Troubleshooting Failure to Feed on a DPMS LR-308

Mr.Maim

Mr.Maim

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Minuteman
Nov 6, 2011
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Phoenix, AZ
#1
'Evening gents. I've been chasing a problem with my DPMS Heavy Barrel Panther LR-308. I get frequent Failure to Feed incidents where the round being fed doesn't make it into the chamber, and the bolt slams into the brass and the bullet ends up wedged at a 30-degree angle halfway in and out of the chamber. Occasionaly I'll have NO round load into the chamber at all. I've had that happen a few times.

So far I've used 145gr, 147gr, 150gr, 155gr, and 168gr rounds. All do it.

I bought the rifle used (barely used) nearly a year ago (private party sale) and have not shot it until recently and discovered the problem after the first magazine.

I have six DPMS steel mags (all new) all do it. I have nine Magpul mags (all new in wrapper) and the two I have tried do it.

Something occured to me as I was looking at the literature that came with the rifle earlier this evening: Does anyone know what the length of a carbine length LR-308 buffer spring is supposed to be? I'm thinking that the buffer spring is too stiff and it may be the wrong spring. The rifle came to me with a Magpul PRS stock installed but came from the factory with an A2 stock. Doesn't an A2 stock have a longer spring than a carbine?

Anyone?

Mr.Maim
 
#5
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bulzeye</div><div class="ubbcode-body">PRS stock should use the same spring as the A2 stock if i'm not mistaken.</div></div>

You're right. I did a little more research than I had the desire to do last night.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TenZero</div><div class="ubbcode-body">Shouldn't be able to mount a PRS on a carbine buffer. The PRS requires the A2 buffer.</div></div>

I was referring to the spring, not the tube.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TenZero</div><div class="ubbcode-body">Does this happen when you cycle the action with the charging handle? Or does it also happen when the action cycles after firing?</div></div>

No, always works manually cycling. It only does it after the first round of a magazine. It almost seems like the bolt carrier is not moving all the way back, so that it either misses the end of the next round and 'grabs' the case side, and not the end of the case, or misses it entirely. I thought the magazine might be sitting too low but there is no way to adjust that on an AR, and six different mags have ruled that one out, I think.

What are the symptoms of insufficent gas pressure in an AR platform?
 
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#6
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I have chased similar problems with various AR10s.

Your buffer might be the wrong the length. I don't know what the buffer length is for DPMS, but this is frequently the problem.

If you load in 1 round in the mag, does the mag lock open on an empty chamber?

Another thing that gets many (me included) with relatively new guns: lube the bejesus out of the BCG. When you think it is over-lubed, add just a little more.

One last suggestion: Midway sells a hydraulic buffer that clears up many problems (assuming it is the right length when starting out.) You shouldn't need it, but it might help.

It is probably the buffer length, might be buffer tube length, but doubtful. DPMS probably sells a buffer with spring, that's where I'd start.

And don't forget to lube!
 
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#8
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Won't be able to work with this until next week. Too busy with work.
frown.gif
 
#9
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

What Rancid said. Try it with only 1 round in the mag, and if the bolt's not locking open, then you have a reasonable starting point that the BCG is not cycling all the way back. Then lube the shit out of the BCG, and see if it will lock open after lubing. Do this first, since it's free, and if it still isn't cycling fully, then start investigating the gas block and buffer.
 
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#11
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Mr. Maim,
Same gun here, had same problem. Try,as already suggested, to see if it locks back when magazine is empty. Mine didn't lock back most of the time so I tried an extra power buffer spring for the standard AR15, it takes a few less pounds pull to lock the bolt than your stock LR308 spring. Problem went away and I don't think any harm has been done to any other parts. Good Luck!
 
#12
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rancid Coolaid</div><div class="ubbcode-body">
If you load in 1 round in the mag, does the mag lock open on an empty chamber?
</div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TenZero</div><div class="ubbcode-body">What Rancid said. Try it with only 1 round in the mag, and if the bolt's not locking open, then you have a reasonable starting point that the BCG is not cycling all the way back. </div></div>

Okay, just so I'm clear: you both mean to put one round in the magazine, fire the rifle, and see if the BCG locks open, correct?
 
