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DPMS Cycling Issue......Please Help!!!!!

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STI_1911_Guy

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 I have a dpms LR 260 remington and have been having problems with it cycling. First off i have replaced the original A2 buttstock with a magpul PRS stock. It was a gift from the girlfriend for christmas. with good intentions but not knowing better she got the ar-15 version not AR-10. In the instructions it said it would work fine functionally on either but the charging handle would hit if the cheek piece is raised when using the ar-15 stock on an ar-10. I dont believe this is an issue in my cycling due to what the instructions said but correct me if im wrong. Now i have fired remington cor-lokt 140 gr and it seems to cycle fine(40rounds). when i tried federal 120gr ballistic tip it would cycle once in a blue moon but never lock the bolt back on the final round. The same goes for the couple handloads i have tried with REM brass hodgdon 414 45 grains and sierra matchking 123 gr federal 210 match primer, Corbon 143 grain sierra matchking. On all the handloads/Federal/Corbon ammo it would always eject the spent case but only once in a great while pick up a new round, but never lock back the bolt. I have tried a couple different mags same results. I have not seen any gas leaks but i am going to try to upload some pictures i have taken of the port and barrel, if they upload correctly great if not sorry and i hope my description alone will help. Any thoughts and suggestions would be greatly appreciated.
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Re: DPMS Cycling Issue......Please Help!!!!!

Use a shorter buffer.

That should fix the issue.

John
 
Re: DPMS Cycling Issue......Please Help!!!!!

can i "cut to fit" the one i have or do they sell them by specific length?
 
Re: DPMS Cycling Issue......Please Help!!!!!

Sounds to me like you are undergassed/port size too small.

Gas guns are not bolt rifles, if you size port to run the smaller bullets with faster burn rate powder you'll be overgassed when you go to big bullets with slower burn rate powder.

First thing you need to do is pick the bullet weight & powder you are going to use. Than size port accordingly.

I wouldn't go trimming the buffer spring, just treating symptom not root cause.
 
Re: DPMS Cycling Issue......Please Help!!!!!

weigh the buffer, and try a lighter one(may be shorter), if that gives 100% function with all loads you could go with it or open the original buffer and change up the weights to make the longer "LR" buffer the same weight. A shorter or lighter spring may do it but I would not cut it as you can not put it back on. If you have an old worn AR spring ( will often be shorter) try that, for heavy bullets you may go back to the stronger spring. Opening the port is another option but if you go to far you will need an adjustable gas port, the best option but $$$
 
Re: DPMS Cycling Issue......Please Help!!!!!

Did this happen after you installed the stock? If so make sure the screw in the back is not too long preventing the buffer from traveling all the way back. I have seen this exact thing occur because of an excessively long screw.Take out the buffer and look at the back of it....if it's chewed up at all that's the problem.
 
Re: DPMS Cycling Issue......Please Help!!!!!

So i was leaning toward a gas problem because if it was a problem with the rifle at all i would think it would do the same for all ammo and not work with any. But since it works with the remington 140 gr cor-lokt it seems to me that it has to do with gas port. I see that with the rifle comes a paper stating that all dpms firearms are tested with remington ammo so i will assume that if they get it to "work with remington ammo" they send it out the door.So will the rifle never be able to work with bullets ranging from 120 gr to 140 gr's without adjustment for each. It seems funny seeing my other AR-15's do fine with 40gr to 75 without any adjustment. My buffer seems fine and it cycles smoothley by hand.
 
Re: DPMS Cycling Issue......Please Help!!!!!

That rifle is not undergassed. Overgassed is your problem. H414 is too slow for 120-130 grain bullets. I can't use H414/W760 in less that 140 grain bullets in my LR260 or my 6.5 Creedmoor.
 
Re: DPMS Cycling Issue......Please Help!!!!!

Only thing that cycled was factory 140. Everything else is ejecting but not picking up next round (or only occassionally cycling) and never locking back.
Overgassed DPMS rifles I've been around will still lock back on empty mag. Would really be twanging the buffer spring to cycle fast enough for mag to not push up bolt catch.


Put an adjustable gas block on it and figure out if over/under gassed.
Other option would be to use some Varget with 120s, get your port pressure down.
 
Re: DPMS Cycling Issue......Please Help!!!!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FCS</div><div class="ubbcode-body">Only thing that cycled was factory 140. Everything else is ejecting but not picking up next round (or only occassionally cycling) and never locking back.
Overgassed DPMS rifles I've been around will still lock back on empty mag. Would really be twanging the buffer spring to cycle fast enough for mag to not push up bolt catch.


