P-64 TRIGGER PULL IMPROVEMENT

[heavyduty77]

I'm passing this information along because I've seen so many posts regarding this issue and thought it might be helpful to provide a slightly different insight into the matter. Bear with me. This is a long post.

I purchased a P-64 for use as a back-up to have on hand while I performed some accurizing work on my 1911. I did some research before the purchase and found this website. Based upon the comments I read, I ordered the 20# recoil and 18# hammer spring from Wolff's the same day I placed the order for the pistol. As soon as it arrived, I installed the springs and test fired the gun at the range. It worked OK, but I wasn't too impressed with the extremely light SA trigger pull. In fact, I experienced an unexpected "double tap" when firing a DA shot due to a combination of the light SA pull, recoil, and a one time inadvertent loose grip (I'll take responsibility for the loose grip; but still!?). The DA was acceptable but the SA was way too light to be used for anything but range work or home defense (definitely not a CCW gun that I'd be willing to carry with that light SA trigger pull!). Oh well, it was certainly well made and definitely would serve the purpose as a backup until the 1911 was back on its feet.

I eventually got back to the P-64 and became intrigued (more like obsessed) with resolving the trigger pull issue. I re-installed the "factory" hammer spring but the SA pull was only slightly improved (the DA pull was now too strong to be able to consistently concentrate on a target and comfortably pull the trigger in a uniform motion). Anyway, for what it's worth, here is what I did to make the SA trigger pull acceptable (to me).

My experience with the 1911 trigger had shown that besides polishing and reworking the hammer hooks and sear angles there are essentially three significant input variables that control trigger pull. 1. Hammer spring; 2. Trigger spring; 3. Sear spring. Although all of these are contained in a three segment "combination" spring, all three of the "forces" can be modified individually on the 1911. I will discuss separately how each of these three forces relate to the P-64:

1. Hammer Spring: Upon close examination of the trigger "action" it became evident that the hammer spring force had only an indirect or secondary effect on SA trigger effort. This secondary influence essentially increased the amount of resistance / friction created between the sear and hammer hooks (primary force is the sear spring). The stronger the spring rate the more resistance / friction generated. I can only assume that the main reason for originally selecting the very strong hammer spring rate was to make the SA trigger effort minimally acceptable.

2. Trigger Spring: The torsional spring used on the trigger serves both as a trigger return spring and as a "tensioner" to keep the trigger bar in contact with the sear. Due to its shape and size, and the small "envelope" that it's designed to work in, it doesn't appear that much can be done to significantly increase its force. (I installed one of Norm's heavy-duty trigger springs. It fit and worked fine but didn't make much of a difference to the SA trigger pull.)

3. Sear Spring: After studying the overall action, as far as I could see, the only place that a beneficial change could possibly be realized was with the actual sear spring itself. (As a side note, take a close look at the sear design itself. Its configuration is also a contributor to the poor SA performance. You'll notice that the difference in distance between the sear pin (fulcrum) and the point of contact with the trigger bar is longer than the distance between the sear pin and the sear plunger hole. This gives a greater mechanical advantage to the trigger and, as a result, a lighter SA trigger pull! I may be wrong but, considering the very strong hammer spring used and the overall sear layout, I can't help but think that the original designers must have made a horrible mistake somewhere in their calculations!

I made several trigger "pull tests" to establish a baseline to use as a comparison for the modifications that I was planning to experiment with. I tested the trigger pull with the original sear and hammer springs and then with two "reduced power" hammer springs (17# and 18#) that I had obtained from www.gunsprings.com. I found that the SA trigger pull only varied by a total of about a half-pound between all three. (By the way, the reason that I used inch / pound readings instead of millimeter / kilogram measurements was very simple; I only had an old spring scale calibrated in pounds!)

The next step was to find a spring that would increase the pressure on the sear. Unfortunately, the area that the sear spring operates in is extremely limited with less than one tenth of an inch of total travel! After a lot of research and many calculations I finally concluded that there wasn't a readily available spring that would both fit into this confined space and provide enough increased force to correct the problem. I was about to give up when I remembered that valve springs used on engines very often use both inner and outer springs to increase the applied force within the same given area. A "booster" spring; of course! I obtained some "universal" springs and, after a few more calculations and trial and error attempts, I ended up modifying one that had an I.D. that would just fit over the original sear spring and still provide a sufficient increase in the spring rate even after shortening it to the required solid height. (Note: the solid height dimension is critical. Due to the very limited range of travel, just a slight difference in length will make a significant difference in the spring rate. Too short and the spring rate will be decreased; too long and you will impart excessive stress / loading into the sear components due to the bottoming out of the spring (solid coil bind) while pressure is still being applied through the trigger.) I then installed the original sear spring and the new booster spring into the gun. (Despite having the frame mounted in a soft jawed vise, trying to install both of the springs in that limited space presented its own problems; more on that to follow.)

The next problem was to somehow increase the working clearance between the bottom of the slide and the new spring. In the original design configuration, the outside diameter of the booster spring was being wedged into the small area formed by the angled surface of the sear (just below the plunger hole) and the bottom of the slide. This interference caused the two "tangs” or "lugs" on the bottom of the slide to be forced over the "wedged up" spring coils with a resultant binding on the lugs / slide. I resolved this interference issue by fabricating a holding fixture for the sear and "spot facing" it to allow the larger diameter booster spring to sit flat against its mating surface on the sear. This spot facing provided enough clearance to allow the spring to sit further down during operation and eliminated the interference problem. WARNING: Operation of the pistol without providing adequate clearance for the larger diameter booster spring will cause damage to the slide!

