6.5 Creedmoor AR10 Cycling Problem

TonyTheTiger

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How stubborn do you have to be to fight your phone constantly correcting your bullshit english. I barely type and Android is correcting my West Virginia high school redneck education. You've got to be some kind of special to defy the constant, faithful, selfless service of auto correct. Frankly I don't even know how a person could pump out such a shitty post.
I have the opposite problem. I've consistently fat fingered so many words that my phone has learned them and tries to autocorrect to them on the rare occasion I type them properly the first time.
 

TonyTheTiger

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It's supposed to be a smart phone. Turns out it can only be as smart as my sausages are precise..
 
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FCS

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….The loads that I was shooting were super hot; 2800 ++ fps with a 142 gr bullet. I should have called it earlier, but after the last outing it became glaringly obvious that this loading is borderline unsafe. My Hornady brass from this test batch (almost all of them) had enlarged primer pockets to the point of being useless after a few firings I had one pierced primer. I trashed the lot and will decrease charge weight from here on out.

PLENTY of chamber pressure, not enough gas tube pressure? Seems like it should have enough gas to cycle three actions. I would question if I am way over gassed except the ejection pattern and my previous experience with other ar platform guns says otherwise.

I cleaned and inspected everything, gas block seems to be free of obstruction, can shoot brake cleaner through the tube and all the orifices just fine, everything seems to function as it should, even the BCG seems to run smooth again. Go figure.

I weighed my buffer; 4.95 oz's... looked like new, bolt travels back into the tube as it should

I ordered some factory ammunition to have a "control group", just to rule out my ammo.

Sooner or later things will get sorted out...

2800+ fps with a 142 SMK from a 22”, rifle length gas system, 6.5 Creed AR?
That’s pretty warm / hot for a 22” barreled bolt gun and is over half your problem with the 6.5 Creed upper not working well.
There is no borderline about it, that load is an accident waiting to happen and rifle / fired brass is giving you plenty of warning signs.

Buffer is too light, probably just fine and dandy for the 308 upper. Appreciably different time / pressure curve for 6.5 Creed vs 308, higher port pressure for 6.5 Creed.

0.076” diameter port size for rifle gas system, if anything is already too big, not too small.

Heavy up buffer, choke down gas, reduce powder charge for 2650-2675 fps w/142 SMK & H4350.

Trying to extract case while under too much pressure. Case is still slammed against chamber wall causing stiction, extra energy needed to extract case which causes failures to function and can look like undergassed.

Close off gas completely.
Find charge weight of H4350 that gives you 2650-2675 fps.
Open gas until bolt locks back on empty magazine.
Fine tune load, gas block setting, buffer weight for 6.5 Creed upper on lower. May or may not be same buffer / buffer spring in lower as used for 308 upper.
 

Just-some-guy

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2800+ fps with a 142 SMK from a 22”, rifle length gas system, 6.5 Creed AR?
That’s pretty warm / hot for a 22” barreled bolt gun and is over half your problem with the 6.5 Creed upper not working well.
There is no borderline about it, that load is an accident waiting to happen and rifle / fired brass is giving you plenty of warning signs.

Buffer is too light, probably just fine and dandy for the 308 upper. Appreciably different time / pressure curve for 6.5 Creed vs 308, higher port pressure for 6.5 Creed.

0.076” diameter port size for rifle gas system, if anything is already too big, not too small.

Heavy up buffer, choke down gas, reduce powder charge for 2650-2675 fps w/142 SMK & H4350.

Trying to extract case while under too much pressure. Case is still slammed against chamber wall causing stiction, extra energy needed to extract case which causes failures to function and can look like undergassed.

Close off gas completely.
Find charge weight of H4350 that gives you 2650-2675 fps.
Open gas until bolt locks back on empty magazine.
Fine tune load, gas block setting, buffer weight for 6.5 Creed upper on lower. May or may not be same buffer / buffer spring in lower as used for 308 upper.
This is what I suspect; the high pressure load has been completed scrapped.

My next decent load was 40 gr. of H4350 at just over 2625'ish fps so this is my next test sample along with a batch of factory Norma ammo. that I am waiting to arrive.

"Close off gas completely.
Find charge weight of H4350 that gives you 2650-2675 fps.
Open gas until bolt locks back on empty magazine.
Fine tune load, gas block setting, buffer weight for 6.5 Creed upper on lower. May or may not be same buffer / buffer spring in lower as used for 308 upper."