Put an adjustable gas block on it and figure out if over/under gassed.
Other option would be to use some Varget with 120s, get your port pressure down.

</div></div>

From my personal experience I will tell you that it is not uncommon for these DPMS 260s to not cycle properly with lighter bullets and H414. I will also tell you that it is fairly common for guys to have problems with Corbon's loads -- all of them. Mine won't cycle with any of the three Corbon loads. They just chose a powder that is not compatible with cycling an AR. The Federal loading not cycling is the only thing I have not seen before, but I have never tried it.
When a gun is overgassed, it does not result in the the buffer being 'twanged'. In fact, the result is quite the opposite. It is a timing issue. If the bore/chamber pressure has not dropped off enough when the bullet passes the gas port, the brass will not have constricted; it will be pushing outward against the chamber walls. That creates too much friction and the bolt will not unlock instantaneously. By the time it does, there is not enough bullet travel in the bore to allow for enough gas pressure the properly cycle the action. If this is the type of gas pressure problem the OP is experiencing, I doubt an adjustable gas block will the solve the problem.
The least costly way to verify if what I am saying is right is to try a powder that is a bit faster.
 
Re: DPMS Cycling Issue......Please Help!!!!!

Need pictures of fired case head with information of what load it is.
 
Re: DPMS Cycling Issue......Please Help!!!!!

So i called dpms and they said to send it in. They said it should not be having problems with the other ammo and to send it to them. So with that being said i am going to give it to them and if they say nothing is wrong then its back to the adjustable gas block and different powders.But before i soak a bunch of money into parts that may not fix it i would like to let the warranty do its thing. I will let every body know what happens and hopefully its fixed.
 
Re: DPMS Cycling Issue......Please Help!!!!!

So i got my rifle back from dpms today and they replaced the extractor, polished the chamber and gas system.......well it still dont work with my H414 and 123 gr matchkings but i have been told others have had problems with H414 and Winchester 760 so i am going to try some varget and see if a considerably faster powder will help or not. If not what else should I do. Drill out the gas port in the barrel/send it back/what?
 
Re: DPMS Cycling Issue......Please Help!!!!!

you should NOT need to adjust the port size for the weapon to cycle properly. i would try switching powder, i have had best results with IMR4350 in my .260rem.
I used to work at DPMS makeing the rifles, if it left the factory it had at least 20 rounds of factory ammo run through it without malfunction.
 
Re: DPMS Cycling Issue......Please Help!!!!!

I hope I didn't make a bad decision on buying a DPMS LR 260. It's on order but they have said 8-10 weeks. I ordered it with the prs stock on it and a few other things. I already have everything it seems like other than the dang rifle. Have some 4350 powder waiting and some Sierra's to load and try. Cross my fingers I guess and hope it works well.
 
Re: DPMS Cycling Issue......Please Help!!!!!

Good luck to you, on all the reviews i have read they said it was a great rifle and everybody seemed to like them i think i got a lemon and it looks like its going back to them again. If it means anything when i did shoot it single shot style for a group it did do .436 inch so if i could get the dam thing to cycle it would be great.
 
Re: DPMS Cycling Issue......Please Help!!!!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: STI_1911_Guy</div><div class="ubbcode-body">Good luck to you, on all the reviews i have read they said it was a great rifle and everybody seemed to like them i think i got a lemon and it looks like its going back to them again. If it means anything when i did shoot it single shot style for a group it did do .436 inch so if i could get the dam thing to cycle it would be great. </div></div>

Most of the posts on this thread are misinformation.

The problem is obvious if you have an AR-15 buffer and buffer spring in your gun instead of an AR-10 buffer and buffer spring. An AR-10 buffer is shorter than an AR-15 buffer so with an AR-15 buffer in your rifle, the carrier can never cycle back far enough (i.e. won't lock back after the last shot, and likely won't pick up rounds out of the magazine either).


In your initial write up you said the stock assembly could be used for both AR-15 and AR-10, and that may be so, but you still need the correct buffer and buffer spring for each application.

Robert Whitley
6mmAR.com
 
Re: DPMS Cycling Issue......Please Help!!!!!

Had the same problem with my LR-308B. Was as simple as a loose gas block. Tightened it and used blue loc-tite, haven't had any problems since.

Hope this helps.
 
