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So I've had my Scar 20 for a few months now and love it. But recoil while suppressed is kind of sharp. I've been seeing some info on other sites claiming the 16, 17 and the 20 were never built to be suppressed. So the jets that FN uses ensure functionality with all sorts of ammo. Some are claiming the 17 especially is much smoother and less recoil when changing the gas jets to a smaller size. Anyone have any info on the 20 jets ? I'll most likely run it suppressed most of the time . Any info would help ?
 

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Call PMM and talk to Jarod. I know I took my 20" 17S barrel down to a 1.25 and it noticeably changed the recoil and the gas was almost nothing with surplus ammo.
 

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I’ll echo the previous post with my 17. I ended up at the same size screw for mine. It cycles nice and soft at the 12 o’clock setting with no can and with the can is much better than the stock size. The 17 comes with a 1.5mm and the 20 comes with a 1.4mm. The size difference comes from the longer barrel having more dwell time. I’ve run the 20 as low as a 1.15mm and it cycles fine thus far. Can is a Silencerco Omega and I run 7.62 milsurp through the 17 and GMM through the 20. Making your own recoil buffers helps a lot as well. I run em in both.
 

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Background:
  • Purchased my first SCAR so looking to learn and getting feedback
  • Have plenty of ARs and other semi-autos. Definitely not my first rodeo
  • I handload almost all my ammunition but will shoot factory ammo from time to time
  • Have several silencers I can run on this platform and will dedicate the one with the best accuracy and reliability
  • I run suppressed 90% of the time and will have the Gas Regulator set to Suppressed.
  • Want reliable cycling and lock back on empty mag for suppressed. Fine-tuning to the razor's edge is not what I'm after.

I've been scouring the internet on gas regulator settings and Gas Jet setup for the 20s, this is what I found:

Gas Regulator is supposed to be set to the 12-o'clock position at all times. No where in the 20s manual does it say otherwise. Internet says (looking from muzzle to buttstock):
  1. 12-o'clock for Normal. Normal gas venting
  2. 2-o'clock for Adverse. Decrease gas venting
  3. 10-o'clock for Suppressed. Increase gas venting

Gas Jet is used to control the amount of gas entering the piston chamber.
  1. With the Default Gas Jet (1.40mm) and Gas regulator in the 12-o'clock position
    • Increasing the Jet size will increase gas to the piston chamber
    • Decreasing the Jet size will reduce gas to the piston chamber


Here are my questions:

  1. Is what I've outlined correct?
  2. Going to order Gas Jets in 1.35mm, 1.30mm, 1.25mm, and 1.20mm. Sound about right?
  3. What is the proper way of determining overgassing without beating up the receiver or bolt and finding out the hard way? ARs you can determine by brass ejection pattern. Goal is to cycle and lock back on an empty mag.
 

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i saw a YT review that pointed out that the 20S manual doesn't say to use the 10 o'clock gas setting for suppressed, but the guy just assumed it was the same as the 17.
 

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Background:
  • Purchased my first SCAR so looking to learn and getting feedback
  • Have plenty of ARs and other semi-autos. Definitely not my first rodeo
  • I handload almost all my ammunition but will shoot factory ammo from time to time
  • Have several silencers I can run on this platform and will dedicate the one with the best accuracy and reliability
  • I run suppressed 90% of the time and will have the Gas Regulator set to Suppressed.
  • Want reliable cycling and lock back on empty mag for suppressed. Fine-tuning to the razor's edge is not what I'm after.

I've been scouring the internet on gas regulator settings and Gas Jet setup for the 20s, this is what I found:

Gas Regulator is supposed to be set to the 12-o'clock position at all times. No where in the 20s manual does it say otherwise. Internet says (looking from muzzle to buttstock):
  1. 12-o'clock for Normal. Normal gas venting
  2. 2-o'clock for Adverse. Decrease gas venting
  3. 10-o'clock for Suppressed. Increase gas venting

Gas Jet is used to control the amount of gas entering the piston chamber.
  1. With the Default Gas Jet (1.40mm) and Gas regulator in the 12-o'clock position
    • Increasing the Jet size will increase gas to the piston chamber
    • Decreasing the Jet size will reduce gas to the piston chamber


Here are my questions:

  1. Is what I've outlined correct?
  2. Going to order Gas Jets in 1.35mm, 1.30mm, 1.25mm, and 1.20mm. Sound about right?
  3. What is the proper way of determining overgassing without beating up the receiver or bolt and finding out the hard way? ARs you can determine by brass ejection pattern. Goal is to cycle and lock back on an empty mag.
whatch this video. relevant part starts at around 3:00 minutes.

