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| Article written by: Mark Trope | |||||||||
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When I was in basic training, the Drill Instructor advised us that: “The hardest thing in the US Army is the trigger pull of an M16!” He wasn’t kidding. The first time on the rifle range, the M16’s trigger pull was so hard; I had to double check to insure I had moved the selector switch to the “FIRE” position! Most Military triggers leave much to be desired. They are designed that way. The long take up and heavy pull insures a nervous soldier on the battlefield won’t have an accidental discharge, or the act of running and jumping into a foxhole won’t cause a rifle to fire. What about standing post in winter, and wearing gloves over icy cold fingers? The Military trigger is designed with all these scenarios in mind. A crisp, clean breaking, fully adjustable trigger is a joy on the range or when you are trying to place a bullet into the kill-zone of a deer. I, not being one to make permanent modifications to my Mil-Surp arms, had already put a No-Drill, No-Tap scope base on my K-31. See article: http://www.surplusrifle.com/reviews2006/stmariescopebaseswiss/index.asp So, I was intrigued when Huber Concepts LLC developed a fully adjustable trigger for the Swiss K-31, one that did not require any permanent medications to the rifle. |
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Before we get into the actual trigger installation, let’s see what the average trigger pull for a Swiss K31 is. With that in mind, I repaired to WEST TEXAS MILITARY SURPLUS, 2413-34th St, Lubbock, Texas 79411, 1-(806)-785-4867, www.gunsandblades.com and checked the pull weigh of every K-31 on the rack.
Testing trigger weight-of-pull requires an accurate gauge. I use Feather River Sports, gauges, www.featherriversports.com, see my review of these trigger gauges: http://www.surplusrifle.com/reviews/measuringtheminimum/index.asp
The pull weighs came in with a high of 4-½ lb, to a low of 4 lb even. I added in the pull weight of my rifle (4-¼), and averaged them. The average weight-of-pull for a Swiss K-31 is 4-¼ lb. Good, my rifle is average. That makes the test all the more accurate.
Now, let’s look at the Huber Concepts Trigger. |
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Trigger comes with a piece of tape to retain the bearing while in shipment (This trigger is Teflon coated also) |
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Allen screw on the right is creep adjustment. Allen screw on the left is ball adjustment |
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Ball is not attached to Allen screw, it’s held on by PTFE grease (More on that later) |
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Huber trigger on the left, Swiss trigger on the right |
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New Huber spring at top, Swiss spring at bottom |
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Allen wrench is included with instruction sheet |
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Trigger pull gauge & screwdriver set |
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The first step is insuring the rifle is unloaded. Next, we have to remove the action from the stock. |
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Removing both barrel bands |
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Remove two screws from the triggerguard, and then action will separate from the stock |
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Details of fire control system; discoloration is not rust, just old oil & dirt |
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This end of sear spring sits under sear pin |
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Carefully release spring with long-nose pliers |
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Spring tension released, entire assembly pivots down |
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Carefully release tension on the sear spring by lifting it off the pin with a pair of long-nose pliers. When released, the spring end will point straight up. |
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Carefully pull here with long-nose pliers |
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By gently pulling the pivot arm with long-nose pliers, the pivot arm/sear/trigger assembly will slide right off the pin. |
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Swiss spring still in its recess, long, upper spring end pointing left sits under tab on sliding ejector. Short, lower spring loop fits in receiver slot |
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Removing the Swiss spring requires long-nose pliers, and shooting glasses or a face shield. Do not have another person or a pet in the area when you perform this step. The Swiss spring is strong, and may go flying when you remove it! Lift the short, spring loop out of its slot in the receiver first. Then grasp the spring and work it out of the round hole in the receiver. Again, be careful, it may go flying as tension is completely released. Before assembling anything let’s do a bit of clean up. |
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Spray disk brake cleaner will wash away any old oil or dirt |
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Old, Mil-Surp arms usually have year’s worth of dry oil, dust & dirt under the wood. Spray disk brake cleaner is used to flush the fire control group recess in the action, and to clean the pivot arm/sear/trigger assembly. Now we can begin the installation process. |
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Installing Huber Concepts spring |
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Long, un-looped end of the new, Huber Concepts spring fits under the tab on the ejector. |
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Using your long-nose pliers, install the Huber Concepts spring in its round recess in the receiver. Make sure the short loop is in its slot, and the long, un-looped end of the spring is under the tab on the ejector. |
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Trigger retaining pin must be drifted out to remove old trigger |
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Now the old trigger is removed by drifting out the trigger-retaining pin. Here’s where I ran into a slight problem. The pin would not drift out! (Note1.) Careful examination revealed that both sides of my trigger pin were very slightly peened over! Hoping the pin was cold-rolled steel, I gave it the file test, yep, the file bit into the steel of the pin. OK, just add 15-minutes to the job time. |
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Filing off one end of the trigger pin peening |
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One end of the peening must be removed before the pin can be drifted out. However, I decided to go one step further. First I drilled a pinhole the entire length of the pin. This step isn’t really required. I did it, but you don’t have to!