This is exactly my plan for my next trip out, I will update the post with my findings. Thank you for all the great advice!
 

gixxer822

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Sounds like the exact issue I’m having with my BA barrel. My barrel gas port was misdrilled, undersized by a lot.

Check your gas key for leaks with an air compressor and soak.
depending on your buffer set up rifle length system already come with heavy 5.5ish ounce buffers. I’m tried the lighter set up in the JP SCS. Have a range report soon. BA is a shit company btw. They aren’t making the BCGs so good luck getting any help if that’s the issue.
 

Just-some-guy

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Got it running!

I went out today for another test / tune session with both the .308 and 6.5 uppers.

First, I bought a KAW Precision gas block dimple / alignment tool and dimpled the barrel for the gas block set screw; this ensured that the gas block was aligned to the gas port. The spaghetti noodle trick did not work for me. Next I sourced a Lancer 10 rd. mag to go along with my 10 rd. PMags. I also picked up some Norma factory loaded 140gr. ammo. and a 10 ounce rifle buffer.

On the 6.5 upper I started with the factory ammo and the gas block closed, single round in the mag. and fired; naturally bolt did not lock back. I repeated this process while incrementally opening the gas block until the bolt began locking back on the empty mag; I then opened the gas block another click. I was still getting strange and erratic ejection patterns and dented case necks so I removed the 4.9 oz. buffer and installed a 10 0z. buffer. Things began to improve and the ejection pattern went to a pretty consistent 4:00 at about a 4' distance. A few case necks were still dented, here and there, but the rifle cycled normally and the bolt locked back on both types of mags when empty.

I then tried my standard bolt gun handloads at 39.2 gr. H4350 and it ran great with those too.

So, the solution appeared to be a combination of:

  1. Misaligned gas block
  2. Too hot of ammunition (initially)
  3. Too light of a buffer
By the end I could rapid fire 5 rounds from either mag. without malfunction and the BCG locking back, ejection 4 - 4.5' at 4:00. Seems to work great now with much lighter loads. I am currently at 250 total rounds fired; future testing will be needed but I am optimistic at this point.


Somewhat unfortunately, the .308 upper didn't like the heavy buffer; it cycled but ejection was all over and the BCG did not lock back after last round fired. Cases with this buffer were going out at 1:00 - 3:00 sporadically and only about a foot or two in distance. With the 4.9 oz buffer it runs great and ejects fine; 4' at 4:00. So, I will have to switch out the buffer when I swap uppers, not a big deal but I am somewhat surprised that the .308 upper didn't like the heavier buffer as it has a regular gas block and I assumed it was over gassed (like most AR's) and would benefit from the 10oz buffer.

Learn something new every trip out...
 
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Just-some-guy

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2800+ fps with a 142 SMK from a 22”, rifle length gas system, 6.5 Creed AR?
That’s pretty warm / hot for a 22” barreled bolt gun and is over half your problem with the 6.5 Creed upper not working well.
There is no borderline about it, that load is an accident waiting to happen and rifle / fired brass is giving you plenty of warning signs.

Buffer is too light, probably just fine and dandy for the 308 upper. Appreciably different time / pressure curve for 6.5 Creed vs 308, higher port pressure for 6.5 Creed.

0.076” diameter port size for rifle gas system, if anything is already too big, not too small.

Heavy up buffer, choke down gas, reduce powder charge for 2650-2675 fps w/142 SMK & H4350.

Trying to extract case while under too much pressure. Case is still slammed against chamber wall causing stiction, extra energy needed to extract case which causes failures to function and can look like undergassed.

Close off gas completely.
Find charge weight of H4350 that gives you 2650-2675 fps.
Open gas until bolt locks back on empty magazine.
Fine tune load, gas block setting, buffer weight for 6.5 Creed upper on lower. May or may not be same buffer / buffer spring in lower as used for 308 upper.
You Sir pretty much nailed your diagnosis! Thanks for the help ; )
 
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FCS

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You Sir pretty much nailed your diagnosis! Thanks for the help ; )

Great to read you have both uppers running well & information was useful.

