Scar 17s

[Eblade2004]

I love my scar 17s, I doubt I'll ever shoot it enough to replicate the problems these tests are producing. 308 ammo is just too expensive these days. It's nice to be informed if there are issues but there's plenty of proven battle rifles that still have quirks that'll never get ironed out, nothing's perfect. If I got to run out of my house someday with one gun it's going to be my scar. It's lighter than any of my other semi 308s and packs a more effective round than my ar15s. At this point in time I consider it to be my best all around option as a potential battle rifle.

 

[swamp2]

I have zero prejudice against the SCAR. To the contrary, I had genuine high hopes for it. When I first saw a SCAR-H bolt, the first thing that came to mind was, "That is way small for a 7.62 NATO bolt." It was no surprise when I learned that they were having fatigue issues with it, at least back in 2010. I didn't know about the SCAR-L catastrophic failures at that time, and only learned of them last week from a guy who participated in their introduction to one of the units within USASOC.

I just learned of the optics-destroying features in March from two independent persons, both with resumes that you can take to the bank, but don't take my word for it.

Here's a link from FN Forums barely addressing the issue and ridiculing it, but I heard about it from no less than 2 people within USASOC, and one in the PMC community, all of whom have used the SCAR-L and -H extensively. These quotes are ones I just pulled with a simple google search, and it the first time I have seen anything of this online outside of SH, because the word of those I heard it from face-to-face was good enough for me. In certain circles, that type of trust still exists.

Nothing wrong with good old face to face communication from trusted sources. However, this does not conflict with the fact that most NON ENGINEERS/NON SCIENTISTS, especially in the firearm domain most often have very heavy biases. Heck engineers can too, but I was referrring more to the actual engineers working on firearms systems. Anecdotal evidence is not really evidence from my perspective. A detailed look at statistical failure rates and/or a detailed engineering analysis approach is required to truly understand the failure of such engineered systems.

Let's use just a bit of this approach to analyze the claim below (I realize it is not your claim/quote but a one you seem to bank on):

1st quote:
"The mass of he SCAR bolt has long been a point of discussion within the community. I have repeatedly talked to FN and Crane folks about this in that this is a well known contributor to the recorded high abrupt peaks in recoil impulse that have contributed to ancillary item breakage from SOPMOD Block II MDNS suite. Conversely, the AR series bolt assembly has a much more manageable bolt mass in the system that gives the residual benefit of a) manageable recoil/controllability in rapid shot sequences and b) more receptive/consistent recoil impulse for ancillary items."

I would say that from an overall plausability/engineering point of view this is rubbish. However, conveniently enough, there is also some data to support that point of view. Have a look at the following:

Please tell me which is the measured recoil profile of a SCAR 16s and which is from the Colt AR-15? Here I am assuming that all of the "terrible bolt problems" with the SCAR-H will also exists in the SCAR-L because the designs are incredibly similar, especially with regards to the bolt, bolt carrier design (its slow and massive compared to the AR-15) and cyclic rates.

Are the peak fore or aft acceleration values significantly different among the two platforms? The answer is a resounding NO. So hmmm, what is actually breaking the optics? Some hocus pocus mystery resonances with faster G's....

By the way the images are courtesy of user Hootiewho over at mcarbine.net in this post: SCAR vs AR; A detailed look... - M4Carbine.net Forums . Great reading for a more technical/engineering approach to a SCAR vs. AR comparison.

By the way the first plot is the Colt 6933 and the second is the SCAR 16s.

Yup. It was speculative on my part, but not a statement. A statement would look like this:

Wow talk about back pedaling and semantics... I firmly stand by my prior claim that a civilian SCAR price has absolutely ZERO ZIP ZLICH to do with keeping them out of crime reports.

The information I have received comes from men I would trust my life with. That is good enough for me.

When this topic came up in another thread, one of the guys in USASOC who actually tested SCARs popped in and backed what I had heard about the optics issue, and I don't know him from Adam. He even posted a pic with him in a HALO rig with the SCAR-L rigged for jumping exposed (not in weapons cases like I'm used to for static-line jumps), and said there were legitimate problems with the system.

