I’m considering getting a hard chromed bcg or a nickel boron one. My question is to those who have experiences with them, which do you prefer? Positives and negatives for each one is welcome.

Phosphate, Geissele nano coating, hard chrome, and NP3 are the only coatings worth considering IMO.

Between nickel boron & hard chrome - I would choose hard chrome.

Nickle boron is "slick" but it is a coating that will show wear & stains if not cleaned frequently.

Hard chrome won't stain.  The chrome is hard and will give a long life of service.

Phosphate also is fine - oil it frequently (as an AR should be)

Phosphates BCGs are hard chromed on the inside surface which makes a smooth surface for wear.  The phosphate surface will hold some lubricant, but again, run an AR "wet" unless there is some extreme environment which precludes doing so.

Nitrided can be good, but look to the inside surface where the gas rings move to see if it is glass smooth or still shows machine marks & ridges. Rough surface inside the Carrier will accelerate wear on the gas rings. While replacing gas rings is both cheap & easy, I'd rather not have imperfections that cause them to wear prematurely.

Bigger_Hammer

This. Avoid boron

Chrome, of the two for me as well.

Hard chrome for me.

Centurion Arms sandcutter

I have both blem and non blem sandcutters and I cant say enough good things about Centurion Arms, their products, and the owner.

I’ve seen the Centurion Arms sandcutter Bolt carrier. Very interesting!

This is the nicest BCG for the money that I’ve ever encountered. Expected to be back in stock later this week. My first choice is Geissele REBCG but they cost 3x as much. https://www.wcarmory.com/microbest-bcg-556-chrome-phos-extract-c158-mpi.htm

Nickel boron stains and tarnishes from heat and carbon. It’s also too slick to ensure a tight fit with gas rings. Nitride is good but also too slick for firm fitting gas rings.

My vote is definitely hard chrome. It doesn’t stain/discolor and also isn’t shiny.

Phosphate or hard chrome, skip nitride or any of the nickel plating

I was in the phosphate camp and still have quite a few, but going forward I'll probably buy all microbest chrome. They're not much more when considering the cost of the gun. They clean up easy after suppressed fire (not that phosphate is hard). For the extra few bucks, that's my current go to for personal ARs.

I used phosphate (colt, toolcraft) and hard chrome (microbest). I prefer the hard chrome. Geissele rebcg or Lmt enhanced would be in play also.

Oil shedding coatings on a bearing surface that requires oil is one of the biggest dumbass moments in AR manufacturing history. NB, nitride, gloss TIN, they’re stupid for a carrier.

Matte hard chrome is perfect, because it cleans up easily but is not made to shed oil. NP3 is also made to have a matte finish that retains oil while still being easier to clean. If I was to really nit pick, I’d say phosphate holds oil too well so it stays in the places that don’t need it.

A hard chrome carrier will look like it was dunked in a construction site porta potty after hundreds of rounds, but it will stay wet longest where it needs it in my experience.

There are 4 (steel) contact points sliding in an aluminum receiver.  What is a harder coating on the whole carrier going to do?

Other than for clean up reasons.  I see no point in anything other than standard phosphate.

This.

I have many regular 'mil-spec' Phosphate carriers from Colt, AO Enterprises, and DPMS. More than one for sure from each different brand...

They all work fine and I honestly can't tell any of them apart from each other than noticing / looking for a special mfg mark that might (or might not) be here or there from one mfg to the other. Specifically talking about stuff one would normally be able to see right away like the staking on the gas key and the overall finish of the machining on the carrier on the different contact surfaces.

When I say contact surfaces - Am meaning the rails that slide inside the upper, the bottom at the back that contacts (and cocks) the hammer, the finish inside the gas key and the bore for the bolt, etc.

Considering that my sample size of each is what it is - I can't tell a noticeably visible difference between any of them. Noticeably visible differences that would not need a bore scope to spot but would otherwise be seen...




Comparing the finish (where parts move and stuff slides) of any of that sort of 'mil-spec' stuff to a Toolcraft NiB carrier assembly is noticeable to me.









I can actually see that Toolcraft polished a lot of stuff before they applied the particular coating.





I am NOT suggesting that any of that extra 'polishing' before coating was 'needed', or going to get off into of the 'if' it may have been an 'improvement' or not garbage but...

I DO like it.



The Colt part in this picture clearly has the finish that it does to be better able to 'hold lube'. That has got to be the superior part...
even though both are within 'spec'.

As others have stated NiB is not a good finish for bolt carrier groups. If going fancy, get chrome. If not, plain old Toolcraft nitride is good to go.

You'll see a lot of people regurgitate nitride carriers having looser bores and nitride bolts being brittle. That was the case in the early days when manufacturers were simply nitriding a milspec carrier and 9310 was just coming out for bolts. Not the case anymore, at least with Toolcraft.

Brown bomber who is an industry metallurgist has a good write up on how nitride is completely incompatible with 9310. I was skeptical until I searched out broken 9310 bolts. There’s literally hundreds upon hundreds of accounts of them breaking prematurely on Reddit.

After owning a couple of the "exotic" finished BCG's over the years (NiB, TiN, NP3), I've come down to the conclusion that either phosphate or chrome are what I like best.

I wanna say that's it's been well established that NiB and TiN are no-go's, but NP3 is still pretty popular with people still clamoring over the Sionics and FCD offerings. My experience with them is that, while yes they do clean up very nicely, they also shed lube very quickly.

My last Sionics NP3 carrier has been relegated to my 18" SPR because it sees far lower strings of fire. Outside of that, the majority of what I own is plain ol phosphate and a couple chrome units, with one being the Centurion, which is pretty sweet.

Just finished a class (1000 rounds total) with a sionics carrier (NP3) and did not have any issues with shedding lube.  That being said, I use ALG VTG for lube, so its a *little* bit thicker.  I also lube the rails to the point where there is a good coating of lube where the carrier rails touch the upper receiver.  When you lock the bolt back, you can see trails of lube where they've contacted the upper.  This is how I have always lubed the AR15, so its not something I've had to change due to the carrier being NP3.

Cleans up with a paper towel, and absolutely no issues with lube slinging off....and if it did, it slung off from spots where it didn't really need to be, so I couldn't tell a difference.

To be honest though, most carriers will lose their coating where the rails ride against the upper anyways, so at least in that critical area, it shouldn't really matter for very long even if it doesn't hold.  

Otherwise, I agree.  Chrome or Phosphate.  Tried the others, found them to be a bust.  But NP3 has done well for me!

There is zero logic behind desiring a rougher surface to hold lube. It's asinine.

I use outboard motor/assembly lube by Lubriplate on my BCG's. It stays put. Another option is Phil Wood's chain lube.

I buy G.I. phosphate BCG's as a rule. The only chrome BCG's I own are in AR-15 M-16 clone rifles for that early 60's vibe.