by Tom Gaylord
Writing as B.B. Pelletier

A history of airguns

This report covers:

  • European military trainers
  • K31
  • Trainer
  • Caliber
  • A major purchase!
  • Where we stand

I’m out at Media Day at the Range today. So tomorrow I’ll start showing you new stuff from the SHOT Show.

About three weeks ago I was cruising the auction website Gun Broker, looking at the listings of one of my favorite dealers. This guy sells oddball and eclectic firearms and, from time to time, airguns. I saw a Hammerli Trainer that was made for the bolt action K31 Schmidt Rubin rifle Switzerland used. I thought I recognized this trainer from Smith’s Standard Encyclopedia of Gas, Air and Spring Guns of the World, and, sure enough, I found it on pages 159-164.

European military trainers

Europe has a history of using airguns as trainers for their military. They used entire guns like the Mars 115 and the Czech VZ 35 ball shooters. They also used conversion kits that went into military weapons to convert them to airguns. There is a rich history of converting firearms like the P08 (Luger) pistol and the 98K Mauser rifle. The beauty of a conversion is the soldier gets to train with the same weapon he will use in combat.

Some of these conversions are powered by CO2 and others are spring-powered. Most of the pre-war trainers originally came packed in a wooden chest. Erma, a famous maker of Mausers, made a lot of the spring-powered trainers. These trainers sell for more than $1,500 when they come up for auction.

But the Hammerli trainer for the K31 Swiss rifle that we are looking at today is one I have never before seen for sale. If I hadn’t read about it in Smith’s I wouldn’t be aware of it. It uses Erma’s spring-powered design, but the K31 action lends itself to such a system far better than a turnbolt Mauser.

The Hammerli is a post-war trainer that American military people at least considered (they are pictured in Smith’s book shooting the trainer), though it’s doubtful our Garand could be converted as easily as the K31.


The 7.5X55mm Swiss K31 bolt action rifle has a straight-pull bolt that doesn’t need to be lifted to unlock and cock the rifle. Just pull straight back on the bolt handle and a cammed mechanism inside the bolt does the rest. It cycles very fast, and a free-floated barrel gives this military rifle legendary accuracy — better than 1 MOA with open sights. Springfields should be so good! On top of that, the trigger pull is just under two pounds and crisp as breaking glass. On the downside, the K31 isn’t much of a battle rifle. It’s more of a target rifle in military garb.

K31 rifle
K31 Schmidt Rubin rifle is the platform for this Hammerli trainer.

K31 action closed
Instead of lifting that bolt handle, just pull it straight back.

K31 action open
A cam rotates the bolt lugs out of engagement as the handle is pulled back. Rifle can also be manually cocked with the ring behind the bolt.


The Hammerli trainer is a barreled spring-piston action that fits into the place where the K31 bolt normally lives. Remove the rifle bolt and install the trainer through the rifle breech and on out through the muzzle. The smooth bore of the trainer barrel fits inside the rifled barrel of the firearm so the lead ball never touches the rifling.

Hammerli trainer
The trainer is a complete spring-piston air rifle that slips inside the K31 action and barrel. It interfaces with the K31’s trigger, but uses its own self-contained cocking system.

Hammerli trainer installed
When the trainer is installed, it looks like the bolt of the rifle and operates the same way.


Smith writes that the trainer fired precision steel balls of .175 caliber. He calls them air rifle shot. Well, .175 hasn’t been the air rifle shot size since the middle 1920s, and this trainer was made in the 1950s or later. So, one way or the other, he is incorrect. I hope to find out what’s right.

I plan to shoot 4.4mm lead balls, unless I can find a source for precision steel balls of the right size. RWS used to import them for the Diana model 30 gallery gun, so I might get lucky and find some in Europe.

The gun is a repeater that accepts from 1 to 6 balls. Each time the mechanism is cocked (by pulling the bolt straight back — just like the firearm), a ball is loaded into position for firing. The mechanism is a BB gun design, where the bolt tip starts the ball moving forward to about 50-75 f.p.s. before the air blast from compression hits it and accelerates it to its maximum velocity. But the velocity is low — I’m guessing in the 200-250 f.p.s. range with steel balls and probably below 200 f.p.s. with lead. Smith does say the velocity is 250 f.p.s. approximately, but he never tested one to know for sure. In his day (1956-57) people didn’t have regular access to chronographs.

Smith talks about this trainer as if it was the Daisy 499 of its day. It was made to shoot at 5 meters, and he mentions that the low velocity was extremely stable and the accuracy was astounding.

Hammerli trainer loading port
The loading port is accessed by rotating a knurled sleeve 90 degrees to the right.

Hammerli trainer loading port open
The sleeve is rotated to the right and you can see where the balls are loaded.

A major purchase!

I knew when I placed my bid that this was going to be a hot item. I was prepared to pay a lot for it because I will get so many articles from testing it. That was good because there was very stiff competition.

If I decide to sell it afterwards, I should have no problem getting my money back, because this trainer comes in a very fresh box! The only thing I think it’s missing is the instruction manual.

Hammerli trainer lbox
A pristine box adds value to the trainer.

As I mentioned, there are fairly well-documented sales figures for the pre-war Erma trainers. Prices start around $1,500 and go up over $2,500 if everything is present. In sharp contrast this Hammerli trainer has no real track record in the U.S. I would guess that it is better-known in Europe, where the majority of them probably still reside. It is a later production item, plus it was made for the Swiss rifle that has historically been used for target shooting rather than combat, so I would expect to see the trainers in excellent condition. The box was a welcome surprise, though.

Where we stand

I don’t have the trainer yet. The images I’m showing are the seller’s from his listing on the Gun Broker website. Since I now own the item I figure they are also mine. Because of the SHOT Show I asked the seller to hold off sending it until I return from Las Vegas at the end of this  week.

The images of the K31 rifle are my personal rifle that I sold a couple years ago. I will borrow a K31 from my gun buddy, Otho, for this series and if I decide to keep the trainer, I will buy another K31 to go with it.

My plan is to do a regular detailed test of this trainer here on the blog. Since the mention in Smith’s book is the only information I have ever seen, my test results will expand the body of knowledge greatly for airgunners here in the States. Smith never shot a trainer, as far as I can tell. You readers are in for a treat!