Again, anecdote, anecdote, anecdote.

Until I see DATA proving otherwise I won't accept the claim that SCARs "eat optics".

 

[LRRPF52]

Nothing wrong with good old face to face communication from trusted sources. However, this does not conflict with the fact that most NON ENGINEERS/NON SCIENTISTS, especially in the firearm domain most often have very heavy biases. Heck engineers can too, but I was referrring more to the actual engineers working on firearms systems. Anecdotal evidence is not really evidence from my perspective. A detailed look at statistical failure rates and/or a detailed engineering analysis approach is required to truly understand the failure of such engineered systems.

The Importance and Relevance of Engineering
I agree 100%. I grew up the son of an uber-engineer who worked on some of the most advanced aerospace systems in DOD. This guy would come home from running detailed and extensive test procedures at one of the CTF's at the Air Force Flight Test Center, Germany, (and other bases) and get into what he really loves with his own research in physics. One of my uncles was a nuclear engineer, and my grandfather was a machinist for Douglas Aerospace, so my childhood, while I thought it was perfectly normal, was anything but.

I self-rate somewhere between a nuckle-dragger and an engineer, and am mostly comfortable in engineering discussions, whether we're talking statistical and elemental analyses, or fundamental aspects of applied physics. I'm not formally-trained, but was raised on an engineering/physics vocabulary during my formative years in a home education environment, in addition to a combination of military, private, and public elementary education. Shooting sessions with my dad involved discussions in physics, while visiting grandpa meant measuring cases with calipers, micrometers, and getting more of his copies of American Rifleman.

Failure Rate
So yeah, I agree that anecdotal evidence is just that. However, when an entire Platoon or Company of Rangers breaks 100% of their optics within a 1 week range package with the SCAR, that tells anyone from the janitor to Einstein that we have a problem.

Taking a Platoon of 42 guys, and all 42 sets of optics broke, when this didn't ever happen anywhere near that failure rate before with the M4A1, I think we can skip the large population, long-term T&E schedule and go back the pre-production RDT&E guns and apply some instrumentation to diagnose what exactly is causing this.

I suspect the knuckle-draggers didn't conjure up the harmonic bolt impact phenomenon theory terminology by looking it up in the rifle manual, and the claims that Eotech and Elcan had to re-engineer their systems to compensate for the unusually high-rate of failure with one particular weapon system do coincide with new models from both companies, namely the XPS and SpecterDR.

End-User Perspective
You have to keep in mind that the sources of these claims are units where untold millions of rounds are burned through M4A1's and other self-loaders on a shoot schedule that was never meant to be digested by the AR15 family of weapons, yet it has performed beyond exceptionally well since the early 1960's in these small communities. During a CQM, SFAUCC, SOT, or whatever the unit calls its high volume individual marksmanship regimens, it's common to burn at least 500 rounds through an M4A1 per day per shooter, often more. I've participated in sessions that have reached 1100rds of 5.56 through my M4 in a 4hr period, and didn't think much of it at the time because everything worked as I expected, and the gun had been beat-up for years.

Now imagine an entire operational element of no less than 42 shooters, running their CQM package like that with a new toy, and 100% of the optics fail. The only factor that changed in our equation is that you removed the M4A1, and substituted it with the SCAR. From a scientific standpoint, there is clearly merit to looking into the source of the problem more. And that's just one Platoon. If I understand correctly, the entire Company had these issues, which would take the number up to well over 100.

Time/g Graphs
As to the graphs that you posted from Hootiewho's analysis on M4carbine.net, those are a time & g-force graph of the cycle of operation comparison of a Colt Model 6933, which is an 11.5" CLGS carbine, and a 16" SCAR. Before you indicated, I did guess that the top graph was for the AR15, and the bottom for the SCAR. Can you guess why I guessed that?

I looked at the "g" values of both, and saw that one of them exceeded +40g and -60g during the bolt closure time window, while the other did not. You'll notice that even the typically-violent 11.5" Carbine, with its much faster cyclic rate, still did not exceed the +40g/-60g threshold. And which firearm DID exceed those limits when the bolt closed? That would be the SCAR-16.

