View Full Version : Buffer system for DD mk18 .70 port
VincentVanPwn3d
04-28-20, 12:42
Looking for some directions on where I should lean towards in a buffer system for my DD mk18 upper with .70 gas port. I currently only have carbine buffer on hand. I don't plan on suppressing anytime soon.
I was leaning towards a sprinco or Geissele spring and a h2 buffer or the vltor A5 system (don't know what weight/spring).
Just curious if anyone with more knowledge could help narrow down some options for me
I primarily train with wolf steel and 55gr handload plinkers. I don't think they are really low charge but for sure not 556 3000fps plus powered.
Anyway, thank for any help
Regards.
I've ran the same gun-DD MK18 with same size port-unsuppressed and suppressed with the H buffer and factory LMT spring. Never had any issues-NOT ONE! Hope this helps. That upper had prob ~5k rounds through FWIW
I've ran the same gun-DD MK18 with same size port-unsuppressed and suppressed with the H buffer and factory LMT spring. Never had any issues-NOT ONE! Hope this helps. That upper had prob ~5k rounds through FWIW
Have you noticed any wear in the cam pin lobe in the upper receiver?
Have you noticed any wear in the cam pin lobe in the upper receiver?
Nothing out of the ordinary. I've seen a few pics of some "additional" wear and never saw anything like that. Just normal wear
I have the A5, H3 buffer and a green spring. It cycles unsuppressed fine, a bit gassy suppressed.
PatrioticDisorder
04-28-20, 17:08
Whatever you do, I wouldn’t recommend the A5 with green sprinco spring, even with an A5H1 or A5H0, unsuppressed with weaker ammo you may have some issues. I’m currently using a standard rifle spring, can use heavier A5 buffers with this, I have a tubbs flatwire I’m going to experiment with, but I haven’t had a chance to test that out yet.
I have 465 rounds through mine, all with a springco green spring and A5H3 without any problems. Most of that was 5.56, but at least the last 60 was Norma .223.
me2hootyhoo
04-30-20, 17:16
H2 with Tubbs flat wire. Smoothest shooter I own. Cycles PMC and wolf, locks back on empty mag, never an issue.
Quit tearing your hair out over the buffer system and use a better band-aid for the over gassing problem. Get a Superlative Arms adjustable gas block and stick with running a stock buffer and spring. It'll shoot better. The block is expensive, but if you add up the cost of a tube, heavy buffer, spring, and wear on your gun, the gas block's cost ain't so bad. I say Superlative Arms because it won't freeze up and become difficult to adjust as carbon builds up, like the set screw models do. Since you mentioned shooting underpowered ammo, it would just take a twist of a hex key to turn up the gas. Or, just tune for the lower powered ammo and run it like that with everything. It will still be getting a lot less gas than it was.
Quit tearing your hair out over the buffer system and use a better band-aid for the over gassing problem. Get a Superlative Arms adjustable gas block and stick with running a stock buffer and spring. It'll shoot better. The block is expensive, but if you add up the cost of a tube, heavy buffer, spring, and wear on your gun, the gas block's cost ain't so bad. I say Superlative Arms because it won't freeze up and become difficult to adjust as carbon builds up, like the set screw models do. Since you mentioned shooting underpowered ammo, it would just take a twist of a hex key to turn up the gas. Or, just tune for the lower powered ammo and run it like that with everything. It will still be getting a lot less gas than it was.
OP stated the gas port size. It’s not over gassed at all. New DD MK18 barrels are .070 instead of the .080 they used to be.
OP I originally ran Sprinco blue and H2 at the recommendation of others here. That worked well with 5.56 but my .223 handloads would not lock back on empty (still cycled, but barely). That same spring and buffet combination would not lock back even with 5.56 when I shot in cold temps (about 24 degrees F).
I dropped to a standard spring and H and that seemed to help in cold temps, but I didn’t try .223 ammo.
Later down the line I added a Law Folder, and with the 2.3 oz adapter plug I found the gun to be very sluggish in the indoor range. I didn’t shoot in the cold, but I made the decision to switch to a carbine buffer and kept the standard carbine spring.
