Acra Glas and Acra Glas Gel were developed specifically for bedding actions.
JB Weld wasn't.
Using something that was designed for a specific task is a better bet.
Substituting another compound that wasn't intended for bedding actions is a crapshoot.
May work. May not.
If it doesn't, you'll have to scrape, grind, or chisel it out and start over. Is the risk of all that worth saving 10 bucks instead of going with the product that was designed for that specific task?
I guess it boils down to how much your time is worth.
I once tried to repair a Colt frame with JB Weld...one that had snapped off the ejector legs and when the guy couldn't get them out, he proceeded to wallow out the holes with a drill. I did the repair, and all looked pretty good...until after about 500 rounds downrange the case smacking the ejector beat the stuff loose in the holes and let the ejector start flopping around again. He sent the frame out to be welded up and have the rail recut.
Tensile strength of JB seems to be good. Shear...not so much. Impact...not good at all.
Probably okay for the sides of the receiver and for a pressure pad in the forend of the stock. Probably not suitable for the recoil lug.
Just my observations and experience.