GPR breechplug

[jweston]

I was shooting over the weekend and couldn't get ignition worth a dang -- which is surprising as the last couple of occasions I was shooting 7 first strikes per 8 shots. So, I decided to pull the ball, which I couldn't -- between the screw puller and the normal tip, I smashed to ball into the breech pug. In order to clear everything, I had to remove the breech plug to melt the ball out. I was surprised at the distance between the vent and the end of the plug. It looks like I need to either increase my load (75 gr FF), or make sure that the ball is in front of the vent (and possibly having walnuting). And getting the plug aligned along the flat is not easy. I imagine that I could measure the treads, multiply by the twist and align accordingly, but I was being lazy. Does someone know the threading for a lyman GPR breech plug?

Thoughts? BBurg

 

[CoyoteJoe]

I guess I don't understand your problem. The GPR has a patten breech with a recess which holds less than 20 grains of powder and the vent is at the rear of that recess. Unless you dry balled (no powder) it would be impossible to ram the ball into the breech plug recess and pretty much impossible even then since you'd be trying to ram a .50 or .54 caliber ball into a recess of less than 3/8".
Pulling a ball with a screw is never easy since the screw expands the ball even tighter into the bore and that bore is fouled with powder residue. Often a good gob of spit or a squirt of liquid lube down the bore will help to soften the residue and make it easier to pull but it is generally easier still to work a bit of powder through the vent to fire the ball out.
I don't know the thread of the GPR plug, no doubt metric, but if you managed to pull the plug without badly marring the plug and barrel you are a lucky fellow, they are best left alone.

 

[MikeChapin]

I thought GPR's had a patent breech. Most of those I have seen will only hold about 10 or 20 grains. Anything above that should put the ball well away from the breechplug and the touch hole.

Patent breachs have a down side in that you have to make sure it's clean. After it cruds up a little, powder will sometimes bridge and not get down into the breach. When that happens, I push in four or five grains of priming powder though the touch hole. That will set off the main charge, or if I screwed up and dry balled, it will pop the ball out.

Don't know what the thread size is on the GPR breach. I would assume it is metric but other than that I can't help you.

If the breachplug is the one you got out of the barrel it should go right back in. The last half flat of turn should take a bit of torque to get it aligned

 

[jweston]

Well, the ball was sure stuck in the plug. I had to melt the lead out on the kitchen stove. It seemed to extend at least a centimeter into the plug; certainly deep enough to fit a 0.490 ball.

I could swear that I hadn't dryballed, but I am starting to have senior moments (in my 40's)
BBurg

 

[J.D.]

If you are seating the ball on the powder with enough force to drive a ball into a powder cavity, you are using waaaaaaaaayyyy too much force.

Chill dude. :haha:

The ball only needs to be in contact with the powder, not driven through it. :rotf:
J.D.

 

[CoyoteJoe]

Well, the ball was sure stuck in the plug. I had to melt the lead out on the kitchen stove. It seemed to extend at least a centimeter into the plug; certainly deep enough to fit a 0.490 ball.
I could swear that I hadn't dryballed, but I am starting to have senior moments (in my 40's)
BBurg

Well, if you didn't dry ball and the ball was driven into the breech plug recess, where do you suppose that 75 grains of powder could have gone? :hmm: Are you the original owner of this gun? The reason I ask is because I'm wondering if the breech plug may have been modified by enlarging the powder chamber. I don't see how else one could ram a .490 patched ball clear into the powder chamber and it is not easy to remove the plug unless it has been previously removed. The plug will normally have a flat face with a counterbore less than 3/8" diameter extending the length of the thread and on back to where the vent enters from the side.

 

[jweston]

I am not the original owner. The plug might have been modified -- I posted because I was shocked at how deep it was.

 

[J.D.]

Just curious, but what is the diameter of the cavity?

A powder cavity that was reamed out too large may be dangerous.

It would depend on the minor diameter of the threads and the diameter of the breech. In other words, how thick is the wall of the breech?

Just food for thought.
J.D.

 

[jweston]

JD, I ended up putting the breech plug back, but the next time I take it off, I will measure. The next thing that I plan to do -- money permitting is get an L&R replacement lock and a 1/4-28 white lightning vent.
BBurg