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Why is there so much lost pressure and powder burns all over the front sight?

3K views 29 replies 14 participants last post by  Fourth Horseman 
#1 ·
My question is since this is my first SCAR, why the heck is there so much lost pressure and powder burns all over the front sight, and the front of the rifle? I mean in slow motion videos the flash that is coming out of the gas regulator switch is as bright as the end of the muzzle break or compensator. Why?? I don't see that happen on any other rifles I own like this one. It doesn't happen with my ACR .556 or with it's 300 Blackout bbl. Has anyone else seen the front of there rifle turning red with powder residue? It's a pain in the @$$ to have to take the forend extension off each time and clean this thing. I like my firearms clean as new and ready to go. I'm hoping this is not a normal issue with SCAR 17's. Thanks for your help and feedback!!!! Gun Firearm Assault rifle Rifle Trigger
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#2 ·
It's not red. It's actually vaporized copper from your projectiles and it occurs with every center-fire rifle. It's just more noticed on weapons which vent excess gases onto their blackened components surfaces.

If your ACR has a muzzle attachment, you'll find copper deposited on it also.

-SS
 
#3 ·
I understand the vaporizing copper, but the color changes with changing powder or purchased ammo. The ACR has and adjustable gas system and the AAC threaded brake for my can and it doesn't leak a speck. There is a different "leaking" issue here. Flames should not come out of a gas adjuster unless it was engineered that way. That's what I'm trying to find out is all of these SCAR vent out all over the front of the rifle. Thanks!
 
#5 ·
Reason you see flame coming out is, as with the muzzle there is unburnt powder coming out, and burning. This is normal. The FS2000, 5.56 weapon, also does this. And I am guessing the SCAR 16 as well.
 
#7 ·
Every gas op semi auto vents gases. If not you'll have pressure spikes and premature wear. Depending on the make and manufacture of the weapon, they will be different on how they vent. Ammo manufacturers will burn cleaner or dirtier depending on what powders and primers is used. Don't forget about the exposed lead in bullets after they're fired will leave residue.
 
#8 ·
If I recall, red is typically a lead oxide color. You might try some HPBT loads and see if that at least changes the color of the deposit. FMJ leave lead exposed at the tail of the bullet.

It won't solve your venting problem, but it could turn your deposits from red to green. :)
 
#11 ·
LOL!!! So nice of you to chip in with the shipping! :thanksrp8: But I think I'll hold onto it and the Leupold Mark 6 3-18x44 with the Horus 58 reticle and it's Mark 6 mount. It truly is my favorite scope I own for this platform. (and I own more scopes than you would ever believe. Seriously!
 
#10 ·
I hear what you're saying, but I'm not sure my scar does what you are saying. Here is a thermal image of me shooting, and there is only a little gas escaping the gas regulator switch, not a ball of fire like you describe.
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#12 ·
I just can't figure out why there is nothing, not a spec of gas leaking out the ACR's gas adjustor. And that's when it is set in either suppressed our unsuppressed mode. I hate the fact it's losing pressure like this. Talk about inconsistent pressure curves and big ES and SD on velocity numbers on the Oehler 5 Ballistic Chronograph. Same match ammo in 2 different other rifles (bolt gun and a LaRue) so ES in this match Lapua ammo at only 12fps.!! Out of my SCAR.... over 62fps. :|
I hear what you're saying, but I'm not sure my scar does what you are saying. Here is a thermal image of me shooting, and there is only a little gas escaping the gas regulator switch, not a ball of fire like you describe.
View attachment 22335
 
#14 ·
I hate to ask this, please don't take offense. Is your gas regulator assembled and set correctly? If you were running it on suppressed mode I could understand more of a discharge. Or if something wasn't tight. I'll chrono some more rounds next time I'm out, but I don't remember having a huge deviation.
 
#16 ·
Thank you for your replies and I truly take no offense - the gas assembly is correct and set to the 12 O'clock position (un-suppressed) Here is some photos of my wife shooting it and you can see the pressure loss even in broad daylight. Closer to night it is really apparent. Gun Firearm Shooting sport Shooting Trigger
Gun Firearm Rifle Shooting sport Shooting
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Gun Shooting sport Firearm Shooting Shooting range
 

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#17 ·
That last photo is showing the hot burning powder escaping at the regulator, and that is purely lost pressure that should be being used for forward velocity and down range energy. What a sad waste of powder / power.
 
