Threaded hole in breech plug on lyman GPR?


March 28, 2003, 10:09 PM
Whats the hole for in the breech plug of a lyman great plains rife (caplock, .54)? I didn't even notice it until I was browning the barrel. I have the rifle done(unless I have something I need to do with the hole). Seems like it should have a screw or something in it to keep from having powder flash back and burn the stock:confused:
I don't think there is any hardware left in my kit, just the extra rear sight, the nipple, and 2 extra screws (1 wood, one machine screw) I don't think the machine screw fits the hole in the breech plug though.
I'm going to have the people at the shop I bought the kit at look it over before I shoot it, so its not too big a deal. But if anyone could clue me in on this I'd appreciate it, I'd like to get the go ahead to head straight for the range once I get time to head back up there, instead of chasing small peices around the bed of my truck for an hour first :D

If you enjoyed reading about "Threaded hole in breech plug on lyman GPR?" here in archive, you'll LOVE our community. Come join today for the full version!
Jim K
March 29, 2003, 11:36 AM
Hi, redneck,

Didn't the kit come with instructions? I am not familiar with that kit, but from your description, it sounds like the hole goes through into the barrel or chamber. If so, please don't fire the rifle until you find out what's what. I guarantee it will do worse than just "burn the stock".

Can you give a better description of the breech plug and the hole? Some breechplugs have a crossways hole through which one of the lockplate screws fits to help hold things together, but those are not tapped.

Other types of breech plugs have the chamber in them. Those may have the hole for a separate bolster or drum which screws into the side of the plug and into which the nipple screws. The bolster may have a small cleanout hole into which a cleanout screw is inserted when firing. The cleanout screw is removed for cleaning inside the bolster.


March 29, 2003, 08:03 PM
I didn't figure I needed instructions anyhow, till I found this dang hole. Pretty easy puzzle up till this point.

Anyway, the rifle has a hooked breech. The tang has a square hole milled into it and is attached to the stock with a long bolt into the trigger assembly and a screw into the stock. The breech plug has a square hook at the end so that you rotate the barrel down into the channel and it hooks on the tang, then you put the keys in (2 of them) in the forearm.
The hole is in the rear face of the breech plug and is roughly 1/2" deep (checked with fine peice of wire, previously I thought it went clear through), which puts the bottom of it about even with the back edge of the barrel. The hole for the nipple isn't real far in front of that, so I'm wondering just how much solid stuff there is between the back of the chamber and the front of the hole. It doesn't match any of the screws included with the kit.
There are no screws from the lock into the barrel or breech on this rifle. The hooked breech and keys hold it all together. The peice that comes out the side, that you screw the nipple into sits in a half moon shaped cut out in the side plate of the lock. There is a hole with a threaded plug already in it in the side of this, which I'm assuming is the clean out hole that you mentioned.

So, if you've got any ideas on what this is I'd appreciate it. I kind of figured not having it right could end up having an effect on my good looks ;) and possibly set me back to square one (with a BUNCH more peices) on building the rifle.

I bought it at the Log Cabin Shop in Lodi Ohio. They seem to carry alot of Lyman Great Plains Rifles, both kits and finished, so someone there should be able to help me out. I haven't even bought powder or anything yet, since I plan on going back and having them check it out and shooting it the first time at their range. I'd like to have it ready to go when I get there though.

March 31, 2003, 07:09 PM
you should have gotten in the kit, a small slotted headless screw to fill this hole. it is your basic clean-out drain which would seem superflous since its a hook breach and can be drained thought the nipple hole but, its there anyway.

On original bp arms, there was frequently a "blow-out" plug in the same place. It was generally made of german silver and designed to blow out if the rifle was overloaded. The deeply threaded hole on the Great Plains and other modern rifles with the feature would probably not serve this purpose as it is questionable that it constitues a line of least resistance.