The trigger pull tests with the new spring arrangement now showed a significant increase of up to 4-1/2 lbs depending upon which hammer spring combination was used. I finally settled on the 17# hammer spring because it gave the most reasonable DA pull and the extra strength of a stronger spring was no longer required in order to increase the SA pull. To verify the modification, I used Snap-Caps to dry fire the DA and SA action well over two hundred times. Then on to the range for live fire tests. 200 rounds of Silver and Brown Bear and not a hitch! The SA pull is now a pleasure to use and I can aim and fire consistently with the control I wasn't able to obtain with the original sear spring. I now have the confidence to use this gun for a CCW. Note: Subsequent to completing the above modification, I ordered some “factory made” springs to the exact specifications required to make the change. I ordered two different spring rates; one provides a 4 lbs S/A trigger pull; the other a 5 lbs pull (I prefer the 5 lbs pull).

Regarding the installation of the springs, try as I might I wasn't able to manipulate the springs and plunger into a position where I could insert the sear plunger pin. Because of the increased strength of the two spring combination, I just couldn't get the sear plunger and springs to align with the hole in the frame in order to insert the plunger pin. The needle nose pliers were being kept from properly aligning the plunger with the plunger pin hole in the frame due to an interference with the top of the hammer. This interference created an acute angle that I wasn't able to overcome. I tried again with the hammer removed but without the hammer in place the top of the sear would rotate forward and wasn't able to restrain the two springs. The springs would just "fly" off the plunger. The "final solution" was to remove the hammer and shape a piece of scrap wood to just fit into the magazine well while sticking up high enough to keep the sear from rotating forward. (Since the end of the plunger sticks through the sear, I had to cut a relief slot in the wood to allow clearance for the plunger.) I was then able to insert the sear plunger and springs straight into the hole in the sear and insert the plunger pin through the plunger and disconnector and into its position in the frame. Be careful here; make sure that the end of the plunger pin is properly inserted fully into its hole in right side of the frame before installing the retaining screw. (By the way, a pair of "4LN" long nose Vise-Grip pliers will come in very handy for this project.) I then installed the retaining screw, hammer and pin, and removed the piece of wood from the magazine well. Final assembly of the hammer spring & strut, slide, and grips was completed as usual.

OK, that's it! Please understand that I am not a professional gunsmith. However, I am quite familiar with machinery and mechanical devices. I started out nearly 45 years ago as an apprentice mechanic working with heavy trucks, automobiles, machinery, welding, etc. The above description of the modifications I made is provided here solely for your edification and in the interest of furthering the knowledge base and information available for the P-64. So, if you do decide to undertake this modification on your own, you do so at your own peril!

[oakchas]

That's a heck of a first post!

more info on the "factory made" springs, and pictures would make this even more valuable than it is.

Thanks HD77,

Charlie

[neoshooter]

Thanks for the post. Any possibility of a few photos of what you did? One of the wooden block in place would be especially helpful.

[conscript47]

Wow... and here I am happy with the 3 pound SA pull!

I am used to match triggers, and decided to just carry DA. I put in the 19 pound spring- because I was worried about reliably firing each round and also about firearm recoil. Remember- cocking the hammer is part of what slows the slide down for each shot. I am leaning more towards upgrading to the 22 pound recoil spring and 17 pound hammer spring, now that I see the primer impact isn't sacrificed. However, I can work with the DA pull with the 19 pound spring; it has actually gotten easier with time.

[heavyduty77]

I purchased the springs from CenturySpring.com. Unfortunately, there is a rather hefty minimum charge that I paid to get the springs. I had hoped to offer them to those interested in making the modification in order to recover some of my costs (and make it much more affordable for those concerned). However, in the interim between placing and receiving the order the "P-64 Resource" introduced the moratorium on limits of sales to those members with ten or more posts. As soon as I reach that number I'll post the offer.

Also please remember, as mentioned in the post, installing the larger spring without the clearance provided by spotfacing the sear will definitely cause damage to the slide.

I'll take some photos of the installation procedure and post them when I get a chance.

[heavyduty77]

Here is the desciption and pictures of the installation procedure for the booster spring & spotfaced sear. It is assumed that the pistol has already been disassembled in order to have removed the sear for the modification. (See closeup picture of the spotfaced sear.)

ASSEMBLY
Step 1 With frame clamped in a soft jawed vise, insert sear and sear pin (Step 1 Picture).
Step 2 Insert the disconnector (Step 2 Picture).
Step 3 Insert the piece of wood door stop molding (2x1-1/4"x3/8") (Step 3A Picture) with trimmed edge towards sear (Step 3B Picture).
Step 4 Adjust 4LN Vise-Grip pliers to grasp sear plunger (larger boss on plunger will face towards the disconnector) (Step 4 Picture).
Step 5 Insert plunger and springs into sear and install plunger pin (Step 5 Picture).
Step 6 Insert plunger pin retaining screw (Step 6 Picture).
Step 7 Insert hammer and pin (a "shoehorning" motion to insert) (Step 7 Picture).
Step 8 Remove wood retainer.
Step 9 Check spring height (top of spring must be below top of sear) (Step 9 Picture).
Step 10 Pull trigger and check compressed spring for coil binding (Step 10 Picture).
Step 11 Remove from vise and re-install caged hammer strut assembly, slide, and grips (Step 11 Picture).
Step 12 Function Test with Snap-Caps and then live on range. Remove slide and check underside after 50 rounds.

http://s844.photobucket.com/albums/ab3/heavyduty77/

[neoshooter]

Thanks for the details. I also am concerned about making the SA too light if I replace the hammer spring, and DA is just too stiff. I'll try your repair, as soon as you can sell the springs. By my count, you have only 7 posts to go! (Perhaps by then, I will have enough posts to see your selling post.)