Chrome vs phosphate bolts

[lysander]

lysansder always has great info.

Does anyone know if the stuff the Daniel Defense and Microbest use is the TDP plating or is it industrial hard chrome?

The current drawings call for hard chromium plating inside the key, and inside the carrier. These are not highly stressed areas, and would benefit from the retention of oil in microcracks in the plated surface.

Nobody in their right mind would hard chromium plate a bolt. These guys know enough about their business to use some form of TDC.

[ABNAK]

The current drawings call for hard chromium plating inside the key, and inside the carrier. These are not highly stressed areas, and would benefit from the retention of oil in microcracks in the plated surface.

Nobody in their right mind would hard chromium plate a bolt. These guys know enough about their business to use some form of TDC.

I have several bolts (mil-spec, check-the-boxes ones) that I have had hard chrome plated by Metaloy. I talked to Chris once for probably 10 minutes about the process. I was primarily concerned with hydrogen embrittlement at the time. I also have a factory Daniel Defense BCG.

Now, I have very few rounds through any of them compared to some of you folks, but have owned chrome bolts or groups for many years and have never had any issues thus far. Did I put 5K rounds through any one of them? Nope. YMMV of course.....and they certainly are easier to clean!

Back in the early 90's I bought a Smith Enterprises chromed BCG. That unit was swapped to a couple of different guns when I sold the host weapon but wanted to keep the BCG. Maybe a couple thousand rounds overall. No problemo. Once cleaned it looked brand new as you can easily see any black carbon with a satin chrome finish. Mechanically I never had any regrets.

I hold your tech opinions in esteem, so not trying to bicker. Just relaying my personal experiences.

[lysander]

I have several bolts (mil-spec, check-the-boxes ones) that I have had hard chrome plated by Metaloy. I talked to Chris once for probably 10 minutes about the process. I was primarily concerned with hydrogen embrittlement at the time. I also have a factory Daniel Defense BCG.

Now, I have very few rounds through any of them compared to some of you folks, but have owned chrome bolts or groups for many years and have never had any issues thus far. Did I put 5K rounds through any one of them? Nope. YMMV of course.....and they certainly are easier to clean!

Back in the early 90's I bought a Smith Enterprises chromed BCG. That unit was swapped to a couple of different guns when I sold the host weapon but wanted to keep the BCG. Maybe a couple thousand rounds overall. No problemo. Once cleaned it looked brand new as you can easily see any black carbon with a satin chrome finish. Mechanically I never had any regrets.

I hold your tech opinions in esteem, so not trying to bicker. Just relaying my personal experiences.

Chromium plating IAW SAE AMS 2438 - "Plating, Chromium (Thin, Hard, Dense)" or SAE AMS 2460 - "Plating, Chromium"?

It is well known that chromium electroplating is related to the reduction in the fatigue strength of base metal . . . . something that is not an issue with Thin, Dense Chromium Plating.

Effect of Chromium Plating on the Endurance Limit of Steels Used in Aircraft

Effects of surface treatments on the fatigue strength of AISI 4340 aeronautical steel

On the Effect of Hard Chromium Plating on the Fatigue Limit of Steel

Study the Effect of Chrome Coating Thickness to Fatigue Strength of the Axle-Shaped Machine Parts

Fatigue Strength of Chromium-Plated Steel

The effect of chromium plating on the endurance limit of 4340 steel

[ABNAK]

Chromium plating IAW SAE AMS 2438 - "Plating, Chromium (Thin, Hard, Dense)" or SAE AMS 2460 - "Plating, Chromium"?

It is well known that chromium electroplating is related to the reduction in the fatigue strength of base metal . . . . something that is not an issue with Thin, Dense Chromium Plating.

Effect of Chromium Plating on the Endurance Limit of Steels Used in Aircraft

Effects of surface treatments on the fatigue strength of AISI 4340 aeronautical steel

On the Effect of Hard Chromium Plating on the Fatigue Limit of Steel

Study the Effect of Chrome Coating Thickness to Fatigue Strength of the Axle-Shaped Machine Parts

Fatigue Strength of Chromium-Plated Steel

The effect of chromium plating on the endurance limit of 4340 steel

What companies offer the THD coating? PM if you don't want to seem like you're shilling.

[lysander]

What companies offer the THD coating? PM if you don't want to seem like you're shilling.

I don't know, honestly, I have never felt the need for a chrome plated bolt.

But if I did, I would write and ask the company which SAE specification they use to plate, and the plating thickness. I would hope all of them that offer chromed bolts would use SAE AMS 2438 and a thickness between 0.0002 to 0.0005".

If you want a company to plate something with TDC, you can google "thin dense chrome" and get an impressive list of people that do that sort of thing.

[MegademiC]

The microcracks seem to be an issue with NiB as well.

[MegademiC]

I have several carriers that have been fired enough to not have any phosphate left on the contact surfaces. So what is 'holding' the lube there now? (at the places that would benefit from less friction)

Oil will migrate as the parts warms up.

[DG23]

The microcracks seem to be an issue with NiB as well.

Any evidence of that?

[Stickman]

My one Chrome carrier sucks at holding lube compared to phosphate. The finish is just too slick/smooth. I have another Fail Zero finish carrier that's even worse.

I still run the carriers on range toys, but I definitely prefer phosphate for any serious rifle.

I talked to John Noveske about BCGs one night while we were drinking beer and watching a river. When asked what type of BCG he thought was best, he replied phosphate coated "just like God intended".

He was of the same opinion and for the same reasons.

[Stickman]

Any evidence of that?

Are we talking Hydrogen embrittlement with NIB?