MP5 QD Flash Hider and BMP K Upper Assy problems? User Error?pics added

4747 Views 24 Replies 7 Participants Last post by heavyarms, Jul 24, 2012

GSC

Discussion Starter · Jun 11, 2012 (Edited)

2

I have a SBR MP5k BMP barreled upper based clone, and is a great shooter, never the first jam, accurate, and all in all a good upper but I just got a QD Hk flash hider. I can tell its 9mm as it wont fit on my .40 by a long shot, but when I slip it on, I can not get the cross bar to go back down. When holding next to the trilugs, it appears as if the cross bar is still too high to latch behind the lugs by a distance roughly equil to the width of the latch bar itself. The FH runs all the way flush to the sight tower. Is the barrel not to spec?I am sure its not the flash hider. Install error/user error

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scottinthegrove

· #2 · Jun 11, 2012

The "cross bar" goes between the lugs, not behind the lug. Put the flash hider all the way on the barrel. Give the flash hider about 1/3 of a turn. Then put the "cross bar" in place. It should then be locked onto the barrel. Good luck with you FH installation problem.

Scott

GSC

Discussion Starter · #3 · Jun 11, 2012

Gotcha. Well I tried that too, and I can not get it to rotate more than 3 or 4 degrees (not much, definitely not locking them in), tried on real german lugs and not working...this has to be user error. What am I doing wrong here?

CHANGaLANG

· #4 · Jun 11, 2012

In '08, I got one of the 3lugged pdw pistols and found the same problem. I compared the pdw's tip to a full size's and noticed that the pdw's tip was not machined correctly. Sooo, I busted out my Dremel and milled off what was out of spec. Flash hider from then on fit and held.

GSC

Discussion Starter · #5 · Jun 11, 2012

Whats weird is it is not fitting on a german barrel I have...But it is a used flash hider so it worked for someone!?!?

The_Crow

· #6 · Jun 12, 2012

I have seen some used flash hiders with so much carbon build up in them they will not go on the barrel. I have had a couple that I had to use a small hammer and chisel to bust the stuff out as it was rock hard. I bet that is your problem.

GSC

Discussion Starter · #7 · Jun 12, 2012

It slides all the way on, it just will not rotate left or right with the latch loose while flush with the base. Its used but not much, as there is just a slight amount of carbon build up. I am baffled by this. Its a QD FH - !?!? Its supposed to be easy.

U.S. Praetorian

· #8 · Jun 12, 2012

Got a question. Is your FH a 1st or 2nd gen? The first have the ribbing on the latch and the 2nd are smooth. I have both and the 2nd gen gave me problems just like you describe. I wound up using a dremel to relieve the area where the muzzle ends. I am not sure what the deal is but it did this on the following barrels:
HK, MKE, RCM and Coharie. The 1st gen slid on and off all these without a problem.

GSC

Discussion Starter · #9 · Jun 12, 2012

It is a 1st gen w/ the ribbed lever.

GSC

Discussion Starter · #10 · Jun 14, 2012

So before I break out the dremel, would it not be the locking bar area that I grind?

scottinthegrove

· #11 · Jun 14, 2012

Just for clarity, when you say you have a "SBR MP5k BMP barreled upper based clone", did you buy the barreled receiver recently? As I recall in the earlier Todd 9mm three lugs, the lugs were a little bit long.

Scott

The_Crow

· #12 · Jun 14, 2012

Bgu301 said:
It slides all the way on, it just will not rotate left or right with the latch loose while flush with the base. Its used but not much, as there is just a slight amount of carbon build up. I am baffled by this. Its a QD FH - !?!? Its supposed to be easy.

If it will not rotate then it is not going all the way on. Do not dremel anything. The flash hiders I have seen with the build up were the same way. Looking inside them they appeared to not have anything causing a problem. The build up was so smooth and shiny it looked normal. If you are sure this is a factory HK flash hider and you cannot get it on a factory HK barrel than the FH has something inside of it causing not to seat properly. We all know HKs quality control and doubt seriously that you have a factory HK FH that needs to be dremeled to fit.

CHANGaLANG

· #13 · Jun 14, 2012

Bgu301 said:
So before I break out the dremel, would it not be the locking bar area that I grind?

When I used the Dremel, one or two lugs is/are what I had to shave down a little. The machinist who made the barrel left the overall lug diameter and individual lug width outta spec.

GSC

Discussion Starter · #14 · Jun 16, 2012

The_Crow said:
If it will not rotate then it is not going all the way on. Do not dremel anything. The flash hiders I have seen with the build up were the same way. Looking inside them they appeared to not have anything causing a problem. The build up was so smooth and shiny it looked normal. If you are sure this is a factory HK flash hider and you cannot get it on a factory HK barrel than the FH has something inside of it causing not to seat properly. We all know HKs quality control and doubt seriously that you have a factory HK FH that needs to be dremeled to fit.

I sure as hell am not dremeling on my SBR, thats for first off. It seats all the way, I see no gap in the f/h and the triple tower. I unlatch it, and let it free. It will rotate about 5-10 degrees, but the latch, compressed, then pressed down, will not shut and is not enough to have traveled far. I and another have muscled on it to no avail, and I certainly dont want it stuck, but I want this to be a qd hider, as in QUICK, not holy crap this is hurting my hands and may need a pivot or strap wrench. I want to have this option.

GSC

Discussion Starter · #15 · Jun 16, 2012

CHANGaLANG said:
When I used the Dremel, one or two lugs is/are what I had to shave down a little. The machinist who made the barrel left the overall lug diameter and individual lug width outta spec.

I dont see that as the problem though, as I tried on a front end sold on the EE, No dice with it, for me or Thomas. Its odd. I will try to shoot some video w/ my phone.

The_Crow

· #16 · Jun 16, 2012

Any chance it is not a factory HK flash hider?

GSC

Discussion Starter · #17 · Jun 16, 2012

Sure, could be a contract. How do I tell the difference. Do Hk's have any markings, or pin differences,?

GSC

Discussion Starter · #18 · Jun 17, 2012

2

Here are pics..

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The_Crow

· #19 · Jun 18, 2012

Is it hitting the cap at the end of the charging handle tube?

HkCHUCK

· #20 · Jun 18, 2012

Ben

When something doesn't work right I try to eliminate as many possibilities as I can. So while it may seem somewhat unusual have you tried installing the flash hider without the front grip in place? If that does not yield positive results I would then try installing it without the front grip and also removing the cocking tube cap as well. I have seen the cocking tube cap cause a problem with a three lug mount for my Trident suppressor on my MP5k-PDW.

The flash hiders I have seen and own have not had any HK manufacturing marks on them or for that matter any marks.
Here is a pic I took of mine and it looks like the ones you posted of yours.

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