#18 ·
Here is a photo of my wife shooting the ACR with 60+ round through it and the bbl at the gas regulator as I stated is spotless and nothing at all to clean up. No loss of pressure. Gun Firearm Sport venue Airsoft gun Shooting range
 
#25 ·
Yes I did. I cleaned the rifle meticulously to the last part and yes for a brand new rifle it was quite dirty. (I'm a fanatic about clean cars and clean firearms) I've checked things out for correct assembly and all.... it is as it should be.
 
#20 · (Edited)
No safety glasses shooting the ACR?

Also the ACR is 5.56, less powder volume compared to the .308 out of the SCAR. You are comparing apples, to oranges.

What Brand .308 ammo you using?

The bullet has left the barrel, as evident by the muzzle flash. The lost velocity you are talking about from the "wasted" gases is so small. IF you were to plug it up so nothing escaped, you would not see a difference, except that it would no longer be semi-auto.

You are really splitting hairs here.

Every semi-auto gas driven gun, via piston or DI. is "losing" pressure, because pressure is used to work the action.
 
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#26 ·
She always wears shooting glasses - she was finished with that mag and I ask her to go back to the rifle for a photo, that all. I understand about the different cartridge capacity - Please. I was comparing one manufacture of a gas auto that doesn't leak powder even at higher pressure levels than the 308 (I have a strain gauge 85) and even with it shooting its 10.5" bbl. Similar design, one leak drastically, the other doesn't. That's what I was comparing, not cartridges. The ammo I was shooting was Fed Gold Metal Match 168gr. Lapua 167gr Match Aficionado, and Hornady 16 A-Max.
 
#21 ·
What sonytec said. get into reloading and understand powder burn rates. you dont want flash in your your 16" scar, shoot a longer barrel so there is more time for the powder to burn off. or load to get maximum burn in a 16" barrel. this is a non issue. educate yourself about ammunition first. comparing two different rifles in different calibers with different ammo with different powder is not a basis for scientific study
 
#27 ·
". educate yourself about ammunition first." Really? Didn't know I'd get slapped here. Ouch! Sorry if I sounded a little too new, or "uneducated". Just to throw in a funny little tidbit of info just for giggles,,, I have worked for two different major ammo and bullet manufactures that you all know and probably love in the last couple decades. (that's why what you said had my wife and I cracking up. But it's ok. How could you have known?) Heck, there is even a couple of photos of me floating around in a couple reloading manuals. The "scientific study" as you state, this is nothing of the kind. Science is "my thing" - FN's SCAR rife design, part tolerances and their efficiency is all I was trying to getting a feel for from this audience. I'm sorry if I came across as "uninformed" while I was bringing up this gas issue to this demographic of SCAR owners. So as far as "get into reloading and understand powder burn rates"..... thank you lol. I think I got that one covered. :) Have a good night Ironhorse6. Shoot straight / be safe!
 
#28 ·
Lefthanded7, don't look now but your OCD is showing. If you look closely at the gas regulator, there is a hole in the end of it that a small amount of gas can escape out of. There are holes on the side to allow more gas out when shooting with the regulator set to the suppressed mode.

This is the tricky part. That is how FN designed the rifle to operate. The engineers who designed this rifle put that little hole there on purpose. I can only assume that they put that hole there because it somehow makes this battle rifle more reliable in filthy harsh conditions. The designers of the SCAR were not concerned about people who want to keep their rifles "as clean as new." No sir, they were also not loosing any sleep over a 60 foot per second velocity spread when using premium competition ammo either.

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The SCAR is designed to work dirty in rough environments and a little bit of residue doesn't matter one bit. If the rifle preforming the way it was designed bothers you, shoot your ACR more.
 
#30 ·
Can confirm this is true for the polymer hand guard which covers the gas block. Source: I own two of 'em.
On the shorter aluminum hand guard the gas block is exposed so you don't get fouling inside the hand guard, however, as I mentioned in my previous post in this thread you do get some carbon buildup on the top of the barrel underneath the gas regulator.
 
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