Sunday, June 24, 2012

Screwing with my trigger (update: information added)

for a lighter and still-safe pull.

DISCLAIMER! WARNING!! READ THIS!!!
This is how I did this mod, and it worked for me, on this rifle; that doesn’t automatically mean it’s a good idea for you to do it. Messing with the trigger mechanism is something to do ONLY if
It’s actually needed
You know exactly what you’re doing
You test it out thoroughly , both before you load it and after.
So if you mess with yours get a BANG noise when you didn't want one, don’t blame me.

Ahem.
The Remington 512 I used for the Accu’rzr testing is a fine rifle, part of the 510 series they turned out: single-shot, box magazine, tube mag, hunting and match Linkrifles. I added a scope to this one, and aside from the basic front bead/rear ‘U’ sights(which worked better for me years back for some reason) there’s only one thing I didn’t like about it: the trigger. Breaks clean, but it’s heavy. Cleaning and lubing did not change it at all. I did NOT want to screw with the engagement surfaces, and after disassembly and a bit of study I found they weren’t the culprit anyway; it's the trigger spring.

In the top rear of the trigger- which is something of a '7' shape- there’s a vertical blind hole, into which fits the trigger spring and plunger. The plunger bears on the safety mechanism and the spring forces the trigger to pivot up at the front to engage the striker. It’s a small, but quite stout spring. So I decided the best option was to replace it.

Yes, you can shorten it; I’ll borrow from Sailor Curt on the CZ82 mag latch spring:
Many people lighten springs by cutting off a coil or two and that is a possibility, but it changes the overall length of the spring. In this case, I don’t think it would be a good idea because the spring’s so short already, shortening it more could adversely affect operation.
This also being a short spring, I didn’t want to cut it shorter; that left either the lightening method Curt uses, or making a lighter spring. ‘Making’ because I couldn’t find anything that would both fit in the hole and be strong enough. And it has to be 'strong enough'; this is what causes the trigger to engage the striker and hold it engaged until you WANT it to release, and it causes the safety to stay in the 'safe' or 'fire' position: make it too light and you run the risk of a bump causing the striker to slip, and I have an allergy in inadvertent ‘BANG’ noises. Or, possibly, the safety could jar into what's the wrong position for the situation(Murphy being the sneaky bastard he is).

For a spring of the same length and travel but less power, smaller diameter wire. So I measured the diameter of the spring wire(.025" close as I could tell) and found some a little smaller, the stuff I used being .024”(music wire, from Ace Hardware in this case).** Then I got the tools together, which in this case consists of
my power driver and a 1/16” drill bit as a mandrel. The driver to spin the (reversed, cutting end in the chuck) mandrel, and the bit because it was just the right diameter, which means slightly smaller than the final inside diameter: remember that wound wire will spring back just a bit when you release it, so when you finish winding and release the tension the spring will become slightly larger in diameter; so you need a slightly smaller mandrel than the inside diameter of the original spring.

Step one: take some pliers and make a almost 90 degree bend in one end.
Two: chuck the mandrel and the short leg of the wire in the driver. Yes, it can be a pain to get both locked in.

Three: Start winding. You have to use your off-hand index finger to support the mandrel, and it bearing on your finger will keep your hand and the wire moving forward evenly, giving you a nice, consistent spring. It’s hard to describe. Start the driver turning SLOWLY, and get the first few turns as evenly-spaced as you can; if you can get that first few just right, those coils bearing on your finger will just move things along, kind of magic to watch. Make it long as you can, you cut a section to length to try, and you can always cut another.*
Yes, this is difficult. Yes, you’ll probably screw up a few; big deal, the wire comes in 3-foot lengths. And remember that if you get a couple of turns wrong at the start, it’s not horrible: just adjust and keep going (I cannot emphasize this enough) SLOWLY. Shift your index finger further along to the good coils if need be. You’ll get it.

Here’s the product, right off the mandrel
You'll notice the first few coils are uneven, then I got it smoothed out nicely.