Then, I clamped one end of the pin in a vice, and using a fine-cut file; carefully filed until just the peened-over part of one end of the pin was removed. Now the pin can be drifted out. |
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A flat-faced drift pin and small hammer drifts out trigger pin. |
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With the peening removed, light taps of the hammer on flat-faced drift pin makes the trigger pin slide out. |
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Trigger pin removed. Note hole drilled length of pin (I did it, but pin DOES NOT need to be drilled) |
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Huber Concepts trigger in place, pin being drifted back in |
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Place the Huber Concepts trigger in place and gently drift the trigger pin back in place. Make sure the hole in the trigger lines up with the pin, and it will go in easily. |
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Huber Concepts trigger installed, notice the peening is filed from the pin |
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A center punch tip rests on the tiny hole in the trigger pin, one slight hammer rap on the center punch will spread end of the pin a couple of thousands, keeping pin in place |
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As I said before, the tiny hole isn’t required. A couple of good raps with a hammer on a center punch, and the pointed end of the center punch will spread a solid pin. |
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Pivot arm/sear/ new trigger assembly will slid over pin |
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Sinclair lube |
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Lube here… |
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Here… |
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And here |
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Since everything is clean & dry, let’s put a bit of high-tech lube on the pivot points. Sinclair, www.sinclairintl.com sells a fine lube. The needle oiler gets into tight spots. |
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Last reassembly step, hooking spring under sear pin |
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After the pivot arm/sear/ new trigger assembly is installed, the long, looped end of the spring will go under the pin on the sear. |
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Adjusting creep screw |
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OK, time to adjust the trigger! STRICTLY following the instructions, I adjusted the creep screw up to the release point, and then backed off ¼ turn. |
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Adjusting ball screw |
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The ball adjustment was almost perfect as it came from the factory. Next comes the “Drop Test” |
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Drop test, you can see how many times I bumped it |
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The rifle must never release the sear until the shooter presses the trigger! After assembling and adjusting everything, the action is cocked, and the butt (the rifles, not yours) must be bumped at least 20 times. If the sear doesn’t drop, all is well. If the sear drops, even once, then more adjustment is required. If you have already put your action back in the stock, then you can bump the entire rifle on a carpeted floor. I choose to do the drop test with the action out of the stock. So, I bumped the tang of the rifles action on a piece of soft, clean pine. Everything was going well, and then the ball fell out of the trigger! Crap! OK, down on hands & knees, looking for tiny ball bearing. |
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Ball held in by PTFE grease |
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PTFE grease in shallow recess of Allen screw |
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Later, much later, I contemplated the tiny ball bearing and the recess it sits in. The Allen screw has a shallow recess in the end. That Shallow recess is filled with PTFE grease. PTFE has amazing lubrication characteristics. However, PTFE grease is thin, and its ability to maintain a suction hold on the ball bearing is marginal. I thought about it a bit, and realized the amount the ball moves when pressing the trigger is miniscule. I felt stiff grease was the answer. |
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| Allen screw shallow recess cleaned of PTFE grease | |||||||||
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50/50 cast bullet lube being put in shallow recess of Allen screw |
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Ball pressed into shallow recess of Allen screw with 50/50 cast bullet lube |
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I cleaned all the PTFE grease from the trigger & ball, then put a good dab of 50/50 cast bullet lube (50% yellow beeswax, 50% Alox 2138F) in the Allen screw’s shallow recess. Even plain yellow beeswax should work. |
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Another view, it’s not going to fall out now |
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Everything was reassembled, and test functioned. The trigger worked perfect, and the ball stayed in place. |
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Testing trigger pull weight |
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Final pull weight is 2-¼ lb, single stage pull |
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The Huber Concepts trigger works! It easily adjusted to an extremely crisp 2-¼ lb weight of pull. There is no take up or creep. If the trigger pin on your rifle drifts right out, plan on spending about 30 minutes doing this job. The Huber Concepts trigger costs about $69.75 + $3.00 shipping. If you want a crisp, fully adjustable, no take-up trigger pull for your Swiss K-31, the Huber Concepts trigger is the way to go. |
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Original Swiss trigger & spring, Huber Concepts Allen wrench (store your original components in old pill bottle) |
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Label bottle, put instructions inside, and cap it |
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| Article written by: Mark Trope |
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