Kurt,
Several years ago Lapua modified the production lots of 223 Rem brass,by making thinner necks,and case walls to increase the volume size of the case. This "New" production of 223 Rem. brass has the word "Match" on the case head,along with Lapua 223 Rem.
Older lots of 223Rem. Lapua brass lacks the word "Match" on the case head,and has a smaller powder volume.
In the new match brass I can run 25.9 grs of V.V. N133 & 52gr. HP Barts Bullet,with Federal 205M primer. The velocity is 3480 FPS in a 24" Broughton barrel ( Standard rifling,with 1X14 twist)
However the older lots of 223 rem. Lapua brass has a maximum load of 25.3grs. of N133 & Barts 52 gr. HP.
The 25.9 gr N 133 load in older brass makes the bolt very sticky and unsafe.
This may be the case with the "New Thinner " 222. Rem Lapua brass that you have,in that it has a larger case volume. If you have a load that comes close to filling the older case,check it in the "New" brass, and see if the new brass has a larger capacity,or fills the case less.
If the new brass has a larger volume,you may be able to load it a little hotter,for a little more velocity.
The smaller diameter neck shouldn`t affect accuracy,as long as you have a smaller button to provide the same neck tension.
I know most folks try for an optimum .002" neck clearance in their chambers,but my 223 Rem. chamber is a "No Turn Neck" and I can`t tell the difference in accuracy between the thinner /"Match" brass, and the older thicker brass,as long as I use a smaller neck sizer button,to provide the same tension.
However the Higher velocities with the New match brass is better in our 200yd. "Club" matches. I also use V.V. N 133 in my 2 Heavy Varmint rifles chambered in 222 Rem & Barts 52gr HP bullets. I know it`s blasphemy to use N133 in the "Duece"
instead of H4198,but I get better velocities,and better standard Deviations as well, using it.
Check the volume,and see if the powder comes up in the case neck as far, in the new brass.You may be able to get a little higher velocities,if the volume is greater. Please work up slowly to the loads I`ve listed above for the 223 Rem.,as they are safe ONLY in my rifle,and may not be in someone elses. Email me privately if you want more info on N133 & the 222 Rem. loads.
Mike Kerwood/Kodiak Alaska