Project Long Branch

I know you 'know your stuff' but my concerns would be there is no support across the rear of the action - NO charger bridge and NO rear sight.

This will allow a lot of flex and will upset how the various components interact.

This from Peter Laidler ............................

This setup is no different than that of the Custom or Supreme No4 rifles supplied by Parker Hale back in the 60's. I see no reason to fret over something that will never come to light Alan. 

To get to the point that Mr. Laidler is describing, the rifle would had to have been consistently used day in and day out for years. I made an exacting clone of a Supreme No4 based off of a Maltby action. I have currently put 255 rounds down range with it and to date, it is still putting everything into the X ring at 100 yards. My dad's Custom No4 that he purchased new in 1966 from the Rod and Gun Club in New Ulm is still capable of MOA groups and recently as three weeks ago, dropped a 8x8 Mule Deer according to my sister. My point here being that, if Parker Hale Ltd was able to hack off the charging bridge and rear sight axis pins of No4Mk1 action bodies, cut the barrels down to 22 inches, fit it with basically a cutdown forend, make their own custom side mounted scope assembly and then call it good, what's there to worry about. The No4Mk2 Maltby with a M47C stamped barrel... 

That'd be a great project and I'd be very interested to see the results - hopefully you'll be retiring very soon !!

Now, there are three dimensional deflections/strains to a uniaxial load, called “poisson’s effect” which is perpendicular to the applied load.  And since the locking lugs are forward of the rear of the action where backsight lugs are located and the load is compressive behind the locking lugs, the poisson’s effect would cause a increase in sectional dimensions at the backsight lugs.  Most common construction materials have a poisson’s ratio around .2 to .3, meaning the transverse elongation is approx .3 times the axial elongation (for steel).  But, I suspect the elongation in the action body from compression forces of firing a cartridge is pretty darn small…it is made of steel after all, not rubber.  Maybe it spreads by .002 to .003 inches (ish).  And what effect does that have?  It is certainly an elastic deformation, meaning it returns to its original dimensions when the load is removed. 

The bolt is probably more susceptible to fatigue from tension stresses at the very tight (nearly zero) transition radius where the short lug meets the bolt body due to bending of that lug.  That very tight radius causes a high localized stress concentration. That’s one of the areas I wants to model with a very fine mesh to capture the peak stress.  

Fatigue life is an exponential function of the localized stress level.  Double the stress and the life (number of load cycles to initiate a fatigue crack) goes down by several orders of magnitude.  This is one reason I don’t like pushing loads up to near max with this action, occasionally, with a limited number of rounds that’s fine, but not for long term use. 

Yeah, stay away from near max loads.  Fine if your shoot a few rounds a year, but devastating if you shoot 1500+ rounds a year like I do.  That’s why I got a few No. 4 rifles, try and spread out the accumulation of fatigue damage and barrel erosion.