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Education / Training Crosman 13XX rifle, a modified 1377 pistol: Part 1

Crosman 13XX rifle, a modified 1377 pistol: Part 1

by Tom Gaylord
Writing as B.B. Pelletier

modified Crosman 1377 pistol
A 1377 pistol, converted to a .22 caliber rifle. My 1377 with a scope presently weighs 7 pounds.

Today’s report is written by reader Benji-Don. This is Part 1 of his 2-part report on modifying the Crosman 13XX air pistol to turn it into a rifle.

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

And now, over to you, Benji-Don.

Crosman 13XX rifle, a modified 1377 pistol

This report covers:

  • History
  • Basic conversion
  • Scope
  • Pump pivot pin
  • Trigger
  • Hammer and hammer spring
  • Barrel band
  • Stock
  • Pump handle
  • Bushing/transfer port
  • Valve
  • New valve and piston
  • Up next

My plan from the beginning was build another air rifle as accurate as the Crosman 1322 pistol conversion I gave to my friend Jim. The key to its success in my opinion was the Benjamin Maximus barrel. I had two barrels for my new Crosman 1377 airgun so I figured I would not have any problems making another rifle just as accurate as the one I gave away.

This gun started off as a 1377 where my old one started off as a 1322 I don’t think it makes any difference in the end. Once the breech and barrel are converted to .22 caliber, the rest of the airgun is the same. I will list my work on the gun in chronological order as best I can remember.

Basic conversion
I installed a Crosman 1399 shoulder stock and .22 caliber steel breech along with a .22 caliber Benjamin Maximus Hunter barrel. These modifications are the basics of the conversion from a pistol to a carbine. Well the barrel is a little long to call it a carbine. I did polish the crown and leade on the Maximus barrel with a Dremel felt polishing tip and medium automotive polishing compound.

I then installed an Athelon Optics 8-34X56 Argos BTR Tactical Rifle Scope. I used UTG 30mm Rings, High, 3/8″ dovetail. I agree with Chris USA it is a bit of overkill. At least I can’t blame the accuracy on the scope, or can I?

Open sights are also a good option as the gun has a long sight radius. The barrel weight and peep sight from the Crosman 2300S pistol would make a good setup.

Pump pivot pin
A solid pin is far stiffer, stronger and wears better on the linkage than the original roll pin. I made a pump pivot pin from a 3/16 inch drill bit. I used a Dremel cutting blade to cut the drill bit to length. I then put the pin in my drill press and cut grooves in each end for “C” clips to hold it in place. I used the Dremel with the cutting blade to cut the grooves while spinning the pin in the drill press.

I wanted a good trigger so I added the two-stage trigger parts from the Benjamin Marauder pistol. It now has a very crisp two-stage trigger.

Note: The Crosman part # 2220-103 “Assy, Grip Frame” benefit might be a better deal and it should be a bolt-on assembly. I did not try to go this route so cannot guarantee the fit. It is the same assembly from the Crosman Silhouette PCP pistol, same part number.

Hammer and hammer spring
To cock the hammer when using the Marauder pistol trigger parts you need to hold the trigger back. Otherwise the sear locks into the groove in the stock hammer. The hammer for the Crosman Silhouette pistol may solve this issue; I have not tried it and don’t know if it is the same diameter. With the grove in the stock hammer you can put the gun on half cock and pump it with a light valve spring; so there is some benefit. Otherwise with the light valve spring it needs to be cocked or halfcocked to allow the exhaust valve to seal for pumping.

This gun was randomly getting valve lock with less pumps than normal — somewhere around 6 pumps. I added about 3/8ths inch of preload on the hammer spring by putting a plug of a 3/16 inch steel dowel in the tube cap. I put a new hammer in the gun and the erratic velocity and valve lock was reduced but not eliminated.

Barrel band
To place the longer Maximus barrel through the stock plastic barrel band the barrel band needs to be drilled all the way through to the barrel diameter. I was not getting the accuracy I wanted so I cut the plastic barrel band off of the pivot pin bracket to fully float the barrel. This did not seem to make much difference. I think it was a little more accurate with the barrel floating.

Eventually I broke down and ordered a metal barrel band/pivot pin bracket from GMAC Custom Parts Ltd. in the UK. That not only made the gun more accurate it also made the pumping assembly more rigid. The pump was able to pump more air per pump with the metal pump bracket.

