I can't help it, as I read this thread I keep thinking "The Mall Ninja got Religion."

So lets move it on and start talking about the most righteously holy ammunition to arm the believers with. I suggest nothing less than 338 Lapua.

I am assuming we get to kick the old lady's bingo groups out of the basement so we can set up our Sacred Shooting Range, or SSR as we call it...

As for consideration of backstops or safe lines of fire, there is no need to think about it.
It will be Church Security shooting, each and every bullet will be individually divinely guided by the hand of the Lord.
Whoever gets hit will obviously have deserved it for their sins, it is not my place to judge here.
The Lord gives life and the Lord takes it away again.

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Lets get a bit of reality here folks.
You are talking about having untrained and unidentified people with guns in your congregation.
What is to keep your other already armed parishioners from opening fire on your parishioners who have appointed themselves as gunslingers?
What about the visiting gunslingers from other churches?

If you shoot somebody in your church do you really think any priest is going to claim resposiblility or do you think he will talk about innocence and God's Wrath a bit more as the cops drag your sorry A** off to jail forever and ever Amen?

If you are really that worried about getting shot in Church either dont go or hire real security with metal detectors and visible presence.
They can sweep everybody entering for weapons and maintain a secure perimeter, they don't even need to be obtrusive to do it.
Along with that they will keep their heads up and stay alert during the prayer and chant sessions.