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PostPosted: Sun Jul 03, 2016 10:18 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
Posts: 286
Location: Hill Spring, Alberta
My Nitro Venom trigger has the two screw mod thanks to Chevota, and they work really well.

But I have three guns with Chinese T-05 copies, (each also with two screws thoroughly polished, and no lawyer spring), and I wanted my Crosman trigger to work as well as those do.

The Crosman trigger is all polished, Tungsten Disulfide coated, lubed, etc., but the first stage was still too heavy.

I realized that the problem was caused by the heavy downward pressure on the sear from that hooked piece that catches the piston. The angle on the back of the hook is about 90 degrees, but when engaged, because of the pin location the piston tries to slide off the hook by forcing that piece downwards. It can't unhook from the piston until the trigger moves the sear out of the way.

I wanted to reduce the pressure, so decided to change that 90 degree angle to something in the neighbourhood of 75 degrees. These numbers are approximate because even if I did the measuring and math, I'm not a machinist. I used Dremel diamond bits.

I realized that this was a bit risky because if I made the angle too acute, I could end up with a "hooked" piston that the trigger couldn't release.

But I had a plan. heh heh heh. 8)

My anti-bear trap mechanism is long gone, so I can cock the gun, and WHILE HOLDING ONTO THE BARREL, pull the trigger.

If, after the mod the piston wouldn't release I wouldn't load a pellet but remove the stock and take the action/barrel onto the back lawn and poke it with a stick. Like you would do with a "dead" snake.

Actually I thought I could get into the trigger box with a small screwdriver.

Anyway, it all worked. I now have my two stage trigger with the first stage being about 1/2 the pressure of before and it's really smooth.

I DON'T RECOMMEND THIS MODIFICATION TO ANYONE, but I love it.

Another adventure in air-gunning.

Peter :D


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PostPosted: Mon Jul 04, 2016 3:41 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
I'm curious about the trigger pull being too much. Mine ends up being ~16 and 24oz for the first and second stage if I don't tamper with it to make it lighter. Was that not enough or did yours somehow end up more than what I get? And while the piston does push down on the sear, it's not much of a factor. Makes me wonder if your trigger is somehow different.
Having the sears catch lock onto the piston isn't all that easy since it cannot reach up in there far enough to hook the inner edge, plus the pivot point of the sear is lower than the piston. So the only way I can imagine it would stick is if the surface of the piston was rough enough and the sears catch sharp enough.
The reduced pull makes me wonder if it's catching somewhat, but not enough to hold it. I'd imagine the tip of the sear and piston surface it rides on will smooth out.
You said two screws, did you leave the oem screw in?
I ask because I want to be sure the guide is clear because I'm not sure if I explain things well enough. I also want to know about any misc problems I'm unaware of.


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PostPosted: Mon Jul 04, 2016 6:28 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
Posts: 286
Location: Hill Spring, Alberta
The trigger on my Nitro Venom is just like all my other Crosman triggers, and the original Phillips head screw is long gone along with the plastic nut, the trigger spring and the small pin it mounted on.

I have the single screw mod described in your guide, through the trigger and pushing on the sear between the two pin holes (the pivot pin and the pin that engages with the anti-bear trap mechanism). I find the guide very clear, and I refer to it quite often. (I printed it out.)

I think you described somewhere (on this forum?) a second screw mod as well.

I drilled and tapped farther down and aft on the trigger blade so that the second screw meets the sear where the pin that engages the anti-bear trap mechanism used to be. That pin is of course gone too.

Now I can adjust for first stage length and second stage weight.

My Nitro Venom has always been very hard to cock. It isn't shimmed or anything like that and only has about 3/16 of pre-load. I think my Xisico BAM28 is easier to cock, but then it has a longer barrel.

I thoroughly enjoy working on my air rifles, so I'm constantly tweaking and trying stuff. I've done a couple of lube tunes and trigger mods for friends (Gamo Hunter 220, and Crosman Vantage). They're happy and I enjoy doing it.

Peter :D


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PostPosted: Mon Jul 04, 2016 8:22 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
That other screw mod is I mentioned before is exactly what you did! For me it's easier to dial in the trigger w/o a second screw becuase once mod 4 is done w/ sears sharpened, it's pretty much exactly how I like it.
I attached a couple pix I made years ago but never added them since few were interested. I think maybe two people ever have asked me about it. If you could, post some pix of yours next time you have it out so people can check it out. I know I'd like to see it, especially if it's a better ideal than mine. One beauty of mods like that and 4 is they're reversible if people screw up or don't care for it. I think some people are scared to try mods out of fear they're ruin it.
Glad the guide was clear. I can't really put myself in the position of not knowing how the trigger works to see if my writing makes sense, so I rely heavily on feedback.

The preload on the nitro will have no measurable effect on cocking effort. I suspect friction and maybe stiction somewhere, like maybe at the nitro seal. The seal can in some cases add a lot if it's dry so I always suggest people grease the shaft. Other than that there's some piston and linkage friction but usually all this stuff is kinda minor unless you're anal like me and want every last bit removed. I don't know about the B28, but the 350's I have are only a couple pounds harder to cock than a Venom. As (I think) described in the guide, the cocking effort is different between coil and nitro, so at the beginning of the stroke the nitro is way harder, up to 3x harder (Crosman coil vs nitro), then the coil catches up but doesn't catch the nitro at peak effort, then the last few inches the nitro gets a bit easier where a coil not so much. So when I say compare cocking effort I really mean at peak since overall is too hard to compare. So I wonder if your B28 spring took a dump, or the Venom has some kind of issue? I guess you get one of those cheapie luggage scales like I use and we could compare. That's how I measure trigger pull too btw.
Btw, if you run across a friend with that new plastic Gamo trigger, which are more and more common now, I have some pix of how to mod 4 that puppy too. It was a member here that did it and provided me with the pix.


Attachments:
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12.JPG [ 91.15 KiB | Viewed 856 times ]
11z.JPG
11z.JPG [ 95.62 KiB | Viewed 856 times ]
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PostPosted: Tue Jul 05, 2016 8:10 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
Posts: 286
Location: Hill Spring, Alberta
Image
As you can see, I didn't get the angles quite right. The screws should be parallel.
Image
A view of the ends of the screws. I put them in my Dremel to round them. Again, I didn't get the angle quite right and the rear one is more to one side than the other.
Image
The bottom of the trigger. The rear screw is a bit too long, but it isn't in the way and I didn't feel like messing with it as it's working well. (Probably tomorrow I'll take it out again and shorten it.) The first trigger I did with two screws, they converged so they have to be flush with the surface or deeper. You can't back both of them out at once

I've done this mod to two of my guns, the Nitro Venom and a Quest. I'm getting better at it, and when I get some more M3 bolts (whenever the mail resumes) my Phantom will undergo the same surgery.

I don't have a drill press or anything, so I just grind flat spots on the trigger and use a punch to help centre the drill bit. I just do the best I can to get things straight, and this is actually a pretty forgiving mod.

There's something really satisfying about shooting a gun or riding a motorcycle that you've worked on yourself to improve it. For me the tinkering is a huge attraction and having resources like this forum with all the experienced people who are willing to share what they've learned is terrific.

Peter :D


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PostPosted: Tue Jul 05, 2016 8:24 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
Great job! And thanks for the pix.
My holes are no better really, I use a cheap cordless drill and hold the trigger by hand while drilling. I put it against a bench since I have to lean on it pretty hard while drilling, but accuracy is all eyaballin. I too make a little flat spot and center punch it, but sometimes use a pointed diamond Dremel bit to make the hole bigger.
The end product never turns out perfect but they certainly work perfect.


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