How to screw studs into helicoils?

When i got my case machined i got them to install helicoils on all studs (I had a few that spun when undoing the heads originally).

I have screwed them all in but some seem to screw in a bit deeper then others, and when undoing bolts they spin out.

Now before i start bolting the heads to 28ft how do i ensure that the studs are in as far as they are meant to go? I tried the double bolt method and almost stripped the thread.
Anything i can try?

Thanks in advance.

Case savers are better than helicoils,
helicoils can be problems in alloy, thats why the factory used solid steal inserts.
What size are the studs 8 or 10 mm ?

If helicoils are fitted correctly they shouldn't move

whatever🤪

sorry yes i meant case savers, i couldn't remember exactly what they were called.

Maybe i should just try the double nut approach again, but i do have a question on how to i undo the second nut as it tends to get real tight.