Back in the '70s somebody (it might have been John Fry)showed up with an action wherein he had installed screws to maintain bolt alignment. It looked like a workable system to me. Likewise, your spring and ball system sounds pretty reasonable. As you say, a bolt which is eccentric by 3 or 4 thou but aligned is just fine. Regards, Bill.

Matt,
How do you square the lugs on a '98 Mauser bolt?

Clark,



I want to know first what the lugs are being squared to, and why?



ASS_CLOWN

Maybe bore centerline AC, it's the only true(+/-) and stable datum that I see as practical. IF: Bore in centered in blank, Threads are true and square in both action and barrel, etc. etc. Read an article by Gordy Gritters in VHA awhile back about the process, and the pains taken to square everything up is probably worth more than it costs IMO. He evaluated barrel dimensions to .0001", groove and bore among other things, recording each measurement for each groove and land. His process for centering and truing threads is extremely precise. The care taken for ensuring true chamber cut is just as important. I'm not a 'smith either, but I see no other approach, and it all has to be true to that datum in any case.

DigitalDan,

But how does one machine the lugs to the datum you seem to be specifing, meaning how do you know the true position of the bolt lugs to the receiver raceways, to the receiver mortise thread PD, to the barrel tenon thread PD, to the barrel bore centerline (centerlines aren't good datums either by the way, at least that is the conventionally held wisdom in the guidelines gonverning GD&T, IIRC)? What effect does a slightly out of square lug have on the transmissibility of the action ie it's harmonics? Is not the squareness of the bolt face to the bore centerline at least as important as the squaring of the lugs? What effect does an out of sqare bolt face have on transmissibility? All this squaring up of this and that, in the reciever anyway, is all about transmissibility aka rifle harmonics. In short, the squaring up stiffens the action, this could be a good thing or a bad thing, depending upon where your action harmonics frequency ratio lies.

I have a rifle, which bears on only ONE LUG (and yes it has two), the receiver is factory stock (probably not real square) and with a factory barrel, this rifle will shoot better than 0.75 MOA every time (groups range from 0.3 MOA to 0.75 MOA)! If I were to spend the time and money to "blueprint" it, what would be the expected outcome? I am a fearing such a bunch of work would be fixin' something that ain't broke, but then what do I know. What do you think?

ASS_CLOWN

Actually most actions bear on one lug only. It isn't possible to duplicate the force loading of firing when
you "true" the lugs. Vaughn "rifle accuracy facts" advocates putting an angle on the lugs to equalize the loading.
Good Luck!

GD&T???

My suggestion is little more than that, I do not know precisely the answer to your question, I thought that was clear. In the end, the objective is that all things be true to the bore, so it makes sense to me that would be a good reference. IF the bore is centered and the barrel threads are cut on the same center.... Perhaps they use the receiver face, IF it's square in the first place. WTFDIK?

I never looked at squaring lugs in relation to harmonics, but rather something done to equally distribute bolt thrust and minimize random receiver/bolt distortion. I doubt any of this ever results in perfection, however, but note that BR shooters are prone to seek it nonetheless. I sometimes wonder if a small bit of lapping might be as beneficial as anything else. Note I said "small", and yes, I know it affects headspace.

As to your rifle, well, I guess I have one or two like that myself and they are unlikely to wind up in a 'smith's shop for that reason. I don't think that groups that meander from .221" to 1.25" in a .35 bore warrants the effort. If it were to be applied at LONG range I wouldn't hesitate, as that isn't terribly precise in terms of accuracy. This opinion in regards a stock Ruger 77, .358 Win., 3 shot groups for the most part, over a span of some 3 years and several hundred rounds.

I shall try to find the Gritters article for a re-read, maybe the answer is there.

Some of Vaughn's work detailed in his book "Rifle Accuracy Facts", dealt with this area in detail. I don't recall the specifics in regard to lug truing, but do recall that he identified and quantified(IIRC) the effects of an asymetrical bolt face on accuracy. One area where I think there would be significant influence with a rifle suffering from all of this would be the deformation of the cartridge head in regards to subsequent firings and head space. Of late I've beeen thinking that headspace consistancy is more important to accuracy than I once thought. All things are relative of course, but it does have a measurable impact, just as cockeyed lugs do. He even found that drilling a second hole in the receiver in opposition to the gas relief port was an improvement in his Remmy. Go figure...

