No they're not the same. PC-7 is thicker, less runny.
You should probably have both, because each might be better for
certain uses, but I use PC-7** almost all the time The only time I
use JB is for little things. The smooth surface of JB can be
achieved in PC-7 and 11 by wetting your finger and smoothing the
surface. (This is why God gave us 10 fingers, so you don't have to
stick the same finger back in your mouth. Tastes bad, and who know,
it might be poisonous! ) I suppose if 10 fingers are not enough, one
could use a bowl of water instead of spit.
PC-7 comes in two 4-oz cans, and yes that's a lot bigger and cheaper
than JB Weld. HD only sells a much smaller size (the cardboard tube
that opens at each end) but Ace Hardware sells the two 4-oz cans and
maybe even two 8 oz cans. I use separate popsicle sticks (Now I'm
lazy and I use separate screwdrivers) to remove stuff from each can,
so there is no mixing or touching inside the can, and I've had one set
of cans at my mother's house last for 20 years without getting old.
I also scratch into the lid a line that corresponds to the seam on the
side of the can so that I can replace the lid just as it was. This is
less important here than with paint, but I do it anyyhow.
I don't know what all JB can do, but PC-7's uses are amazing. It will
stick to glass. I used it to patch a hole in the bottom of a pot,
then forgot to take the pot off the stove and boiled out all the
water, and still the pot didn't leak. (I decided I didn't want to
cook food in a pot with such a patch, but that only limits me wrt
food. )
PC-7 is workable after it sets, with a file and maybe a knife.. I
patched a gear in a electric miixer, like for mixing in a bowl. Then
I carved teeth into the patch. That time it only worked for a minute
or two, maybe 20 revolutions, until something caught on something and
it broke, but that it worked at all was pretty good. I don't think
any other glue I have had would have lasted even more than a couple
seconds.
I made a cap for my wine sack with PC-7. Big plastic threads on the
winesack. I had to use pliers to take the new cap off, but after
that it screwed on and off. I don't remember if I put vaseline on
the plastic threads before I put the PC-7 on, but usually I do, if it
has to be removed.
And the most amazing thing was when I was 23 and living with two girls
and a kitchen that was practically a slum. The faucet ran all the
time and the 1" or 1.5 metal drain pipe was rusting through and
dripping at a place a half-inch or inch long. No valve to turn off
the water, so I put the PC-7 on the drain pipe (This was the first
time I'd used it) and when the dripping water made it fall away, I
pushed it back. and I did this every minute of two for no more than 10
minutes, by which time it had set. And after that the drain didnt'
leak. Even though the faucet kept running, slowly. It was
incredible.
**PC-11 is like PC-7, but white.