When I ordered the barrel band I also ordered a brass safety pin from GMAC. That eliminated all of the plastic parts I am aware of.

At this point in the build, Vana2 came out with his DIY custom stock blog report and I could not resist building a stock and pump handle.

I filled the lower grip frame with aluminum plates to match the outer thickness of the frame. I JB-welded plates and frame together to provide a more solid attachment for the stock. With the thickness of plate I was using, the right side of the frame required two layers and the left side, one. I also added an additional screw on each side of the stock near the base of the pistol grip. The stock single screw on each side of the pistol grip relies on friction and some nubs in the grip that do not provide much resistance to torque when pumping. With the additional screws the stock is rock-solid.

To make the stock I used three pieces of Douglas Fir laminated together. The wood was 80+ year old drawer fronts from our kitchen. It had a nice tight grain that is hard to find nowadays. It was easier for me to make the cut out for the grip frame by making a center piece of wood the same thickness as the frame and then laminate two sides on to make the stock. I think that is the best way to go for this gun. Cutting out the grip frame inside of a solid piece of wood would be a real challenge for me. The stock is not a beauty but it is solid and works well. I added a stop on the stock so it sets in my gun rest at the same location for every shot.

modified Crosman 1377 stock and grip parts
The center and left layer of the stock and the aluminum plates for the grip frame.

Pump handle
I made the pump handle out of two pieces of the same wood laminated together. To mill the handle out for the pump lever I made a router table which I mounted on the side of my table saw. That allowed me to use the table saw rip fence with the router. To start and stop the milling/routing I clamped two stops on the rip fence, one to set the start of cut and one to end the cut. I then could accurately run the pump handle between the two stops. One notch needed a sloping cut so I added a wood ramp at that angle clamped to the fence. The pump handle then rode up the ramp as it was pushed between the start and stop blocks.

This poor man’s milling process should work for quite a few different gunstocks. It is not hard to match the action and barrel shapes with the right router bits. Router bits come in all shapes and sizes. Half circle router bits make it easy to route out the groove for the barrel or tube.

modified Crosman 1377 pump handle S
The pump handle and part of the linkage that fits in the handle.

Bushing/transfer port
At the higher number of pumps, enlarging the transfer port increases the pellet velocities some. I initially drilled my transfer port bushing out to 5/32 (0.156) inch and then to 11/64 (0.172) inches and tested with the barrel port at the stock size. I later opened the barrel port to 11/64 inches but did not find any significant increase in pellet velocity vs pumps.

In my previous modifications to 1377 and 1322 guns I did nothing or very little to the valves and had no issues. I was very satisfied with the performance of the guns.

This gun had unacceptable valve lock from the beginning. What I am calling valve lock in this case is partial valve lock. That is air left in the valve after the shot is taken. The gun fires but with a lower velocity. This is common in many multi-pump airguns and usually is not significant. Valve lock can be affected by the pellet and pellet weight, but in this case the pellet was a small factor.

To rectify the problem, I replaced the valve spring with an ultralight valve spring. The ultralight spring did make a huge difference. The pumping effort for the first 3 or 4 pumps were almost as light as the first pump. Once the valve pressure builds and the maximum pumping force shifts past the force to open the valve spring makes little difference in the pumping force. But I was still getting irregular pellet velocities. I think the valve was not closing fast enough on the first few pumps so less air was pumped. I was also getting partial valve lock at around 10 pumps. At this point I changed to a light valve spring that took care of the slow closing valve in the first few pumps and gave more consistent velocities for the first eight or ten pumps. I was still getting partial valve lock though.

New valve and piston
At this point I replaced the valve and piston. I had not tried a custom valve and piston before and decided this would be a good opportunity to see what difference they make in the guns performance. I ordered a flat top piston and valve from Peter Nollan on eBay. It is not cheap but well worth it in my opinion. It has a piston that’s adjustable while in the gun, so the dead space can easily be minimized. The valve has increased volume and a larger and angled exhaust port.

With the new valve in place, I tried the same three springs and ended up using my light spring. The gun now dumps all the air when fired – even tested to 15 pumps which is the most I have tried so far. Both the very light spring and the stock spring did not seem to close the valve fast enough when pulling the piston back for the next pump and thus did not give as high velocities per pump.

modified Crosman 1377 flat top piston S
The piston rod can be adjusted while in the gun!

