6mm ARC cycling issue

[sfvshooter]

I tried to go back and read others who have similar builds and my problem is a little different (or maybe it's not).

I have an Odin 18" rifle + 2" 6mm ARC barrel with a Superlative Arms adjustable gas block. Initial setup with with an H buffer. Loaded a Duramag 6.5 grendel mag with 1 round each time and adjusted the gas block until it locked back on an empty mag.

I then tried loading additional rounds, but anytime I loaded more than 2 rounds, bolt ended up sliding over the round. With 2 rounds, it worked fine. With more than 2 rounds, bolt slid over the next round.

During 2 additional trips to the range, I tried different mags (6.8 spc, 7.62x39, and even bought ASC 6mm ARC mags), but same issue. With some other mags, it wouldn't even cycle with 2 rounds. I tried JP silent spring, Kynshot recoil buffer, H1 buffer and tried to open/close the gas block more, but no luck.

I've read others have had problems with finding reliable mags for 6mm ARC so I can't tell if it's that or if it's a build (gas/buffer) issue.

Any suggestions?

 

[Mike_in_FL]

You have a +2 gas system on an 18" barrel so you have very little dwell time. I would go back to a simple spring and the lightest buffer you have and tune to open on an empty mag. THEN add 1 or 2 more clicks of gas for reliability. Check for functionality with the Grendel and ARC specific mag first. I wouldn't have much hope of the other two working.

If it's not picking up a round you either have too much gas, which I doubt, or too little and it's short stroking which is what I'd guess.

How many rounds are through the rifle at this point? Are you running it wet? Do you have some resistance because nothing is broken in yet?

Stop throwing so many parts at it. If you don't have a simple CAR buffer, take a weight out of the H.

 

[2aBaC̶a̶]

likely your magazine.

 

[r.tenorio671]

... in the early days advent of 6mm ARC there were quite a few problems reported on the Odin 18" rifle + 2" 6mm ARC barrel. The majority or "resolutions" in subsequent feedback was those owners ended up enlarging the gas port, some enlarging gas port in combinations of lighter springs, BCG's, buffers, etc. If you ran your SA AGB "fully opened" and still had issues, an AGB won't do anything to help an already under-gassed rig.

 

[Dino11]

... in the early days advent of 6mm ARC there were quite a few problems reported on the Odin 18" rifle + 2" 6mm ARC barrel. The majority or "resolutions" in subsequent feedback was those owners ended up enlarging the gas port, some enlarging gas port in combinations of lighter springs, BCG's, buffers, etc. If you ran your SA AGB "fully opened" and still had issues, an AGB won't do anything to help an already under-gassed rig.

The gas port on the Odin barrel is already .101 in diameter. That's pretty big to start. I wrote up a fix in another thread. Most are running a carbine RE and having issues. You just need to go against the grain and run a lighter buffer and spring, and I know this goes against what most folks are used to but it works. And it makes for a nice soft shooting rifle. I run a Rifle RE and that only made the problem worse. I had to make my own weights for the rifle buffer and get the weight down to 3.8 oz and run a -10% spring.

 

[67rschev]

I have the Odin 18 inch with a plus 2. For reliability, needed to run a -10% spring as Dino has stated above. I will get a look at which weight buffer I had settled on when I have the time. Have a low mass carrier to experiment with, but other projects have taken priority over this one.

 

[2aBaC̶a̶]

You got it to work and lock open on empty mag with 1 or 2 rounds loaded...

But the subsequent posts seem to allude to undergassing as a problem which means it's so light that the upward pressure of more than two rounds in the magazine pushing the BCG is enough for it not to cycle?

What gas setting did you arrive on when you got it to lock back on empty mag?

 

[sfvshooter]

Discussed with my gunsmith and he enlarged the gasport. Tested at the range today and it ran flawlessly with the ASC 6mm ARC mag.

He did mention it might become over-gassed over time, but since I have an adjustable gas block I can adjust as needed

Seems like a design flaw by Odin.

