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Air Guns Modifications — yes or no?

Modifications — yes or no?

This report covers:

  • Good or bad?
  • Velocity
  • Longer barrel
  • Barrel length on a spring-piston airgun
  • Other mods
  • Stage one tune
  • Airgun equivalent
  • Last mod — new stock
  • Summary

Today I address a subject that I suspect is on the tip of many tongues in the airgun world — modifications. 

Good or bad?

I’ll tell you up front that some modifications work well and others do not. Those that are sold as kits by reputable dealers like Pyramyd AIR or manufacturers like Vortek, are the safest bet. You have watched me install several modification kits in this blog and if they were these kind of kits the results were always spot-on.

There is no all good or all bad when it comes to mods. So, it’s worth considering what works and what doesn’t.


Many airgunners want more velocity. Some want to shoot heavier projectiles at the same velocities at which their guns now shoot light projectiles and that’s the same thing. What works?

Longer barrel

A longer barrel will increase the velocity of a pneumatic or CO2 gun — to a point. That point is somewhere around 24-28 inches of barrel for a pneumatic and 14-18 inches for the gas gun. For a big bore PCP the limit might be a few inches longer. Beyond these points you reach the area of diminishing returns, where you may get a few more f.p.s. at the cost of a barrel that’s way too long. And, in the one test I once did with a CO2 rifle, the velocity actually diminished after about 18 inches of barrel, as I recall.

But, wait a minute. There is more to it than just the length of the barrel. It’s also the valve that the air or gas flows through and the chamber that is behind that valve, if there is one. You can’t add a long barrel to a CO2 pistol and expect much velocity gain unless the valve is also modified in some way. And a longer barrel on a multi-pump pneumatic like the Benjamin 392 can only use the air that’s in the gun. For example, adding three inches of barrel to a 392 won’t increase the velocity on three pumps of air as much as it will on 8 pumps. So barrel length goes hand-in-hand with the valve, plus the space behind the valve where the high-pressure air or gas is coming from.

Barrel length on a spring-piston airgun

A longer barrel can speed up a pneumatic or gas gun. But a spring-piston gun is different. For them the barrel needs to be made shorter — to a point. For instance, the barrel on an Air Arms TX200 Mark III is about 9 inches. It looks longer because there is a steel jacket around the barrel that holds the baffles that silence the report. But the actual rifled barrel is just 9 inches long, more or less.

In the 27 years I have been writing about airguns I’ve heard of several people who have cut off the barrels of breakbarrel springers in the hopes of increasing velocity. That never turns out well. I often find out about it when they ask me if I know of a source for a barrel for a certain air rifle. Dragging the story out of them takes time but in the end they were after more velocity because they heard that a breakbarrel produces its maximum velocity in the first 6 to 9 inches. After that the pellet is coasting, and in their minds, slowing down.

According to tests done in the 1970s by the father-son team of Cardew there is truth to the short barrel being all that’s needed for a spring-piston powerplant. The piston in those guns compresses a small amount of air that hits the pellet with a blast. After that, the air pressure keeps dropping, the farther down the barrel the pellet goes. With a pneumatic if the valve stays open after the pellet starts on its way the pressure behind it may drop, but it still remains higher than ambient air pressure. It’s like pushing a car. It takes a lot of effort to get the car started but once rolling, not as much push is required.

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Other mods

I’ve addressed velocity. What are some other modifications that can be done to airguns? Before I get into that subject, though, how about one from the world of motorcycles — specifically Harley Davidson.

Stage one tune

A stage one tune for a Harley engine consists of a less restrictive air intake and exhaust and a tuneup for the electronic brain that runs the engine. It means more fuel is available and the engine runs less lean. Since no internal parts are changed, the stage one tune is very popular.

Stage one tunes tend to lower the operating temperature of most Harley engines, and Harley engines do suffer from high operating temperatures. And this tune is recognized by and even promoted by the Harley Davidson Motor Company.

But I met a guy who ripped out the fuel injection on his Harley and replaced it with a carburetor. He told me he felt the engine ran better with a carb, though he did admit that he had to adjust the carb often. Same guy told me that after 11,000 miles he needed a new engine. He said that to me with a straight face!

That would be my example of a mod that doesn’t make any sense — just like when BB Pelletier had the catalytic convertor cut out of his 1976 Ford Pinto and a straight pipe welded in so he could run leaded gas. Two years later old BB couldn’t register his Pinto in a new state, and he lacked the money to have the catalytic converter reinstalled. Duh!

Airgun equivalent

What’s the airgun equivalent to a stage one tuneup on a Harley? How about a Vortek PG4 SHO kit for your HW 50S? It’s gonna shoot better, have less vibration and cock with the same effort. BB has one of those kits on hand and plans to make that switch for you in this blog.

