AR 10 DPMS feeding issues

[cohunt]

If I'm not mistaken, and I may be, the PSA 308 lowers/uppers don't play well with other manufacturers. I thought they were somewhat proprietary.
I think that the issue w 80% 308 lowers gets into the fact that there is no "standard" with the "LR308" type platform.
I'm sure that someone has had a successful build with a 80% 308, but I've read about more failures than successes with it.
I've stayed away for that very reason.
Someone with more knowledge could probably correct my thinking.

Mine works fine-- had issues with a proprietary lightweight upper similar to a dpms Gen 2 but different , learned a lot !!!-- built my own lightweight upper and it's fine...real mishmash of parts too

 

[Citified]

Like you, I built a lightweight upper, 16" barrel with an aluminum 80% lower. I was careful however in selecting the JP adj gas block and tube and the trigger assembly.
2 3/4# trigger. I have a scope
on this one currently for load development at the range and am working with a captured recoil assembly.
My others are heavier and in different calibers. Fun project.

 

[hzy1369]

To start the trouble shooting on a gas gun first you need to put one round in the mag allow the bolt to close and see if it fires? Did it pick up the round and fire? Bolt lock open on empty mag? It could be under/over gassed buffer to heavy/light, but you need to go step by step the gas block could be out of alignment have it bore a scoped to check or google the spaghetti noodle trick

 

[Rckymtnshooter]

There is an inherent issue with a lot of the 80% LR308 type lowers. I believe it has to do with how the mags are held in the lower. I think they are held too low. I saw the exact thing on a friends build. It would double feed constantly. He tried an adjustable gas block, buffer and spring.
Even tried 3 different types of mags.
Nothing worked.
He finally changed the power to an Aero Precision 308 lower.
The gun runs flawlessly.
It was the lower

I think grandedirt has it right. I was helping g a friend with an 80% lower that was having the exact same issue. Feeds the left round but would not pick up the right round. The bolt face would not make contact with the right round.
We tried a number of different manufacture mags with the same results. Took my fully functioning Aero rifle and started swapping upper and lowers and bolts around and without a doubt t it was that 80% lower that was the problem. The mags just don't seat high enough.
Did some searching on the web and found d other people talking about the same issue with 80% lowers. Some had fixed the problem by modifying the mag catch to raise the magazine.

 

[Citified]

Very interesting. Never had that issue but only built 5 80%s mixed with polymer and aluminum. All fed ok with steel mag and Magpul. Just saying.

 

[blvette75]

Howdy, all. I finally bit the Bullitt, and got myself an AR. It's an 80%, built by a friend of mine. Near as I can tell, he did a good job. Let's assume he knows what he is doing.
The issue is, it jams. I know NOTHING about gas guns, so I want to tinker with this thing, fix the problem, and in the process, learn something.
On another thread, lots of GOOD information was given. Not my thread, so here we go...
So far, I have polished the feed ramp. Seemed to help some, but I did not document failures previously, so I don't really know. What I DID learn was it's from the right hand column in the magazine that these "jams" occur. Some of the guys in that thread suggested adjusting the mag lips up a touch to allow the cartridge to stick up into the bolt path more. Having decided to try that next, I noticed the back end of my mag wraps around the case head. Seems to me that if I just bend the lips up, only the shoulder will come up, and I want the entire shell to come up. Am I right? So that means I need to cut the back of the mag , to free up the whole feed lip. Am I all funkered up here ?View attachment 361354

