Wear & tear **UPDATE**

[Rifleshooterscar]

I do think I've come to the root of the problem.

I field stripped the gun to where the moving parts assembly could move freely in the upper (removed recoil spring). I made the following observations:

The bolt can wobble around quite a bit in the carrier. If upward pressure is put on the bolt as the BCG is slid forward from open to closed (with the bolt starting in the fully unlocked position), the bolt will contact the barrel extension in the areas where every picture has shown wear. With just a little upward pressure, I can make it so the bolt is very difficult to close. With even less, I can cause it to snag and still eventually slide in. There is even a small amount of hang-up if I simply flip the upper upside down. If I flip the receiver upside and hold the bolt up (i.e. making it so the bolt should not snag) then it doesn't snag (as expected).

I think two things may be at fault here (and I can't reliably tell which it really is):

Bad machining on a batch of bolts and or carriers to which there is so much movement that this can occur.

or...

My stent using unmodified Pmags caused the problem by pushing the moving parts group up slightly.

From reading in other threads, I think I would guess with the latter. I will try to get in touch with others who have had this problem to see what FN has done to fix it and if their weapons exhibit the same behavior still. I would also like to see S/N ranges where this has occured. For the record mine is in the 19XXXX range.

As I noted, when assembled with a proper magazine, the problem does not seem to exist anymore. I will be fiddling with it some more to try and confirm my thoughts, and take it out tomorrow and run it with just USGI magazines. I will post the results then.

Edit: I just tried the same thing with my 17S and was able to induce similar things, though I do note that there was much less bolt "wobble" naturally in the 17S. The lack of an aftermarket magazine with similar issues and the lesser amount of bolt wobble may account for why this is never observed in a 17S.

Lastly, the bolt catch may not be the only problem with non-USGI magazines. Slightly higher feed-lip/seating heights may also have an affect moving the bolt.

I still post my feelings about P-Mags I won't use them and hope others will not use them. IMHO the best non-metal Mag. is the Lancer Warrior.

[SgtStrykerUSMC43]

If the magazine drives the BCG up and causes any issues, simply stop using that magazine. Magazines are much cheaper than SCAR bolts.

[Kyohte]

If the magazine drives the BCG up and causes any issues, simply stop using that magazine. Magazines are much cheaper than SCAR bolts.

Well, the range trip went as planned today. There was only minor wear that seemed new (I really couldn't tell if it was new wear or if my marker had possibly burned off). Most of the markings survived the session of 120 rounds.

The issue remains, however, that when I tilt the rifle beyond 30 degrees or so off vertical, the lugs still catch on the top of the barrel extension. Can someone (like sgt) see if this happens in their rifle (flip the rifle over, hand cycle it and see if the bolt catches a little?

Thanks.

Edit: My 17S hangs up when upside down, so this might not be something I need to worry about.

[Talhoffer]

I pulled my 16 down today to clean it, I ran 400rds through it last Saturday and it has had over 2500rds through it before that. I looked closely at the the bolt and barrel extension, on the two top lugs it has the same two small little marks as is shown in the pics from the OP and the barrel extension is free of marks. My rifle even has the same small mark in the bottom side of upper receiver from the bolt catch.

With the rifle laying upside down I reinstalled the BG and slid the BG into battery, it slid home smooth and did not hang up but if I pushed the BG to the non ejection port side as I slid the BG forward I could observe the bolt hit the barrel extension and see it get pushed slightly to the center of the extension as it went into battery. I have check over the bolt body, the bolt carrier, the barrel extension, the cam pin, and the rails in the receiver for the BG and none of them show any excessive wearing in my rifle.

With around 3K worth of rounds run through my rifle it doesn't look any different than the OPs rifle, except dirtier.

[SgtStrykerUSMC43]

This:

I pulled my 16 down today to clean it, I ran 400rds through it last Saturday and it has had over 2500rds through it before that. I looked closely at the the bolt and barrel extension, on the two top lugs it has the same two small little marks as is shown in the pics from the OP and the barrel extension is free of marks. My rifle even has the same small mark in the bottom side of upper receiver from the bolt catch.

With the rifle laying upside down I reinstalled the BG and slid the BG into battery, it slid home smooth and did not hang up but if I pushed the BG to the non ejection port side as I slid the BG forward I could observe the bolt hit the barrel extension and see it get pushed slightly to the center of the extension as it went into battery. I have check over the bolt body, the bolt carrier, the barrel extension, the cam pin, and the rails in the receiver for the BG and none of them show any excessive wearing in my rifle.

With around 3K worth of rounds run through my rifle it doesn't look any different than the OPs rifle, except dirtier.

...and the fact that I don't have any SCAR's in current inventory. I'm waiting on (2) each of the SCAR-H and SCAR-L select-fire variants and hopefully they'll be here before Spring.

[Kyohte]

Well, aren't you useful!

Kidding, of course.

I guess I won't worry about this, since the geometry of the front of the bolt lugs isn't overly important. I'll be sure to keep an eye on it and will update if it gets worse or anything happens. I plan on seeing what happened to the guys on M4carbine if possible, as well.

[DaveinCT]

My 16s is a year old now and probably close to 4000rnds through it. It devoured 440rnds of the Federal green tip this morning in about an hour which the 22 degree weather helped. I break mine down after every trip out which I did again this afternoon and the bolt and barrel extension are in great shape. I never shot mine with a Pmag that wasn't modified and I check everyone of them with the grip and magwell off the gun, snap the mag in and make sure the bolt lever doesn't come up at all. I do have the wear mark on the bottom of the upper where the bolt latch goes through which to me seems normal wear.

[SgtStrykerUSMC43]

Well, aren't you useful!

Nope. Completely useless, actually...

[Turnanewleaf]

I wish I never found this thread...ignorance is bliss.

My 17S shows bolt wear, albeit on the opposite side of the lugs as the OP. See the edges knocked down in the left of the pic. 150 rounds.

IMG_4035_1.jpg

[Kyohte]

That is a first for a 17S. I have come to the conclusion it is not something to worry about. Here is why:

The front of the lugs aren't of much importance. I have only found 5, maybe 6 reports of this online, meaning there are probably many more unreported instances. Lastly, I found no occurances of bolt failure in SCARS.