#13
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Todd629</div><div class="ubbcode-body">Mr. Maim,
Same gun here, had same problem. Try,as already suggested, to see if it locks back when magazine is empty. Mine didn't lock back most of the time so I tried an extra power buffer spring for the standard AR15, it takes a few less pounds pull to lock the bolt than your stock LR308 spring. Problem went away and I don't think any harm has been done to any other parts. Good Luck! </div></div>

Do you know where you got the spring and who makes it (a link if you have a moment to find it). Do you mean one like an Advanced Technology or a Wolff?
 
#14
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Gentlemen, thank you for all the responses. Just got back into town and will troubleshoot this this weekend. Based on the responses from everyone, I'm going to test the following and post back my results:

1) Buffer length: correct for the DPMS? I'll look that up and measure. It looks factory.

2) If you load in 1 round in the mag, does the mag lock open on an empty chamber after firing the round? I'll try.

3) Clean an re-lube the BCG, Bolt, Chamber, etc. I actually don't have a chamber brush for this yet. That is on the "to do" list for tomorrow.

4) Check to make sure gas block is tight: Don't know how to check alignment. I'll also run a pipe cleaner down the gas tube to be sure it's not obstructed.

5) I have the Factory DPMS trigger that comes on the LR-308B. I do have a brand new Geissele Super Dynamic - Enhanced, ready to be installed, but not until I resolve this issue.


Thanks fellas. I'll get to clean the rifle tomorrow and hit the range on Sunday before football starts. I'll report my findings back.

Thanks!
 
#15
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Hopefully this will help clear up the buffer question...

I snapped a photo of a DPMS 308 buffer/spring next to a DPMS 5.56mm buffer/spring. Let us know if somehow a 5.56mm buffer got in there and is causing short stroking. You can see the length difference in the photo.

2ui96hf.jpg


ETA: Obviously, these are rifle buffers/springs. Hopefully you don't have a carbine system in the PRS stock.
 
#16
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

My buffer measures 5.280" end to end. I am running an A2 stock/buffer tube on it. If it's bolt over base jams, probably not enough gas, which would sound opposite to most folks experience with DPMS 308's. You should NOT rule that out though. Checking alignment of the gas block such that the gas passage in the block lines up with the barrel is a good idea.

Does the upper buttplate screw have a small hole in it? You can have issues if it does not. This hole is to allow air to bleed from behind the buffer as it cycles. Currently mine does not have the small hole, but functions ok, not sure if that's best though.
 
#18
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I would check gas port alignment as stated before and the bolt lock back check by putting a single round in with an empty mag. I have experienced something similar, but mine was over gassed and catching the spent shell and the next live round was being partially stripped and crimped at 30 degrees by the bolt. Just another scenario for ya. Good luck!
 
#19
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Fellas, thanks for all the responses! Apologies for the delayed response on my part... business travel...


I finally got out to the range today. Shot 25 rounds of 147gr and 10 rounds of 168gr. The bolt only locked back ONCE, and that was on the first shot. After that, with a single round in the magazine, no bolt lock back. I'm pulling my spring and buffer to measure now (thanks Petey for the picture and AlterEgo for the measurement!) <span style="font-weight: bold">but I have absolutely no idea how I can verify the gas port alignment</span>. Please enlighten me!
 
#20
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Buffer and Buffer Spring measurements:

Buffer is 5.288" which syncs with Petey's picture and AlterEgo's measurement.

Buffer weighs 5.35-oz.

Buffer spring is 12 5/8" long which is significantly SHORTER than Petey's picture above.
 
#21
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I think our springs are pretty similar in length if you subtract the part of the buffer that extends beyond the spring. Keep in mind I have a few rounds on that spring, too, so I wouldn't worry if they're not dead nuts equal.

However,if you count coils it appears that you have a 5.56mm action spring in there.
 
#22
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Ok, just pulled the spring so I could get a true measurement w/o the parallax in the picture having an effect... 12-9/16" so we're basically identical.

