Gunsmithing Implications of Metal Selection on "trued" faces

[Oddball Six]

Extracting a subsequent question from the broader Remington 700 truing thread...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AZPrecision</div><div class="ubbcode-body">Are the bolt lugs harder, or the receiver lugs harder?

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In almost every circumstance the receiver is harder than the bolt.

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I am trying to understand the direction of this question. A notable exception here could be the RSR from Surgeon Rifles, just as an example. MY (perhaps flawed) understanding is that the body of the receiver is 416R and the bolt is 4130 chrome moly.

416R Reciever
http://www.matweb.com/search/DataSheet.aspx?MatGUID=30e7827a70ba4e05920d0e24fcb973c4

4130 Bolt Body / Lugs
http://www.matweb.com/search/DataSheet.aspx?MatGUID=e1ccebe90cf94502b35c2a4745f63593


Does it matter? Why?

 

[lvcatfish]

Re: Implications of Metal Selection on "trued" faces

I did not want to post in the other thread and appear to speak for someone else. Please be aware that those links you reference deal with generic material properties for common commercially available metals. Actual materials can be purchased with properties "to spec". Original material properties can also be modified by additional working (in this case heat treating or annealing) by the shop who manufactures a finish product.

I don't honestly know whose bolt lugs are softer (or harder) than the action lug abatements. It is highly likely that the manufacturer (or all manufacturers) has altered the material properties between the time they purchase the stock and sell the completed action.
A good product designer will have intimate knowledge of and control the "weakest link" of a system. Call the weak link a fuse if you will. Reasonable control of failure is what makes a good design (and designer). I offer the design opinion that allowing the lugs to be softer protects the action from damage at the expense of the bolt. This is not to say that having the bolt lugs harder is not a safe design but rather provides a potentially more expensive fuse when needed.
I have observed some seriously deformed bolt lugs a few times.

Just food for thought.

 

[Jim See]

Re: Implications of Metal Selection on "trued" faces

many custom action makers use ss bodies and cm bolts. Less chance of lug galling, then SS on SS.

 

[Oddball Six]

Re: Implications of Metal Selection on "trued" faces

Im sorry, perhaps I am sporting my stupid hat today but I am afraid that I don't understand what the implication of the bolt lug being softer or harder than the action lug abatement.

Ivcatfish, I certainly agree that matweb provides nothing more than a random look at one type of treatment of a given material and nothing more.

Its useful as a starting point to understand the materials at issue, but I dont understand the issue that the two 'smiths were looking at back and forth so its hard to have any kind of eye at making ANY interpretation of the data.

So my question remains, why should I, or a gunsmith, or the action manufacturer care about the material of the two components. What would he/she/they be looking to mitigate or enhance in the relationship of the two parts?

Is it merely removal of material over time from surface contact wear? That is what I thought of at first but it seemed like there was more important than that when CDixon and Keith were talking about it in the other thread.

 

[lvcatfish]

Re: Implications of Metal Selection on "trued" faces

Fair enough, perhaps my response was too blunt. I have never designed an action. I have extensively studied materials science and the philosophy of design.
From a practical and functional standpoint if two metals make high pressure cyclical contact and have the same hardness then there is high potential for galling action. Stainless steels are particularly prone to this and it deals with their grain structure and changes to it. Galling potential can be largely mitigated by having slightly different hardness properties between the two materials. Judicious use of a suitable lubricant doesn't hurt either. If the lug/abatement surface galls then you have several problems: bolt throw will feel like crap and you are potentially altering headspace. Neither of these is desirable.

From a safety standpoint, if you consider the function of the lug/abatement interface it is to maintain headspace (and allow chambering/extraction). The safety component is huge. If there is a design overload (bad reload, squib or whatever) the excess pressure and forces must go somewhere. If the bolt lugs are softer than the lug abatements then the bolt lugs are likely to deform and absorb much of this energy. In extreme cases of overpressure this energy dissipation of the softer surface is not enough and things go boom. I have seen deformed bolt lugs on several rifles as a result of chamber pressures getting toasty. If an action were designed with the abatements softer than the bolt lugs then the overpressure damage would be more likely to the action itself. It is cheaper to replace a bolt than an action. In any event, serious consideration should be given to shit-canning the entire setup if this type of overpressure occurs.

Generally speaking harder metals have more brittle tendencies and softer metals have more ductile tendencies. Barrel steel is fairly soft to help ensure ductility.
Hope this helps.