting the same place.  If so, then the gas block won't fix the problem.  It will slow the bolt down, which overall is good, but if the cases are hitting at manual velocities, the ejector spring is the cause.  Adco sells a bolt dis-assembly tool to make this easy.  

Unfortunately, I don't know what spring to use.  DPMS doesn't have one on their site.  Which might mean it is an AR15 spring.

I thought 5-6:00 ejection is short stroking unless its the ejector spring as stated above? Bouncing off the deflector and then forward is still a 5-6:00 ejection ?

I installed the JP adjustable gas block and the ejection is at 4 o'clock and the dent is almost undetectable. I also installed the JP 3.5 trigger. I was somewhat apprehensive about the trigger installation but it went well. The trigger is great with a clean break and no over travel. Just for grins I tried some Remington Managed recoil 308 and was able the adjust the gas block to operate the action with the reduced power cartridges.

Thanks for all the suggestions. Next is a good scope & mount.

Malcolm