Recently I changed to an A5H0 buffer and BCM rifle spring (intermediate/A5 extension of course). I’ve only got a magazine of 5.56 handloads fired with this newest combo but ejection was more consistent than with the carbine spring and buffer. I’m assuming this is due to the spring inside of the A5 buffer that keeps the weights in the same position.
OP stated the gas port size. It’s not over gassed at all. New DD MK18 barrels are .070 instead of the .080 they used to be.
If he's looking to tune with a buffer and spring, he'd be better served with tuning the gas. Less bolt velocity and less reciprocating mass is a good thing, isn't it?
PatrioticDisorder
05-02-20, 06:37
If he's looking to tune with a buffer and spring, he'd be better served with tuning the gas. Less bolt velocity and less reciprocating mass is a good thing, isn't it?
I’m sure the superlative arms adjustable gas block is good for tuning for larger gas ports (I see Triarc uses them, probably a good sign it’s a good product), but it won’t help OP with his Mk18 barrel, these barrels are in no way over gassed. A5 buffer system, offers a wider range of adjustments but probably not necessary.
Agreed. Plus an adj gas Black is probably the last thing I’d mess with unless it was really needed.
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ruckusjuice
05-02-20, 12:40
OP, is this a completed build that’s having cycling issues or do you just have the upper and are looking to complete the build?
...Less bolt velocity and less reciprocating mass is a good thing, isn't it?
No. The right amount of reciprocating mass at the right speed is needed for the right timing.
turnburglar
05-02-20, 18:18
No. The right amount of reciprocating mass at the right speed is needed for the right timing.
This.
I remember watching a video with Jim Sullivan and he said the AR design actually does better with MORE buffer weight than less. My adjustable gas MSR10 subjectively shot better with an H3 over a carbine buffer.
To the OP; I have a 0.071 GP 10.5 that seems to do well with a H2 and regular carbine action spring. Its had easily 2 cases though it like that, and probably needs a new buffer spring. Ejection is very consistent.
davidjinks
05-05-20, 10:06
Same setup, I use a colt H3 buffer with standard buffer spring.
I will run the heaviest buffer I can in all of my rifles that will reliably run the weakest ammo I use. SBR’s get H3 and 16-18” with collapsible stocks get H2. All rifles use a standard buffer spring.
Looking for some directions on where I should lean towards in a buffer system for my DD mk18 upper with .70 gas port. I currently only have carbine buffer on hand. I don't plan on suppressing anytime soon.
I was leaning towards a sprinco or Geissele spring and a h2 buffer or the vltor A5 system (don't know what weight/spring).
Just curious if anyone with more knowledge could help narrow down some options for me
I primarily train with wolf steel and 55gr handload plinkers. I don't think they are really low charge but for sure not 556 3000fps plus powered.
Anyway, thank for any help
Regards.
Run a A5H2 on mine with zero issues over thousands of rounds.
No. The right amount of reciprocating mass at the right speed is needed for the right timing.
Well, that's the question. What is the right amount of reciprocating mass? You don't want to go too light because that will affect function. Your rifle gets dirty...it gets harder to ensure that the bolt will strip a round off of a full mag and go into battery...the weight necessary to do this is what is needed. Why would you want to add more mass beyond that if you can just turn the gas down to obtain the same effect as adding a heavier buffer?
My colt with 10.3 runs with a h3 geissele Super 42, and an LMT enhanced bcg. It’s smooth as butter unsurpressed. But I only shoot m193 and m855.
I think other dudes here are missing the part where you said you shoot wolf steel.
I doubt my rifle would function with underpowered ammo. Honestly this is going to have to be trial and error on your part.
Sent from my iPhone using Tapatalk Pro
Well, that's the question. What is the right amount of reciprocating mass? You don't want to go too light because that will affect function. Your rifle gets dirty...it gets harder to ensure that the bolt will strip a round off of a full mag and go into battery...the weight necessary to do this is what is needed. Why would you want to add more mass beyond that if you can just turn the gas down to obtain the same effect as adding a heavier buffer?
