DPMS .308 FTF ever round???

[VIVALABASS21]

Hello all,

I just completed my first LR308 using mostly DPMS parts.  Once I charge the BCG it will shoot the first round fine and eject the empty casing but will not feed the 2nd round or it will feed it half way and and the bolt will be locked halfway open.

 

I purchased the complete DPMS oracle upper already assembled so I assume it shouldn't have any issues... ???

I built the lower myself using a billet lower and a CMMG lower parts kit.   The  stock is a DPMS  A2 assembly, and I made sure it had the correct .308 spring and buffer.  I tried (3) different magazines; metal DPMS mag, 7.62 PMAG, and ACS metal.

All (3) had the same problem using multiple types of ammo.  First shot goes bang every time but never a second shot without pulling the charging handle and ejecting a live round so it will feed the next round, then bang again....and so on....

I tried disassembling it again and oiling all parts really well.  I also tried another A2 .308 spring and buffer and nothing has helped so far

attached is a pic of everything I have tried today.

 

Any additional info would be great.  Thanks!

[washguy]

Hey Vival Okie dokie of course its a timing/cycling problem...so you have to do the the bolt catch lock back function

one round in the mag....charge it to chamber...pull the trigger....and after the boom..does the bcg lock back? that test right there gets you to the starting point of the malfunction :) Wash

[Dane Armory]

Timing/Cycleing ... Do the can of air test. First thought is to check the alingment of the gas block and the gas port hole.

[survivalshop]

Hey Vival Okie dokie of course its a timing/cycling problem...so you have to do the the bolt catch lock back function

one round in the mag....charge it to chamber...pull the trigger....and after the boom..does the bcg lock back? that test right there gets you to the starting point of the malfunction :) Wash

As said, one rd. in mag. & see if it will lock the bolt back on empty mag. & that will tell you if its under gased or binding some where .Check for loose carrier gas key , check gas rings on bolt . That Carbine gas system should have plenty of authority to cycle the action.

[VIVALABASS21]

Okay, good idea.  I'm headed out back now to try your guys' advice.  Be back later with the results...Thanks again.

[unforgiven]

Welcome from Indiana brother VIVALABASS.There is alot of knowledgable guys here.

[Robocop1051]

WET WET WET WET WET WET.... Did I mention WET!!!!

Those new parts are really heavy and gritty. You need to eliminate ALL the friction until the parts are worn in together. Even with off the shelf parts.

[VIVALABASS21]

Tested it again yesterday afternoon.

So far I tried drenching it with RemOil and it still jammed with every round.

When I charged the chamber with only (1) round per mag. and shoot it, the bolt locks open about 50% of the time.

All of the spent casings have a scratch down the side with a dimple at the base of the neck and the neck opening is crimped.

I will buy a can of air tonight to test the gas port.

 

Thanks again...

[VIVALABASS21]

here's what the empty casings look like

[Dane Armory]

WET WET WET WET WET WET.... Did I mention WET!!!!

Those new parts are really heavy and gritty. You need to eliminate ALL the friction until the parts are worn in together. Even with off the shelf parts.

by wet RobO means... Oil running down your armm and dripping on the floor. Spashing in your face.

Mobile One is a favorite. I like Castrol GTX. Do this on the break in only. RemOil is great lube just not for break in.

Still it is acting like its not getting gas back to the carrier.

[survivalshop]

here's what the empty casings look like

Normal

[survivalshop]

by wet RobO means... Oil running down your armm and dripping on the floor. Spashing in your face.

Mobile One is a favorite. I like Castrol GTX. Do this on the break in only. RemOil is great lube just not for break in.

Still it is acting like its not getting gas back to the carrier.

Can you manually, with an empty mag in the rifle , pull the charging handle back & the bolt locks back ? With no abnormal resistance on the way ?

[Zebra644]

The shell casing dent and scratch is normal. Check the rings on your bolt to ensure the spaces in the rings are not alligned so that  gas is not escaping. Check the gas key for propper allingment. Then check the gas tube/block as also previously mentioned. I would also look at the bolt stop to see if any markings are on it  since you built the lower and also look at your hammer and disconnector for any abnormal wear or marks. Then i would lube the inside of the buffer tube with a heavy teflon based oil like Break Free for stainless and select fire guns. I have used it for years nd never had a problem. As previously stated oil the bolt carrier group and the inside of the upper where the it travels. 

Edited December 23, 2013 by Zebra644

[EasyEJL]

I don't get the ding, but frequently get the neck bend in, and all sorts of scratches, and I'm not getting FTFs using 40+ year old surplus 7.62 ammo.

[shibiwan]

Perhaps it's a buffer/buffer sping issue....?

[Tripledeuce]

    Sounds like gas  port , to me.

    Respectfully

    Terry

[washguy]

Perhaps it's a buffer/buffer sping issue....?

Perhaps it's a buffer/buffer sping issue....?