Re: DPMS Cycling Issue......Please Help!!!!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Exhogflyer</div><div class="ubbcode-body">Did this happen after you installed the stock? If so make sure the screw in the back is not too long preventing the buffer from traveling all the way back. I have seen this exact thing occur because of an excessively long screw.Take out the buffer and look at the back of it....if it's chewed up at all that's the problem. </div></div>

OP. Did you check the screw as per Exhogflyer's post? That would be the first place I would check since by your original post it sounded like the problem started when you put the PRS on.
 
Re: DPMS Cycling Issue......Please Help!!!!!

The buffer and buffer spring are the ones that came with the rifle it is not a buffer issue. I think it has to be a gas port issue. Does it make sense that it would have to be enlarged to shoot 120 grainers or not. I also checked the screw in the buttstock and it is not touching
 
Re: DPMS Cycling Issue......Please Help!!!!!

no,you should not need to enlarge the gas port. it should work with all factory ammo. have you tryed using more lube?
 
Re: DPMS Cycling Issue......Please Help!!!!!

Dude, do not mess with the gas port. For peace of mind, make sure the gas block's port is properly lined up with the barrels gas port. Remove the gas block and with a pencil mark an index point in line with the gas port on top of the gas block. Do the same on the barrel. Re-install the gas block. I had 2 LR-308's with gas blocks misaligned and had no more issues after aligning them. And my lR.260 is awesome by the way
 
Re: DPMS Cycling Issue......Please Help!!!!!

So I took the bolt out of the carrier group and slide the carrier in here with the gas key attached and I could see that when the key slide over the tube it would push the key on the carrier would push the tube ever so slightly to the left. Could the barrel nit be out of alignment and the gas tube not sliding straight info the carrier key cause a problem. The movement isn't much but it is noticeable
 
Re: DPMS Cycling Issue......Please Help!!!!!

This may seem like a silly thing but try oiling your buffer spring with some ATF . Just a light film on it . Take a look at how rough the buffer tube is as well . I had an AR that short stroked a lot when using PMC Bronze 55 grain ammo , this was when it was new . Travis Gibson had me pull the buffer spring out and put some fancy Helicopter transmission fluid on it and after that it ran like a champ .
 
Re: DPMS Cycling Issue......Please Help!!!!!

So yes after it cycles half way and kicks the spent shell out it then closes on a empty chamber. But today i bought some more remington 140's lubed the shit out of it racked it a few times and went and shot it. 15 rounds of rem and no malfunctions. Next i tried 10 rounds of my H414 123 gr matchking and all failed to fully cycle except 1 which did cycle. I then replaced the gas tube and tried rem. again and it worked fine. tried some more 123 matchkings and it didnt work would still only eject and not pick up the next. I tried both magazines with the same result. The gas block looks good. I did take the bolt out of the Bolt carrier group and slid the carrier in the upper receiver and noticed that when the carrier key slid over the gas tube it pushed it slightly to the left. Its not much. I dont know if the barrel nut could be pushing the gas tube to the side and the carier key is not getting a good seal on the tube or how much that affects it. I dont think this is the problem. I want to get some 140 gr matchkings and try handloading them see if it works. The rifle should function with 120's shouldnt it or are they only designed to work with 140's. and if i got an adjustable gas block would that help by making the hole smaller to raise the pressure.
 
Re: DPMS Cycling Issue......Please Help!!!!!

yes i have tried h414/varget/4831/win 760 none of them have worked
 
Re: DPMS Cycling Issue......Please Help!!!!!

So its going back to DPMS one more time. Freakin awesome i F@#$ing hate this shit.
 
Re: DPMS Cycling Issue......Please Help!!!!!

STI_1911_Guy,

We received your 260 upper on 2-11-11

Upon inspection we replaced the extractor, polished the chamber, oiled carrier assy and test fired 40 rounds of various factory ammunition with no malfunctions.

We shipped the upper back on 2-25-11 in 100% operational condition.

The ammunition warning below is listed on our website and on page 127 of our catalog.

<span style="font-weight: bold">"Using reloaded ammunition will void warranty. Modifying chamber or barrel voids warranty. This includes re-reaming of chamber, re-turning barrel to a lesser diameter and/or re-threading barrel for compensator or attachments."</span>
 
Re: DPMS Cycling Issue......Please Help!!!!!

So what you are saying is there is a problem with the lower receiver and now I'm stuck with it. Or what should I do?
 
Re: DPMS Cycling Issue......Please Help!!!!!

What he is saying is the problem is most likely your reloads which they can not garantee it will work with
 
Re: DPMS Cycling Issue......Please Help!!!!!

