GTA
PCP - HPA - C02 Gate => Crosman Discovery Forum => : melloroadman June 23, 2008, 07:15:00 AM
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I was able to get some chrony numbers in before my pump quite working so I only got about 60 shoots on the mod but I am happy with it . It is light and really has no creep its a keeper as far as I can tell so far. Thank you Crosman team A for showing us the way . It does to the Discovery what the GTXIII does for the Gamo issue . I have a GTXIII in my storm and this mod is just about the same trigger fill as it . I say this so some of you have a comparison to go by. It is also as safe as a factory gun in that sear spring pressure and engagement have not been altered . My chrony numbers are consistent again . Which makes me happy and should help the 50 yard shooting I will try after I get a new pump from Crosman . Here are the numbers . Again same pellets CPH 10.5 FILLS 1900 - 1100 . I realize the new gun had slightly higher numers but that could be temperture related and the hammer was bone dry of lube and now it has some resistance do to lube. Marvin
NEW RIFLE
1 903
2 914
3 912
4 902
5 905
6 904
7 903
8 910
9 914
10 909
11 910
12 906
13 905
14 893
15 902
16 892
17 883
18 887
19 881
20 867
2 SCREW MOD
1 887
2 871
3 868
4 874
5 900
6 892
7 891
8 868
9 860
10 850
11 876
12 883
13 822
14 890
15 869
16 874
17 871
18 860
19 859
20 833
LOWER LINK MOD
1 848
2 870
3 854
4 867
5 865
6 864
7 871
8 867
9 869
10 876
11 876
12 872
13 874
14 860
15 860
16 856
17 857
18 856
19 850
20 846
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Thanks Marvin, looks like I may be moving a pivot point myself.
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A nice picture write-up is due. Marvin?
P.S. Great work!!
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Please read and if I need to take pictures I will . Just let me know. Marvin
http://www.network54.com/Forum/275684/message/1214268953/PICTURES
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As always remember to be extra causes after any trigger mod and KEEP YOUR FINGER OFF THE TRIGGER UNTIL YOU ARE READY TO SHOOT the first few times until you become familiar with the pull again. Marvin
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Hey Marvin is the "two screw mod" that you performed this one?: http://www.spiralsol.com/airgunmod/1005.pdf
Thanks
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Yes it was .And no I was not happy. Also look closely at it and you will see that you are playing with sear engagement and pressure which can make a gun unsafe. The mod I did with the lower link is much easier and safer. It is not my idea if you follow my post . It is something Crosman did on their A TEAM F/T RIFLES . I just followed in their steps by reading other post . Stop and think about it . Its a leverage helper that's all. The first rifles produced did not have the three holes in the trigger case and the people before me had no alterative for a fix . Big Ed's has a adjustable sear on the market now that changes the leverage point with the sear for about $30. This lower link just changes the leverage on the lower link instead of the sear. With the adjustable sear some of the adjustment is still made by sear depth contact . The choice is yours but I will not do the screw mod again . Either the link or the sear is the way to go. If you do the link it cost you nothing but time and if you do not like it you can put it back to stock and order the sear.
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Thanks a lot Marvin. I will do the lower link mod according to your instructions in your post.
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It really transformed the trigger to a decent one. Being lazy, I did not grind the surface of the link or center punch it. Just drilled a tiny pilot hole first, and then enlarged with 1/8" (?) drill bit. Worked like a charm! I also did not replace the trigger blade spring, instead cut mine by one "loop".
Safety warnings!
1. Rifle could misfire or bump fire if the safety pin is not inserted back into the trigger group.
2. The safety will not work anymore in my rifle, even when engaged, it allows trigger blade to move enough to release the sear. This should be fixed easily by either grinding the trigger link or the lower link mating parts. That would increase trigger travel in the 1st stage.
I shot my disco today for the first time after installing few mods (HDD, trigger, muzzle break) and it is a completely different rifle. Can't wait to do accuracy testing!
