Bills explanation is exactly why I replace a cam pin every 3K rounds.
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Bills explanation is exactly why I replace a cam pin every 3K rounds.
If the bolt is the weak, stressed part, how does replacing the cam pin help? Or do cam pins break too?
Do you mic your cam pins to determine wear? If so, how much do you see across 3,000 rounds? Or do you assume they wear enough to the point that just be safe you replace it?
I don't measure them. I just replace them every 3K along with the extractor w/spring & Crane 0-ring and pin, gas rings, ejector and spring. It may be a bit much but my ARs run very well. These parts are very cheap, so is oil. Usually the cam pins have a lot of finish worn off of them by 3K.
I measure the buffer spring every 3K as well to make sure it isn't below spec. length. If it's too short it's replaced as well.
Bump...
Amazing thread, gents. :)
I was browsing the usual manufacturer's websites and noticed that Patriot Ordnance has a roller-cam-pin that I have not seen before. Could this roller cam pin (coupled with a slightly tighter fit) reduce the stress placed on the cam-pin hole in the bolt?
a shame this kind of thread doesn't happen anymore.
you do realize this thread is 200 years dead and buried right?
i've heard about POF's "advanced" BCGs, but never really investigated.. i'm guessing their cam pin is basically a big bearing? if you can reduce friction between bolt and cam pin, you can reduce erosion of the cam pin/hole (play), which will reduce bolt breakage at the hole, in theory.
bolt breakage at the hole can also be reduced by consistent proper hardening.. the studies ive read about bolt breakage have shown that it takes both play AND uneven tempering to prematurely break a bolt.. but "prematurely" is the key term.
You can buy a chromed cam pin a whole lot cheaper than a roller-gadget. It won't gall like a cheaper, commercial cam pin.
Here's the link to the POF page that has a pic of the roller cam pin:
http://www.pof-usa.com/slideshow/rollercampin.html
A pic is worth a thousand words.
Sinister, would a Hard chrome cam pin and hard chrome bolt be even better? Also, would a hard chrome bolt reduce the pitting that was spoken about?
And, yes I realize that this thread was a dinosaur, Bkb....I just couldn't help myself. :rolleyes: Fountains of knowledge here on this forum, I tell ya!
i wasn't ripping on you, just dissing on you. ;)
i wish they'd show a shot of just the pin itself.. it looks like the only part that "rolls" is the top, which doesn't seem like its gonna help pin/bolt erosion much or even any.. also, that big ass bearing is gonna keep it from being used in DI carriers.
I put one in my National Match rifle when I went from cherry to Distinguished and President's Hundred. I got tired of changing out mil and commercial cam pins as they got all galled up.
bkb00 is right on that the POF roller is on the head and not the body of the pin that cams in the slot. Old school M60 machinegunners had to constantly check the cam area on the operating rod because of the galling. This got me inspecting the pin on M16s/M4s.
I replace my cam pins every 2-3K rounds. Doing this I notice bolt life seems to be a little longer.
answered my own question.. i have a little-used SDMR with a Y/M chrome BCG
this cam pin has exactly 90 rounds on it
http://c2.ac-images.myspacecdn.com/i...61c73f6efd.jpg
http://c1.ac-images.myspacecdn.com/i...225309c1a4.jpg
the bolt hole erosion isn't through the chrome yet, but the carrier marks are definately all the way through
I use the LWRC cam pins. They are indexed and are well heat-treated. Mine look great after beaucoup rounds.
Clint on 68forums sells 8620 cam pins with a good heat treat also.
How many manufactures are using mim pins now?
Anyone seen a Failzero cam pin up close and personal with an acceptable round count on it?
Was wondering if their coating held better than the hard chrome as advertised.
They have a front pointing arrow.
Guys, I got them from LW years ago. I recommend you email them if you don't see them.
What benefit does "indexing" the cam pin provide? It seems obvious that it would ensure that loads (and wear) would always act on the same location of the pin, but does reversing the pin's orientation, thereby varying the bearing surface, and the direction loads are applied, hurt anything??
By keeping it indexed, you are allowing the surfaces to 'mate' with the slot in the bolt carrier.
It should let them take a set and then wear at a reduced rate. If you keep reversing it, then it can never do this.
I see (said the blind man as he picked up his and saw). Allow me to ask two more obscure questions:
1. Is the hardness of the cam pin consistent across it's cross section, or is it it surface-hardened?
2. What are the critieria/ wear tolerances used to determine when a cam pin should be replaced (this may have been answered earlier)?
hardness would depend on the process the manufacturer used but i would suspect that it would surfaced hardened only to avoid the part being too brittle.
iirc the lwrc cam pin was made of pre-hard steel, not sure what but these were originally subcontracted components.
one of the benefits of indexing the pin is a much smoother unlocking. wear on the part should be too great and i have never seen one worn out but i have seen a broken one.
I recently sent an LWRC upper receiver back, and old upper receiver, since one of the screws that held the gas tube on the Bolt Carrier sherred off(yes I know it looks like a gas tube but it is solid and that is what the piston rams against, pushing the BCG back)
I thought it kinda weird but I wanted to simply buy a new BCG to have as a spare and simply send the broken one in for repair. They were not doing that yet, that is selling BCG parts, but said they should be doing that soon (about now.)
That said, my upper reciever came back and I almost could swear it was brand new. Barrel looked great - different gas block for sure and one hell of a great looking BCG - I mean this was different and impressive. Especially impressive at no cost to me and all for a sheared screw. I know some folk rag on them but I find their Customer Support awesome and they do stand behind their product.
Blankwaffe, I'm the gunsmith at FZ. an EXO coated cam pin will not wear like a painted or phos coated part. the coating is nodular structured and will not flake off. instead when mated with an EXO coated carrier, it shows very limited wear. you can see a burnished mark where it makes contact, but even impact does not separate it from the part. we have been an OEM part coating for LWRC rifles since Jan of this year.
Thanks again for the info scrambler.
Ive been eye balling the Failzero BCG for a couple months now...guess I need to get off the wallet and get one to see for myself instead of asking stupid questions all the time.
Are the cam pins and other individual EXO coated parts available as replacements/spares as well?
That's interesting. Given these statistics it is surprising the market isn't glutted with reinforced bolts like the LMT SOPMOD bolt which is thicker at the cam pin hole.