Okay guys and gals, this article is about the basic Crosman trigger present in the Discovery & Maximus, 2240, 2400KT, 1377 & 1322, etc. And I want to jump right to the final thoughts. This tuneup has made my Crosman guns way more enjoyable to shoot. Big time. I find I'm reaching for them far more often than I have in the past. It has made them fun again, and after all that's really what counts. Not to overstate it, they're no match for a fully adjustable trigger that's received a similar amount of attention. If you want that, do the Marauder retrofit and don't look back. But if you find it hard to drop that kind of coin on a new trigger group, please read on.
So what all does this tuneup involve? Four things:
- smoothing and polishing - the basis for most every trigger tune
- reducing the pull weight - a lighter spring combined with #1 makes this possible
- eliminating the sideways slop in the trigger blade - a mildly annoying thing that makes a trigger feel cheap
- eliminating the sear spring's interference with the housing - this is a key source of annoying stick-slip-stick-slip behavior. Doesn't affect all guns but seemingly most.
Okay so let's jump in. First order of business is to deal with that Mickey Mouse sear. Oh my, it's a piece of sh... stamped steel that looks like it was cut out by an angry beaver. Pictures are better than words so I'll let these be the guide.
To understand a little better about what we're dealing with, the following graphic shows the type of edge produced by a shearing operation. If you look closely at your sear as it is delivered from the factory, you can make out the shiny burnished portion and the dull fractured portion. You can also feel the slightly radiused rollover on the top side and a sharp burr on the bottom side. Our aim is to get rid of all these things.
Besides the obvious flattening and polishing visible in the photos, I recommend also taking a few angled passes to remove the burr on the tearout side. If all our parts remain perfectly orthogonal, the burr is irrelevant. But there is some play in the parts and they will twist on the pivot pins which gives some opportunity for the burr to introduce friction so I like to go ahead and knock it down.
For best results, I also recommend smoothing the hammer. I had already done that to mine some time ago and I didn't want to remove the breech and barrel to pull it out for a photo, but at some point I'll come back and add it to this article.
For the trigger, smooth and polish the rounded face that presses against the sear:
Now with all the contact points smoothed, you may still feel some hitches in the pull...the stick-slip-stick-slip thing I referred to earlier. If you don't, you can skip this part. If you do, it's easy to chalk it up to whatever friction remains in the system but that may not be the actual cause. Take a close look at the spring while you pull the trigger. The coils tend to drag on the sides of the trigger frame. There's a beveled edge that keeps it from snagging hard but the interference is enough to be easily felt.
In that case, make a little guide block as shown. It fits into the rectangular channel underneath the sear and is just tall enough to keep the spring out of the trigger frame so it can't catch on anything. This one was done with hand tools so don't let that stand in your way:
That's it, now on to assembly:
Start by doing a dry fit to make sure everything goes together okay. Use this step to determine if your spacer washers are right to take up the side play but not so thick as to cause things to bind up. Similarly, check that the guide block moves freely when you exercise the trigger. Once you're happy with it, lubricate the contact surfaces and do a final assembly.
The resulting trigger pull should be much smoother now and between 8 - 16oz depending on the strength of your hammer spring.
I hope this helps!
Okay, this is pretty funny. Today I'm looking at the little spring guide I made...
And I suddenly realize I'm looking at a Lego piece. We have 5 boys aged 2 - 12, and consequently enough Legos to start our own Lego museum. So I rummage though one of the many organizers filled with Lego blocks and pull out a couple of similarly sized pieces. Over to the calipers and it's precisely 0.31" square. No kidding, exactly the same cross section as the one I made.
It works like a charm:
The little cap on top is a smaller diameter so my 1/4" ID spring isn't a snug fit but it has no negative effect and the trigger works just as smoothly.
you say not too shorten the sear hammer interface area but why not
if it high enough to hold the hammer, taking a 1mm off the top will only help not hurt
the faster you can disengage the hammer the lighter the trigger pull
I,ve done it and liked the results and sear are cheap
Wendell, thanks for your positive comments. Regarding the spring, I've accumulated a bunch of random springs over the years so I have no idea where it came from but I just checked a Harbor Freight spring assortment # 67562 and it has a 9/32" OD x 3/4"L x 0.022" wire that could be stretched a bit to work in this application. This assortment has served me well in several airgun projects...its value is much higher than the few dollars spent on it, despite having a bunch of extension springs I'll never use.
Marflow, that's good to know the sear engagement can be reduced. I don't generally mess with it on a direct sear like this that has been fitted with a very light spring. But if I hadn't been able to eliminate the stick-slip behavior, I would have to reconsider so thanks for bringing it up.
Way back in the day, we used to totally reconfigure for a better mechanical advantage, best mod ever. The wire that extends the sear is soldered in place. The other end is rounded, polished and rests on a tiny stainless "plate" that's epoxied to the top of the trigger. All pins are removed and replaced with brass tubing, JB Welded in place. Polish, polish, polish and use moly lube. This gun is a 2040 with a LW .20 barrel. Stupid accurate once the trigger was solved.
