What size cleanout screw for percussion bolsters/snails ?

[Rolf]

Been working on drawing a left-handed percussion plug with Qcad using plans+ measurements from Bob Roller and Curtis. According to my drawing the bolster wall will be 4.33mm (0.170") thick.

Is this enough for a clean screw?
If so, what size thread, screw head size (diameter + thickness)?
It would be great if someone could post measurements taken from cleanout screws.

Best regards
Rolf

[JPK]

I make them without a “clean out screw” because they are unnecessary and always get buggered up.

[P.W.Berkuta]

Here is a left-hand breach plug I made for an Ohio style rifle. It was made out of 1018 mild steel. The clean out screw is tapped for an 10-32 screw (not the one shown). If you use a smaller diameter clean out screw then you will have ignition problems as the flame channel will get clogged fast.

[Daryl]

Now THAT is pretty cool, the drum being part of the breech block. A drum but not a drum. A patent breech that looks like a drum.

[Bob Roller]

He manufactured shavings of steel and the breech was a by product .I used an 8x32 on a couple of caplocks I made but none on the 451 with the Don Brown breech.
Bob Roller

[D. Taylor Sapergia]

Rolf:  A clean out screw is not an asset.  On patent breeches, sometimes you find a slotted screw head on the offside of a breech, but it is not a clean out screw.  It is a machine screw that has been installed to fill a hole that enlarges the inside cavity of the breech.  It is never meant to be removed, which will almost certainly ruin the head of the screw.  On drums on rifles and pistols of the percussion system, you sometimes see the head of a screw in the centre of the outside end of the drum.  Again, this is a machine screw that has been used to seal a through hole that connects the nipple seat to the inside chamber of a breech...it is not meant to be repeatedly removed for any purpose.  Again, trying to remove these will always result in a buggered screw head.

[Rolf]

Rolf:  A clean out screw is not an asset.  On patent breeches, sometimes you find a slotted screw head on the offside of a breech, but it is not a clean out screw.  It is a machine screw that has been installed to fill a hole that enlarges the inside cavity of the breech.  It is never meant to be removed, which will almost certainly ruin the head of the screw.  On drums on rifles and pistols of the percussion system, you sometimes see the head of a screw in the centre of the outside end of the drum.  Again, this is a machine screw that has been used to seal a through hole that connects the nipple seat to the inside chamber of a breech...it is not meant to be repeatedly removed for any purpose.  Again, trying to remove these will always result in a buggered screw head.

Thank you for your replies.
I got the same answer from Curtis today. The cleanout screw on his rifle is not removeable.
Why drill a hole in the bolster for this screw?
It makes more sense to drill the hole for nipple in the bolster and then connecting the fire channel by drilling from the oposite side.
This would leave the bolster wall intact, and you would have a much longer, stronger screw filling the excess hole from the oposite side.
This should make a safer plug.
Am I missing something?

Best regards
Rolf

[Bsharp]

I off set the cross hole using 12-28 thread [.182] from the back side. [.020 down and forward] To get more threads on the nipple.

I angle drilled the powder hole at 30 degrees, helping to pack the nipple channel when loading.

[Dphariss]

If the breech design is good and proper cleaning is done a cleanout screw is a waste of time and metal.

[P.W.Berkuta]

To all the above answers - yes that is an assembly hole to create a flash channel from the nipple to the main charge - how else would you get the flame from the nipple to the main charge? Yes - the channel could be cast in but if the breach plug is machined from a solid chunk of steel that channel could be very tricky to drill. The hole could have been plugged so that no screw is needed. The manufacturer decided to install a slotted screw instead so that the end buyer COULD use it as a clean out path if they so wanted to. I see no difference than removing the nipple to clean the area below the nipple or maybe use a pipe cleaner to do the job. Maybe some people never remove the nipple for fear of damaging the threads . There are some nay-sayers that feel they know better than some well-established firearms manufacturer - good for them. For me if there is a screw and I can remove it to do my cleaning I will use it just as I will remove the nipple to do my cleaning. So - call it what you will - assembly hole, clean-out hole, remove it or don't remove it the choice is yours. I for one will use it as a clean-out hole .

[D. Taylor Sapergia]

If you intend to remove the screw for whatever purpose, be sure to case harden it after you have made a nice clean deep screw-driver slot.
The flash hole connecting the charge to the nipple can be drilled from the end of the breech plug.  But first, the threaded journal must be in the neighbourhood of 1/2" in length, and the front end must have a cupped cavity at bore size.  Then the drill can be run in at an angle to connect to the nipple seat.  Great care must be taken to ensure that the drill does not perforate the threaded journal at the bottom of the threads.  Most Hawken breech plugs are made in this way.  This eliminates the need for a cross hole through the plug, and the subsequent machine screw to fill the hole.