Clean out screw is stuck!!!!!

[docone31]

I picked up an used .45 full stock for my wife to learn front stuffing. I can pick the nipple channel , but, the clean out screw has probably never been removed.
I want to remove it and replace it with a metric allen screw.
Any advice on its removal short of drilling and threading?
It sat for a while with a ball in the barrel. No powder, just a ball.

[Topper]

Poor some Kriol or other penetrating oil down the barrel.
Tilt barrel so that the oil can get into the ballast and let it soak for at least 3 days.
Then barely tighten screw to break it loose and try to remove.
If no go, let it soak longer.
Eventually the oil should creep into the threads.

[docone31]

Too late.
I tried to tighten the screw just a little to back it out a little more.
Dang head came right out!
It was mild steel.
I am in the process of center drilling, then makeing a larger hole to either back out the main body, or diamond drilling it out.
If I am lucky, I can preserve the threads. Other wise, I will retap to the next size.
I had hoped it would be easy.
The person before me had really buggered up the head.

[mooman76]

You could replace the drum. They generally run about $5.

[docone31]

I opened it up to the threads. It appears to be the same threads as the nipple.
What thread size is the Italian nipple?

[docone31]

Never mind.
I chased the threads, by happen stance I found a grade 8 allen bolt. 10/24. It not only went right in, it cleaned out the threads also. Tomorrow I go to my local hardware store. I am going to get a pan head Allen bolt. Don't need them but 3/8". It locks down tight, and matches the threads.
It is an older rifle. Might be 6X75 was the better fit. The one I tried worked without changeing the threads.
I used diamond burrs. On my Flexshaft, I have an RPM enhancer for diamond bits. A little beeswax for lube, and I could grind only the thread section after removeing the body leaving only the threads. Once I got the bolt started, it pushed out the remaining "coil".
Worked better than I thought it would.