Stopped By An Angle Stop -- So What Went Wrong?

When our pex plumbed house was built we had a spare bathroom roughed-in. Yesterday, I tried to install angle stops on the sink stub-outs and immediately got a leaker.

The copper stub-outs had paint on them which I removed with my fingernail. I then polished the copper with 0000 steel wool. I cut one stub-out to length with a tubing cutter, cleaned it up, and examined it for deformation, scratches etc. before putting the angle stop on.

The angle stop was a BrassCraft compression type. I followed the instructions on the box to the letter. One drop of oil on the threads, no tape or putty, finger tight, then one half turn with a wrench. That half turn was a bear.

Of course it leaked.

I tried tightening further but couldn't budge it with the stubby wrenches I was using.

I removed the stop. It came off easily. The ferrule slid easily on the pipe, there was no sign of pipe deformation.

So, what went wrong? Anyone have any idea? Chinese or Indian stub-outs maybe? I recently ran into a problem with black iron pipe made in India. It's OD was out of spec (too big), so the thought crossed my mind that the stub-outs might be an out of spec offshore product (under size or too hard a copper).

This morning I examined the angle stops that were installed when the house was built. They were all Watts brand. Is that a more forgiving brand?

I did not install the second stop. I want to figure out what went wrong first.

Thanks for your help.

Bigger wrenches is the usual cure. But, I NEVER tighten anything using a formula. Hand tight and a half turn with a wrench may work for 50% of joints, but I can guarantee that it will NOT tighten all of them. My procedure with angle stops is,,
1. remove from the box.
2. snug the nut against the sleeve so it stays in place.
3. slide the valve onto the copper.
4. Tighten the nut using two wrenches.
5. Keep tightening it until you are sure it will not leak, usually when it will NOT turn any further.

The "hand tight plus half turn"...that is my formula for plastic pipe threads. Read hj for a better idea on compression fittings.

My formula would state
1) Keep inward pressure on the valve so it the pipe remains bottomed out.
2) Carefully tighten the nut and notice when the valve doesn't rotate as easily on the pipe. This indicates the ferrule is starting to bite.
3) Half turn further from here. If you feel that the valve can turn on the pipe when twisted by hand, go another half turn.
3½) Go another half turn anyway!