I'd give DPMS a call and see if they'll send you the spring you need. Part number: 308-BS-10B
 
#24
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

generally I slide the block forward and mark the hole in the barrel just back from shoulder where the block sits, then I look at the tube alignment with that mark I made. When looking down on the barrel from the top the gas tube should sit evenly over the top of the mark I made. It is not very scientific but it works. Also sometimes you can slide the block forward and a carbon ring will exist on the barrel around the gas hole and that is a tell tale is things are lined up.
 
#25
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Maim,
Edit: I agree you want to check the gas block alignment -- probably the first thing that should be checked other than the gas key suggestion below.

Don't know if you have done this arleady, but you may want to verify that your gas key is not leaking. Check to ensure that one or more of your gas key screws are not broken.

Apart from that, you initially listed this as a LR-308B. The rifle in your pics bears little resemblance to that rifle in its stock form. For example, the "B" model comes with a high-rise slick side upper receiver, non-chrome bolt, no flash hider (or threaded muzzle), smooth handguard, A2 stock, etc.
While it is technically possible (I think) to order a "B" model with all those changes/upgrades, it would have made more sense to start from the "T" platform.

I would speculate that this rifle was build by its previous owner, but you may know more about its origins.

I don't remember if this had been previously suggested, but did you ensure that the PRS was not installed with the long, original screw that came off the A2? I don't think the bolt would lock back at all if that was the case, but just another though.

edit: another thing to check if this was, if fact somebody's build project:

This is a long-shot, but it is technically possible that the builder used an AR-10 pattern barrel with a DPMS patter gas tube (just a tad to short for an AR-10 barrel). I have never seen the effects of this, but would speculate that it results in an insufficient gas impulse imparted on the bolt causing a short stroke.
 
#26
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Matt2143: I just completed removing the handguard and gas block. Quite a PAIN IN THE ASS with the Daniel Defense Lite rail having such a small interior diameter (1.44"). I'll post pictures in a sec., I could use some opinions.

Bowslngr: WOW! Your knowledge of the DPMS platform, and my rifle is... WOW. You sir, know your stuff!. I bought the rifle secondhand, previous seller claimed 50 rounds and the (lack of) wear on the inside of the uppper receiver, bolt, and bolt carrier prove that to be pretty accurate. I think it was likely less considering the problems I'm having, and the rifle is largely unchanged from when I purchased it, except for the bipod, monopod, optic and mount, BUIS, and furniture. It has been sitting in my safe for nearly a year and I don't have the seller's info anymore (private party sales in Arizona do NOT require documentation/transfer/bill of sale/LEO notification, etc.) so I suspect that the seller had the same issue, but I am unable to contact him and ask. I just need to figure out what the issue is.

Ultimately, I don't know what the ordered configuration was unless I call DPMS with the serial number. I have all the paperwork that came with the rifle when new but no build sheet so I suspect that it is a completely "build to suit" rifle.


Checked the gas key: it is on solid and there has been no rotation of the gas key screws. The staking is good.

Checked the buffer/stock screw and the length is correct. Peering down the tube I can see that the screw does not protrude into the buffer area. Removing the screw and measuring it, OAL is .740". Interestingly, it is hollow with a hole that passes through the head, presumably to vent gasses backwards. I have not seen that on any of my AR-15 buffer/stock screws.
 
#27
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Okay, I removed the gas block. It *might* have been a tiny bit off center, but not enough to block the port (I think). More interestingly, it looks like it is leaking based on gas residue left on the barrel (see picture) could this be part of the problem? The gas block is a stock DPMS unit, a little mangled from rail installation I suppose, the tube feels like it is stressed to reach up (from the barrel) into the upper receiver which may be a leak source, and of course there is carbon buildup at the bolt carrier gas key end of the tube.

Could any of these be the cuplrit?

(removed gas block pics. Sorry guys I'm hosting these forever)
 
#28
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Hmmmm.
I had that same gas block on an alternate caliber build I did once and it leaked pretty badly as well. That rifle short stroked too. That said, when I replaced the gas block with a different model it never really solved the problem completely. I wound up opening up the gas port a bit and the problem went away.
It is hard to tell how much it has been leaking in the pics of your rifle since the barrel has a black finish, and quite often I think minor gas block leaks wind up sealing themselves after a while with carbon deposits.
Having said all that, you might benefit from trying another gas block. But I would hate to see you spend a lot of money chasing this problem around unsuccessfully.