When you rebarrel the 6.5 Creed upper, 22” barrel w/+3” gas will get you closer to being able to run same lower w/o putzing with different buffers. Ironically, probably be about 0.076” port @ +3” also.

6.5-8 Oz buffer would probably be about right for the 308 if cycles but fails to lock back w/10 Oz. Rifle has to run smoothly to be reliable and accurate.
 

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This thread is gold. I just went to the range to test out a new Proof barrel I put on my AR10. Shot lights out BUT wouldn't cycle reliably. I'm thinking that I have a similar issue. I loaded up 41.5gr H4350 with 140gr ELD and even with the gas block all the way open the rifle would cycle intermittently. Went home and used a borescope to realign the gas block and next time I'm going to try dropping my charge weight. Interesting thing is there was no pressure signs on the brass at all.

Would you guys recommend just moving right up to an H buffer weight? I'm currently running a JP LMOS and JP enhanced bolt with the JP SCS set at the standard buffer weight but I do have a couple tungsten weights laying around.
 

reubenski

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This thread is gold. I just went to the range to test out a new Proof barrel I put on my AR10. Shot lights out BUT wouldn't cycle reliably. I'm thinking that I have a similar issue. I loaded up 41.5gr H4350 with 140gr ELD and even with the gas block all the way open the rifle would cycle intermittently. Went home and used a borescope to realign the gas block and next time I'm going to try dropping my charge weight. Interesting thing is there was no pressure signs on the brass at all.

Would you guys recommend just moving right up to an H buffer weight? I'm currently running a JP LMOS and JP enhanced bolt with the JP SCS set at the standard buffer weight but I do have a couple tungsten weights laying around.
My 6.5CM Proof cycled fine with 2 tungsten weights but even better with 3 tungsten weights. I was only running about 4 clicks from open on an SLR AGB. 24" barrel. 120SMK's at 2750.
 
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gixxer822

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Need more info. Not locking back? Not chambering next round? What have you tried to fix it? Was the gas block misaligned
 

Billiam1211

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Need more info. Not locking back? Not chambering next round? What have you tried to fix it? Was the gas block misaligned

If you're referring to my post. Put 50 rounds down the tube yesterday and never achieved bolt lock on last round. SLR Sentry 8 clamp-on adjustable gas block, I started gas shut off and worked my way up in clicks until fully open. Cycling was intermittent, so I'd get 2 or 3 rounds to cycle then no extraction or failure to extract. The bright side is accuracy was awesome. I printed quite a few groups in the .5s while tuning. I loaded 50 rounds at 41.5 gr of H4350 + 140 gr ELDs. From what I read on this thread, seems it may be too hot for an AR10 platform - but I will determine that on the next range trip.

When I returned home from the range, I took off the gas block and re-aligned it using a borescope. I'm 100% sure I see the port lining up and I can see the set screw on the AGB move back and forth which would restrict/open gas flow so that shouldn't be an issue next time. I'm also going to lower my charge weight on my loads and likewise up my buffer weight on the JP SCS and see what the results are next time. The interesting thing is my brass showed no signs of pressure at the primer or on the case head, so I hope the buffer issue can solve it because I'd like to run my reloads at 41.5 gr / 2,740 FPS if I can.
 

reubenski

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If you're referring to my post. Put 50 rounds down the tube yesterday and never achieved bolt lock on last round. SLR Sentry 8 clamp-on adjustable gas block, I started gas shut off and worked my way up in clicks until fully open. Cycling was intermittent, so I'd get 2 or 3 rounds to cycle then no extraction or failure to extract. The bright side is accuracy was awesome. I printed quite a few groups in the .5s while tuning. I loaded 50 rounds at 41.5 gr of H4350 + 140 gr ELDs. From what I read on this thread, seems it may be too hot for an AR10 platform - but I will determine that on the next range trip.

