Tight bolt, flute it?

Of001

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Nov 5, 2020
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Canada
So ive got myself a mauser m12.
I love it, but i have a couple of issues. The most important is the bolt. Its tight. Very tight. With any oil whatsoever it requires more force than i like, or think it should require to move and leaves a rib of oil at the rear of the action and mag well. I only use a drop. The manual does not say to oil or not, just wipe clean the action.

I plan on cerakote for the barrel and outside of the action. My understanding is that cerakote has some lubricity especially when applied thinly. Is this true? At least for cerakote brand
Somewhere i saw a "pro" version application that is extra thin.

Should i/could it help to flute the bolt, or flute AND cerakote the action? the bolt?

I get adding material will tighten things but do you think removing 80+-% surface area (more towards a shallow 'skeletonizing' than the widely spaced 50/50 flutes) and adding lube will work or cancel eachother out?

Maybe jewling to add a a few thousands space/hold oil?
 

longrangebo

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Oct 8, 2005
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236
I have one that worked the way you are talking about, A Lawton 8000 I got the bolt fluted and it is great!
 

tobnpr

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May 30, 2013
Messages
336
Is this a new rifle (under warranty)?

Fluting reduces surface contact area so it should help (far as I know, the concept was first introduced by AI on their AW rifles to reduce the possibility of ice freezing up the bolt- not a good outcome in combat). It also provides a way to help shed grit- but IMO the bolt isn't correctly fitted based on your description.

NEVER coat in this condition. Depending on the application (benchrest rifles can have less clearance than hunting/combat rifles- you don't want a speck of grit to bind up your bolt!), you want minimum .002-.003 thou clearance in the raceway from the smallest dimension on a hunting rifle. Production receivers usually vary from end to end.

Cerakote, properly applied, adds .002 to the bolt (.001 ea side). Heavy-handed spray will lessen clearance more.

Assuming you're hunting with this rifle, I'd contact Mauser service- this is not how it should be. They're not inexpensive rifles, and if the bolt is that tight it's very possible it will bind up at the least opportune time. I'd have them replace the bolt with one of correct fit.
 
Last edited:

Of001

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Joined
Nov 5, 2020
Messages
15
Location
Canada
Odds are your bolt or action are slightly bent making things tighter, nothing you mentioned will help but only make it worse, you need clearance first before Cerakote will make things run better, it will certainly not make it better if your bolt is already tight!!
That was my first thought. Luckily i know a guy and it isnt the issue. He said runout is <.001
 

Of001

Member
Joined
Nov 5, 2020
Messages
15
Location
Canada
Is this a new rifle (under warranty)?

Fluting reduces surface contact area so it should help (far as I know, the concept was first introduced by AI on their AW rifles to reduce the possibility of ice freezing up the bolt- not a good outcome in combat). It also provides a way to help shed grit- but IMO the bolt isn't correctly fitted based on your description.

NEVER coat in this condition. Depending on the application (benchrest rifles can have less clearance than hunting/combat rifles- you don't want a speck of grit to bind up your bolt!), you want minimum .002-.003 thou clearance in the raceway from the smallest dimension on a hunting rifle. Production receivers usually vary from end to end.

Cerakote, properly applied, adds .002 to the bolt (.001 ea side). Heavy-handed spray will lessen clearance more.

Assuming you're hunting with this rifle, I'd contact Mauser service- this is not how it should be. They're not inexpensive rifles, and if the bolt is that tight it's very possible it will bind up at the least opportune time. I'd have them replace the bolt with one of correct fit.
Ive sent them the measurements of the bolt and action, I'm guessing they will be to spec, +one -other so tight in the middle.

Symmetry on the action is within measurable tolerance but about 1.5thou narrower at the rear 3cm of the action, less than 1 thou total gap. Also either the guide (raceway?) On the bottom of the bolt is narrow/shallow or the the action bit ( pin? That moves guides the bolt.

Doing a force test apparently showed more force needed on top of the bolt (showing binding on the bottom) when compared to a tikka, sako, and anschutz ( all tight actions).

Ill wait to hear from mauser but my guy suggested flapping out the first inch of the action 2thou and sanding down the bolt guide pin thing, whatever it is called, a hair each way.

Reasonable advise considering the diagnosis?
And yes for hunting, also his equipment to measure this is top end sharks with frikin lasers typw stuff.
 

tobnpr

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May 30, 2013
Messages
336
Symmetry on the action is within measurable tolerance but about 1.5thou narrower at the rear 3cm of the action, less than 1 thou total gap.

This is where your issue is. Less than .0005 per side wouldn't be acceptable to me, the tiniest bit of "whatever"- practically dust will bind the bolt with so little clearance. That's even tight for a BR rifle. I use precision ground gage pins to check the raceway dimensions, high-tech certainly will get you the numbers you need.

I'm curious as the what Mauser says their factory spec/standard is for clearance. Keep us updated.
 
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