Home Forums Hunting & Shooting Muzzleloaders Lyman great plains hunter lock issues

Just picked up a Lyman great plains hunter with a lock issue.If you set the rear trigger,the hammer will catch on the half cock notch.If you use only the front trigger ,it will fall,but has a atrocious trigger pull,about 20 lbs,Id say.
Any ideas for a quick fix?
Probably make a trip up to Trackofthewolf this weekend,if I cant get it ironed out before hand.

Take the screw out of the side that hold the lock in an clean it . U will have to take ram rod out and wedge out then barrel then lock break free clean the lock up ,dry it then use transmission fluid for oil .Put back togather but don't overly titeing the screw should work great then

IMO savage is probably pretty close . Unless what your telling us is that the lock will not cock to the full cock and hangs only at the � . In which case its a issue with the trigger .
If that�s NOT the case then the problem is most likely the fly .
a) its not there . IE the PO lost it
b) its gummed up and not falling into place
c) it has a burr that�s catching the sear and acting like its catching the half cock .

Take the lock out and inspect it . Work the lock slowly ,with the lock in the up right position . you should see the fly move down and cover the � cock as you work the lock from the fired to full cock and back again . If you don�t see the fly . Then that�s your problem . You need one .
If you do see it but when the lock is in the full cock position , the tip of the fly is still up near the full , then you probably have a burr . If that�s the case then when you fire the lock and it catches , you will see the sear hung up on the fly .

The way a lock works for a double set or single set trigger is different then one with a single bar trigger .
When you use either of the above two without being set , they work just as a single bar trigger does .
IF it�s a hunting type set trigger NOT a target set trigger . The difference between the two is that . One allows the lock to be fire without setting the trigger . The other requires the trigger to be set before you can cock the lock to full .

Let me see if I can explain this difference.
With a single bar trigger , when you start your pull , what your doing is placing pressure against the sear . When that pressure reaches a given point , the sear will slip from the tumbler notch . The required amount of presser to trip the sear is determined by 3 things
1) the depth of the full cock notch
2) the angle of the full cock notch
3) the point and angle of applied leverage. Ie. the position of the trigger .

When enough pressure applied to slip the sear , our finger is still creating pressure on the trigger . As the resistance to that pressure is suddenly reduce , our reflex is not quick enough to let the pressure off the trigger . Because of that we hold the sear away from the tumbler with finger pressure and the lock falls completely .

With a double or single set trigger , of which there are different designs . But basically with the most common design like the one you have .
The set trigger is the one firing the lock . NOT the trigger your pulling on .
What happens is that as you pull the set trigger , the click you hear or feel , is the sound made of that trigger engaging under a notch in the front trigger .
The set trigger is then held to that notch by spring pressure .
All the trigger adjustment screw does is set the amount of aloud engagement of the rear trigger ,to that notch in the front trigger. As you pull the front trigger your changing the angle of the notch that�s holding the set trigger in place . At a give length of movement the set trigger �rear trigger � is released /slips from the notch .
The force of the trigger spring then slams the rear trigger up into the sear with enough force to disengage it from the tumbler notch . But because there is not the continual pressure being applied to the sear , the sear is not held away from the tumbler . So as it slides along it .If the tumbler doesn�t have a interrupter/ �Fly � to cover the � cock Or the fly doesn�t fall down and cover the � cock , then the pressure of the sear spring will force the sear to fall into the � cock notch .
Where with the fly or properly working fly , it covers the half cock notch , allowing the sear to slide along the fly and past the � cock . .

Now if that fly gets a small burr on its edge , the sear can catch that small burr and act like its catching the � cock .
This burr is most commonly caused by a dirty lock or repeated test firing of the lock with it or the gun laid on its side .
What happens is that as you cock the lock with the gun up right , the tumbler turns along the sear . The fly is dragged up towards the full cock . But it hits its stop just short of covering the full cock . As the sear drops into the full cock , the fly is supposed to fall down and cover the � cock .
But if the fly becomes gummed up so it doesn�t fall away OR if your one of those people who continually cock and fire the lock with the gun on its side , then what happens is the sear pushes the fly in front of it as the lock is fired . When the fly hits its lower stop , instead of the sear gliding smoothly across the fly , the sudden jar of the fly stopping creates a bounce to the sear . That bounce then starts to produce a burr. When the burr gets big enough then the sear will catch it and stop the lock