Here’s the original spring and the replacement
Original on the left. Yes, the replacement has fewer coils per inch. I would suggest, after cutting a section off, use a stone or- my favorite- a cutoff wheel on a dremel to smooth the cut ends.


As to getting the original out, clear the rifle, and pull the bolt. Then remove the action/barrel group from the stock. You have to drift out the trigger pin and remove the safety to do this job, so I used a bench block to support the receiver
and a brass punch to push out the trigger pin. You don't have to remove it from the receiver, just drift it over enough to free the trigger, which will then slip down.
Actually removing the trigger involves pulling another pin so you can remove the whole trigger assembly; it's connected into the feed mechanism. You don't have to do that for this job, so I left it connected. Now, see that piece sticking up at the top rear? That's the spring plunger. You can't take it out now, because the safety is in the way; so you flip the receiver over
and unscrew that screw; you'll have to hold the safety lever in place to break it loose, mostly likely, but after that it should just unscrew. The lever and screw lift off, and you can pull the safety itself out the back. They look like this
once removed. If you work on one of these, note the end with the ears; those ears go to the left and down when you reassemble it. The end of the shaft is slightly smaller diameter and fits into the hole in the receiver, and if the ears aren't down things don't work. At all. The area between those ears is shaped so the plunger bears on it and compresses(would that be pre-loads?) the spring, both giving a nice 'click' between 'on' and 'off', and giving the trigger the pressure it needs to properly engage the striker.
(Yes, you can take the safety out first; but if you do make sure you're in a place where, if the plunger and/or spring comes out while you're removing the trigger pin, they won't fall out and go walkabout; don't ask how I know that)

I put the replacement spring and plunger into the trigger and reassembled everything.

Then started testing. I worked the bolt(after making sure nothing was hiding in the magazine that shouldn't be there), both gently and then hard and fast; no unplanned ‘snap’ noises. Then put a #6 snap cap in and found the trigger pull was much lighter and still clean. Excellent, so far. So I kept working the bolt, banged the butt on the floor, whacked the side of the stock with my hand a few times, all trying to make the striker slip, and it stayed cocked.
Note: I cannot emphasize this enough, if you mess with the trigger mechanism AT ALL, you HAVE to test it thoroughly; there are no shortcuts on this, do it right or not at all.

I don't have a trigger pull scale, so I rigged up a 'string to the trigger, add weight to the cup' mess and tried that; according to it, the trigger now breaks at about 4.5#. Feels lighter than that to me; if it is indeed accurate weight, then the original pull was around 8-10#.

So took it to the range to try, and for the first ten rounds I worked the bolt gently, then hard and fast(making damn sure the rifle was pointed downrange), and it behaved just as it should. And the lighter pull definitely made it easier for me to keep the shots where I wanted, especially offhand.

So that’s how I lightened the pull on this rifle.
DISCLAIMER! WARNING!! READ THIS!!!
This is how I did this mod, and it worked for me, on this rifle; that doesn’t automatically mean it’s a good idea for you to do it. Messing with the trigger mechanism is something to do ONLY if
It’s actually needed
You know exactly what you’re doing
You test it out thoroughly , both before you load it and after.
So if you mess with yours get a BANG noise when you didn't want one, don’t blame me.

Note: I was using the camera with the timer on a tripod for the shots of me holding the stuff, a very handy thing that is. As long as you can hold whatever you're doing long enough for the timer to run down.

*There are several ways to do this. If you can find a machine screw with the right diameter and thread pitch, you can use that as the guide, and get very nice springs. You can use a lathe set up to cut threads or with a suitable tool to turn the mandrel and control the pitch of the windings(I've seen pics, haven't tried it myself); you can make a crank of a proper-diameter wire to wind the spring around. Or if you’re lucky you can visit Ace or Lowe’s or someplace and find a spring that’ll work and save all this messing around. If you're one of those "I need that" types, sometimes Numrich or somebody will have a big bag of assorted springs for sale, you might find the right size in one of those.

