Jackie Schmidt, posting on Benchrest Central, observed that there may have been some production changes with Lapua 220 Russian brass. This brass is commonly used as the parent case for fire-forming 6 PPC cases. The newer 220 Russian brass has slightly thicker neckwalls, and, according to Jackie, the new brass is more consistent in overall neckwall thickness.
WTS New 220 Russian Lapua brass
Reloading Cases, Lapua Brass
220 Russian « Daily Bulletin
Neck-Turning « Daily Bulletin
New Lapua 220 Russian Brass — Thicker Necks? « Daily Bulletin
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220 Russian « Daily Bulletin
220 Russian « Daily Bulletin
Lapua .220 Russian Brass (Boxes of 100) - May of London
upload.wikimedia.org/wikipedia/commons/a/ab/Rifle_
220 Russian « Daily Bulletin
220 Russian « Daily Bulletin
Lapua Brass Cases – Extreme Range Outfitters
Blaser Tactical 2 (LRS 2, R93, R8) Loads
Lapua Brass - 220 Russian (4PH5013) - Box of 100