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Bolt Motion Question

This is a discussion on Bolt Motion Question within the The M14 forums, part of the M14 M1A Forum category; When pulling the oprod back, I get about halfway through the stroke until the back of the bolt is making some contact with the receiver. ...


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Old April 30th, 2020, 07:52 PM   #1
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Bolt Motion Question

When pulling the oprod back, I get about halfway through the stroke until the back of the bolt is making some contact with the receiver. With some amount of extra force, I'm able to chamber a round and fire. It fires/extracts rounds just fine, but this seems like a less-than-optimal amount of friction. I'm curious if this is normal or if it should be a smoother action.

EDIT: Added a photo of a ballpoint pen pointing at the corner on the receiver that's making (aggressive) contact with top of bolt. Note the long scrape on bolt face.
What I'm seeing seems excessive (but what do I know?). The best description is that it kind of hits a wall (like a two-stage trigger) as the bolt is pulled back, and that second stage has a hell of a draw to it.
I can see/identify the corner on the receiver where it's making contact and scraping - should I file this down?.

EDIT 2: While posting replies in this thread, I broke the rifle down again and noticed that the scraping on the bolt only occurs when the trigger guard is locked into place. If I remove the trigger assembly or even just unlock the guard, there's no more scraping - it feels like I imagine it should.

EDIT 3: VIDEO! I can't embed it, you'll have to click the link https://imgur.com/MRrgx8r
First I show it smoothly operating with the trigger guard open, then I close it to show the "wall" I described above and the scrape.

EDIT 4: Screwdriver points at contact point(s) inside receiver. Following that worn ridge towards the bore is the same corner the ballpoint pen points at.
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File Type: jpg WTvPu8d.jpg (860.7 KB, 15 views)

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Last edited by electricnic; May 1st, 2020 at 12:02 PM. Reason: Attaching photos instead of linking to them
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Old April 30th, 2020, 08:17 PM   #2
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? Sure it is not cocking the hammer? You do grease the underside of the bolt and top of the hammer?

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Old April 30th, 2020, 08:19 PM   #3
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The hammer is already cocked - this happens every time I pull back the bolt (i.e. I'm not dry-firing in between pulls). It's all greased!

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Old April 30th, 2020, 09:29 PM   #4
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Well then shoot it and see what breaks!

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Old April 30th, 2020, 09:30 PM   #5
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Quote:
Originally Posted by JEFFJP_N_JJ View Post
Well then shoot it and see what breaks!
I've done that about 1500 times over the course of the past year. Nothing breaks; all rounds feed and eject fine, but that's not the point. Is this resistance supposed to be there? Should the top of the bolt contact the underside of the receiver? It seems like it shouldn't, but I don't want to assume.

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Old April 30th, 2020, 09:45 PM   #6
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Quote:
Originally Posted by electricnic View Post
Should the top of the bolt contact the underside of the receiver? It seems like it shouldn't, but I don't want to assume.
The bolt has to contact the receiver someplace, otherwise it would flop around like a fish.

The ridge on the upper back side of the bolt is one of the few grease points. It will rub along the underside of the receiver roof. There is a little stub on the left side of the bolt as well. Those are the only things keeping the bolt from wobbling. The insides of some receiver are not as smooth as others, but after 1500 rds, your rifle should be broken in just fine. Any place you see worn finish, apply a dab of Lubriplate.

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Old April 30th, 2020, 09:45 PM   #7
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Well it seems you have answered your own question!

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Old April 30th, 2020, 09:55 PM   #8
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Quote:
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The bolt has to contact the receiver someplace, otherwise it would flop around like a fish.
I get what you're saying, but I'm still not sure how much contact is normal.

What I'm seeing seems excessive (but what do I know?). The best description is that it kind of hits a wall (like a two-stage trigger) as the bolt is pulled back, and that second stage has a hell of a draw to it. I can see/identify the corner on the receiver where it's making contact and scraping. The top face of my bolt has a long scrape on it from this contact (see attached photo).
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Last edited by electricnic; April 30th, 2020 at 10:16 PM.
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Old April 30th, 2020, 10:05 PM   #9
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The longitudal scrape on the topside of the bolt is not normal. Check the roof of the receiver for abnormalities. Is part of the clip guide pin sticking out?

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Old April 30th, 2020, 10:12 PM   #10
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Clip guide and its pin are removed. This scrape doesn't line up with that hole, anyway. Should I file the offending corner down (I edited in a pic to my first post with a photo of it)? This seems like a solution but I'm not going to do it without some expertise giving me a thumbs-up.


Last edited by electricnic; April 30th, 2020 at 10:32 PM.
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Old April 30th, 2020, 10:22 PM   #11
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If the burr was caused when the clip guide was removed or a scope installed, I would file it down and enjoy the rifle.

If the burr has been there since the rifle was new, I would give SAI Customer Service a call. They will remove the burr and hopefully refinish the bolt.

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Old April 30th, 2020, 11:03 PM   #12
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Quote:
Originally Posted by KurtC View Post
If the burr was caused when the clip guide was removed or a scope installed, I would file it down and enjoy the rifle.
I don't think it's from the clip guide pin at all. Those features are a few mm from where the scrape is.

While posting replies I took the rifle down again and noticed that the scraping only occurs when the trigger guard is locked into place. If I remove the trigger assembly or even just unlock the guard, there's no more scraping - it feels like I imagine it should.

VIDEO! https://imgur.com/MRrgx8r
First I show it smoothly operating with the trigger guard open, then I close it to show the scrape.


Last edited by electricnic; April 30th, 2020 at 11:19 PM.
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Old May 1st, 2020, 05:16 AM   #13
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OP, are you sure that is the point making contact with your bolt? I only ask as I tried to duplicate whatever conditions would causing that. I took my M14, and worked the bolt, leaving the hammer cocked and the action locked in the stock, and tried to see what points were making contact.
As far as I can tell, on my rifle, the section of the bolt that would have wear such as you have shown, does not come close to making contact as the point you are showing. The section of the bolt with the wear mark does not come anywhere near the spot you are showing as a point of contact. The only part of the bolt that comes close to that is the top of the right locking lug.
I suspect that the place making contact is further back. There's a similarly shaped part of the receiver at the end of the bolt lug slot, just forward of the right sight knob. I suspect that is the point of contact.
There should be a good 1/8" clearance between the place on the bolt that has the wear mark, and what you are indicating as a point of contact on the receiver.

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Old May 1st, 2020, 06:27 AM   #14
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That part of the bolt makes contact when the rear bearing land contacts hammer.It overcomes the resistance pushing the bolt up against receiver passage and right side shelf.

Location of trigger group as it sits in stock/receiver affects resistance.You can look for burrs or rough spot ,see pic where ink pin is pointing.

See contact wear to TRW bolt ,the shelf is at the top rear of bolt slot .
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Old May 1st, 2020, 08:02 AM   #15
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Not related to the scrape mark on bolt. But even with the hammer cocked, when the bolt is moved rearward the bolt does press downward on hammer, so a little resistance will be felt.

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