FN SCAR issues

[Slater]

Could it be said that the SCAR-H is a more reliable and durable weapon than the G3?

[WickedWillis]

While yes I was quite aggressive in supporting HD. There were several reasons.

#1 much of the complaints about the HD product (while early were limited but real) were driven by those who stole the designs.

#2 the positive that came out of the company, was all my work. New designs, push for CMM, CAD, and other in house production, QA/QI efforts, testing and evaluating, raising investor capital, the stuff sold to SOCOM, the blog posting, the push into the Senate and House Defense committees, Recoil articles, getting NGSW, CCLTF, and other projects off the ground.

The Patents that bracket FN from developing their own gun without me. I solved the harmonics, suppression, bolt cam path way, back plate side screws, and a myriad of other issues. I made every single part of the gun in house at one time. With absolutely no support of any type from FN. Even got the USASFC G8 to stop from cancelling their support of the program in 2016 by flying to Bragg and showing the target engagement committee guys the 6.5 and 260R kits (before 6.5 was really a thing) and the 7.62x39 system.

All my work. (while having a second full time job, a family, and at one time an ODA CDR of a NG SF tm as well)

#3 Because I was so deep in I was blind to the fact that those closest to you are the ones that can do the most damage.

Wow that is a ton bud.

Sounds like your heart was really into this 100%. I'm sorry that something went south. Does this close any door going forward of another company being THE aftermarket SCAR go to?

[Combat_Diver]

I've been a SOCOM armorer down range in Afghanistan/Iraq since Oct 14'-present (1 yr off). My primary customers have been SEALs and SF. During this years never really had to work on many Mk17s as they just work. I've replaced the following

2 bent bolt handles
1 folding stock thumb latch
1 barrel (shot out)

Now I haven't seen every single gun that is brought into theater but the Mk17 SCAR just runs. Issued optic is the ELCAN 1x6 power. The Elcan 1x4 is for the URG/URGIs. Borrowed one of the 18Bs SCARs and put 4 cases of M118LR thru the gun in a month. No issues in semi or auto. Back in 16' in Iraq with the SEALs, never fixed a single SCAR of theirs.

IMG_1259 (1).jpg


CD

[Fox33]

To all... Got a bit distracted there by the business aspects.. Rhino... BTW the COI is why I retired early...

So as to my underlying perspective on the SCAR 17S and Mk17. (as they are different)

#1 the Mk.17 which has a few elements that are different (636gram BCG vs 600 for the 17S) and other tiny things. That as that as much as NSWC Crane is maligned, they do their job. The new CAR-H accessories approved for use on the Mk.17 are just fine. New cans and other items that are within the inventory and the companies that build them are acutely aware of the energy profile. The 8's, FN, and others are doing their jobs. I really don't have much to add to the Mk.17 at this point that wouldn't be COTS accessory, other than recoil energy suppression technology.

When I started down this path, that work had not been done. The gun had been in the inventory for about 3 years and the mk.16 was still issued. Stocks, magazines, optics, NV, thermals, triggers, and suppressors were all issues on the Mk.17. I do not see that as the case anymore.

Everything issued for the Mk.17 has been though the ringer and tested to work on the gun.

#2 The commercial market version is a different story.

I see one major problem one, midsized one

The biggest issue for commercial market SCARs is suppression. Something from an article I wrote.