Jim K
March 31, 2003, 11:40 PM
Hi, Mec and Redneck,

Mec, that looks like an ordinary cleanout screw to me. It can be used to drain the barrel in cleaning, but its original purpose is to allow insertion of a pick to clean crud out of the bolster when the gun misfires. Quicker than pulling the nipple or drawing the charge.

You have me on the blowout plug, but I have been out of the BP arena for a while, so maybe I have forgotten. In other applications, the term can mean either a safety device to relieve excess pressure or a way to "blow out" a line using air pressure.

The only way I have seen it used in firearms is to mean a plug welded into a barrel to patch a hole where the barrel "blew out" due to an internal defect. This is usually something done by collectors of antique arms to cover up a defect that would significantly reduce the value of the gun.

In any case, the hole Redneck describes is at the back of the breechplug, where a gas release would shatter the stock and probably injure the shooter. I don't blame him for wanting to know what it is for before he fires the rifle.


April 1, 2003, 07:25 AM
your loosening crud explaination is clearer than mine. On the german silvier plugs- I've seen pictures with them located in about the same position as this screw and captioned to explain that they serve as an excess pressure valve.

April 1, 2003, 03:50 PM
Thanks, but thats not the hole I'm referring too.
The hole on my rifle is in the hook of the breech plug, parrallel to the bore. Its about a half inch deep and threaded.
The clean out hole your talking about, did come plugged just like the one in your picture.
I'm really starting to wonder what the deal is here, since this is supposed to be such a popular gun and nobody knows what I'm talking about :confused:
Thanks for going to the trouble with the picture and all though.

Gerald McDonald
April 1, 2003, 04:59 PM
Okay redneck, I hope you know how much trouble you put me through to do this. Went to the safe and started digging out the GPR, a Randall knife fell from the top shelf and as I was making a grab to keep it from hitting the ground, I jammed my knuckles into the door frame of the gun safe so now I am typing this with one hand while holding my left hand over the trash can so the bleeding will stop. Anyway I took my GPR down (one handed) and I also have the hole you are talking about. Dont know what its there for but there is no screw in mine. My guess is the same breech is used on different guns and the screw probably is used on one of them.

April 1, 2003, 09:46 PM
Thanks I appreciate it. I'm assuming you have shot it before ? ;)
Sorry about the busted knuckles, but you see I brought an important issue to light with need a bigger safe, or another safe, or a HUGE glassed in wall O guns display set up or something :D

Gerald McDonald
April 1, 2003, 10:58 PM
Thanks for bringing the fact that I need a bigger safe to light, I will point it out to my wife and see if I can get her in agreement. I havent shot the Lyman alot but I did recently run some loads of about 120-130 grains of ff behind a round ball through it with no problems. It was put together from a kit by a custom black powder rifle builder who does a few Lymans for people who dont wish to spend the 1200-1600 that his base rifles start at. He oil finishs the wood, browns the barrel and color case hardens all the furniture. He didnt mention the hole to me and this was several years ago so I doubt there is a problem with it. My main shooter is a Jonathon Browning Mountain Rifle in 50 I picked up used a few years ago, nothing else sees much use.

cracked butt
April 1, 2003, 11:56 PM
My GPR has this hole also, it doesn't appear to have any function on this rifle, I don't worry about it. I would imagine that the maker of the barrel probably spec'ed the barrel to work in several different brands of rifles.

April 2, 2003, 09:01 PM
Hey Thanks again everybody!
Sounds like, it was only put there to aggravate me ;) I guess I don't have to worry about shooting it now. I'd still like to know exactly what it is just out of curiosity though. I may try to get in touch with Investarms, if I get some spare time. If I find anything out I'll be sure to post it.
Good luck talking the wifey into that full wall, bullet proof glass, remote operated, display case Gerald :D

If you enjoyed reading about "Threaded hole in breech plug on lyman GPR?" here in archive, you'll LOVE our community. Come join today for the full version!