I think in attempting to prove your point, from an engineering standpoint, you added credence to what I have heard, and this is literally the first time I have seen those graphs. While 20g's over the threshold of the more violent 11.5" AR might not seem significantly more to the layman, I can assure you that -20g on top op of an existing -40g's is no joke when it comes to electro-optical aiming systems. To further quantify that we are spiking that g load within .004 seconds, you can see the problem, if you have even a Reader's Digest understanding of materials strengths.

Excellent graphs, as I really haven't seen them before. I also like how he pointed out what I feel is one of the main strong points of the SCAR (cam track geometry), but also could be the contributor to the increased g's on bolt closure. You will notice one flaw in the comparison to the operating parts weights, in that the analysis starts out with weighing the bolt carrier group of the AR15 without the buffer, and the complete reciprocating group of the SCAR, since the SCAR has no buffer. Notice what happens to the weight differences when you add any of the AR15 carbine buffers to the AR15 BCG when compared to the SCAR BCG/PISTON...the H buffer takes you .7 oz heavier than the SCAR's total reciprocating mass, the H2 buffer takes you 1.5oz heavier, and the H3 takes you 2.3oz heavier. He used the H3 in his 11.5" 6933 Colt, as indicated in the graphs.

Most people aren't aware, but the first prototype AR10A had a one-piece BCG/buffer, that slid forward out of the gun when disassembled, as did the upper receiver.
http://i13.photobucket.com/albums/a261/jimbo1227/AR10SMRJan1998Page1.jpg

Some Pertinent History
For some reason, Stoner went to a sectional design that separates the BCG from the buffer. When the AR10 was scaled down to the AR15 around the .222 Remington cartridge, a telescoping buffer assembly was eventually used, called the Edgewater, which was replaced several years later with the current buffer design after the Colt Model 602, when the XM16E1/early Model 603 was introduced. This current buffer design has reciprocating masses within an aluminum buffer body, which segments the rearward and forward recoiling impulses to deal with dwell time and carrier bounce. What that means is that instead of having one large operating part slam back into the breach or extension, the impact is divided between the reduced weight of the carrier and the follow-on impact of the buffer weights.

Contrasting Designs w/ Recoil Mitigation
Another thing that I also would suspect as a culprit to this increased g spike on the SCAR's return stroke impact is that the operating parts travel in the SCAR is significantly longer than the AR15's. This increases the travel time of course, but also allows the mass to gain more momentum during the return stroke in the cycle of operation.

Great Discussion
I'm actually glad we had this discussion, because a lot of clarity has potentially emerged for me. I'm sure the engineers at FN are well-aware of this, and I suspect that the desire to have a common upper receiver for both the SCAR-L and SCAR-H created the excessive travel time of the SCAR-L's operating parts.

 

[swamp2]

LRRPF52: I agree there is some good discussion happening here and I'm glad to participate and continue to keep it civil. It's also great to hear about your background/grounding in science and engineering. That background, formal or not, adds a great perspective to the understanding of technical and engineering aspects of such discussions.

when an entire Platoon or Company of Rangers breaks 100% of their optics within a 1 week range package with the SCAR, that tells anyone from the janitor to Einstein that we have a problem.

Taking a Platoon of 42 guys, and all 42 sets of optics broke, when this didn't ever happen anywhere near that failure rate before with the M4A1, I think we can skip the large population, long-term T&E schedule and go back the pre-production RDT&E guns and apply some instrumentation to diagnose what exactly is causing this.
...
Now imagine an entire operational element of no less than 42 shooters, running their CQM package like that with a new toy, and 100% of the optics fail. The only factor that changed in our equation is that you removed the M4A1, and substituted it with the SCAR. From a scientific standpoint, there is clearly merit to looking into the source of the problem more. And that's just one Platoon. If I understand correctly, the entire Company had these issues, which would take the number up to well over 100.

