Accurate, easy to use test stands

Defense & Munitions (DAM): Why is force measurement in firearms and munitions important for defense manufacturers to conduct?

Jacob Morales (JM): Before manufacturers make a single firearm part, testing materials is a key step for quality control. Tensile and force testers are used to ensure materials meet quality standards based on ASTM or ISO standards, depending on the provider’s requirements for raw materials prior to manufacturing components.

Firearm component examples include springs, triggers, and ammunition. All these parts must be assembled, or in some way have force testing applied to them.

There’s typically a requirement needing to be met which makes certain a part functions the way it’s expected to without failure. If the equipment fails when you need it, or has a problem in the usage process, someone could get hurt or have an even worse outcome.

DAM: The FMS and MMS single column motorized test stands are accurate and easy to use. With this in mind, how are workers trained to use this equipment?

JM: When the customer receives the equipment, we schedule a technician and force equipment specialist to visit their facility. We review the application information as to what they’re trying to test, and generally spend a day demonstrating how to set up the equipment.

During the visit, the technical and force specialist makes sure the equipment is in a suitable, stable spot so that it doesn’t receive interference from external sources. Importantly, we also provide instruction on how to properly set up and design tests. It’s very one-on-one and involved. Also, our personnel are very experienced with setting up unusual tests, including automation if customers want to have the tests in-line with manufacturing processes.

DAM: What are the benefits of using the FMS or MMS stands compared to other testing equipment?

JM: The advantage with an encoder-driven motorized test stand is you can obtain the position and how far parts travel, so you can test more than just the load. If you need to test different qualities of different components of firearms or munitions, you can do that with one test stand.

If you require multiple machines to test various items, that’s another area you can add to as well. Since FMS and MMS stands are computer-driven, you can even automate a lot of the processes.

Many customers have stated our software is significantly easier to use than other programs they have tried. The interface is more streamlined, and the test process is significantly easier.

DAM: When using the FMS for trigger pull testing, how does the system collect and present the information for quality control?

JM: Often, there’s a standard provided with the components being tested. For example, springs come with spring sheets. The sheets have information regarding what’s considered the spring’s free length, solid height, and the expected load across that entire length. A test setup could include relevant data collection information regarding those targets, and return an output showing you whether or not it fell within or outside of tolerance.

For example, imagine a 6" long spring that can be compressed down three inches before the coils contact each other. The machine can reach that point and measure the loads at different heights along the travel length, and again when it returns to the spring’s original height.

Importantly, the force system and its integrated software collect data points and present them on a graph. While the system is doing a pull test, the tension values are shown as an X-Y graph where the X-axis is distance and the Y-axis is load. As it travels upward, the line moves across the X-axis. When it makes contact with the trigger and starts pulling, it moves up along the Y-axis, producing a crest to the value of the load going up until it goes past that point where the trigger sets off the firearm and then it goes back down. If there’s something for it to catch after that, it’ll go back up again.

There’s a point that the trigger will come to a hard stop where pulling on it won’t engage any mechanisms, and the load will go back up at that point. However, a test designer would have included a step to stop the test before or during that point, so it doesn’t damage the firearm.

Generally, the force system data export as a comma separated values (.csv) file, which can be read by programs such as Microsoft Excel. Many people will use a spreadsheet format so they can graphically represent that data outside of the controller software. They can see specific data point targets and the time increments when those samples were taken, and compare the distance, the load, and even the speed at that point.

DAM: What inspired The L.S. Starrett Co. to create the trigger pull testing fixture?

JM: We were approached by a firearms manufacturer looking to test trigger pulls specifically. They were looking to significantly increase the ease of running tests compared to their existing method.

We designed and manufactured a fixture to lock in the firearm in a downward pointing direction with a hook mechanism and magnetic safety so it didn’t damage the firearm. If it pulled too far, the magnet separates the hook from the crosshead to prevent damage. The magnet is strong enough to allow the hook to pull the trigger; and the machine reads tensile loads.

Please note that while I refer to the hook mechanism as pulling on the trigger, if you were holding the firearm, you would “squeeze” the trigger, compressing it between your finger and the grip in the palm. The firearm fixture serves similarly, though it reads the forces in terms of tension instead of compression, as the trigger is pulled by the hook while mounting the firearm pointing down, and locking it in by orienting it based on the muzzle, nozzle, and grip.

DAM: How is force measurement used in forensic application and how does that differ from its use in product testing?

JM: There isn’t a lot of difference between the forensic application and the testing application. You’re not likely to test the extraction of a piece of ammunition after it’s been used; once it’s left the casing, it’s spent, and it’s significantly changed since it left the barrel. Testing forces of its extraction is probably not going to give useful information.

Going back and testing unspent, off-the-shelf ammunition would be helpful if, for example, there was still some of the original, new ammunition available.

DAM: How do you think these testing standards will impact the future of defense manufacturing?

JM: Testing standards ultimately ensure that better quality equipment goes out in the field. If firearms are used for defense, domestically or internationally, then there will be confidence that the equipment will work. No one wants anyone to use a firearm that fails when least expected.

DAM: How have these products impacted military applications, law enforcement, and the recreational use of firearms?

JM: Being able to test trigger pulls and verify functionality of the firearm is certainly useful, especially if you’re going into a situation where either you need to prove the firearm was raised too high so it couldn’t go off accidentally, or lowered to the point where it could.

For law enforcement, the forensic application is surely very important. For recreation, safety is top-of mind, so having confidence in a manufacturer’s quality control is critical.

The L.S. Starrett Co. – Metrology Division
https://www.starrettmetrology.com/firearm

About the author: Grace Koennecke is the editorial intern with GIE Media’s Manufacturing Group of magazines.