Privi - your collection is about empty cases, not brass ready for shooting - I thought. In looking at a case, can you see .002" or .010" difference in shoulder length? Both these measurements are shorter than many standard rifle's headspace, let alone a wildcat which has no SAAMI
restriction. You must measure what is needed for shoulder, etc, and form them accordingly if that is your wish. Some need necking up straight then re-necking, while others don't. Check some reamer printouts and then form the cases accordingly. Note that most wildcats are just that - they're wildcats and measurements from one chamber to another only meet the 'close' category. Shoulder lengths can vary a lot from rifle to rifle, although they might have the same ctg. stamp.

Headspace problems are created by those who shouldn't be shooting Wildcats. In order to shoot any Wildcat, one must have an understanding of headspace and how to manage it perfectly - ie: fit the round to the chamber - perfectly. Then, the brass will last almost indefinitely. Lack of this knowledge leades to headspace problems & thus the myths are born - which are then expounded upon by gun-rag writers needing a few more 'words' income. These guys usually meet the "shouldn't to shooting wildcats" category. An accomplished handloader can properly headspace ammo in a .30/06 case blown out straight to an improved .005" per side taper. - no shoulder at all. Not many would do it, but they are capable and know what has to be done.

As to headspace on belted cases - measure the headspace on a number of different belted cases and see what you get. They should all be within the SAMMI standard of .007", same as rimless, but aren't. BTW - .007" headspace in a chamber is very sloppy work, but normal for many factory gun makers. You'll find factory ammo to have short shoulders as they rely upon the belt to 'sort-of' hold the case back against the bolt. The shoulder blows forward upon firing, then gets shoved back all the way again by an unknowing reloader when he full length sizes. FL sizing is the main culprit in creating excessive headspace for a chamber that is within SAAMI specs. This is why some rifles eat brass in 2 or 3 firings - insipient head separations - the ONLY cause is excessive headspace, whether it's in belted magums and any other modern case. There are 2 causes for this. Lack of knowledge and gun-prep cover both.

As to the .458" .400 Whelen shoulder, this is actually .004" larger than most of the Ackley shoulders on that case. My own .376/06IMP has a larger .460" shoulder with a .470" case diameter - .005" taper per side - function is perfect. It shows what can be done to the '06 case. The case capacity of the .400 Whelen should be about 80gr., 2 gr. more than my .375's case at 78gr. Varying case brand can increase or decrease this measurement by up to a few grains.