6.5 Creedmoor AR10 Cycling Problem

[Just-some-guy]

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?

 

[celltech]

6.5 Creed actually has a higher port pressure than .308...so unless the barrel has an undersized port there should be *plenty* of gas. What does the brass look like? Is there actually too much gas trying to cycle it early?

 

[mtrmn]

SOAK the BCG in oil during break in

 

[Just-some-guy]

6.5 Creed actually has a higher port pressure than .308...so unless the barrel has an undersized port there should be *plenty* of gas. What does the brass look like? Is there actually too much gas trying to cycle it early?

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.

 

[Just-some-guy]

SOAK the BCG in oil during break in

I had it fairly well lubed; there is lots of very fine sand that blows around where I shoot, so I tend to use gun grease on the carrier and BCG and it stays in place and collects less dust and grit. In my AO soaking a BCG in oil just tends to make a big mess.

It may need some break in, as I am just now nearing 100 rounds fired total.

 

[bfoosh006]

When you say the adjustment screw is all the way out... how many full turns is that ?

The SupArms bleed off GB can be confusing to adjust.

This video explains it best for me..

 

[rpoL98]

... 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 ...

all of my large-frame lowers have the same buffer (5.3oz), same spring, and I use the adj GB on the uppers. This way I can "push pin" and swap out the uppers: 308, 6.5CM, barrel lengths from 14.5" through 24". That concept does work, and works well. I went with SLR adj GB's. But Superlative's get good reviews too, personal preference.

I did have one BA 14.5" 308 barrel (carbine), came with a gas port of .055", ended up drilling that out to .0730" to get that one to work with my "standard lower". That was my only instance for undersized gas ports for AR-10 barrels: BA, Criterion, Faxon, Rainier, Anderson, KAK.

OBTW, my 24" 6.5CM barrel has a gas port of 0.072" (std rifle-gas). if that's any help. Your 22", std rifle-gas 6.5CM, slightly shorter dwell-time, should be about that size, maybe slightly bigger by a few thousandths. Could be slightly smaller, but then the GB would have to be opened up proportionally.

 

[mtrmn]

I had it fairly well lubed; there is lots of very fine sand that blows around where I shoot, so I tend to use gun grease on the carrier and BCG and it stays in place and collects less dust and grit. In my AO soaking a BCG in oil just tends to make a big mess.

It may need some break in, as I am just now nearing 100 rounds fired total.

Let me modify my advice. Put a few drops of oil in the gas exhaust holes in the BCG every 3-4 rounds and see if that helps prevent the malfunction. This will keep the rings lubed during the break-in, and it will help troubleshoot/eliminate this possibility. If it continues to malfunction as before, then you know that's not the problem. Large frame ARs tend to need more bolt lube during break-in than the small frames do for some reason.

Also, insure the gas tube is the proper length. It should terminate halfway in the cam pin cutout in the upper receiver. Too short and it will cause all sorts of wonky problems that make no sense at all.

 

[Mattrmvpd]

Try a heavier buffer as well.
I had a similar issue with a .308. Thought it was the BCG but ended up being a buffer and spring issue.

 

[Just-some-guy]

When you say the adjustment screw is all the way out... how many full turns is that ?

The SupArms bleed off GB can be confusing to adjust.

This video explains it best for me..

I'm at 18 clicks, which is supposed to be all the way open; less than 18 clicks restricts the gas, more than 18 clicks starts to bleed off the gas.

 

[Just-some-guy]

all of my large-frame lowers have the same buffer (5.3oz), same spring, and I use the adj GB on the uppers. This way I can "push pin" and swap out the uppers: 308, 6.5CM, barrel lengths from 14.5" through 24". That concept does work, and works well. I went with SLR adj GB's. But Superlative's get good reviews too, personal preference.

I did have one BA 14.5" 308 barrel (carbine), came with a gas port of .055", ended up drilling that out to .0730" to get that one to work with my "standard lower". That was my only instance for undersized gas ports for AR-10 barrels: BA, Criterion, Faxon, Rainier, Anderson, KAK.