 

[shortround91]

I had a similar issue with my 300 Ham’r that I built when the cartridge was new. Of course like you I was way undergassed opening the port up a touch did the trick for me as well. My ARC build started with feeding issues as well my fix was a total rebuild on the new elander 6.5 mag. I disassembled a Lancer 10 rounder and installed the spring in the Elander 10rd mag. Since then I haven’t had a single issue feeding with that mag

 

[El Viejo]

I had a similar issue with my 300 Ham’r that I built when the cartridge was new. Of course like you I was way undergassed opening the port up a touch did the trick for me as well. My ARC build started with feeding issues as well my fix was a total rebuild on the new elander 6.5 mag. I disassembled a Lancer 10 rounder and installed the spring in the Elander 10rd mag. Since then I haven’t had a single issue feeding with that mag

I have an 18" Ballistic Advantage 6 ARC barrel with a non-adjustable mid-length gas system and an Aero Precision BCG. From the very beginning, I have been using a Thunderbeast suppressor. I have two kinds of intermittent feeding problems using only Elander 6.6 Grendel mags. Given the other comments in this thread, I am guessing the combination of components is resulting in an under-gassed rig.

First question: Did you replace the Elander spring to get more upward push in the mag? Absent a spare Lancer mag, where would I get a stronger mag spring?

Second question: For at least one round in a 10 round mag, the bolt fails to close fully. A simple push on the forward assist is needed. Does this suggest that I need a stronger spring or more weight?

 

[shortround91]

I have an 18" Ballistic Advantage 6 ARC barrel with a non-adjustable mid-length gas system and an Aero Precision BCG. From the very beginning, I have been using a Thunderbeast suppressor. I have two kinds of intermittent feeding problems using only Elander 6.6 Grendel mags. Given the other comments in this thread, I am guessing the combination of components is resulting in an under-gassed rig.

First question: Did you replace the Elander spring to get more upward push in the mag? Absent a spare Lancer mag, where would I get a stronger mag spring?

Second question: For at least one round in a 10 round mag, the bolt fails to close fully. A simple push on the forward assist is needed. Does this suggest that I need a stronger spring or more weight?

I have an 18" Ballistic Advantage 6 ARC barrel with a non-adjustable mid-length gas system and an Aero Precision BCG. From the very beginning, I have been using a Thunderbeast suppressor. I have two kinds of intermittent feeding problems using only Elander 6.6 Grendel mags. Given the other comments in this thread, I am guessing the combination of components is resulting in an under-gassed rig.

First question: Did you replace the Elander spring to get more upward push in the mag? Absent a spare Lancer mag, where would I get a stronger mag spring?

Second question: For at least one round in a 10 round mag, the bolt fails to close fully. A simple push on the forward assist is needed. Does this suggest that I need a stronger spring or more weight?

Yes I’m absent one Lancer mag now but there only for my 300 Ham’r so not a huge loss there. The Lancer spring also has less pressure on it compared to me a oversprung Elander, I even filled it let it sit for a month just to see if the spring would loosen up a bit. Maybe I needed to go 3 month? Who knows there, now I am also running a carbine tube and spring with a standard buffer so nothing fancy on that end at all. As for mags I have 3 dedicated mags it’s for the ARC a factory 6mm Stoner a D&H Tactical says 6.5 Grendel but works flawlessly however doesn’t like 2.260 OAL loads they just won’t fit and of course the modified Elander. I have also thought about removing the spring from a 10 round magpul as well just to test if things work out throw them Lancer back together

 

[shortround91]

Yes I’m absent one Lancer mag now but there only for my 300 Ham’r so not a huge loss there. The Lancer spring also has less pressure on it compared to me a oversprung Elander, I even filled it let it sit for a month just to see if the spring would loosen up a bit. Maybe I needed to go 3 month? Who knows there, now I am also running a carbine tube and spring with a standard buffer so nothing fancy on that end at all. As for mags I have 3 dedicated mags it’s for the ARC a factory 6mm Stoner a D&H Tactical says 6.5 Grendel but works flawlessly however doesn’t like 2.260 OAL loads they just won’t fit and of course the modified Elander. I have also thought about removing the spring from a 10 round magpul as well just to test if things work out throw them Lancer back together

By the way the 300 Ham’r is one of my favorite 300 yard rounds mine shots sub .5 groups all day long pretty much with any hand load I throw at it.

 

[El Viejo]

By the way the 300 Ham’r is one of my favorite 300 yard rounds mine shots sub .5 groups all day long pretty much with any hand load I throw at it.

I think I understand that you were trying to provide less upward push from the magazine to reduce the amount of resistance to stripping and chambering the top round. Correct?

Are you running your 300 Ham'R suppressed?

 

[shortround91]

I think I understand that you were trying to provide less upward push from the magazine to reduce the amount of resistance to stripping and chambering the top round. Correct?

Are you running your 300 Ham'R suppressed?