"Suppressors stifle weapon signature such as flash, noise, and pressure. They do this by managing the gas expended by the cartridge once it has finished propelling the projectile down the barrel. This means we must understand gasses to understand how suppressors work. Once we understand how gasses work, then we can understand how SCARs are particularly affected by suppressors. Then we can decide what options are ideal.
To understand gasses in a general sense we need to understand three laws. First is Boyle’s law which is at a constant temperature relationship between the pressure and volume of a gas is proportional. Simply, if you add twice the gas you add twice the pressure. Second is Charles’ law that states at constant pressure, the volume of gas increases or decreases by the same factor as its temperature. When gas gets hot, it expands. Third, Lussac's Law is pressure of a volume of a gas is directly proportional to the gas's temperature. The hotter a gas gets the more pressure it exerts. So you can see that amount of gas, the pressure it exerts, and the heat are the three primary issues facing suppression.
The SCAR platform is extremely suppressor sensitive. Other systems are as well, such as the H&K G28/417/MR762 series of rifles. AR variants have very large and robust buffer systems. While the HK MR762 with a certain suppressor exceeded the G rating on our accelerometer, there was little discernable from the shooters perspective. This is due to the fact the HK MR762 buffer system is massive and the MR 762 is probably milled from the armor of Tiger tanks hidden in a bunker under Obendorf, Germany.
The SCAR on the other hand has a relatively small volume short stoke gas piston system. Remember Boyle’ law, more gas means equal increases in pressure. Then remember Charles’ law volume of gas increases under heat. Suppressors add both to a SCAR’s gas piston system in spades. This is a big deal. Remember when I said I could break a SCAR on demand. While I won’t give all the details, it involves a suppressor, and here is what happens.
When you put a non-optimal suppressor on a SCAR you can get bolt speed increases as high as an extra 50%. When viewed from a velocity squared times ½ mass perspective, that is huge. That is an immense amount of extra load on the operating system. With the bolt moving up to as much as 50% faster, you can easily exceed the design loads of the system.
I first noticed this when I was issued a Mk.17. We had just finished a combat rifle marksmanship course. I used my Mk.17 with a 13” barrel and a Suppressor. I noticed that the gun was running somewhat sluggish. It seemed to unlock from battery a bit slower and rougher than normal. What I also noticed is that I left the gun in an unsuppressed setting on the gas block. I had put unnecessary stress on the operating system by my own negligence. What I found is that I had made a burr at the very front of the inside of bolt cam pathway on the bolt carrier group. This was causing drag on the bolt and bolt cam pin during function. Some sanding and polishing during cleaning, I never had the problem again.
This event has always stuck with me. I remembered that this burr was where the thinnest part of the bolt carrier group is located. There has been a few commercial SCAR 17 bolt carrier groups splitting in this same location. This is not an indictment of the system. It is an indictment of what the user puts on the SCAR.
Let me explain how this is happening. The rifle is fired, the projectile passes the gas jet, gas begins to fill gas block, the suppressor also begins to fill. Due to the suppressor not being optimally designed for the SCAR, the gas in the barrel begins to back up on itself. Sometimes the gas is so backed up it is visible coming from the cartridge ejection port as the weapon operates.
The gas in the barrel moves to the path of least resistance, into the gas system. Remember Boyle’s law, more gas equals more pressure. The gas systems work faster, harder and hotter than intended from the pressure. It pushes the bolt carrier group back much faster and harder than intended. The bolt, which is still locked into the chamber, provides for a sturdy support for the bolt cam. The bolt carrier’s accelerated rearward travel causes the thinnest part of the bolt carrier group, the bolt cam pathway, to slam into the high strength and well supported bolt cam. Instead of a smooth unlocking action, the action is more of a ripping the bolt from the chamber. The energy is moving to the path of least resistance.
Under enough load this might cause damage or in some cases failure of the bolt carrier group in and around the bolt cam pathway. Imagine not using the clutch in a car to change gears. It is the poorly integrated suppressor that causes the load to exceed the engineering of the system. Like I said velocity squared is the important part of the equation. This is a repeatable event under the right conditions with a particular set of items used with the SCAR.
FN designed the gun to work with certain parts, their parts. As a manufacturer I understand this perspective. Once a gun gets to its owner there is no way to control what they are going to do to it. Switching out gas jets to meet the gas flow of the suppressor is one option to the solution. This relies on a competent gunsmith. Also, it only deals with the filling of the gas system issue. It does not relieve all the extra bolt speed and over pressure issues I’ve discussed. If you add heavy use or full auto fire into the equation, Boyle’s law becomes exceedingly relevant. Your results will vary, user beware. "

[Fox33]

The other issue is with optics not properly hardened.

from another article

"Just under that Aluminum continuous top rail is a 1.3 lb hardened steel bolt carrier group running back and forth. There is a lot of energy running right under that rail. Energy being transmitted by a stronger and much denser material than the receiver is made of. Which leads to the second part of the discussion, Constructive interference.
Energy transmitted into metals are transmitted into other materials in direct contact. A metal, even the 7000 series type the SCAR receiver is made out of, is acted on by the steel bolt carrier it begins to absorb this energy and dissipate it resulting in vibrations. The vibrations can compound on each other and even amplify each other. This is added vibration is called constructive interference. The metals if “weaker” than the one transmitting energy, they will have little ability to dissipate that energy. This means if the bolt carrier group is steel, the receiver is a 7000 series aluminum, and the scope mount is 6000, that energy is getting transmitted to the body of your optics. This compounding energy transfer is why NSWC Crane had to harden many of the scopes and optics used by USSSOCOM for use with the Mk.17"

[call_me_ski]

I was always under the impression that the SCAR receiver was 6000 series Al. Is the above article correct and the receiver is 7000 series?