OBTW, my 24" 6.5CM barrel has a gas port of 0.072" (std rifle-gas). if that's any help. Your 22", std rifle-gas 6.5CM, slightly shorter dwell-time, should be about that size, maybe slightly bigger by a few thousandths. Could be slightly smaller, but then the GB would have to be opened up proportionally.

Thank you!

 

[Just-some-guy]

Let me modify my advice. Put a few drops of oil in the gas exhaust holes in the BCG every 3-4 rounds and see if that helps prevent the malfunction. This will keep the rings lubed during the break-in, and it will help troubleshoot/eliminate this possibility. If it continues to malfunction as before, then you know that's not the problem. Large frame ARs tend to need more bolt lube during break-in than the small frames do for some reason.

Also, insure the gas tube is the proper length. It should terminate halfway in the cam pin cutout in the upper receiver. Too short and it will cause all sorts of wonky problems that make no sense at all.

Thank you, solid tips; I will look into these things.

 

[Just-some-guy]

Let me modify my advice. Put a few drops of oil in the gas exhaust holes in the BCG every 3-4 rounds and see if that helps prevent the malfunction. This will keep the rings lubed during the break-in, and it will help troubleshoot/eliminate this possibility. If it continues to malfunction as before, then you know that's not the problem. Large frame ARs tend to need more bolt lube during break-in than the small frames do for some reason.

Also, insure the gas tube is the proper length. It should terminate halfway in the cam pin cutout in the upper receiver. Too short and it will cause all sorts of wonky problems that make no sense at all.

I just checked my gas tube; it is a couple millimeters shorter than the one in your picture in relation to the cut out in the upper receiver. Is there a "standard" overall length for a rifle length gas tube that I can referrence?

Thank you.

 

[rpoL98]

I just checked my gas tube; it is a couple millimeters shorter than the one in your picture in relation to the cut out in the upper receiver. Is there a "standard" overall length for a rifle length gas tube that I can referrence?

Thank you.

BA (and Criterion) use the std AR-15 length gas tubes. Rifle length should check in at about 15-1/8".

usually, when it's too short, it looks like this:

that usually happens when the barrel gas length uses the Armalite AR-10 standard (such as Faxon DPMS AR-10). But BA doesn't, they use the regular old dime-a-dozen AR-15 gas tube lengths.

the Armalite AR-10 rifle-length gas tube is 15-1/2".

 

[mtrmn]

BA (and Criterion) use the std AR-15 length gas tubes. Rifle length should check in at about 15-1/8".

usually, when it's too short, it looks like this:

that usually happens when the barrel gas length uses the Armalite AR-10 standard (such as Faxon DPMS AR-10). But BA doesn't, they use the regular old dime-a-dozen AR-15 gas tube lengths.

the Armalite AR-10 rifle-length gas tube is 15-1/2".

The AR15 Rifle length gas tube is supposed to be 15-1/4" to 15-3/16". At least 1/4" shorter than the AR10 tube. If your gas tube does NOT reach the halfway point of the cam pin cutout then it is essentially too short. If the new tube reaches PAST the halfway point a little bit you can get by with that. My mid-length (11-3/4" AR15 length) tube was too short on my 308 and I had to locate a longer "Armalite AR10 carbine length" tube (12-1/16") for my Faxon 16" barrel. This simple change solved a world of weird problems I was having.

 

[bfoosh006]

Gas tube length wise, FWIW, all my PA10's and PA65's use the AR15 length gas tubes... never had any issues with those "shorter" lengths.
Various gas system lengths and barrel lengths., various barrel manufacturer's .
Criterion, Ballistic Advantage ( same barrel / caliber you are using ), PSA / DC machine, Faxon, Krieger ( only one with smaller, more practical gas port size than the others )

Yours might prefer the longer Armalite length... hard to say.

