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Viking187, out of curiosity, did you ever run an aluminum butt stock on your rifle ?
Ran the OEM stock exclusively. Reduced the aperture on the gas jet using the whistling past a graveyard techniques on this forum. It isn’t the rifle’s fault. It’s operator error. And I accepted the risk when I put a suppressor on the rifle.

I’m electing to not shell out another $600 so that I can lose a few decibels on a loud rifle.

I don’t have the money to try another can, or buy another BC and rail. And, again, we’re talking about a small percentage change in the noise level.

I also would rather shoot a loud rifle than store a quiet one in a safe.
 

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FLet me see if I can understand how the bolt moves back faster than the carrier when the SCAR is suppressed. My understanding is the gas through the aperture hits the piston which in turn hits the carrier kicking it back. The bolt is attached to the carrier and the carrier pulls the bolt back. How can the bolt travel faster than the carrier? Also when the bolt is forward it is locked so it can’t rotate until the carrier pulls it back out of the locking grooves. That cam pin in the bolt has no rotational force applied to it as long as the bolt is all the way forward when the trigger is pulled. The only way the bolt can rotate and cause the cam pin to fracture the carrier is if the bolt failed to go all the way forward when the trigger was pulled. Am I correct? So how can a suppressor cause this fault?
 

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Ran the OEM stock exclusively. Reduced the aperture on the gas jet using the whistling past a graveyard techniques on this forum. It isn’t the rifle’s fault. It’s operator error. And I accepted the risk when I put a suppressor on the rifle.

I’m electing to not shell out another $600 so that I can lose a few decibels on a loud rifle.
The bolt moving faster than the bolt carrier is what caused the BC to fail.
The back pressure from the suppressor caused the bolt to move faster than the BC. Maybe another can has a more compatible pressure, but I don’t have the money to try another can, or buy another BC and rail. And, again, we’re talking about a small percentage change in the noise level.

I also would rather shoot a loud rifle than store a quiet one in a safe.

What can were you using? I apologize if I missed it but I didn't catch it in your posts.
 

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I'm just thinking aloud here, and I'm just guessing - plz don't take this as gospel or even intelligent - just curious and wish to carry on with this whole scenario....I see BOTH bolt carriers cracked in the exact same place and same manner. By just looking at the pics, the scenario of what Viking187 says - the bolt moving faster than the carrier looks logical. But as Mike Canter describes, it seems like an impossibility for the bolt to move without the bolt carrier being tapped back by the piston first. I think we can all agree to that. The only way for the bolt to move before the carrier is in a split millisecond the mere pressure from the bullet igniting and the additional back pressure from the suppressor could cause the actual bolt to begin it's rearward motion without the assistance of the carrier. I just don't know if that's possible, and I'm kind of doubting it. In my opinion - and Lord knows I'm guessing here - I'm out of my league on this subject and have been wrong before - I just look at the pictures, and notice it's the thinnest part of the carrier where it broke, and where the cam pin rotates at. I think it's simply the additional force of shooting suppressed breaking the carrier at it's most logical and weakest point of it.

I don't know what kind of steel the carrier is made of. The SCAR 16 was made first if I'm not mistaken, and doesn't seem to suffer from any of the things the 17 does - like being hard on optics, canting receiver screws with aluminum butt stocks, or destroying electronics. This will not be a popular thing to say, and again, I could certainly be wrong about this - I'm forming a pretty uneducated opinion - but it seems the rifle's design on the 17 is being pushed to it's limits on the 7.62 x .51 caliber. I think it can handle it, but is just beginning to reach it's outer limits. I have always wished it had a little beefier way to retain the back plate than those tiny screws/fasteners that have but like 3 revolutions of turning into the receiver and inner rail. I would think a little more length and diameter would help. I think designing it with as many compatible parts as possible plays a role in why it's designed the way it is. These are the first pics I've seen of damaged carriers, so it's hard for me to call into question of what kind of steel the carrier is made of, but a little harder steel coupled with a beefier fastening technique for the 17 would be my preference. I'd love to see a gen 2 of the SCAR 17 - but I don't see it coming.

