My brake barrel got shot not closed

if the barrel is still straight I would say a broken spring or piston stem..

I concur with cosmic. Possibly a busted spring. Being about 30 years old, the rifle probably needed the piston seal replaced anyway. I would say now is a good time to tear into it and check things out. Spring and seals are available from here.
http://www.airrifleheadquarters.com/page/page/251485.htm
or here
http://vortekproducts.com/ourstore/Airgun_piston_breech-seals?page=1

One thing to check first. Take the stock off and see if the cocking linkage is grinding against anything. Look for heavy wear or metal to metal scrape marks. If I recall I had to make a custom delrin bushing for one I worked on to smooth it out.

If you get the spring or spring kit also order a piston seal and a breech seal... Airrifleheadquarters get my vote..

Yep, just checked my notes. The trouble may be the cocking shoe dragging across the spring and the lever needs to be shimmed a bit with a piece of delrin. If you find that is the issue, PM me and I will walk you through the process.

Folks, I'm trying to visualize how this scenario would have damaged the gun. So would discharging the rifle w/the breech not sealed be about the same as discharging it w/o a pellet? Or could it have closed itself fast enough to gave kept the piston from slamming into the end of the tube and the damage was from something else?

ETA- I'm guessing it was like a dry fire but wanted to check w/the experts before making any assumptions.

Check the cocking shoe and the piston for damage. 

same as dry fire..