I do use heavy, for the chosen system, buffers ... 5.3oz 2.5" for DPMS pattern carbine , 5.4oz 3.25" for Armalite pattern carbine , and a 9.3oz 308 rifle length buffer... and Tubbs 308 Flatwire recoil springs in all of them.

What is the weight of your 308 lower buffer and what brand recoil spring ?

All mine have SLR Adj. GB's... all are "happy" at 6 clicks open from the available 15 clicks fully open.

I am a fan of Adj. GB's and heavy buffers / Tubbs 308 Flatwire recoil springs

At this point , maybe the grease is causing an issue ? I would try it with normal rifle oil and see if that helps.

I suggest triple ( ? ) checking the gas system is all snug, looking for any possible leaks.

Also , next time it gets sluggish... do the single mag fed, fire , lock back of the BCG test.... maybe repeatedly to see if the BCG is short stroking.

What mags are you using ?

And does it do it with factory ammo ? ( sorry if I missed that )

 

[Just-some-guy]

A

Gas tube length wise, FWIW, all my PA10's and PA65's use the AR15 length gas tubes... never had any issues with those "shorter" lengths.
Various gas system lengths and barrel lengths., various barrel manufacturer's .
Criterion, Ballistic Advantage ( same barrel / caliber you are using ), PSA / DC machine, Faxon, Krieger ( only one with smaller, more practical gas port size than the others )

Yours might prefer the longer Armalite length... hard to say.

I do use heavy, for the chosen system, buffers ... 5.3oz 2.5" for DPMS pattern carbine , 5.4oz 3.25" for Armalite pattern carbine , and a 9.3oz 308 rifle length buffer... and Tubbs 308 Flatwire recoil springs in all of them.

What is the weight of your 308 lower buffer and what brand recoil spring ?

All mine have SLR Adj. GB's... all are "happy" at 6 clicks open from the available 15 clicks fully open.

I am a fan of Adj. GB's and heavy buffers / Tubbs 308 Flatwire recoil springs

At this point , maybe the grease is causing an issue ? I would try it with normal rifle oil and see if that helps.

I suggest triple ( ? ) checking the gas system is all snug, looking for any possible leaks.

Also , next time it gets sluggish... do the single mag fed, fire , lock back of the BCG test.... maybe repeatedly to see if the BCG is short stroking.

What mags are you using ?

And does it do it with factory ammo ? ( sorry if I missed that )

All good information!

I am currently running a standard KAK 5.4 oz rifle buffer and the spring they sell for the AR10, aka nothing special.

Using oil may be a solution as the grease and the accompying grit that built up may be slowing the carrier down enough to cause problems; I didn't seem to have this issue when I was load testing last time out. I will try oil next time as suggested and see if there is any change.

The gas system is what I suspect the problem is; I have moved the gas block a few times trying to ensure the port is properly aligned. This has been challenging since I don't have an air compressor to blow through the tube as I adjust it, so trying to get optimal alignment has been challenging. I don't see any evidence of leaking gas at the gas block. I had a similar problem with a small frame AR awhile back and it was a leaking gas block. I will have to re-check this if the other solutions fail to work.

I am using Pmags and firing my own ammo. I have been looking for some factory ammo to try out on my next outing but it is both scarce and expensive!

Question: What effect does increasing weight to the buffer have on cycling? Does a heavier buffer cycle with less gas pressure, or more? In other words, if the system is undergassed will increasing buffer weight help, or hinder the operation. Same for buffer spring, I would assume that a lighter spring would allow the system to cycle with less gas pressure.

Thank you for your advice, it definitely gives me some things to look at.

 

[TonyTheTiger]

Question: What effect does increasing weight to the buffer have on cycling? Does a heavier buffer cycle with less gas pressure, or more? In other words, if the system is undergassed will increasing buffer weight help, or hinder the operation. Same for buffer spring, I would assume that a lighter spring would allow the system to cycle with less gas pressure.