The opposite to that would be the guy who has a “special” tune for the valve on your Benjamin Marauder. He claims you’ll get more shots and higher power. When you make the switch and don’t get either one he tells you, “Well, I did!” When you want to switch back to the old valve you discover that the guy has machined a part of your gun that renders it incapable of switching back.

Last mod — new stock

BB did this one in front of all of you. His new-style Benjamin 397 stock was shaped so he couldn’t see the open sights on the rifle. You got to see that in Part One of that report.

Benjamin 397
The new style Benjamin 397 has a synthetic stock with a very high cheekpiece.

397 maple finished
Reader Hank made this gorgeous curly maple stock for BB’s 397. Now BB can use the peep sight on the rifle and he is proud of the way this rifle looks.

A new stock seems like a less risky modification than many others I mentioned — unless you are modifying the old stock. Remember — you can’t uncut wood!


No matter what, at some point many of us will want to modify some airguns. I just started the discussion today. It’s now time for you to talk among yourselves.

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.

60 thoughts on “Modifications — yes or no?”

  1. BB,

    Modifications to make the gun feel better such as trigger and stock are well and good. Modifying the powerplant is where it starts to become iffy especially if whoever is doing the modification does not really know what they are doing and literally playing it by ear (claiming that the velocity is higher because the gun is simply louder doesn’t work when a chronograph is around to prove it!). The British have gone to that point where they have worked within their constraints to make their gun as smooth and accurate as possible. At the end of the day it is as long as you are satisfied with what you have.


  2. This is a easy one today.

    Plain and simple know what your doing before you do it. If your not able to think ahead then you probably shouldn’t be doing it.

    Anybody ever try to put scope rings on a new gun? 😉 A little measuring will end a problem even before you get started. I bet if I think more there are more examples from reading the blogs that could be said.

    And not only on the blog.

  3. Something to consider,
    We all know that shooting a springer without a pellet will eventually damage the piston face. Without a pellet in the barrel to slow down the air escaping from the barrel the piston will slam home violently. Opening up an air passage has the same effect.
    I picked up a Winchester version of the Daisy 1894 lever action rifle. It had a wood stock but was seriously under powered. Very comfortable to shoot, aside from the horrible trigger, because the air transfer tube at the piston head was so restricted you could hear air hissing out of the barrel long after the BB left the gun.
    I retrofit some old original Daisy parts to change just about everything back to an original Daisy setup with a much larger hole in the air tube that was stock back then and the power increased dramatically. However the piston really slammed home now and I lost the smoothness it had and don’t expect the piston to last as long as it would have. Not sure if I actually won or lost in the modification. But initially I wanted more power and got it.

    • Bob M,

      The important follow up to that is could you do anything to mitigate the problem of the piston slamming and did you? Was that condition then normal with all the other original Daisy models?


  4. BB,

    As some have and will point out, with some forethought a modification can be a good thing. Having an understanding of how your modification will affect something is also quite useful. Unfortunately for many that is frequently learned through experience.

    In the world of PCP airguns, my AirForce air rifles taught me very much. I was able to make little incremental modifications to see their affect and if they were not successful, I could easily revert to original. You personally have seen what I could do with an Edge and I believe there was so much more it was capable of.

    An issue that many do not mention, but usually rears its ugly head is cost versus results. Quite often meaningful modifications are going to cost. When does the cost of the modification become higher than the value of such? I personally do modifications as a learning experience. That I consider invaluable. Also, I tend to do much research before tinkering. That helps to insure that my tinkering will be successful with the results I am looking for.

    Sometimes it is just cheaper to buy an airgun that does what you want in the first place.

    • RR,

      You know, I never even mentioned that I took my .22 caliber TalonSS from 24 foot-pounds to 44 foot-pounds just by installing a barrel that was twice as long.


      • I remember those experiments. You did them with the Edge a while back also. I was looking for an 18 inch barrel when we traded. I wanted to see if I could get it over 12FPE.

  5. It is possible to modify an airgun to make it significantly more powerful, significantly more accurate, significantly smoother shooting etc. However, it is very seldom done at a reasonable cost and almost never increases the value of the gun. In almost every scenario, the owner would be better off selling the gun he had and buying a gun designed with those features he desires. Or, if you are determined to have a modified gun I highly recommend that you buy one already successfully modified by someone experienced at the specific modifications you want on the secondary market. You can usually buy the modified gun at about the same price as a stock gun you now have if you watch the classifieds.

    I can’t talk about motorcycles but how many of you have seen guys spend thousands of dollars souping up cars that will never run with even an older Corvette.

    Buy something designed to do what you want it to do.

    David Enoch

    • I second that sentiment. Having never served, I greatly appreciate those who have served our country to protect the freedoms and the way of life we often take for granted.