The point is, that turning down the gas is not beneficial in this weapon and will result in an unreliable gun. The Crane spec gas port for a 10.3” Mk18 of ~.070 is designed around full pressure, true 5.56 ammo and mixed suppressed use. It may still function with less gas than that, maybe, or with .223 ammo, until it gets cold or dirty.
Another way of thinking about this is that Sionics reduced gas port 11.5” barrel has another 1.2” of barrel and the same size port. The M4 has another 4.3” of barrel, ~40% longer, and only 0.007” smaller port, or ~10%. Don’t make me do the math on port area. (Edit: the difference in port area is in the neighborhood of 20%)
10.3’s deserve suppressors.
Well, that's the question. What is the right amount of reciprocating mass? You don't want to go too light because that will affect function. Your rifle gets dirty...it gets harder to ensure that the bolt will strip a round off of a full mag and go into battery...the weight necessary to do this is what is needed. Why would you want to add more mass beyond that if you can just turn the gas down to obtain the same effect as adding a heavier buffer?
First I would say the MK18 was built as a system with or without a can the gun will function fine with an H2 buffer. Second, most military weapons dont use a adjustable gas block unless they are dead simple (SCAR as an example). They require initial tuning, more maintenance and can work themselves loose (depending on the type) which would also be unacceptable for a military weapon. In this case IMO, unless he has a can with a ton of back pressure and cant handle the gas to the face he would be far better off adjusting buffer weights or moving to a A5 system.
You don't want to go too light because that will affect function.
Exactly my point. For the widest span of operation, the action of the AR must be timed right. To achieve correct timing, the right amount of mass must be moving at the right speed. Too little or too much mass throws it off
Why would you want to add more mass beyond that if you can just turn the gas down to obtain the same effect as adding a heavier buffer?
Turning down the gas isn't the same thing as adding a heavier buffer. I tested three different buffers (carbine weight, H & H2) in an 11.5" upper equipped with an adjustable gas block. Short version is the AR achieved full function with all three buffers with the same gas block setting. Closing the gas block one more click meant the AR would eject but not lock back with all three buffers. I also discovered that while the carbine buffer needed the same gas setting as the two heavier buffers, recoil was the most violent with the carbine weight buffer. Carbine weight buffers are too light.
(NOTE: An AR with a carbine weight buffer isn't over gassed. It's under buffered. It just acts like it's over gassed. You can't just turn down the gas flow to get an AR to run right with a buffer that's too light.)
Well, that's the question. What is the right amount of reciprocating mass?
The right amount of reciprocating mass is a full auto carrier and an H, H2, A5H2 or rifle buffer when using 5.56 spec ammo. If you want to run a lighter buffer (say, the carbine buffer) ammo pressure has to be reduced. Remember, the rifle buffer is the original and it's heavier than the H and H2.
An AR has to be tuned to the ammo used. The gas drive, reciprocating mass and spring rate all have to be balanced against each other. If you change one, you have to change all three. The gas drive itself is a balancing act of pressure, flow and mass of the gas. You cannot just keep reducing the gas port. At some point, you have to change pressure (port location, ammo) flow (gas port diameter, pressure) and gas mass (ammo). There is also blow down time- the time it takes the pressure in the bore to drop down to atmospheric. Specifically, the time it take the pressure at the gas port to drop to a level it will no longer pressurize the action. Contrary to popular belief, the expansion chamber in the carrier does not pressurize enough to cycle the action until after the bullet uncorks the muzzle. If the blow down time is too short, there's not enough gas to operate the action. If the blowdown time is too long, gas flow become too difficult to control with the gas port diameter.
If it sounds like rocket science, that's because it is. The good news is, the AR is a mature system and the baseline for what works is well established. It's when you wander outside that baseline that things get complicated and your AR stops being reliable.
Start with a regular carbine spring and an H2. If it needs a heavier buffer, use an H3. That's how a MK18 is setup.
