I've owned my AP4 for about 3 years. I use this rifle for hunting and only use premium hunting ammo. For years I used Hornady's Custom SSTs and then switched to their Superformance GMX. The GMX, I was not to happy with it's performance, so I now use Federal's Trophy Bonded. I must say, with any one of these bullets, I'll get under 1" at 100 yds. This rifle is very accurate and has been a champ for hunting. Here recently, I've been having cycling issues. Not sure the proper term, but the issues I've been having: Double Feed, 2 bullets trying to load in the chamber at once. Now more so, it's not cycling another round into the chamber (making my follow up shots, well, impossible).

I've read that this isn't an "uncommon" issue with the AP4s, as well, people suggested to change the buffer to Slash's Heavy Duty. I don't mid buying a heavy duty buffer, but has anyone had this same issue with this rifle? If so, what did you do to correct it?

Thanks!

While I think investing in a Slash CAR-10 buffer is a good investment, I think you issue may lie with your magazine.  Have you tried a few different mags to see if this solves your problem?

I've seen this - armorers in here suggested a fix and it cured it for me. failure to extract, due to weak/failed extraction system parts. Extractor jerks off the rim of the case prematurely before complete extraction and the spent case is not ejected properly. Get Crane o-ring kit from Bravo Co. Pull your extractor and spring and make sure everything is clean, lubed, extractor lips ok, pivots freely on the pin - polish up if neccesary. Assemble with new spring + little rubber spring insert + Crane o-ring. I've had mysterious multi-symptom feeding issues like yours and this cured it - very reliable w/no ftf's since. Weak extraction causes all sorts of crazy stuff to happen - especially when the round disengages from the extractor mid-stroke somewhere....

edited to add: also dont forget to check/clean/lube ejector while you are at it...

What other advantages will I have with the Slash CAR-10 Buffer? I don't mind making the investment (especially if it cures this issue). But, wasn't sure what else I would gain from it?

Yes, I've used two different factory mags, same result....

I did send DPMS an email about this issue, here's their response:

The most common issue with the 308/762x51 rifles is under lubrication. Please try to lubricate the entire carrier assembly once with good heavy gun oil. That fixes close to 95%of the issues right away. Completely drench the carrier assembly in the oil and let me know how that works. If that trick does not fix it please let me know and I will get the rifle back here to look at for you.    

Thanks,
Mark Imholte | Customer Service
DPMS Firearms,
3312 12th St SE
St. Cloud, MN 56304
Phone:  1-800-578-3767
Fax:      1-320-345-9249

I'm sure these guys know what they are talking about... The comment about "Completely drench the carrier in the oil", kind of makes me a bit nervous. Is this common procedure to do on an AR style rifle?

I would suggest a thorough trouble-shooting, after cleaning some key areas.  I saw this happen with a gun that had been used in a river crossing, and there was mud in the relief hole in the back of the extension tube.

Check its performance with different mags, starting with 1 round checking for bolt lock.  Then load 2 and check for proper extraction, ejection, feeding, and chambering.

If it fails that, break it down and look at the gas block-is it secured still?  Are there significant signs of excessive gas leakage?

Is the carrier key still properly attached to the carrier?

After about 2,000 rounds through the DPMS bolt carrier group, you need to replace your ejector spring, or at least clean out the ejector channel in the bolt.  You might be very surprised what you will find in there.  A buddy of mine found brass wrapped around the spring filling in the space between the coils, which caused ejection and feeding problems exactly as you have described.

The extractor spring needs proper tension-not too much, or too little.  Trouble-shooting your individual rifle will let you know where that balance is, and using the extractor spring upgrade kits often creates more problems on top of your original problem.  Buying a buffer will do jack and squat for your ejector if it's clogged, or spring broken.

I suggest a Bolt disassembly tool that will allow you to easily remove the ejector roll pin.

If you have been running your own loads in this rifle, I bet that your ejector is the likely culprit.  Let us know, and check the ejector spring condition anyway.

Hi my son-in-law is having the same problems with his Bushmaster Orc. I assume it has the same BCG (as the DPMS). Does the Armalite (AR10) extractor spring kit fit this bolt? I assume the kit from bravo company just fits AR15 bolts

I was going to suggest he get the Armalite carbine buffer tube/receiver ext, their carbine buffer and spring, I was under the impression that DPMS rifles ran better with the longer Armalite buffer tube etc. I don't want to get this stuff if a spring kit will solve the problem.