Up next
Finally we are at the end of the long trail I went down with this gun and we can move on to the next part — performance.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

62 thoughts on “Crosman 13XX rifle, a modified 1377 pistol: Part 1”

  1. WOW Benji-Don,

    You have some mad fabricating skills! Mad.
    Can you make something similar through the Crossman Custom Shop? Wish I knew more about pneumatics to really appreciate your work. Are you in any way related to “Another Airgun Blog”?
    Now how about making a recoilless springer?

    Good work!


    • Yogi,

      Kind of Mad Max, or MAD magazine. Most of my work is a little funky.

      You could come close with the 1300KT pump Carbine and you can get it with a Lothar Walther barrel. I would say that would be verry nice.


      • Benji-Don,

        MAD Magazine! Now that is a pleasant blast from the past. I wonder if MAD ever did a parody of Mad Max.

        An excellent mod you have there. With the trigger you put in it I’ll bet it’s a dream to shoot.


    • Siraniko

      To adjust the piston, loosen the set screw 1/4 turn and then use a 5/64 allen wrench in the holes to rotate the piston. You should feel the piston stop against the valve just before the pump handle ls closed all the way. Instructions come with the piston and it is easy to adjust.


  2. Don,

    Excellent report. I did enjoy your innovative approaches to various challenges. I have found that during projects,… coming up with inventive ways to do something,… without the proper/ideal equipment,…. is as much fun as anything. Nice work on the pump handle.

    Looking forwards to the performance report.

    Good Day to you and to all,………. Chris

    • Chris U,

      You know I enjoy tinkering with the airguns as much as shooting them.

      I cleared the trees and brush up at my cabin for a 100 yard range from the back porch. I need to pile some logs for a backstop and then will be able to stretch out my RAW gun. I got 1.09 inches 10 shots at 80 yards so it is going to be a challenge for me to get 1 inch at 100 yards. It should be fun trying.


      • Don,

        Excellent. It so nice to have 100 available right off the back porch. Mine is about 40′ from the front door,…. so almost as good as the deck/porch.


  3. In the second paragraph below New valve and piston, I should have said: The stock valve spring closed the intake valve soon enough but also closed the exhaust valve earlier when shooting than my light spring and gave lower velocities.

  4. Don,

    We are in the presence of a master tinker. You almost have me rushing out to get one of these pumpers. If I did not have a pumper project laying in front of me right at this moment, I would.

    I am really hoping mine will give me the performance I am looking for. You have given me some tips to keep in mind as I bring mine up to par. Thanks!

    By the way, get that stack out there! The RAW will do it.

        • I have thought about getting a long range pb but can’t shoot it in my backyard. lol Then you need to be extremely meticulous reloading, I don’t even sort my pellets.

          It is a top scope for the money. Chris USA recommended it.

          • Benji-Don,

            The 13XX is a really underated platform and most buyers never find out about all the aftermarket upgrades that are available. I have been tempted and succommed a number of times and built semi-custom pistols using the Crosman 13XX/22XX pistols and rifles. What stops me is when I do the bottom line on how much it cost to take a $45-85.00 basic platform and turn it into a good shooter. Thinking….hmmm…I should probably buy a couple of those Benjamin Maximus barrels…Benji-Don YOU are a Modding ENABLER!!! MUST GO SHOOT what I have!!! I can get over my modification addiction….

            “Then you need to be extremely meticulous reloading, I don’t even sort my pellets.”

            I’m with you totally on not sorting pellets and certainly would be disappointed with you if you washed, lubed and weighed them ;^) My groups beyond 500 would probably get worse if I reloaded my firearm ammunition! So I collect my once fired quality brass and sell it to those who practice (often to total frustration) that arcane skill set. I use the cash I save on components and equipment to buy the very best commercial ammo by the case(s) and spend the time on (what I consider the more important element…) mindful shooting.

            Great blog today Don and complete introduction to the Modification Addiction!