 

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Background:
  • Purchased my first SCAR so looking to learn and getting feedback
  • Have plenty of ARs and other semi-autos. Definitely not my first rodeo
  • I handload almost all my ammunition but will shoot factory ammo from time to time
  • Have several silencers I can run on this platform and will dedicate the one with the best accuracy and reliability
  • I run suppressed 90% of the time and will have the Gas Regulator set to Suppressed.
  • Want reliable cycling and lock back on empty mag for suppressed. Fine-tuning to the razor's edge is not what I'm after.

I've been scouring the internet on gas regulator settings and Gas Jet setup for the 20s, this is what I found:

Gas Regulator is supposed to be set to the 12-o'clock position at all times. No where in the 20s manual does it say otherwise. Internet says (looking from muzzle to buttstock):
  1. 12-o'clock for Normal. Normal gas venting
  2. 2-o'clock for Adverse. Decrease gas venting
  3. 10-o'clock for Suppressed. Increase gas venting

Gas Jet is used to control the amount of gas entering the piston chamber.
  1. With the Default Gas Jet (1.40mm) and Gas regulator in the 12-o'clock position
    • Increasing the Jet size will increase gas to the piston chamber
    • Decreasing the Jet size will reduce gas to the piston chamber


Here are my questions:

  1. Is what I've outlined correct?
  2. Going to order Gas Jets in 1.35mm, 1.30mm, 1.25mm, and 1.20mm. Sound about right?
  3. What is the proper way of determining overgassing without beating up the receiver or bolt and finding out the hard way? ARs you can determine by brass ejection pattern. Goal is to cycle and lock back on an empty mag.
There are only 2 gas settings. Looking from the Butt forward there is 12:00 which is full gas to the action and 2:00 which is reduced gas to the action. There is no "suppressed" setting as such. I've played with gas jetting on both my 17 and 20 a fair bit both suppressed and unsuppressed. On my 20 with Omega suppressor I went down as small as 1.15 but ended up having the occasional failure to lock open. I went up to a 1.2 and all is well. Bear in mind the ammo used will somewhat dictate the gas jet size. In my case I normally run Malaysian milsurp and it's tuned for that. However when I go for long range nowadays I'll run some GMM. The GMM is a bit hotter than the milsurp and so still cycles just fine. I did the gas jet sizing on the 10:00 setting so as to allow for more gas if needed by going to the 12:00 setting. For setting the jet size go down in size until it doesn't lock open and then go up one size. On the 17 it's an easy process as the jet is easily accessible but to change it on the 20 the barrel has to be removed. If you're running milsurp ammo it tends to be a little less pressure so I'd start with a 1.2. If your running commercial stuff with a bit more pressure you could start with a 1.15 and see if it cycles properly. The can you use will also have an effect on jet size as well depending on how much or little back pressure it has. More back pressure would need a smaller jet and vice versa. The recoil on mine with the 1.2 jet, Omega can and a recoil buffer is plenty soft enough that my 10yo boy runs it with no issues at all. He's made repeatable hits on steel at 600 and always wants to run it when we go out to the long range.

P.S. I watch IV8888 all the time but Eric is incorrect about the piston setup in the Scar. It's not a long stroke but a short stroke piston. However that being said their results are about on par with what I've seen from my 20. I've run it out to 870 yards on a standard size steel silhouette with about the same accuracy or a bit better when there's no wind. It's a good stick if you do your part and feed it with good food.
 

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So I know I'm digging up an old thread but thought I'd share something I learned tonight.

Took my new 20S down tonight to change the jet out to something a tad smaller. Best I could measure it came to 1.45. Went to a 1.30 based on past experience with my two 17S rifles, find out if that works fine tomorrow. Anyway, when looking at the gas plug the two holes looked the same and measuring them confirmed that. So NO DIFFERENCE in the two settings if you think going to the suppressed setting will make a difference. Thought that was odd and went ahead and swapped in my Mototech 3 position one. Just thought this was weird considering my 17S plugs both have different size holes in their plugs.
 

