How do you determine if there is a patent breech?

[Sparkitoff]

In particular, I have a .54 GM barrel for a T/C with 1:70- twist. Actually I have 2, a percussion and a flintlock. Not just for these two but from now on, how can I tell if one of these PB's are present?

 

[tenngun]

Look to where your breach plug joins the barrel. If there is a line about an inch or so from your tang you have a patten breach plug. On the other hand if your barrel goes back to the tang it’s not.
TC made all their guns with a pattan breach I think.

 

[Zonie]

In particular, I have a .54 GM barrel for a T/C with 1:70- twist. Actually I have 2, a percussion and a flintlock. Not just for these two but from now on, how can I tell if one of these PB's are present?

Most likely, your barrels for the TC's has a chambered patent breech.

If the breech plug in the barrel has an interlocking lug on it that mates with a steel block with a tang on it, it will be some type of patent breech. These plugs have a hole in the center of the threaded area where the plug meets the bore. This hole is almost always smaller than the bore size.
This type of breech plug is designed to let the barrel tip up and be removed from the stock, usually by removing one or two barrel wedges that go thru the forearm of the stock.

If the breech plug has only a long tang sticking out and looking from the rear you can see the threads on either side of the tang, it is a plain breech plug without the patent type of powder chamber. The face of the breech plug where it meets the bore will be flat or slightly concave.
This type of breech plug requires the removal of at least one and usually two screws that go thru the tang plus removing any barrel wedges or pins that hold the barrel in the stock to remove the barrel.

If you are unsure, shine a good flashlight beam down the bore while you peek down to the bottom.
If you see a flat face without a hole in the middle, the plug is a plain style breech plug.
If you see a hole that is slightly smaller than the bore going down into the face of the breech plug, it is a patent breech.

 

[Melnic]

Just to add to the above, a $25 USB borescope from Amazon is a good investment. Not only for muzzleloaders but you will find other reasons to have one eventually if you DIY around the house. I have one that is wifi ($35) and hooks up to my phone that I have taken to gunshows. that and one of these to drop into a bore and shine light back up on me when you are not allowed to open the action or for muzzleloaders

https://www.amazon.com/gp/product/B00SXLSLJ0/?tag=skimlinks_replacement-20