by Tom Gaylord
Writing as B.B. Pelletier

Today’s report is a guest blog from reader Ian McKee who writes as 45 Bravo. He’s going to tell us about the Crosman Mark I pistol he recently acquired and what he did to fix the leak it came with.

If you’d like to write a guest post for this blog, please email me.

A history of airguns

Over to you, Ian.

Crosman Mark I and II reseal

by Ian McKee
Writing as 45Bravo

This report covers:

  • Just kidding!
  • Four major changes over the years
  • I got this one cheap
  • It’s mine!
  • Bringing it back to life
  • BB’s end cap
  • Resealing both caps
  • How did it go?
  • Outer barrel removal
  • Wrong o-rings

Back in December 2018, and January 2019, B.B. reviewed a classic Crosman Mark I pistol in .22 caliber.

There were many comments about how it worked internally, and how the power adjuster worked, so today I thought I would give you a little peek inside the gun.

Mark II disassembled
Here is your peek of a disassembled pistol. This is actually a Mark II I photographed some time back. The parts of the two pistols are identical except for those pertaining to the caliber.

Thank you, that concludes today’s blog.


Just kidding!

I could not do that to you. Here is a synopsis to refresh your memory.

The Crosman Mark I and Mark II (.22 and .177 calibers, respectively) pistols are airgun versions of the classic Ruger Mark I and Mark II .22 rimfire pistols. They share the same grip angle, sight profile, and overall profile of the iconic Ruger rimfire pistol.

Ruger Marl 1
Ruger’s Mark I pistol.

All Crosman Mark air pistols retained an adjustable trigger throughout their production run, which was 1966 to 1986, but had other changes in their design over the years.

Four major changes over the years

The flip-style piercing cap was changed to a button-style piercing cap, similar to what’s found on the Smith & Wesson 78/79-series air pistols.

The metal bolt guide that was secured in the frame by a screw on either side below the rear sight was changed to a plastic bolt guide that is retained by 1 screw that’s hidden under the rear sight blade.

The power-adjusting screw that was located under the barrel was eliminated.

And to hold the grips they changed from using screws with countersunk heads to screws with flat heads, as shown.

Mark I grip screws
There are two different grip screw head profiles and grips that match them.

If you use the countersunk screws on grips made for flat-head screws, you will crack them, and it is not easy to find replacements.

There were some other minor changes over the years, but these were the big ones.

I have been a big fan of these pistols over the years, and have owned and resealed more of these than I have of the Smith & Wesson 78/79G series. In my opinion, the adjustable triggers of the Crosman guns are better than the adjustable triggers of the S&W guns. The engineer that designed these air pistols later had a hand in the design of the Smith & Wesson guns.

I got this one cheap

I saw this pistol online with a $50 or best offer price tag, and no photo. These two things together usually tell me to run away and let someone else take the chance.

I got to thinking I could always use it for parts, so I took the bait and contacted the seller. I found out he lived not too far away, and decided on a face-to-face look at the pistol.

He sent some fuzzy photos by text, that didn’t help my feelings about the deal.

In the ad he said the gun had leaks. When I finally saw it, it was one of the roughest Mark Is I have ever seen. It had been repainted several times, and at some point, someone had covered the bare spots with a permanent marker to make it all black again.

Mark I right
Right side.

Mark I left
Left side.

I put a CO2 cartridge in it and it vented all of the gas out of the piercing cap while I shot it a few times. [Editor’s note: Doing this in front of the seller is a big negotiating tip, because it emphasizes the fact that his gun doesn’t work!]

From this short examination I knew 3 things:

1. This was an early model Crosman Mark I in good mechanical condition.

2. All of the parts were there.

3. It did NOT leak out of the barrel, when it vented the gas.

It’s mine!

I made a ridiculously low offer, and he accepted. When I got it back home and on the bench, I started by cleaning off the permanent marker with alcohol.

I knew it was an older model, but did not realize how old, as in serial number 000659! There is not even a date code.

Mark I serial number
This is an early Mark I.

I now own one of the first ones made and also one of the last ones made.

Bringing it back to life

I put a second CO2 cartridge in it to check it out on the bench. It vented the gas in about 30 seconds and it all came from the piercing cap. That told me the valve seal was still good.

I shot it over the chrono as it was venting. The gun was cold from the CO2 cool-down, but it still registered 485 f.p.s.

Most times the leak is because the tiny o-ring in the piercing cap deteriorates. The piercing pin moves up and down in the older models by a lever. You flip the lever one way to pierce the CO2 cartridge, then return to its normal position to let the CO2 into the gun.

Some online disassembly guides say you have to remove the snap ring at the bottom of the cap and then drive out a roll pin. That is the hard way. The easy way is to use a 3/8-inch wide (9.5mm) screwdriver blade in the slot inside the piercing cap. Use it to unscrew the cover that contains the 006-sized o-ring.

