Hi goggles, looking forward to seeing you in Ottawa in a couple of weeks. Check out the
"CGN beer night" that Maynard suggested (starting at post #8)
The
"new Sierra 155 Palma" bullet (#2156) has a stated bc of 0.504, the
older Sierra 155 grain #2155 (used to be called "Palma" bullet) has a stated bc of 0.450:
I assume you are using the #2155 Sierra 155 grain HPBT - this is the Palma bullet that was introduced in 1992. This was the original 155 grain target bullet; it was quite a modest design (the story behind it is interesting), and just about every 155 grain bullet that has come out since it has been a lower-drag (higher bc) bullet. It was and still is a fine bullet. Many matches have been won with it, and many matches will continue to be won with it. This year at the Imperial Matches in Bisley, they used ammo loaded with the Sierra 155 for the first time, and saw really great results. In one fell swoop they have solved the ammo problems that have plagued shooters at Bisley for a good long time.
To confuse things, Sierra has recently introduced a new 155 grain target bullet, #2156, which they are calling the "Palma" bullet. It is a new design, and it looks to be extremely promising - it is fully the ballistic equal of the other top-of-the-line 155 target bullets (e.g. Lapua 155 and Berger 155.5), it seems to be easy to load to good accuracy (which has always been an advantage of Sierras over many other low-drag target bullets), and it seems to be well-suited to relatively short-throated chambers. I can't wait to get my hands on some; I expect that it will become my standard match bullet (at this time I used the Lapua 155, and also used the Sierra #2155 as a back-up). Some month or year, we'll be able to get our hands on bullets again (!), and we'll all get to try the #2156s. NCRRA does a periodic "group buy" of Sierra target bullets, which it sells to DCRA members at attractive bulk pricing.
The next time you care to do some load development, you might find it useful to work your load up in 0.5 grain increments. With a 30" target barrel and the typical target rifle setup, you'll likely find that velocities in the upper 2900s or the low 3000s are safe, accurate and consistent (with a good chance that they give more consistent velocities than loads in the high 2800s/low 2900s). FWIW my S155 (#2155) loads run about 3000fps, with SDs of 12-15 (thrown charges of Varget), and my Lapua 155 loads run 2950-ish, with SDs of 8-ish (weighed charges of Varget).
The length you trim to is not at all critical. You just want to avoid having overly long cases "pinch" the bullet, which can cause accuracy and/or safety problems. The "advantage" to trimming them to 2.000" or 2.005", is that it'll be a bit longer before you have to trim them again; trimming tends to be a hassle that most people try to avoid (except the Giraud owners, I hear they enjoy trimming!). Trim to whatever length your Lee trimmer gives you, and be happy with that. Do be sure to do a thorough and conscientious job chamfering and deburring the case mount, this makes your future loading *much* more pleasant. Since you're mostly neck-sizing your brass, you won't need to trim very often. When it comes time to full-length size them, there are ways to correctly FL size brass that results in very, very little case length growth. With good methods, you can get more than ten firings before trimming is necessary.
