Forums.NitroExpress.com

Yes, it does make a lot of sense. Let's take that full circle.

From Graeme Wright's "Shooting the British Double Rifle":

Quote:

Geoff MacDonald who makes the Woodleigh brand of projectiles did an experiment which illustrates the difference in barrel stress with different projectiles. After checking for correct bore and groove diameters, Geoff turned down a section of a .375 barrel until it had .090" wall thickness. He then forced various projectiles through the barrel USING A HYDRAULIC RAM. On the outside of the barrel he had a micrometer set up to measure any expansions of the barrel. When forcing a soft point through, the barrel has no measurable expansion at all. However, a steel solid gave .0005" expansion to the barrel, although the barrel did spring back after the bullet had passed."

In other words, the jacketed soft point compressed, engraved, and conformed to the bore, with no elastic deformation of the barrel at all. With the steel jacketed solid, compression occurs (due to the soft lead core), but not enough to avoid elastic deformation, and the barrel steel returns to it's pre-stress dimensions. This is not the cause of OSR.

Steel will always return to it's pre-stress dimensions after elastic deformation. That's the DEFINITION of elastic deformation. If it's elastic limit is exceeded, it's original dimensions are permanently altered - which is the definition of PLASTIC deformation. By definition, OSR is plastic deformation. The dimensions of steel can't be altered by stress any other way.

Woodleigh's tests confirm what has long been known - the thin barrel walls common to quality double rifles DO expand SOLELY due to the passage of a bullet too hard to entirely conform to the bore. One of the bullets used in the test was a dead soft LEAD bullet with a thick gilding metal covered steel jacket. The soft core makes it compressible, although less so than a copper or gilding metal jacketed soft point expanding bullet, and elastic, not plastic, deformation occurs. A conventional mono metal bullet (one with no thin full-caliber bands to obviate the problem) has no soft metal core, making it perfectly NON-compressible, and plastic deformation occurs.

On that note let's consider this statement again:

Quote:

"The material used to manufacture Barnes Banded Solids will not obturate at less than 45,000 psi."

Again, no .40+ caliber double rifle cartridge operates at pressures that high. To complete the circle, consider this again:

Quote:

So, we know that the bullet can't obturate, for two reasons. The material used is too hard, and there's no compressible core. Barnes says the bullets are slightly undersize, which I don't contest. That helps, but it can't be an answer. A hard .407" mono that has to pass down a .400" bore/.408" groove barrel still has a lot of metal to displace - metal that Barnes specifically states is difficult to displace - in order to conform to the bore. In the thin tubes of a double rifle, that's almost a guarantee of problems.

The fact that something this basic seems so hard to understand utterly escapes me.

--------------------
"Serious rifles have two barrels, everything else just burns gunpowder."

Post Extras