I'm sure my opinion may be open to flames, and I'm fine with that - as I'm not rock solid on it - just thinking aloud, and welcome and even hope to be shown a different light. So no offense taken to arguments on this - in fact welcome. These are only two instances of thousands of SCAR 17's being shot that have had a problem. Perhaps there are more we haven't heard about, but either way, the rifle has proven to be very good and reliable. For myself, I'm not shooting suppressed, and have had an excellent track record out of my 17 - so I'm still very happy with the platform, and still think over all, with all things taken into consideration, it's possibly the best battle rifle out out there. It doesn't look like we are ever going to see the APC 308 make it to the American market as I haven't heard much on it, but I suppose that rifle could rival the 17. Either way, that's my current opinion on this whole thing - subject to change with further information and education on the matter. I still feel comfortable having this light weight 308 carbine slung over my shoulder as my outback protection. Like I THINK optics manufacturer's are coming around to making beefier scopes after the introduction of the 17 platform, perhaps companies will begin to take into consideration of trying to alleviate some of the back pressures designed on suppressors. Will companies step up for a single rifle platform ? I just don't know.
 

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I'm just thinking aloud here, and I'm just guessing - plz don't take this as gospel or even intelligent - just curious and wish to carry on with this whole scenario....I see BOTH bolt carriers cracked in the exact same place and same manner. By just looking at the pics, the scenario of what Viking187 says - the bolt moving faster than the carrier looks logical. But as Mike Canter describes, it seems like an impossibility for the bolt to move without the bolt carrier being tapped back by the piston first. I think we can all agree to that. The only way for the bolt to move before the carrier is in a split millisecond the mere pressure from the bullet igniting and the additional back pressure from the suppressor could cause the actual bolt to begin it's rearward motion without the assistance of the carrier. I just don't know if that's possible, and I'm kind of doubting it. In my opinion - and Lord knows I'm guessing here - I'm out of my league on this subject and have been wrong before - I just look at the pictures, and notice it's the thinnest part of the carrier where it broke, and where the cam pin rotates at. I think it's simply the additional force of shooting suppressed breaking the carrier at it's most logical and weakest point of it.

I don't know what kind of steel the carrier is made of. The SCAR 16 was made first if I'm not mistaken, and doesn't seem to suffer from any of the things the 17 does - like being hard on optics, canting receiver screws with aluminum butt stocks, or destroying electronics. This will not be a popular thing to say, and again, I could certainly be wrong about this - I'm forming a pretty uneducated opinion - but it seems the rifle's design on the 17 is being pushed to it's limits on the 7.62 x .51 caliber. I think it can handle it, but is just beginning to reach it's outer limits. I have always wished it had a little beefier way to retain the back plate than those tiny screws/fasteners that have but like 3 revolutions of turning into the receiver and inner rail. I would think a little more length and diameter would help. I think designing it with as many compatible parts as possible plays a role in why it's designed the way it is. These are the first pics I've seen of damaged carriers, so it's hard for me to call into question of what kind of steel the carrier is made of, but a little harder steel coupled with a beefier fastening technique for the 17 would be my preference. I'd love to see a gen 2 of the SCAR 17 - but I don't see it coming.

I'm sure my opinion may be open to flames, and I'm fine with that - as I'm not rock solid on it - just thinking aloud, and welcome and even hope to be shown a different light. So no offense taken to arguments on this - in fact welcome. These are only two instances of thousands of SCAR 17's being shot that have had a problem. Perhaps there are more we haven't heard about, but either way, the rifle has proven to be very good and reliable. For myself, I'm not shooting suppressed, and have had an excellent track record out of my 17 - so I'm still very happy with the platform, and still think over all, with all things taken into consideration, it's possibly the best battle rifle out out there. It doesn't look like we are ever going to see the APC 308 make it to the American market as I haven't heard much on it, but I suppose that rifle could rival the 17. Either way, that's my current opinion on this whole thing - subject to change with further information and education on the matter. I still feel comfortable having this light weight 308 carbine slung over my shoulder as my outback protection. Like I THINK optics manufacturer's are coming around to making beefier scopes after the introduction of the 17 platform, perhaps companies will begin to take into consideration of trying to alleviate some of the back pressures designed on suppressors. Will companies step up for a single rifle platform ? I just don't know.
You aren't the only one thinking this. Frank plumb over at handl defence has done some write ups on the 17.
The 762 was shoehorned into this dude and it could definitely benefit from a second evolution. I'm sure these events are not that common. But I know that when I twist on my can I whisper some sweet nothings to my rifle in Hope that it makes it through. We have learned alot about this system since it came out en mass and hopefully fn will do a revision... or the aftermarket comes through. FN is pretty slow so my money is on the aftermarket. But at the same time there are only a few companies that have tackled the guts of the machine, and maybe two of them have went after the bolt carrier group. And nothing has hit the market to date.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 