If doesn't work, fix it.
Exactly my point. For the widest span of operation, the action of the AR must be timed right. To achieve correct timing, the right amount of mass must be moving at the right speed. Too little or too much mass throws it off
Turning down the gas isn't the same thing as adding a heavier buffer. I tested three different buffers (carbine weight, H & H2) in an 11.5" upper equipped with an adjustable gas block. Short version is the AR achieved full function with all three buffers with the same gas block setting. Closing the gas block one more click meant the AR would eject but not lock back with all three buffers. I also discovered that while the carbine buffer needed the same gas setting as the two heavier buffers, recoil was the most violent with the carbine weight buffer. Carbine weight buffers are too light.
(NOTE: An AR with a carbine weight buffer isn't over gassed. It's under buffered. It just acts like it's over gassed. You can't just turn down the gas flow to get an AR to run right with a buffer that's too light.)
The right amount of reciprocating mass is a full auto carrier and an H, H2, A5H2 or rifle buffer when using 5.56 spec ammo. If you want to run a lighter buffer (say, the carbine buffer) ammo pressure has to be reduced. Remember, the rifle buffer is the original and it's heavier than the H and H2.
An AR has to be tuned to the ammo used. The gas drive, reciprocating mass and spring rate all have to be balanced against each other. If you change one, you have to change all three. The gas drive itself is a balancing act of pressure, flow and mass of the gas. You cannot just keep reducing the gas port. At some point, you have to change pressure (port location, ammo) flow (gas port diameter, pressure) and gas mass (ammo). There is also blow down time- the time it takes the pressure in the bore to drop down to atmospheric. Specifically, the time it take the pressure at the gas port to drop to a level it will no longer pressurize the action. Contrary to popular belief, the expansion chamber in the carrier does not pressurize enough to cycle the action until after the bullet uncorks the muzzle. If the blow down time is too short, there's not enough gas to operate the action. If the blowdown time is too long, gas flow become too difficult to control with the gas port diameter.
If it sounds like rocket science, that's because it is. The good news is, the AR is a mature system and the baseline for what works is well established. It's when you wander outside that baseline that things get complicated and your AR stops being reliable.
OK, I had some trouble reconciling what I was absorbing here, so I went out to the range yesterday. I did about 500 rounds playing around with a couple of things I'm working on, on my 10.5.
Well, I settled on a plain old flash hider. The comps are too brutal for what they do and I also played around with my gas block and a few buffers. What can I say? I made sure that my pistol was tuned to run reliably on a wide range of ammunition and then wound up on an H2 buffer. Still the same reliability and the gun shot softer. I opened the gas block up another 1/4 of a turn for good measure and called it a day.
As it turns out, the barrel that I have has a .073" gas port. I guess Corona solitude has me going a bit nuts. Thanks for all of the info.
