In this post I am going to cover modifications that can be preformed to increase accuracy and performance. Most if not all of these mods are covered individually on this site so I will only be identifying the mods and explaining the benefits of each. I'll start with accuracy mods then move on to performance mods. Performance mods can also serve as accuracy increases due to providing a flatter trajectory, reduced wind effect, and providing the power to shoot higher ballistic coefficient pellets.
Accuracy Modifications
Securing the barrel
The first accuracy modification I'll cover is securing the barrel to the shroud. The barrel is secured to the shroud by the front sight blade insert. The factory inserts can be accurate and a good fit, but most are loose. For the ones that do fit well from the factory they can still loosen up over time. Using a 3D printed or machined muzzle adapter will capture the barrel and mechanically attach to the barrel shroud securing it and providing more consistency from shot to shot. The best muzzle adapters mechanically attach to both the barrel and shroud. There is a well know modification that has circulated the internet involving tape. That mod, commonly called the tape mod, uses tape such as electrical tape around the barrel where it inserts into the front sight insert. The point of the tape is to fill the gap between the barrel and the sight insert. While the tape mod is virtually free it is also the least effective of the three methods listed.
Aluminum Muzzle Adapter
3D Printed Muzzle Adapter
Daisy Tape Mod
Removing the Lawyer Spring
Removing the "lawyer" spring will improve trigger pull but also allow the gun to fire with the bolt open. The lawyer spring is the flat spring located above the trigger and protrudes through the valvebody just behind the loading port.
The trigger and hammer must be removed to remove the flat spring.
Ron's Trigger Modification
For brass tube guns and guns that are not over pumped considerably this is one of the best modifications you can do to a Daisy. Ron's trigger mod will reduce trigger pull to around two pounds. This mod relocates the hammer spring off the trigger. It utilizes a new hammer spring and a light trigger return spring. I install this mod on all of my vintage guns.
Ron's Trigger Mod
A Warning About Trigger Modifications
Trigger modifications that involve the hammer or trigger sear should not be done. The hammer and trigger are not made of hardened metal and wear over time. The large overlap of the two sear surfaces are what holds the hammer. Grinding or placing material in the sear to reduce travel can lead to the sear edges wearing and rounding off, leading to the the gun going off unexpectedly. Those type of modifications also often leave the safety inoperable. These adverse side effects are often not immediately apparent but develop over time as the sear surfaces wear. Ron's trigger mod relocates the hammer spring off the trigger to reduce pull force but it leaves the sear surfaces untouched. Ron's mod is a safe and effective trigger modification. It is the only Daisy trigger modification I endorse and use.
Receiver Bridging
Bridging the receivers is a great accuracy improvement. This modification is for metal receivers, the plastic receivers already have this modification. I retro fit metal receivers to most of my newer model guns for the stability, durability, and aesthetics of the metal receivers. Bridging the receivers involves adding screws to the top of the receivers at the front and back. The added screws directly hold the two receiver halves together just below the dovetail. This greatly improves stability. From the factory the metal receivers are only mechanically attached through the stock bolt at the mid-rear of the receivers. They only attach to the frame forward of the stock bolt. The frame is not boxed where the receivers attach and is too flexible to keep the receivers bound together. The receiver halves will often separate at the top of the receivers. While the separation may not be large it is very significant when using a scope because the dovetail for the scope mount is only on the right receiver. By bridging the receivers the right receiver is held more securely and therefore the scope is less likely to move over time.
Receiver Bridge Post
Wood Stock and Forearm
While this one may be a matter of preference wood furniture on a Daisy can increase performance from a stability advantage. Most long range firearms are heavy for a good reason, stability. Wood furniture is attractive and adds an acceptable amount of weight. The wood stock attachment (steel plate and draw bolt) is also much more solid and stable than the plastic attachment method. To upgrade to a wood stock means replacing plastic receivers with metal vintage receiver halves. If upgrading to a wood stock is out of the question an alternative is to remove the butt plate from the plastic stock and fill the stock with calk to add weight. I am in the process of creating router templates for making wood forearms and have designed an adapter to allow the use of Mossberg 500 stocks on 880 metal receivers.
Optics
While iron sights are proven and some shooters are incredibly accurate with iron sights, scopes are proven to improve accuracy with most shooters. A good air rifle scope can be purchased for a modest amount compared to long range firearm scopes. Depending on the air rifle and intended use a low power or red dot scope can be the perfect complement. For air rifles shooting for dime size targets out to 30 yards can benefit from a mid power scope such as a 3-9. Finally for guns intended to be shot out to 50 yards and beyond a 12 to 16 power scope is beneficial. For scopes in this category an adjustable objective is very helpful for range estimation.
Range estimation for air rifle shooting at distance is important given the larger trajectory arc over firearms. Leapers UTG 3-12 x 44 AO scope is a fantastic scope for the Winchester 1977XS or PBL modified 880/901. In fact it is the scope on the 822 at the top of this page. I add AO handwheels to my UTG scopes for focus adjustment and range estimation. I simply bring the target in focus and read the range from the handwheel.