When I returned home from the range, I took off the gas block and re-aligned it using a borescope. I'm 100% sure I see the port lining up and I can see the set screw on the AGB move back and forth which would restrict/open gas flow so that shouldn't be an issue next time. I'm also going to lower my charge weight on my loads and likewise up my buffer weight on the JP SCS and see what the results are next time. The interesting thing is my brass showed no signs of pressure at the primer or on the case head, so I hope the buffer issue can solve it because I'd like to run my reloads at 41.5 gr / 2,740 FPS if I can.
How long is your barrel? I'm doing 2740 with 140's using StaBall. It's a bit hot using 4451. 2800 with 130's. 24" Proof
 

Billiam1211

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Doesn't sound like too hot a load to me
Yeah that's why I thought that would be a good load to start at for break in. Almost every 6.5 CM barrel I've used shot tight groups around 2750 fps. My bet is the gas block was either slightly off or the buffer weight increase will help time things correctly. Unfortunately I have to wait until next weekend to continue testing :(
 

Billiam1211

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My 6.5CM Proof cycled fine with 2 tungsten weights but even better with 3 tungsten weights. I was only running about 4 clicks from open on an SLR AGB. 24" barrel. 120SMK's at 2750.

Got out Friday and tried out the heavier buffer weight, and it worked out. I ran 2 tungsten weights and 5 or 6 clicks open on the AGB and rifle started cycling. I only ran 50 rounds through the rifle, but it ran like a champ using the same exact load at 2,740 fps.
 
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reubenski

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Got out Friday and tried out the heavier buffer weight, and it worked out. I ran 2 tungsten weights and 5 or 6 clicks open on the AGB and rifle started cycling. I only ran 50 rounds through the rifle, but it ran like a champ using the same exact load at 2,740 fps.
Im at 5 or 6 clicks open as well. Sounds like a person could build a recipe of compatible parts to make people's experience in putting a 6.5 CM AR together a lot easier
 

Mike_in_FL

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    Im at 5 or 6 clicks open as well. Sounds like a person could build a recipe of compatible parts to make people's experience in putting a 6.5 CM AR together a lot easier

    I know @padom has before. He's stated specifically what he uses regarding the JP SCS, spring, weights, etc. The search function is your friend here.
     

    reubenski

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    I know @padom has before. He's stated specifically what he uses regarding the JP SCS, spring, weights, etc. The search function is your friend here.
    No need to search. I'm not looking for info. More confirming that JP SCS's with all tungsten weights and the heavy spring, heavy BCGs, Proof barrels, and SLR has blocks(specifically those components; not as examples) will make a large frame Creedmoor easy to run.

    Padom has said before that he uses LMOS BCGs so you are actually referring to different components
     

    Phil G

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    My search skills are obviously lacking. If anyone has the link to Padom’s JP SCS, Spring Weights, etc. handy, I would be grateful.
    Thanks
    Phil G
     

    Mike_in_FL

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    padom

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    @padom knowledge bomb us

    I've built and fixed for Hide members shit going on 50-60 6.5cm large frame gassers over the last 8-9 years, most have been with LMOS JP carriers and yes I have a very specific recipe as stated after lots of combination testing with AGB, carrier and SCS....

    But....I have built 10-15 with RCA Full Mass Carriers so I have some data on that combo as well.

    Most recently.....past 1.5-2yr or so...ALL AR builds of mine, large and small, I've done away with problematic, pita to adjust, seizing AGB's... yes, I know, I know...if you come home and tear it down and clean it up and remember the settings and number of clicks and work it in and out and Kroil it up it won't seize....guess what, no thanks I have better things to do with my time. I own them all, SLR, SLA, Syrac, JP, Seekins..put enough rounds through them and they all seize

    I now only USE RCA BCG's with adjustable gas keys and they are the tits...adjust just like a AGB, fast, easy to do...you can even buy just the AGK for your existing BCG if you want...

    Once I get back into the gun room today I'll post up my combos I have used...

    Note....all my combos are with rifle length buffer tubes and PRS stocks for my large frame gassers and precision small frame gassers
     

    padom

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    Looking at my notes for LMOS gassers.....here is my SCS setup...then my procedure to tune gas is as follows


    22" 6.5cm Bartlein's, +2 gas
    JP LMOS BCG
    SCS with 2 tungsten weights
    Yellow spring

    Tune the AGB till it locks back on a round. Then shoot 25-50rd (more is better) but with only 3rd in the mag at a time. Make sure it locks back every time... It might not. Which means you need to open the gas block up 1 or 2 more clicks.. ...


    For full mass BCG....you'll want less weights and lighter spring combo than mentioned above. ....ill post my combo in a little bit...but to tune for your rifle do this


    Tune the AGB till it locks back on a round. Then shoot 25-50rd (more is better) but with only 3rd in the mag at a time. Make sure it locks back every time... It might not. Which means you need to open the gas block up 1 or 2 more clicks.. ...

