.45ACP diameter is 0.452", which yields a cross sectional area of 0.6418 in^2. Multiplying by 20E3 lb_f/in^2, you get 12837 lb_f.

My pressure cooker at home is ~14" diameter, which yields a cross sectional area of ~154in^2. Multiplying by a (likely conservative) 100 lb_f/in^2 relief pressure, you get 15394 lb_f. There are, granted, probably some volume / force dispersion things going on, but the pent up forces themselves can be comparable.

When you do blast radius surveys for industrial equipment, pressures in the neighborhood of 5psig cause serious concern (www.mbindustries.com.php5-9.dfw1-2.websitetestlink.com). When considering damage potential, it's critical to include the area over which a force is applied. 8psig can be just as scary as 80,000 psig (well, if said force is blowing a building over onto you, that is. Or a manway / manhole cover).