Military Step Barrels

[jred]

Dumb question of the day:     Why were military rifles fitted with stepped barrels while commercial rifles were not?   Is there a benefit to stepped barrels when the barrel heats up due to rapid firing or is there a weight advantage of some sort?     

[Aardvark]

Stepped barrels are cofigured to relieve stress at precalculated points along the axis line.

[Mikey]

Stepped barrels of the day were also designed to better distribute heat over the course of sustained fire in combat whereas commercial rifles were designed with a different role in mind.  Mikey.

[1911crazy]

Stepped barrels of the day were also designed to better distribute heat over the course of sustained fire in combat whereas commercial rifles were designed with a different role in mind.  Mikey.

Right Mikey;  The stepped military barrels are more heavy duty so the have less barrel warpage during sustained fire.  The more metal is also more of a heat sink too so it takes a while to get it hot.  Modern hunting rifles weren't manufactured with this thought in mind there made to shoot less rounds when hunting so heat isn't a problem unless your trying to use it as a military weapon(heavy use).  Now what about the sniper rifles of today?  There all using thicker heavier barrels.

[jred]

Thanks for the information.  It all makes sense.  Next Question:  If stepped barrels perform better when heated up from sustained firing, wouldn't they be as good as fluted barrels (assuming both were otherwise the same)?   Would the larger diameter of the stepped barrel at the receiver add stiffness  to the barrel and improve the barrel harmonics vs the fluted barrels equal diameter?   

[Mikey]

Hmmmm, interesting thought.  I can understand the physics of fluted barrels cooling faster by displaying more surface area but I do not believe the design would hold up to sustained fire without overheating due to barrel thinness at the bottom of the flutes. 

I believe the larger diameter of the barrel shank at the receiver adds stiffness to the barrel, stepped or otherwise, and allows the barrel to establish its own harmonics.  Theoretically though, I think the harmonics of a fluted barrel would differ from those of any other barrel design as the fluting might affect the unimpeded motion of the harmonic sine wave created by the contour of the barrel.  I could also be totally wrong.  I also think that fluted barrels need to be of a larger diameter to incorporate the fluting - this is different than with other contours. 

Did I say this right???  Mikey.

[Aardvark]

Maybe this will help:

Paul Mauser found that rifle barrels have 3 distinct vibration points.  He also found that the continuous firing of magazine after magazine of ammo would cause the barrel to expand longitudinally.  By putting steps in a barrel, the vibration was reduced.   Stepped barrel Mauser rifles require a small amount of clearance between the front of the step and the recess in the stock to allow for the longitudinal expansion during rapid firing. The clearance allows the barrel to expand without jamming into the wood.   Often, dried grease, grit or a combination of both will have worked their way into the clearances.  Carefully scrape it out.   If a stock has been swapped, the clearance may not exist at all.  If that is the case, use a Dremel tool or scrappers and relieve the stock.  (Source: “Mauser Bolt Rifles” 7th Ed, Ludwig Olson, F. Brownell & Son, Montezuma, Iowa, 1976)   

[bluebayou]

Not that I am a machinist, but I always wondered why the later wartime barrels were still stepped.  It seems like a lot of manufacturing work considering the other time saving methods that were used.  I am talking Mausers here.