Best trigger job science - PullPrint Part 1
Welcome back to Jim's Armory. This one's a bit different from the usual teardown or range review — Jim's been heads-down on a side project for the past three weeks, and this video is the first look at what he's building: a homemade trigger pull profiling machine he's calling the PullPrint Pro. It's not a product, not a review, and definitely not polished yet. It's a science project in progress, and Jim walks through what it does, how it works, and why he thinks it matters for anyone trying to actually understand a trigger instead of just describing it.
What the Machine Does The PullPrint Pro automatically pulls a trigger and measures the weight throughout the entire stroke, plotting it as a graph. From that single pull, Jim can see pre-travel, creep, the break, and the reset, all mapped out with real numbers instead of just a subjective feel. He notes there's a commercial product that attempts something similar, but in Jim's view it doesn't measure reset and doesn't get the same resolution. His rig is currently capable of recording up to 3,000 samples per second — a level of detail he admits has actually been more of a challenge than a help so far, since it's picking up noise he still has to filter out in code.
How It's Built Under the hood, the setup is a stepper motor (soon to be replaced with a servo motor), a load cell to measure force, a microcontroller, an analog-to-digital converter to read the load cell, a stepper motor controller, a power supply, and a USB connection back to a computer running his software. The stepper motor's step-by-step rotation currently introduces small oscillations into the graph — motor noise Jim is working to eliminate with the servo swap.
Running a Test Jim demonstrates a live test on his Mac 9DS 2011 — the only gun he says he's currently willing to risk on the machine, since it's taken off and bent or broken parts a few times already. The process starts with micro-jogging controls to bring the finger close to the trigger, followed by prompts to rack the slide and confirm the safety mechanisms are disabled. The machine finds the face of the trigger, confirms contact, and then runs the pull — tracking the stroke out to the trigger stop, then measuring the return and reset after another rack of the slide.
Reading the Graph The resulting profile on the Mac 9DS shows the trigger sitting just under two pounds to reach the wall, with pre-travel, creep (which Jim attributes to the sear scratching against the hammer hooks on this gun's less refined parts), the break, and then a small circle marking the hammer striking the firing pin. From there the metrics stack up: a 1.88 lb pre-travel peak force, a 4.1 lb break force, lock time of 34 milliseconds from sear break to hammer strike, overtravel, reset travel, and a reset authority — the valley subtracted from the peak — that Jim translates into what your finger actually feels: a 1.2 lb snap on this gun. He also pulls a raw spring rate of about 4.2 lbs per inch, assuming no sear or other parts were in the way.
Pro-Tip: If you want to compare trigger feel between guns in a way that's more than a impression, look at reset authority specifically — it's the number that tells you how much "snap" you'll actually feel at reset, not just how far it travels.
Why Jim Is Building This The idea traces back to Jim's reaction to the Staccato's trigger, which he calls incredible. That led him to wonder whether he could take a gun like the Mac 9DS — about as inexpensive as the 2011 world gets — and bring its trigger up to that same standard. The problem, in his view, is that you can't really know if two triggers are alike unless you shoot them side by side, and even then it's subjective. A quantified profile solves that: instead of comparing triggers the way you'd describe a scotch — short pre-travel, breaks like glass, no creep — Jim wants hard graphs he can hand to a customer, showing exactly what a gun's trigger measured before and after work, or overlaying one gun's profile against another to chase a specific feel. He also mentions picking up a Prodigy that he says shoots poorly right now, with a heavy trigger pull and an overly tight spring — a possible future subject once the machine is further along.
Final Thoughts The PullPrint Pro is still rough — Jim points out he's not a professional coder and may end up bringing in help to get the software over the finish line — but the core concept is already producing real data. His goal is to make trigger work measurable and repeatable rather than descriptive, so that a budget-friendly gun like the Mac 9DS, or something like a Romulus, can be tuned to compete with what you'd get out of a much more expensive gun. More parts are on order, a digital microscope has been added to the shop, and Jim says he's about to start tearing guns apart in more depth to see what's achievable.
Follow along and come back for the next update — Jim plans to keep documenting this project as it develops, so subscribe if you don't want to miss where it goes next.
