View Full Version : cam pin wear
https://imgur.com/a/ywtf7nK
I have this POF roller cam pin. It seems to be wearing faster than my other cam pins in other BCGs/rifles. Usually I can kinda feel a groove on the cam pin along where the finish is worn. With this it feels like a crack.
How do you know it's time to replace a cam pin?
That roller doesn't do anything. I'd just install a standard milspec cam pin and rock on.
I know the roller won't do anything for the cam pin but it should reduce wear on the upper. Either way, I think you're right. I will just replace it because this is wearing way too fast.
Good idea. If a cam pin breaks in the wrong place, you can get a kaboom. I had an AR-10 do this to me. Wrecked the upper receiver and was not an enjoyable experience for me.
I know the roller won't do anything for the cam pin but it should reduce wear on the upper. Either way, I think you're right. I will just replace it because this is wearing way too fast.
It just seems like another solution in search of a problem. A broken in AR with standard phosphate BCG parts runs slicker than snot. Yeah sure the standard cam pin takes a tiny little chunk out of the upper receiver to create it's own clearance on a brand new gun. Is that a problem? No. The standard parts just flat work.
Page 2 has a picture of upper damage from using the round cam pin in a DI gun https://www.m4carbine.net/showthread.php?203204-POF-Roller-Cam-Upgrade
Page 2 has a picture of upper damage from using the round cam pin in a DI gun https://www.m4carbine.net/showthread.php?203204-POF-Roller-Cam-Upgrade
Thank you for sharing. Looks like the POF roller cam pin is a gimmick.
For piston guns, probably not. You'd have to get a new gas key to use it on a DI gun, that they made a modified gas key so it could be used on a DI gun tells me they are marketing it to DI AR owners.
correct me if i’m wrong but the cam pin is a sacrificial part to be replaced as needed as it wears. this is cheaper and faster than replacing an upper.
constructor
07-10-23, 08:29
correct me if i’m wrong but the cam pin is a sacrificial part to be replaced as needed as it wears. this is cheaper and faster than replacing an upper.
Agree, they are soft(not hardened) to take some of the shock out and help slow down breakage of the bolt at the tail. I believe they were designed long on the side instead of square to distribute the load in the cam pin track.
The Sig Spear LT has a replaceable steel contact patch in the receiver, that is the correct improvement.
I have an H&M Blacknitride+™ treated cam pin as a spare. I did not intend to use it with a phosphate carrier as I presume that would transfer wear to the track. Perhaps I should not use it with a nitride carrier either? Is the nitride case hardening shallow enough to allow the load distribution you describe?
Agree, they are soft(not hardened) . . .
Rockwell C45 to 48 ain't exactly soft.
Rockwell C45 to 48 ain't exactly soft.
Is that a case hardness? Do you have an opinion on the use of a nitride treated cam pin with either a nitride carrier, or mil-spec phosphate? How hard is the cam track on a mil-spec carrier?
constructor
07-10-23, 23:01
Rockwell C45 to 48 ain't exactly soft.
Softer than 60 isn't it?
Here's some for you, try these out and let the rest of us know how things go.
deltateamtactical.com
H&M Nitride Heavy Duty
AR-15 M4 M16 Mil-Spec Cam Pin
Mil-Spec Cam Pin Genuine AR-15/M16 parts made to military specifications by a government contractor.
Nitride finished Rockwell Hardness is 80-85 where QPQ nitride Increases exterior hardness To above chrome
Specs So 3x harder than regular finished cam pins.
These often replaced parts should be replaced or inspected every 5000 rounds
Nitride Cam pin life is 10,000+ rounds 2x that of Phosphate
Isn't the cam pin being "softer" a good thing? That way it it will fail before it start wedging the bolt apart?
constructor
07-11-23, 08:16
Isn't the cam pin being "softer" a good thing? That way it it will fail before it start wedging the bolt apart?
yes......
Is that a case hardness?
No, it is through-hard.
Do you have an opinion on the use of a nitride treated cam pin with either a nitride carrier, or mil-spec phosphate?
Generally, one part should be harder than the other, but if they are equal it's not a big problem it just introduces some uncertainty as to which parts wears faster.
How hard is the cam track on a mil-spec carrier?
It is roughly Rockwell C58 to 63. Nitriding yields similar hardness, that is pretty much limited by the fact it is an steel alloy.
Hi Lysander,
Speaking of cam pin wear, is the wear on the upper receiver an issue overtime on the AR-15?
Just recently I saw a detailed video about the QBZ-191 (https://www.thetruthaboutguns.com/what-a-deep-dive-on-chinas-qbz-191-service-rifle-can-teach-us-about-the-armys-new-xm5/), basically a Chinese piston AR knock off, where they build another lever around to address the cam pin wear (increase longevity) on the upper receiver.
Sounds like over-engineering to me but I'd like to know your experience with the AR.
70608
If you put some oil on the left side of the cam pin head every 1,000 rounds or so, you shouldn't have a problem.
Putting mechanism to lock the bolt forward has been around on many designs since the early 1910s, currently, H&K has been doing it on their designs quite a bit.
Just remember - "More parts = more potential parts to break"
And M16/M4 upper can go at least 36,000 rounds* and not show problematic wear in this area, if properly lubricated.
*Probably more, but, I can't say more, as no test I know of has gone longer than 36,000 round per single weapon.
If you put some oil on the left side of the cam pin head every 1,000 rounds or so, you shouldn't have a problem.
Putting mechanism to lock the bolt forward has been around on many designs since the early 1910s, currently, H&K has been doing it on their designs quite a bit.
Just remember - "More parts = more potential parts to break"
And M16/M4 upper can go at least 36,000 rounds* and not show problematic wear in this area, if properly lubricated.
*Probably more, but, I can't say more, as no test I know of has gone longer than 36,000 round per single weapon.
So it's a trade-off. Either have a required maintenance, or more moving parts. Whatever fits depends on your needs.
There are other things that's interesting:
1. They have completely redesign the retaining pin mechanism and get rid of that "flimsy cotter pin". I think it states in the patent where the cotter pin is only good at a certain spot, or it'll risk falling out, and looking to combine the best of both worlds. Is it true?
70614
2. Not only it's a dual-spring extractor, they're also oblique to it to reduce horizontal movement. Is this what people called "extractor vibration"?
3. it's a four lug design with a fixed ejector.
#1 and #2 sounds skeptical to me, and for #3 I'd think it depends on more factors than just four lugs.
What's your take?
A rather complicated method of retaining the firing pin and still has the disadvantage of having a small separate firing pin retaining which can get lost. Why didn't they just make the retainer pin spring loaded and permanently retained?
A rather complicated method of retaining the firing pin and still has the disadvantage of having a small separate firing pin retaining which can get lost. Why didn't they just make the retainer pin spring loaded and permanently retained?
Bureaucracy decision? Showing off their skills? It feels like they don't trust their troops in the field.
I don't get what they mean by "falling out". Do they want to move it to another location, just to have a more complicated mechanism?
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