SCAR17 - Reducing Vibration and Recoil Impulse for Optics?

penguinofsleep

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Nov 26, 2020
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Hi everyone - I have been a lurker on this forum for several years now and appreciate the good info here.

Anyways, I've read through a few threads here and elsewhere about the S17 (still) eating optics, even for recommended scopes such as the ELCAN, NF NXS or NF ATACR with recommended mounts such as the ADM Delta mount, etc.

After ~10 years it seems like the generally accepted theory is that 1) the vibration of the upper, 2) the forward recoil impulse, 3) the relatively sudden recoil impulse causing by moving parts, and 4) the (reciprocating) heavy mass of the carrier all seem to work together to destroy optics.

Has anyone tried to reduce the above successfully by mounting or adding dampening materials or physical items to the SCAR with any success with regards to less or no more dead optics? Or at least say doubling or tripling the time it takes an optic to die?

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My own thoughts, I have not tried any of the below with enough rounds, I may be completely wrong about the viability, etc etc:

1a) I suspect vibration of the upper is the easiest to fix - Dynamat is often used on car bodies to absorb excess vibrations that cause noise. Limbsaver or Bowjax clamps, wedges, or stick on pads are often used on compound bows (limbs, riser, and/or string stop) to reduce vibration and noise and I imagine can similarly be clamped or stuck onto the upper or scope mount to reduce vibrations. I also imagine something similar to the above would be be used asymmetrically - similar to how a tuning fork with uneven legs (or pinching one leg yourself) won't vibrate very well because it's out of resonance.
1b) The recoil impulse also needs to be transmitted from the moving parts through the upper through the mount into the optic. This leaves places to introducing dampening materials as well. May include mounting a thin layer of damping foam (many types, but various open/closed cell butyl and PET foams come to mind first) or energy absorbing gels (think of stuff in knee or elbow pads, shoes, etc.) onto the receiver (asymmetrically), between the optic mount and the receiver somehow, or within the scope rings themselves.

2) I suspect the forward recoil impulse can be reduced in part by the above. However, I can't think of anything that would be attached or stuck to the end of the bolt carrier that would significantly reduce impact that would be both durable enough, wouldn't negatively impact function of the firearm, and would actually be available or affordable to "average" people outside (i.e. not 5 or 6 figure specialty materials for lab use). I also wouldn't do anything simple like reducing the spring rate of the recoil spring (so it can't push the carrier back into battery as hard) w/o changing anything else in the system (namely an adjustable gas block... which I don't think exists for the S17). In short, probably not much can be done here.

3) Similar to #2, I can't think of anything that could be done to the moving parts that would be both durable and wouldn't negatively impact function of the firearm.

4) Only think I can think of here is lightening the bolt carrier. However, given expensive, proprietary, and not typically available bolt carrier, I haven't heard of anything shaving weight off of their carrier (and also lightening the recoil spring rate with it) before.
 

ScarlettRed

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I would dip the whole rifle in plastidip followed by the finest goose down feathers you can buy and then gorilla glue egg crate foam on the scope. LOL. Just kidding. I think your overthinking it. I have never damaged a scope on my scars and don't worry about it. On the "internets" stories get magnified 1000x over what they are. Get a high quality scope with a good warranty. I understand your theory as I myself have thought about such things. A couple simple things to start with are a moto tech soft compound buffer pad. Parker mountain machine small aperture gas jets. Stick with the polymer rifle stock interface to the back of the reciever. KDG is aluminum, so no go. If you can borrow a mk 20 stock it really improves the shooting experience. Chris Bartocci of small arms solutions recommends an aluminum lower as he thinks it absorbs the harmonics far better. I have a Leupold mk5 and mk6 on mine and have little worry. Lighter well built scopes are thought to handle recoil better due to lower inertia. Damn, after reading all this maybe I should have gotten an LMT. Ha
 

HUNTERVASSER

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  • Mar 31, 2018
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    Never had an issue with mine...other than the mount itself. Still holds a zero and the optic has been great. I did realize that the stock flash suppressor is pretty brutal. The LANTAC Dragon is a softer shooting brake, IMHO.
    F6AF9462-2FD8-46EE-85C9-42F0C400C3FE.jpeg
     
    Last edited:

    Gasgun

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    If you don’t go cheap, you won’t have any issues.27CA18CC-C864-4BBE-AD3E-703E255A0BD3.jpeg
     

    LRRPF52

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    This is the first I’ve heard that they trash NF, Vortex Razor, or high-end Leupold (Mk5/6).