I appreciate any help.

I also have a Bushmaster Orc but mine runs fine.

According to DPMS, they are telling me to oil the snot out of it and that has cured 95% of the issue with cycling properly... It's worth the try, cheapest route so far..

Also, I found this the other day:
http://762ar.com/general/dpms-chrome-versus-phosphate-bolt-carrier-group/

As more guys dive in to building their own DPMS compatible 308 AR another detail is becoming apparent. These weapons clearly function better out of the box with the chrome bolt carrier group than the phosphate coated counterparts. The reason is simple, lubricity. These weapons have a lot of bearing surface. Bearing surface equates to friction.  This is also why these weapons need a lot more oil when new. Quite simply the chrome bolt carrier group moves much more easily than a phosphate coated one in the upper receiver.

I will try that! Last time we were out we oiled the BCG pretty good and still had cycling problems. I will try to lube it better next time out.

Thanks

Oil the $hit out of it, worked on mine

i also suggest  the chromed bca's mentioned above - have converted all mine over; bought from fulton armory - they are slicker and clean easier, for sure.

i will second what the guy above mentioned - i'll bet you a case of beer its that exact failure to extract/eject issue he described. I had these exact ftf's with new rifles and bca's. every carrier i've bought came with an inner and outer extractor spring. after trial and error, i found the way to go is replace the inner spring with the little rubber plug, and run the o-ring. 100% reliable now. i have verified this by jerking all this back out and putting the stock parts back in and I get ftf's again. ymmv. no amount of oil will stop extraction malfunction. nor will any funky buffer cure it. just my personal experience and advice,  take it or leave it.

DPMS - Thanks again for clarifying this again and sharing the link... I will drench the carrier in oil and see what happens. I have no doubt if the problem continues, that DPMS will do their best to help me. This rifle is the most accurate rifle in my safe and my first goto rifle when I plan to hunt.

How many rounds have gone through it?

I had one DPMS LR-308 that had an out-of-spec extractor.  They sent me a replacement free of charge, which fixed the failure to extract problem, so they do respond to customer service issues in my experience.

I would guess about 200 rounds or less. I only use this rifle for hunting, no spray and pray or field day at the range...

At 200rds, you should not be having issue with the ejector, unless you loaded some insanely hot loads that blew primers or extruded the brass into the ejector channel (seen it-done it).

The other possibility I can think of is the gas system.

As for lube, I always lube the action with Slip 2000, which is a thick, high viscosity lubricant that works great in AR's, both big and small.  My BCG is very wet.

I've only kept to factory hunting ammo, nothing crazy... I'll looking for the Slip 2000. After I get a some free time, I'll lube it up really good and see how she does. Thanks for the info..

Are you using a 5 round magazine? If you are who is the manufacturer?  The AP4 uses a carbine length gas system. To correct my extraction problem I switch the buffer tube to the Armalite buffer tube (longer) using also the action spring along with the H3 buffer.
     Double feed problem was the DPMS five round Mag. Matter of fact the CProducts five round mag was a little better. As for the extractor mine was good and still is.

     RJ

Certainly try out a Magpul magazine.  Some DPMS mags are meh.

Take a look at your brass.  Is it scored up (deep scratches along the case body)?

Clean your weapon thoroughly.  See if you can see tool chatter (look like rings/scratches) in the chamber.

If so get the chamber polished.

DPMS will help you out to fix any problems.  

I did my own chamber polishing with a flex hone and it made a world of difference.

Mine are the factory magazines, hold 19 rounds (or something like that). I might invest into a CProduct mag, just to test out.. Thanks!

Magpul is always been good with their products. As for scratches on the casings, I have not noticed (but I haven't been looking either). Next time I pay attention to it...
I'm pretty good about cleaning my weapon and oiled. But, maybe lighter on the oil than what DPMS recommends. I'm going to drench the carrier in oil and see what that does.
Thanks!

CProducts is no longer in business.  Magpul 20 round mag's are good, but I can't with those.

  RJ

UPDATE:
 I did what DPMS guys told me to do. I drenched the carrier in Oil and off to the range I went... Not one cycling issue, which I'm satisfied that this cured the problem.

