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9/13/2016 11:59:43 PM EDT
Correct me if I am wrong but it is my understanding that the bolt is kept in the extended position during cycling in way of the cam pin nob kept in the 12 o clock position by the walls of the trough in the upper receiver for the charging handle. If so wouldn't the bolt stop force the bolt to compress on last round bolt hold open which in turn would cause the steel nob to dig into the left side of the aluminum trough? Is that something that would happen? Or is that not how it works at all?
9/14/2016 12:36:57 AM EDT
[#1]
Yes, you are correct.  During counter recoil, the left side of the cam pin head rubs against the left side of the slot in the upper receiver, and the right side of the carrier key rubs against the right side of the slot in the upper receiver. The side loading pressure on these components increases with any resistance to forward movement applied to the bolt, such as feeding rounds from the magazine,  and engagement of the bolt stop.

Luckily, it is not something to be overly worried about. Engineers sized bearing surfaces and limited the cam pin free travel to prevent the cam pin impacts causing any significant damage to the upper.  Lubricate the appropriate surfaces,  and the upper receiver will probably outlast the barrel and bolt a few times.
9/14/2016 1:15:14 PM EDT
[#2]
Thanks. I guess sometimes I just think too much.
9/16/2016 8:51:28 AM EDT
[#3]
If you are losing sleep worrying about wear you could install a roller bearing cam pin. POF offers these as a retro fit kit. Maybe someone else too.



9/16/2016 11:01:07 AM EDT
[#4]
I wasn't worried about the cam pin head dragging on the side of the trough as much as it repeatedly impacting one spot alongside the trough on last round bolt hold open. Thus the smaller bearing surface on the roller bearing would actually have me worry more. Also I'm on DI so correct me if I'm wrong but if I were to use this wouldn't I have to remove the gas key every time I disassemble the BCG?
9/16/2016 12:26:45 PM EDT
[#5]
No, you just notch the gas key a little to allow clearance. I don't use them so I've never had to do it.

This pic shows the clearance notch. I think the POF kit comes with a pre notched gas key to use.

9/16/2016 7:34:47 PM EDT
[#6]
the cam head will ride the interior of the upper, just like the base of the gas key will
the wear is negligible, simply lubricate the weapon in wear locations

Quoted:
Thanks. I guess sometimes I just think too much.
View Quote


i'm down with it, it means you're thinking about how the weapon functions
9/16/2016 8:44:45 PM EDT
[#7]
This is an excellent topic.  For some reason I've never even THOUGHT about how the cam pin and gas key ride in the upper, and how their surfaces bear on the upper's surfaces.
9/20/2016 4:50:12 PM EDT
[#8]
Quote History
Quoted:
This is an excellent topic.  For some reason I've never even THOUGHT about how the cam pin and gas key ride in the upper, and how their surfaces bear on the upper's surfaces.
View Quote


This.
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