After bending a mainspring barrel cover and ruining it I found a better way. I now use an inexpensive watch case press that I purchased from Harbor Freight (item# 91621) for about $15.00. It came with a set of nylon dies including two flat dies. After placing the body of the barrel on the lower die and carefully lining the cover up in the correct position, I can just snap the two parts together. It does a perfect job and does not distort the cover.
That’s good to hear David.
I’ve just replaced them by putting it upside down on my round steel staking block, putting the protruding arbor into a close fitting hole. Then I press down gently and snap the top on. Nice flat and hard surface for it to align with….everyone has a trick or two for these !