by Tom Gaylord
Writing as B.B. Pelletier

Sig Sauer’s new ASP20 gas spring breakbarrel air rifle breaks ground in many areas!

Part 1

This report covers:

  • Sig thinks inside the box!
  • They balanced the trigger
  • Anti-beartrap
  • Assembly continues
  • The Keystone breech
  • Piston and gas spring assembly
  • One more brilliant feature
  • Summary

We left off at the start of the ASP20 assembly station, looking at the Glidelite cocking mechanism. The next item I saw was shocking — an American-made air rifle trigger — the Matchlite! Is it as nice as a Rekord? That is something each shooter has to decide for themselves, but I will describe how it works when we go to the range. Right now I will just tell you what it does.

Sig thinks inside the box!

When I first saw this rifle at the SHOT Show I told Sig Air vice president Joe Huston that shooters were going to fiddle with the screws in the Matchlite trigger. Historically they do this with every new airgun trigger. When Beeman warned them not to fool with the Rekord’s screw 51b, it was like a neon sign, telling them where to start! For some odd reason, Joe just smiled back and said nothing.

The trigger comes with two adjustments — one for pull weight and the other for the length of the first stage pull. The lowest pull weight is 2.5 lbs. and the highest is 3.5 lbs. An adjustment screw allows you to adjust between these limits in 2-ounce steps. Period! The screw bottoms out when turned to the limit in one direction and turns without effect when it reaches the other limit. Between the two limits you have full control to set the pull where it best suits you.

The other adjustment is the length of the stage one pull. If you don’t want a 2-stage trigger, stage one can be adjusted out. If you want a long first stage you can have that.

Think of a box that looks like this.

ASP20 trigger box
The Matchlite trigger has been designed so all the adjustments are contained inside this performance “box.”

Sig has given us a sporting trigger that’s light, crisp and can be adjusted to suit — to the limit of the adjustment parameters. If that was all there was it would be great, but now let’s look at the trigger that I watched being assembled part-by-part.

ASP20 tour
Ed Schultz (center) is about to start the tour of the ASP20 assembly line. The trigger is first.

We watched the worker assembled each part of the trigger. He used a special fixture to hold the parts while the pins were pressed in.

The trigger blade is a special polymer, reinforced with fiberglass. It is relatively straight and feels quite positive when you pull it, but I will say more about that when we go to the range.

Sig has selected a two-hump sear contact design for the trigger that works in concert with their stage adjustments. They call the gold part a trigger stage bracket. It pushes up on the sear that is just above it (not seen here). When you adjust the first stage length you are moving the pivot point of this setup, if I understand it correctly. This same design approach can be seen in Mauser military triggers, but Sig has taken it to a different level to make the adjustments exact and precise.

ASP20 trigger
This is the trigger, assembled. The gold part is the two-humped trigger stage bracket I mentioned. The anti-beartrap still has to be installed.

They balanced the trigger

“And then, at step two, a miracle occurs…” is the punchline to a scientific joke. Well, at Sig, it ain’t no joke! They balanced the trigger assembly!

The parts that were used in the trigger were dimensioned and made from materials that allowed the finished unit to balance, fore and aft, on its pivot pin. That makes it extremely sensitive to each adjustment!

ASP20 trigger discussion
The Matchlite trigger evoked considerable discussion! Photo provided by Sig Sauer.

ASP20 trigger balanced
I photographed this back in the conference room, after the tour, The Allen wrench passes through the trigger pivot pin hole and, as you can see, the trigger is balanced. The anti-beartrap rod is not attached.


Sig put an anti-beartrap device in the trigger to prevent accidents. As all airgunners know, you NEVER release the barrel while it’s open for loading. Anything made by man can fail and your fingers could be seriously injured if the breech closes on them. I didn’t appreciate that people were not aware of that until we were on the range and I saw several of our tour group who are not airgunners release the muzzle of the rifle to load. They were all corrected, of course.

ASP20 trigger beartrap
The first stage travel screw is adjusted through a screw in the trigger.

trigger drawing
This drawing of the trigger shows the anti-beartrap rod leaving the front of the trigger assembly (on the left) to connect to the action.The green domed part on the upper right is the trigger pull weight adjustment.

Assembly continues

As assembly moved on, Ed showed us the barrel and breech. It’s held in the action forks by a large pin. And here is the important part. The number one problem with a breakbarrel rifle is barrel droop. Special scope mounts are made to counter the problem that almost every breakbarrel has. Sig decided not to have the problem, so when they bored the hole for the pivot  pin, they bored the spring tube forks and the breech together! They were held in alignment as the one pivot hole was bored. And afterward that barrel remains mated to that spring tube.

Terry Doe said that other airgun companies create solutions for the barrel alignment problem. Sig designed the problem out, altogether! I wish I had been clever enough to think of that.

ASP20 pivot pin
The pivot pin fits into the hole drilled through the action forks and base block. The parts remain together from this point on. The pin is held in by a single Allen screw, because no sideways force is needed.

This way the barrel never gets out of alignment with the spring tube. They cannot get out of alignment, because of the second brilliant thing they did. Sig invented the Keystone breech!

The Keystone breech

The number two problem with breakbarrels is a breech that wobbles from side to side in the action forks when the breech is closed. Not all guns have the problem, but far too many do and there is little or nothing that can be done to fix them when they do. Sig decided up front not to have this problem or the barrel alignment problem. They invented a breech that locks the barrel tight without requiring spring-loaded locks. It has no name yet, but unofficially everyone is calling it the Keystone breech. When you see the shape you will understand why.

ASP20 keystone breech
The Keystone breech works by those flanges (arrows) bearing against the sides of the action forks as the barrel is closed. The detent slips under its catch in the action forks, drawing the breech tight into the spring tube.

Piston and gas spring assembly

The ASP20 is powered by a gas spring. The piston has a seal up front and some sort of synthetic piston ring at the back to cancel vibration. The piston seal was lubed with what appeared to be a moly paste.

We were shown the installation and lubrication of the piston seal, followed by its installation into the spring tube. Like spring gun tuners everywhere, Sig has to take this step carefully, or risk cutting the seal on sharp edges in the tube. For day 2 of production they did a good job, but I expect one more special tool will be created for this procedure — a blunt screwdriver to ease the seal past the sharp edges. I know I need one.

ASP20 piston installation
Sig installs the piston just like the rest of us. Care is taken to avoid nicking the piston seal.

One more brilliant feature

If you have ever disassembled a precision breakbarrel spring gun, you have probably encountered the thin shim washers that help the breech pivot without friction. In some rifles those thin washers can be a pain to install — especially when the rifle is new and the action fork is tight. Sig did something very clever here. They machined flats on the base block that take the place of those washers, and can never slip during installation! Just lubricate them and slide the base block into the action forks.

ASP20 Diana baseblock washer
Other breakbarrel guns like this Diana 45 have thin washers that are often hard to install when assembling the rifle.

ASP20 baseblock
Sig did away with the washers and just machined washer-shaped flats (arrow) on both sides of the baseblock. Nothing to slip out of alignment during installation.


Whew! I will finish final assembly tomorrow and take you to the range, where many of your questions will be addressed. If writing was aerobic, today would have been a hard cardio. There is so much to tell about this new rifle! Yes — AND the new scope that comes with it!