Ed Harris
posted this
29 April 2010
Actually Jeff, when I was at Ruger I had pressure barrels made with the standard .312 groove and also with .308 groove diameter and tested them extensively with a variety of UK, Cdn. and US .303 military and sporting ammunition.
Using the SAAMI and CIP dimensioned sporting chambers, NOT the sloppy WWII military “trench” chamber, the pressure rise with the tighter groove diameter did not appreciably exceed the sample pressure standard deviation, the difference was about +2,500-3,000 cup. While the reference ammunition used for the pressure test calibration was somewhat higher than normal, the differences observed were within permitted statistical limits. The corrected sample averages were in the upper range of Cdn. military standards and well within the design limits of the Ruger No. 1 and of sound No. 4 rifles which are properly set up.
My Cdn. Long Branch custom No. 4 has a hammer forged Heym barrel having the normal 7.62 NATO rifling form and dimensions, but was chambered with a .303 British pressure barrel reamer. It handles ordinary UK and Cdn. .303 Mk.VII ball and MkVIIIz ammunition just fine, as well as the Privi Paritsan with no hard bolt opening or high pressure signs. Reloading case life is also quite good. The rifle has about 3,500 rounds on it and headspace has been maintained, I haven't had to swap a bolt head.
In my handloads I use published data from the Speer No. 13 and normal Remington, Sierra or Speer .303 bullets and velocities agree with published data. Several friends had similar custom No.4s made on Long Branch or Savage actions about the same time and there have been no pleasant surprises.
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia