I recently purchased a cut down mr556, it has the mr556 and the gas block has not been closed.  I finally got it out yesterday and ran a couple mags through it, it failed to lock back at one point.

1. Should I weld the gas port?

2. is the gas port in question, the hole in the front of the gas block?  I've been unable to locate an answer to this and all of my prior experience is with DI guns.


Any recommendations?  Its something I can do but I want to make sure i'm 100% right on how, when, why, and where to do it.  thanks



2/17: Failure to chamber issues
I ran about 40 rounds through the upper today and while it did lock back at the end of every magazine, it also failed to chamber a round 3-4 times in this period.  The bolt would be open, caught on the next round, but it was not pushing said round into the chamber.  Thoughts?

Here is what i'm working with
-standard forged lower with no reliability issues, standard fcg group
-started with a regular spring and H2 buffer, when it failed to chamber a round i switched to a standard H buffer (same spring) and it did it with that buffer as well
-ejecting around 1-2 o'clock
-i used 3 magazines, i dont believe that this happened on just one of the magazines but i need to verify (all 3 usgi mags, 1 is an HK mag)
-standard .223 ammo (xm193, pmc .223), nothing fancy.

The gas port on the gas block has been completely closed via weld.  
The rifle is well lubed.

Thoughts?
Try a carbine buffer?  I feel like the issues is not necessarily being under gassed since it is ejecting at 2 o'clock

Anyone have experience with this?


I went ahead and welded it closed; range time to follow.

I don't have a whole lot of information on this, but the guy who did mine is a member here, NoScoE30, and probably could tell you far better than I.  

As I understand it, the latest (non-A5) 10.4" gas blocks have a smaller port in them, but earlier ones were closed.  

~Augee

Yes have the gas port welded. My advice is to send it to jayson at IGF get the full work up and call it a day

This is correct. If you weld it up it will be overgassed with a can. Marvin Pitts is working on mine, he is pretty much the man with these. IGF is good too but they don't port the 10.4" blocks as far as I know.

Or just get original HK 10.4" gas block, drop it on the barrel and you will still have old one to play with or sell to someone who want to play with it (I converted mine into adjustable gas block for example).

http://www.hkparts.net/shop/pc/HK-416-10-4-Upper-Gas-Block-132p1543.htm

thanks guys.  Suppressors are a no go in illinois so i went ahead and welded it closed; it turned out pretty nice actually after some slight work with a file and then i just painted it up.  I debated on buying an HK 416 gas block but i wanted to try this first.  Hoping to try it out this weekend.

Glad it works for you! I have mine at 14.5" (for 3Gun use) but just helped friend to convert his MR223A3 into 11" version (shortest HK415A5 is 11"). Very handy rifle.

See the edited OP, i'm not having reliability issues.

Glad it's working now

I'm assuming you meant you're now having reliability issues?

If so, honestly, I'd go post on HKPRO and see what they have to say, the MR556/HK416 isn't particularly common/popular here, and the Piston subforum is a pretty low-traffic area.  The HKPRO HK416/417 HQ isn't exactly the fastest moving forum out there, either, but it seems to get new posts/topics about as frequently as this subforum, and is devoted exclusively to HK416/417 and related weapons.  

~Augee

Thanks.  Yes, I meant now.

Can you provide more info on what's happening when the rifle fails to feed?  Is the bolt missing the rim of the cartridge and sort of stalling out on the case body?  If so, I'd guess you're actually a bit overgassed and, as a result, the bolt is outrunning the mag.  Maybe try the gun with the heaviest buffer you can find.  See if that makes a difference.

All I know is that the 10.4" gas blocks HKparts.net that Montala linked to have no gas vent. The new HK416D 10.4" guns have a vent. I am afraid it might be over gassed as well. Are you using the HK buffer and spring?

If rifle was working fine with unmodified gas block, then probably reduced power spring was used to accommodate much less force from piston to BCG. Now, with closed dump hole, you must increase spring force.

Use standard HK buffer and spring. This rifle is designed to work with much stronger recoil spring. If you do not have those, use closest you can get to original configuration. AFAIK Spikes were making HDTP buffer that was practically a copy of HK416 buffer. Try some +10-20% recoil spring.

Also getting to HKPro.com and asking there will not hurt. Lot of knowledgeable and helpful guys there.

Thanks guys.  Picked up an hk buffer and spring and ran it today with no problems.  Hope that's the solution

Yes, that IS the solution. You are now running it in configuration it was designed to be used. But take in mind that HK416 in 10.4" has rather high cyclic rate (intentionally - to make it more reliable in adverse condition, when dirty or when not properly lubed, etc.) so you need good magazines that can keep up with feeding ammo. Older Magpul mags had a problem with that from time to time. New Gen M3 are designed to run fine in HK. Also Lancer AWM mags are good choice there.