  5. Benj-Don,
    The Crosman 13xx series may never be an Izzy pistol with the fancy pumping linkage,
    but I really enjoyed your process. Thanks for sharing! I have a 1377, it is not there yet.
    I am going for an indoor x ring machine, but I still have more things to figure out about it.
    Off to work…

      • Don,
        I got my 1377 from PyramydAir; and I also ordered the steel breech and rear sight from them. I have the metal barrel band (big improvement as you noted), and it sports a 12″ barrel in .22 caliber; it’s a really nice little gun, but not in the league with the one you are reviewing here! I can’t wait to see the performance; with that long barrel and the piston mods, I’m sure it’s gonna perform far and away above my little pistol. =>
        Great report!
        Looking forward to the rest,

  6. Don
    Yep cool guns. Very interchangable are the 1300 series guns. The Marauder pistol grip parts and the Discovery/Maximus parts as well as the 2240’s.

    I don’t have this gun anymore sold it for a real good price thinking something would come about with it but never seen anything happen.

    It was made from a 1322/77 and I used a Discovery trigger and barrel and steel breech on it.

    Making me also remember Hiveseekers blogs on the 2240 Crosman custom shop guns.

    But here is a real short video of the pumper I made using Discovery parts. And to note it was the only easy way to post a picture and such on the blog when I made that gun. We didn’t have the picture posting option we have today back then when I built the gun.

    Here is the YouTube link of the video. It’s only like 5 seconds long incase somebody is worried about a long load time.

    • GF1,

      I have learned much about these guns from you. I am still waiting for someone to make a good efficient multi-pump rifle with all the features we have talked about.


      • Don
        And thank you.

        And wasn’t posting my reply to steal your blog. Just wanted to mention some of the other stuff that can be done with these guns.

        And I had to cut the Discovery stock to make the pump handle and mill it out to fit the pump linkage. Wasn’t to bad to do.

        But still have yet to make a stock from scratch like you did. Think I will be saving that project for when I retire and have more time. I’m sure I will need it for my flub ups I make. But yep fun stuff all the way around.

      • Don
        Since we’re on the subject of modding and interchanging parts.

        Here’s my Maximus how it’s been dressed for a while now. And yep it has a true two stag trigger assembly from Marauder pistol parts. The trigger adjusts out just as well as a Marauder rifle trigger and the 1720T I had. And yep I’m pretty sure you seen pictures of it already but figured I would post the picture for the readers that haven’t yet. But for sure like these Crosman/Benjamin guns.

        • I used the Crosman stock you have on your Maximus to outline my wood stock. I then changed the lines to what I liked but cut it out to the original lines, another senior moment. Those moments also increase after retirement, I love retirement though.

          • Don
            I like the stock on your gun. And yep the good ole 1399 stocks. What would we do without them.

            And I think I will follow your idea of using the 1399 stock as a template to make a wood stock somewhere down the line. But I do know from experience that they just don’t have a high enough comb on them. I’ll definitely try to make mine with a higher comb.

            And to bad you don’t have access to a lathe. You could of made your pump handle into a Tootsie roll handle.

            Again just throwing out some ideas. You did a nice job on making your gun what you want. I like that alot.

            • Well you know I love the tootsie roll handles. I wanted this one to sit flat on my gun rest/vice to control cant. With the pumper comming out of the gun rest on each shot for pumping I wanted all the help I could get for consistency. That is why the front of the pump handle is flat on the bottom with vertical sides.

              I wood also love to have a metal lathe.

              • Don
                Good idea on the squared off pump handle and your shooting bag. I’ll have to remember that when I try my hand at making a wood stock.

                And yep so much can be done with a lathe and Bridgeport. If you got one I bet ya you would have it for a long time.

  7. Benji-Don,

    That’s good to know. Can I assume that the same is true with either .177 or .22 barrel?


    P.S. I’ll accept an answer from anyone who knows.

    • Shootski,

      That article brought me back 45 plus years to my material science class, I had a hard time with that class, it was a lot of memorization.

      No apologies needed.


      • Benji-Don,

        I think we all have had classes like that.
        I enjoyed school and didn’t mind doing the hard work but I always hated memorization; especially when it was not really essential but rather simply required at the whim of a professor or Flight Instructor.


    • Shootski,

      Careful there, fella. Your rust hypothesis is going to lead to forum ads to the tune of, ” Wonderful old Gallery Gun. American Walnut stock, and Lothar Walther barrel, and all metallurgy is pre-coherent twin boundaries discovery era.”