**Yes, the original wire may have been .024" also; I was using a caliper to measure, and a thousandth is within my margin of error. But near as I could tell, the replacement wire is slightly smaller diameter.

One more note: Something to remember on making springs is that the act of winding the wire around the mandrel won't just form a coil, it will actually work-harden the wire a bit(I think, this is opinion and I haven't dug around for confirmation/negation of it), which can make a spring a touch stronger than you might expect. I don't think it's enough to be a big factor most of the time, but thought I'd add this on

Added: Bob had a question:
...is the spring you made tempered properly to act as a spring? That is to say, when it is compressed, does it return to true reliably? Is it hard enough to flex without taking a "set?" Is it still soft enough to prevent snapping from brittleness?
Good questions. Here's my answers:
From what I've read, the small-diameter music wire like this isn't heated and quenched: when it goes through the drawing process, it's not annealed after the last draw, and the work-hardening of the process gives pretty much the same effect. Add in the work-hardening of winding it, and it's stiff enough to make a nice coil spring and tough enough to take repeated cycles without collapsing or taking enough of a set to not function reliably. If you've never messed with this stuff, it's very hard and flexible. Small-diameter stuff like I used can be worked cold. I've made a number of them over the years with this stuff, in different sizes, and they're all still working; a gunsmith I used to know had made some also, and so far as I know they're all still in service. Larger-diameter wire, unless you've got some kind of equipment to handle that much pressure you'd have to heat it to be able to wind it, and then you would have to harden and temper it.

A lot of springs are made this way: suitable wire wound cold on the appropriate mandrel to give the desired finished size and strength.

All the springs of this type I've made have been for something like this job, they don't undergo complete compression when they're worked(like a recoil spring, for instance), and I've never thought to measure original length to compare to current. That would be an interesting experiment: make a spring, measure the length, put it through a number of compression cycles and measure again... Dammit, see what you've started? Now I've got to disassemble that and measure, and then make another spring and a test rack of some sort...

4 comments:

Bob said...

Question, and I ask this out of a small knowledge of tempering/heat treating: is the spring you made tempered properly to act as a spring? That is to say, when it is compressed, does it return to true reliably? Is it hard enough to flex without taking a "set?" Is it still soft enough to prevent snapping from brittleness?

I'm just curious, not criticising.

Gerry N. said...

When I was a callow yoot of some 20 Summers I acquired a MAB .22 Auto pistol. I liked it. A LOT. Until the extractor broke and flew Deity knows where along with it's spring and plunger. My local (within walking distance) gunsmith wanted an extortionate amount of geld to make, procure replacement parts, around $20 as I remember. That kind of money would have got me and my romantic interest at the time a nice dinner, a movie and a tank of gas to get us back to her apartment so......

I got hold of a piece of air hardenting drill rod, sawed and filed on it for a couple of hours, until it functioned as an extractor, made a plunger out of a piece of 12D bright common nail chucked in a power drill and turned with a file. Then tried half a dozen small springs starting with one from a ball point pen. I finally liberated a broken guitar string from a buddy and wound several springs on sundry mandrels until I got the OD coil I needed. I tried varying lengths until I chanced upon one that functioned. Drove out into the tules to test it. Everything worked fine, and continued to do so for at least five years. I traded or sold that pistol for something vital at the time and haven't heard about it since. Lessee....25 from 67 is what?.....42? That's 42 years, what's the expected serviced life of a cheap .22 auto pistol anyway? I've made hundreds and hundreds, dozens maybe, of springs from music wire. For years I'd beg broken wire guitar and piano strings from Stan Boreson's Music in Faraway, Exotic Ballard in NW Seattle. He closed his store about fifteen years ago, but I still have a shoebox full of sundry sizes of music wire, so useful and so cheap.

Gerry N.

Sigivald said...

Also, places like (first thing I found searching) Lee Spring will probably have something that meets the specs for any plausible size.

Theresa said...

Great post you have here. Very detailed and I would say you are working magic with that trigger. I am more into knives though. The Spyderco Manix 2 Knife I got last month is well conditioned and ready to be used at any given time.