17 Mach 4 vs 17 Remington Fireball

[hicard]

I am loading 17 Mach 4 loads and firing them in my new 17 Remington Fireball using light-moderate loads and am getting a lot of split necks in my 221 fireball brass after reducing them to 17 caliber.  Is there enough difference between the 17 mach 4 and the 17 Remington Fireball to cause a problem or are they, in fact, the same size?  What could be causing all these neck splits?

[skb2706]

Work hardened brass. Anneal the necks before you size them down and they will be fine.

[LaOtto222]

I am not sure if you are reducing new 221 FB brass down to 17 Rem FB or you are using brass that was already reduced down for the 17 Mach IV or you are using old (loaded before) 221 brass. If the brass has been work hardened then annealing should take care of it. If you are using 17 Mach IV reloads in the 17 REM FB then there may be neck differences in the two chambers. The Mack IV and the 17 FB are the same cartridge. Remington just legitimized it by naming it their own. The 22-250 REM was a wildcat load for years before Remington made it a standard loading. This has been done to many cartridges over the years. 7MM-08 is another example. Wild cats are just that and chambers can vary from one gun to the next because there is no standard. You might check loaded neck diameter/chamber clearance. If there is too much room there it will split necks. The more brass is "worked" the more it to hardens. That is one reason so many neck size only to reduce the working of the brass. The likely cause is a work hardening problem.

[hicard]

Thank you guys for the information.  I suspected that overworked brass was the problem, but just wanted to check if anyone might have a different answer.