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FLet me see if I can understand how the bolt moves back faster than the carrier when the SCAR is suppressed. My understanding is the gas through the aperture hits the piston which in turn hits the carrier kicking it back. The bolt is attached to the carrier and the carrier pulls the bolt back. How can the bolt travel faster than the carrier? Also when the bolt is forward it is locked so it can’t rotate until the carrier pulls it back out of the locking grooves. That cam pin in the bolt has no rotational force applied to it as long as the bolt is all the way forward when the trigger is pulled. The only way the bolt can rotate and cause the cam pin to fracture the carrier is if the bolt failed to go all the way forward when the trigger was pulled. Am I correct? So how can a suppressor cause this fault?
I’m not qualified to talk about the physics, so I’ll edit my post above. If my posts don’t show it, I don’t know much about firearm mechanics, which is another reason for me to stick to stock configurations.
All the posts and videos aren’t going to pay for the repairs to my rifle, so I’ll be shooting it stock from now on.
 

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I didn’t mention the can because it came from an established company with a good reputation. The damage was caused by the nut behind the butt pad, not what was in front of the barrel.
 

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Viking187 I don't think you have any reason to be hard on yourself. As for the mechanics of firearms, I myself have been corrected on here before. We have some pretty knowledgeable people on this forum. It's a good thing too, answers can be found that are hard to come by here. You haven't done anything thousands of others haven't done by shooting your 17 suppressed. Unfortunately, you and TBROWN1911 were the unfortunate ones this has happened to. You were smart enough, and kind enough to take the pics, and share your experience with the fine folks on this forum - you stepped up to the plate with valuable information. The fact you haven't used an aluminum butt stock in the past is good to know. Nah man, you did good !

Infidel/Crusader, I've heard of Frank Plumb, haven't read a whole lot from him, but know he has raised concerns regarding the SCAR 17. I stay away from the whole Handl Defense topic on this forum though, as you probably know, brings out anger and hatred on this forum only seen by men caught cheating on their wives with their best friend lol. And I'll agree I don't think I'm alone in the thought process regarding the effects of recoil on the 17. This has been a good and informative thread.
 

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I didn’t mention the can because it came from an established company with a good reputation. The damage was caused by the nut behind the butt pad, not what was in front of the barrel.
I'm not implying that the can was the culprit. However, it may be valuable to track which cans are potentially causing excessive back pressure in this platform. Then we may be able to identify which ones the Scar 17s likes and which it does not.

I respect that you are insulating the company in which I agree it's not their fault. Though, leaving out this detail doesn't shed the full amount of light on your particular experience. It's a missing variable.


It would be great if knowledgeable ones like Sarge or Jarod would chime if they have some definitive info to add. Sometimes they are met with so much haste I don't blame them for not.

I'd like real answers, I'm a big enough boy to not car from who. :mrgreen:
 

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I hate to keep posting in this thread - but I think I have a viable question and point here. A couple weeks ago, I shot my SCAR 17 in the suppressed setting without it being suppressed, just to see if it would recoil less and still function reliably. I had a fail to feed - that is - it didn't go completely into battery on one of the rounds. I went back to the 12 o'clock position after that, and of course had 100% reliability. My question is, if you tune the gas jets for shooting suppressed, isn't it possible you are messing with the reliability of the rifle when shooting unsuppressed ? I remember watching a vid from Inrangetv where they had malfunctions with the 17 while shooting unsuppressed, and the owner of the rifle had tuned his gas jets for shooting suppressed. They switched the jets back to the OEM configuration, and everything functioned fine. It seems to stand for reason this would be true. I linked the vid onto this post - and it's right at one minute in they have the malfunctions. Then a couple minutes later they explain how the shooter had put in different jets to set it up more for suppressed shooting. And when they went back to the OEM jets, the rifle shot just fine.

