Author: DairyFarmer
Subject: Resizing cases for my Lithgow.
Posted: April 06 2015 at 7:27am
Only straight walled cases (like pistol cases) don't need trimming every reload. A case with a shoulder, and especially a shallow shoulder like 303 Brit, need to be trimmed EVERY TIME.
http://www.303british.com/id20.html
Subject: Resizing cases for my Lithgow.
Posted: April 06 2015 at 7:27am
 Pukka Bundook wrote:I would have thought that a once fired case would not need trimming, but maybe so! |
| The 303 British suffers from "droopy shoulders". Good in its day, the shallow angle was designed to help in loading and placement of the long stranded propellant "cordite", within the case. While good for factory production then, it's a real problem for the reloader today. Any cartridge with shallow shoulders is more prone to case stretching, case wall thinning and thickening around the neck. Maximum loads fired from these cases accelerate the process. Canadian gunsmith Ellwood Epps saw the problem and corrected it. He knew that steeply angled shoulders helped modern spherical and extruded powders burn more within the case and less up the barrel. His solution was to increase the shoulder angle to 35 degrees from 16. At the same time, he decreased the body taper by over 50 thou. The resulting improved cartridge showed a 15 % velocity enhancement over the standard 303 British when fired from the P-14. After consulting with PO Ackley, Mr Epps reformed the cases with minimal body taper and sharply angled shoulders. Reduced body taper lessens the rearward pressure effects on the bolt and lugs (bolt thrust). Sharp shoulder angles inhibit forward brass flow, which reduces the need to trim cases as often. Originally, the improvements were made to increase brass life, not to produce a higher velocity round. Mr Epps knew that reshaping the case into a more efficient design would yield this secondary benefit, but considered improved case life to be the most important factor. |