    After you have done that, inspect your brass, is it ripped to shit, heavier extractor marks, raised burs or looks like the case rims are getting ripped up? If so, your BCG isnt staying locked long enough and its starting to move to the rear before the pressures have subsided enough for the brass to retract, so its literally ripping it out of the chamber too early.... If you have to go up to the next heaviest spring, repeat all the steps I mentioned above again then check your brass again. You will find a combo that shoots great and damages your brass the least.
     
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    Mocadon

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    Where can I buy a 10oz carbine buffer weight? I'd like to try it on my Adams Arms P2 in 6.5 Creedmoor because on certain loads it's clearly trying to extract the case too early and I'm running a 5.5 oz weight now at 33% (setting 4) gas. I'm running suppressed with an Omega 300.
    Doesn't seem to be an issue unsuppressed.
     

    msgriff

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    Where can I buy a 10oz carbine buffer weight? I'd like to try it on my Adams Arms P2 in 6.5 Creedmoor because on certain loads it's clearly trying to extract the case too early and I'm running a 5.5 oz weight now at 33% (setting 4) gas. I'm running suppressed with an Omega 300.
    Doesn't seem to be an issue unsuppressed.
    Talk to Clint at Slash's Heavy Buffers. You're going to need to know the length of your existing buffer and the internal depth of your RE/buffer tube. Don't forget to tell him you have a piston gas system.
     
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    Mocadon

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    Talk to Clint at Slash's Heavy Buffers. You're going to need to know the length of your existing buffer and the internal depth of your RE/buffer tube. Don't forget to tell him you have a piston gas system.
    Thanks! I just emailed him. 👍
     

    Fighting the good fight

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    So here is my issue... I built an AR10 (DPMS style) in .308 with a Criterion 18" rifle length gas system, standard weight rifle buffer and spring, and a Toolcraft BCG; this setup runs flawlessly with pretty much all my loadings and with the factory ammunition that I've (sparingly) used.

    I decided that I wanted to build another upper in 6.5 Creedmoor. I am using a Ballistic Advantage 22" Premium barrel (rifle length gas) Superflous Arms adjustable gas block, and a Toolcraft HP BCG. Since assembling this upper, and during load development I have had continued issues with cycling. The problem appears to be short cycling.

    When I developed a load for this upper I began using SMK 142gr bullets with H4350 powder at 39 grains and worked my way up to 42 grains; I had short stroke issues with the lighter loadings (39.0 and 39.5), but things seemed to be reliable at higher loadings. This was all done with the gas block in the most "open" position. However, I was only testing 5 rounds of each charge weight.

    Today I took the upper out to sight it in and initially it seemed to work fine with the load I chose (42 grains of H4350 / SMK 142's); ejection was initially at 3:00. After twenty rounds or so it started to short stroke and the ejection pattern moved to about 4:00. The gas block remained in the most "open" position throughout, I have also verified that the gas port is in alignment with the block.

    So, here is what I am wondering about. With the .308 upper the rifle has been super reliable. With the 6.5 upper it has always appeared to be undergassed. Could my issue be the standard .308 rifle buffer and buffer spring? I am temped to change out the buffer spring to a lighter one, but I really don't want to change the parts of the lower; I thought it would be cool to have a large frame gas gun with two uppers in different calibers that could just be push pinned on and things would work...

    I could go hotter on my loads, but I am already seeing signs of minor pressure, so I don't think that is the best option. I haven't done a lot of testing with any factory ammo. due to me not having any currently, but I have never had issues with developing functional ammunition across multiple calibers in the past.

    Any ideas?
    I had the exact issue not to long ago with a 22" 65 build it wouldn't even run factory sometimes let alone loads i was working up. I came on here everyone was telling me 2 things. I needed an adjustable gas block. I dont know why cause it was short stroking so all that would have done was help me restrict the gas even more. I already was short stroking that would have made it worse. Then i was also told to get a lighter spring. I was running the standard aero carbine 308 buffer kit. So i thought about it and i actually went against the grain. Im grateful for all the advice but i went in the opposite direction. I went to a heavier buffer. In my mind it made more sence to go to a heavier buffer. More inertia from the gas and weight of both the bcg and heavier buffer was enough to compress the spring a little more and it got my bcg to go back further. Never had a cycling issue since. So sometimes you have to think outside the box. That extra ounce and a half or so have the bcg and buffer enough inertia to travel further back to complete the cycle. Not to mention very well over lubed helps alot as well
     

