POF gas key and roller cam pin "upgrade" for AR15/AR10 BCGs.

[MCMXI]

I've always preferred rolling vs. scraping/sliding metal to metal contact particularly when the metals in question have significantly different hardness. POF is now offering roller cam pins for AR15s and AR10s. I have a couple of POF ARs (P415 and P308) and for $20 each the roller cam pin is a no brainer so I put them in both. Installation is a drop in since there's no gas key to worry about.

I was impressed with the roller cam pins on both POFs so I decided to upgrade my DPMS DGI bolt carrier group. The DPMS upper only has 383 rounds through it and yet already there's some "damage" (wear) on the upper due to the standard cam pin (damage shown with red arrows).

Installation requires the removal of the factory gas key and installation of the POF gas key which has a clearance "notch" for the new roller cam pin. I torqued the gas key screws to 45 in-lb and staked them in place. The action feels noticeably smoother and I hope that the new cam pin will avoid further damage to the upper. I won't claim to know if the standard cam pin could do sufficient damage to adversely affect the unlocking of the bolt, but for the money, the POF upgrade is cheap insurance plus it decreases drag on the BCG. I suppose I could have used a Dremel to grind a notch in the factory gas key but since the POF key is coated (and the key marks were light) I figured I'd change it out.

 

[R.W.Dale]

Wouldn't reducing friction on this particular part effect cycling speed and force though? In essence making your rifle be a little bit overgassed (assuming it's not undergassed)


That would be my only concern before I buy a couple.

 

[MCMXI]

Wouldn't reducing friction on this particular part effect cycling speed and force though? In essence making your rifle be a little bit overgassed (assuming it's not undergassed)

That's a good point, but variations in buffer springs (length and k value) and buffer weights will most likely outweigh the difference in drag on the bolt carrier group as a result of the roller cam pin. This is obviously a SAWG on my part but regardless, the action is noticeably smoother and there should be less damage to the upper, which may or may not be an issue. Also, once the harder oxide layer (anodizing) is worn off, the rate of wear may increase. I would be interested to know if anyone has ever experienced bolt issues (unlocking) due to wear on the receiver from the standard cam pin.

 

[PercyShelley]

Krochus, I don't think that you'll increase the rearward velocity of the BCG much with this modification. The friction between the cam pin and the upper receiver occurs during the forward movement of the BCG, as this video explains:

http://www.youtube.com/watch?v=6JmIQXkoog8

 

[Tirod]

If the cam pin causes as much of a problem as shown, the firearm wouldn't work at all. Riding the bolt home causes the exact same problem - the magazine spring pressure is so high it won't allow the case to move forward.

The answer is to hold the bolt open, load the magazine, and release the bolt. It will act much more like the higher speed DYNAMICS of the action, and operate the weapon per military instruction.

I have no problem with saying cam pin friction may be a problem in the AR. It is likely just as much a problem when the case is driving the bolt carrier back during the FIRST part of the cycle. As demonstrated, the pin drags then, too, because of the case being pushed out of the chamber from residual gas pressure - which is what cycles the action.

The military instructions for maintenance state to lube the cam pin channel generously, and that is what does work. Carbines have been tested to work for 2,500 rounds run dry as a bone, and 25,000 without cleaning - but lubed generously.

I have no problem with the POF cam pin, but the video and it's assertion is bogus. Lower the magazine spring pressure and the problem is resolved. Use a clock spring that operates with a single set pressure, instead of additive, and the bolt rides home against a single set pressure. No more loading two rounds short - and the entire mag depth can be used, no short stacking because a spring is spiral wound in the way.

It's the inefficient magazine design causing the problem, fix that.

 

[kwelz]

A solution in search of a problem.

 

[MCMXI]

A solution in search of a problem.

Hmmm ... the voice of wisdom ....

 

[kwelz]

I am sorry. I must have missed the Thousands of ARs and M4 failing because of the cam pin. I am all for progressions in technology. But this seems to be more like the Accuwedge than say a B.A.D. device.

 

[Acera]

So many AR guys are intent on "Fixing it until it is broken".

 

[12131]

So many AR guys are intent on "Fixing it until it is broken".

You can count me out.

 

[WarMachine]

Krochus, I don't think that you'll increase the rearward velocity of the BCG much with this modification. The friction between the cam pin and the upper receiver occurs during the forward movement of the BCG, as this video explains:

http://www.youtube.com/watch?v=6JmIQXkoog8

I've seen this video pop up from time to time, and I've been unable to replicate it on ANY AR I've tried it on.

