It is a year to year crapshoot with pressures of commercially available ammo. All that is required to satisfy SAAMI is pressure below 12,000 psi with a modern 20 ga. Mfg. ammo changes recipes (and pressure) depending on what's available component-wise. Does the gun require low pressure ammo? If a 1941 Cashmore requires low pressure ammo, then it would be too hot. Then there's the pesky issue of 2.5" versus 2.75" ammo. What's chamber length? Gil