 

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Some have reported using different gas control screws with success. Most have reported that the 1.35mm gas screw in the 17s (with the 16" barrel) strikes a balance of reliability between shooting suppressed and unsuppressed.

All while reducing the recoil and beating on the rifle.

I'm fixing to order a 1.35mm for my 17s and a 1.8mm for my 16s sbr. Just waiting for PPM to get a few other items back in stock. Wink Wink Nod Nod. :-D
 

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If you read my previous post explaining how the SCAR gas system works I think you will see that is not causing the damage to the carrier BUT it doesn’t hurt to match the gas jet to your application.
 

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In any proper failure analysis, it is prudent to identify variables.

This is the best way to isolate variables that impact the function, and possibly there are many variables that 'stack' to induce a result.

(This is why I cannot TOLERATE to watch many of the YouTube "tests" that are conducted & uploaded!)

Here are SOME of the many variables I see at first glance:

EXTERNAL:
Cartridge powder and weight
Bullet weight
Environment temperature & direct sunshine on cartridges & weapon
Weapon temperature
Weapon Lubrication
Shooting supported / unsupported
- Bipod
- Stance & style


INTERNAL:
Round count on weapon
Weapon completely OEM
- Shoulder stock
- Trigger assembly (aluminum/plastic)
- Trigger
- Buffer spring
- Buffer Spring recoil pad
- Charging handle
- Aftermarket receiver screws
- Gas setting
- Gas jet size
- Magazine size & how many rounds in mag
- Muzzle device
- Additional handguard/rails
- Forward Grip
- Flashlight mounted
- Optic(s)
- Suppressor use


Many of these variables affect the gross weight of the weapon, this may allow the weapon to work easier or harder, accounting for the overall mass of the weapon when the firing impulse is absorbed or transmitted.

Too many people will point to their favorite poo-poo target or variable and say "THIS IS WHAT IS WRONG!!" - without addressing, eliminating or accounting for ALL the factors that may contribute or detract from the result.



Another issue that may have been discussed is the time after cartridge ignition and the bullet passing the muzzle.

Excessive Back Pressure.

WITH A SUPPRESSOR There is increased pressure IN the barrel when the bolt carrier goes to the rear, unlocking the bolt.

This higher pressure in the barrel PROPELS the bolt rearward faster than the bolt carrier dragging the bolt rearward.

The end of the rearward cycle movement of the bolt carrier group results in an increased hammer effect because the bolt is still moving with increased inertia. (rather than the inertia of being pulled rearward)

This hammer impact and rotation of the bolt within the bolt carrier forces the carrier key UP, putting torsion and torque on the screws which manifests as canted screws.


So ONLY addressing the gas jet size means that the bolt carrier is moving with less rearward force, but the bolt may STILL be propelled rearward, and the ensuing hammer effect collision be the result.


Hence FNH's warning about NOT using their suppressor which may vent the barrel of back pressure better than quieter, but, higher back pressure suppressors.

Just some thoughts. (I am not going to shoot my SCAR-17 suppressed!) :evil:

~Will
 
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After re-reading through some of the older posts here and on AR15 dot com, and I believe there is something to Handl Defense's approach to gas port tuning by going LARGER than the 1.5mm (1.64mm & 1.7mm). As it would SEEM that a larger port would allow excessive pressure to BLOW-BY the piston and reduce the back pressure IN the barrel.
 

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Discussion Starter #35
After re-reading through some of the older posts here and on AR15 dot com, and I believe there is something to Handl Defense's approach to gas port tuning by going LARGER than the 1.5mm (1.64mm & 1.7mm). As it would SEEM that a larger port would allow excessive pressure to BLOW-BY the piston and reduce the back pressure IN the barrel.
I would be interested to see a side by side comparison of the recoil impulse with different sized jets. Does anyone on here run the larger sized jets that HANDL recommends?
 

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Handl Defense Gas Jet "Tuning Kit"...I purchased HD"s "Tuning Kit" several months ago when there were 3 jets included in the kit; a 1.64, a 1.70 & a 2.30. Since that time the kit has been reduced to just the 1.64 & the 1.70.