The heavier the reciprocating mass and/or spring the more gas you need to run it. So if you're already undergassed you either need lighter components, hotter ammo or a bigger gas port

 

[Just-some-guy]

The heavier the reciprocating mass and/or spring the more gas you need to run it. So if you're already undergassed you either need lighter components, hotter ammo or a bigger gas port

That is what I thought, thanks for the clarification.

 

[DangerRanger]

I think your hole is too small.

 

[rpoL98]

is your Toolcraft BCG nitride (or phosphate), or nickel boron? a while back I had some problems with multiple NIB 308 BCGs (all the same brand, but not Toolcraft), sticking, that was alleviated by replacement with nitride BCG, same brand. the same phenomena doesn't occur with any of my AR-15 NIB BCG's. it's odd, but, oh well. I think it came down to how the coating was applied.

but I still think your hole is too small. can you get a measurement of your gas port?

 

[Just-some-guy]

I think your hole is too small.

This is what I am starting to believe. Since I have an adjustable gas block, opening the barrels gas port slightly shouldn't have any negative effect because I can ultimately control the gas flow with the gas block. Correct? In other words, there really is no downside to opening the port slightly for experimentation purposes in this instance.

 

[TonyTheTiger]

This is what I am starting to believe. Since I have an adjustable gas block, opening the barrels gas port slightly shouldn't have any negative effect because I can ultimately control the gas flow with the gas block. Correct? In other words, there really is no downside to opening the port slightly for experimentation purposes in this instance.

Correct. Don't overdo it.

 

[rpoL98]

This is what I am starting to believe. Since I have an adjustable gas block, opening the barrels gas port slightly shouldn't have any negative effect because I can ultimately control the gas flow with the gas block. Correct? In other words, there really is no downside to opening the port slightly for experimentation purposes in this instance.

please make sure you have the wire-gauge drill bits. just having the fractionals just doesn't ...

 

[bfoosh006]

Should you decide to drill... make sure you don't over drill into the rifling on the opposite side.

And drill bits that small are easy to break.... so go slow at the drill press.

Drill bit size chart...
https://www.custompartnet.com/drill-size-chart

You might consider e-mailing BA , and asking what your gas port size is on that specific barrel.

I looked to see where I wrote my same barrels gas port size.. but can't find it.
Don't hold me to it... but I want to say it was around .088- .093

If need be.. I could loosen the gas block and measure it again for the sake of just doing so.

The gas system is what I suspect the problem is; I have moved the gas block a few times trying to ensure the port is properly aligned. This has been challenging since I don't have an air compressor to blow through the tube as I adjust it, so trying to get optimal alignment has been challenging. I don't see any evidence of leaking gas at the gas block. I had a similar problem with a small frame AR awhile back and it was a leaking gas block. I will have to re-check this if the other solutions fail to work.

Also... while this sounds cheesy.. consider the dry piece of uncooked spaghetti noodle trick for a reasonable gas block alignment.

MAKE SURE you get the 2 pieces of spaghetti out !!




Drill bit size chart...

 

[mtrmn]

If you decide to drill, find a wood dowell at the hardware store that will fit the bore. That will help protect the rifling on the opposite side. Go SLOW

 

[Just-some-guy]

Update:

So here is what is new to this thread; I removed the gas block and found no evidence of gas leaking.

The gas tube measures 15 1/8" long and appeared to be lined up properly, gas block looked to be in proper alignment as well.

The gas port was difficult to get an accurate measurement as I don't have an unlimited amount of tools, but it was originally smaller than .0076" as that size drill bit would not fit into the port. I estimate that the port was originally from the factory somewhere around .0072 or .0073" I then successfully enlarged the port to .0076".

The bolt carrier did have some stiction due to my lubing it with grease so I re-lubed with light gun oil and it travels smoothly and the bolt locks up to the barrel extension lugs smoothly.

The bolt carrier travels well back into the extension tube as normal and travels smoothly.

