CAM PIN HITTING CHARGING HANDLE, ok or not ok?

[brettskywalker]

I just noticed this last week when cleaning my rifle. I was wiping down the charging handle & noticed wear marks on it where the gas key hole is. The wear marks are NOT in the hole for the gas key, but above the hole on the inside, where the metal makes a 90 degree turn from vertical to horizontal. I put the CH & bolt in the upper & found when the BCG is in its forwardmost position the cam pin is hitting that part of the charging handle. Is this a normal wear spot or is something out of whack?? No failures of any type last time at the range, or the time before that, or the time before that & so on

 

[Plazzman]

I just looked at my AR and have not noticed any wear on the charging handle from the cam pin. Have shot many rounds through it. I am sure someone will come up with the answer you are looking for.

 

[WR Moore]

If the wear spot you refer to is at the forward end of the charging handle on the inside of the closed end of the charging handle, it's normal. Exactly how do you think the charging handle retracts the bolt carrier group (BCG)?

Would you please buy Patrick Sweeney's book?

 

[brettskywalker]

Yes that is the spot im talking about. It just raised some concern because i never noticed until last week. When i did a basic function test pulling the CH back it grabs the carrier at the base of the gas key. The marks on the CH are at the top where its almost a 90 degree turn going from vertical to horizontal. I ll take a picture & post it in a minute.

 

[brettskywalker]

Ok here are 2 pics of the spot. The toothpick is pointed directly at the side that appeared the most worn, in the 2nd pic the affected area is directly to the left of the toothpick. If this is normal so be it. But the side i pointed to in the 1st pic showed more wear or damage than the other side. It almost looked like that side had been hammered on causing the aluminum to fold OVER the outside edge of the CH. I took a jewlers file & ran it parallel to the outside edge of the CH & took a very small amount of material off of those spots

 

[brettskywalker]

I mentioned in another thread that im new to the FORUM, not new m4 & ar15 rifles. If some1 doesnt know the charging handle pull the bcg back they are the people that need to buy sweeneys book. I wouldnt mind if some1 bought for me though.

 

[eschoendorff]

If the wear spot you refer to is at the forward end of the charging handle on the inside of the closed end of the charging handle, it's normal. Exactly how do you think the charging handle retracts the bolt carrier group (BCG)?

Would you please buy Patrick Sweeney's book?

Why? The book isn't THAT spectacular. If you cannot ask questions on a forum, then why bother hanging out here?

 

[nitewatchman]

I believe here however is that the Charging Handle is being battered in the corner radius. Pretty obvious to all that the charging handle pulls the Bolt Control Group to the rear BUT it should be contacting on the vertical inside face of the Charging Handle Tip. To contact the inside corner something would appear to be out of kilter like perhaps the radius is too large and in addition there is debris or something amiss in the upper assembly.

My 15T (and other AR's) show a little bit of polishing on the anodized surface of the vertical tip but no flow or batter after a fair amount of use. There should only be contact when the Charging Handle is pulled to the rear or when the Bolt is released with the Charging Handle not locked into place in the upper. The OP's Charging Handle also looks to be painted rather than anodized indicated by what looks like paint chipping. Who is the Charging Handle made by?

At any rate the Charging Handle should not be able to contact the Cam Pin ever. The tip of the Charging Handle engages the flat machined into the top of the Bolt Control Group and is held in contact and prevented from rising and slipping off by the Tube portion of the Gas Key passing through the hole in the end of the Charging Handle. If the Charging Handle was limited only by the groove in the Upper Receiver the friction could increase the force required to pull the Charging Handle to the rear.

First cause that comes to mind assuming that the shoulder is intact on the top of the Bolt Control Group, is a loose Gas Key but that is normally guided by the grove in the bottom of the Charging Handle and a loose key going into battery will mark the inside of the groove and batter the end of the Gas Tube if it functions at all.

Bottom line, normally nothing should touch the inside corner where you show the metal flow. If it persists coat the surface with Machinist Prussian Blue or Red (never dries, like a grease) cycle the weapon and look for transfer onto the offending part. If you don't have Prussian Blue, Lipstick will work but it will insult your rifle.

nitewatchman

 

[brettskywalker]

Thanks nitewatchman, thats the kind of response i was looking for. The charging handle is the factory 1 that came with my m&p 15x. If the gas key is loose would i be able to tell by handling the carrier? It feels solid & havent had any failures. Come to think about the wear marks didnt appear until after i replaced the gas rings on the bolt. Looking down into the upper reciever there is a wear mark or possibly a gash in the area that i think is cut out for cam pins head to rotate in. As far as debris, i keep the rifle near spotless inside & out & never run it dry, it only gets dirty while shooting. I ll attach a pic of the spot inside the upper i am talking about. It is possible the CH wasnt locked in, i will prob do as you suggested by putting a good grease on the spot,shoot the gun & trace it.