Since you have it pulled apart, what markings are on the barrel?
 
#29
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I've thrown over 3K into this rifle so far... my interest is solving this issue to enjoy the thing is much greater than my need to save a few bucks. That said: I found that Troy Industries has a nice low profile gas block that will fit this barrel and fit underneath the PITA Daniel Defense rail system.


When you say that you opened that gas port up, did you do that on the barrel? How did you know how much to open? Not something I'd do without other troubleshooting first... but I'm curious how you knew how much to open.
 
#30
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Here is a question: I just counted the coils on my buffer spring. It matches Petey's 5.56 buffer spring and NOT the .308 spring he pictured.

How much of an impact could that have?
 
#31
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I am a bit of a tinkerer. I went down to the local Grainger store and bought a bunch of wire guage drill bits, figured out which one was the next size bigger than my current hole (yes, in the barrel), and opened it up with that one. Then put the thing together and test fired it. If I remember correctly, I got the results I was looking for by going up 2 sizes.

When drilling, you have to be really careful to only go deep enough to get through to the bore. You don't want to bung your rifling up by hitting the other side:)

You really shouldn't have to to this with a DPMS 308 though. As I think someone noted earlier, being undergassed is not something they are known for. If you are dealing with a DPMS barrel, I think your problem lies somewhere else.
 
#33
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Since you have it pulled apart, what markings are on the barrel? </div></div>

At the chamber end there is a marking that looks like a letter "I" or "H" with a mark inside it that I cannot make out (I can post a pic if you'd like), at the muzzle end "DPMS CAL .308 1-10"
 
#34
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">I am a bit of a tinkerer. I went down to the local Grainger store and bought a bunch of wire guage drill bits, figured out which one was the next size bigger than my current hole (yes, in the barrel), and opened it up with that one. Then put the thing together and test fired it. If I remember correctly, I got the results I was looking for by going up 2 sizes.

When drilling, you have to be really careful to only go deep enough to get through to the bore. You don't want to bung your rifling up by hitting the other side:)

You really shouldn't have to to this with a DPMS 308 though. As I think someone noted earlier, being undergassed is not something they are known for. If you are dealing with a DPMS barrel, I think your problem lies somewhere else. </div></div>

Okay, good to know. I have a drill press and every concievable drill bit size in HSS bits so if it comes to that, I get your logic, thanks!
 
#35
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

I think the buffer spring could very well be the source of your problem. According the data I just checked, an AR15 buffer spring has a compressed length of 3.168" while that of a 308 platform has a compressed length of 2.448"

My guess is your buffer spring is not allowing the bolt carrier group to cycle far enough to the rear.
 
#36
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Don't know, but I would get the right spring in there before I did anything else. </div></div>

Yeah, I'm calling DPMS customer service to get the exact correct part number for the correct spring. I'm going to order a new spring and a Troy Industries low profile gas block.

http://troyind.com/%20/rail-systemsacces...ofile-gas-block
 
#38
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Hope it works out for you. </div></div>

Thanks for your help!


Just got off the phone with DPMS. My buffer is correct, my buffer spring is the correct length but the tech agreed that it has a few too many coils, but should not make a difference.

Suggested the following:

- Clean the heck out of the bolt, carrier, upper receiver.
- Run the bolt carrier VERY wet.
- Polish the barrerl chamber using red Brillo pad and a drill to spin it (gave me detailed suggestion on how to do that).
- Correctly re-mount the gas block.
- Stick to heavier ammo (162gr and above) though this is not a "rule" just a suggestion and every rifle is different.
- .308 ammo only (which is what I have been using).

Soooo... I have my next two evenings cut out for me, don't I?
wink.gif


I'm very happy with DPMS's customer support!
 
#39
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Maim,
Edit: I agree you want to check the gas block alignment -- probably the first thing that should be checked other than the gas key suggestion below.