Exactly Shibi Viv said he bought the complete upper,but he built the lower.....soo...its prolly the wrong spring/buffer combo in conjunction with an A2 stock.....although the upper can still have a gas leak or a torqued up gas tube

Viv break open the rifle...point the muzzle down and drop the bcg....it should almost go into battery.

Yes a new gun can be tight,but ive built 7 of these and have never had to drip oil over the place...wet yes,but geez it doesn't take much :) Wash

[VIVALABASS21]

Okay sounds like the only thing left that could possible be causing it is a gas port/gas block area. I'll check it tonight.

Thanks again...

 

Note:

It shouldn't be a spring/buffer issue.  I bought the A2 stock as a kit directly from the DPMS dealer at a local gun show and he made sure I had the correct spring/buffer for the .308 build.  I also bought an extra LR308  A2 spring & buffer (for extra parts) from that same DPMS dealer and I installed these yesterday just to verify that it wasn't the problem.  So to clarify, I have tried (2) LR308 A2 springs, and (2) LR308 A2 buffers and both have given the same result.

[survivalshop]

Could you measure the buffer & weigh it . Also count the coils of the spring & measure it .

 

Yes, it could be under gassed if gas block out of alignment & it does need to be checked , I don't care who made it .

[Dracomeister]

Viv, I recently picked up a factory DPMS LR 308 and started out with the same problem.  Read the postings and saw the "dripping with oil" comments but couldn't (or wouldn't) believe it.  Tried the Rem Oil, no joy, got a jug of Mobil 1 5w30 out of the trunk of the car, dumped it all over and in the action, slung out some all over the gun room floor and proceeded out to the range ... never had another issue.  After about 50 rounds went back to Rem Oil and still working like a champ. Give it a try Robo & Dane are right, it has to be "sloshy wet".

[Robocop1051]

This is a 16" carbine barrel launching a .308... I think we might be going the wrong direction with the gas.

 

It's entirely possible that you have too much gas. Your bolt carrier can be traveling so fast that the next round in the magazine isn't making it up fast enough to go into battery. This can also be the reason that you aren't locking back every time. The BCG is just too fast for the other "standard" parts.

 

Remember, there is no real "standard" for the .308 AR rifle. Most of us tinker with parts until we get that "sweet spot". Some get lucky with off the shelf stuff.... Some of us spend the $$$.

 

I'm willing to bet that you could go one of a few routes, depending on your ability and budget;

1. Get an adjustable gas block and dial in the gas a bit.
2. Install a heavy buffer from www.HeavyBuffers.com
   1. Don't forget the AR10 buffer as well.
3. Take a look at the Tubbs Carrier Weight System (CWS). Be forewarned, they don't fit in every BCG.
   1. This is a cheap trade off, and not quite as good as the above options.

[survivalshop]

 

This is a 16" carbine barrel launching a .308... I think we might be going the wrong direction with the gas.

 

It's entirely possible that you have too much gas. Your bolt carrier can be traveling so fast that the next round in the magazine isn't making it up fast enough to go into battery. This can also be the reason that you aren't locking back every time. The BCG is just too fast for the other "standard" parts.

 

Remember, there is no real "standard" for the .308 AR rifle. Most of us tinker with parts until we get that "sweet spot". Some get lucky with off the shelf stuff.... Some of us spend the $$$.

 

I'm willing to bet that you could go one of a few routes, depending on your ability and budget;

1. Get an adjustable gas block and dial in the gas a bit.
2. Install a heavy buffer from www.HeavyBuffers.com
   1. Don't forget the AR10 buffer as well.
3. Take a look at the Tubbs Carrier Weight System (CWS). Be forewarned, they don't fit in every BCG.
   1. This is a cheap trade off, and not quite as good as the above options.

 

This is where hand loading would be a big help. Bolt bounce is an option to look at , the carbine gas system has plenty of excess gas.

But , the bolt hold open should not be effected by it  , its got the mag pushing up on the bolt stop & as long as the BCG goes past it , it should stop it . Of course the Bolt stop would have to working to spec's .

[Rsquared]

I'm still willing to bet that he's undergassed for some reason. Block alignment, gas port issue, tube placement, loose gas key, bad gas rings (unlikely but always worth a check). If he was moving too fast, it would be acting the same as it does with a suppressor.....ie....trying to jam a 2nd round down the pipe before it can eject the 1st one. That would sound like a more "classic" cyclic rate issue. Sounds like the carrier doesn't have enough Hmmmph. Which is strange for a carbine length in the first place.

[VIVALABASS21]

I had to wrap up the LR308 since its a Christmas gift for my father in-law.  Once he opens it, I can proceed to trouble shoot the problem.  I'm taking down a list of notes based on all our your suggestions.  I'll get back at it in a couple days.

 

Thanks again everyone.  I really appreciate being able to join a forum and quickly getting loads of useful information from knowledgeable people.

[Rsquared]

Damn. Sounds like you're father-in-law is a getting a nice gift. They can all be fixed my man.

 

Well.......except maybe some RRA's.

 

Oh yeah, Oh yeah.......I said it.......bring it on! :box1:

Edited December 24, 2013 by Rsquared