I just put together a PSA upper and a DSA  complete NiB coated bolt carrier and NiB coated charging handle, the thing is tight as hell, to tight work the bolt carrier with the charging handle, so I swapped out the entire carrier assembly with one from another rifle (no NiB coating) it works great, from there I swapped out parts with the new bolt carrier and they worked until I got to the new gas key.

The new NiB coated gas key refuses to mate up to the gas tube of any of my rifles, (as far as I can tell the alignment of the gas tube and key are fine) I found a unused gas key in my spare parts and put it on the new NiB coated carrier and it works great.

Anybody else had problems with coated or plated gas keys / bolt carriers? Thanks for your help!

That is a problem I have read about that can occur with NiB "coatings" that were not correctly applied.  Since you state that the alignment looks fine the coating is the likely suspect.

I only run black nitride bcg's.

Ok, thanks for your help Dano. So far this rifle runs fine for the ten shots put through it in the back pasture.  One last thing, not sure if this matters but the coating is NP3 not NiB , not sure what the difference is. Thanks again.

MyakkaVice,

I think that I just experienced the same undersized ID issue on the gas key with a NiB (Nickel Boron) coating BCG.  Non-firing tests revealed nothing out of the ordinary, including the headspace.  Added a little FireClean and everything moved smooth as glass.  Several  5.55mm rounds were then fired through the carbine length gas system on the Daniel Defense barrel without issue.  The initial function testing went as planned.

I then added an AAC 762-SDN-6 suppressor to the 51T muzzle brake on the end, and fired downrange.  Once.  The next round was stripped off the magazine as expected, but the bolt carrier did not chamber fully.  It stopped just short of the bolt entering the locking lugs on the barrel extension.  It was jammed up pretty good, and fortunately I was able to use brute force on the charging and a little more FireClean to eventually retract the BCG.  Tapping it out using a dowel down the barrel on a live round was not an option.  Word to the wise:  Buy quality 7075 T6 charging handles.

I removed the bolt from the NiB BCG and moved it forward slowly to determine the problem.  It was making contact and stopping a short distance after entering the gas key.  I pulled the NiB BCG out and then tried two BCM phosphate coated BCGs, actuating them by hand.  These freely moved in/out and the bolts locked up without any issue.  I have not removed the FSB to measure the actual size of gas port on the DD barrel, but my past readings indicate that Daniel Defense doesn’t drill oversize gas ports that lead to overgassed systems.  This is one reason I went with the DD barrel.  And there is no apparent misalignment of the gas tube in the receiver or the gas key on the carrier.

Here is my theory.   I suspect that the "as-manufactured" ID of NiB coated gas key was slightly larger than the OD of the stainless steel gas tube when I started, and it worked fine for 5.56mm under normal pressures.  As soon as I added the suppressor and fired, I believe that the gas tube expanded in the gas key ever so slightly due to the increased back pressure from the addition of the suppressor, and the new outer diameter (OD) at the end of the gas tube is now just large enough that it cannot completely enter the gas key that has an undersize ID due to the NiB coating.  And I further theorize that the gas keys on any of my standard phosphate coated BCGs still should work because the phosphate coating didn’t reduce these gas keys’ ID as much as the NiB coating may have done, allowing more variability in the tolerances of the gas tube’s OD.  Does this hypothesis seem reasonable?

I am hoping to get out to the range and try again this weekend with one of the BCM phosphate coated BCGs inserted.  And I’ll use a magazine to load and fire one shot at a time so the magazine will lock the BCG back after each firing.  This will allow me to inspect the system thoroughly after each test firing and move the BCG forward by hand (and without another live round in the chamber) so I can prove out my theory without jamming the BCG again.

Redhawk34

Dano nailed it. The coating takes up all the tolerance. My NIB BCG was tight as hell when I got it, but after racking it probably a hundred times it started to work smoothly. And its even smoother now that I have 200 or so rounds on it. Keep it well lubricated as well once you get it to where itll actually cycle the action