Mauser M03 - Disassembly and Trigger Design

Readers of this blog will be familiar with my praise for the Mauser M03 trigger. It is every bit as good as described by John Miall, the Australian importer for Mauser and Blaser, in our first conversation about German rifles a few years ago. In this earlier post I listed the Mauser M03's trigger as the first of a number of factors that led me to select this system from amongst the range of European rifles I studied.

I disassembled my Mauser M03 Deluxe a couple of days ago and took some photos with my iPhone along the way. They weren't very good so I did it again yesterday, with a proper camera on a tripod and with bounced flash. I was impressed with what I found inside my Mauser. The pictures help demonstrate how the quality feel and operation of the M03's trigger, and its inherent safety, is the result of good design.

First I had to find the two small cuts in the rubber butt plate, which would allow a No 2 Phillips head screwdriver to loosen the upper and lower screws. I lubricated the screwdriver tip with a tiny amount of petroleum jelly, to help it slip within the rubber. The screwdriver was new, with nice sharp teeth, which helped me avoid damaging the screw-heads. I worked each screw a few turns at a time, moving the butt plate away from the stock progressively. This kept the screw-heads retained within the rubber. The heads of the screws are nicely rounded so an alternative approach is to work on one at a time, backing the first one out through the slit in the rubber butt stock, then holding the butt stock in place while working the second one out. The rubber didn't tear when I tried it this way; the lubricant probably helped.

A No 2 Phillips screwdriver will loosen the two butt plate screws

Once the butt plate was removed I progressively loosened off the screw at the front of the receiver, with a Torx 25 screwdriver, and the Allen head cap-screw holding the rear of the receiver, with a 6mm hex driver. I needed quite a long extension to reach the head of the cap-screw through the hole in the butt. From the T-handle to the tip of the hex driver measures 250mm, which was just long enough.

A Torx 25 driver is needed for the Mauser M03's front receiver screw.

250mm of reach is needed, with a 6mm hex driver, to loosen the M03's rear receiver screw.

A Mauser M03's Allen head cap screw, which secures the rear of the receiver to the stock.

I lifted the receiver assembly out of the stock without much difficulty, but felt some resistance when the magazine catch pressed against the wood and the rubber strips on the sides of the stock's receiver recess. I was careful to avoid bumping and damaging the sharp, top edges of the Deluxe's beautiful walnut with the magazine catch, which protrudes slightly from the left side of the receiver. There was no need to press in the magazine release button; doing so didn't improve clearance. I found I needed to raise the front end of the receiver slightly to ease the trigger lever out from the trigger guard.

With the receiver out in the open I was able to admire its excellent engineering. I should add that it wasn't mere curiosity that caused me to pull my most beautiful Mauser to bits. I had a good reason actually. When I purchased my two 140th anniversary edition M03s from Mialls, with 270 Win and 30-06 barrels, I selected them from stock and arranged for their gunsmith to adjust the triggers to suit my preference before delivery. I asked for 950 grams for the normal trigger and 250 grams for the set trigger. At the same time I ordered a Mauser M03 Deluxe with 6.5x55 and 243 Win barrels, both without iron sights. These needed to be made for me by Mauser in Germany. They duly arrived about five months later, whereupon a muck-up at my end with the Permit to Purchase paperwork meant that there wasn't time for Miall's gunsmith to adjust the Deluxe's trigger before quickly shipping to me, to beat the permit's expiry. Net result - my M03 Deluxe had a noticeably heavier normal trigger than my other M03s. It was around 3 & 1/2 lbs, or 1600gm. Fortunately, all three had the same set trigger weight - 250gm. This was handy, because I pretty well always used the Deluxe, with only the 6.5x55 or 243 Win barrels, over sandbags and with the big, heavy Kahles K624i scope, for sniping at small and distant targets. Nevertheless, I wanted the normal trigger weight of the Deluxe to be the same as the other two M03s. This would avoid the kind of problem I had the one time I went to use the Deluxe's normal weight trigger. I had the 243 barrel installed while I was spotlighting and found a fox, snuffling around a fallen tree trunk. It was only 100m away, thereabouts. I wanted to get the shot off quickly, but accurately. When I put weight on the normal trigger with my calibrated finger, nothing happened. I thought, 'Oh, I haven't cocked it.' But I had. I tried again, pressing a little harder. Still no shot. Then I remembered, 'Ah, this is the one that hasn't been adjusted'. I must have said that out aloud because the fox looked straight at me. I took a moment to push the trigger forward, to set it. My sooky-la-la finger worked well with the set trigger and yes, the fox fell over.

When I looked closely at the trigger mechanism I noticed that the trigger pressure spring was riding over a pin (the trigger spring pin), which had a head at one end and stepped down at the other end, to fit through a hole in the trigger catch. There was also a small bushing fitted on the pin, sandwiched between the head of the pin and the end of the pressure spring. This bushing is not seen in the first picture below, but it's there in the second picture, though not mounted on the pin. There were no screws for making adjustments to the trigger setup.

