Some people Just can't seem to think properly.
I just happened to have my Speer # 11 manual handy opened to the section for 243 loads.
At the very top are how they tested the loads in the book.
Rifle Ruger 77 barrel 22" twist 1-10
Cases WW, primers CCI 200 & 250
Way some have posted here that is what you need to use any of the loads for the 243 using the Speer #11 manual,. Can you use the rounds in a Winchester, Remington or any other brand.
YES
Can you use other companies cases like federal, Remington or others with out fear
YES
Can you use different brand of primers,
YES
The Speer #11 manual list a starting load for every weight of bullet and a max load for every weight of bullet.
Case brand does not make one bit of difference as long as the recipes in the manual are followed because all information in the manual is universal which makes them safe in any brand of case. I also have been reloading since I cut my teeth on a old hull or case. 90% of the calibers I reload for are mixed cases.
So as long as you follow the manual you are safe with mixed cases.
Nice thing about the #11 Speer manual they use a real rifle to test the loads.
Some manuals they used a universal receiver to do the test. So you would look silly trying to hunt with a universal receiver because that is what to book says is safe.
Al