Is there any benefit in running the roller cam in a DI carbine?
I know I can't think of any benefit, but POF sells a kit for the DI gun.
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Is there any benefit in running the roller cam in a DI carbine?
I know I can't think of any benefit, but POF sells a kit for the DI gun.
I have one and haven't had any problems with it yet. My action does seem a bit smoother in its operation, however I don't see it as something you should go out and spend the money on with the expectation of it making your carbine "better" or more reliable. I won mine so it cost me nothing.
From strictly a curiousity standpoint, do you believe that your rifle could, would, or could not function if the roller started to fail by becoming loose or whatever, to outright failing with actual parts seperation but remaining captured by the upper housing and carrier, yet still able to cycle perhaps until the next time things are taken apart?
IOW, given that a conventional part can fail too, is the roller plausibly at least reasonably close to 'trustworthy' as the standard cam or even relatively as durable?
Again, strictly curious on your thoughts as I'm not gonna buy one just to find out, but that doesn't mean I don't want to know.
One the earliest original designs had rollers, why would the designer leave them off of following designs if they were necessary?
There's 'neccisary' and there's 'cost effective'.
The two don't always go hand in hand at the manufacturing contract level, nor does the designer have the final say in such things.
He may 'want', but the powers that be will 'have'.
The bearing may or may not have been better, but certainly the pin as it exists now is significantly more cost effective and gets the job done adequately to a level where it doesn't hurt money wise to just toss it at X interval and put in another one.
SI think it would function about like a standard cam pin when it breaks. In all honesty, I cant see the new roller cam breaking as it "appears" to have less visible wear than a standard cam pin I have at the same 5k round count.Quote:
Originally Posted by GTifosi
It does change the wear slightly on the upper where the pin unlocks.
Has anyone ever just machined the wear into the upper?
These pins luckily seem very solid manufactured, the tolerances are something I would never play with and it is well built. In saying that it does seem to have a failure mode that the pin doesn't. That is the roller could come off.
If it locked, then it would maybe take some energy from the bolt group and maybe cause issue with the firing pin, there was a gun called the Hack 7 that had a round (not roller) firing pin that didn't rotate and was problematic.
The square on the standard pin keeps this rotational tendency from happening. The roller cam and a DI system just doesn't sound like a lifelong marriage.
I am scared of cam pins considering that is something thing that could kill you if it were to break.
Quote:
Originally Posted by armatac
The roller could come off, however its no different than the top of a standard pin head shearing off...which I have seen. The roller like any other part could fail, however it appears to be under less stress by design when compared to the standard pins.
Did the head break where the stress relief groove is?
I change them frequently, they get that sinusoidal wave mark on the side, that is where I thought they would break.
I have always thought that the TDP should be tweaked to reduce the cam pin shaft O.D. by about .03" so the bolt would last longer. Bolts sometimes seem to elongate and crack around the cam pin on some high stress guns.
wahoo95, call UVA and tell them that the football team doesn't get cheerleaders next year if they don't start a turnaround.
...But a piston AR company markets a product so it must be better? Naw dude.Quote:
Originally Posted by mikeahe
I, too, own a POF roller cam pin. I havent noticed any significant increase in the smoothness of the unlocking action and while it may reduce stress somewhat... I believe that regular cam pins manufactured by reputable companies have more history of reliable performance behind them than any piston AR company can conceive of. Again, solution searching for a problem IMO.
we're speaking technically here so there's no need to discredit a product by ignorant merits, is FN a stupid piston company,HK? is the AR 180 a stupid piston gun?
Is the Pin HK added to the barrel extension that prevents the extractor from lifting while bolt is in the extension stupid? I truly think that is cool, that bails out so many bad situations with suppressed systems.
The reason I initially tried it was imagining the loss of power when rounds are stripped from higher capacity magazines. The cam head is within the receiver slot at this point and I thought it was worth trying. In the end I don't know if it does anything over a lubed gun because there truly is nothing wrong with the existing pin.
Frank (POF) was one of the first people to apply some of those all too cool coatings to production items and it was from his time in Aerospace, not in this eternally unevolving industry.