High End Scope - Leapers UTG 3-12 X 44
Mid Range Scope - Hammers 3-9 X 32
Budget Scope - OMMO 3-9 X 40
Performance Modifications
Over pumping
Most of the performance modifications require opening the gun up, but the one performance increase that technically is not a mod, is to over pump the gun. In factory form, I would not pump more than 12 times with newer guns that use an abutment pin. For the older guns that use the brass tube, those guns can technically be pumped to valve lock without danger to the internals. You'll probably not want to pump as many times as it would take to reach valve lock, if it will even lock. Those vintage brass tube guns will handle 20 pumps per shot forever. The abutment pin guns will bend the abutment pin if pumped too many times. If you want to pump an abutment pin equipped gun up to 20 times the abutment pin needs to be replaced with a strong steel dowel pin (4140 Steel - 1/8" Dia. X 11/16" long). I still inspect and if needed replace the abutment pins at the end of each season. I pump all of my guns 20 times and have only had one part failure (bent abutment pins not included) on over 20 air rifles and 10s of thousands of shots. I shoot everyday but usually only two to four shots at a time, several times a day. My primary use for my Daisys are long range plinking and hunting so I don't mind pumping 20 times. If I shot many times in a session then the 20 pump count would get tiring.
Hammer Tuning
The hammer is what pulls the poppet out of the transfer port which allows the compressed air to flow to the barrel. There are several hammer designs that have been manufactured over the years so if you are replacing a hammer compare it to the one it is replacing. Some sears are "thicker" just forward of the cocking fin and will not move the poppet as far from the transfer port. I have seen this reduce the FPS of rifles by as much as 100 FPS. The reason is because the thicker hammers will engage the valvebody and stop traveling (poppet barely lifts off the transfer port) before the more slim hammers. One performance enhancement is to remove material in the circled area of the picture below.
By doing so the hammer will be able to pull the poppet further from the transfer port which will increase air flow and reduce the chance of valve lock. 1/16th of an inch is a good place to start but I would caution about removing up to or more than 1/8" as it may weaken the hammer to the point of bending. When filing put the hammer in the valvebody without the spring or trigger and manually work the hammer up and down to see where it is contacting the valvebody when in the fired position. The point of contact is where material needs to be removed to increase poppet travel.
PBL Power Modification
If you have a 880 family of guns (880, 901, 822, etc...) that uses an abutment pin (i.e. no brass tube), then the PBL power mod will make a huge power increase. The PBL requires replacing the factory piston head and elastomer with a Winchester 1977XS (its really a Daisy) piston head and spring. Also the compression tube air slot will need to be extended by approximately 1/8". The PBL mod can increase performance by up to 50%. You can expect 15 to 16 FPE at 20 pumps with 16 grain pellets (JSB Monster).
Poppet Tuning
The poppet is a source of performance increase. The newer poppets retaining spring is much stronger than the older screw-in poppets. By replacing the poppet spring with PC024-250-7500-MW-0660-CG-N-IN, the poppet will pull out faster and further. Also by replacing the factory retaining ring with washers and a 2mm E-clip the poppet lift can be tuned by adding washers. Place a 3mm washer next to the E-clip then you can add 4mm washers above the 3mm washer. The 3mm washer provides good contact with the E-clip and the 4mm washer makes good contact with the 3mm washer and fits the hammer fork very well. The factory crimp clip is much smaller than the 4mm washer and can compress the hammer fork over time (higher PSI due to smaller surface area) which reduces poppet travel. I have seen that reduce performance and even lead to partial valve lock. The poppet return spring can be trimmed by cutting off coils to further reduce travel force required. Just be careful not to cut off too much to where the poppet will not seal the transfer port. If you plan on tuning the spring pressure it is a good idea to have multiple springs incase you cut off too much. I will be testing additional springs in the future in search of a drop in spring that does not require any "tuning".
22 and 25 Caliber Conversions
Upgrading the caliber of the Winchester 1977XS and PBL modified Daisys can increase performance through increased efficiency due to the larger working surface area of the larger calibers.
There is a tradeoff between power, penetration, and trajectory. For the 1977 the 22 caliber is the best tradeoff of power, penetration, and trajectory. The 1977 in 25 caliber and the PBL modified Daisies in 22 caliber make for great small game hunting out to 50 yards. A 880 converted to 22 caliber is basically an 822. With the PBL mod it will make around 18 FPE at 20 pumps with 18 grain pellets. The 1977 in 22 caliber will make around 25 FPE with 25 grain pellets, and finally the 1977 in 25 caliber will make around 28 FPE with 31 grain pellets. I would not suggest increasing the caliber on the brass tube guns or unmodified newer style 880s because they do not have the power potential to push the heavier pellets to make it a worthwhile modification. The Winchester 1977 has the power to increase up to 25 caliber with simply an upgraded abutment pin and overpumping.
Daisy 22 Caliber conversion
Daisy 25 Caliber conversion