Thanks for the feedback so far.. I'll be doing my first 1,000 yrd trials with the 300 PRC soon here in July so I'll see how that turns out. But to respond here per comments:
- Reference shoot all on same day in this order:
- 300 PRC load: New lapua brass no trim; BR primers; 81.2 grn H1000; Berger 215 Hybrid Target; seated at ~3.7" COAL (ojive 2.915")
(All reference 5 shots - 100 yrd range - indoor - no wind)
1) NEW BRASS loaded 3/15/25 : 2924 fps - 6.4 STD (first 5 - 30 sec cooling per) easy <MOA)
- all centered with scope
2) 1st Resized loaded 6/19/25 : 2916 fps - 9.8 STD (next 5 - 30 sec cooling per) clear 1.5 MOA - 3 small separate groups
- new brass has 2.255" neck which I bumped up too 2.262" neck distance (from fully free formed 2.270" max")
- new brass trimmed to 2.564
- impacts 1.2" left; 1.2" right and 1.3" down of dead center
3) NEW BRASS loaded 5/31/25 : 2930 fps - 8.7 STD (next 5 - 30 sec cooling per) easy MOA)
- impacts lower half of 1" circle
- To be fair, I now try to clean between every 100-200 rounds in the bolt. This may be a mistake for PRC loads? I'll clearly check to see next time I can try.
- I now have 2nd reused brass from the 1st time redo attempt. Now trying to follow the same exact process for neck resize with mandrel and inside case lube as with new brass. Maybe doing that before case cleaning with 1st fired brass caused tention issues but neck lude is always last.
- I may just have to accept that I need to resize all future brass the exact same way and re-do a seating depth / power charge to tune it back in. I should throw in that my barrel now has only about 150 rounds through it so unclear if/how breaking in changes any other parameters here?
Some notes:
- I'm not clear on how many rounds you fired. It looks like only 5 per. If so, that's not nearly enough to get any meaningful data.
- Your brass prep steps contain some important steps, namely annealing, mandrel and neck lube.
- Lapua brass has EXTREMELY tight necks out of the box. Using a mandrel opens them up somewhat, but because they are so tight, they spring back more. This yields a higher seating force, which corresponds to a higher force holding the bullet in the neck. Neck lube helps here, but virgin necks will still deliver substantially higher forces.
- Anything that impacts how the bullet starts moving (e.g. the force holding the bullet in the neck, powder temp, bullet weight, etc.) will change the pressure profile. When you change the pressure profile, you change how the bullet accelerates. This, in turn, can have a down range impact.
- So, your new brass potentially yielded decent results because the pressure profile was a good match for your chamber/barrel/bullet combo. As soon as you fired and annealed it, everything changed. There is less force holding the bullet in place, meaning the pressure curve is a little flatter, meaning the acceleration starts slightly sooner and is slightly lower.
- This is why I don't waste my time doing load dev with virgin brass. While the impacts of using virgin brass are small, they are there.
- You haven't played with seating depth at all. This can, and usually will, make a significant impact. In the image below, these are seating depth tests from a few years ago. The lower right (don't ask me why I started there - I don't know) was 5 shots from my 300 PRC with 230 Berger OTMs seated .015" off. The upper left is 3 at .018" off and the upper middle is 3 at .021" off. I stopped the test at that point, set my remaining rounds to .018" and validated.
What I do:
- Fire enough rounds using virgin Lapua to get 50 fired cases - minimum.
- Run a ladder to find an area that gives you decent SDs - you don't have to run the entire range dictated by a loading manual. I usually start in the regime where I want the velocity to be, drop down a bit, then go up at .3 grains per 5-shot group. This won't definitively tell you what's good, but you get a pretty good idea of what's bad. Pick a couple of the more promising "not bad" loads and load up like 20 of each to validate.
- If you're lucky, like I just was with my 300 PRC using a new powder (VV N568), while doing the ladder you happen to be at a seating depth that works. Otherwise...
- Do a seating depth test starting at like .015" off and move up at .003" increments. With Berger hybrids, you will usually find something that works before you hit .030". The highest I've ever gone before hitting a good setting is .039". Most tend to hit before .030"
- Validate the seating depth.