I just pulled my AR out of the safe to try it again, and my BCG moves freely regardless of how much pressure I put on the bolt face. My upper, BCG, and bolt are all BCM.

Has this worked on anyone else's rifle?

I don't have any problems with the POF pin as I'm sure it will work fine. However, I also don't have any issues with the standard pin, that also works fine. And that "wear" will usually progress to a certain point, and then stop. Reminds me of the "flame cutting" debate with revolvers.

 

[Shawn Dodson]

Interesting concept. I'm inclined to let others test ruggedness and reliability of a small roller bearing that's swaged to the cam pin.

Thanks for sharing. Good luck!

 

[PercyShelley]

I've seen this video pop up from time to time, and I've been unable to replicate it on ANY AR I've tried it on.

I just pulled my AR out of the safe to try it again, and my BCG moves freely regardless of how much pressure I put on the bolt face. My upper, BCG, and bolt are all BCM.

Has this worked on anyone else's rifle?

I don't have any problems with the POF pin as I'm sure it will work fine. However, I also don't have any issues with the standard pin, that also works fine. And that "wear" will usually progress to a certain point, and then stop. Reminds me of the "flame cutting" debate with revolvers.

I can replicate it no problem on the Olympic upper. The fundamental cause of the additional friction should be universal to gas operated AR uppers. Whether or not it's enough additional friction to cause failures to feed is another issue.

Here's my reasoning; the amount of additional friction the bolt carrier and cam pin cause by being rotated into the sides of the upper will be a function of how lubricated they are, and by how much friction they encounter stripping a round from the magazine (and the cotangent of the cam track and a bunch of other stuff). This means that for sufficiently slick magazine feed lips there won't be enough additional friction to cause a problem. The AR-15 carrier is fairly heavy, and there's a pretty heavy buffer and a pretty heavy return spring all trying to mash themselves forward, after all.

The AK design goes to pains to avoid this problem. There's a little kink in the cam track which keeps the bolt from being torqued until just before lockup occurs. AK's also had to use magazines from manufacturers with much more erratic quality control than Western industry would consider acceptable. There's also the semi-disposable nature of AR-15 magazines. If you had a magazine that had enough friction in the feed lips to pre-rotate the cam pin and carrier to wedge them and cause a failure to feed, you'd just throw that magazine out. There's a mandrel kit for fixing bent or dented AK magazines; I don't think that Warsaw Pact militaries saw AK mags as being particularly disposable.

Therefore, I conclude that the reason the AK avoids the cam pin friction problem is because it would likely be feeding from such erratically spec-ed magazines that it would have to. The AR-15 is more sensitive to bad magazines, but we throw bad magazines out anyway and don't consider it a big deal.

 

[MCMXI]

I am sorry. I must have missed the Thousands of ARs and M4 failing because of the cam pin.

POF hasn't made that assertion and neither have I. I simply stated that I prefer rolling metal to metal contact rather than sliding. As for the roller cam pin, POF simply states the following:

Reduces friction and drag of the bolt carrier
The roller cam pin rolls as the action moves
The roller cam pin is NP3 coated
The body is Mil-spec hard chrome plated
The pin can operate without the need to lube

This is consistent with POFs main objective ... to build reliable AR rifles that run without lubrication, particularly since many of their customers run the rifles with suppressors attached. POF has been one of the leaders in looking for ways to run the AR platform "dry". The Army has been looking into ways to run the M249 without lubrication since they know that lubrication attracts dirt/dust/carbon etc which can affect reliability.

A roller cam pin may offer increased reliability, particularly if the rifle is being used with a suppressor. Without a suppressor attached, maybe the roller cam pin has marginal benefits. So at worst, all I have is a spare cam pin. On the other hand, if the smoothness of the BCG movement is anything to go by, maybe my ARs will function more reliably. Based on the 42 rounds fired on Sunday from my P308, I think it's the latter, but then again, I'm one of those intent on "Fixing it until it is broken" ... yeah, that's it.

 

[Shawn Dodson]

So at worst, all I have is a spare cam pin.

At worst it can break into pieces.

 

[MCMXI]

At worst it can break into pieces.

Possible but unlikely given that I don't subject my ARs to anything like the abuse that POF puts their test rifles through. All POF rifles are shipping with the roller cam pin now ... they must think fairly highly of it. I have nothing more to add to this thread. I'm pleased thus far with the roller cam pins and if they break or cause problems I'll definitely report back with an update. So let's leave it as no news is good news.

Thanks.