Good question. I haven't started load development yet, but what I did notice when I started collecting load data is that I saw a lot of 2209 (H4350) loads around 42.5-43.5gr and even over 44gr with 140-142gr projectiles. ADI lists its maximum as 41.5 for the Sierra 142 SMK (and 40.0 for the 140gr Hornady A-Max), while Sierra lists 41.9 (142 SMK) and 42.0 (140 SMK).
Most of the loads I collected were with large primers.
To put things into perspective, the small primer brass - Lapua - has a smaller case volume than just about all other 6.5CM brass, so it will spike more pressure for the same load - at least in theory.
The moral of the story is you're going to have to work your load up. But I did come across a couple of interesting videos that show the difference between the small primer Lapua brass and large primer Hornady brass using the same load (41.3gr 2209/H4350 and 140gr Hornady ELD-M).
The small primer brass was not only 20-30fps faster, it was more accurate. The video maker did say it was colder on the day he tested the large primer brass, so that may have accounted for the lower velocity.
Small primer 6.5CM review:
https://www.youtube.com/watch?v=ZPu0DzIgKNkLarge Primer 6.5CM review:
https://www.youtube.com/watch?v=ypI6D-i57ukThe real advantage to using small primer brass is brass life, as small primer pockets stay tighter longer. There's another video where they got 20+ reloads from a single Lapua small primer 6.5CM case.
Personally, I'll be using small primer brass for my target shooting - as the cases will get many reloads - but I'll probably also work up a hunting load using once-fired large primer (cheap Federal 140gr ammo at $29 a box) brass so I don't have to worry about losing it out in the field.
I guess it really depends what you want to do with your loads - what sort of accuracy you're looking for - and how often you think you'll be reloading them. The Lappy brass isn't cheap - especially in 6.5CM - and is anywhere from $180-$200+ per 100.
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