I don't know the answer to your question; nor do I know where you could find out for sure. But an educated rough guess would be in the 20 to 21" range. I say this because the .22 WMR is said to begin losing velocity at around 18.5" of barrel length, and the hornet has a smidge & a half more powder. If it were me, I'd cut it to 21", maybe 22". You might just get more velocity than from the 26".