Azar - I load for a Tikka T3X and a M96 (I once had a CZ550 in the same caliber). I've found, like you, considerable variation in reloading data with most of the older manuals using the M96 or M38 and 46,000CUP as the MAX pressure. Initially, I assumed that using new brass and a newer, more modern, rifle in this caliber would yield significantly higher velocities than that published by all the powder and bullet companies. I found my M96 had a rather "generous" chamber and full length resizing demonstrated an excessive amount of stretching even on moderate loads. When I loaded the same rounds in the CZ, I could reload my cases more times, but could not drive the bullet significantly faster. While researching further, I found some of the brass I was using had the "head size" of the 30/06 at .470 where all the "datum" specified for the case indicated the correct size was .476 (Lyman #47) to .480; a case head size more like the 8X57 round. I then relegated my old cases to my M96 adjusting my die to "partial" resize. This procedure helped, but did not extend the life of my cases more than one or two extra firings in the M96.
For the CZ, I bought new Lapua cases and a couple dozen Norma cases I found at a gun show. Both cases met the "published" standard for the 6.5X55 and have shown the "hoped for" longevity of most of the calibers I work with (.223, .243, .270, 30-06, .35 Whelen, 9.3X62, etc.).
Now (finally), that brings me to your subject of reloading the 160gr Sierra semi-spitzer bullet in a "modern" 6.5X55 or S.E., which designates the Europeans higher pressure standards. My initial thought was I had "broken the code" on being able to exceed the velocity numbers, I would surely succeed using new properly "spec'd" cases in my Tikka. I did succeed, as did you; however, just not the way I expected. Practically all the reloading data I was using used a "test" firearm with a 29.5" barrel whereas my CZ550 had a 20.5" (carbine) and my new Tikka T3X has a 22.4" BBL Logically (if that actually figures in - ha!), if I can achieve the same velocity from the much shorter barreled rifles accomplished by the long barreled M96 with long case life, excellent accuracy, and "legendary" trajectory, I have accomplished quite an achievement! The various reloading manuals record the following with 160gr bullets (double check for accuracy!): 1) Sierra - 2500fps with a 29" BBL 2) Hornady - 2300fps with a 29" BBL 3) Lyman #50 - 2386fps with a 24" BBL 4) Norma - 2519 with a 24" BBL. While not all these sources sources use H4831, they give a "base line" for loading the 6.5X55 and what velocities we can expect.
You (and I) have reached 2500fps with a 160gr bullet in a much shorter barrel than that used in a much longer one! You also accomplished this feat while using much less of your "chosen" powder to reach this power level! Why? Maybe because your rifle has much tighter chamber tolerances, shorter "lead", or more defined rifling due to "tooling" that isn't 124 years old! Hopefully the 6.5X55 will continue to be more popular as we enter the "second faze" of the 6.5 Creedmore "craze".
