FTF /FTE on new DPMS Oracle

[commanderjjones]

I got the rifle about two months ago and immediately installed a lower profile gas block so I could install a 15" handguard. Other than bolt-ons (scope, bi-pod, etc...), the rifle is all stock and using the factory metal DPMS 20 round mag. I never shot it before installing the LPBG, so I'm not sure if it would have cycled fine in stock form.

Functioned fine for the first 20 rounds of cheap UMC FMJ's.

Shot 20 rounds of Rem CoreLokt 150gr and the FTE and/or FTF started, but only about every 4th shot or so.

Now shooting Federal 168gr Sierra Match Kings, it progressively got worse with the 3rd clip, until I was basically shooting a bolt action by the 4th clip.

Found a broken extractor spring when I took it apart to clean and lube. So I replaced that with a double spring from Sprinco and now it will eject again, but is still getting some FTF jamming. Difficult to tell but I think that maybe the bolt is not cycling far enough to eject the spent case, but far enough to feed a second, so they end up jammed together.

Where should I start next? Should I try a P-Mag, or could I have my gas block misaligned? I'll be honest that I installed the LPGB before seeing a couple of posts and videos about the importance of precise alignment. So I just centered the screws in the recesses, shoved it back against the barrel shoulder, and tightened it up (added blue Loktite to the screws). I really hate to take the guard back off to check that (just painted the entire rifle), but my gut tells me that's my most likely culprit.

This thing is really starting to piss me off. Never had ANY of my rifles give me this sort of issue (much less a BRAND NEW one), but I have a feeling that my ignorance may have caused this.

[edgecrusher]

As much as you are trying not to... it’s the obvious first check. Second is how well lubed are you running it? It should be near dripping wet, lots of big metal parts mating together. I would check your extractor and spring again. None of this is too uncommon. There was nothing wrong with what you did, you made your rifle yours.... but..... make sure you did it properly or else you have a big paperweight.

[commanderjjones]

Thanks for the response.

Yeap, unfortunately right now it's exactly what you said......a big paperweight. I could shoot quicker with a bolt action.

I lubed it up pretty wet. Not what I would consider "dripping", but what I would normally consider on the verge of excessive. I'm normally much more sparing on my other weapons.

I'll check the extractor and spring again before I do what I was dreading....taking the LPGB back off.

Is there a trick or alignment tool that I can use to make sure that the GB is "perfect", or should I just use the tape and pencil mark method? I'm not an AR guru, but am very mechanically inclined and have a good eye for level, plumb, and centered......so I doubt it's off by much. Then again, I guess it doesn't take much at all to block the necessary pressure.

[COBrien]

https://hbindustries.net/store/shop/ar15-gas-block-aligner-7-62mm/

[commanderjjones]

2 hours ago, COBrien said:

https://hbindustries.net/store/shop/ar15-gas-block-aligner-7-62mm/

Awesome! Thanks for the link.

Man, that's so simple that I can't believe that I didn't think of that. Hell, I can make one of those at home with a short piece of the proper size welding rod.

[mrmackc]

Hey guy you can have these ready to use for less than a Pepsi and bacon cheeseburger and fries, the welding rod may bugger up your barrel and hang up in the gas port.

[COBrien]

1 hour ago, commanderjjones said:

Awesome! Thanks for the link.

Man, that's so simple that I can't believe that I didn't think of that. Hell, I can make one of those at home with a short piece of the proper size welding rod.

These are designed with the sole intention of being able to be broken off by a cleaning rod. I'm with mrmackc -- I'd spend the little bit of money and get the right tool.

Plus, they come with 6 different diameters, for different port sizes. You can (ideally) do 6 rifles.

[commanderjjones]

15 hours ago, mrmackc said:

........the welding rod may bugger up your barrel and hang up in the gas port.

I realize that's a possibility, but thanks for the warning/advice. I'm a master metal fabricator, so I can do this without damaging the port or rifle.

I haven't had the chance to shoot it yet, but I'm almost certain that was not the problem. I marked the GB before I took it apart and it was definitely indexed correctly. Plus the port in the gas block is more than double the size of the barrel port, so alignment would've had to have been significantly off to be blocking any of the barrel port. I'll shoot it tonight (if I don't get rained out) to confirm, but I'm afraid that I'm still looking for a solution.

I forgot one VERY important detail. It double fired 3 times (6 shots) in the last test of 20 rounds.....after I installed the new double extractor spring. I'm far from an expert, but could it be possible that it's short cycling so short that it wasn't engaging the disconnector? Am I wrong in thinking that a short cycle "could" cause both issues (FTE/FTF jam and the double fire)?

I'm going to order another mag to test (still using the factory DPMS metal 20 round). Any recommendations on the most reliable?

[98Z5V]

Did you put this rifle together?

Disconnector spring looks almost identical to a bolt catch spring - but the disconnector spring has one larger coil on one end of it - and the larger coil gets installed facing down. "Snaps" in to the trigger body.

1. You can put it in upside down, in the disconnector, and cause the disconnector to not function properly.

2. You can install it in your bolt catch, and jam up the bolt catch when the larger coil gets stuck.

3. You can mistakenly install the bolt catch spring in the disconnector, and it can fall out - because it doesn't have a larger coil to keep it in place.

The double-firing is a big issue...

[mrmackc]

3 hours ago, commanderjjones said:

I realize that's a possibility, but thanks for the warning/advice. I'm a master metal fabricator, so I can do this without damaging the port or rifle.

I haven't had the chance to shoot it yet, but I'm almost certain that was not the problem. I marked the GB before I took it apart and it was definitely indexed correctly. Plus the port in the gas block is more than double the size of the barrel port, so alignment would've had to have been significantly off to be blocking any of the barrel port. I'll shoot it tonight (if I don't get rained out) to confirm, but I'm afraid that I'm still looking for a solution.

I forgot one VERY important detail. It double fired 3 times (6 shots) in the last test of 20 rounds.....after I installed the new double extractor spring. I'm far from an expert, but could it be possible that it's short cycling so short that it wasn't engaging the disconnector? Am I wrong in thinking that a short cycle "could" cause both issues (FTE/FTF jam and the double fire)?

I'm going to order another mag to test (still using the factory DPMS metal 20 round). Any recommendations on the most reliable?

Master Metal Fabricator, is that kind of like a welder?

[commanderjjones]

5 hours ago, 98Z5V said:

Did you put this rifle together?.............The double-firing is a big issue...

No, I didn't put it together. Other than the LPGB, is it a factory fresh Oracle......only about 2 months old.

Yeah, double firing is a HUGE concern. Couldn't help but think about the possibility of it emptying a clip without me being ready.....or possibly worse.

I've got a LaRue trigger on order (ordered it about 4 weeks ago), but haven't received it yet......and I haven't been into or disassembled ANYTHING in the lower yet.

[commanderjjones]

Just a good news update.............

Evidently the LPGB alignment was causing the FTF/FTE issue because it went away after I removed and reinstalled it. I measured it as precisely as I could (with digital calipers) and swear it is back in the exact same spot as it originally was, so maybe there was a small piece of trash that was dislodged in the R&R process??? At any rate, that is resolved.

The double fire issue still persisted in the initial test, then I discovered that the hammer pin had worked it's way loose. Although I hadn't done anything to cause that to happen, failure to catch that was my newbie mistake. After correcting that, it is now functioning 100%. I fired 2 full mags of 20 rounds each (1 mag fired slowly with pauses between each shot, and the other in rapid succession) without a single firing or feed issue.

At last, I'm finally confident enough to step in the woods with this thing. I'm a happy camper. 

 

[98Z5V]

Standard mil-spec trigger in it?  If so, that hammer pin should have a groove in it's center, that the hammer j-spring locks into.  It shouldn't be able to work itself out of there, if it was locked in with the j-spring.

If the hammer pin does NOT have a groove in it's center, and only grooves on the outers - it's a trigger pin.  If that were the case, you could probably find the hammer pin installed in the trigger...

Most of them look like these - and you put them where ever...

There are some that are manufactured as hammer-only and trigger-only pins, though.  Worth checking.  You can inspect the j-spring in the hammer at the same time, that way.

Edited April 30, 2018 by 98Z5V

[commanderjjones]

1 hour ago, 98Z5V said:

Standard mil-spec trigger in it?........You can inspect the j-spring in the hammer at the same time, that way.

 

Thanks a lot for that info'. I'm still learning.

Yes, it's the standard trigger. It seemed to "pop" into a detent when I pushed it back in and it didn't show signs of movement after 40 rounds. I assume it's good for now, but I'll definitely keep a very close eye on it. I've got a LaRue trigger on the way (it's been on order for 6 weeks today), so I'm hoping that will be here any day now and probably won't bother taking the trigger apart until I receive the new one.

 

[COBrien]

The LaRue MBT comes with a nice set of trigger and hammer pins, so that should fix any issues you have.

However, if you continue to have issues with the hammer and/or trigger pin sliding around, you can always fix it for good with a set of anti-walk/anti-rotation pins, like the ones from KNS Precision. I've put them in both of my builds just for a little extra insurance. $30ish is worth it, to me.

[commanderjjones]

13 hours ago, COBrien said:

.....you can always fix it for good with a set of anti-walk/anti-rotation pins, like the ones from KNS Precision. ......

Good to know that's an option.

So if there are companies making pins that are specific to anti-walk and anti-rotation, I assume this must be somewhat of a common issue? Maybe not "common", but also not highly unusual?

Although I already knew it's something that anyone should always do, I'll definitely be giving my rifle a quick "once over" from this point forward. I think it's sort of like driving a car.....we all know you're "supposed" to always do a quick walk around before driving it, but how many people ACTUALLY do that?

[98Z5V]

It doesn't happen often, at all, with quality parts and proper assembly.  It's not something you'll see from someone, everytime you go to a range.

Anti-rotation pins came about like this: Registered Full Auto receiver, you want hammer pin holes egged out over time, due to pin rotation, on that expensive receiver that you can't replace? 

Another great use - pistol caliber carbines with blowback operation are hard on hammer pins.  These go a pretty long way to solving that, but it's not 100% all the time everytime. 

 

[308kiwi]

6 hours ago, 98Z5V said:

It doesn't happen often, at all, with quality parts and proper assembly.  It's not something you'll see from someone, everytime you go to a range.

Anti-rotation pins came about like this: Registered Full Auto receiver, you want hammer pin holes egged out over time, due to pin rotation, on that expensive receiver that you can't replace? 

Another great use - pistol caliber carbines with blowback operation are hard on hammer pins.  These go a pretty long way to solving that, but it's not 100% all the time everytime. 

 

Add to that, most 'drop in' cartridge type AR triggers don't use the hammer and trigger springs to retain the pins like std triggers do, anti walk/rotation pins solve this issue.

I've seen a few hammer pins break through the middle groove and start walking out of the lower, like 98Z5V said, 9mm carbines are good at this. As an aside, Glocks are capable of doing this as well, the top  pin has a groove machined in it that locks into the slide catch spring, have seen two of them break through the groove and walk out of the frame on high round guns. Machine a groove in anything and you've created a weak point, same reason toilet paper always tears at the perforations

Edited May 1, 2018 by 308kiwi