Western Arms 1911 not blowing back far enough
 

WA 1911 Hi capa running on propane w/ silicone oil added

Only about every other shot will actually load the next BB because the slide doesn't go all the way back.

Any ideas?

Did you try lubing the slide a bit?

try using duster gas

You may have a weak hammer spring or the flow valve on the mag is gummed up. Try cleaning the flow valve on the mag and give it a drop of oil. If that fails, then the issue lies in the gun.

At times it will not blow back at all, but it will fire the bb properly.

Any metal lubricant good for all the moving parts in the slide?

Use silicone oil or grease for all moving parts. But if you're very careful, lithium grease is good on moving metal parts. Don't get it on the rubber.