Have a DPMS 2nd gen in 6.5 Creedmoor- Had similar issues with mine had bought some polymer mags which appeared to caused some feeding issues, and had failure to go back to battery. Got some metal ones seemed mitigate the feed issue some, the other contributing factor on mine was it was over gassed(really was beating up the interior of my stock, actually was catching my recoil buffer on the side of the stock, there was a small groove worn in it by my BCG (What I thought was doing the damage anyway or maybe a groove was always there), eventually purchased a adjustable gas block, better stock with an alternative recoil setup in the stock, adjusted all of the polymer mags to match the metal ones and now those feed fine with a different muzzle brake, another trigger it shoots fine now, took a long while to play with it, AR10s are more problematic to set up, not sure I would do it again. I was really frustrated with it and put it down for about a year and wound up buying a Bergara HMR in 6.5 Creedmoor. Then systematically addressed each issue by the time I got it to run properly could have just bought a higher end production AR10 and would have gotten the same result. But at the end of the day there was satisfaction in making it run properly and now it has similar accuracy as the HMR (not quite as good but close enough the mule deer can't tell the difference). The Bergara I can shoot through the same hole at 100 yards if I do my part with some factory ammo(even the cheap stuff and hand loads). Good luck and have fun.

 

[C-130 Dude]

I recently diagnosed an issue with magpul sr25 mags for a new Aero build

my two 10 rounders would not lock back on empty

my four 20 rounders would correctly lock back on empty

close examination revealed different followers

the 10 rounders would not clear the right side feed lip enough to allow for lock back
I attempted to sand them to work correctly
no luck yet

an email to magpul revealed that individual SR-25 followers are not available for sale
but I was welcome to buy more mags

What a load of crap! Buy more... BS!

 

[C-130 Dude]

agreed on the weight !
mine are so heavy they cannot be anything but bench rest guns
14 lbs with a scope and mount
I use a padded machine gun sling

Mine is 14 lbs w/o scope

 

[C-130 Dude]

Thanks, Dude
It had a Magpul in it, it did the same thing. Got a C-Products, still did it. I believe we're on the right track, cause my mag with shells in it don't look any thing like any of the pics posted here. It's heartening to know and experience strangers offering advice. I really appreciate the time everyone has taken to offer up advice, experience, humor. I'll see what happens Sat or Sun when I go shooting.

Please post back. I'll come back to see what's up. I have had SO many hassels with building AR308s. I'm glad to help out. Have fun this weekend. Don't forget to post back.

 

[C-130 Dude]

Just went back and re-read my post. It should say built by a friend of mine and I . He basically held my hand thru it. Thank you for looking out for me.

Whew...

 

[WYO300RUM]