    The optics that can take a beating have all the optical elements and modules epoxied into the tubes permanently, and use high quality gears/turrets.

    There are scope mounts already on the market that were built specifically to add rigidity to the SCAR’s exuded aluminum receiver so that the combination of flex and resonant waveform harmonics don’t resonate as violently as they normally do.

    The SCAR’s gas system length is the real challenge, as it was set to the short barrel configuration as the default, which also drove the length of the receiver/handguard length and gas system length on the 16” barrels too.

    SCAR CQC


    SCAR-17S



    The 16” barrel is simply too long for what amounts to a CLGS 7.62 NATO rifle. There is too much plug dwell time. So FN applied all the band-aids they possibly could to try to tame the cyclic rate, using port jets, tungsten powder in the bolt carrier, high action spring weight, and the elongated cam pin helix taken from the Hk G36 (improvement on the AR-18).

    That slows the rearward momentum of the carrier, which compresses on a very stout action spring. That stout action spring then sends the carrier with its dead-blow effect tungsten powder back into battery, slamming the bolt into the breech and the carrier into the barrel extension with enough force to break most of the optics out there, including most civilian thermals.

    The main reason we have the FN SCAR program is because big Army told SOCOM they couldn’t adopt the LMT enhanced BCG, as it might find itself into M16A4s and cause short-stroke malfs. The whole reason behind the LMT enhanced carrier was dealing with the excess gas from CLGS M4A1s shooting suppressed, which put the cyclic rate too fast for reliable feeding.
     

    iktomi

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    Aug 14, 2017
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    My understanding is that the SCAR H was designed around the M80 round and a low back-pressure suppressor.

    The reciprocating mass is substantial...

    Adding energy to the system (running higher pressure loads, or a high backpressure suppressor, etc.) can exceed the forces the system was designed around, and result in breakage of stock parts.

    You can reduce the inlet gas at the piston system by sourcing alternative gas jets. (Parker Mountain Machine).

    From there, you're into DIY mods.

    When I went down that road, I bought lots of duplicate parts anticipating that I would fuck some things up.

    The 17 I worked on was an inherently accurate gun out of the box shooting 168s.

    A variety of questionable decisions later, it turned into an extremely soft shooter, maintained tight groups, and is tuned against a high-back-pressure suppressor.

    Its ejection is anemic.

    It cycles lethargically.

    In the end, the work probably turned a perfectly good battle rifle capable of running mil surplus 7.62 just fine, into a strange 16" precision range toy.

    Personally, I think there's way more flexibility in tuning AR-10s to accomplish anything the SCAR platform can do.

    My experience in tuning the SCAR was a fun exercise and thought-provoking.

    Unless you have an unlimited budget or an itch you just have to scratch, my current inclination would be to leave it unsuppressed and shoot 147s through it.
     

    Gasgun

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    Unless you have an unlimited budget or an itch you just have to scratch, my current inclination would be to leave it unsuppressed and shoot 147s through it.

    This is where I’m at with the SCAR.
    It’s an accurate, reliable, reasonably light weight run and gun carbine.
    I’m not going to try to turn it into something it’s not.
    I run 147 FMJ through it almost exclusively, but I have a decent stash of Hornady 155 gr. TAP if I ever need the gun for anything serious.
     

    GUNNER10

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    My understanding is that the SCAR H was designed around the M80 round and a low back-pressure suppressor.

    The reciprocating mass is substantial...

    Adding energy to the system (running higher pressure loads, or a high backpressure suppressor, etc.) can exceed the forces the system was designed around, and result in breakage of stock parts.

    You can reduce the inlet gas at the piston system by sourcing alternative gas jets. (Parker Mountain Machine).

    From there, you're into DIY mods.

    When I went down that road, I bought lots of duplicate parts anticipating that I would fuck some things up.

    The 17 I worked on was an inherently accurate gun out of the box shooting 168s.

    A variety of questionable decisions later, it turned into an extremely soft shooter, maintained tight groups, and is tuned against a high-back-pressure suppressor.

    Its ejection is anemic.

    It cycles lethargically.

    In the end, the work probably turned a perfectly good battle rifle capable of running mil surplus 7.62 just fine, into a strange 16" precision range toy.

    Personally, I think there's way more flexibility in tuning AR-10s to accomplish anything the SCAR platform can do.

    My experience in tuning the SCAR was a fun exercise and thought-provoking.