Glenn in Texas
Excellent tutorial, great illustrations.
I'd add three things. Moly paste will react with the zinc die cast frame, and form an abrasive paste, so keep it off the frame (and some triggers, there were a few versions over the decades that were die cast, it's usually obvious)
Dry spray moly , sprayed on the working faces of the striker and sear, then rubbed in with a poly soaked Popsicle stick or similar will permanently reduce steel to steel friction, the moly bonds to the steel.
I like to bond the pins into the frame, after a light polish(or better yet, replacement with oversize pins) Locktite sells a thickened product in an easy to use tube, they change the name every few years , but it's something like "loose part repair' or "bearing mount"
Don't use a dremel on trigger parts, you'll get a wavy, curved surface. What you want is flat and square to the pivots.
The edge in the red circle in your photo "Sear side view" should be sharp, it looks to be quite rounded. Typically, the edge where the trigger "breaks" is sharp and square to prevent creep and facilitate trigger reset should you decide not to take the shot. If it works for you, so be it but I'm a stickler for keeping the edges of sears clean and sharp.
-Scot
It's a great lubricant but doesn't bond: https://en.wikipedia.org/wiki/Molybdenum_disulfide
-Scot
Classicalgas, you brought up an interesting point about an incompatibility between zinc parts and molybdenum lubricant. I was trying to do some research on it but am not having much luck. Can you point me to a source?
I found some stuff on the subject of it oxidizing (i.e. molybdenum disulfide becoming molybdenum trisulfide) and speculation that makes it become abrasive but that seems to be incorrect based on this paper http://www.nlgi-india.org/images/PDF/Yakov%20Ephsteyn.pdf and some other credible sources.
I did not find anything specific to zinc unfortunately.
Wendell, using graphite to lubricate a trigger group doesn’t appear to be a common practice. About the only place I see it used is on the hammer of PCPs where there is concern about low temperature use and the potential for liquid lubricants to become viscous enough to affect the hammer strike.
Moly is preferable when the loads are extremely high, suitable for 250,000psi up to 400,000psi according to various industry figures. That’s well up into the realm of yield strength of hardened tool steels. My gut instinct is that’s way outside of the loads seen by a typical trigger group, but let’s look at some numbers to see if it makes sense. Take a hypothetical example of a 16lb hammer spring (a strong hammer spring by most standards), and let’s assume the sear is 1/4” wide and the edge holding the hammer just before it’s released is 0.002”. The load in that case is 32,000psi. Moly is rated for roughly 10x that load. Graphite on the other hand is rated for something like 5,000 – 20,000psi according to industry sources, so perhaps that makes a reasonable case for why it isn’t the best choice for trigger groups.
BTW, the load carried by the sear of a powerful springer would be much, much higher so I would definitely want to use moly in that case.
As a general rule, I don't lube any trigger parts. It's just asking for dust to stick, lube to dry out, etc. but in the case of the trigger in question here, it's necessary. The load on the final catch is fairly substantial and since it acts as the sear as well (not the case with higher end triggers), it needs to be lubed. I think Steve in NC posted years ago about altering the bearing side of the catch and on a 392, I think I made a jig and ground it as a radius so the striker essentially didn't move while the trigger was being pulled. You've definitely given this a thorough look, smooth, square and sharp are exactly on the right track, the lube will just need a little replenishment from time to time.
-Scot
Here's a brief reference that implies that moly can adhere to steel surfaces... https://www.sciencedirect.com/science/article/abs/pii/0043164873900410, but you can test it yourself. Do a trigger tune, lube it with you usual lube, test the pull weight average for ten shots. Dossasemble, degrease, burnish in moly under pressure, reasemble and retest.
I'll see if I can find the moly zinc reaction info..it was mentioned on the old yellow years ago, but I discovered it after liberally lubing the guts of a DA repeating co2 pistol, in which most of the complex mechanism was made of die cast parts. The trigger got gritty and forces went way up in just a few magazines full. I never got that gun to feel right again.
https://www.sciencedirect.com/science/article/abs/pii/0043164873900410...refers to conditions under which moly will bond to steel, but try it yourself. On a degreased trigger and sear, that you've previously tested for pull weight... clean the parts well, rub the moly in hard, reassemble and relube. The surface pressure at the sear contact surface is high enough that the extra lubricity of the moly'd steel give a slightly lower static friction than most oils or greases.
I'll look for the zinc/moly reaction, but I read it on the old yellow years ago, after ruining a co2 repeater (that had a complex DA mechanism made mostly of die cast parts, with lots of contact surfaces) Within a few magazines of re-lubing with moly paste, the trigger was gritty, and trigger effort about doubled, it felt like I'd put valve grinding paste in the gun.Full disassembly careful cleanup, and lubing with lithium grease helped, but didn't fix the gun.