    Mike_in_FL

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    I had the exact issue not to long ago with a 22" 65 build it wouldn't even run factory sometimes let alone loads i was working up. I came on here everyone was telling me 2 things. I needed an adjustable gas block. I dont know why cause it was short stroking so all that would have done was help me restrict the gas even more. I already was short stroking that would have made it worse. Then i was also told to get a lighter spring. I was running the standard aero carbine 308 buffer kit. So i thought about it and i actually went against the grain. Im grateful for all the advice but i went in the opposite direction. I went to a heavier buffer. In my mind it made more sence to go to a heavier buffer. More inertia from the gas and weight of both the bcg and heavier buffer was enough to compress the spring a little more and it got my bcg to go back further. Never had a cycling issue since. So sometimes you have to think outside the box. That extra ounce and a half or so have the bcg and buffer enough inertia to travel further back to complete the cycle. Not to mention very well over lubed helps alot as well

    What you're saying fixed your rifle pretty much contradicts what you're saying it was doing.

    You're using words such as "short stroking" which implicitly tells everyone reading this that there's not enough gas to run the gun. In actuality it sounds like you had too much gas and your BCG was running too fast for the magazine.

    So if a heavier buffer solved the problem you were over gassed, not under gassed to begin with. Your explanation of how a BCG moving with the same gas pressure can suddenly move a heavier object against a spring and further compress it, makes no sense.

    People are trying to solve your problem for free, right?
     
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    Mocadon

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    My 3 cents;
    1. All things being equal, 6.5 Creedmoor has more gas than.308.
    2. If you've built up some copper fouling or built up a carbon ring, then your pressures will start to increase and the gun may start to extract early.
    3. A heavier buffer and spring often seems to cure #1 and #2. But also try turning the gas down. If you're really short stroking then clean the gun and strip the copper and try full gas again. It's possible to have early extraction symptoms and also short stroke.

    Good luck.
     

    padom

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    What you're saying fixed your rifle pretty much contradicts what you're saying it was doing.

    You're using words such as "short stroking" which implicitly tells everyone reading this that there's not enough gas to run the gun. In actuality it sounds like you had too much gas and your BCG was running too fast for the magazine.

    So if a heavier buffer solved the problem you were over gassed, not under gassed to begin with. Your explanation of how a BCG moving with the same gas pressure can suddenly move a heavier object against a spring and further compress it, makes no sense.

    People are trying to solve your problem for free, right?

    Overgassed...my exact thoughts....
     

    Paradox

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    New Jersey , USA
    That's a good question, the brass looks pretty normal; not dinged up, not scuffed too bad. The primers (CCI 200) are flat with a very slight crater around the firing pin strike. I did have one pierced primer today, which has never happened to me before.

    I have been theorizing that there is a lack of gas pressure based off of the ejection patterning. However, I could turn the gas block down / restrict it, and see if that helps.

    What it does exactly is: I load 5 rounds in the magazine and then proceed to slow fire. The rifle cycled fine for about the first 20 rounds, then it started to fail to pick up the next round off of the magazine, so the bolt closes on an empty chamber and goes into a type 1 malfunction / "click". After I run the charging handle it will fire the next few rounds fine, then repeat the malfunction. As this happened I noticed the ejection pattern seemingly went from 3:00 to 4:00 o'clock at about 3 - 4' away.

    So far, it is not a "major" problem; maybe it just was getting dirty as the wind was blowing the fine grit into the action pretty good. However, the .308 upper runs and runs under the same conditions and never complained once. On the plus side, this upper seems to shoot pretty accurately right out of the gate.
    I had the same issue with a factory dpms, amd it all came down to some machine marks on the bcg, so i took it apart ran some emory paper on rhe rail points, soaked overnight in motor oil, drained cleaned, reoiled the shit out of it and it worked fine, so i rapid fired a hundred rounds or so and no more issues and will eat any ammo you pit in it.
     