Well, you sure started out the harder way to learn about ARs. The AR10 versus the AR15 platform, home spun input in parts selection, machining, assembly........sink or swim throw the kid in the creek, see if he's SEAL material, or NOT...... Even before we had driver's licenses, cousin and I were given an old car with "transmission trouble." First step....remove tranny on neighbor's drive (yeah, I don't either....) second step.....???above our pay grade.....beat the Hell out of us????. Uncle came home, first question, did we run it, confirm issue, troubleshoot it? UH, that wasn't on our project plan!!! My first engine for one of my early Vettes....'62, I let a "friend" machine/thread the rocker studs because his dad had a vertical mill......we jimmied the lock on the shop.......first mistake.....many followed. NOW YOU TELL ME, the studs are NOT to look like a Hemi porcupine. Spent more fixing his expertise than I could have bought new hipo heads for. It has been a L-O-N-G road from that tranny through Engineering BS/MS degrees, 50 years of business/product/wealth building, learning to learn first when possible. Welcome to ARs....JUMP RIGHT IN!!! They are addictive, the Legos/Lincoln Logs/Tinker Toys of guns.....but, not necessarily fully interchangeable between platforms, brands, designs. You "assumed" .....ever hear what assume says when broken apart......your home boy knew what he is doing, and still, here you are.....tranny removed. Just funning with you. Been there, done that, learned this. It's more fun on this side of the "O****" learning curve. Opportunity presents itself to you on a platter...er, AR10. I paid my dues in spades, and trannys.....NEXT!!! (Never saw myself becoming a grouching old ***, but here I am.....KILLING IT!!!!) You state you know nothing about gas guns. First step in the right direction.....point proven.....too late. But, what do you know? Are you technical, a troubleshooter, a fixer, or NOT....a tranny yanker??? Both Brownells and MidwayUSA have great free AR learning videos on their sites. Also, American Gunsmithing Institute (AGI) has great AR gunsmith, function, assemble, dis-assemble troubleshooting videos for ARs and most other firearms. Maybe a friend, or forum member, might have the AGI video you could borrow. (I've got them all, but no longer waste heartbeats chasing loaned stuff with unknowns. Not sorry.) Check YouTube for surprisingly helpful videos. Often videos are more helpful than typed forum responses. Old boss, VP at Mary Kay, used to say, "Assume competence, but follow up like Hell." How many proper functioning AR10....or even AR15..... assemblies has your home boy completed previously?? Is he the retired SEAL Armorer,....doubtful or you wouldn't be here.......... or living-in-mommy's-basement guy? Are you the FNguinea pig? Did he select the parts? Assemble everything? Machine the 80% receiver on a mill or a drill-n-jig rig??? Your home spun input is another variable. IE....don't assume anything. Be aware that long action 308 platform AR is not "Mil-Spec" as the 5.56 platform is/can be/isn't necessarily. All AR10 manufacturers fabricate to their own prints, designs....some not interchangeable, compatible. Are all the assembly parts from same manufacturer, a complete one supplier kit, or a hodge-podge of mix-'n'-match good deals. Mix-'n'-match on bigger platform can induce function problems more so than 5.56 platform. Might "mix-'n'-match" upper and lower assemblies and mags with known proper functioning like assemblies to see if you can isolate the area of the issue. Magazine issue, upper issue, lower machining issue..... Compare your design....gas system length/parts/assembly, bolt carrier assembly, return spring/buffer assembly,........to known functioning gun systems. Confirm mag feeding in other functioning full assembled gun. Confirm upper function with known good mag and known functioning lower. ARs like to be run wet, especially new. You can machinist blue a cartridge in area being damaged and with another orientation mark to specifically confirm where the mark originates. Check those areas for minute burrs that might cause drag. The AR world is your oyster. Good luck. Keep everyone updated. Happy tranny pulling.....

Whewww !