So did this actually occur? Did we have an entire Platoon/Company make a change, WITH ALL other potential variables held fixed (key question along that line is did they also get a new batch of optics along with the switch to the SCAR). And of course is this heresay or documented? Could it have been as simple as a bad batch of optics? I'm not saying that is what happened, just that is it more likely that than one 7.62 SA rifle recoiling dramatically harder than another.

the claims that Eotech and Elcan had to re-engineer their systems to compensate for the unusually high-rate of failure with one particular weapon system do coincide with new models from both companies, namely the XPS and SpecterDR.

Again, problems with the rifle or problem with the optics, who knows.

Time/g Graphs
I think in attempting to prove your point, from an engineering standpoint, you added credence to what I have heard, and this is literally the first time I have seen those graphs. While 20g's over the threshold of the more violent 11.5" AR might not seem significantly more to the layman, I can assure you that -20g on top op of an existing -40g's is no joke when it comes to electro-optical aiming systems. To further quantify that we are spiking that g load within .004 seconds, you can see the problem, if you have even a Reader's Digest understanding of materials strengths.

Let's put the differences in perspective here...

The peak backward/forward recoild forces measures are:

-Colt: -53/+40->+50 (positive peak value unfortunately cannot be read with good accuracy perhaps due to a plot marker)
-SCAR: -70/+50

-Difference: 10-17g
-Worst case scenario: 32% increase

This also assumes that the instrumentation and sampling rates were adequate to fully and accurate capture these narrow peak values. A more careful test could definitely reduce the margin.

What do you think the same said failing optic(s) might do on an AR-10, 12 Ga shotgun, .338 Lapua or even heaven forbid a .50 BMG rifle? I will guarantee such a change will represent a lot more than a 32% increase in peak recoil differences. I don't have any good data handy but just from the basic projectile speed and weight one can calculate that the .338 Lapua provides about 10 times the recoil energy of a 5.56x45. Yes 10 TIMES. Thus having a mere 32% safety margin on a rifle optic sounds like as much if not more of a problem than an "outrageously unmanageable" recoil difference from one platform to the next. Could it be that said optics were approved for an AR-15 ONLY and no other weapons from the harder recoiling group above? Could it be that multiple optics fell into this same "sweet spot" of barely having enough margin to work in an AR-15 but in no harder recoiling platform. Last but not least it is worth adding that the clear and consistent report about felt recoil is that the SCAR-H is significantly lighter than other AR-10 or similar platforms. I do not know if the SCAR-L maintains a similar reputation vs. the AR-15.

Another thing that I also would suspect as a culprit to this increased g spike on the SCAR's return stroke impact is that the operating parts travel in the SCAR is significantly longer than the AR15's. This increases the travel time of course, but also allows the mass to gain more momentum during the return stroke in the cycle of operation.

Highly speculative and probably incorrect. This would only be the case if the bolt was accelerating when if fact it is decelerating post ignition and working against recoil spring.

In closing I would like to offer a quotation from one of my all time heroes the astronomer and science advocate Carl Sagan. He said,

"extraordinary claims require extraordinary evidence."

I think that statement is entirely apropos in this discussion and in the examination of this claim.

 

[LRRPF52]

If the M4A1 SOPMOD Block II and Mk11's aren't breaking MDNS (Miniature Day/Night Sight), and the SCAR's are, that's a huge problem. Those are very expensive units.

If you could figure out a design making the SCAR's BCG with a sectional buffer, that would be one approach to possibly fixing the increased chambering and locking G's.

I deal with a lot of snap-shooting from behind cover drills, where natural vertical cover is available. You need minimum exposure, but bore clearance under optic so you don't blast the cover in front of you, even though you have line-of-sight. Weapons like the SCAR and HKG36 make this extremely difficult, let alone having a significant hold over for Close Quarters Marksmanship where shot placement is especially critical, particularly in shoot/no-shoot scenarios, like the one we just are learning about with the officer that placed 7 out of 8 rounds into a suspect, and 1 went into the female hostage.

 

[swamp2]

If the M4A1 SOPMOD Block II and Mk11's aren't breaking MDNS (Miniature Day/Night Sight), and the SCAR's are, that's a huge problem. Those are very expensive units.