Yes and worked like a charm. I’m sitting at 13 months now waiting on my form 4 you have to love the ATF these days

 

[Mac679]

I have an 18" Ballistic Advantage 6 ARC barrel with a non-adjustable mid-length gas system and an Aero Precision BCG. From the very beginning, I have been using a Thunderbeast suppressor. I have two kinds of intermittent feeding problems using only Elander 6.6 Grendel mags. Given the other comments in this thread, I am guessing the combination of components is resulting in an under-gassed rig.

First question: Did you replace the Elander spring to get more upward push in the mag? Absent a spare Lancer mag, where would I get a stronger mag spring?

Second question: For at least one round in a 10 round mag, the bolt fails to close fully. A simple push on the forward assist is needed. Does this suggest that I need a stronger spring or more weight?

I'm running 24 round E-Landers with an 18" Proof. I've run it for the last 3 Quantified Performance matches. First match I had issues pop up where it would inconsistently fail to feed. From the look of things, it seemed like the magazine would get sluggish after so many rounds and not keep up with the BCG (and the rifle isn't overgassed). So after that match, I ordered some Wolff extra power AR15 mag springs for 3 of the mags (individual mags I knew I had problems with were in that group). Those 3 became my test bed and I used them exclusively during train up and during the match. Since then I have not had the issue repeat itself for 2 matches and practice sessions prior to. I've passed that fix along to others who were having E-Landers and it seems to have fixed their problems as well. Might be worth looking into.

 

[FromMyColdDeadHand]

Why run a +2 on a 18inch barrel? Or maybe I'm confsued, I would call a rifle length gas as 'standard' on a 18inch- is this rifle+2 or carbine+2? How does it compare to rifle gas length?

 

[shortround91]

First Wow am I happy finally first thing get the usual message my paperwork still in limbo a few hours later a text that my suppressor paperwork came back approved go figure deny a disabled Army vet who’s never been arrested just don’t get 13 months when efiles have already started approving. So after a 13 month wait it’s finally on the way . Now I’m running a rifle length gas system but am using a carbine buffer system instead of the suggested rifle buffer on my build. I did get to do a little more testing with some 107 Match kings that turned out excellent also.

 

[El Viejo]

I'm running 24 round E-Landers with an 18" Proof. I've run it for the last 3 Quantified Performance matches. First match I had issues pop up where it would inconsistently fail to feed. From the look of things, it seemed like the magazine would get sluggish after so many rounds and not keep up with the BCG (and the rifle isn't overgassed). So after that match, I ordered some Wolff extra power AR15 mag springs for 3 of the mags (individual mags I knew I had problems with were in that group). Those 3 became my test bed and I used them exclusively during train up and during the match. Since then I have not had the issue repeat itself for 2 matches and practice sessions prior to. I've passed that fix along to others who were having E-Landers and it seems to have fixed their problems as well. Might be worth looking into.

Thanks for the tip. I will give it a try. BTW, I have been running the E-Lander 10 rd mags both for load testing and for hunting. I figured if I couldn't drop a deer with 10 shots, I would take up a more dramatic sport like tiddlywinks.

 

[hlee]

Elander mags have been a big no-go in 2 6.5 Grendels and a 224 predator in my safe. They look amazing, but the follower binds with the smallest amount of dust or fouling. I know that ASC mags get a bad rap, but they are GTG in my 3 rifles.

 

[shortround91]

Thanks for the tip. I will give it a try. BTW, I have been running the E-Lander 10 rd mags both for load testing and for hunting. I figured if I couldn't drop a deer with 10 shots, I would take up a more dramatic sport like tiddlywinks.

I’m only 10 rounders also for the ARC and Ham’r I bench shoot them and the 20-30’s etc get in my way

 

[r.tenorio671]

I have an 18" Ballistic Advantage 6 ARC barrel with a non-adjustable mid-length gas system and an Aero Precision BCG. From the very beginning, I have been using a Thunderbeast suppressor. I have two kinds of intermittent feeding problems using only Elander 6.6 Grendel mags. Given the other comments in this thread, I am guessing the combination of components is resulting in an under-gassed rig.

First question: Did you replace the Elander spring to get more upward push in the mag? Absent a spare Lancer mag, where would I get a stronger mag spring?

Second question: For at least one round in a 10 round mag, the bolt fails to close fully. A simple push on the forward assist is needed. Does this suggest that I need a stronger spring or more weight?