Well, you sure started out the harder way to learn about ARs. The AR10 versus the AR15 platform, home spun input in parts selection, machining, assembly........sink or swim throw the kid in the creek, see if he's SEAL material, or NOT...... Even before we had driver's licenses, cousin and I were given an old car with "transmission trouble." First step....remove tranny on neighbor's drive (yeah, I don't either....) second step.....???above our pay grade.....beat the Hell out of us????. Uncle came home, first question, did we run it, confirm issue, troubleshoot it? UH, that wasn't on our project plan!!! My first engine for one of my early Vettes....'62, I let a "friend" machine/thread the rocker studs because his dad had a vertical mill......we jimmied the lock on the shop.......first mistake.....many followed. NOW YOU TELL ME, the studs are NOT to look like a Hemi porcupine. Spent more fixing his expertise than I could have bought new hipo heads for. It has been a L-O-N-G road from that tranny through Engineering BS/MS degrees, 50 years of business/product/wealth building, learning to learn first when possible. Welcome to ARs....JUMP RIGHT IN!!! They are addictive, the Legos/Lincoln Logs/Tinker Toys of guns.....but, not necessarily fully interchangeable between platforms, brands, designs. You "assumed" .....ever hear what assume says when broken apart......your home boy knew what he is doing, and still, here you are.....tranny removed. Just funning with you. Been there, done that, learned this. It's more fun on this side of the "O****" learning curve. Opportunity presents itself to you on a platter...er, AR10. I paid my dues in spades, and trannys.....NEXT!!! (Never saw myself becoming a grouching old ***, but here I am.....KILLING IT!!!!) You state you know nothing about gas guns. First step in the right direction.....point proven.....too late. But, what do you know? Are you technical, a troubleshooter, a fixer, or NOT....a tranny yanker??? Both Brownells and MidwayUSA have great free AR learning videos on their sites. Also, American Gunsmithing Institute (AGI) has great AR gunsmith, function, assemble, dis-assemble troubleshooting videos for ARs and most other firearms. Maybe a friend, or forum member, might have the AGI video you could borrow. (I've got them all, but no longer waste heartbeats chasing loaned stuff with unknowns. Not sorry.) Check YouTube for surprisingly helpful videos. Often videos are more helpful than typed forum responses. Old boss, VP at Mary Kay, used to say, "Assume competence, but follow up like Hell." How many proper functioning AR10....or even AR15..... assemblies has your home boy completed previously?? Is he the retired SEAL Armorer,....doubtful or you wouldn't be here.......... or living-in-mommy's-basement guy? Are you the FNguinea pig? Did he select the parts? Assemble everything? Machine the 80% receiver on a mill or a drill-n-jig rig??? Your home spun input is another variable. IE....don't assume anything. Be aware that long action 308 platform AR is not "Mil-Spec" as the 5.56 platform is/can be/isn't necessarily. All AR10 manufacturers fabricate to their own prints, designs....some not interchangeable, compatible. Are all the assembly parts from same manufacturer, a complete one supplier kit, or a hodge-podge of mix-'n'-match good deals. Mix-'n'-match on bigger platform can induce function problems more so than 5.56 platform. Might "mix-'n'-match" upper and lower assemblies and mags with known proper functioning like assemblies to see if you can isolate the area of the issue. Magazine issue, upper issue, lower machining issue..... Compare your design....gas system length/parts/assembly, bolt carrier assembly, return spring/buffer assembly,........to known functioning gun systems. Confirm mag feeding in other functioning full assembled gun. Confirm upper function with known good mag and known functioning lower. ARs like to be run wet, especially new. You can machinist blue a cartridge in area being damaged and with another orientation mark to specifically confirm where the mark originates. Check those areas for minute burrs that might cause drag. The AR world is your oyster. Good luck. Keep everyone updated. Happy tranny pulling.....

Whewww ! XLNT ! Hey, Ole' Red is a tranny puller .

 

[UncleDano]

UncleDano
I believe this was mentioned in the other post before this one was started at the request of the other poster. This is a new post started by Gregg C. Somewhere in that lengthy listing he mentioned the bcg not coming fully rearward when fired but hasn't said anything about it since then.
He has stated if he locks the bcg fully back with the stop and single loads from the mag, it chambers ok.
Cohunt has suggested the cartridges are not sitting properly oriented in the magazine and Gregg seems to agree his are not nose up. He was going to fix this by tweaking the mag lips and test fire it this weekend

None of my mags in .308 or 6.5 Creed have the bullets nose tipped up - but are perfectly level with the mag lips. So I am not sure I agree with this "fix".

I have had the other problem of the bcg not coming fully rearward, even with the lightest buffer (3.8 oz.). This I solved by replacing the standard AR10 spring (11 1/2" lg.) with a Luth-Ar AR10 spring which is 9 1/2" long.

 

[BigDon]

The shim doesn't raise he barrel. It extends the barrel slightly away from the lower thus decreasing the angle of the feed ramp relative to the magazine. The shim kit comes with 4 0r 5 shims of different thicknesses that look like washers and they slip over the chamber end of the barrel. this increases the distance between the mag and the feed ramp. I just looked on Midway and couldn't find them but a friend is checking and will let me know where he got his.

Aero Precision has these in multi packs.

 

[wolffo]

BCG length and weight, rear tube length, springs length and lbs., buffer weight and length are all different per manufacturer

my Aero nickel BCG is a few ounces heavier than their nitride BCG
its now the fanciest and most expensive paperweight I have

and wilson makes a +1/8" gas tube for AR10s
didnt work in any of my AR10s !