[Absalom]

This is a Czech military unit mark. P stands for infantry; I’m not aware of a capital letter I meaning anything, so that might be Roman numeral 1. I’ve seen numbers higher than 1 before the P and those were Arabic, so that’s puzzling, but still the most likely reading is first infantry regiment, weapon number 231.

 

[Absalom]

I’m not sure battalion works. The pre-1937 Czechoslovak army had 17 infantry divisions with three infantry regiments each, so since a battalion is a sub-regimental unit, there would have been potentially 51 1st Battalions. Without a regimental identifier, the marking wouldn’t have been very useful. But I’m just applying logic, which doesn’t always work historically; do you have an actual source?

 

[Absalom]

I have a reference that shows IP as Instructor's School.

That is interesting. Can you just image-post a screenshot of the relevant entry so we can all easily view it?

 

[Absalom]

Thanks! Very good, that’s clear enough. I think in view of the fact that the Czech are not generally known to have used Roman numerals, reading this as IP and going with the interpretation in your list makes sense. So does having guns assigned to a school. We all know the P on Lugers for Polizeischule from that period.