Chris
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Chris I am glade you are happy and yes it is important to keep the safety pin in the trigger group . If not there is not enough spring pressure applied to the sear . But I have not had any issues with my safety after doing this mod it works fine . Are you sure you have the sear spring engaged in the pin slot on the safety pin . If done as I described the only change in the link is the leverage point . The link and sear should be in their original locations and all other geometry the same. If the safety worked before it should work now. Marvin
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I don't really know why it wouldn't work anymore. I took it apart again and put it back together. Same thing. I ended up grinding a bit off the sear. It added more free travel to the trigger, but it's still good and now the safety works.
Chris
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melloroadman - 6/23/2008 6:00 PM Please read and if I need to take pictures I will . Just let me know. Marvin http://www.network54.com/Forum/275684/message/1214268953/PICTURES
So what was the end result from this lower link trigger mod Marv ?
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Marvin, If you have the gun apart in the future, a picture of the modification would be very much appreciated. And thanks again for the disco pats list. BTW I have posted some numbers on the "Yellow Disco Forum"
jeff124
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Since my rifle was apart anyway, I took pics of the mod. Second pic shows the trigger housing with 3 holes for link pin.
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Chris thank you .Now if we could get a machinist to make a new lower link with the contact bar on the end of the lower link instead of where it is at and lengthen the back of the sear arm to add more leverage I think we would have a super trigger . But then again that is probably what Crosman is keeping under cover right now. Then again may be Mr. Tuna will read this and get to work on a new project. Marvin
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Thanks for the great pix, just what I needed.
jeff124
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You all might want to check me on this, but with back of the napkin calc's for the tune of the lower link, moving the contact bar out just lengthens the fulcrum distance on the lower link to the SEAR thus increasing the force needed to be applied by the trigger. I looked at this by moving the new lower link fulcrum point from Chris's tuned location of 1/4 inch to the right only out to 3/16 inches forcing the whole lower link to be moved to the right by 1/16 inch. The input fulcrum distance from the trigger remains the same and the output fulcrum length on the lower link gets longer. The distance from the SEAR fulcrum point to the contact point gets longer also by the same 1/16 inch. Ultimately, it looks as though the force required in this will actually go up. From the back of the envelop calculations, if you assume the original force required to be applied to the sear by the contact bar is 1.0, then the 1/4 inch tune by Chris drops the force input required at the trigger from a relative value of 1.38 to about 0.54. With drilling the new hole in thelower link at 3/16 inches rather than the 1/4" of Chris's mod, you move the whole lower link and subsequently the contact point on the SEAR to the right by 1/16 of an inch; a force advantage. Hower, the force reduction on the SEAR does not make up for the loss of advantage by moving the fulcrum point and the napkin calcs say that the new resultant force required would be a relative 0.762. Worst case, there will be no change what-so-ever. So to really see an advantage, I think you would have to have a different Lower Link, SEAR and SEAR fulcrum point - essentially a whole new trigger assembly. I think Chris's change is the best you can do for the existing trigger components and trigger fulcrum points. By the way, I used measurements off Chris's photos so there is some error involved.
Scott
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Hi Chris,
Did the mod, it works very well, the trigger is so light that my groups are getting more compact since I can hold the grip lighter too.
Scott
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Hey Scott, didn't mean to be rude by not replying, but I simply did not notice your last 2 posts from 3 week s ago.
Anyways, since I did the mod I had a chance to shoot and chrony the disco more. It turned out that doing the "hole mod" and cutting the trigger spring made the trigger too light and the sear dragged on the hammer and slowed the rifle down. This result might not be typical! But it happened to my rifle. I started fudging with the sear and dremel tool trying to shave some of the top of the sear that locks the hammer. That made the rifle unable to cock. I left it alone for awhile, thinking I would need a new sear ordered. Last weekend I approached the modified sear again with the dremel, shaped the top some more and developed a more pronounced notch for the hammer to lock into. I polished all mating sufaces nice and applied some moly on it. To my own big surprise it resulted in even better trigger, without the drag on the hammer, safe, pronounced 2 stage (1st stage maybe a tad long) but the break is much crisper than ever. Next time I have the disco open I will make sure to take some pics of the new sear. I definately do not reccomend this modification, as I feel that my result is pure coincidence.
I like my disco whole lot better now.
Chris