      • Halfstep
        You asked the other day when we was talking about the new style Daisy wadcutters to post some targets with my laminate stock HW30s.

        Well it’s been windy here lately. But it was pretty calm today.

        Here is a 50 yard group I shot today. It was calm. There was a 4 mph wind coming from straight behind me. So I never feel any of it cause the house blocks it as well as my shooting range goes down hill very gradually.

        But I have to say that this probably is the best ever shooting gun I have had with wadcutters all the way out at 50 yards. Usually about 35 yards is it from what I have seen throughout time. The best dome pellet for this gun is the JSB exact 8.4’s. it shoots the same groups as the Daisy wadcutters. About 8 other pellets just don’t do it for some reason.

        Anyway here is a picture of a 10 shot group with a penny to the side of it and the same group with the penny layed over the group. It’s Daisy wadcutters at 50 yards.

        Trust me I was well pleased to see the results. It’s a thumper at 59 yards when it hits a tin can at 59 yards with the wadcutters.

        • GF1,

          That is amazing both gun and pellets for 50 yards. Oh and you too. Are the new daisy wadcutters that much better than the earlier ones? I just put in an order but will be getting 4 tins next time. You cant beat the price for a good pellet.

          • Don
            Yep it was 50 yards. I typed 59 yards. I hit the 9 instead of the zero and didn’t catch it.

            And both targets are the same target shot by the HW30s. I put the penny off to the side on one picture and put the penny over the group on the next picture.

            And yes from what I seen of how they looked before and after and also shape and size changed. Plus my shooting results are better with the new style Daisy wadcutters verses the old ones.

            And yep try them. But maybe not 4 tins at once. You might not like them. But maybe you will. Let me know if you try them.

        • GF1,

          I bet I could have seen the smile on your face from here when you got groups like that with any pellet at those distances with a springer, much less with a cheap Pellet like the Daisy WCs. If you haven’t done it already, try their HPs. You never know. I just bought a tin of their pointed pellets by mistake and they are apparently redesigned also. They are much better formed and cleaner with a different skirt shape than they used to have. I’ve shot them just a little and so far they are as bad as the old style, so I wouldn’t waste time on them.

          What sort of sights are you using and were you using the artillery hold?


          • Halfstep
            I have never had that good of groups out at 50 yards with any kind of wadcutters. Yep totally happy. And they are transferring energy well to my steel spinners at that distance.

            And I have tried the Daisy pointed pellets. They do work with my Colt Python like you have but not in other guns I tryed them in. And haven’t tryed the hollow point Daisy’s. I probably should but just never have.

            Here is the scope I have on it. Matter of fact the same scope is on my Sig MPX but that scope has the Weaver rings with it. HW30s has the scope that’s in the link with the 3/8’s dove tail rings. Excellent scopes for only costing $49.00 and the rings are included.

            Here’s the link.

            Oh and I was resting the gun directly on the bag with my fore hand rested on the bag and pointing finger rested on the stock and barrel as well on the left side of the gun. And that’s the black laminate wood stock HW30s I got from the place out on the left cost.

            But yep I’m happy with the results. And I have already got about 4 starling out at 50 yards trying to open up the corn on the stalk to get them a feast. A nice little thump and they was going south and nose down. Again happy with the results.

  8. Half,
    That may be…but it could also cause manufacturers and classified adds by sellers that say: all metallurgy is post-coherent twin boundaries corrosion causation discovery.”. It may also be at the heart of why newer PCP show signs of air cylinder/tube corrosion much more often than the early PCPs!
    I worked with avionics and we had tremendous issues (Phantom Faults) with micro-corrosion on cannon plugs that required anti corrosion protocols be performed every time a cannon plug was connected and/or disconnected. It really got far worse when we were provided with “new revolutionary” metallurgically enhanced cannon plugs and pins!

    The future is bright! (Pun intended)


  9. Off topic- SIG Whiskey3 Scope

    SIG emailed me back about the scope:

    Thank you for contacting Sig Sauer.

    The new ASP20 riflescope is the Whiskey3 ASP 4-12×44 airgun Scope. This is a brand new item, and is our own optic developed by Sig Optics. Specifications for the scope are still forthcoming and will be posted to our website shortly for review via the following link:



    Aaron Weeden
    Customer Service

    They list the price at $149.99 and is available now with free shipping.

    John Carlisle

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