A while back, I posted pics of my SCAR 17 malfunctioning with a suppressor attached. It was overgassed, and the bolt carrier was hitting the back of the receiver (the plastic butt stock) hard enough to bounce the next loaded round out of the mag on occasion even with the gas regulator in the suppressed setting. Well, today I finally got around to fixing it and wanted to share my findings.

The stock gas control screw was 1.5mm. I ordered all the screws from midwest gun works between 1.20 and 1.45mm. I settled on using the 1.35mm screw after trying all of them. It still cycled with authority, locking the bolt back on the last round, etc even unsuppressed. But with the suppressor, the recoil was MUCH less than with the stock gas screw, it didn't sting my cheek, and more importantly there were no malfunctions.

About 60 rounds were fired after fixing the issue; all fired flawlessly. 3-4 rounds were put in the mag each time to test the bolt locking open on the last round.

Of course, this post required a pic:

Have you tried firing it with the new gas screw and without the suppressor attached?

Yes I did that today. Both ways (suppressor/ suppressed setting, unsuppressed/unsuppressed setting) worked flawlessly

Close up pics? I'm not familiar with the screw you are talking about, then again I just got my scar.

Can you report how the rifle reacted with the other gas ports installed?  Especially the smaller sizes and the eject patterns for each.

What suppressor and muzzle device is being used?

ETA: what ammo was used for testing? One type or multiple types?

Ammo: Privi Partisan 145 gr. 7.62
Unsuppressed gas setting/ No suppressor
AAC 51T muzzle device

1.20mm: Did not eject spent case.
1.25mm: Ejected spent case, did not chamber next round in magazine
1.30mm: Ejected spent case, chambered next round. Bolt locked open intermittently on last round in magazine.
1.35mm: Functioned perfectly, bolt locked to rear on last round in magazine every time.

After reaching this point, I used the AAC 7.62 SDN-6 with the regulator on the suppressed setting.
Ammo: Privi Partisan, Winchester 150 gr. power points

1.35mm: Functioned perfectly with both ammo types. No issues at all, recoil was significantly reduced compared to the stock 1.5mm gas control screw. Bolt carrier is not hitting the rear of the receiver nearly as hard. Gun runs much smoother.

Take a look at this cross section of the gas block.



You access the gas control screw through the top of the gas block after removing the regulator plug. This makes tuning the cyclic rate of the SCAR very easy.  Usually quite common after a barrel chop but I've never seen an issue on a unmodified factory barrel.  

Glad it was that easy to fix!  

This is why FN drilled holes into the blast chamber of the AAC cans they were delivering to SOCOM. A lot of piston guns can't handle backpressure.

Was the old screw worn or wearing in any way?

I didn't measure it, but it acted the same way from the get-go and the problem never got any worse.

Interesting information...





Anyone have any input on whats listed here?





http://handldefense.com/product/scar-gas-control-jet/





Edit: and whats needed to remove the stock gas screw, thought I remembered mention of a special tool, but looks like a small enough hollow bit driver would work...



 

All the sizes listed on the Handl Defense sire are larger thn the 1.35.  They start at 1.7 and go larger.  Where did you get smaller ones?

Not the OP, but I get my SCAR parts here:





http://www.midwestgunworks.com/page/mgwi/ctgy/scar-parts



I didn't even look at the sizes Handl offered, they seem way off compared to stock...



 

Midwest Gun Works is where these came from

Great info OPS. Thanks! I thought my 17 was cycling hard. I always shot with it on the suppressed setting because of this. Still hit hard. I haven't shot it with my suppressor yet but was only expecting it to get worse.  I am going to give this a try.

Anyone know why Handl made their gas jets so much bigger than the stock size? They have a 1.7mm which they recommend for their 16" 7.62 guns. Seems like an awfully big jump over the 1.5mm stock size.

1919man, thanks for the good info.

I really don't understand why they didn't select a gas screw or a gas system that would prevent this problem from the beginning. I thought the whole point of my SCAR's adjustable gas block was so that I wouldn't need to deal with this problem? I guess FN had no intention of selling something to civilians for suppressed use (considering their barrels lack an appropriate shoulder), but if the SOCOM AAC cans had to be modifed for this gun, then they have a design issue that needs to be addressed. This makes me want to trade it in for an AR-10 variant.

I only have about 200 rounds through my suppressed SCAR-17 with a Surefire SOCOM 7.62 can, and I haven't had any issues with the gas block set to suppressed mode. Work is what prevents me from taking it out to the range these days.  When I shoot it more later this year, I'll try to see if I wind up breaking the damn thing before I change anything around. For a $2.5k rifle, it should work as intended.

The rifle does work as intended.  The scar barrel shoulder is minimal for weight savings (as is the entire barrel profile), and for the most part, until very recently, military's of the world didn't use or issue suppressors on rifles.  Further, the FNH scar specific suppressor is designed to work on the scar as made from the factory.  Even AAC modified its SDN-6 for issue on the scar rifle.

The issue here is more from the suppressor being used then the rifle it is being used on.  Note the AAC SDN-6 suppressor being used is not the new technology surefire SOCOM suppressor you are using.  Surefire dumped its entire old line in favor of the SOCOM line and the improvements made to run on the new rifle technologies coming out.  Further, surefire makes a scar specific suppressor and muzzle device that overcomes over gassing, and the small shoulder for muzzle devices.
(NOTE: I am not a surefire fan boy.  The surefire is what I have, and what I am working with.  The AAC SDN-6 is an excellent can and works well too.)

I am interested in this topic since I run an old school surefire SS762 can (an older reflex design no longer made).  I too have noted what I consider over gassing on my rifle with the suppressor attached.  I haven't experienced malfunctions from running suppressed, but the action speed and violence of recoil is higher then when run without the suppressor attached.  I too have been thinking about experimenting with smaller gas screws (I call em gas jets since they are very much like carburetor jets from Holley carbs).  With the OP doing the initial testing, I can limit my purchases to two sizes and do my own testing.

What muzzle device were you using? Slightly off topic but I continue to hear conflicting information regarding the use of the AAC brakes on the SCAR 17.

Just the AAC 51T FH. Supposedly you can't use the brakeout or muzzle brake.

Thanks 1919man, just tried my new saker on a scar 17 and it was way overgassed on both setting, now I just ordered a new gas control screw and hopefully it will help.

The gas screws are #8 if anyone is looking at this diagram.

My black 17 one is so-overgassed that it craters primers on my reloads that show no pressure marks in any of my other 308s.  I'm going to try the 1.35 and 1.40 screws, thanks to you.
It'll run without issue on suppressed, without the suppressor, too.

My FDE 17 wasn't as bad, but I'm getting back my barrel from Marvin tomorrow.  He cut the barrel to 13.7 and pinned a MAMS on it to take it to 16.1".  Hopefully, the 2.3 inches he lopped off will reduce the gas pressure.

Just got the .35, .40, .45 in the mail from Midwest, I'll update after I try it out. I'll start with the .35

I think you'll be pretty amazed at the difference.

What insert bit/wrench will I need for this?  I'd like to have it ready to rock when I get the screws.

I just used a flat blade screwdriver to get the screw out. It's slotted so you can do that. A magnet and pair of needle nose pliers are good too.

Thanks!