Not familiar with the MDNS, is this more rumored failures where the SINGLE change is rifle X for the SCAR-H? I'd love the see the actual evidence if more than rumors. Again, regardless of how trustworthy the person(s) the rumor is sourced from. Trusting a person is not the same as trusting the quality/completeness/scientific accuracy of the information they provide.

If you could figure out a design making the SCAR's BCG with a sectional buffer, that would be one approach to possibly fixing the increased chambering and locking G's.

I think the FNH engineers who work(ed) the SCAR program would strongly disagree that such a "fix" is needed. I've seen nothing to indicate that very marginal optics is not a contributing factor.

 

[LRRPF52]

To familiarize more with the accessories that are being developed, employed, and improved upon for these weapons, read this:

http://www.dtic.mil/ndia/2007smallarms/5_8_07/Gatewood_300PM.pdf

I was in 2 different units that tested Land Warrior systems, which is the trend for the future moving forward. It won't just be an optic and electro-optical aiming devices on small arms, but no less than 3 new types of electronic components will proliferate. These include:

* Digital compass
* Laser range finder
* Miniature Thermal Weapon Sights (TWS's have already been standard with a certain segment of the weapons since 2003.)
* Round counter
* Weapon camera

Whether we agree or disagree with the trends in small arms accessories, they are still moving forward with them. I was very apprehensive about Land Warrior when I saw the proof-of-concept system in 1994. By 1999-2000, they had miniaturized & ruggedized everything to an acceptable system, and it provided real-world advantages that we demonstrated in several Advanced Warfighter Exercises at Ft. Bragg, JRTC, and other locations.

Instead of needing a huge SOFLAM unit, imagine having that capability integrated into a carbine: http://3.bp.blogspot.com/-9dcuswYGF...AAANI/Fylg98ytSrw/s1600/SOFLAM-Sl2-web-lr.jpg

That's basically the direction that not only the US, but many developed nations are going.

The Miniature Day/Night Sight is just the latest evolution of weapon-mounted optics & night vision. http://www.planetrainbowsix.com/armm/images/MDNS.jpg

 

[Shotplacement]

I carried a scar heavy overseas. It was an incredible weapon once you got used to the ergonomics

 

[Mandalorian]

So I had the SCAR 17s. LOVED IT.. but only after I dumped more money into it. For the money that you pay for this rifle you would want a better trigger- I shelled 3200 last year for mine as well. Nothing beats shooting a .308 with one hand (stock folded) very cool indeed. I ended up putting in a Timney Trigger and I stared hand loading at the same time my groups went sub MOA at 100yards.. I had a bunch that ended up being all within a .5" box (larue print out targets) - So I wanted to continue with this rifle but then found myself looking at POF's- and I am in the middle of a Trade for one right now. reason? to make the SCAR a really great gun- you have to then drop in 1200.00 barrel from Hi- Desert Dog.. Good folks btw.. so it was a never ending project.. changed out the grip- which has limits.. Ergo or Tango down- no others fit without physically modding them. barrel as is heats up and you really cannot hold it without gloves after one mag. so burn is a factor.. then it actually gets to melting stuff to your barrel- sling and what ever touches it. be aware of this. bottom rail is short so point of bi-bod is odd- you can purchase an extended rail.. more money.. on and on.. the weight is 8 Lbs for a 308 that is insane.. but after you pretty it up to how you like to shoot.. well time- money- and weight are all spent.. on something that already came out of the box heavy on the price. thing long and hard on this.. I did truly love it.. but in the end after a year of parts and spending .. well I am now hanging my head low. dont jump unless the light is really green.

 

[McCrazy]

We were issued a few weeks ago a new laser (LA-5D) that the only thing I was told about was "these are for the SCARs and aren't supposed to break like the old ones during recoil." We were not issued new lasers for our M-4s or any other weapon systems.

Seems to me if Crane is developing ruggedized sighting systems specifically for the SCAR-H then they are aware of issues. That being said, I still have yet to witness an optic failure on a SCAR-H that blame on the gun itself. To caveat that we do usually shoot our M-4s a lot more than the SCARs.