How Horn tools make Tesro sporting weapons more precise

0.5 millimeters - that is the size of the 10-ring in air rifle match shooting, a discipline where the shooter fires at a target from ten meters away. The target face, or the black area, has a diameter of 30.5 millimeters. The diameter of the ten is only 0.5 millimeters, with a tolerance of +/- 0.1 millimeters. For the shot, the shooter aims using a diopter and a front sight tunnel.

To consistently hit the black, it requires not only a steady hand and concentration but also a precise air rifle. These are sporting devices that fire projectiles using cold gases. Oxygen and, rarely, CO₂ are used for this purpose. Rifles with a muzzle energy of up to 7.5 joules and a caliber of 4.5 mm are permitted. The maximum weight of a competition air rifle is 5,500 grams.

The company Tesro from Bächingen an der Brenz specializes in the manufacture of these precision rifles. Together with his father and the company's founder, Peter Römer, Daniel Römer produces the sporting weapons that athletes from international leagues and numerous amateurs trust.

To maintain almost micrometer-accurate tolerances, Römer relies, among others, on precision tools from Paul Horn GmbH. Special attention is paid to the groove for guiding the trigger mechanism. Here, the engineer relies on the Horn milling system M310 with internal coolant supply.

High manufacturing precision is required for accuracy

"The trigger weight for air rifles is on average around 25 grams," explains Römer. "Compared to defense weapons, like pistols, with a trigger weight of 2,500 grams, it is feather-light." This is where the first important focus for precision lies. If the groove for guiding the trigger mechanism has play, it leads to an imprecise shot with such a low trigger weight.

For this reason, Römer places high demands on the precision and surface quality of his aluminum components. Tolerances of a few micrometers are therefore the order of the day. Römer illustrates this with an example: "If I have an axis offset of 0.01 millimeters on a part milled on both sides over a length of 20 millimeters, this inaccuracy has an extreme effect on a shooting distance of 10 meters. Especially if I have to shoot at a 0.5-millimeter point."

Milling system M310 from Horn delivers the necessary precision

For the 8-millimeter wide groove, which serves to hold and guide the trigger mechanism, Römer relies on the M310 milling system. The disc milling cutter with a diameter of 125 millimeters has twelve teeth. The tool is equipped with three-edged indexable inserts of type S310, which are screwed on the left and right. "We have been using the tool for this groove from the beginning," says Römer. The tool mills the groove in three cuts, which are divided into one roughing cut and two finishing cuts.

"The performance and precision have been delivered by the tool since the beginning. However, we initially struggled with the usual chip jamming during groove milling," explains Römer. "For this, we had to interrupt the process after groove milling to clear the groove of chips. Otherwise, the subsequent tools would have been affected."

EMO 2025: These were the innovations and highlights of the trade fair

The machine tool industry met in Hanover in September. We have compiled examples of innovations presented in machine tools, tools, and accessories.

Internal coolant supply eliminates chip jamming

Horn provided a remedy with a further development of the M310 tool system. The problem of chip jamming was resolved by the internal coolant supply, as they are washed out by the coolant.

With the expansion of the portfolio for parting and slot milling, Horn responded to the requirements of the users. Horn offers the tool base bodies of the M310 milling system with internal coolant supply. This enables a longer service life of the indexable inserts used and a resulting reduction in tool costs.

Furthermore, the internal coolant supply in slot milling results in higher precision, as no heat from the shear zone is transferred to the component. In addition, the flushing effect of the coolant, in conjunction with the geometry of the cutting edges, prevents chip jamming in deep grooves.

Horn offers the parting and slot milling cutter in two variants. The variant as a screw-in cutter is available in diameters from 50 to 63 millimeters with cutting widths from 3 to 5 millimeters. As a shell-end milling cutter, the base bodies are available in diameters from 63 to 160 millimeters. In addition to other geometries for use in different materials, Horn also expands the cutting inserts with a geometry for milling aluminum alloys.

Römer is satisfied with the performance of the current Horn tool systems: "Horn is my partner of choice when it comes to parting, groove, and slot milling. Although they are not inexpensive tools to purchase, the performance is at the same high level from start to end of service life."

Source: Paul Horn GmbH