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AR308 cycling problems... is this over or under gassed?
- Thread starter cunnerman
- Start date
I have 1 rifle that has possibly an armalite gas system (rock river) 26", but uses fal mags and the bcg is different (longer I think) than dpms? I'll check it against the 18" rock river also if it uses a rifle length gas?
Here's my gas tube history/summary before my next range test...
Base setup (to recap for anyone starting on this page):
- Wilson Combat 20" Super Sniper .308 barrel
- Wilson Combat goofball proprietary "rifle length" gas
- Superlative Arms adjustable gas block
- White Oak Armament 15.375" custom-length gas tube (15-3/8")
- Aero M5 upper
- Aero 308 BCG
- Armalite AR10 receiver extension kit (AR10REKIT01) w/ H3 buffer
See pics below.
Gas tube comparison...
1st try - Wilson Combat AR10 rifle length gas tube (15.5"); too long and overgassed...
2nd try - Wilson Combat AR15 rifle length gas tube (15.125"+); too short and undergassed...
3rd try - White Oak custom 15.375" tube centered in cam pin cutout; not yet tested, fingers crossed...
Base setup (to recap for anyone starting on this page):
- Wilson Combat 20" Super Sniper .308 barrel
- Wilson Combat goofball proprietary "rifle length" gas
- Superlative Arms adjustable gas block
- White Oak Armament 15.375" custom-length gas tube (15-3/8")
- Aero M5 upper
- Aero 308 BCG
- Armalite AR10 receiver extension kit (AR10REKIT01) w/ H3 buffer
See pics below.
Gas tube comparison...
1st try - Wilson Combat AR10 rifle length gas tube (15.5"); too long and overgassed...
2nd try - Wilson Combat AR15 rifle length gas tube (15.125"+); too short and undergassed...
3rd try - White Oak custom 15.375" tube centered in cam pin cutout; not yet tested, fingers crossed...
I have a number of Wilson combat barrels ..
First their website tells you the proper gas tube for the barrel ...some need the odd ball size from Wilson...some do not. I use a 3.8 buffer, standard spring, on a carbine reciever extension.
Then every Wilson combat and most every one else's barrel I've used needed to be drilled to the next larger gas port size...ya gotta drill it out....easy precise in a milling machine about 5 minute job, as shown. Can be done in drill press, use a sharp drill and cutting oil to cut down on burr, polish inside of barrel on newly drilled port
Done...
First their website tells you the proper gas tube for the barrel ...some need the odd ball size from Wilson...some do not. I use a 3.8 buffer, standard spring, on a carbine reciever extension.
Then every Wilson combat and most every one else's barrel I've used needed to be drilled to the next larger gas port size...ya gotta drill it out....easy precise in a milling machine about 5 minute job, as shown. Can be done in drill press, use a sharp drill and cutting oil to cut down on burr, polish inside of barrel on newly drilled port
Done...
Attachments
So, what's the verdict, is the new tube gonna solve your cycling problems. Inquiring minds want to know.
I put my sandman on my build with the short tube and it ran fine. Borderline undergassed but ran atleast. Took the suppressor off and it turned into a single shot, would extract and eject but wouldn't pick up the next round. Excited to try it with the new tube when it arrives, but looks promising
If it's not ripping off the case rims and ejecting at 1 o'clock... it probably under gassed. Common and I drill out just about every gas port, in every barrel, including Proof Research, then add an adjustable gas block, and done...works every time. Use standard milspec buffer and spring on everything carbine, and everything rifle. So you can run 10 uppers on one lower no problem. You can run into more problems with titanium bolt carrier, but that's different bird. The 9 mm blow back is also in that mix.
I don't know if 6.5 is different but I would think a 20" +2 barrel would be intended to run suppressed.
Sorry for the delayed response guys. The holidays were hectic and I had a tough time getting out to the range.
>>>>> Long story short, the new gas tube did NOT solve the problem, but there were some improvements.
With the new gas tube and SA gas block at 18 clicks at the range yesterday, I got the following...
- Most ammo (Federal factory hunting rounds 168-175gr) did NOT cycle. (bad news)
- Browning 168gr Long Range Pro factory ammo did cycle consistently and reliably. (good news)
- Felt recoil was noticeably improved. (good news)
- Based on the slow-mo video footage I took, the bolt is definitely moving further to the rear. (good news)
- ...but the bolt is still not moving fully clear of the ejection port and is not stripping a new round. (bad news)
- Ejection pattern is 3:00-3:30 and about 8' away from shooting position. This is the best ejection pattern and distance I've had yet; in previous tests the spent casing just dribbled out of the ejection port onto the table. (good news)
When I got home I spent a while talking to the guys at Sprinco and they think I'm just borderline undergassed/oversprung... so I ordered a Sprinco Blue, which is the next step down from the Red on the stiffness scale.
I feel like I'm mostly tuned, but am now venturing into the undergassed realm some people complain about with Wilson Combat barrels, which is why so many guys online seem to be drilling out their WC gas ports (which I still want to avoid).