[RHINOWSO]

I've been a SOCOM armorer down range in Afghanistan/Iraq since Oct 14'-present (1 yr off). My primary customers have been SEALs and SF. During this years never really had to work on many Mk17s as they just work. I've replaced the following

2 bent bolt handles
1 folding stock thumb latch
1 barrel (shot out)

Now I haven't seen every single gun that is brought into theater but the Mk17 SCAR just runs. Issued optic is the ELCAN 1x6 power. The Elcan 1x4 is for the URG/URGIs. Borrowed one of the 18Bs SCARs and put 4 cases of M118LR thru the gun in a month. No issues in semi or auto. Back in 16' in Iraq with the SEALs, never fixed a single SCAR of theirs.

IMG_1259 (1).jpg


CD

Thanks for the real world, user feedback. Cheers.

[WickedWillis]

To all... Got a bit distracted there by the business aspects.. Rhino... BTW the COI is why I retired early...

So as to my underlying perspective on the SCAR 17S and Mk17. (as they are different)

#1 the Mk.17 which has a few elements that are different (636gram BCG vs 600 for the 17S) and other tiny things. That as that as much as NSWC Crane is maligned, they do their job. The new CAR-H accessories approved for use on the Mk.17 are just fine. New cans and other items that are within the inventory and the companies that build them are acutely aware of the energy profile. The 8's, FN, and others are doing their jobs. I really don't have much to add to the Mk.17 at this point that wouldn't be COTS accessory, other than recoil energy suppression technology.

When I started down this path, that work had not been done. The gun had been in the inventory for about 3 years and the mk.16 was still issued. Stocks, magazines, optics, NV, thermals, triggers, and suppressors were all issues on the Mk.17. I do not see that as the case anymore.

Everything issued for the Mk.17 has been though the ringer and tested to work on the gun.

#2 The commercial market version is a different story.

I see one major problem one, midsized one

The biggest issue for commercial market SCARs is suppression. Something from an article I wrote.

