HK417 design fault

[willo]

Anyone familiar with the H&K 417 16inch recce model. A good all rnd versatile platform albeit with some design faults. The bolt houses two ejector posts which are exposed by two open ports on the bolt unit located between the locking lugs. The rifle is designed around a direct impingement system for gas regulation which typically means less fouling in the receiver group. H&K marketed heavily on this however the inclusion of grooves in the chamber to assist with cartridge extraction allows excessive and rapid build up of carbon fouling onto the forward area of the receiver group to include the open ports to the ejector posts.

The result is a malfunction typically known as a 'stovepipe' stoppage in as little as 500rnds due to excessive carbon build up on the ejector post and accompanying springs.

Anyone familiar with this happening? It is particularly evident during colder temperature as the carbon fouling is less viscous.

 

[.30US]

I'm not real familiar with the 417, but have an issued 416 next to me. I'm a little confused by your post. Can you post some photos identifying what you're talking about? Unless I'm really off on the 417, it was designed, like the 416, around a short-stroke piston system rather than a direct impingement gas system. I'm assuming there are differences in the 416 and 417, as I've put tens of thousands of rounds through my work rifle in poor conditions with minimal affect.

 

[willo]

Yes you are right, apologies for the confusion, I meant to write short stroke, the 417 is the same as the 416 in this regards......don't ask me why but must have had direct inpingement on the mind as I was typing.......should have checked before posting.

Nonetheless the problem remains the same. I've attached some pics

 

[.30US]

Definitely different than my 416. I don't have the two holes on my bolt like that. We don't have any 417s here, but I'll ask around to see if any of the guys that went through the Crane course had any experience with it.

 

[willo]

The problem is easily rectified by cleaning the posts and accompanying springs however this requires special tools which most end users don't carry and is definitely not the maintenance you want to be carrying out in the field due to the chance of loosing a number of small components.

A full bolt strip is the only answer which means workshop attention. I can only imagine the ports are in place to allow for lubrication?? however due to the rapid build up of carbon on this part of the bolt, the ports and internal ejectors very quickly become constricted. First signs of the ejectors not functioning correctly are seen as expended rounds begin to fall closer to the ejection port and not the usual 1.5-2 meters at the 2 o'clock.

You notice on the attached the picture the expended cartridge has distinct linear carbon traces from the neck to case head. This is evidence of the grooves within the chamber which allows the excessive gas to be pushes back onto the front portion of the bolt group and upper receiver.

I've seen 20inch 417's with bolt units without the ports and as you say the 416's don't have the ports either. I have seen other AR's with this type of port however. Any idea as to the purpose of this design would be helpful and out of curiosity does your 416 have similar grooves in the chamber?