Anyway, off to the library. I'll get back on this'n.

teal,

I won't argue with you about doing a "thorough" job of blueprinting a rifle.

With regard to the experiments you suggested. I did do some of that many years ago, albeit somewhat limited as we (yes there were several of us working together, it was the good ol' days) worked with only two rifles. What we learned from this limited DOE (limited in that we only looked at two designs M70 PF and M700) is that the OVERWHELMING BIGGEST BANG FOR YOUR BUCK , with regard to accuracy was obtained from barrel quality (including the chambering job). The better the barrel, and the more concentric the chamber was to the bore, etc, etc, the better.

Right behind the barrel quality came bedding! One cannot allow the barrelled action to move around and change contact points between barrel and stock. If it doe the system stiffness is adversely affected and harmonics increase in both magnitude and frequency. What we learned back then was that softer was better, with regard to heavy match barrels (that mean they seem to dramatically prefer being free floating).

Drawing from memory (it has been ~ 15 years) the accuracy potential associated with barrel quality was ~ 50% without proper bedding and 90% with proper bedding. Everything else you can imagine to do to a rifle amounted to ~ 10%.

We decided early on that in order to comprehend what the benefit of each "tweak" was we needed to properly bed the barreled action. If we did not we have had a "moving" target with regard to transmissibility aka harmonic response of the system, and we basically had a "random function generator".

Like I said at the beginning of this post, I would NEVER tell someone NOT to do a thorough job, but in the interest of learning I will always ask why, and desire to understand their objective (measureable) reasoning.

Lastly, barrel fluting, if done properly, does in fact improve accuracy potential. I do not necessarily believe however that one can "mass produce" a "one fluting design fits all" barrel, though. In theory it could be done, and probably can be done, but one must understand that to be effective the ratio of barrel stiffness to barrel mass (dynamic stiffness) must increase in a significantly positive manner over a non-fluted barrel for the fluting to be effective in increasing the natural frequency of the barrel and therefore reducing the transmissibility of the system as a whole. Put into simple english, it ain't so simple the fluting MUST be done in a precise manner and the math MUST be done.

For whatever it is worth there you have it, the grand total of my knowledge (such as it is and I probably know more just don't remember it right now).

ASS_CLOWN

With most Mausers, anyway, the action is made of mild steel and strength and wearing qualities are imparted by casehardening. Remove or significantly thin that case hardening in the name of truing and you are inviting setback due to the battering of the lugs. Have the action re-casehardened and you'll almost certainly get enough warping to undo your efforts.

I'd leave this one alone.

leftoverdj,

Quote:

---

strength and wearing qualities are imparted by casehardening

---

Right and wrong with regard to case hardening.

Strength - WRONG

Wearing qualities - RIGHT

One additional benefit of case hardening is SMOOTHNESS of motion IF the surfaces are polished first that is.

Set back is a sub-surface failure of the material, the case has NO effect, UNLESS said case is very deep say 0.060"+ and then a few thousands removed by lapping is insignificant anyway.

ASS_CLOWN

The case hardening, properly done, IS deep, though not as deep as Ass Clown claims is needed for the effect it gives. Double casehardening was the norm although there were times that the second treatment was skipped. The classic example is the Brazilian 1908 on which some lots were given only a single treatment and which are plagued with setback problems when rebarrelled to high pressure cartridges.

This subject was beaten to death here a little over a year ago and a search will pull up the info. It will also pull up the info on available recase hardening services to prevent the problem.

Perfect screen name, btw.

Leftoverdj,



You are free to believe whatever you like about casehardening, "mild" steel as you call it. May I ask you what your metallurgical and/or mechanical engineering creditials are? I understand if you do not wish to disclose them, by the way (I sure as hell am not going to tell you what mine are ).



Unfortunately, this discussion is only remotely related to the subject matter of this thread, so for everyone's benefit I will drop this.



ASS_CLOWN



EDIT - oh heck I will tell you my "creditials"! I am a simple ol' mechanic, nothing more! Pretty sorry, eh?