I re-aligned the gas block using the "spaghetti noodle" trick and reassembled everything. All that is left to do is test it out and see if things have improved or if I ruined the barrel... Upon reflection, with as hot as the loads that I was firing last trip out were (41.8 gr. of H4350 under 142 gr SMK's at 2800 fps; near max loading) I shouldn't have had any sluggish bolt conditions. The primers showed that there was high pressure; the system should not have needed the gas block wide open to run that hot of a load. Hopefully now I can have a bit more gas and bleed off some excess with the adjustable gas block. I will report back with results after I get a chance to test, hopefully in a few days.

 

[Just-some-guy]

So the issues continue...

Went out today twice, once in the morning and again in the afternoon. The morning session I was still getting the same result as before; same sporadic 4:00 ejection pattern. Same "most open" setting on the gas block. I tried loading a single round at a time in the magazine several times, failed to lock the bolt back every time when empty. Basically still seemed under gassed and lazy even with the slightly enlarged gas port. I tried lubing the BCG with light oil, lots of oil, less oil, nothing seemed to solve the problem.

I decided to take a second trip so I could try a different bolt carrier group, so I ran it with a Toolcraft and a Lantac BCG, the Toolcraft seemed to cycle pretty reliably, I was able to fire multiple rounds with semi-automatic fire without stoppage but still failed to lock the bolt back on an empty magazine. In general, on this trip the rifle seemed to work okay, some improvement, but still seems like it's under gassed. With the .308 upper on the rifle is a CHAMPION! Runs and shoots great. For as much money as I have invested in the 6.5 upper it should work just as well, something is not right.

Some things I have noticed:

The ejection pattern is sporadic.

Things seem to worsen as the rifle heats up.

A lot of the spent cases have a dented or crimped case mouth after ejection, don't know why.

The bolt lugs on the 6.5 barrel seem very tight; the Toolcraft bolt sometimes binds due to this as the bolt lugs couple with the barrel extension lugs.

I have never been able to utilize the adjustable gas block; it is alway in the "most open" setting just trying to get enough gas to cycle this rifle.

As mentioned previously, the 6.5 should have "plenty" of gas; I am just not seeing and/or feeling that. I am contemplating opening the gas port even more. Honestly, the only reason I haven't trash canned this barrel and gotten something else already is that I am happy with it's accuracy, but reliability trumps all for me.

 

[DangerRanger]

Have you called BA

 

[Just-some-guy]

Have you called BA

Not yet, I am thinking that I should.

 

[rpoL98]

i'm puzzled. seems like at 0.076" your gas port is in the ball park for 22" barrel. you could try a regular non-adjustable lo-pro gas block, just to rule out the adj gas block as the gas bottleneck.

 

[Just-some-guy]

i'm puzzled. seems like at 0.076" your gas port is in the ball park for 22" barrel. you could try a regular non-adjustable lo-pro gas block, just to rule out the adj gas block as the gas bottleneck.

That's my project for today; remove the gas block, inspect and clean it out. This deal shouldn't be as complicated as it has become. Back to checking the basics...

 

[hlee]

Dented and crimped case mouths are from bouncing off of the brass deflector- or the side of the receiver. Look for 1/2 moon brass marks on the receiver- that is where the brass is hitting on exit.

 

[whatsupdoc]

So the issues continue...

The bolt lugs on the 6.5 barrel seem very tight; the Toolcraft bolt sometimes binds due to this as the bolt lugs couple with the barrel extension lugs.

Take the barrel nut off and check how mush slop there is between the barrel extension indexing pin and the upper receiver notch.
If there is too much slop the barrel may rotate too far when tightening the barrel nut and cause the bolt to bind.

 

[Maxduty]

Just a thought. I'm under the impression that most ar10s are over gassed off the bat. Could it be possible that the case pressure is causing stiction, slowing the bolt carrier down or the stiction you mention below?

A lot of the spent cases have a dented or crimped case mouth after ejection, don't know why.

