I have a Jarrett model that I bought new in Dec. of 06'. It will not run commercial ammo under 180gr. Commercial 180's or higher runs fairly well in it. Handloaded 180gr TC's with a length of at least 1.190" work the best for me.
I am using factory mag tubes with factory followers and springs and Dawson base pads. The mags will hold 20rds reliably. I tried Arrendondo followers once, nothing but problems.
The only thing changed on the gun was I added an Ed Brown wide ambi safety, and changed the recoil spring to a 12.5# IMSI spring.
I have roughly 6,000 rounds through the gun. That is 22 matches plus practice at least 2 or 3 times a month. The gun works good for me.
Hope this helps,
Tom