GPR-Kit..Lock Problem??

Hi there,

A couple of weeks ago I was quite lucky und could get a GPR .50 cal. for just 50 euros on egun.The gun is obviously a Kit-Gun that someone just put together on only one weekend. :grin:Still lots of work to to..will be fun to fix it up a little.

The bore looked quite nice,so I burned a little powder with it to see if everything works.Seemed to be a nice shooter after all :thumbsup: .
But.

The hammer on half-cock position doesn`t clear the nipple enough to put a cap on.
That´s my first GPR so I just wondered if that would be normal..
And also even with a quite small charge of 50 grs Pyrodex RS and a PRB the hammer flies back to that weird half-half cock position during the shot.
Anyone got any ideas what the problem could be??

Sorry for my bad english,I try my very best but I´m from sweden.. :wink:

greetz Jan

Yes, the low hammer is typical of the Lyman GPR and of Thompson Center Hawkens as well.

As for the hammer blowing back into the half cock position, that too also happens quite often with these guns, even with a light powder load like your using.

Changing the nipple to a Tesco beryllium copper nipple (which often has a smaller thru hole) might eliminate the hammer blow back and these nipples should last you for the life of the gun.
They are very strong, tough and flame resistant.

Your English is far better than my Swedish.

The hammer comes back farther on some than others. I agree the Lyman nipples are no good and you should get a good replacement like the Tesco.

Your English is far better than my Swedish. ditto that!

Moguai said:

The hammer on half-cock position doesn`t clear the nipple enough to put a cap on.
That´s my first GPR so I just wondered if that would be normal..
And also even with a quite small charge of 50 grs Pyrodex RS and a PRB the hammer flies back to that weird half-half cock position during the shot.

Click to expand...

I agree that the hammer height at half cock is a little variable between individual guns, but too low in all of them. I just developed the habit of not capping till I pull the hammer back to full cock.

As for the blow back, I've never seen that in a lot of Lymans and TCs, with one exception:

Some people advocate enlarging the hole in the nipple for using Pyrodex. That's a bad idea, as it increases blowback as you describe.

I'd replace the nipple with a new one as already recommended and I bet the problem goes away.

I suppose some genius might have shortened and weakened the hammer spring, but that would be even more birdbrained than enlarging the hole in the nipple and a lot more expensive to fix.

Thanks a lot guys for that quick response! :v

Alright that`s good to hear at least that the low-hammer prob is quite normal with the GPR`s.I could live with that one
But that hammer blowing back thing irritated me that much that I ordered a L&R replacement lock and,thanks to your answers(appreciated that!),a better nipple.
I´m anyway taking the whole gun apart just now and I`ve spent so little on the purchase that I think it`ll be worth it.

@ brownbear

You said that some people enlarge the hole in the nipple to be able to use pyrodex...
Why is that??I´m using pyrodex in pretty much all of my guns without any problems at all..
(the real stuff is almost impossible to get over here and if so you get to turn your house into a concret-bunker.. )

The position of the hammer at half cock was designed to prevent a cap from coming off the nipple when walking in the woods or field. Nothing worse than raising a gun to your shoulder, cocking the hammer, lining up the sights on game, and pulling the trigger only to find the gun go " CLICK", because the percussion cap fell off. The companies decided it was more useful to provide a barrier to the cap falling off, than to raise the hammer enough so that its easy to cap the nipple at half cock.

By all means, replace that factory nipple As soon as possible. Those Berylium-bronze nipples have impressive performance records, and are drawing a lot of fans. Blow back is Dangerous! Don't fire the gun again until you replace that nipple.

Always wear eye glasses( goggles) and hearing protection when you shoot these guns. The eyes and ears you save will be your OWN! Guten Noben.

Moguai said:

@ brownbear

You said that some people enlarge the hole in the nipple to be able to use pyrodex...
Why is that??I´m using pyrodex in pretty much all of my guns without any problems at all..
(the real stuff is almost impossible to get over here and if so you get to turn your house into a concret-bunker.. )

Click to expand...

Supposedly it allows more flame from the cap to reach the powder. That may be so, but it also allows more hot gases to escape through the nipple.

I found that switching to a HotShot nipple or an Ampco bronze nipple solved any Pyrodex misfire issues nicely without the hammer blow back.

Speaking of the low half cock position, I'm not sure if you know but the lock in your gun is made for use with the double set triggers.

Once the hammer is raised above the half cock position a small steel part in the tumbler (called a "fly") prevents the sear from engaging the half cock notch again until the hammer is lowered below that position.

While that lock is in your gun the correct way to install the cap is to raise the hammer to the full cock position.
Then, carefully lower the hammer with your thumb to just touch the cap and then raise the hammer back up to the half cock position.

You cannot lower the hammer directly from full cock to half cock if the lock has a fly in it.

Your replacement lock will also have a fly in its tumbler so when you install it, the same rules apply although I believe the replacement locks "half cock" position will be high enough to allow capping without raising the hammer further.

The beryllium copper alloy (proprietary name Ampco) nipple is made by Treso (Tesco is a British supermarket chain). The part number for the Lyman GPR is 11-50-03; it's a 6mmX0.75mm thread.

The L&R lock will have the same problem as the Lyman lock if you don't change the nipple.

As BrownBear said, enlarging the nipple hole for Pyrodex is assumed to allow more flame to reach the powder. In fact, the opposite is true; it actually cools the gas and lowers the pressure so less gas at a lower temperature arrives at the powder charge. Pyrodex has a higher ignition temperature than real black powder so a hotter gas is sometimes deemed necessary. I've never had a problem with it, however.

Treso nipples have a very small gas chamber and I think you'll find it works much better.

O'my a voice from the land of June, July, August & Winter, during my work career I spent considerable time in Stockholm, beautiful country.

Actually, I would suspect an altered nipple by the previous owner. This condition might also the be case with a used rifle purchase if the previous owner "dry fired" the rifle and thus malleted the nose of the nipple.

As BrownBear mentioned I have always used Hot-Shot nipples on my Investarms(Lyman&Cabela's) rifles with great success. However, after a lot of use, I have had to mill(sand) down the nipple nose diameter to get the "CCI Mag 11" cap to seat correctly.

Hope this helps,

@Osage :grin: yeah that`s kinda true..winters are quite long and summers awfully short up here..But beautiful country ,you`re right.

Thanks all for your great help!Appreciated it a lot.The new nipple did the trick!Shoots now very reliable,even with bigger loads of Pyrodex and 777,without any problems and hammer blow-backs. :thumbsup:

By the way,that`s the gun I was talking about.Got it refinished.A little at least.I´m not that experienced gunmaker.Just stripped the stock off ang stained and oiled it,cleared all the metalparts and browned the barrel and cold-blued the Rest.Kind of like it now.
Just the wood of the stock is actually quite boring..didn`t appear to me at all like walnut.Does anybody know if investarms ever used a different wood for the GPR?