Dumb question

I don't mean to be rude, but why wouldn't it be safe to use without anything in the holes? The screws certainly don't do anything structural

Yes it's safe and fine to fire without anything in the holes.

A hardware store will have your plugs, take a screw with you for thread size !!

Steve H said:

I'd love to but the closest "store" is 30 miles down the road

Click to expand...

In that case assuming the holes do not bother you they will harm nothing for now. If some "crud" gets in there its simple to blast out with cleaner. Will be fine till you can get some plugs.

The open holes will do no harm at all. I’m pretty sure they are 6-48 which you won’t find at most hardware stores. Any gunsmith or sporting goods store that mounts scopes will have plug screws left from those jobs. Until you can find some, fill the holes with candle wax to prevent crud from accumulating.

There are vanishingly few "dumb questions" when screwing around with 50,000+ PSI chamber pressures.
Gins often used carefully optimized screw pitches to go with hardened screws.

For many years chamber pressures where measured using lead and copper 'crush' cylinders.
The LUP (Lead Units of Pressured) and CUP (Copper Units of Pressure).
A carefully designed and specified lead or copper cylinder (they often looked like just a thick disc of metal)
was acted on by the chamber pressure and the change in thickness carefully recorded.

Piezo Cylinders are used now and they allow a tighter bound on the actual numbers in PSI.
A few rounds had pressures reduced when the Piezo systems show pressures higher than had been estimated in the past.
I had a lot of fun in a couple of Ballistics Labs developing the Piezo systems.
Scared the brown stuff out of any number of Engineers and Technicians I worked with.

We had many layers of protection on the Pressure Test Barrels and actions.
Developed some 'interesting' ways of firing those test guns remotely.

You really want a hardened screw to ensure you have not created a weak spot of any consequence.

Steve H said:

I'd love to but the closest "store" is 30 miles down the road

Click to expand...

Here ya go, in stock for about $2 each-
https://homesteadparts.com/shop/sights-rear-elevators-c-87_167.html