Now that we are stuck with useless 941 I have a few questions.
How long can a friend borrow a rifle for hunting and load development?  (I know that is allowed but don't know how long)
Example, my friend lives in Eastern Oregon, I live in the valley.  He has much better access to shooting range and reloading equipment.
Can I lend him my bolt action rifle to work up a load for me and he also use it for varmint hunting which might be months at his place?
 He obviously would not be in the process of using for hunting "all" the time as it would be stored in his vault other times until such time as I can pick it back up.

Can I do this or must it be transfered to him then transfered back each time?

Similarly if me and a friend want to buy a varmint rifle together (expensive bolt action set up with high end scope), can we both go to the dealer and both get back ground checks done so we "co-own" it?

Who's gonna know?
Maybe every day he has it is the first day he's had it.

I didn't know there were any gun laws out there

This.  The whole law is a fucking joke right now.  Later, when we realize that it was just the first step to a full on registry in Oregon, well, then it won't be so much of a joke.

According to SB941, unless your friend owns a business that develops custom loads, it isn't allowed at all. Why are you under the impression it is?

"Can I lend him my bolt action rifle to work up a load for me and he also use it for varmint hunting which might be months at his place?"

No, you can not.

"Can I do this or must it be transfered to him then transfered back each time?"

Has to be transferred each time.

"Similarly if me and a friend want to buy a varmint rifle together (expensive bolt action set up with high end scope), can we both go to the dealer and both get back ground checks done so we "co-own" it? "

Nope.

All this of course assumes you care about and intend to follow this illegal law in the first place...

Reminds me of what a leftist liberal at work said when I told her only responsible gun owners follow the law -- "Well, at least someone is following the law..."

Looks like we both have a few idiots at work.