AR bolt assy question, plain, chrome, or TiNo

A

AmericanFreeBird

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I've seen a variety of AR bolt assy's available some just blued or parkerized, some chrome plated, and some Titainium-Nitride plated. The Titainium variety are the most costly for sure.

What are the benefits of the Ti over the Chrome over the plain jane variety? is there really a big difference?

AFB
 
You also see TiN coated 1911 barrel bushings and M14 gas pistons and other parts. The purpose is to reduce wear. TiN is very hard, and a hard surface has better lubricity against a softer material if they are both smooth. Make no mistake, however, if the TiN job was done properly, you are moving virtually all the wear from the bolt to the upper, and I can't see how that helps your wallet in the long run.

I would stay with carbon steel parts and get them cryo-treated. This can double wear life on chrome-moly steels. With stainless the improvement is only about 20%, so the cost becomes a questionable investment with SS.

Then I would apply a semi-permanent lube, like Plate+. A 72 hour soak for the bolt and for the upper up to the bolt lugs (keep this out of the chamber - there's some unsettled controversy about the effect of lubricated chambers on boltface thrust, so for now, just err on the side of not doing it). Another product is MolyFusion from Shooter's solutions. It will go on in 20 minutes with added heat (hairdryer level heat). You could also try Mil-comms' TW3000, the gattling gun lube, or maybe better still on proven wear prevention would be Microlon gun juice. These last two are Teflon based. All provide some corrosion resistance, substantially reduce wear, and continue to lubricate even in the absence of oil.

Nick
 
if the TiN job was done properly, you are moving virtually all the wear from the bolt to the upper, and I can't see how that helps your wallet in the long run.
Click to expand...
The AR15 bolt does not touch the upper receiver.
 
Correct. I was being sloppily brief, but my point remains that I don't see the advantage of moving the wear from the bolt to the bolt carrier and the locking lugs in the barrel extention, all of which reside in the upper (though the latter are of less concern, since the barrel will likely have to be replaced before the bolt carrier goes).

My apologies.

Nick
 
The bolt is fine as issued. If you wish to go hard chromed that will be fine, but I doubt you'll wear out the standard bolt.

The new trend in competition is to have a lightened reciprocating mass (bolt) hence the titanium, but this is a small gain, often at the price of reliability. Hard chrome is just easier to clean and resistent to wear (although it will chip)

Spend your money on a good barrel, trigger and a free float tube. All you need to shoot tight and/or compete.
 
The new trend in competition is to have a lightened reciprocating mass (bolt) hence the titanium
Click to expand...
The "Ti" coating AFB referred to is a gold colored coating called TiN. It's like hard chrome but different. Hence it alone has no effect on carrier mass. The only lightened carriers I'm aware of are the new JP SS, the old JP aluminum (anodized), and the MSTN hard-chrome.

According to Paul E @ MSTN, competition was not the original source of the lightened bolt carrier idea. I believe he said it originated in NSW for faster follow-up shots, but was canned because it caused supply problems.
 
Unclenick, cryo treatment doubles the wear on crome-moly steel ???? No way.As a metallurgist I have been researching cryo for a long time.Most of the claims are BS. Stick to proven things like hard chrome and don't listen to the hype from companies that do cryo.
 
Well thanks for the advice and information gentlemen, I wen't ahead and ordered me a plain-jane parkerized assembly. Being a "clean freak" anyway, I don't find cleaning to be a problem as I usually clean the crap out of every peice I own. Chrome just wasn't worth the extra $$$s for me to justify. This piece shoots really accurate for me.

BTW, if you ever get the chance to buy a bolt-carrier assy. from model one sales, DON'T :barf: . They are crap. This one I have is brandy new and the extractor spring is weak and causes stovepipe jamms and hanging brass problems. I'd stick with the more expensive DPMS or Rock River brands.

AFB
 
If you want a clean bolt...try Carbon Cutter from the Slip 2000 people

Soak it for a hour and it ends up looking like new

And it is totally non-toxic
 
Camp Perry Trip

AFB:
I popped up to Commercial Row at Camp Perry yesterday, and lo-and-behold, DPMS Panther had titanium nitride (TiN) coated bolt carriers, too. You get your choice. Frank White at Compass Lake Engineering (who built my Bushmaster-based match mouse gun) sells each barrel with a matching bolt. I value that pairing over any surface treatment.

