CO2 Repeaters - Are BB Pistols Generally Louder than Pellet?

[Just-a-Guy]

May seem like a silly question (and if history is an indicator, I'm probably posting in the wrong place).  But...

Don't laugh, but I am actually looking for a loud airgun.  Since my son and I are plinking in the basement mostly, I've found he gets a kick out of firing the CO2 repeaters with blowback.  I think it feels more real.  And it's good practice for rimfire shooting later.  So I was trying to sort through the various guns to see which had the most "realistic" sound and feel (yes, I know, it's not possible, but relatively speaking). 

The Umarex Desert Eagle seems cool, but is a huge pistol, too big for his small hands (10 years old).  The Walther PPS and the Umarex XGB seem more like it.  But in doing my research, it seems like the "loudest" guns were the BB guns.  Is this a fair observation?  And if so, why?

Any other thoughts or suggestions would be appreciated.

JAG

[daveb50]

I think it's the ones with the shortest barrels that give the loudest POP. Probably caused by more Co2 released than needed to push the BB along before it's expelled.  I have a Colt Defender BB pistol that's pretty loud. Not a blowback, but otherwise very realistic.

[D14Jeff]

wear hearing protection .

[silent_airman]

I have a Tanfoglio Limited Custom that can make my ears ring with a fresh cartridge. It's a big hefty BB pistol with full blowback. I love shooting it.
https://www.pyramydair.com/product/tanfoglio-limited-custom-co2-pistol?m=3238