"Suppressors stifle weapon signature such as flash, noise, and pressure. They do this by managing the gas expended by the cartridge once it has finished propelling the projectile down the barrel. This means we must understand gasses to understand how suppressors work. Once we understand how gasses work, then we can understand how SCARs are particularly affected by suppressors. Then we can decide what options are ideal.
To understand gasses in a general sense we need to understand three laws. First is Boyle’s law which is at a constant temperature relationship between the pressure and volume of a gas is proportional. Simply, if you add twice the gas you add twice the pressure. Second is Charles’ law that states at constant pressure, the volume of gas increases or decreases by the same factor as its temperature. When gas gets hot, it expands. Third, Lussac's Law is pressure of a volume of a gas is directly proportional to the gas's temperature. The hotter a gas gets the more pressure it exerts. So you can see that amount of gas, the pressure it exerts, and the heat are the three primary issues facing suppression.
The SCAR platform is extremely suppressor sensitive. Other systems are as well, such as the H&K G28/417/MR762 series of rifles. AR variants have very large and robust buffer systems. While the HK MR762 with a certain suppressor exceeded the G rating on our accelerometer, there was little discernable from the shooters perspective. This is due to the fact the HK MR762 buffer system is massive and the MR 762 is probably milled from the armor of Tiger tanks hidden in a bunker under Obendorf, Germany.
The SCAR on the other hand has a relatively small volume short stoke gas piston system. Remember Boyle’ law, more gas means equal increases in pressure. Then remember Charles’ law volume of gas increases under heat. Suppressors add both to a SCAR’s gas piston system in spades. This is a big deal. Remember when I said I could break a SCAR on demand. While I won’t give all the details, it involves a suppressor, and here is what happens.
When you put a non-optimal suppressor on a SCAR you can get bolt speed increases as high as an extra 50%. When viewed from a velocity squared times ½ mass perspective, that is huge. That is an immense amount of extra load on the operating system. With the bolt moving up to as much as 50% faster, you can easily exceed the design loads of the system.
I first noticed this when I was issued a Mk.17. We had just finished a combat rifle marksmanship course. I used my Mk.17 with a 13” barrel and a Suppressor. I noticed that the gun was running somewhat sluggish. It seemed to unlock from battery a bit slower and rougher than normal. What I also noticed is that I left the gun in an unsuppressed setting on the gas block. I had put unnecessary stress on the operating system by my own negligence. What I found is that I had made a burr at the very front of the inside of bolt cam pathway on the bolt carrier group. This was causing drag on the bolt and bolt cam pin during function. Some sanding and polishing during cleaning, I never had the problem again.
This event has always stuck with me. I remembered that this burr was where the thinnest part of the bolt carrier group is located. There has been a few commercial SCAR 17 bolt carrier groups splitting in this same location. This is not an indictment of the system. It is an indictment of what the user puts on the SCAR.
Let me explain how this is happening. The rifle is fired, the projectile passes the gas jet, gas begins to fill gas block, the suppressor also begins to fill. Due to the suppressor not being optimally designed for the SCAR, the gas in the barrel begins to back up on itself. Sometimes the gas is so backed up it is visible coming from the cartridge ejection port as the weapon operates.
The gas in the barrel moves to the path of least resistance, into the gas system. Remember Boyle’s law, more gas equals more pressure. The gas systems work faster, harder and hotter than intended from the pressure. It pushes the bolt carrier group back much faster and harder than intended. The bolt, which is still locked into the chamber, provides for a sturdy support for the bolt cam. The bolt carrier’s accelerated rearward travel causes the thinnest part of the bolt carrier group, the bolt cam pathway, to slam into the high strength and well supported bolt cam. Instead of a smooth unlocking action, the action is more of a ripping the bolt from the chamber. The energy is moving to the path of least resistance.
Under enough load this might cause damage or in some cases failure of the bolt carrier group in and around the bolt cam pathway. Imagine not using the clutch in a car to change gears. It is the poorly integrated suppressor that causes the load to exceed the engineering of the system. Like I said velocity squared is the important part of the equation. This is a repeatable event under the right conditions with a particular set of items used with the SCAR.
FN designed the gun to work with certain parts, their parts. As a manufacturer I understand this perspective. Once a gun gets to its owner there is no way to control what they are going to do to it. Switching out gas jets to meet the gas flow of the suppressor is one option to the solution. This relies on a competent gunsmith. Also, it only deals with the filling of the gas system issue. It does not relieve all the extra bolt speed and over pressure issues I’ve discussed. If you add heavy use or full auto fire into the equation, Boyle’s law becomes exceedingly relevant. Your results will vary, user beware. "

The other issue is with optics not properly hardened.

from another article

"Just under that Aluminum continuous top rail is a 1.3 lb hardened steel bolt carrier group running back and forth. There is a lot of energy running right under that rail. Energy being transmitted by a stronger and much denser material than the receiver is made of. Which leads to the second part of the discussion, Constructive interference.
Energy transmitted into metals are transmitted into other materials in direct contact. A metal, even the 7000 series type the SCAR receiver is made out of, is acted on by the steel bolt carrier it begins to absorb this energy and dissipate it resulting in vibrations. The vibrations can compound on each other and even amplify each other. This is added vibration is called constructive interference. The metals if “weaker” than the one transmitting energy, they will have little ability to dissipate that energy. This means if the bolt carrier group is steel, the receiver is a 7000 series aluminum, and the scope mount is 6000, that energy is getting transmitted to the body of your optics. This compounding energy transfer is why NSWC Crane had to harden many of the scopes and optics used by USSSOCOM for use with the Mk.17"

Thanks for all this awesome information Fox.

[Fox33]

I was always under the impression that the SCAR receiver was 6000 series Al. Is the above article correct and the receiver is 7000 series?

It is actually a euro specific blend. Now FN will listen to me, but does not tell me much. This is what I was told by someone from the mothership. A euro blend close to US 7000 series in property. ( I do not know the exact EU spec)

Based on the MPA numbers I've been able to guess. Knowing 7075 does not extrude easily but this blend is formulated to extrude well. My guess is the SCAR upper comes in north of 300 MPA. Which would be close to most 7000 series. I also think materials have changed since 2012. (I know the polymer is different).

To be honest I'm a medic by trade and do not have the background in metallurgy to discuss the finer points. But I'll stand by what I was told and who told me.

[Artos]

Tagged for later...recently shortened my barrel a hair & added a new trigger & adaptor for the can. Has been shot very little since but ran flawless & obviously need to put more lead down range.

Thanks gents.