Usually an over gas sign. The cases are being slammed into the deflector.

The bolt lugs on the 6.5 barrel seem very tight; the Toolcraft bolt sometimes binds due to this as the bolt lugs couple with the barrel extension lugs.

I feel like this may be slowing the bcg down, throwing the timing off for picking up the next round.

 

[Just-some-guy]

Found out a few things today.

The gas block was rotated a tiny bit, which may have covered the port by maybe 5%. I straightened it by "eyeballing" it and the spaghetti noodle trick the best I could; I ordered a KAW dimple jig and will dimple the barrel when it arrives and put an end to the misalignment issue for good (hopefully)

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...

 

[Maxduty]

Found out a few things today.

The gas block was rotated a tiny bit, which may have covered the port by maybe 5%. I straightened it by "eyeballing" it and the spaghetti noodle trick the best I could; I ordered a KAW dimple jig and will dimple the barrel when it arrives and put an end to the misalignment issue for good (hopefully)

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...

I think you may be on to something there. Looking forward to updates just for the information.

 

[rpoL98]

i guess i shoulda asked this earlier, do you get last round bolt hold open? bolt locks back when the mag is empty?

 

[Just-some-guy]

i guess i shoulda asked this earlier, do you get last round bolt hold open? bolt locks back when the mag is empty?

No, last time out everything worked as designed (for the most part), except for the bolt locking back on an empty magazine. If the BCG had been locking back on an empty mag I would have celebrated as a success.

 

[Just-some-guy]

No, last time out everything worked as designed (for the most part), except for the bolt locking back on an empty magazine. If the BCG had been locking back on an empty mag I would have celebrated as a success.

I am beginning to think the problem may be it's over gassed; the BCG is outrunning the magazine followers ability to catch the BCG.

The gun feels like the BCG may be slamming back into the buffer, the brass is getting hammered (dented mouths, enlarged pockets, cratered / flat primers), and the ejection is sporadic (sometimes 4', sometimes 12").

The picture in this thread looks like my brass / the problem sounds a lot like my problem:

Dented Case Mouth. What is the cause?

The rifle is an Armalite AR-10 chambered for 260 Rem. I run the rifle with a TBAC silencer (hence the dirty brass). The gas block, handguard and barrel nut had recently been removed for some maintenance work. The 'smith may or may not have gotten the gas block to align correctly with the gas...

www.snipershide.com

I havn't been experimenting with reducing the gas pressure via the adjustable gas block since I have been assuming that the problem was a lack of gas. I have just kept the gas block at the maximum open position.

Once I get my order of factory ammo, straighten out my gas block on the port with my KAW tool, and get another magazine to try I will go back out and experiment with adjusting the gas block to vent off some excess gas pressure and see what happens.

 

[rpoL98]

I am beginning to think the problem may be it's over gassed; the BCG is outrunning the magazine followers ability to catch the BCG.

The gun feels like the BCG may be slamming back into the buffer, the brass is getting hammered (dented mouths, enlarged pockets, cratered / flat primers), and the ejection is sporadic (sometimes 4', sometimes 12").

The picture in this thread looks like my brass / the problem sounds a lot like my problem:

Dented Case Mouth. What is the cause?

The rifle is an Armalite AR-10 chambered for 260 Rem. I run the rifle with a TBAC silencer (hence the dirty brass). The gas block, handguard and barrel nut had recently been removed for some maintenance work. The 'smith may or may not have gotten the gas block to align correctly with the gas...

www.snipershide.com

I havn't been experimenting with reducing the gas pressure via the adjustable gas block since I have been assuming that the problem was a lack of gas. I have just kept the gas block at the maximum open position.

Once I get my order of factory ammo, straighten out my gas block on the port with my KAW tool, and get another magazine to try I will go back out and experiment with adjusting the gas block to vent off some excess gas pressure and see what happens.

that's why I asked about whether the bolt locks back. if it's overgassed, the bolt catch would still work, and lock back the bolt on mag empty. usually.

