View Full Version : BCM 11.5 over gassed
Thoughts & options please / tnx. Not interested in either AGB or inserts.
Oddly get similar ejection pattern suppressed & unsuppressed
- M855
- H3
- New carbine spring
- Will run 100% suppressed
https://youtu.be/y4cFEz9BLYg
https://youtu.be/bJmUMYcvty8
I got a BCM 11.5 upper in like April or something and noticed it was pretty gassy. Initially I was just using an H buffer but ended up going to an H2 which seemed to calm it down a bit, and it still seems to run Wolf steel cased stuff, but if the ejection pattern is any indication, just barely.
The BRT EZ-Tune gas tubes are a pretty simple way to address over gassing too. Literally as easy as....changing a gas tube. I used one in a different 11.5” upper that was overgassed and it worked quite well.
Before calling it over gassed I would at a minimum measure the gas port. On a fighting carbine it should be close to 0.069-0.071
Optimal spring and buffer combinations are Sprinco Blue Spring/H2 Buffer or the A5 System with a Sprinco Green Spring/A5H2 Buffer.
Of course neither change the gas port diameter.
FWIW I have a 2019 BCM ELW 11.5 with a 0.072 gas port size which is acceptable.
Before calling it over gassed I would at a minimum measure the gas port. On a fighting carbine it should be close to 0.069-0.071
Optimal spring and buffer combinations are Sprinco Blue Spring/H2 Buffer or the A5 System with a Sprinco Green Spring/A5H2 Buffer.
Of course neither change the gas port diameter.
FWIW I have a 2019 BCM ELW 11.5 with a 0.072 gas port size which is acceptable.
Agreed and I will measure this one and another BCM 11.5 I have.
I can’t see how it’s flinging 855 brass unsuppressed at 1-2 with an H3 and not over gassed.
It does run though...
Thoughts & options please / tnx. Not interested in either AGB or inserts.
Oddly get similar ejection pattern suppressed & unsuppressed
Ejection pattern is an indication as to how well the extractor & ejector are working, not how the AR is gassed. A weak extractor spring will move ejection angle forward regardless of gas drive. There will also be a more dramatic change in ejection angle with a change in carrier speed with weak extraction than if the extractor & spring are up to spec.
Short of an AGB, the best way to determine if an AR is over gassed is felt recoil. An over gassed AR wil have sharp recoil as the buffer slams into the rear of the RE. However, this assumes the buffer is the correct type and mass. Determining the correct type and mass is simple. Buffers with solid weights (not powdered) are the correct type. For 5.56 ARs, H2, A5H2 & Rifle buffers have the correct mass. H buffers are good but H2 buffers are better. Carbine weight buffers are too light.
A properly gassed AR using a buffer with too little mass (carbine buffer) will have sharp recoil and feel like it's over gassed.
Over/under gassing cannot be fixed by changing buffer weight. It can only be fixed by addressing the gas drive. That means using the proper diameter gas port or changing ammo pressure. (Changing ammo pressure may require changing reciprocating mass.)
Personally, if I were going to run an H3 (equivalent in mass to a rifle or A5H2) I would run an A5 RE and an A5H2 buffer. The H3 seems to be on the ragged edge of performance for a carbine type buffer & spring for a 5.56. Might as well switch to an A5 RE and gain the advantages of running a longer buffer & a rifle spring.
Five_Point_Five_Six
09-06-20, 09:10
Ejection pattern is an indication as to how well the extractor & ejector are working, not how the AR is gassed. A weak extractor spring will move ejection angle forward regardless of gas drive. There will also be a more dramatic change in ejection angle with a change in carrier speed with weak extraction than if the extractor & spring are up to spec.
Short of an AGB, the best way to determine if an AR is over gassed is felt recoil. An over gassed AR wil have sharp recoil as the buffer slams into the rear of the RE. However, this assumes the buffer is the correct type and mass. Determining the correct type and mass is simple. Buffers with solid weights (not powdered) are the correct type. For 5.56 ARs, H2, A5H2 & Rifle buffers have the correct mass. H buffers are good but H2 buffers are better. Carbine weight buffers are too light.
A properly gassed AR using a buffer with too little mass (carbine buffer) will have sharp recoil and feel like it's over gassed.
Over/under gassing cannot be fixed with a heavier buffer weight. It can only be fixed by addressing the gas drive. That means using the proper diameter gas port or changing ammo pressure. (Changing ammo pressure may require changing reciprocating mass.)