Stay tuned for the next range report with the Sprinco Blue spring!
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Just found a Reddit bloke who had success with the A5/SR25 7-7/8" length RE tube, a SA agb, and Sprinco Blue buffer spring. Hopefully this means I'm close to the end of the road on this one...
I went to the range today with the AR10 I built about the same time as you same barrel , but I used the standard WC gas block and a magpul moe rifle buttstock with areo tube and buffer spring combo. Never have had cycling problems and I used the recommended gas tube that WC listed on their website, just wondering why you chose yo use the adjustable GB for a standard 308 gun , that's usually for 6.5CM. Maybe the carbine buttstock combo is causing some of your problems too , if you have a A2 buttstock and tube assembly might try that and see if it helps.
Ahhh. I see, makes sense. I'm working up some hand loads for mine, not impressed with the accuracy of factory ammo so far , would have thought the Fedral GMM168 would have been the cats meow , but best I could do was 1.5 moa at 100yrds. Did get Sub moa with my 1st hand load but it showed signs of over pressure so back to the drawing board on that one.
In case I missed something, are you stating you're using an AR15 rifle spring with that A5? The spring should be to long and compress longer than an AR10 rifle spring. Either someone had a typo or just gave out wrong info intentionally? Due to the extra length (3/4") of an AR10 bcg could be an issue. Using an A5 buffer tube ~(7 5/8" internally) with an AR10 (not necessarily armalite) sr25 (not sure about m110) should only function with an AR10 rifle length spring and an AR15 carbine buffer (carbine buffer lengths, AR15 3.25" AR10/SR25 2.5").
All dependent on NOT being sfar and fal length carriers. AR10/SR25 carrier length is 7 7/8" (carrier only).
I've tried both combinations in my A5 RE tube. The Sprinco Red spring (recommended for overgassed AR 308s) and the Armalite EA1095 AR-10B OPERATING SPRING. Neither cycle efficiently, but the Sprinco Red did work reliably with Browning 168gr Long Range Pro factory ammo and the new gas tube.
Both springs allow full retraction of the charging handle. I haven't bothered with the Tubbs spring, because I know it's too stiff for my setup.
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In the springco only offer 2 springs for the 10 platform (I think both are carbine) unlike the 15's having 5-6 carbine springs. When you use the chargehandle does it go just pasted the bolt catch or further? It should go past the deflector (about 1/4-3/8" past the bolt catch) to allow for timing/lag.
Here's the distance clear from the ejection port with the AR10 spring (same with Sprinco Red), maybe 1/4" past the bolt catch. And I can also feel the standard length buffer bottoming out on the back of the RE tube with both springs. But it's definitely not moving past the deflector...
Needs to go back further. Take off the upper, remove the bcg and check on how far back the carrier will go
Attachments
!/2" clearance between the bolt lugs and the bolt catch is way too much. You'll start seeing broken catches, bent pins and broken pin ears. You also might be striking the lower receiver extension hub with the body of the carrier.
From me compressing it doesn't hit the buffer retainer and the rear of the carrier where the firing pin is doesn't touch the buffer tube. All of my AR's are manually checked this way and run without any issues. As far as during when it's fired and traveling back that far, I can't say if it does? What I can say is it does work. I have very few AR's (15 and 10's) that have more than 2k rounds in each of them. There is the possibility of broken catches, but none so far. The compressed reference (pic) is to see if the spring is causing the lack of travel for the catch to engage other than just by using the chargehandle. Spring diameter and the amount of coils can cause it to short stroke if the combination of both are not having a specific amount of compressed length. It needs more than just clearing the catch for it to engage or it will override and be mistaken for undergassed.
I was hoping @cunnerman for the golden egg with the gas tube length to get back to enjoying his firearm!
It might just be the way that you're measuring and whether the bolt is in or out. I, like most, measure the clearance distance with the firearm assembled, so that the bolt would be away from the carrier. I manually engage the bolt catch, then while keeping slight rearward pressure on the charging handle so it's firmly seated against the gas key, I mark the top of the charging handle where it exits the upper. I then pull the CH all the way rearward until the buffer is bottomed out, then mark the CH again. Remove the CH and measure between the two marks. Although there is no actual spec on that clearance distance I have my own spec and tolerance.
Do you mind sharing your personal spec and tolerance for this measurement?
Ahhh... Didn't realize you had the bolt in the rearward position. With the bolt back (in the carrier), my distance is about the same...
Yours...
Mine...
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Honestly, I was hoping that was it.
I even measured the RE tube to make sure it was to spec, hoping maybe it was just too short. It's a hair under 7.75", but I wouldn't think that's enough to cause my problems. Back to hanging hopes on the blue spring we go...
I use 0.200" +/- 0.040", but I think that it's more important to know what performance and component issues to look for when at the high or low end of whatever clearance dimension you're comfortable with. Also, what may be an issue with one build spec might not be a problem with another.
Got the Sprinco BLUE spring installed and am going to try and get out this weekend to test it.