.....was that a typo on your gas system? I don't ever recall BA ever offering MID-LENGTH GAS on their 18" tubes, only the 16" tubes. Unless you bought it new, directly from BA or one of their affiliated distributors, you might want to confirm it actually is a BA offering. The other question I have is what brand of upper and lower are you using, mixed or same brands? This is a factor that can affect the feeding issue you are encountering and MAY NOT actually be the magazines fault, especially if there is enough variance in tolerances or "stacking" that affect the magazines interface, fit & function with the rest of the components.

...it is unlikely that an 18" tube with MID-LENGTH GAS would be "under-gassed", especially when run with a suppressor. If anything, it may actually result in a higher cyclic rate and outrun the feed rate of the magazines. You didn't specify what kind of feed issues you're experiencing or detail how/where your fired cases "eject" to. This is one possible area that can be used to identify gassing functionality/issues.

...are the bolt failures to close fully occurring with factory ammo or handloads? Early batches of Hornady Black w/105 BTHP had COAL's that were long causing jamming into the lands, which could prevent the bolt from fully closing (as well as pressure spiking). What buffer spring are you using, that is ONE of the factors that could affect the BCG movement for the feed/lock cycle. Another factor is if magazine interface is off enough to create "drag" on the BCG cycling....which can also contribute to feeding and bolt closure issues you mentioned.

....both the Duramag and E-Lander mags (26, 24, 17 & 10) have all worked 100% in my build, which uses an 18" BA w/RLGS and a standard carbine buffer system. I do use an SLR AGB, something I do on ALL of my AR's in multiple calibers/lengths. I have only run my handloads, factory ammo has not been available in my locale.

 

[shortround91]

I had the same issue with factory ammo hitting the lands. I set them back a touch and had no issues after.

 

[El Viejo]

.....was that a typo on your gas system? I don't ever recall BA ever offering MID-LENGTH GAS on their 18" tubes, only the 16" tubes. Unless you bought it new, directly from BA or one of their affiliated distributors, you might want to confirm it actually is a BA offering. The other question I have is what brand of upper and lower are you using, mixed or same brands? This is a factor that can affect the feeding issue you are encountering and MAY NOT actually be the magazines fault, especially if there is enough variance in tolerances or "stacking" that affect the magazines interface, fit & function with the rest of the components.

...it is unlikely that an 18" tube with MID-LENGTH GAS would be "under-gassed", especially when run with a suppressor. If anything, it may actually result in a higher cyclic rate and outrun the feed rate of the magazines. You didn't specify what kind of feed issues you're experiencing or detail how/where your fired cases "eject" to. This is one possible area that can be used to identify gassing functionality/issues.

...are the bolt failures to close fully occurring with factory ammo or handloads? Early batches of Hornady Black w/105 BTHP had COAL's that were long causing jamming into the lands, which could prevent the bolt from fully closing (as well as pressure spiking). What buffer spring are you using, that is ONE of the factors that could affect the BCG movement for the feed/lock cycle. Another factor is if magazine interface is off enough to create "drag" on the BCG cycling....which can also contribute to feeding and bolt closure issues you mentioned.

....both the Duramag and E-Lander mags (26, 24, 17 & 10) have all worked 100% in my build, which uses an 18" BA w/RLGS and a standard carbine buffer system. I do use an SLR AGB, something I do on ALL of my AR's in multiple calibers/lengths. I have only run my handloads, factory ammo has not been available in my locale.

Tony:

I finally had time to check on the receiver and the ammo. The description says 18" barrel and mid-length gas. I used an Aero Precision M4E1 upper receiver with a 6.5 Grendel BCG and a Stag lower receiver. The buffer spring is a JP captured spring. What is the measurement for the gas tube to confirm whether mid or rifle?

If anything, I would have assumed over-gassed given the suppressor, but I was wondering if the reason to not close the bolt fully or to fail to pick up a round was because there wasn't enough forward spring pressure that I sometimes associate with not enough gas. I had a combination of 5 boxes of 103-ELD-X and 10 boxes of 105 ELD Black plus handloads using Berger 95 gr Match VLD and the once-fired brass. During barrel break-in, I used mostly the 105 Black. I was planning to run some load tuning rounds this weekend. I will take notes whether handloads or 105s are related to the failure to push a load home.

I will measure ejection distances this weekend, but I am guessing 6-10' for most.

How would I check on the mag interface slowing down the BCG forward momentum?

No AGB, just standard fixed low profile ordered from Aero. Can you install an RLGS on an 18" barrel? I can easily install an AGB from SLR or anyone else, and I can swap buffer springs. I would like this gun to feed reliably.

