AR Sponsor
Posted: 6/17/2010 7:25:23 PM EDT
|
The gun is a DPMS ap4 with a 762 chamber. It runs flawless with 308 ammo, not 1 problem. With surplus I will get FTE's. It will strip a new round with the empy jammed up in the upper reciever. It happens with the factory mags as well as P-mags. It happens with radway and dag. I think its extractor related and am going to get a new extractor and spring, but want some more input.
Specifics are it will leave a spent case in the upper and strip a new round and jam up. The bolt will always lock back on the last round with surplus, so I don't think it's under gassed. On the spent rounds that are jammed up in the reciever, there is no mark from the ejector, but there is a really slight ejector mark on the cases that do make it out of the rifle. The rims on the brass are not beat up from the extractor, so I don't think it's a timing or overgassed issue. The extractor does have a polished look to it on the lip, but no chips out of it, and on spent 308 and 762 rounds you can see a slight inprint from it on the ones that eject. I can feel it catch my fingerprint groves if I drag it across my finger. The extractor spring has an inner and outer spring, not a single. I tried adding an o-ring in ar-15 fashon, but made no difference, but I could not feel a difference pushing on the extracor with the o-ring, so I added a second o-ring. Have not shot it with the second o-ring, but it feels more like a nice 556 setup now with the second o-ring, not nearly as soft as before. The gun is kept clean and lubed properly. Any input? Thanks for looking. Dan |
|
Quoted:
The gun is a DPMS ap4 with a 762 chamber. It runs flawless with 308 ammo, not 1 problem. With surplus I will get FTE's. It will strip a new round with the empy jammed up in the upper reciever. It happens with the factory mags as well as P-mags. It happens with radway and dag. I think its extractor related and am going to get a new extractor and spring, but want some more input. Specifics are it will leave a spent case in the upper and strip a new round and jam up. The bolt will always lock back on the last round with surplus, so I don't think it's under gassed. On the spent rounds that are jammed up in the reciever, there is no mark from the ejector, but there is a really slight ejector mark on the cases that do make it out of the rifle. The rims on the brass are not beat up from the extractor, so I don't think it's a timing or overgassed issue. The extractor does have a polished look to it on the lip, but no chips out of it, and on spent 308 and 762 rounds you can see a slight inprint from it on the ones that eject. I can feel it catch my fingerprint groves if I drag it across my finger. The extractor spring has an inner and outer spring, not a single. I tried adding an o-ring in ar-15 fashon, but made no difference, but I could not feel a difference pushing on the extracor with the o-ring, so I added a second o-ring. Have not shot it with the second o-ring, but it feels more like a nice 556 setup now with the second o-ring, not nearly as soft as before. The gun is kept clean and lubed properly. Any input? Thanks for looking. Dan What's the round count through the rifle ? DPMS are notorious for rough chambers . What type of 308 is working,bullet weight ,ect.? |
Actually the chambers are not "rough" they are minimal chambers which do give excellent accuracy 
Now if you have problems with 7.62x51 surplus ammo there is a fix . First clean the chamber using a chamber brush, then get some J B Bore cleaner and wrap a patch around a suitable brush with the J B and gently rotate the brush with your cleaning rod. This will polish the chamber and enable you to use surplus.Now flush the chamber out with some bore cleaner and might as well clean out the bore while you are at it to make sure all the JB is gone. If this does not fix it contact DPMS and they will fix it for you 
John |
The gun has probably almost 1K through it. Any 308 works in it, winchester , remington, and a couple types of ppu, all from 150-168 gr. I think the extractor is worn and has weak springs, it just feels a lot softer pushing on the extractor than any of my ar-15's. I checked out the chamber and it nice and smooth, shells slide in and out of it nice. The last time I had a rifle with a tight chamber the extractor was messing up the rims on spent shells, there are no marks on the rim on the shells that jammed in this rifle. I know 7.62 and 308 are slightly different in specs, but do you think it could still be the chamber even though the rims are not torn up? I just find it baffling that it only happens with surplus
Edit. I really don't want to mess with the chamber, so if it's not extraction issues, no more surplus 
|
| It was a weak extractor spring causing the FTE's. It felt really weak compaired to my ar-15's when pushing on it at the face of the bolt. So I o-ringed the spring in ar15 fashion and it made no difference, still felt soft. Stuck a second one one the spring and it felt like a 556 gun with the spring, ring and little plug. Still easy to put the pin in too, don't have to press too hard. Shot 60 rds of radway and dag through it tonight and not one stop, much better than a fte after every few rounds. Brass is not getting torn up either from the chamber being too tight. still don't understand why it only did it with surpluss though. Maybe the slightly different rim or slightly lower psi of the load. |
AR Sponsor