It sounds like you have got there eventually which is the main thing.
It was probably the initial heavy cuts that caused a few issues. These inserts like a lighter cut, a higher speed and a faster feed. A good reference guide can de found at :
Cutting Data

Rather than turn down long lengths of material you can obtain ground imperial silver steel if you think it suitable here:
Silver Steel Imperial including: Stubs R004AK & Stubs R006AK

I hope this helps in some way,

Reg