Mete:
See:
Meng. F., et. al., Role of Eta-Carbide Precipitation in the Wear Resistance Improvement of Fe-12Cr-Mo-V-1.4C Tool Steel by Cryogenic Treatment, ISIJ International, Vol. 34, No. 2, p 205-210, 1994.

Nick
 
Unclenick, yes I,ve read that .It's ridiculous to try to extend what's happening in a complex high alloy tool steel to what's happening in 4140 .Even at that the effect of eta carbides has not been thoroughly proven.On another forum I had an exchange with a metallurgist in one of the companies that does cryo.The question was -where is the all research to prove all the claimed benefits of cryo ? He couldn't give us anything beyond the paper you mention.So I stand by my statement -most of it is hype !!!
 
Just my .02, but I use Smith Enterprises hard-chromed bolts and carriers in my ARs. The main reason is that in my experience it seems that carbon does not stick to them as much and clean up/maintenance is easier. For lubrication, I've switched over to MD Labs XF-7 for everything.

Denny
 
Mete,

This controversy is interesting, since it should be fairly easy just to test. The commercial operators (who obviously have an interest in these cryo treatment claims being true) are all full of testimonials of multiple life expectancies on everything from drills and saws (the high alloy tool steels you mention) to brake rotors on police cars brakes (not-so-fancy casting alloy).

What had caught my attention originally is information no longer on Delstar's web site. Delstar never did cryo treatment themselves, but had published information on it for awhile since they were doing it to their Accumax barrels at the time. The page I remember listed stainless steels in general as showing 20% increase in wear, and chrome-moly getting the doubling of wear effect. I gave this claim some credence because Sierra ballistician Kevin Thomas had published an article in Precision Shooting in which he had shot out several test barrels by infiltrating them into Sierra's normal bullet QA testing program, some cryo treated, some not, but all stainless steel. He observed a barrel life extension, if I am recalling correctly, from about 3500 rounds to about 4000 rounds, or a little over 14%. I viewed this as close enough to that 20% claim for cryo treated SS in general to make it plausible. A good enough correlation, in other words. The test chambering was .308, I believe, firing the Sierra 168 grain Matchkings over their standard test loading. It also would seem to confirm there is at least some wear improvement effect on any heat treatable steel, confirming the view of cryo treatment is an extension of the heat treating process, and not just for high alloy tool steels.

Several sites also reference work by an R.F. Barron at Louisiana Polytechnic. Do you know anything out about this player and whether he is legitimately credentialed?

Nick
 
I'm not familiar with Barron. The NRA tests were inconclusive.Some custom barrel makers said it does nothing [they would have an interest in making a more accurate barrel], some said it doesn't do anything but would cryo the barrel on request, and Krieger says it's wonderful but they have cryo equipment .The Benelli website has photos of the microstucture of cryoed and un cryoed barrels which is total nonsense [I have nothing against Benelli in general ,I'm very happy with my Benelli].I'm willing to learn but I'd like to see real research whether it is for guns , knives or anything else.
 
Mete,

The problem (and this spills over indirectly to another thread on the poor economics of gunsmithing) is that nobody but the military is well-positioned to do a statistically significant study. Kevin Thomas only had three firing points in his study at Sierra, and even then it took some months for all those thousands of identical rounds to make it through his test barrels. Statisticians don't like any sample size under 21+ to draw conclusions from. We would need that many guns shooting out that many control barrels, all using the same lot of ammunition and testing both for group size and longevity. Then we'd need another otherwise-identical set of cryo treated replacement barrels shot the same way to test barrel life and comparative accuracy, also fired with that same lot of ammunition.

For sliding, though, it ought to be easy enough to test with some kind of unlubricated reciprocating piston arrangement. If fact, you would think just measurements looking for decrease in the coefficients of friction or an increase in yield or an increase in the thermal conductivity of the treated metal would be pretty good indicators of whether wear resistance increase had occurred or not? Most university engineering departments can measure the first two, while their physics lab might be equipped for the latter; if not, a bell jar k-testing apparatus isn't that hard to build. Now that you've alerted me to the fact cryo treatment is controversial among metallurgists, I'm thinking of looking into that. For a lone experimenter it sure beats footing the bill for 42+ barrels, cryo-treatment for half of them, and a lot of a couple hundred thousand rounds of ammunition to shoot them out with.

Nick
 
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