Marking cam pins?

[Dr. Bullseye]

I didn't bring them up as a topic of discussion, I brought it up to give them a frame of reference as to why they shouldn't be concerned with your opinion or remarks. No one cares if you mark your cam pins or not, and no one has said you had to. Go back and read Ned's post, or don't, and continue on ignoring the facts that have been laid out in front of you by them.

Just so we are on the same page, copy and past just the facts you mention in your next post, please.

[Dr. Bullseye]

I didn't bring them up as a topic of discussion, I brought it up to give them a frame of reference as to why they shouldn't be concerned with your opinion or remarks. No one cares if you mark your cam pins or not, and no one has said you had to. Go back and read Ned's post, or don't, and continue on ignoring the facts that have been laid out in front of you by them.

Well then, as a frame of reference, what was your experience with Ultradynes since you are an expert?

[Ned Christiansen]

I can't help but agree that some data would be nice..... right now it's just logic and theory, but pretty strong in those areas-- but that's just my opinion.

Thing is, to get actual data on this or anything takes a tremendous amount of time and money, same as with any of the many other incremental, theoretical improvements that we fuss over at times (that applies to gun people car performance people, bike / bicycle people, et al).

So my take is "can't hurt, might help". For you guys talking about marking your own, I would absolutely not do it with a punch, don't go hitting a hardened part with a hardened tool. Dremel a little arrow into it, or a dot or something, lightly.

[Disciple]

I have done extensive testing using custom ground gage pins to track when wear becomes a concern. Some people have a philosophy where they shoot until something breaks or fails. I like to know before something breaks or fails so I can avoid a catastrophic malfunction.

It sounds like there is data, but it did not originate free of cost and there is no obligation to freely provide it. I am grateful that he gave the free tip to mark cam pins. I could not ask for more.

[nightchief]

I can't help but agree that some data would be nice..... right now it's just logic and theory, but pretty strong in those areas-- but that's just my opinion.

Thing is, to get actual data on this or anything takes a tremendous amount of time and money, same as with any of the many other incremental, theoretical improvements that we fuss over at times (that applies to gun people car performance people, bike / bicycle people, et al).

So my take is "can't hurt, might help". For you guys talking about marking your own, I would absolutely not do it with a punch, don't go hitting a hardened part with a hardened tool. Dremel a little arrow into it, or a dot or something, lightly.

Oops. Guess I'll be replacing the cam pin sooner than later.

[sinister]

You can buy very hard chrome bolt cam pins. NP3 eventually wears.

I've seen literally hundreds (if not thousands) of M16s and M4s that will eventually need new bolts and cam pins. I've broken two bolts in over 40 years of shooting the M16/M4 family -- one to sheared lugs and one separating at the cam pin hole on an SF CQB School student carbine with an unknown and ungodly round count.

Machines eventually need high-wear part replacement. Nothing designed to function with high-stress and high-pressure parts lasts forever.

[lysander]

All, I can say is: "Congratulation" to the two guys that thought this up.

Given the tolerances between the pin and the cam slot, and how much wear you are going to see before tossing the cam pin, and the fact that the cam slot is a 45 degree helix, your saving nothing.

The cam slot is a 45 degree helix and symmetrical, other than the length of the straight sections. That means the major contact area on the cam pin is at 45 degrees on the front side (unlocking), and the minor wear area is at 45 degrees on the back side (locking).

Guess what happens if you rotate the cam pin 180 degrees? The two contact areas switch sided, but the area that contacts remains the same.

Keeping the cam pin in one orientation would theoretically half the life, but realistically, I don't think it matters one wit.

[VLODPG]

There is always a lot of controversy about the videos and content from my courses. It's not intentional, nor am I offended if people politely disagree.

Marking the cam pin has less to do with saving the life of the cam pin and more to do with extending the life of the bolt.

The more you do to minimize wear and slop between the bolt and cam pin, the longer the bolt should last.

When you allow excessive amounts of slop between the cam pin and the bolt, you increase the chance of stretching or breaking the thin webbing at the edges of the cam pin bore.