 

[El Viejo]

I'm running 24 round E-Landers with an 18" Proof. I've run it for the last 3 Quantified Performance matches. First match I had issues pop up where it would inconsistently fail to feed. From the look of things, it seemed like the magazine would get sluggish after so many rounds and not keep up with the BCG (and the rifle isn't overgassed). So after that match, I ordered some Wolff extra power AR15 mag springs for 3 of the mags (individual mags I knew I had problems with were in that group). Those 3 became my test bed and I used them exclusively during train up and during the match. Since then I have not had the issue repeat itself for 2 matches and practice sessions prior to. I've passed that fix along to others who were having E-Landers and it seems to have fixed their problems as well. Might be worth looking into.

What's the Wolff SKU? I called to order, and the person on the phone said AR15 mag springs was not on their list. Maybe it was a different vendor.

 

[r.tenorio671]

Tony:

I finally had time to check on the receiver and the ammo. The description says 18" barrel and mid-length gas. I used an Aero Precision M4E1 upper receiver with a 6.5 Grendel BCG and a Stag lower receiver. The buffer spring is a JP captured spring. What is the measurement for the gas tube to confirm whether mid or rifle?

If anything, I would have assumed over-gassed given the suppressor, but I was wondering if the reason to not close the bolt fully or to fail to pick up a round was because there wasn't enough forward spring pressure that I sometimes associate with not enough gas. I had a combination of 5 boxes of 103-ELD-X and 10 boxes of 105 ELD Black plus handloads using Berger 95 gr Match VLD and the once-fired brass. During barrel break-in, I used mostly the 105 Black. I was planning to run some load tuning rounds this weekend. I will take notes whether handloads or 105s are related to the failure to push a load home.

I will measure ejection distances this weekend, but I am guessing 6-10' for most.

How would I check on the mag interface slowing down the BCG forward momentum?

No AGB, just standard fixed low profile ordered from Aero. Can you install an RLGS on an 18" barrel? I can easily install an AGB from SLR or anyone else, and I can swap buffer springs. I would like this gun to feed reliably.

....barrel measurements should be used to determine gas system type, not the gas tube length (especially if incorrect tube was installed/provided). With the barrel already installed you can measure the distance from the front of the receiver to the back of the gas block or rear edge of gas block journal to determine which gas system the barrel was ported with. This page has both a good visual and video on how to use this method >>> https://www.riflespeed.com/How-to-Select-the-Correct-Gas-Control-for-Your-Carbine_b_2.html

.... I would suggest that if you have a spare "regular" buffer spring handy or one you can swap from another known working rifle, you use it instead of the JP for your next test, especially if you are unsure of what "tune" the JP springs/weights are at. I also suggest you leave your fixed gas block in place during that test. Replacing too many parts at same time can lead to new/more issues and not reveal any solution to the original issue. Eliminate issues one at a time until you have reliability, then you can "upgrade" as desired but armed with specific knowledge to use in your upgrade selection/configuration.

...ejection direction is more relevant than distance. A 3-4 o'clock pattern is desired, forward of 3 is indicative of over-gassing and as it moves closer to 1 indicates amount of over-gassing

....magazine interference/drag might be indicated by excessive scrape marks on the tops of the feed lips of the magazine, follower or casing bodies. The other method is by "feel" when manually manipulating the charging handle, which is really a subjective thing and not overly reliable.

...ANY type of gas system can be ported on ANY barrel length, but a "Rifle Length Gas System" is the typical type used for 18" barrels.

EDITED: You may also want to check the end of the gas tube that enters the BCG's gas key for any wear marks indicating it is "rubbing" excessively (canted, not straight) and slowing it down or "peening" at end (too long) preventing full closure.



Good luck moving forward!

 

[Mac679]

What's the Wolff SKU? I called to order, and the person on the phone said AR15 mag springs was not on their list. Maybe it was a different vendor.

60905 for 1
60906 for 3
60907 for 10

https://www.gunsprings.com/index.php?page=items&cID=2&mID=1&dID=79#493

 

[Lazyfaire]

likely your magazine.

This is where I would start. Are you using a standard 5.56 magazine? While it will work to a degree, due to the fat, short cartridge they do not rise very well on the follower. It was an early problem that did not have a solution. Like .22 Mag cartridges, make sure they all fit flat against the back of the magazine. But designated 6 ARC magazines are readily available now.

I do not use an adjustable gas block in mine. It works perfectly. Maybe its more complicated than it needs to be. IMHO