Sorry for the loss of your cow. Sometimes the best efforts go south.

A general rule of thumb I use is to not pull harder than what 2-2.5 strong men could pull by hand. Calf pullers are a necessity of course but you can exert more pressure than should be used with one. After you've done it for a while you develop a feel for how hard to pull. A good slick OB lube is a necessity too. Bottom line is you can hurt a cow by pulling too hard.

If you can't make progress by traction, it's time to resort to C-section or fetotomy. If live calf, obviously a section. If fetus is dead, fetotomy is first choice. The calf is cut up enough to be delivered without excessive traction.

I realize not everyone in the cattle business has access to a veterinarian that does bovine practice. That's a can of worms I'm not going to open right now.

Always drink upstream from the herd...cowdoc...