This cover is threaded and acts as a screw to hold the small o-ring in place. It looks in the photo like the piercing pin will prevent unscrewing it, but the end of the pin is actually below the screw slots. Remove this cover. In a moment I will describe and show a newer style end cap that has some different parts and comes apart differently.

With the cover off, use a dental pick to remove the old o-ring. It is probably hardened and will break into fragments when you pick at it. It may not even look like an o-ring, but it is tight around the base of the piercing pin.

Once all the small pieces are out of the cap and the o-ring groove is clean, lightly lubricate the new o-ring with your choice of lube, center the new o-ring over the piercing pin, and push it into its recess. Then screw the cover back into place over the o-ring.

Mark I cap 1
The screwdriver fits into the slots on either side and unscrews the cover. The tip of the piercing pin is below the slots. The cap looks brassy in this photo but it is really steel.

Mark I cap 2
This picture with a different angle shows how the o-ring sits at the base of the piercing pin.

Check the large o-ring that seals the end cap to the pistol. Is it still pliable? It can look okay and yet be brittle and useless. If it is okay, lubricate it. Then insert a new cartridge and test it, listening for leaks.

[EDITOR’S NOTE: When I looked at my Mark II end cap from a very late pistol I discovered it was made differently inside. I contacted Ian and he provided the following information.]

BB’s newer end cap

BB was following this article and rebuilding an end cap of his own. His is much newer (made in 1977) and has a slightly different design. I disassembled a newer end cap like BB’s for you to see. Instead of the threaded plate that holds the tiny o-ring, there is a star washer inside the cap. Believe it or not, that star washer is not held inside the cap by anything other than its own fingers. Use a small dental pick or something similar to get under it and pull it out of the cap.

Turn the cap over and tap it sharply on the wooden bench and the plate that looks like a screw but isn’t falls out. The o-ring can then be seen around the base of the piercing pin.

Like the other cap you need a sharp pick like a dental pick to get the small o-ring out, as the space is small.

Mark I new cap 1
This is the newer Mark I and II end cap.

Mark I new cap 1a
Reach under there with a small strong hook or a hooked dental pick and pick the star washer out of the cap.

Mark I new cap 2
The newer end cap apart. The cover with the screw slots has no threads and should come right out of the end cap, once the star washer is out.

Mark I new cap 3
BB followed my instructions and has disassembled his cap. Now he is picking out the tiny petrified o-ring around the base of the piercing pin.

Resealing both caps

After the o-ring groove is clean, lubricate and install a new 006 o-ring. If you have an old cap, screw the threaded plate back on top of the small o-ring. If it’s a newer cap insert the plate that looks like a screw, then insert the star washer and press down on it with a screw driver that has interchangeable bits. But leave the bit out of the driver. You want to press down on the edges of the star washer, but not touch the piercing pin in the center.

How did it go?

My new/old pistol has now been holding gas for a month. When I test-fired it, I noticed it was significantly louder than my other Mark I pistols, and it only had 1 cocking power level, none of the other ones I had ever handled or worked on had just 1 setting. I had to see what was going on inside.

I ran it across my chrono, at room temperature, it registered 545fps with Crosman Premier 14.3gr. domes, this thing was smoking!

Outer barrel removal

Using a pair of needle-nosed pliers, or snap-ring pliers, turn the front barrel nut counter-clockwise and the outer barrel will back out, as it is under spring pressure from the hammer spring/power adjuster. It just slides off the inner barrel.

Mark I muzzle
The piston barrel sleeve is held on the barrel by a nut at the muzzle.

Some previous owner had inserted a 5mm thick brass spacer to add extra preload to the hammer spring. That’s where the extra power was coming from.

In the photo below, the power adjuster can be seen, and the hammer and cocking knobs. The power adjusting screw just increases the preload of the hammer spring.

Notice the hammer spring has a extension that goes through a tiny hole in the cocking knob rod to keep the knobs from rotating. It’s shown in the detailed photo below.

Mark I hammer assembly
Mark I hammer assembly.

Mark I hammer detail
Mark I hammer spring detail.

After reassembling the hammer without the extra part the pistol is back to where it should be at 478fps, and 2 cocking power settings.

Wrong o-rings

What happens when you use o-rings that are not resistant to co2 gas? They swell much larger than their normal size.

Mark I normal o-ring
This is a normal-sized end cap o-ring. You can barely see it!

Mark I enlarged o-ring
When the o-ring absorbs CO2 gas it enlarged like this! It took over an hour for this o-ring to return to normal size. This makes the end cap difficult to remove when you want to replace the CO2 cartridge.

I am sure the other o-rings inside are the same as this one, but they are captive, and should not be a problem, so I am going to order a seal kit, and get to know it for a few weeks. Then I want to repaint and reseal the pistol.

Are there any suggestions for a good durable paint, that can be applied by someone with less than average painting experience?

And, of course I will document the rest of the rebuild for everyone.