      • Roamin Greco,

        You asked about the Ballistol SDS yesterday and if that was for all or just some:
        Product Name : Ballistol Multi-Purpose
        Manufacturer Product Number : W5860CT, W5862CT, W5958CT
        It indicated the liquid Ballistol from the 4fl oz to the multi gallon sizes.

        Your welcome for the Veterans Day Wish.


      • hihihi,

        Point well taken.

        I am anti-war and anti-industrial-military complex. And I am hardly a militarist. Nevertheless, those who serve do indeed help to keep us safe at a personal cost. But you are of course right. I was presuming too much.


  6. B.B. and friends,
    Then there is the piston buttons for a noisy springer mod. I bought some Jim Maccari old school buttons, which are flexible dots that are simply glued on to the aft end of the piston with cyanoacrylate glue and sanded to fit inside the compression tube. I used three of them spaced evenly around. Add a GRT trigger, some TIAT and my old twangy Crosman Quest became a much, much smoother shooter with a lighter. more predictable trigger pull.
    I still call that gun one of my favorites, even next to my fancy imported springers. Part of my fondness for the rifle is due to the successful tune that calmed the shot cycle and improved its inherent accuracy and the other part is that I did the work myself.

    • Michael
      Especially like that. Heck I don’t wait for a warranty to run out.

      Depending on the gun and the mod if I want it I do it regardless of the warranty.

      It’s my money and I’ll spend it how I want. 😉

      • Gunfun1,

        I have heard the 50 mph thing about Yugos, too.

        Here is an absolutely true story for you, no urban myth. It happened to me personally. One summer in the mid to late 1980s I drove my dad’s Chevette back to Illinois from my folks’ Wisconsin summer cottage. On a level highway it topped out around 53 mph. When I was going down a hill, it would get up to 60-65 mph. Then, when I got through the vallley and was moving uphill on the other side, it sometimes got down to a top speed of 10-15 mph! Thank goodness there are no mountains in southern Wisconsin, or that car would have had a negative top speed!


        • Michael
          I know about the Chevettes. One of my wife’s older brothers had one. It was a nice clean car. Black with black vinyl interior and a stick shift. He gave it to my wife and she drove it for a year or so around town. She sold it and got a Chevy Monza with a factory small block Chevy V8 in it. Talk about a difference between two cars. That little Monza ran.

          Oh and they did offer a very limited amount of Chevettes with a small block Chevy V8 in them. Bet that would of surprised a few of the muscle cars running the streets back in the day. That would of been a heck of a little sleeper car.

  7. BB,

    I disassemble, clean, inspect, deburr, polish, re-lubricate and upgrade hardware as required most things I buy. Sometimes, adding a shim or two to tighten up tolerances makes a big difference to how smoothly things work.

    Curious, do you consider that to be a “modification”? I kinda look at that as “fine tuning” or “pre-emptive maintenance”… fix it before it becomes a problem.


      • B.B.,

        Agreed. And sometimes tools and toys wear out and need periodic maintenance and improvement if components have advanced in quality and performance since the item was manufactured. For example, consider all of the times when you replaced a crumbled leather seal with a synthetic one or a damaged or poor-fitting spring with a new one. Those aren’t exactly mods.

        The filter caps in an audio or musical instrument amplifier (especially if it is a vacuum tube amp) require replacement every 15-30 years whether the thing gets fired up now and then or just sits on a shelf collecting dust. Worth noting is that capacitors of 2021 are superior in materials and manufacturing to vintage ones. Older is often better, but not always. Sometimes old is just . . . old. (No jokes about old coots like me!)


      • B.B.,

        Oh, and your using the “there is a fine line between” phrase reminds me of one of my favorite lines in “This Is Spinal Tap”: “There’s a fine line between clever and stupid.” ;^) That is the funniest movie I have ever seen.


  8. BB,
    I’ve got a Vortek kit for my HW30S that I am also thinking of installing, but after lubing the existing internals and adjusting the trigger, the gun shoots so well that I’m not in a hurry to modify it.

  9. FM’s Rule of Modification is IIABDFI – If It Ain’t Broke Don’t Fix It. More so if you don’t know what the heck you’re doing and don’t have the proper tools needed to do it. Take it back, there is one modification planned for the Benjamin Max kindly given by GF1 – gonna put a sling on it. 🙂

    Don’t see you as a Pinto type of guy, B.B.; at least you did not buy a Yugo. Can’t talk though – drove an awful Ford Prefect for a year in the ’60s. It wasn’t FM’s fault; his dad insisted on buying it even though FM was trying to convince him to buy the cheaper used VW Beetle on the lot. The crafty salesman talked him out of it – “the transmission is noisy in second gear.” Well, they were noisy back in them days.