    Unless you have an unlimited budget or an itch you just have to scratch, my current inclination would be to leave it unsuppressed and shoot 147s through it.

    This is pretty much where I am at with the scar. I think the platform has its merits, but I think that at this point in the its development and adoption, it really should be more refined than what it is at the moment.

    For example,
    In regards to controllability, The shape of the stock combined with heavy reciprocating mass give the scar a weird recoil impulse, when shot next to say a decent AR10.

    The Trigger while reliable is really something that I would expect from PSA.

    It has this weird gas system that has suppressed and unexpressed gas setting but FN does not warranty their guns of a can is mounted, while I understand there position, its 2020, and there is a good chance that most of your commercial customers, probably have one. The Scar 17 does not even have enough shoulder on the barrel to mount a can without an aftermarket solution.

    There are also no heavy/accuracy barrels for the 17 and no Light weight carbine barrels for the 20. one is almost forced into a complete second rifle, when a simple barrel swap would do the job.

    The best part of all this is everything that we know about the Scar is anecdotal where certain solutions "should" be good to go, but for most is unwarranted trial and error. Might work out, might create an 8lb, 3000 paperweight.
     

    mewillis

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    It has this weird gas system that has suppressed and unexpressed gas setting but FN does not warranty their guns of a can is mounted, while I understand there position, its 2020, and there is a good chance that most of your commercial customers, probably have one. The Scar 17 does not even have enough shoulder on the barrel to mount a can without an aftermarket solution.
    The best part of all this is everything that we know about the Scar is anecdotal where certain solutions "should" be good to go, but for most is unwarranted trial and error. Might work out, might create an 8lb, 3000 paperweight.

    I had 2 17's a few years back and parts were difficult to find if even available. And then the warranty issue running supressed while pretending the adjustable gas system is for dirty ammo only I sold them and moved on. CS is everything in my opinion and FN just doesn't cut it unless maybe you have deep pockets like big green..........
     

    GUNNER10

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    I had 2 17's a few years back and parts were difficult to find if even available. And then the warranty issue running supressed while pretending the adjustable gas system is for dirty ammo only I sold them and moved on. CS is everything in my opinion and FN just doesn't cut it unless maybe you have deep pockets like big green..........

    Its just such an odd rifle/system. I am not implying that its not a great rifle in some respects, especially if you have access to FN cans and say lake city ammo.

    Parker mountain machine has done a couple really good videos talking about the 17, more specifically about its gas system and its need to be tuned. While it appears that he is a big fan of the rifle, one of his statements struck me as very odd. He gave an account where he tuned the rifle at sea level and and when he took the rifle and shot it at higher elevation he began to experience issues with undergassing, so environment is something that needs to be taken into account when tuning its gas system.

    That sort of blows my mind, that inorder to run your average can, it has to be tuned to the point of the rifle may malfunction if their is an environmental change or risk destroying its carrier. I know that there are ports and can combo's that are pretty safe bets these days but i think the premise is valid.

    One of the other things that strikes me as odd is the development of the 20. If the 17 is so accurate, why does the 20 exist? If the 20 is a product improved scar(which I am inclined to believe) why is the 17 still produced?
     

    GUNNER10

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    This is the first I’ve heard that they trash NF, Vortex Razor, or high-end Leupold (Mk5/6).

    The optics that can take a beating have all the optical elements and modules epoxied into the tubes permanently, and use high quality gears/turrets.

    There are scope mounts already on the market that were built specifically to add rigidity to the SCAR’s exuded aluminum receiver so that the combination of flex and resonant waveform harmonics don’t resonate as violently as they normally do.

    The SCAR’s gas system length is the real challenge, as it was set to the short barrel configuration as the default, which also drove the length of the receiver/handguard length and gas system length on the 16” barrels too.

    SCAR CQC


    SCAR-17S



    The 16” barrel is simply too long for what amounts to a CLGS 7.62 NATO rifle. There is too much plug dwell time. So FN applied all the band-aids they possibly could to try to tame the cyclic rate, using port jets, tungsten powder in the bolt carrier, high action spring weight, and the elongated cam pin helix taken from the Hk G36 (improvement on the AR-18).

    That slows the rearward momentum of the carrier, which compresses on a very stout action spring. That stout action spring then sends the carrier with its dead-blow effect tungsten powder back into battery, slamming the bolt into the breech and the carrier into the barrel extension with enough force to break most of the optics out there, including most civilian thermals.