Don't know if you have done this arleady, but you may want to verify that your gas key is not leaking. Check to ensure that one or more of your gas key screws are not broken.

Apart from that, you initially listed this as a LR-308B. The rifle in your pics bears little resemblance to that rifle in its stock form. For example, the "B" model comes with a high-rise slick side upper receiver, non-chrome bolt, no flash hider (or threaded muzzle), smooth handguard, A2 stock, etc.
While it is technically possible (I think) to order a "B" model with all those changes/upgrades, it would have made more sense to start from the "T" platform.

I would speculate that this rifle was build by its previous owner, but you may know more about its origins.

I don't remember if this had been previously suggested, but did you ensure that the PRS was not installed with the long, original screw that came off the A2? I don't think the bolt would lock back at all if that was the case, but just another though.

edit: another thing to check if this was, if fact somebody's build project:

This is a long-shot, but it is technically possible that the builder used an AR-10 pattern barrel with a DPMS patter gas tube (just a tad to short for an AR-10 barrel). I have never seen the effects of this, but would speculate that it results in an insufficient gas impulse imparted on the bolt causing a short stroke. </div></div>

The last point is a good one. Please post a picture showing where the end of the gas tube sits in the upper receiver when it's all assembled (with bolt carrier removed, though). I have a Krieger M110 barrel on a DPMS, but even though you can specify a DPMS barrel extension when ordering a barrel through Krieger they drill the gas port in the Armalite position. Thus, I had to put an Armalite gas tube in my DPMS rifle otherwise the length would've been wrong for this particular barrel and the gas tube/bolt carrier interface would've been off. This is the type of situation bowslngr is describing.
 
#40
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

The barrel markings on his barrel verify that it is a DPMS barrel. Like I said, it was a long-shot.

I am surprised to hear that the DPMS guys think an incorrect buffer spring will work though.

Maim,
I meant to ask you before what your spent brass looked like. If your chamber is rough, you will probably see evidence of it on your spent brass: lots of tiny scratches running lengthwise.
 
#41
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Just a couple more thoughts...

1 - I'd absolutely get the new spring in there. As bowslngr said, not only is the compressed length different but the spring constant is different.

2 - Is your gas block rubbing that bad on the DD Lite rail interior? I'd recommend a gas block that will keep your barrel free-floating (for accuracy), so it's good that you're looking for a low-profile block that'll fit inside. The DD Lite rails are a pretty tight squeeze. I have a CMMG Micro block on a DPMS 308 Carbine w/ DD Lite rail and it has worked very well; it was smallest gas block I could find at the time years ago when I built the gun.

3 - I wouldn't be worried by the gas blow-by at the gas port. From what I can see in the pictures, I personally don't think that it's excessive.
 
#42
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">The barrel markings on his barrel verify that it is a DPMS barrel. Like I said, it was a long-shot.

I am surprised to hear that the DPMS guys think an incorrect buffer spring will work though.

Maim,
I meant to ask you before what your spent brass looked like. If your chamber is rough, you will probably see evidence of it on your spent brass: lots of tiny scratches running lengthwise. </div></div>

Also, does it look like your gun is trying to 'rip off the rim' on the fired cases? Can you see where the extractor bent the rim or leaves excessive marks? These stupid 308s are so overgassed at times that the weapon is trying to eject the case as it is still obturated in the chamber. You'll see signs of this in the rim some of the time. This is more common in the shorter gas systems.
 
#43
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Petey</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">The barrel markings on his barrel verify that it is a DPMS barrel. Like I said, it was a long-shot.

I am surprised to hear that the DPMS guys think an incorrect buffer spring will work though.

Maim,
I meant to ask you before what your spent brass looked like. If your chamber is rough, you will probably see evidence of it on your spent brass: lots of tiny scratches running lengthwise. </div></div>

Also, does it look like your gun is trying to 'rip off the rim' on the fired cases? Can you see where the extractor bent the rim or leaves excessive marks? These stupid 308s are so overgassed at times that the weapon is trying to eject the case as it is still obturated in the chamber. You'll see signs of this in the rim some of the time. This is more common in the shorter gas systems. </div></div>

Good point, and question Petey. I don't think he should be having that problem with factory ammo, but could be. When I have seen that type of problem before, it has been with lighter bullets and slower powders.
 
