M*CARBO Brotherhood

FN 509 malfunction

I was just curious if anyone had any issues running steel ammo with the Mcarbo spring kit? I have yet to have a single malfunction with my gun until after installing the spring kit. This weekend I had 10 boxes of Remington steel cased ammo. On Friday I shot 4 boxes of the steel ammo without any issues without springs installed. On Saturday I installed the springs and went to the range. I shot 3 boxes of the steel and my gun would lock up once every mag. I inspected the rounds and noticed no primer strikes. I then ran 5 boxes of regular Federal Brass ammo with no faults. My apologies I am a new gun owner and this is my first gun.


Welcome @ReedyMonster
I have an FNS9 with the full 509 kit installed. I have not run steel cased ammo after doing the springs, but she did not them or aluminum cased at all prior to the install. FN pistols can be VERY picky about what you feed em so after issues running non-brass cased ammo w/ stock springs, I never tried again. Blew the rear of em through an ar9 just to use them.
Since you just did the springs, it wouldn’t surprise me that it changed the dynamics altogether.

Not be rude but, did you give her a good deep cleaning after Friday’s session? Steel ammo generally runs dirtier and some manufacturers slather a lacquer coating on them to help prevent corrosion. This may cause a bit of “gumminess” to build up at the feeding after shooting some causing feed and fire issues. The lacquer on lacquer here being the “hot” issue for me. The rounds sound like they weren’t chambering properly for no striker mark to appear.
Brass cases usually have a much better finish to them allowing for easier feeding and extraction plus no build up from vaporizing trace amounts of lacquer.
The next thing is (and no offense) you didn’t have something put back right on reassembly after the install, only to correct the issue which your inspection. Did you take the slide off after running the steel but before running brass on Saturday?

And some pictures please. We like them around here :+1:t2:


Yes sir I clean my 509 after each trip just to familiarize myself with the gun and build good habits. I removed the slide and inspected it during 4 magazine changes of the steel. It would happen on the 2-4th round of the magazine. The trigger would pull but nothing would happen and then the trigger was dead. The slide took alot of force to rack and eject the round.Then it would run the rest of the mag. I will try to replicate the issue this weekend with proper documentation. I really love the feel of the trigger now. My heart sank because I thought I did something wrong with the install, but the brass runs well.


Sounds like you got rounds hanging up and she’s not cycling fully. I wouldn’t say it’s the springs/gun or ammo directly. I think it’s a combo of the three considering she was fine with steel before the install. Like I said, they finicky. And if your having to really put some force on it to rack it and get the jam out, she’s not chambering properly imho.
Did you inspect the misfed rounds for any signs of damage? What capacity mags did it happen on, or was it multiple size mags? Are you still with the factory trigger and extractor?


@ReedyMonster Another thing would be to load up your mags with dummy rounds and hand cycle them and see if you can “feel” any inconsistencies in the cycling. You may need to be a bit aggressive with it and do it a few times to know what a normal cycle “feels” like, but you should feel it if it’s something major. Most dummy rounds are aluminum too which I had issues with, so you may just find the same problem.


this may not apply to your current problem but it would not hurt to check your manufacturing date just to be sure:

FNS Service Bulletin | FN®

The ‘recall’ is voluntary as FN claims the condition is so ‘rare’…

Also, a fair amount of owners have now reported broken strikers on various FN forums.

Anybody wanna buy a 509C in .40S&W?


I actually practice my dry fire daily with aluminum snap caps which are cycling fine. However I do not have enough snap caps for a full mag. I did inspect the rounds with no sign of damage. I put some of the same rounds back in and they would run. I was running 3 factory 15 round mags and it occurred with all 3 mags. Also the mags were cleaned recently. I have a factory trigger and extractor.


Ok. Now I’m scratching my head a bit especially if she’d take them a second time and pop them off.

The most I can say now would be to put a few hundred through her to loosen her back up. I know my needed to be after the spring and striker install. If you can get ‘em try different capacity mags and see if it happens across the board there. That would help narrow it down a bit.
Have you done anything to upgrade the striker? The Apex striker and new associated parts may be worth a gander.
Was the steel ammo different from the brass? (i.e. 115 gr vs 124 gr. / Hollow point vs ball)


I don’t bring knowledge of the platform, but I do offer this truth. Steel is very likely to be loaded with “harder” primers. Inspecting primers on the dead trigger rounds will answer my curiosity. Heck, simply comparing primers on fired brass vs steel will determine if there is a difference.

If you swapped the hammer spring for a lighter spring, it is almost certainly the answer.

At any rate, defensive or carry ammo should be brass. Steel becomes the ultimate failure drill ammo of choice. Win win.


Fear not. The 509 series is not included in the recall. They use the same striker, but the rest is somewhat different. The full size 509 is actually more akin to the FNS9-C with regards to the trigger.
Just get the Apex striker and the newer release striker hardware and you’ll be golden. The two together should be no more $70 shipped.