Thank you everyone for your assistance and input.

You might have a weak buffer spring.  I have hear of buffer going bad after so many rounds.  Check out www.davidtubb.com for buffer springs

Yes.

Good to hear you got it running OP..

Rumor has it that an A2 stock with the normal rifle buffer also fixes some issues concerning Carbine stock feeding and extraction woes..

Maybe thats why the heavier buffer you hear works actually does..

I went A2 stock on my DPMS LR-308 as I wanted to avoid any issues..

1300 rounds and 0 issues.. from Hornady SST/TAP to Mil-Surp.. even with TulaAmmo..  .. and no drenching required.. I was using Miltec TW25 and a few drops of oil.

We got  the bushmaster Orc running good as well. Drenched it in oil and put some grease on the lugs then cycled it 50 times. Then we cleaned and re-lubed. I took it to the range, it ran with no problems! I also put bravo extractor upgrade kit in it.

Thanks!

I notice that many of the DPMS LR-308 models don't have a bolt assist.  With the cycling issues mentioned here, wouldn't a bolt assist be something nice to have in a self-defense situation?  Or do the cycling problems mentioned not involve out of lock bolts?

Not for a double feed like the OP had. The FA is only good if you have bolt that does not lock up or you need to load quietly.

Double feed.  Type 3 stoppage. I skip the tap, just drop the mag, rack roll and observe, charge three times, lock it back, new mag in and paddle.  You back at it.  Don't even worry about retaining the mag most of the time it is the culprit.

P-Mags are great. If you can use the full 20 round one for hunting in your state go for it.  I can but only load 5, all that ammo gets heavy and is not needed.  You can get the cut down or blocked too.

I agree that a lot of rifles, both new and old, require proper lubrication. But, no one likes to have oil weeping out of every pore and getting on their hands and face.  Now a disclaimer;  I'm in no way involved with the following product or anyone who sells it. I just know it works and have sung its praises a many forums over the years:

I'm going to recommend you try the Miltec 1  http://www.militec1.com/   It's a modern, 'dry' lube product that has worked in both modern rifles like my array of black rifles (including my .308) as well as my Garands, carbines, etc.  You clean it throughly to rid it of any other lube and then apply the Miltec, then wipe off the excess.  You'll think that it's dry but this stuff seeps into the pores of the metal....even the barrel.   Anyone who shoots a Garand knows how vital proper lube is and slathering on grease in the channels is the only way to get it to cycle correctly and throw the brass as the proper angle.  Miltec works to spec in the Garand and it's worked perfectly for my black rifles as well. (I've shot both at Camp Perry, too.)  And, it doesn't weep all over the place.  If you're having lub issues and don't want to constantly be reoiling I'm going to recommend that you give this stuff a whirl.  It also will not attract dirt or dust since it is 'dry'.  Our troops use is (I know because I just met an Afgan vet who told me about his experience with it) and Miltec even gives the stuff to them for free!  At their website you'll see dedicated photos by them.  

Anyway, I just thought I'd drop that info here.  This stuff is amazing and anyone I've turned onto it has thanked me.  I've used it in over 25 different semi-auto MBRs from all over the world over the past 15 years with 100% success.  I now use it exclusively in my DPMS LR308b and it's been perfect.

Rome

Ive had my lr308 for about 2yrs now. I had issues as well with ftf-fte.

In my case, I look,d inside the chamber with a HD Snap-On bore scope, located the problem right away. After some cleaning of the chamber with a slow speed drill,real fine lapping compound, then some more cleaning with JB bore cleaner, it took the ruff spots out of the chamber. In my case, without a dought, the chamber needed some attention. Course, it help,d having a HD bore scope. its like performing an endoscopy on your barrel.

In my mind, I never went the "run the rifle wet" routine. sure, theres components that need some lubricant, but not in the chamber. Alls oil does is attract powder fouling/brass debres quicker..inmy book..thats a no-no. Il,l use dry lube with teflon on the trigger mechanism as to not attract powder fouling or brass debres.

I havent had a ftf-fte since. the rifle turned out to be a good tack driver for the money
Im shooting that rifle so much that its putting a dent in my pocket due to the sickness we all know as "reloading"....i cant stop though!....I need help!............"hellow, dr Phil"?.