Jeremy Kerbs

Product systemsCase study

XTM® Modular Grip System

A hand stop kit and textured rail covers that lock together with one snap-on interface, so grip, index, and cover work as one configurable system on a Picatinny rail. Seven US design patents; both products are still sold by Magpul.

Exploded render of the kit in pink: the two-part hand stop with its bolt and nut, the finger index, and half and full covers laid out in rows

At a glance

Problem
Shooters were adding hand stops to rails already fitted with Magpul's XTM covers, and the parts didn't match.
My role
Owned the design end to end: sketching, CAD, design for manufacturing, and high-speed impact testing.
Result
Launched as the XTM Hand Stop Kit and Enhanced Rail Panels; 7 US design patents; both still in Magpul's line.
Client
Magpul Industries
Role
Lead industrial designer: concept, CAD, design for manufacturing, and impact testing
Timeframe
2011–2012
Team
Ask from business development; production CAD handed off for mold design
Disciplines
Defense · Injection Molding · DFM
Outcome
7 US design patents; both products still sold by Magpul
Client
Magpul Industries
Role
Lead industrial designer: concept, CAD, design for manufacturing, and impact testing
Timeframe
2011–2012
More details
Team
Ask from business development; production CAD handed off for mold design
Disciplines
Defense · Injection Molding · DFM
Outcome
7 US design patents; both products still sold by Magpul

Context

Magpul makes polymer accessories for rifles. Its XTM panels are snap-on covers for the 1913 Picatinny rail, the toothed mounting rail on a rifle’s handguard. The covers protect unused rail and give the support hand something better to hold than bare aluminum teeth.

As an industrial designer at Magpul, I was handed the ask by business development: a modular grip system that people could reach for and configure, and that made the rail comfortable to hold. From there I owned the design end to end, across two products: the XTM Hand Stop Kit and the next-generation XTM Enhanced Rail Panels.

Problem

The parts on the rail came separately, so they behaved separately. Hand stops were catching on, and people bolted them onto rails already wearing XTM covers, but nothing was designed to fit together.

  1. Bare rail is hard on handsExposed 1913 teeth are uncomfortable to grip and snag slings and gear.
  2. Covers fixed comfortXTM panels covered the teeth, but they were only covers.
  3. Hand stops caught onShooters added them as travel limiters and as an alternative to angled foregrips.
  4. The parts didn’t matchHand stops often didn’t line up with the XTM covers next to them.
  5. A rail that didn’t work as one surfaceGrip, stop, and cover were three separate purchases that didn’t fit together.
From my November 2011 project review: hand stops were popular, but they didn’t match the covers already on the rail.

Constraints

  • Fit every NATO-spec 1913 rail, even though rails vary in tolerance from maker to maker.

  • Match the existing XTM panel’s length and width so old and new parts interlock. Weight was capped against the same panel: the hand stop could weigh no more than three panels.

  • Mold in glass-filled nylon, with wall thicknesses the material could flow through and fill.

  • Keep tooling simple: a cavity count and size that gave a reasonable cycle time and output, no cooling fixtures, and as few slides and lifters as possible.

What I did

The key move: one interface for every part. The hand stop, a finger index, a half cover, and a full cover all lock to each other with the same interlocking tabs as the XTM panel. Users can arrange grip, index, and cover in any order along the rail, and use half and full covers to set the spacing.

Sketch sheet with dozens of hand stop, finger index, and rail cover thumbnails, plus larger perspective studies of the hand stop and its rail profile
Where it started: dozens of hand stop and index forms, rail-profile sections, and perspective studies, sketched before any CAD.
Multi-view line drawing of the finger stop: top, side, front, and rear elevations, bottom view, and three perspective views
The finger stop drawing, February 2011. The rail-gripping profile and the cover tabs share one geometry.
Exploded render of the kit in flat dark earth: the two-part hand stop with its bolt and nut, the finger index, and textured half and full covers in a line
The system exploded: a two-part hand stop clamps with one bolt, and the index and covers snap in with matching tabs.

Then I designed the rest of the system around it.

  • Redesigned the XTM panel as the Enhanced panel, with a more aggressive grip texture and reinforced polymer. It still snaps on around accessories that are already mounted.

  • Added a clip inside the panel to route weapon-light and laser cables. Separate cable-cover and tape-switch concepts explored the same goal but didn’t go to market.