Personally I check ejection on all my Stoner's: I look for 3oclock-4oclock. I recommend Sprinco springs: I replace all of my milspec springs with the cryo'd versions. At .070" gas port (Colt Spec) for MK18 would likely be a "Red Carbine" Extra Power Sprinco Spring. I use these on all my earlier Colt M4's which were gassed hotter than the newer Colt M4. Earlier A2 I use "Sprinco Blue Carbine" springs. I like a bit more power than OEM within the timing confines of the ideal 3-oclock ejection pattern. Additionally I recommend an H2 weight buffer. If you switch to the hybrid you're best doing with a Vltor A5 kit and I can't recall if they are still using Sprinco springs, if not, Sprinco has an A5 recommended spring and pay the additional $2 for cryo. I have never had a Sprinco spring equipped carbine fail to eject or seat a round clean or dirty. It's worth the added peace of mind for small money. I have had OEM/milspec springs peter out at 2000ish rounds on a dirty carbine. I also believe they stress the bolt out, which is compounded by an Carbine weight buffer. H1, H2 delay the bolt unlock long enough so the lugs take less wear, and the combination reduces in less bolt bounce. I have a Colt with over 12K rounds and the original bolt looks fantastic, and the barrel is still a shooter. I have lost track of how many over gassed guns I have seen in my travels that are trash because the owners used 3oz buffers and do not replace the milspec springs every 2-3k rounds. Given the price of a good Colt spring, I just prefer Sprinco and forget about it: but I have nothing against Colt/LMTmilspec springs as long as they get swapped out on schedule. I also recommend replacing the ejector and extractor springs with Sprinco cryo. Sprinco will help you select the right springs if you need the help. I run a Valkyrie with a Sprinco Red Carbine spring and MGI buffer and it drops brass in a nice small pile at right about 3:30. I have found the Sprinco springs to be forgiving in cross compatibility between different models of M4 and franken rifles. I don't shoot cheap ammo, I shoot 5.56N mostly federal lake/military surplus stuff. I just finished a Maxim pistol build and I choose to gas it down because the barrel is an old Colt/SAW 10" HBHRT type: as the gas port is massive: .082" and Maxim's spring is it's own thing at a H1 weight. The custom gas tube, spring, and mini buffer address the timing well. But you should be good with just a H2 and Sprinco Red Carbine if you want to use Carbine Extension. Keep in mind the A5 is leaning towards mid-length gas system I believe: and you don't have that with a MK18. Good luck!
I have a Giselle system lover. eplaced all other AR recoil parts with his and LOVE THEM. Give him a call for tech questions re: .70 port.
I run a BRT .65 gas tube, H buffer and Tubbs spring in my FBI HRT 11.5 that has a .70 gas port, 50/50% suppressed and Non suppressed. Runs like a sewing machine. So yes .70 is overgassed IMO, especially suppressed.
I run a BRT .65 gas tube, H buffer and Tubbs spring in my FBI HRT 11.5 that has a .70 gas port, 50/50% suppressed and Non suppressed. Runs like a sewing machine. So yes .70 is overgassed IMO, especially suppressed.
I have a 11.5" Remington Defense SOCOM barrel: it's CHF and chromed well. I was planning on doing a SOPMOD BlkIII build, which is essentially a HRT with a shorter barrel and I like the HRT better to be honest. I need to email Remington and get their gas specs. Do you have HRT build specs or a link to the info? TIA
I have a 10.3 DD with a .07 port. Mine has a standard carbine spring with a H buffer. It runs very smoothly and piles the brass up at the 4 o'clock position.
I have a 10.3 DD with a .70 port. Mine has a standard carbine spring with a H buffer. It runs very smoothly and piles the brass up at the 4 o'clock position.
It will work fine but will likely stress your bolt lugs out. It might also lower the reliability if you are shoot rapidly or suppressed. .07” port is well sized for a 10.3” barrel carbine. .7” you might need a 5lb buffer and one of those special springs.. :P
You got an .070" gas port? You lucky dog, mine was so overgassed it notched case rims and blasted me in the face with smoke every time I put a can on it. I had to have BRT threaded inserts put in mine to get it down to .070" but now that it is I run a Sprinco WHITE and an H buffer with a bare muzzle and an H2 buffer with a can.
I like the way it feels bare muzzle with the H2 but it's not flinging the empties out there with quite as much authority and probably wouldn't run trash civilian ammo quite as well if it was super dirty.
You got an .070" gas port? You lucky dog, mine was so overgassed it notched case rims and blasted me in the face with smoke every time I put a can on it. I had to have BRT threaded inserts put in mine to get it down to .070" but now that it is I run a Sprinco WHITE and an H buffer with a bare muzzle and an H2 buffer with a can.
I like the way it feels bare muzzle with the H2 but it's not flinging the empties out there with quite as much authority and probably wouldn't run trash civilian ammo quite as well if it was super dirty.
I just finished a 10.3" Colt SAW/HRT Heavy build and the gas port is "YUUGE!" I used the BRT custom tube and it runs like a sewing machine with a l Maxim Defense H1 System. I was worried the system was too light, but it drops brass at 3 oclock in a nice pile. Recoil is pretty mild also. I don't shoot cheap ammo however, .556 dropping at 3 usually cycles junk ammo.