I compared what I was seeing in the Deluxe receiver with one of my other M03s (which is why a fella should always have at least two). I used a mirror and a torch to look at just the right angle down through the receiver and into the trigger mechanism. I could see the part of the trigger pressure spring that meets the head of its supporting pin, but no bushing. I also looked at the only useful photo of the underside of an M03 receiver that I'd found online, as well as at a parts diagram. In both of these, the length of the head of the pin appeared to be longer than that of the pin in my Deluxe. The head of those pins looked to be about the same as the combined length of the head of my Deluxe's pin and the bushing. Readers have probably figured out what I concluded, i.e. inclusion or removal of the bushing would place more or less tension on the trigger pressure spring and thereby create a heavier or lighter weight for the normal trigger.

Mauser M03 - the trigger pressure spring rides over the trigger spring pin.

Mauser M03 - fitting this bushing onto the trigger spring pin will increase the weight of the trigger.

Mauser M03 receiver, bolt, barrel and butt plate.

Mauser M03 - the trigger spring pin with longer head for the US market is visible.

Mauser M03 - cropped to show the longer head of the trigger spring pin

But what about the picture found online, showing the longer head of the trigger spring pin? It's the one that's two pics above (click on it to see the full size version, or see the cropped version below it). Well, I happen to know who took that photo. He lives in the United States. It seems to me that M03s made for export to the US are fitted with non-adjustable triggers, of the heavier kind. The optional Combi Trigger is not available either, so, no Euro set-trigger delicacy for my American friends. You're all ex Marines or Navy Seals as I understand it; your fingers are too damn strong!

My Mauser M03 Deluxe now has a normal trigger weight that is the same as the other two, and that's a good thing.

The overriding point here is that the Mauser M03 trigger design is simply excellent. For some countries the weight of the normal trigger is adjustable between either crisp and firm, or crisp and a little less firm. It appears that for the US market, it's just crisp and firm. The normal trigger mechanism has no adjustment screws that can work loose. All M03 triggers, whether adjustable or not, will provide crisp, predictable and reliable performance every time. By design.

The Combi Trigger's set trigger mechanism is easy to use, easy to adjust externally (I haven't bothered - 250gm is light enough) and easy to unset, however great care needs to be taken when using it.

It would be very interesting to get input from M03 users in various countries on their trigger weights, via comments here or a post to the Mauser M03 Blog Discussion Forum (see link at top). If a trigger scale isn't handy, balance the rifle on its butt on a kitchen scale. The increase in weight from your finger to release the trigger is the trigger weight. :-) Please check that the rifle is unloaded! Any holes made in your ceiling are your fault.

Notes on Reassembly

I was careful when lowering the receiver into the stock to avoid damaging the sharp edges of the walnut or the rubber strips inside the stock's receiver recess.

I fitted both the Allan cap screw to hold the rear of the receiver and the front screw with its clamping piece loosely before progressively tightening them. Comfortably hand tight on the cap screw using the T-piece and hex driver was 5 to 6 Nm when I checked with my small torque wrench. I did the front screw up with a Torx screwdriver until it was snugly tight and wouldn't come undone, but no more. I'll report back if this reassembled receiver doesn't produce good groups with its 6.5x55 and 243 Win barrels.

Update: having now fired this rifle again, with the 243 Win barrel installed, the reassembly settings described above worked well from the first shot. Link to video of the confirmation shot.

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This post is about the design of the M03's trigger, but I have to mention the cocking/safety mechanism while I'm writing. The key point of difference between a Mauser M03 with its cocking lever and most other rifles with a 'traditional' safety is this:

• a traditional rifle's safety operates by blocking the unintended release of the firing pin in some way, where the firing pin spring has already been placed under tension, as a result of closing the action. That is, the rifle is ready to fire, and will, if the trigger is bumped and the safety has not been put on, or has inadvertently been bumped off, or can't hold back the strong firing pin spring due to some kind of failure. Many rifles of this kind have a safety lever that moves a short distance along the longitudinal axis of the rifle, i.e. in the direction rifles tend to jostle up and down as we walk while hunting. Contact with clothing, a belt, a backpack or the branch of a bush could flick the safety up, from Safe to Fire.

• with the Mauser M03, when its cocking lever is sitting at the 'S' for safe position, the trigger sear is not engaged with the trigger catch and the firing spring inside the striking piece is not tensioned for firing. The firing mechanism is relaxed; the rifle is not cocked. The safety mechanism is not being asked to sit there, ready to hold back the strong force of the firing pin spring (e.g. Win Model 70), or actually holding it back until that force is handed over to the trigger sear to hold back (e.g. Rem 700). With the M03, the safety (i.e. the cocking lever) can't be flicked or bumped to the fire position inadvertently. It can only be swung from the safe position to the fire position by a deliberate act of pushing the strongly sprung lever through an arc of 90 degrees, transverse to the long axis of the rifle. I can't see how the cocking lever could be moved from Safe to Fire accidentally. With the Mauser M03, instead of pushing a safety up and over a hill to block the rifle from firing, the cocking lever has to be pushed up and over a hill to enable it to fire. It is a very safe design.