  • Iterated the hand stop through more than a dozen CAD revisions, adding cord management underneath, trying different grip textures, and strengthening it against impact.

  • Designed for manufacturing in glass-filled nylon and handed the production CAD to the mold designers.

Then I tried to break it. I dropped rifle uppers fitted with the hand stop onto a ledge and filmed the impacts with a high-speed camera. The first design failed when the face of the stop took the hit.

Four high-speed video frames in a grid: the hand stop approaches a ledge, strikes its edge, shears off the rail, and flies free
December 2011, 5,000 frames per second, left to right, top to bottom: an early hand stop hits a ledge edge and shears off the rail.
The full drop, slowed by the high-speed capture (4 seconds, no sound).

The footage showed the culprits: stress concentrators at the angle points. I removed them and added internal stiffening ribs that absorb most of the shock, so the stop can hit something without breaking.

Render of the two-part hand stop separated, showing triangulated internal ribs inside the clamp half
The fix: internal ribs in the hand stop absorb impact instead of concentrating it at the corners.
Rows of molded black Enhanced rail panels and two hand stops lined up on a desk
Molded Enhanced panels and hand stops lined up for review.

Outcome

The kit launched while I was at Magpul, and both products are still in the line today: the XTM® Hand Stop Kit (MAG511) and the XTM® Enhanced Rail Panels (MAG510). Both have National Stock Numbers, so they can be ordered through the US military supply system.

The assembled kit, a hand stop followed by textured covers and the finger index, sitting on a stack of red 2012 Magpul catalogs
The production kit on a stack of Magpul’s 2012 catalogs.

7

US design patentsAll name me as an inventor (Google Patents). Filed 2011–2012, granted 2012–2014, assigned to Magpul Industries.

What I’d do differently

The snap system was secure and very robust, but it was a little hard to use: removing a panel takes the tips of two rifle rounds and some patience. I’d look for a way to keep that strength and make removal much easier.

  • Sketch sheet of hand stop and finger index concepts, with rail-profile sections, side-view thumbnails, and larger shaded perspective studies
  • Top-down render of the assembled kit on a rail: textured covers, the finger index, and the hand stop clamp in a single row
  • Render of the assembled kit from below, showing the snap tabs inside the covers, the finger index, and the hand stop in black
  • Render of the assembled black kit in perspective: textured covers and finger index ahead of the Magpul-branded hand stop with its bolt
  • Side-view render of the assembled black kit: textured covers, the finger index in the middle, and the hand stop at the end
  • Render of the finger index split into its two halves, showing the interlocking tabs and the molded Magpul and XTM-I markings
  • Exploded render of the black hand stop: the two clamp halves pulled apart with the bolt and nut, showing the internal ribs
  • Render of the black hand stop from above, showing the rail-gripping channel and the cover tabs along both edges
  • Render of the black hand stop from the front, showing the grooved grip face, the Magpul logo, and the recessed bolt head
  • Render of the black hand stop from above, with Patent, Made in USA, XTM-HS, and Magpul markings molded along the rail tabs
  • Render of an early finger index concept split into two halves, with studded grip texture along the curved edges
  • Front-view render of the finger index concept, a tapered grooved finger stop between two studded cover sections
  • Render of an early wide finger index concept from below, with a studded curved edge and a grooved grip face
  • Render of an early finger index concept from the side, with a tapered grooved finger stop and studded curved edges
  • Render of one half of the finger index, showing the snap tabs, the grooved finger stop, and molded Magpul and XTM-I markings
  • Line drawing of a finger index concept in front, top, and end views plus two perspective views
  • Exploded render of the full kit in black: the two-part hand stop with bolt and nut, then the finger index and textured covers trailing behind
  • Render of the assembled tan kit from below, showing the snap tabs and molded part markings on the covers, index, and hand stop
  • Side-view render of the assembled tan kit: textured covers, the finger index in the middle, and the Magpul hand stop at the end
  • Product photo of black textured covers, the finger index, and the hand stop on a rifle handguard rail behind a weapon light
  • Product photo of a rifle handguard with textured covers, the finger index, and the hand stop on the lower rail
  • Product photo of textured black rail covers and the hand stop installed on a rifle handguard, shot in low light

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