I havent tried any of them yet, figuring that the larger the orifrice opening, the MORE gas is released to accuate the piston. Maybe in the 10 o'clock suppressed position, this is not the case. Handl Defense doesn't have an explanation on how their tuning kit is to be used.

No matter what, Uncle Sucker has chosen the Surefire SOCOM RC-2 suppressor for use on the SCAR's, so surely SCAR's being used in the field to kill the Evil Doers aren't having their BCG's self destructing because they're being used with a suppressor...
 

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So, unsuppressed rental guns converted to full auto can run 200,000 rounds over 5 years.

Add a suppressor and aftermarket stock and it will crap out in 5,000 rounds?

Something wasn't kosher there, glad you got taken care of by FNH.

I'm about to break my rear screws loose and re-torque them and will probably confirm torque regularly from now on and I sure as heck won't be using anything with a metal landing pad for the buttstock. I think I will also start replacing my recoil spring every 5,000rds just like I do with my ARs and M1As.

Does anyone have an ejection pattern chart for the Mk17? It would be nice to have instant visual reference on whether my rifle was over/under gassed or over/under sprung while shooting.
 

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I’m not qualified to talk about the physics, so I’ll edit my post above. If my posts don’t show it, I don’t know much about firearm mechanics, which is another reason for me to stick to stock configurations.
All the posts and videos aren’t going to pay for the repairs to my rifle, so I’ll be shooting it stock from now on.
FLet me see if I can understand how the bolt moves back faster than the carrier when the SCAR is suppressed. My understanding is the gas through the aperture hits the piston which in turn hits the carrier kicking it back. The bolt is attached to the carrier and the carrier pulls the bolt back. How can the bolt travel faster than the carrier? Also when the bolt is forward it is locked so it can’t rotate until the carrier pulls it back out of the locking grooves. That cam pin in the bolt has no rotational force applied to it as long as the bolt is all the way forward when the trigger is pulled. The only way the bolt can rotate and cause the cam pin to fracture the carrier is if the bolt failed to go all the way forward when the trigger was pulled. Am I correct? So how can a suppressor cause this fault?
Handl Defense Gas Jet "Tuning Kit"...I purchased HD"s "Tuning Kit" several months ago when there were 3 jets included in the kit; a 1.64, a 1.70 & a 2.30. Since that time the kit has been reduced to just the 1.64 & the 1.70.

I havent tried any of them yet, figuring that the larger the orifrice opening, the MORE gas is released to accuate the piston. Maybe in the 10 o'clock suppressed position, this is not the case. Handl Defense doesn't have an explanation on how their tuning kit is to be used.

No matter what, Uncle Sucker has chosen the Surefire SOCOM RC-2 suppressor for use on the SCAR's, so surely SCAR's being used in the field to kill the Evil Doers aren't having their BCG's self destructing because they're being used with a suppressor...
I thought I had read somewhere that for a SCAR suppressor that FNH recommends a gas overpressure hole be drilled in the suppressor in the first expansion chamber? It may have been anecdotal for previous cans though.
 

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So, unsuppressed rental guns converted to full auto can run 200,000 rounds over 5 years.

Add a suppressor and aftermarket stock and it will crap out in 5,000 rounds?

Something wasn't kosher there, glad you got taken care of by FNH.

I'm about to break my rear screws loose and re-torque them and will probably confirm torque regularly from now on and I sure as heck won't be using anything with a metal landing pad for the buttstock. I think I will also start replacing my recoil spring every 5,000rds just like I do with my ARs and M1As.

Does anyone have an ejection pattern chart for the Mk17? It would be nice to have instant visual reference on whether my rifle was over/under gassed or over/under sprung while shooting.
I wonder if the SCAR-20 has a metal plate where the hinge plate would be on the -17? Or is that piece plastic like on the -17?
 

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I wonder if the SCAR-20 has a metal plate where the hinge plate would be on the -17? Or is that piece plastic like on the -17?
That's a very good question. I also wonder in the SCAR-20 is possibly softer gassed than the SCAR 17 since it's a precision rifle. The outer part that slide over the "ears" of the rear receiver plate looks like anodized aluminum in the pics I've seen.
 
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