HK MR223 failure to feed in cold

[Near miss]

The gas port should measure 1.5mm diameter, the gas vent should also measure 1.5mm diameter. The set up is identical between the MR556 and the HK416 with a 16.5" barrel. Difference between the two is the heat treatment of the barrel and whether the barrel is chrome lined.

The adjustable Norwegian gas block is not set up for the MR556. Normally an adjustable block is not required if the rifle is tuned correctly.

Running M855 ammunition we test these rifles down to -65 Centigrade without problems when the correct artic lubricant is applied. All standard lube must be carefully removed and the firing pin channel is best left dry.

Interesting!
What do you think is the reason then?
Also, do you know how the norwegian 416 was made differently if the gas block is not set up for 556/223 versions?

 

[bill alexander]

Ammunition is the first thought. The HK guns are typically set to use M855 with the pressure curve vs temperature defined for this ammunition. It is sometimes overlooked that the propellant must also be suitable to maintain the gas pressure at the port within the operating limits of the weapon at temperature extremes.

The Norwegian gas block is set for the port size used in those barrels and the ammunition the customer specified. While I have not tested this on an MR556 it is doubtful that it mimics the behavior of the regular gas block. I may be wrong.

 

[Near miss]

Ammunition is the first thought. The HK guns are typically set to use M855 with the pressure curve vs temperature defined for this ammunition. It is sometimes overlooked that the propellant must also be suitable to maintain the gas pressure at the port within the operating limits of the weapon at temperature extremes.

The Norwegian gas block is set for the port size used in those barrels and the ammunition the customer specified. While I have not tested this on an MR556 it is doubtful that it mimics the behavior of the regular gas block. I may be wrong.

Ok, just wanted to make sure you are within the same lines that ammo is the key.

In my opinion/guess, the Norwegians doubtly chose any smaller port hole on their barrels to make it artic so most likely the gas block should be oversize for the drilled hole in my barrel, which should not really be a problem, right? Just my thought process on the matter.

I have good weather now and my friend just bought a brand new LMT 16" for super cheap so a range trip is due. I try to lend a scale that I could take the whole weight of the buffer, I think it is quite interesting to see if it is the standard 5oz weight.

 

[Near miss]

Ok,
I used quite crappy scale but it showed the 50g test weight 50,1g so it is close enough for this job.

And so I have now changed the weight of buffer.
It weighted 149g / 5.26oz.

I took around 8g/123gr of tungsten powder away, the whole amount of the powder in the buffer weighted 117,2g / 4.13oz. It was mostly very small stuff with few bigger granules in it.

The buffer now weights around 141g / 4.97oz

7.1.2023 for archival information:
The buffer most likely was either modified by the previous owner (2 types of tungsten granules, very small and big) but it could be manufacturer error too as it seems HK is really creative with buffer weights. Of course these are different models with different specs. I could not find any unofficial or official knowledge of the A3 buffer weight.

From HKpro forums:
416 AF = 4.50oz (128g)
416 BA = 4.85oz (137g)
MR556A1 = 5.00oz (142g)

So it seems the 141g is probably a good bet.
I have still not ran into any issues.