We need to be clear,

DPMS never said or implied <span style="font-weight: bold">"there is a problem with the lower receiver and now I'm stuck with it."</span>

We are trying to help you out, you listed that factory ammunition functioned.

We tested your upper assy at DPMS using factory made ammunition with 100% operation. With that being said the lower assy would not be suspect.

Please use factory made ammunition for 100% operation.
 
Re: DPMS Cycling Issue......Please Help!!!!!

I am glad you are trying to help me out and I am sorry if I came across wrong. But what I am saying is that it functioned with Remington ammo but no other factory ammo I tried including Corbon 142 gr matching / federal 120 gr ballistic tip / or the 120 gr spitzer so since the only difference between you and me is you used a lower you have because I didn't send mine so I thought since that's the only difference it had to be the lower. But what should I do then because it still won't work for me with anything but Remington
 
Re: DPMS Cycling Issue......Please Help!!!!!

We used Federal 120 grain Nosler and Remington 140 grain Core-Lokt for testing.

Did you use the <span style="font-weight: bold">supplied</span> upper buttstock screw from Magpul when installing PRS stock? The A2 screw is to long for the PRS Stock resulting in the buffer contacting the screw.

Also, is the bolt carrier assy <span style="font-weight: bold">well</span> oiled with a quality brand?
We have noticed that many LR-308 (260 included) plattform users <span style="font-weight: bold">under lubricate</span> the bolt and carrier assy resulting in short stroking.
 
Re: DPMS Cycling Issue......Please Help!!!!!

Yes I did use there screw that was supplied and it's not hitting the buffer I'm not sure what else to try. Some one at dpms said to run the 120's I would have to open the port and put an adjustable gas block on. I really like the rifle but it just won't work for me. And I did put alot if lube on the bolt carrier atleast alot more than normal. I wouldn't think it would be this finicky and what else should I try?
 
Re: DPMS Cycling Issue......Please Help!!!!!

Basically please help. What should I do? I want to get it working. Is there a number I can contact you at?
 
Re: DPMS Cycling Issue......Please Help!!!!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DPMS Firearms</div><div class="ubbcode-body">We used Federal 120 grain Nosler and Remington 140 grain Core-Lokt for testing.

Did you use the <span style="font-weight: bold">supplied</span> upper buttstock screw from Magpul when installing PRS stock? The A2 screw is to long for the PRS Stock resulting in the buffer contacting the screw.

Also, is the bolt carrier assy <span style="font-weight: bold">well</span> <span style="color: #FF0000">oiled with a quality brand? </span>We have noticed that many LR-308 (260 included) plattform users <span style="font-weight: bold">under lubricate</span> the bolt and carrier assy resulting in short stroking. </div></div>

DPMS,

What lubricant do you recommend? I am using areosol RemOil is that a good lube to use?

Bob
 
Re: DPMS Cycling Issue......Please Help!!!!!


Bob,

We have found that Rem-oil is great for bolt guns and pumps ect... BUT it doesn’t work very well in AR style rifles.

Gunslick, mil-tech, break-free, lucas, masters work better.

Additives like Teflon, graphite or dry lubes are troublesome also.
 
Re: DPMS Cycling Issue......Please Help!!!!!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DPMS Firearms</div><div class="ubbcode-body">
Bob,

We have found that Rem-oil is great for bolt guns and pumps ect... BUT it doesn’t work very well in AR style rifles.

Gunslick, mil-tech, break-free, lucas, masters work better.

Additives like Teflon, graphite or dry lubes are troublesome also.
</div></div>

Thank you very much for the advice. I'll be getting some lucas tomorrow.

Sorry for the Hijack
 
Re: DPMS Cycling Issue......Please Help!!!!!

also have lr .308 which had the same symptoms. check gas ring alignment, gas block alignment, and i lubed mine with 30wt motor oil really oily (might not be uber cool, but it worked).
also one thing i noticed was that when the bolt carrier came backwards across the hammer that there was a good deal of friction/pressure. which has been alliveated after several hundred rounds.
 
Re: DPMS Cycling Issue......Please Help!!!!!

STI_1911_Guy,
Do you have an aftermarket trigger in that rig? If so, which one?
 
Re: DPMS Cycling Issue......Please Help!!!!!

I do not have an aftermarket trigger but i do have a an aftermarket pistol grip and i have the magpul prs stock(the ar-15 version grlfriend gift didnt know better) but it uses the original buffer tube/spring/buffer and the screw isnt hitting the buffer.
 
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