Personally, if I were going to run an H3 (equivalent in mass to a rifle or A5H2) I would run an A5 RE and an A5H2 buffer. The H3 seems to be on the ragged edge of performance for a carbine type buffer & spring for a 5.56. Might as well switch to an A5 RE and gain the advantages of running a longer buffer & a rifle spring.
This is sound advice.
Ejection pattern is an indication as to how well the extractor & ejector are working, not how the AR is gassed. A weak extractor spring will move ejection angle forward regardless of gas drive. There will also be a more dramatic change in ejection angle with a change in carrier speed with weak extraction than if the extractor & spring are up to spec.
Short of an AGB, the best way to determine if an AR is over gassed is felt recoil. An over gassed AR wil have sharp recoil as the buffer slams into the rear of the RE. However, this assumes the buffer is the correct type and mass. Determining the correct type and mass is simple. Buffers with solid weights (not powdered) are the correct type. For 5.56 ARs, H2, A5H2 & Rifle buffers have the correct mass. H buffers are good but H2 buffers are better. Carbine weight buffers are too light.
A properly gassed AR using a buffer with too little mass (carbine buffer) will have sharp recoil and feel like it's over gassed.
Over/under gassing cannot be fixed with a heavier buffer weight. It can only be fixed by addressing the gas drive. That means using the proper diameter gas port or changing ammo pressure. (Changing ammo pressure may require changing reciprocating mass.)
Personally, if I were going to run an H3 (equivalent in mass to a rifle or A5H2) I would run an A5 RE and an A5H2 buffer. The H3 seems to be on the ragged edge of performance for a carbine type buffer & spring for a 5.56. Might as well switch to an A5 RE and gain the advantages of running a longer buffer & a rifle spring.
Roger that. As you know Don I’m mostly a shooter with a bit of AR knowledge built in :)
That said I’ve got a new Colt bolt which I can throw in for comparison.
I’ll get the port measurement too.
Before calling it over gassed I would at a minimum measure the gas port. On a fighting carbine it should be close to 0.069-0.071
Optimal spring and buffer combinations are Sprinco Blue Spring/H2 Buffer or the A5 System with a Sprinco Green Spring/A5H2 Buffer.
Of course neither change the gas port diameter.
FWIW I have a 2019 BCM ELW 11.5 with a 0.072 gas port size which is acceptable.
The ELW barrel has a .625 journal. Does the OP's barrel have that, or a .750 journal? All other things being equal, barrels with same size gas ports will function differently with different sized journals.
turnburglar
09-06-20, 10:42
@Mistwolf-
Thanks for diagnosing ANOTHER one of my guns. My BCM 16 ELW started putting brass 1-2 o clock recently. I didn't suspect that it magically became over gassed, because it is still my smoothest gun to date despite ejection angle. Im gonna replace the extractor spring with a new spring co 5 coil and see how she goes.
The ELW barrel has a .625 journal. Does the OP's barrel have that, or a .750 journal? All other things being equal, barrels with same size gas ports will function differently with different sized journals.
People talked shit when I brought that up a couple years ago. Morons.
If you're not interested in a BRT option, then you need to replace the barrel.
The only 11.5" barrels optimized for suppressed use in my opinion are BRT, Sionics, and Triarc.
Looks over gassed for sure.
Your best options are an EZTUNE gas tube or OPTIMUM barrel.
This tube is setup for dedicated suppressed use with an H or H2 buffer.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-SUPP-CAR-p154960008
Both of these are setup for 50/50 suppressed use with a buffer swap.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-MIX-CAR-p194049554
https://blackrivertactical.com/WP/BRT-11-5-OPTIMUM-CQB-Light-Barrel-p206839864
Thoughts & options please / tnx. Not interested in either AGB or inserts.
Oddly get similar ejection pattern suppressed & unsuppressed
- M855
- H3
- New carbine spring
- Will run 100% suppressed
https://youtu.be/y4cFEz9BLYg
https://youtu.be/bJmUMYcvty8
Looks over gassed for sure.
Your best options are an EZTUNE gas tube or OPTIMUM barrel.
This tube is setup for dedicated suppressed use with an H or H2 buffer.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-SUPP-CAR-p154960008
Both of these are setup for 50/50 suppressed use with a buffer swap.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-MIX-CAR-p194049554
https://blackrivertactical.com/WP/BRT-11-5-OPTIMUM-CQB-Light-Barrel-p206839864
Are you not recommending the Custom Tune Gas Ports anymore?
ColtSeavers
09-06-20, 12:43
Apparently BCK)M started porting their 11.5s with a .076 gas port.
https://www.m4carbine.net/showthread.php?225373-What-is-the-best-11-5-barrel-money-can-buy&p=2879238#post2879238
You're going to want an H3 and Sprinco Blue if not Red to try and tame recoil without buying adjustable stuff.
