Finally fount the micrometer.
M4 bolt = .512 OD at the cam pin
and .101 wall thickness at cam pin
HK bolt = .53 OD at the cam pin
and 1.11 wall thickness at cam pin.
M4 bolt = .101 lug thickness
HK bolt = .101 lug thickness.
Obviously, my eyes decieved me regarding lug thickness, but I was correct about the bolt diameter difference.
Like I said earlier, an M4 bolt fits freely into the MR556 carrier even with gas rings, but the HK bolt will only fit part way into an M4 carrier. It stops just before the cam pin hole is fully inside the carrier. This is caused by the piston ring bore on the inside of the carrier itself.
An examination of the HK bolt and the M4 bolt (noveske) show that the bolt lug joints (angles at the rear of the lugs where they transition from the rear of the lug into the rest of the bolt, a 90 degree transition)) are more radiused on the HK bolt, allowing for better fatigue resistance. Matter of fact, every angle and joint on the HK bolt is radiused, and to a better extent then anything on the DI bolt. Any metal worker will tell you that sharp angles create weak points in your material, and HK seems to have made every attempt to minimise this issue.
Not to beat the nitriding drum, but here are some thoughts regarding a real easy way to PiP the M4 system:
At this time, I have a single HK bolt that has been QPQ nitrided. I had my MR fully QPQ nitrided when I understood that this process imparted better corrosion resistance the chrome, had a lower coefficient of friction then chrome, and penetrated twice as deep as chrome plate adds to the steel. All great things.
What I learned AFTERWARDS, is that nitriding also increases the fatigue strength of the base material by nearly three times as much. Around 270%. Meaning that with the lower coeficient of friction (especially with lube added) between both a QPQ nitrided barrel/barrel extension and bolt, coupled with the increased fatigue strength of the nitriding process, my nitrided bolt should last an easy 20k rounds or more.
Looks like I need to send my spare off for nitriding as well, and I think that I'm going to start having all of my DI parts nitrided too.
At this point, I can't find a single negative aspect of nitriding gun parts.
Best part is that even a single dip nitride will enhance the base material greatly and it's a cheap process and when done in bulk, doesn't add a whole hell of a lot to the overall cost of a rifle.
If this became part of the TDP for Mil guns, I think they would find the overall performance of the M4/M16 platform increase greatly, with very little cost increase.
Last edited by GrumpyM4; 06-06-12 at 18:11.
Reason: Further observations
It is missing the point to think that the martial art is solely in cutting a man down; it is in killing evil. It is in the strategem of killing the evil of one man and giving life to ten thousand -Yagyu Munemori
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