        • Gunfun1,

          My father’s mechanic once told him when my dad picked up his old tired Chevette, “Soon you’ll need to replace that Hamster and wheel under the hood.”

          Never drove a Yugo, but you know what they say about Russian cars, so few of them were exported because most broke down before they could be driven onto a ship.


          • Michael
            I seen a few of those Yugo’s on the road back in the day. Never drove one. And you probably never would of got me behind the wheel of one back then. That was when I was into big V-8’s in muscle cars. If I remember right somebody said if you got a Yugo up to 50 mph going down hill you were lucky. Maybe true. Maybe not.

            This was for your reply below. There was no where to post.

    • FM
      And that is a good mod for Max.

      And darn anyway now you done it. Everybody is gonna think old Gunfun1 is a good guy now. 🙂

      Can’t wait to hear how that goes. Gunfun1 a good guy. Right. 😉

  10. BB, Wood grips for the Colt SAA bb pistol. I would say ditto on my P08, even if it didnt originally come with them. The Colt will need a holster too, so I can practice my draw. I dont own the real versions of these, but I suspect the SAA and a 1911 are the best for their purpose. Plus, the revolver hanging on the back of an office chair really warms up the place. I liked the stock Marauder valve with the adjustable transfer port feature, and was sorry I upgraded to a valve that doesn’t have it.
    I will downgrade back to one that does soon, after I get my Colt and rig. You can see the bb in the end there.
    Best, Rob P.S. I cannot wrap my brain around mixing fake ammo in with live ammo, but I’ll stop there, because I am sure I am not alone.

  11. People spent hundreds, maybe thousands, modifying the power plant, barrel, trigger, and other things without even thinking about how well the gun fits them. Stock fit, in my opinion, is probably the most important thing. Skeet and Trap shooters spend a great deal of time and money to make sure the gun fits them well. Field target and benchrest shooters for the most part, have fully adjustable stocks to allow fitting the gun to their style of shooting. Put a 1,000 hp motor in a car without doing suspension work and the car won’t perform to its potential. All modifications work hand in hand. You will never know how accurate your gun is if the stock doesn’t fit you.

  12. I think ‘modifying’ the myriad conditions besides airguns themselves, can make considerable differences to the shooting experience too. For example, the choice of location, target, distances, whether alone or in company, etc, etc…

  13. B.B.,

    I vote YES!

    Especially on sight mounting systems and trigger groups.

    I’m surprised that you made no mention of sight systems.
    I am currently changing many of my bases over to Mil Spec Picatinny because I am TIRED of the mounting issues you and most of us have experienced. For most of them I use a 20 or 30 MOA change of plane (sometimes refered to as CANT) since I typically shoot at longer ranges.
    Ever since my first Crosman 22XX pistol/carbine/rifle I have at a minimum used Brass bearings to hold the trigger, changed spring rates frequently if not used aftermarket adjusters, trigger shoes, and actual custom triggers. On occasion i have changed Transfer Ports, barrels, valves, regulators, and done valve/plenum/reservoir modifications.
    I do think through modifications/upgrade before making or buying them. I also use the applicable math to determine what can be expected in terms of performance change for each mod and then all modifications in total.

    I still have a few stocks that need to be swapped/modified for fit and better sling mounting systems. I really like flush mounts!


  14. RidgeRunner, Michael > 1894 BB Rifle
    My last entry was late last night in CA not early today. Had to sleep.
    The air passage in this rifle is a long tube, 2″ or so, attached to the piston head and is a ‘T” shape where it attaches so the cylinder air can enter through the sides of the hollow tube. Been 10 years since I did this, a little foggy.
    So you cant drill all the way through it. You would need an extended drill bit to open it up from one end. The air tube is always within the cylinder end seal as the piston travels back and forth and it picks up or pushes a BB from the spring feeder / magazine below as the piston moves forward to fire.
    This tube came in at least three different inside diameters to reduce power as the years past. I suppose the middle size one would be optimal for all round performance but I will let the big one remain.
    Michael, I originally got this airgun to rebuild / repair my ‘first’ airgun the Daisy 1894 and perhaps swap the wooden stock over too. Another entry for that story on the trigger.

    • Michael
      This Winchester version, though made by Daisy turned out to be a totally different animal designed by lawyers. The original used the hammer to knock the piston retainer out from under it and this one uses the trigger to pull it out from under it. Completely different set up and I don’t believe you can help it other than more grease. I retro fit the entire Daisy action set up. With enough modifications to do a blog on it, and was, but they discontinued making it in a short time anyway. Probably because of the trigger?

        • Yes they they retained the same cocking action as the 1960’s Daisy but that’s about all. They modified some internal parts too that I believe operated the now ‘decoration only’ hammer during cocking.
          Back at you later, a full day ahead for me.
          Bob M

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