Friday, July 16, 2010

Making a Bulk-Fill Cap for a Crosman 160--Part 1

Been shooting the Crosman 160 for a week now. I like the rifle, but I'm not a huge fan of using two CO2 cartridges at a time. While I know you can use one full and one empty cartridge in the gun at the same time, I'd prefer to fill the gun from a paintball tank. It'd be a simple matter to order up a bulk-fill cap from either Bryan & Associates or Mac1 as I've done in the past, but I wanted to try my hand at making my own this time around. (And get a break from wood-related projects.)

First a quick word and rant about o-rings and our occasional lapse in mentioning sizes or screwing them up altogether.
As I received the old 160, the o-ring in the cap was a replacement and wasn't exactly CO2 friendly. It's on the right and has swelled with absorbed CO2 gas. The one in the middle has also absorbed some CO2. The o-ring on the far left is new. I kinda hate to measure o-rings from old guns. The one in the gun has obviously been replaced and who's to say that it was the correct size? It sure wasn't the correct material.

OK, so this bulk-fill thingy... It was 9:00 PM and I didn't have a tap to match the Crosman gas tube thread size. So, I looked through my magic parts box and found something useful. Up top is the original cap from the 160. Below is a spare cap from a model 600 semi-auto pistol. I think I can use the retaining ring to mate an otherwise homemade bulk-fill adapter to the 160 rifle. The snap ring has been removed.

Pulled the knurled retaining ring off the cap body. The retaining ring is the key piece as the gas tube thread size is the same on the 600 pistols and 160 rifles.

Gonna start by making a plug to seal the gas tube. Cut a piece of 0.750" tool steel. It's about 1.7" long.

Faced the ends down.

Used a Taig parting tool (Taig part number 1173) to cut a groove 0.100" wide. Slow turning speeds and lots of cutting fluid are needed or the edge of the blade will be destroyed almost instantly and need to be resharpened.

Helps to have minimal blade protrusion from the holder. This stiffens the set up. Flex is not advantageous. OK, the groove diameter is 0.600" at the bottom.

Cut a second groove as a back up. Overkill is OK here. There's plenty of room inside the bore of the gas tube and I need the machining practice.

These will hold the o-rings to seal the 160's gas tube.

Test fit of the o-rings.

Need to make the front of the plug small enough so the retaining ring from the 600 fits over it.

Cleaned up the shoulder that the retaining ring will bear on.

Turned down to 0.579".

Another view.

The long end will be the front.

Ring slip fits. Barely.

Pressure testing. One, two... The first cartridge is new. Second, empty.




Almost seated.

Snugging down the retaining ring seals the deal. Cocking and firing the gun pierces the first cartridge. The replacement plug held pressure! The plug was left long to allow enough room for the 1/8" NPT fitting I have yet to make. In the next few days, I'll need to make that fitting, connect it to the plug and make a simple valve that will seal the cap as the paintball tank is removed after filling.


Anonymous said...


Again I am amazed at how simple that looks. My Father-in-law has an old bench top mill(?) that he never uses. I'm thinking maybe I could play around with it for a couple of years to see what comes of it.

Of course I don't expect to do what you're doing with just a couple years under my belt, but I think I can surprise myself good or bad. Pretty sure I could turn some barrel clamps/front sites for my 1377 anyway.


Anonymous said...

So with this plug finished as a bulk fill adapter rifle will not need the two cylinders, right?

And what kind of pressure will we be talking? Same as the eliminated cylinders?

The volume of pressurized CO2 looks like almost doubles(?), giving more shots per fill?


derrick38 said...

The only trick is to be willing to give it a try and figure out what works.
You're correct. The two 12g cartridges will not be needed once the bulk-fill cap is done. The gas tube will be filled from a paintball tank.
The gas pressure will be exactly the same--between about 900 and 1000 psi depending on temperature. There will be more gas volume than 24g (provided by the two 12g cartridges), so there will be more shots available at full power.

Anonymous said...


I took my 1377 down and began my first clean-up / restore job yesterday. I am finding that while my garage is FULL of useful and often used tools and equipment, I am very under equipped for this kind of job. looks like I will be making some equipment purchases soon, prolonging my air gun wish list purchases!!

I was going to document the process via pictures, but camera no longer functions consistently. (ie., it's broken).

I could not get the air valve (?) out of main tube, as it would've required more force than I was willing to use, so I left it in and wire wheeled the rust and old finish off. cleaned and painted all parts that will show. giving 24hrs for cure time for paint and will re assemble today. I live in 100deg.+, 20%- humidity, so I am sure the cure time is good.

Thanks for the inpiration, keep ya posted.


Anonymous said...

Ha! InSpiration. Sticky keyboard.

I got it done. I jumped the gun on cure time for paint. Had to give it a light finish after assembled and some pellets through it. Going to let it cure for a few days. I plan on going through with a complete rebuild and mods later, when I get all the parts.


Unknown said...

Hi Derrick
I'm glade to find your posted artificial because it looks like building one is the only way that I will get to try this on my 160. All the normal places for a purchased adapter have come up empty and so I would like to ask you, are you still happy with the out come of the build? And what would you do differently if you built another?