#44
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Yes, it is a DPMS barrel and a DPMS gas block, but I'm more than happy to post pics. It's the least I can do for the amount of help and time you two, and everyone else that has posted to this thread, have devoted to this. I am MOST GRATEFUL!

The top one is that barrel marking I cannot make out. Just an FYI. The second is the best measurement I can get with my caliper. I don't have a long arm caliper. That length should put it snugly into the gas key (second pic).


(removed pics after a year)
 
#45
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">I am surprised to hear that the DPMS guys think an incorrect buffer spring will work though.
</div></div>

I agree, I am ordering a replacement spring along with that Troy gas block.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Maim,
I meant to ask you before what your spent brass looked like. If your chamber is rough, you will probably see evidence of it on your spent brass: lots of tiny scratches running lengthwise.</div></div>

I'll post a pic on that in a sec. There is one consistent scratch at the neck of every case that has me wondering.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Petey</div><div class="ubbcode-body">
1 - I'd absolutely get the new spring in there. As bowslngr said, not only is the compressed length different but the spring constant is different.

2 - Is your gas block rubbing that bad on the DD Lite rail interior? I'd recommend a gas block that will keep your barrel free-floating (for accuracy), so it's good that you're looking for a low-profile block that'll fit inside. The DD Lite rails are a pretty tight squeeze. I have a CMMG Micro block on a DPMS 308 Carbine w/ DD Lite rail and it has worked very well; it was smallest gas block I could find at the time years ago when I built the gun.

3 - I wouldn't be worried by the gas blow-by at the gas port. From what I can see in the pictures, I personally don't think that it's excessive.</div></div>

1. That is absolutely going to get replaced.

2. When mounted, there is less than a millimeter of clearance between the gas block and the rail. I don't know how the thing got so hacked up. It was like that when I took off the DD rail yesterday for the first time, and I'm not a "bull in the china shop" type when it comes to my guns. Nevertheless, the Troy one I mentioned above has a smaller OD on the bottom than the DPMS one pictured so it should be good. I'll look into that GMMG model before I buy though, thank you for the suggestion. The bull barrel is the main problem. ...and I don't feel like replacing a perfectly good $325 rail if I don't have to.

3. The DPMS guy said the same. He said gas blowback is common, unless excessive it should not be a problem.


Thanks guys!
 
#46
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Petey</div><div class="ubbcode-body">Also, does it look like your gun is trying to 'rip off the rim' on the fired cases? Can you see where the extractor bent the rim or leaves excessive marks? These stupid 308s are so overgassed at times that the weapon is trying to eject the case as it is still obturated in the chamber. You'll see signs of this in the rim some of the time. This is more common in the shorter gas systems.</div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Good point, and question Petey. I don't think he should be having that problem with factory ammo, but could be. When I have seen that type of problem before, it has been with lighter bullets and slower powders.</div></div>

I'm lining up brass now for some pictures. It'll take a few minutes.
 
#47
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mr.Maim</div><div class="ubbcode-body">Yes, it is a DPMS barrel and a DPMS gas block, but I'm more than happy to post pics. It's the least I can do for the amount of help and time you two, and everyone else that has posted to this thread, have devoted to this. I am MOST GREATFUL!

The top one is that barrel marking I cannot make out. Just an FYI. The second is the best measurement I can get with my caliper. I don't have a long arm caliper. That length should put it snugly into the gas key (second pic).

BarrelMarking.jpg


Gastube1.jpg


GasKey1.jpg

</div></div>

That "flaming H" mark on their barrels is the best kept secret in the AR world. As near as I can tell, nobody aknowledges knowing what/who it represents -- and DPMS won't say.
 
#49
Re: Troubleshooting Failure to Feed on a DPMS LR-308B

Okay, here are some shots of the brass from my last test. Note the scratch in the neck of every case and the corresponding 'ding' mark on the throat of every case. Don't know if that is normal, but it sure is consistent regardless of bullet weight.


(deleted pictures sorry)
 
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