 

[easyliving]

I have similar (chips) pricks in the upper receiver of both of my M & P 15's as shown in your photo. I have one that is a 1:9 twist with the dust cover and forward assist. I fired it saturday and when I was cleaning it I found the chips that look as if pricked with an ice pick and also on my ejection port where you close the dust cover. On the same weapon, I have two more chips on the charging handle. Again, on both sides, right at the point where the rod begins . Looks like two shiny diamond ear rings against the black background.
A few minutes ago, I inspected my other M and P 15. It also has the same type of chips on the charging handle and on the upper receiver, chips very similar to yours. This one is an 1:8 twist without the forward assist and dust cover.
What I did was to do a google search "chips(pricks), upper receiver" and modified that to get more hits.
Having said that, I took photos and I was going to send them to Smith and Wesson but I found pics very similar to mine on line but posted a few days ago. I found this thread by accident.
I also read of incidents involving similar weapons with less than 500 rounds fired, bushmaster, rock island and those who never have had any issues at all.
One veteran shooter said the chips in the upper receiver was cause by the cam pin on the bolt. One person recommended obtaining a black pen from birchwood-casey and marking the chips? Another said it was a machine, and would get pings which is true, should be able to continue to shoot. I never use any type of wire brush on the interior my weapon. When I clean the upper receiver in the area of the gas port, I use a cleaning patch dabbed with lub,wrapped around the brush that comes with the kit. Friday, I am taking mine to a gun smith for a check out inspection.
I am no expert, but I am curious.....

 

[easyliving]

I have similar (chips) pricks in the upper receiver of both of my M & P 15's as shown in your photo. I have one that is a 1:9 twist with the dust cover and forward assist. I fired it saturday and when I was cleaning it I found the chips that look as if pricked with an ice pick and also on my ejection port where you close the dust cover. On the same weapon, I have two more chips on the charging handle. Again, on both sides, right at the point where the rod begins . Looks like two shiny diamond ear rings against the black background.
A few minutes ago, I inspected my other M and P 15. It also has the same type of chips on the charging handle and on the upper receiver, chips very similar to yours. This one is an 1:8 twist without the forward assist and dust cover.
What I did was to do a google search "chips(pricks), upper receiver" and modified that to get more hits.
Having said that, I took photos and I was going to send them to Smith and Wesson but I found pics very similar to mine on line but posted a few days ago. I found this thread by accident.
I also read of incidents involving similar weapons with less than 500 rounds fired, bushmaster, rock island and those who never have had any issues at all.
One veteran shooter said the chips in the upper receiver was cause by the cam pin on the bolt. One person recommended obtaining a black pen from birchwood-casey and marking the chips? Another said it was a machine, and would get pings which is true, should be able to continue to shoot. I never use any type of wire brush on the interior my weapon. When I clean the upper receiver in the area of the gas port, I use a cleaning patch dabbed with lub,wrapped around the brush that comes with the kit. Friday, I am taking mine to a gun smith for a check out inspection.
I am no expert, but I am curious.....

 

[WR Moore]

Sorry about the tone of the last post. I reference Mr. Sweeney's book because it's readily available and has a lot of good information, rather than BS. BTW, trying to figure out who made the charging handle would be difficult, requiring S&W invoices to try to figure out who they might have bought them fromm when that rifle was made. FWIW, ARs are like cars, no manufacturer actually makes all the parts.

Now, with the pictures: After thinking about my original entry at this point, I've very carefully considered the movement of the bolt carrier group. The wear on the upper receiver by the clearance cut may be just the carrier rubbing. There is a contact rail on reach side of the gas block, like the two on the bottom of the carrier. The rail on the left side of the gas block passes right over the area showing wear. Depending upon tolerance stack, the rail might be able to impact the edge of the cam pin cutout, causing the finish wear. However, there's another possibility. When the BCG move forward in normal operation, the bolt is pushed back to it's battery position by the case head. If you let the BCG slam forward without feeding a round, the bolt will move forward until it hits the rear face of the barrel. It may or may not move completely into battery. Depending upon tolerance stack between chamber, barrel and barrel extension machining, the cam pin might be in a position to strike the forward edge of the cut out. Likewise, it might catch the rear edge when retracted. Possibly the answer here is not to allow the BCG to slam into battery if it's not actually feeding a round.

I'm mystified by the marks at the curve on the charging handle. The cam pin doesn't come anywhere near that, nor does the gas block. By any chance have you had some double feeds? Possibly as a result of overenthusiastic magazine insertions that caused the top round to jump into the action? A round or rounds that lodged in the gas tube area could mark the charging handle like that. Been using the charging handle for anything else or possibly dropped something on it while it was out of the rifle? It also dawns that the gas block gas neck could contact that area while installing the BCG during reassembly.

If you use any mechanical device it's going to show wear in contact areas. If you want a flawless finish. Shine it up real good and put it in a display box.