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    Paradox

    Sergeant of the Hide
    Full Member
    Minuteman
    Mar 22, 2022
    235
    71
    New Jersey , USA
    So here is my issue... I built an AR10 (DPMS style) in .308 with a Criterion 18" rifle length gas system, standard weight rifle buffer and spring, and a Toolcraft BCG; this setup runs flawlessly with pretty much all my loadings and with the factory ammunition that I've (sparingly) used.

    I decided that I wanted to build another upper in 6.5 Creedmoor. I am using a Ballistic Advantage 22" Premium barrel (rifle length gas) Superflous Arms adjustable gas block, and a Toolcraft HP BCG. Since assembling this upper, and during load development I have had continued issues with cycling. The problem appears to be short cycling.

    When I developed a load for this upper I began using SMK 142gr bullets with H4350 powder at 39 grains and worked my way up to 42 grains; I had short stroke issues with the lighter loadings (39.0 and 39.5), but things seemed to be reliable at higher loadings. This was all done with the gas block in the most "open" position. However, I was only testing 5 rounds of each charge weight.

    Today I took the upper out to sight it in and initially it seemed to work fine with the load I chose (42 grains of H4350 / SMK 142's); ejection was initially at 3:00. After twenty rounds or so it started to short stroke and the ejection pattern moved to about 4:00. The gas block remained in the most "open" position throughout, I have also verified that the gas port is in alignment with the block.

    So, here is what I am wondering about. With the .308 upper the rifle has been super reliable. With the 6.5 upper it has always appeared to be undergassed. Could my issue be the standard .308 rifle buffer and buffer spring? I am temped to change out the buffer spring to a lighter one, but I really don't want to change the parts of the lower; I thought it would be cool to have a large frame gas gun with two uppers in different calibers that could just be push pinned on and things would work...

    I could go hotter on my loads, but I am already seeing signs of minor pressure, so I don't think that is the best option. I haven't done a lot of testing with any factory ammo. due to me not having any currently, but I have never had issues with developing functional ammunition across multiple calibers in the past.

    Any ideas?
    I'm gonna say theres not a thing wrong with it other than, just like me you probably don't understand the term run it wet. That means let that thing drown in it i broke the bolt down, soaked in oil overnite then let it drain off, cleaned it, then oil the shit out of it and in my case with a magnifying glass there was some roughness on the bolt rails so i used a little emory cloth on it. so that and soaking it to death i pumped 200 rounds through it and now its fine. by the way 4pm is not short stroking, its perfect from 3-430. oil it first , once you start messing with the buffers and springs for a band aide you'll wind up chasing more issues. Have you tried any factory ammo? M80s or 168s? and have you done the one round mag test? My post was almost identical to yours and after all the bs it was simple breakin and a shit ton of lube.

    Read this before messing with buffers.

    ar10-buffer-weights.jpg

    AR-10/AR 308 BUFFER WEIGHTS​


    There’s a good amount of information out there online already when it comes to what buffer weights and springs you should use for AR-15s but not a whole lot of clarity when it comes to AR 10 buffer weights. Today, we aim to remedy that. We’ve gotten great feedback on customers utilizing our AR-15 buffer weights blogs and now want to do AR10 buffer weights and springs the same justice.
    ar10 vs ar308 lower receiver

    To figure out which AR-10 buffer weight and spring combination will work best in your AR10 or LR308 rifle, you’ll have to first understand some key differences between the AR-10 and LR 308 platforms. Essentially, here are the main takeaways that you should know:
    • AR10 is a term often incorrectly and interchangeably used with LR308.
    • Most people actually mean LR308 when they say “AR-10”.
    • Armalite 10 rifle parts are largely not interchangeable with the AR-15.
    • Several LR-308 parts are universally interchangeable with the AR15.
    • The shape of the two different upper receivers are different but have no functional difference.
    • AR-10 refers to Armalite’s design.
    • LR308 refers to the DPMS design. Sometimes also called ‘AR-308’.
    • DPMS stands for Defense Procurement Manufacturing Services (company’s full name is DPMS Panther Arms).
    Going forward we’ll continue to use the term ‘AR-10’ (in your head you can replace this term with ‘AR-308’ specifically because that’s what we sell) just think of “AR-10” as an overarching, caliber specific designation and not a reference to the original Armalite rifle.

