The big difference in reloading bottlneck H&H belted cases and bottleneck rimless cases is that darned H&H belt. Top shooters have known for over 60 years that unless one sizes the case body all the way back to it, accuracy will suffer.
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After WWII when folks used the .300 H&H Magnum and later the 30 and 28 caliber cartridges bases on large cases with the H&H belt for 1000-yard matches, they learned that best accuracy happened when new cases were used. It wasn't until someone (top riflesmith Elmer Shook, I think) cut about 1/4th inch off the bottom of a .30-.338 full-length sizing die then cut its top off just below the shoulder, smoothed off the sharp edges and used this die to size the case body all the way to the belt. Conventional full=-length sizing dies left about 1/32nd of the case body just in front of the belt unsized. This special "body sizing die" seemed to work best after a conventional full-length sizing die was used. And the case shoulder has to be set back to almost its new position so the case headspaces on the belt like it's designed to.
Top military 1000-yard shooters gave up on full-length sizing and just used new cases all the time. They must have given away thousands of .300 Win. Mag or .30-.338 Win. Mag. cases to all the civilians at the big matches.
Both military and civilian top shooters tried neck sizing but the results were never consistantly great. Once in a while someone did great with neck sized cases, but the folks who used new cases or full-length sized cases second sized with the special body die (or double sized) shot the best scores much more consistantly.
My own tests confirmed this. I've worn out four .30-.338 barrels shooting 1000-yard matches. Each one's been tested at least twice for accuracy using neck-only sized cases as well as single full-length sized, double full-length sized and just brand new cases. I fired 15-shot test groups at 1000 yards as follows:
Neck-only sized cases, 12 to 22 inches.
Single-full-length sized cases, 8 to 15 inches.
Double-full-length sized cases, 5 to 7 inches.
New cases, 5 to 7 inches.
I recommend you stay away from belted cases unless you're willing to double size them with proper full-length dies.