 

[RobbinsHGray]

I’m not happy to say this is another I built an A.R. 10 and I’m having problems thread awesome for those of you can do it and I suppose the ones who can don’t often talk about it being broken so the threads are heavy with those who have problems doing it There sure are a lot of posts with people having problems building their own A.R. 10

Maybe someone should start a thread it’s just about I built an A.R. 10 and it works great got to have at least 500 rounds through it 5 x 5 targets showing 1MOA or better groups and then talk about how you built it if you had to rebuild it more than twice you can’t post.

Otherwise I say just buy a JP and call it done

 

[Mattrmvpd]

Its been my experience the .308’s are pretty easy to get running. Its the 6.5’s that have had some issues.

Spring-Buffer-BCG can cause major issues building large frame gas guns.

Gas tubes and holes done from factory are normally good to go…

i am still thinking a buffer weight issue or tuning of the buffer spring for this

 

[rpoL98]

on my afore-mentioned 24" 6.5CM, on my SLR adj GB, i have it at 7 clicks open. On the SLR, the instructions say 15 clicks is wide open. so yeah, you should not need to run it wide open with a gas port of .076 on your 22".

neither here nor there, hindsight, etc, on my new builds, I usually start off with the gas block at just a couple of clicks (1 or 2), and then open it one click at a time, only loading 1 rd in the mag, until i get last round bolt hold open, "dialing in the gas block setting". I guess you skipped that step. sorry bout the monday morning quarterbacking. chalk it up to lessons learned. now you know everything that I know.


ETA: i'm also using a 5.3oz or 5.4oz 308 carbine buffer (2.5"), KAK or Primary Arms Expo, and I have 1 from Slash. and I use Slash's 308 carbine buffer spring ($15). you should be good with your 308 carbine buffer spring, since you can fine-tune using the gas block. and AR-15 "M4" buffer tube (inside depth 7"). That in a nutshell is my secret sauce.

ETA2: I'm still puzzled about why, if you're overgassed (that's a big if), your bolt catch doesn't flip up on mag empty. dayuum, your BCG must be cycling at supersonic speed if that's the case, not even enough time for the bolt catch to spring up, or something funky about your mag, activating the bolt catch.

 

[TonyTheTiger]

ETA2: I'm still puzzled about why, if you're overgassed (that's a big if), your bolt catch doesn't flip up on mag empty. dayuum, your BCG must be cycling at supersonic speed if that's the case, not even enough time for the bolt catch to spring up, or something funky about your mag, activating the bolt catch.

I've definitely seen small frame guns so overgassed that they didn't lock back. And of course the first instinct was to assume it was undergassed.

 

[FunkyTownScout]

You can put pressure on the bolt lock back lever to assist with your off hand. That'll accelerate and assist the mag catch. If it locks back like that then probably over gassed.

 

[Just-some-guy]

I’m not happy to say this is another I built an A.R. 10 and I’m having problems thread awesome for those of you can do it and I suppose the ones who can don’t often talk about it being broken so the threads are heavy with those who have problems doing it There sure are a lot of posts with people having problems building their own A.R. 10

Maybe someone should start a thread it’s just about I built an A.R. 10 and it works great got to have at least 500 rounds through it 5 x 5 targets showing 1MOA or better groups and then talk about how you built it if you had to rebuild it more than twice you can’t post.

Otherwise I say just buy a JP and call it done

Well, I first built this rifle with a .308 upper and it ran great from the onset; 100% reliability, good accuracy. Totally happy with that build. It was only when I decided to add the 6.5 upper into the package that I experienced issues. I'm sure with some trial and error tuning it will soon be solved and then I will be smarter for having the experience and learned from it; this is part of the "hobby" to me. To each their own...

 

[TonyTheTiger]

Jesus Christ. I never realized how dependant I am on periods, comma's, and apostrophes until I read this post.

I almost pulled this meme out of storage for that post.

 

[TonyTheTiger]

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]

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