Anyway . Probably way more then you wanted to know . But IMO if one knows how a lock and set trigger works , its very easy to diagnose and narrow down whats possibly causing an issue

I've had three GPR's, and they all had the problem. Taking the lock apart, an polishing all the parts that need it cured it.

now that you bring this up . one of the issues i find with the lyman locks is that they use a cheep thin piece of plate for a tumbler bridle . the fly , on some of their locks fits over a pivot type of post . it doesn�t have a shaft like the better quality locks .
if your bridle plate gets warped , it will allow the sear to slide behind the bridle and catch the 1/2 cock notch .
I have had a couple Lymans in my shop with that problem

Not having anything else to do today I decided to take aprt the lock,and see what I can find.
Sure enough,the inside of said lock,if full of burrs and metal filings.
Time to find a stone,or diamaond card,and get on it.
Ill report back later with my progress.

after spend a few hours filing and stoning the lock,I put it all back together ,and still the problem persisted.
I removed the lock from the stock,and cocked and released the hammer a few times,and the problem is obvious.
The lock is so poorly assembled,the sear simply pushes the fly to the side,and catches on the half cock notch,there is enough slop in its construction to allow the fly to stick out,rather than block the sear.
Ive decided to think for awhile ,before trying to fix it.
Any suggestions?Im thinking the easiest would be to put a slight bend in the plate,much like the bend in a key to hold the barrel in.

by the way,is it normal for the sear pivot screw to not tighten down on the plate? if it would,it may just be the key to keeping the fly from sidestepping when the hammer falls.
Either it is too long,or it is not intended to tighten down.

I wonder what all that lock polishing does to the warranty if the new owner cannot fix it himself?

Yep you have a warped tumbler bridle.
Cause . Someone not tightening down the pivot bolt properly. Then coming back and doing just what your thinking the fix would be . IE tightening the plate all the way down tight to the sear .

See what happens is that this screw is only supposed to be tightened to the point it starts to impart drag onto the sear . Then its backed off so that the sear is in free play .
If one leaves it over tightened and then tried to cock the lock , the tumbler as it turns stretches the plate .
As I said in a prior post . It doesn�t take much to warp the plate because Lyman uses a cheep piece of soft [bleep] to make the plate
By the time the person figures out that they have to loosen the sear pivot , its to late , the bridle is warped enough that it no longer holds the fly down .

You have to get the warp out of the plate or replace the plate . Either that or the Fly will not stay in it bed and between its stops .


Was this photo taken prior to you polishing because im not seeing any of the areas you should have polished being polished ?

the lock plate should be polished .
The sear nose should be polished
The tumbler should be polished where the sear rides , where the tumbler rides on the lock plate and where the tumbler rides along the bridle
The edge of the fly should have a smooth even polish .
the bottom of the sear bar should be polished as should the top of the trigger bars. that way they also slide smoothly

In other words any area where metal slides across metal , you should have polished

If done properly , i would not think there would be a problem . if done improperly to the point a person started removing metal with stones to the point the lock became sloppy . then you would probably have an issue

Thank you,sir,for the photo work,I really apprieciate the help.
First of all,let me say,I now have the lock operating correctly.I was able to determine the tumbler bridle plate was indeed warped,away from the fly.Judicious application of a poundicator, and an anvil, flattened out the plate enough to keep the fly in place,but not so much as to cause friction.
I did not try to polish much ,as I only had a small file,but it was enough to deburr the edges(visible in photo),and clean up as many rough spots as I could find.There were alot of those,to be sure.
I didnt want to go ahead and polish alot of the contact points,as some of these foreign made guns are made of soft metal,(as noted)and surface hardened to stop wear.Also,the lock has been noted to be quite sloppy in fit,and any removal of matieral wouldnt help .
Anyway,the parts are now held together enough that the fly isnt simply pushed out of the way,and allows the set trigger to be set,and the hammer to drop completely.
Looking forward to try it out this week.

you shouldn�t polish to the point you remove a lot of material thus making the lock losser then it already is .Simply look for any burr�s . those you can remove . The rest you want to smooth out .
This means that sometimes scratches have to stay but that�s ok , as long as you don�t have sharp edges.
Fine diamond plates work well for polishing , so does real fine emery. In some cases just a rag with lith liberal use of brasso will help enormously