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Posted: 12/28/2007 7:10:25 PM EDT
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I have a DPMS panther lite 16, chambered in 5.56. Today at the range, I fired Georgia arms .223 through it for the first time (I normally fire Remington 55gr .223 FMJ). After 3 rounds, the rifle failed to extract the casing. When I cleared the mag and casing, I noticed the extractor ripped through the lip of the casing. I figured it was a one-time occurrence, so I continued to fire. Every few rounds, I encountered the same issue. I am positive that his issue is not due to cleaning. I spent 6 years in the military and had just cleaned and lubed the rifle the previous night. Just to be sure I field stripped the AR after the 3rd occurrence and found no noticeable issues. I had 30 rds remaining of the Remington ammo which my rifle fired flawlessly. What could cause this? Could it be just crappy ammo or is this a larger issue? I should add that my friend has a Smith and Wesson M+P AR15 and fired the Georgia ammo without any issues. Thanks in advance for any insight you can provide. |
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First off, I'm pretty sure that you barrel/chamber is 5.56 Nato, even if stamped 223. The only barrels that DPMS chambers in 223 on request is their 1-8 CMP barrels. If the rims are being torn off, then chances you have problems with either over pressure, over function or just a chamber that is still rough/tight and has not been polished out through live fire. Have you check the spent primers to confirm working or over pressure, and if they did check out normal (spent primers not flattened out), it could be that the loads where loaded with too slow of powder allowing the bolt to unlock too soon causing the extracting with the case still too pressure bound to the chamber walls. Note: with the use of slower powders used, the burn peak dwell is much closer to the gas port that if the powder was of the correct burn for the action. This really doesn't always translate to a faster moving bullet, just more pressure down the gas system to unlock the action. IN the below link, check out the charts in regards to barrel length and unlock pressures. Also, when you look at the charts, keep in mind that the bell peak is normal power, while powder that burns slower than this would have a longer dwell burn causing more residual pressure at the port. Really, when all else fails, just post a few photo's of the spent case (back and side veiws) and we can tell you just what is up with the rifle/ammo. |
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I went to the range today. fired 200 rds of remington .223 without any issue. Switched back to the Georgia Arms in order to get a malfunction...... Only took two rds. Here is the spent casing. Please note that the scratch in the primer was caused by the live round attempting to feed while the spent casing was still cambered. http://i60.photobucket.com/albums/h31/captainswife/Brass1.jpg http://i60.photobucket.com/albums/h31/captainswife/Brass3.jpg http://i60.photobucket.com/albums/h31/captainswife/Brass4.jpg |
Timing issue? Extractor seems to be working fine. Does this spent cartridge fit good in the chamber and does it extract easily? It does not look like overpressure so look for possible timing problems (to large of gas hole, to light of buffer, bad or short spring, etc.) |
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The short version, Your chamber is a bit on the rough/reamer-grooved side (see the rings in the spent case brass side starting just above where the inner web stops on the case). As for the GA ammo, although it's not going over max working pressures, it is loaded with slower than normal burning powder causing too much residual barrel pressure at unlock for the spent case to be extracted cleanly. The fact that the chamber is a tad on the rough/grooved side is not helping the problem out a bit. The solution is to get DPMS on the phone regarding the chamber. If the chamber is not chrome plated, then the barrel may be savable. If plated, it needs to be replaced since any form of cleaning up the chamber will remove the chrome plating. From there with a smooth chambered barrel, you can retest to the GA ammo to see if it's usable, or will need to be returned. |
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