I have done extensive testing using custom ground gage pins to track when wear becomes a concern. Some people have a philosophy where they shoot until something breaks or fails. I like to know before something breaks or fails so I can avoid a catastrophic malfunction.

FWIW, I mark my cam pins with a starter drill bit.

Thank you for the explanation. I just received my PA back in stock notification for the FCD cam pins to go along with my new bolt heads.

Edit: Thanks Chad,Roger and Ned for your sharing your valuable input.

[jerrysimons]

All, I can say is: "Congratulation" to the two guys that thought this up.

Given the tolerances between the pin and the cam slot, and how much wear you are going to see before tossing the cam pin, and the fact that the cam slot is a 45 degree helix, your saving nothing.

The cam slot is a 45 degree helix and symmetrical, other than the length of the straight sections. That means the major contact area on the cam pin is at 45 degrees on the front side (unlocking), and the minor wear area is at 45 degrees on the back side (locking).

Guess what happens if you rotate the cam pin 180 degrees? The two contact areas switch sided, but the area that contacts remains the same.

Keeping the cam pin in one orientation would theoretically half the life, but realistically, I don't think it matters one wit.

The contact points of the bolt carrier cam track on the cam pin thats wears the grooves into the cam pin flips around with the cam pin, sure (whatever its shape), but the focus of the SOTAR cam pin is eliminating the shock loading that happens with the pivoting of the cam pin inside the bolt at the extremes of movement (the staring and starting and stopping) by taking up the slop usually made by the space double sided grooves form. That pivoting movement functions to pry the bolt apart at its weak point as the assembly is jerked back and forth. Equating the way a single side of the cam pin is marked by the carrier cam pin pathway with how the forces inside the assembly interact at the extremes of its range of motion is flawed.
Half the life? Hardly! Nobody here is making that type of claim for a gain. It's in error to claim that magnitude to its detriment.

[lysander]

The contact points of the bolt carrier cam track on the cam pin thats wears the grooves into the cam pin flips around with the cam pin, sure (whatever its shape), but the focus of the SOTAR cam pin is eliminating the shock loading that happens with the pivoting of the cam pin inside the bolt at the extremes of movement (the staring and starting and stopping) by taking up the slop usually made by the space double sided grooves form. That pivoting movement functions to pry the bolt apart at its weak point as the assembly is jerked back and forth. Equating the way a single side of the cam pin is marked by the carrier cam pin pathway with how the forces inside the assembly interact at the extremes of its range of motion is flawed.
Half the life? Hardly! Nobody here is making that type of claim for a gain. It's in error to claim that magnitude to its detriment.

There is an error in your logic.

The cam angles for locking and unlocking are equal, the bolt carrier is a cylinder and the cam pin is a cylinder. This means the contact areas as the pin moves forward are exactly the same as the contact areas as the pin moves backwards only rotated 180 degrees. That means the wear areas are exactly the same.

The increase "slop" is caused by and increase in clearance between the parts, so if you want to reduce your shock loading, you want to reduce the amount of wear. The pin is softer than the carrier so most all the wear in on the pin.

The loading during the unlocking camming is much greater that the loading during locking camming, therefore the "front" of the pin will wear faster than the "back". If you keep one side towards the front all the time, the front wear will accumulate faster than the back. If you switch pin orientation regularly, or randomly, the wear will be distributed equally on the front and the back of the pin, so on average the amount of wear on any one face will be less.

Also, the cam pin does not bottom out in the cam track during locking, the carrier stops on contact with the barrel extension well before the pin reaches the back end of the cam slot, so this side doesn't wear at all. The highest load on the cam pin is at the end of unlocking when the pin bottoms out at the front of the cam slot. Again, randomly switching the orientation of the cam pin will reduce the wear on any one side.

If you want to reduce the loads on the hole in the bolt, the way to achieve that is find a way to reduce the amount of wear on the face of the cam pin that faces forward. Flipping it 180 degrees every now and again is a better way to do that than leaving one face always facing forward....

Personally, I think liberal use of a good lubricant in the cam slot is a most cost effective way of achieving the desired end.