I don't think you need to look at the piston line as an enemy breed, it's like you're fighting your brother saying he's totally genetically screwed. Stoner didn't do any more with DI after the project. Our (the AR) weapon is amazingly good because of the work we have done with the TDP, production, processing, and a commitment to making things better. Not because it was inherently the best from the very beginning.
Ok. I get where your coming from, in the technical sense. But, don't you think Stoner might have thought he finally got it the way be wanted it.Quote:
Originally Posted by armatac
The pin in the receiver extention, was not his idea, it was someone else's R&D. Roller cam, coatings,etc... evolving technology from other sources. And wasn't a piston was one of his designs?
I agree with what you on the improvements made in TDP make the modern weapon great, don't you think he did a good job of laying the foundation?
Not arguing, just sayin...
I think DI is one of the best systems, but I really can't tell if that is because we have done such a good job with it , and I too don't want to argue.
AR18/180, is the true parent to modern short stroke/tappet piston guns.
Stoner was around 32 when he did the AR10, he never did another DI system after the 15(retirement exemption with Reed Knight). Piston or DI, and rotating bolt are good parameters for a sound design and what their (stoner/sullivan/freemont) design legacy has shown us.
Sullivan is still alive, and he is not the largest fan of DI. When I read the SAR article I was amazed at how much was just done on a whim but has never ever changed. The .223 round wasn't that well thought out but it does a fine job.
In meeting people in this profession I come across 2 types of thinkers. 1 type is the type that says everything was very well calculated and basically perfect and if we vary we dont know what we are doing because we don't know what they were thinking when they did it originally, the other type is the type that puts all in question and occasionally misses the historical relavance of some designs and where they lead.
They both have their issues. In the end if it works it works. Maybe looking past fouling and kinematics the DI system provides a more reliable cycle from the compressible flow type push of its "piston".
The ultimax is the best gun ever invented hands down(my opinion but that is all that matters in this head).
I would like to get my paws on an ultimax.
But yes, I agree. They were trying new things, and hey, thinking outside the box is what got us to this point. I don't know of any system that is perfect or could stand a few tweaks.
Getting back to topic, I really need to try a roller cam in a DI. Just for my own curiosity.
http://www.youtube.com/watch?v=6JmIQXkoog8
Here is a interesting video, may show a argument for the use of the POF roller cam pin.
I've got a POF roller cam pin in my Ruger SR-556C. The pin's been in the gun pretty much since new and I'm coasting up on 6,000 rounds fired.
The stud or shaft or body or whatever you want to call it has the usual wear patterns from its interaction with the bolt carrier but the roller is looking fine. It is still tight on the shaft with no signs of loosening.
I doubt there's any real benefit from the use of the roller but it doesn't seem to have caused any problems, either. I don't notice any increased smoothness in the action or anything like that. And I've still got a small amount of cam pin drag in my upper.
Quote:
Originally Posted by armatac
The LMT MRP upper has an angled cut in the receiver just behind the cam pin recess.
brent31, yeah that video shows what drag there is, we should see a similar test done with one upper using a lubed cam pin and a roller pin. I'll do it if nobody else hasn't already but I don't really have the time now.
That with a cam like move in the wear area (LMT MRP) apparently. I like, I like a lot. This maybe would help reduce "break-in" wierdness.
I think this is something that just might make the DI even more reliable, atleast it should operate for a longer time if the ultimate failure mode is attributed to the system weakening due to loss of energy.
I did try this in my LMT upper with a POF roller dry and could not get the BCG to bind like it did in the video.Quote:
brent31, yeah that video shows what drag there is, we should see a similar test done with one upper using a lubed cam pin and a roller pin. I'll do it if nobody else hasn't already but I don't really have the time now.
Quote:
Originally Posted by brent31
Can you take a video and post it here?