    The main reason we have the FN SCAR program is because big Army told SOCOM they couldn’t adopt the LMT enhanced BCG, as it might find itself into M16A4s and cause short-stroke malfs. The whole reason behind the LMT enhanced carrier was dealing with the excess gas from CLGS M4A1s shooting suppressed, which put the cyclic rate too fast for reliable feeding.

    I agree with this,

    The question that I have is, why... After 15 years, has FN made no attempt to modify the 17's existing gas system? That is part of the reason that I am at best luke warm on the 17.

    Why have we not seen a "mid length" gas system to mitigate some of the need for band aid solutions? I really think that having the same gas system for everything from a 10.5 inch 5.56, to a 20 inch 6.5 creedmore is an inherently flawed approach.

    Even from a modern ergo's perspective, a super short railed hand guard really doesnt lend it self to the most efficient shooting positions or set ups.

    The AK, FAL, HK9 series, AR and pretty much every military rifle in the past 50 years, have had differing gas system lengths base on what the rifle was designed for.
     

    BravoSector1

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    I've modified my SBR'd SCAR 16S and 17S with the gas jets from PMM with great results. This can be accomplished by the end user at a very low cost. Highly recommended if you're shooting this platform suppressed. Plenty of cracked carriers out there due to over gassed systems.
     

    Hippy_Steve

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    I'm starting to walk down the road of SBRing and suppressing my 17s. I plan to cut down my barrel to 13" and mount a 762-RC2 to it as a dedicated can. Gas jet tuning is definitely on the list of things to do.
     

    LRRPF52

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    I agree with this,

    The question that I have is, why... After 15 years, has FN made no attempt to modify the 17's existing gas system? That is part of the reason that I am at best luke warm on the 17.

    Why have we not seen a "mid length" gas system to mitigate some of the need for band aid solutions? I really think that having the same gas system for everything from a 10.5 inch 5.56, to a 20 inch 6.5 creedmore is an inherently flawed approach.

    Even from a modern ergo's perspective, a super short railed hand guard really doesnt lend it self to the most efficient shooting positions or set ups.

    The AK, FAL, HK9 series, AR and pretty much every military rifle in the past 50 years, have had differing gas system lengths base on what the rifle was designed for.
    Making a new gas system length would require a new piston/op-rod/carrier, as well as a totally new receiver length, followed by the type of due diligence that a company of that size will do to test the rifles extensively.

    Right now, with the short barrel-based gas port configurations, they’re selling them faster than they can make them, including the 20” guns off the shelves of Local Gun Stores. One of the only semi-auto rifles I’ve seen recently on LGS shelves have been FDE SCAR-20Ss, all of which have sold. Due to price point, they sold last, but they sold.

    As long as people see Navy SEALs with them in pictures, it doesn’t matter how compromised the design is, it will sell. People will passionately subscribe to the marketing hype and lay down GAP-10 G2 or SR-25 money for a cheap extruded aluminum upper, polymer lower, mediocre-at-best FCG, that has to have several hundred invested to make it shoot (Geissele Super SCAR $325). Once you upgrade a basic SCAR-17S with KDG handguard, ACR stock, and Geissele SSCAR FCG, that’s another $925.

    Now imagine you’re the director of civilian sales to the US market at FN. Someone on your team comes up to you and proposes a major design change to the rifle that will require hundreds of thousands of dollars or Euros in R&D. After laughing in his face, you will most likely consider his future employment with the company and whether or not he’s a good fit anymore.
     

    GUNNER10

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    You are not wrong, and to a certain extent, as was displayed with their space guns, they tend to develop a weapon for a particular program, and proceed to sell them as is, until they are no long viable. I think that the scar will stick around for quite some time due to its adoption down range even in limited roles.

    i guess my thing is that the scar was supposed to be this light weight, low cost, modular replacement for a number of systems, and at least on the commercial side, its sort of meh... Its reliable but doesn't really do any remarkably

    At 1200 bucks it would be an interesting rifle, at 3 grand, not so much. I will eventually sell mine.
     

    LRRPF52

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    The main thing I don’t like about the SCAR is the receiver height, aside from the gas system length.

    The AR-16 and AR-18 seem more ideal to me. The AR-16 was Stoner’s stamped receiver piston design chambered in 7.62 NATO. Sullivan & Fremont scaled it down into the AR-18, just as they did with the AR-10 to the AR-15, and later did with the Stoner 62 to the Stoner 63.