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Some things to remember about the 20S. First, it comes in 2 different calibers, .308 and 6.5 Creedmoor, and the gas jets that work in one will not perform correctly in the other. My 17S 13" SBR with a Surefire SOCOM RC-2 suppressor shooting military surplus ammo likes the 1.35mm gas jet the best. Since the 6.5 Creedmoor has a much higher chamber pressure than the .308, several owners have said that the sweet spot for their 6.5 Creedmoor running suppressed is with a 1.10mm gas jet.

Finally, there's been much discussion regarding the pros and cons of the Mototech 3-position selector, which does have 3 different size holes. It's probably 50/50 from those that have purchased them that they are of a benefit worthy of the cost. You may want to consider purchasing one and see if that provides the recoil reduction that your seeking.
 

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bbuttons17s,
Not sure you even read my post. I too have a couple 17S rifles that I've done gas jet testing with and used that information to install a new smaller one in my 20S....which is the 7.62 1:10 twist version. I also already have a Mototech plug which I've also installed in my 20S. This is all to reduce the overgassing of the gun both suppressed and unsuppressed. The primary point of my post was to let people know the 20S plug has no different gas hole sizes and thought that unusual.
Thanks
 

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bbuttons17s,
Not sure you even read my post. I too have a couple 17S rifles that I've done gas jet testing with and used that information to install a new smaller one in my 20S....which is the 7.62 1:10 twist version. I also already have a Mototech plug which I've also installed in my 20S. This is all to reduce the overgassing of the gun both suppressed and unsuppressed. The primary point of my post was to let people know the 20S plug has no different gas hole sizes and thought that unusual.
Thanks
didn't the guy from pmm say there is a larger bypass for the gas to vent?
he rambles a little bit so i didn't watch it again.

 

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didn't the guy from pmm say there is a larger bypass for the gas to vent?
he rambles a little bit so i didn't watch it again.

He may have, I'll have to watch that video again. Thanks

Just thought that both gas plug holes being identical size was odd as it would make going from 12 to 10 worthless.
 

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It is the same gas hole size...but once you go to 10 o'clock...it activates the venting...so no it is not "worthless"...you want that additional venting option when running suppressed...

If you plan on running suppressed...you either need MotoTech gas plug or step down to a 1.3mm gas jet...I would also recommend torx back plate option and rubber buffer pad...

This applies to all suppressors outside of an OSS...
 

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It is the same gas hole size...but once you go to 10 o'clock...it activates the venting...so no it is not "worthless"...you want that additional venting option when running suppressed...

If you plan on running suppressed...you either need MotoTech gas plug or step down to a 1.3mm gas jet...I would also recommend torx back plate option and rubber buffer pad...

This applies to all suppressors outside of an OSS...
I'm pretty good with design and understanding the mechanics of something, I'm an electro/mechanical hardware engineer and love to tinker.

That all said, the OEM gas regulator has two holes of equal size for the gas coming through the jet to the piston. Either hole also vents through the front hole of the regulator, I'm just not seeing where 12 vs 10 o'clock makes any difference....I could be missing it though.
I agree with all else you said....I did go to a smaller jet, 1.3 for now to test, and I also installed the Mototech buffer and gas plug(the lowest gas setting on which doesn't lock into place like it did on the 17S). What's the torx back plate option you spoke of, not familiar with that?

Thanks thehun.
 

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Eddie sells replacement Torx screws for the back plate. The stock hex screws don’t grab 100% of the threads in the back plate. Eddie’s screws are slightly longer (and Torx) so able to grab more thread to mitigate screw canting.
 

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When you switch the gas plug to suppressed setting (10 o clock) it exposes this machined in cut out and two small vent holes that line up to a machined vent cut inside the gas block (about 1 o clock):
140677


Which then allows for you to vent excess gas when suppressed not just on the front vent hole but also to the side of the gas plug...it has nothing to with what job title you hold (no need to flex...seen too many engineers make a fool of themselves regarding firearms when they brag about them being engineers and how they know their stuff)...it has everything to do with understanding how the system works...which in this case...you did not...but I am happy to help you understand it (after all we are in this together)...

MotoTech backplate torx upgrade allows you to run about 10 in/lbs more torque (and as the above posted suggested...more threads to engage on) against the back plate...thus helping negate canted rear receiver screws (this more applies to people with KDG and other aluminum stock adapters but its a good insurance policy when a SCAR is ran suppressed)...I actually upgraded all my screws to torx...for the simple fact that they are a lot harder to strip than the lame allen heads...

Here is a link: Back Plate Torx Screw Set (mototecheng.com)

I've done a full torx conversion on my 20S from MotoTech...
 
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