throat erosion / barrel degradation formula

[zini72]

My gun smith told me about a technical paper that was written several years ago. It theorized a formula for designing a case with optimum shoulder angle to neck length for optimum efficiency and minimizing throat erosion.

Any body know where to view this "paper" or who wrote it?
Allegedly the thearies in the paper were later tested and proven.

 

[fdshuster]

zini72: Not much information to go by, so I'm just guessing, but there is/was a theory floating around that it had to do with the shoulder angle and case neck length. The basic idea was that a steeper shoulder angle ( ex: the 40 degree of an Ackley Improved vs. the 20 degree of a 243 Win.) would help to keep the blast of powder inside the confines of the brass case, instead of in the throat area where they would have a sandblasting effect on the bore surface. A longer neck length would also serve to "protect" the surface of the bore. It can be easily seen if you lay a straight-edge along the shoulder area of a drawing of several cases with radically different shoulder angles, and note how far that "line" would extend out of the confines of the case (neck area). I subscribed to that belief, ( reinforced by an article in a shooting publication/ long ago/ cannot locate it), but have since changed my mind after it was "discussed" on this site, and some very valid points were made showing it was not true. Speedy Gonzales also has some informative postings on this subject, on this site, somewhere, buried in the archives, approx. 2 1/2 to 3 years ago? Most believe erosion is simply caused by the amount of powder being burned in relation to bore diameter. Ex: A 22 cal. bore with a powder charge ( "in-the 40's"), like a 22-250 vs one with 22 grs. like a 222 Rem. ???

 

[fdshuster]

zini72: O.K." found it. Go to the search tab, click-on and in the "search for": strip, type in "throat sandblasting theory". Then hit "search", click-on the blue background title "throat sandblasting theory" and you have the posting, with diagrams, by Speedy.

 

[zini72]

Frank, thanks for the info. It is all very interesting. I beleive SMC also has some theories on throat erosion, I havn't read them all yet. Thanks again for your comments, you guys are great.
Edward