ColtSeavers
09-06-20, 12:44
The ELW barrel has a .625 journal. Does the OP's barrel have that, or a .750 journal? All other things being equal, barrels with same size gas ports will function differently with different sized journals.
How does the extra .0625" the gas has to travel make any difference?
.625 is the gas journal diameter. The gas port is shorter in length, the smaller the gas journal. Therefore, a smaller journal needs a smaller port, all other things being equal.
This is basic fluid dynamics. You can demonstrate this at home. Take a straw and blow through it as hard as you can. Then cut it shorter and repeat. You'll notice that the shorter the straw, the easier it gets to blow through.
ColtSeavers
09-06-20, 12:56
.625 is the gas journal diameter. The gas port is shorter in length, the smaller the gas journal. Therefore, a smaller journal needs a smaller port, all other things being equal.
This is basic fluid dynamics. You can demonstrate this at home. Take a straw and blow through it as hard as you can. Then cut it shorter and repeat. You'll notice that the shorter the straw, the easier it gets to blow through.
Yes, I should have said the .0625" difference in travel between .750" and .625" gas block journal diameters.
It does make a difference despite the fact that the distance is not that great. It’s due to the high pressure. Just as a .005 inch gas port diameter change can make a big difference, so does a small difference in the length of the port.
The ELW barrel has a .625 journal. Does the OP's barrel have that, or a .750 journal? All other things being equal, barrels with same size gas ports will function differently with different sized journals.
It is indeed an ELW bbl
Sent from my iPhone using Tapatalk
Looks over gassed for sure.
Your best options are an EZTUNE gas tube or OPTIMUM barrel.
This tube is setup for dedicated suppressed use with an H or H2 buffer.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-SUPP-CAR-p154960008
Both of these are setup for 50/50 suppressed use with a buffer swap.
https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Preset-MIX-CAR-p194049554
https://blackrivertactical.com/WP/BRT-11-5-OPTIMUM-CQB-Light-Barrel-p206839864
So CQB light vs SB suppressed bbl?
The CQB Light runs really well with a suppressor and is in stock now.
The SB runs slightly better 100% suppressed, but gives up the flexibility to run without the suppressor and is not currently in production.
So CQB light vs SB suppressed bbl?
Are you not recommending the Custom Tune Gas Ports anymore?
Curious about this as well.
The CQB Light runs really well with a suppressor and is in stock now.
The SB runs slightly better 100% suppressed, but gives up the flexibility to run without the suppressor and is not currently in production.
Tnx for the response
I plan to in order:
- ensure it’s not extractor / ejector related with a quick bolt swap as @mistwolf touched on (felt recoil is subjective, but it doesn’t “feel” overly so)
- ez tune gas tube
or
- CQB light bbl
everready73
09-08-20, 13:18
Curious about this as well.
I think he was recommending based on the OP where OP said he didnt want an adjustable gas block or insert. That only really only leaves a gas tube or new barrel as options
I think he was recommending based on the OP where OP said he didnt want an adjustable gas block or insert. That only really only leaves a gas tube or new barrel as options
Gotcha.
I missed that part. Was just curious, as I'd think the Gas port insert would be the best way to fix it.
Correct.
I think he was recommending based on the OP where OP said he didnt want an adjustable gas block or insert. That only really only leaves a gas tube or new barrel as options
Best is subjective. The gas port certainly would work, but is significantly more trouble to install. The EZTUNE gas tube is really easy and generally takes less than 5 minutes to do.
Gotcha.
I missed that part. Was just curious, as I'd think the Gas port insert would be the best way to fix it.
Correct.
Best is subjective. The gas port certainly would work, but is significantly more trouble to install. The EZTUNE gas tube is really easy and generally takes less than 5 minutes to do.
It's what you guys recommended to me as the most durable option when you guys were just coming out with the Tubes. Figured it'd still be the case.
I guess not "best" in terms of ease of install.
It must be overgassed. I am running an H3 in my BCM 11.5 with a LAW folder which I assume adds weight to the BCG since it used that little extension and with a can it still runs Wolf steel case just fine.
It's what you guys recommended to me as the most durable option when you guys were just coming out with the Tubes. Figured it'd still be the case.
I guess not "best" in terms of ease of install.
Remove gas tube, install new gas tube vs remove FH, gas tube, gas block, drill/tap gas block, insert port, re-install GB, GT, FH.
I don't regret getting the port back in the day (in an FSB, even) though the tube is super easy.
Andy
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