I can try, won't be till the weekend.
engineering never works like that. Everything is a compromise, and when you're working on a time sensitive project trying to win a military contract that's a part of the compromise. I do think it's a very good system and it really is the first modular adaptive rifle. This roller cam thing is neat, but i'm not interested in beta testing it. :DQuote:
Originally Posted by fixit69
Not this guy again, his "test is full of BS. The AR doesnt work like that. There's this thing called a gas system that provides the P-V work, not gravity or finger movement. Regular cam pins work fine, just replace them at regular intervals. A "smooth" hand cycling AR doesnt mean shit, Ive held plenty of perfectly reliable ARs that hand cycled roughly.Quote:
Originally Posted by brent31
Wouldn't the "gas system" only contribute to function while the BCG is moving to the rear? All the video shows is that pressure on the bolt while moving forward will cause the cam pin to turn slightly causing binding. I just thought it was interesting.Quote:
Originally Posted by vicious_cb
I can't tell what you are referring to,Quote:
Originally Posted by vicious_cb
(feeding)
If you are pushing on the bolt, and pushin on the back of the carrier,(which all AR types do) The cam pin is biased by the inside of the receiver to not allow the bolt to rotate. fact
This is a sliding friction, the part sliding is the lengthways stretch of the cam pin, Friction = coefficient of dynamic frictionXNormal load (normal load is a function of main spring, and cam path),
If you had a pure roller, there isn't really a friction loss in relation to the force supplied by the main spring.
Bearing vs. Bushing
You want to measure if there is a diference? I will give you a test.
Take a Full auto and a cyclic timer. If the roller significantly lowers resistance, the cyclic should go up a bit.
pact might work,
in the end a simple test of taking a cam pin head, pushing and sliding it along anodized aluminum in the long (and thin)direction, versus a roller pin with the roller against the anodized aluminum is the comparison.
guns work, I mean I just think this is something that is a good "upgrade" as it reduces drag. Drag on a working firearm isn't an issue unless it is extremely fouled or something else is wrong. So if this does help the extremely fouled condition I think it is a good idea.
looking forward to seeing some video tests:)
No, I didn't say I was going to do the test. I just proposed it as a way to quantify it.
I have neither the timer or the class three to do it.
Would not the "push" portion that jams the cam pin against the left receiver wall be just for a split second while the bolt interacts with the top round in the magazine? Once the round is stripped from the mag and no longer held by the feed lips, I'd think the force against the bolt and cam pin would be gone. Or at least reduced dramatically. Once the bolt is almost closed and the extractor is being forced over the cartridge rim, the bolt is inside the barrel extension and acting against the extension and cam pin slot rather than the "slop" in the bolt carrier.Quote:
Originally Posted by armatac
You are correct I think (in feeding), the largest force on the receiver from the cam pin would be from initial contact with the cartridge. It would continue to use small some force though until the cam pin actually reaches the cutout in the receiver to rotate, so the total possible drag length would be the distance from initial contact with cartridge in mag to the cutout in the receiver, which should correlate with the bolt head reaching the chamber face.
I'd also guess that intertia would have some affect on this. The bolt's high forward velocity would probably be pushing against the rear of the bolt, causing the cam pin to rotate in the cam pin groove slightly.
This is how I see it.
I have a 12" upper that is run suppressed quite a bit... it is over gassed and it shows it. there is a 1/16" deep groove in the upper from the cam pin.
So,
If I throw in a POF roller cam and just reduce the surface area, there should be reduced wear. Add that the POF cam rolls should also help, but we'll see how long it lasts.
I put roller cam's in all my uppers, some new and some old. I will report back what happens.
Bumping this topic up as I'm seeing a little unusual wear in the cam slot on my Noveske as well. I'm also seeing those not too uncommon ding marks in the buffer too. Both of these make me wonder if everything is "to spec" in my gun. I hope so as I'm still waiting on ATF approval to make this a real SBR.
My carbine buffer did not have the ding marks when running the RRA chrome bolt. ~500-600 rounds. They appeared after swapping in an unknown manufacturer's H buffer and an LMT bolt. Hmm, soft aluminum crappy Chinese knock off H buffer maybe?
Both bolts "look" fine. No sharp edges or burs on the cam pin nor near the rear buffer retention pin slot.
Yep, not worried much about the buffer, more worried about the marks in the upper's cam slot. Pic:
http://tapatalk.com/mu/4609648b-fbf2-8d56.jpg
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