It's noticeably "softer" when charging compared to the red spring, so hopefully this is the perfect balance.
It's noticeably "softer" when charging compared to the red spring, so hopefully this is the perfect balance.
*** WE HAVE SUCCESS ***
Got to the range today and successfully fired 2 rounds of three different kinds of ammo. All of which cycled properly with the Sprinco Blue spring, and locked open on the last round.
Here is my working recipe for Wilson Combat and Superlative agb (for others who may stumble onto this thread):
Ammo Tested:
The BCG cleared the ejection port in all videos/tests, and all casings landed around 3 to 4 o'clock about 6-10' from the firing position. Last round bolt-hold-open worked on all three tests.
After finishing my tests I ended up having one short-stroke with the Federal 165gr Trophy Copper ammo. Upon getting home I realized the bolt was a little dry, so I'm going to chalk it up to that for now. I also just need to get some regular 308 ammo and "break things in" a little bit, beyond the few test shots I've been doing when I'm at the range. I'll eventually get back out to do some more testing with a wet BCG and maybe try some different buffer weights, but I'm in no rush and am very satisfied with the results thus far.
FWIW, the Federal 175gr Sierra MatchKing was the most accurate in consecutive shots, and will probably be what I use most for target shooting moving forward. I'll also stick to the Federal 175gr Terminal Ascent for hunting.
A sincere "thank you" to everyone who helped me out and sent advice to me on this... I think we can now consider this one solved!!
Got to the range today and successfully fired 2 rounds of three different kinds of ammo. All of which cycled properly with the Sprinco Blue spring, and locked open on the last round.
Here is my working recipe for Wilson Combat and Superlative agb (for others who may stumble onto this thread):
- Wilson Combat 20" 308 fluted Super Sniper Barrel
- Superlative Arms adjustable gas block set at 18-clicks (4.5 full turns)
- 15.375” custom length gas tube (White Oak)
- Aero Precision M5 / 308 upper and lower
- Armalite receiver extension kit with H3 buffer (#AR10REKIT01 - this is the longer 7-7/8" or A5 length tube) *minus the spring
- Sprinco Blue Spring
- Toolcraft 308 Double Ejector BCG
Ammo Tested:
- Federal 165gr Trophy Copper
- Federal 175gr SMK
- Browning 168gr Long Range Pro
The BCG cleared the ejection port in all videos/tests, and all casings landed around 3 to 4 o'clock about 6-10' from the firing position. Last round bolt-hold-open worked on all three tests.
After finishing my tests I ended up having one short-stroke with the Federal 165gr Trophy Copper ammo. Upon getting home I realized the bolt was a little dry, so I'm going to chalk it up to that for now. I also just need to get some regular 308 ammo and "break things in" a little bit, beyond the few test shots I've been doing when I'm at the range. I'll eventually get back out to do some more testing with a wet BCG and maybe try some different buffer weights, but I'm in no rush and am very satisfied with the results thus far.
FWIW, the Federal 175gr Sierra MatchKing was the most accurate in consecutive shots, and will probably be what I use most for target shooting moving forward. I'll also stick to the Federal 175gr Terminal Ascent for hunting.
A sincere "thank you" to everyone who helped me out and sent advice to me on this... I think we can now consider this one solved!!
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OUTSTANDING!!!!*** WE HAVE SUCCESS ***
Got to the range today and successfully fired 2 rounds of three different kinds of ammo. All of which cycled properly with the Sprinco Blue spring, and locked open on the last round.
Here is my working recipe for Wilson Combat (for others who may stumble onto this thread):
- Wilson Combat 20" 308 fluted Super Sniper Barrel
- Aero Precision M5 / 308 upper and lower
- Armalite receiver extension kit with H3 buffer (#AR10REKIT01 - this is the longer 7-7/8" or A5 length tube) *minus this spring
- Sprinco Blue Spring
- Toolcraft 308 Double Ejector BCG
- Superlative Arms adjustable gas block at 18-clicks (4.5 full turns)
Ammo Tested:
- Federal 165gr Trophy Copper
- Federal 175gr SMK
- Browning 168gr Long Range Pro
The BCG cleared the ejection port in all videos/tests, and all casings landed around 3 to 4 o'clock about 6-10' from the firing position. Last round bolt-hold-open worked on all three tests.
After finishing my tests I ended up having one short-stroke with the Federal 165gr Trophy Copper ammo. Upon getting home I realized the bolt was a little dry, so I'm going to chalk it up to that for now. I also just need to get some regular 308 ammo and "break things in" a little bit, beyond the few test shots I've been doing when I'm at the range. I'll eventually get back out to do some more testing with a wet BCG and maybe try some different buffer weights, but I'm in no rush and am very satisfied with the results thus far.
FWIW, the Federal 175gr Sierra MatchKing was the most accurate in consecutive shots, and will probably be what I use most for target shooting moving forward. I'll also stick to the Federal 175gr Terminal Ascent for hunting.
A sincere "thank you" to everyone who helped me out and sent advice to me on this... I think we can now consider this one solved!!
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