    ARE AR 15 AND AR 10 BUFFER SPRINGS THE SAME?​

    rifle length carbine and spring vs carbine buffer tube and carbine buffer and spring

    Technically, yes. All AR10 buffer springs and buffer weights are going to be able to fit in any AR-15 or LR-308 rifle. Whether they will make your rifle cycle consistently and perform reliably is a different story. That’s why there are specific buffer spring designs and various buffer weights which will work better or worse for certain length rifles. But yes, AR-15 and AR308 buffer springs specifically are the same length which makes them directly interchangeable.
    You can actually run your AR10 rifle without any “AR10 buffer” and just use the spring. Only the first couple or few shots will work but the experience will not be pleasant. The violent action of the BCG going back and forth will be more intense and cause more wear and tear on your gun. There’s also no guarantee that the gun will cycle consistently.
    The main difference in the AR buffer springs lies in the length. Going back to the actual AR-10 (Armalite design), the interchangeability is not reliant on whether you’re using an AR10 or AR308, it’s actually a buffer tube issue. AR15 style stocks are compatible with both AR15’s and AR10’s, hence the compatibility, because they use the same length buffer tubes. But if you use an A1/A2 style stock it will require a longer spring.

    AR10 BUFFERS (LR 308) EXPLAINED​

    traditional rifle and carbine buffer

    There are three types of buffers – rifle buffers, carbine buffers and adjustable buffers. So when do you use a carbine buffer vs a rifle buffer? Carbine buffers or buffers with weights that fall under the H2 or H3 category are most commonly what AR-10 owners should be using along with carbine length butt stocks. Rifle buffers are really only used with the A1/A2 style buttstocks due to the rifle buffer tube being longer. Basically every buffer used today is going to be some sort of carbine length buffer.
    Why are buffer weights important? If you were to shoot with just a buffer spring and no buffer weight in a full auto/select fire AR-10 — you’d likely experience light strikes and because the timing of the bolt going back and forth would be off and not completely in sync with the hammer.
    odin works ar10 adjustable carbine buffer

    Having a buffer slows that cyclical action down to help you avoid light strikes, promote reliable cycling of rounds being fired, ejected and properly fed into the chamber. Once dialed in, you might surprise yourself with a softer and flatter shooting AR10 style rifle than you initially expected. You also don’t want too heavy of a buffer either otherwise you risk slowing down that bolt way too much which would cause malfunctions or failures.

    CHOOSING AN AR10 BUFFER WEIGHT​

    odin works adjustable buffer weight chart

    Generally speaking, don’t get hung on the rifle length buffers. AR10 carbine buffer weights will range anywhere between 3.8 to 5.4 oz for any AR10 style rifle. But that weight range can also depend on where you’re getting the AR 10 buffer from as well. The chart above is specifically for Odin Works’ adjustable buffers which allow users to tune their buffer weight to get your AR308 rifle cycling just the way you want.
    There’s no “one size fits all” answer when it comes to the topic of AR10 buffer weights and springs because there are just so many factors involved. Namely, the rifle length, ammunition load, buffer weight, buffer spring type, whether you’re shooting suppressed, etc. Some experimentation or trial and error is going to be inevitable but with this information you can make a better and more educated guess. Unlike the AR-15 buffer weights, we don’t have a chart for you based on length of rifle for AR-10s because there is less of a barrel length difference in AR10 style rifles. Most barrels are going to be around 18” to 20”.
    But understanding the symptoms, like if you’re experiencing short stroking or a failure to feed or eject — will also help you know what you’re dealing with and advise your next move. Below, you’ll see a figure for how to diagnose the “health” of your rifle’s ejection angle based on which direction empty casings are flying after extraction. This concept applies to the AR-15 just the same as the AR-10 or AR-308.
    ar-15 ar-10 casing ejection angle chart

    DON’T FORGET ABOUT THE GAS BLOCK​

    A lot of people seem to forget how big of an impact the gas block can have on the shooting experience of any AR platform rifle. Most factory built guns are going to come with an overgassed gas block which will promote higher reliability between different parts and a wider variety of ammunition loads.
    But when you’re building your own rifle from the ground up that tends to get in the way of properly tuning your rifle. That’s why it’s highly advantageous to have an adjustable gas block as it could mean the difference of your rifle cycling or not. Still, it’s best to think about the adjustable gas block as a fine tuning process whereas the majority of your guesswork is going to be within the buffer system.