Ken Elmore loves to hog out gas ports.
Dude is a legend but ruins barrels.
Ken Elmore loves to hog out gas ports.
Dude is a legend but ruins barrels.
Had a number of conversations with Ken and he has never recommended enlarging gas ports. He wont even work on a barrel that has been over ported. He had in the past modified the ports for suppressed use but I am not aware of Ken to "hog" out gas ports. I have seen a lot of people claim their parts are SA to sell them. Ken adheres to Colt Defense gas ports specs: which have changed over the years but has remained the same for some time now.
I have experience with several 0.070 10.3’s, since that’s my favorite setup.
Strictly unsuppressed, H2 buffer, Carbine spring. It’ll run everything.
If you’ll only run full power 556, I would go to H3.
If you go suppressed, go to H3 with extra power spring, whether that be 42 or blue.
Having said that, My URGI runs everything with 42 and H2. However it’s well broken in. Whereas my brand new mk18 would only run brass.
My Geissele will run steel unsuppressed but won’t lock back.
Hope that helps.
I have experience with several 0.070 10.3’s, since that’s my favorite setup.
Strictly unsuppressed, H2 buffer, Carbine spring. It’ll run everything.
If you’ll only run full power 556, I would go to H3.
If you go suppressed, go to H3 with extra power spring, whether that be 42 or blue.
Having said that, My URGI runs everything with 42 and H2. However it’s well broken in. Whereas my brand new mk18 would only run brass.
My Geissele will run steel unsuppressed but won’t lock back.
Hope that helps.
I run extra power springs on all my Colts. I adjust the buffer weight to get my preferred ejection pattern and take the pressure into consideration to mitigate bolt wear. I set them up to run dirty by using the extra power springs. The buffer handles several separate functions and taking Stoner and Sullivans wisdom into consideration its important to go a bit heavier than you need. I used to run a MGI buffer in my M4 and a piano spring before I found Sprinco.
Had a number of conversations with Ken and he has never recommended enlarging gas ports. He wont even work on a barrel that has been over ported. He had in the past modified the ports for suppressed use but I am not aware of Ken to "hog" out gas ports. I have seen a lot of people claim their parts are SA to sell them. Ken adheres to Colt Defense gas ports specs: which have changed over the years but has remained the same for some time now.
Part of his ‘reliability package’ is to open the gas port, at least on 14.5” and 16” barrels.
Part of his ‘reliability package’ is to open the gas port, at least on 14.5” and 16” barrels.
I have read this in his order description: but at the same time it specified SA will not work on modified Colt barrels. Do you have a SA gas port example you can cite? Ken discussed this years ago with myself and several others, and he mentioned that he opened it up to spec "if needed": and there was discussion to the port sizes, and Ken mentioned Colts newer port size being the specified standard. I have an older M4 Carbine and its definitely well gassed, possibly over gassed, but I have not pulled the FSP and measured the gas port. I was told they had issues with cut downs at one time which would make sense: this could be a older issue when Colt was using rifle length gas ports in carbines? What are your thoughts?
A rifle length port is .093”. I don’t think that would even work on a carbine barrel.
As fas I know, 14.5” and 16” Colt carbine barrels have ALWAYS been ported at .0625”. The earliest ones I’ve been around were 16” 1/9” twist hbar and even those were .0625”.
A rifle length port is .093”. I don’t think that would even work on a carbine barrel.
As fas I know, 14.5” and 16” Colt carbine barrels have ALWAYS been ported at .0625”. The earliest ones I’ve been around were 16” 1/9” twist hbar and even those were .0625”.
I remember seeing some old commercial 16" carbine barrels with huge gas ports .080" ish. And once listening to some industry guys explain why they needed a larger gas port to run crap ammo. I had a good laugh and pissed them off a bit. Oh well, always a justification to make a quick buck and a bit with a bit of halfassery.
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