by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- More than just spring guns
- What a loading tap does
- How it works
- Precision machining
- Pick your pellets
- Power levels
- Don’t do this often!
Today’s report is historical, and also a lengthy answer to reader Brad’s question from yesterday. He said the following:
“Sorry, I’m going off topic but I have a fascination with this [Diana] model 50 I’ve been shooting. The tap loading feature of this rifle prevents any seating of the pellet snugly in the breech. Because of this I cannot consistently gage the depth. Does this effect it’s accuracy? And because it is not snug, does it allow the piston to slam into the end of the compression chamber like a dry fire? Love the rifle, just curious. Thanks again.”
Brad is shooting a Diana model 50, which is an underlever spring gun that loads through a rotating tap. We have looked at many spring guns over the years that load that way, and I have made comments about them from time to time, but I have never taken the time to fully explain everything I’m going to touch on today. It is time to consider the taploader.
More than just spring guns
First, let’s understand that loading taps are found on other types of airgun powerplants besides spring-pistons. There are pneumatic air canes from the 19th century that load through a tap. And the pneumatic and CO2 guns made by Giffard are taploaders.
The loading tap of this Giffard CO2 pistol can be seen at the top of the receiver.
Airgun maker Dennis Quackenbush put a loading tap on the Liege Lock (same design as the outside lock) that he made in the 1990s. That gun ran on CO2 or air that was compressed to a lower pressure.
I bet if I thought about it more I could come up with other powerplants that have used loading taps. That being said, though, they are found on spring piston powerplants more often today than on anything else. So Brad’s Diana model 50 is the kind of airgun we think about when we consider taploaders.
Haenel model 311 bolt action target rifle has a manual loading tap.
BSA Airsporter Stutzen has a manual loading tap.
Hakim military trainer made by Anschutz has a loading tap that opens automatically when the underlever is cocked. After loading the shooter closes it manually.
What a loading tap does
A loading tap provides a means of loading a pellet without exposing the breech of the barrel. Therefore, the barrel in a taploader is fixed — it doesn’t move. The tap is a fixture that “taps” into the powerplant, allowing a pellet to be put in line with the air transfer port and the breech without exposing the breech. It’s not that the maker doesn’t want the breech exposed, but with the loading tap the barrel does not have to move.
How it works
The loading tap rotates 90 degrees to the boreline, exposing an opening for the pellet into which the pellet is dropped. The photos above show that clearly. All the taps I have seen require the pellet to be dropped in nose- (or point-) first. When the tap is rotated closed, the nose of the pellet is at the front, to enter the barrel and the tail is at the rear, to catch the blast of air when the gun fires.
Inside the tap is a conical chamber that’s smaller at the front (the part that ends up next to the breech) and wider at the rear (where the pellet is dropped in, and also next to the air transfer port when the tap is closed). The taper is slight. It has to admit the largest pellets in the caliber for which it’s made, but it also has to guide the pellet very precisely into the breech of the bore when the gun fires.
Brad noticed that he can’t control the depth of the pellet in the breech, because the tap is not the gun’s real breech. That is true, but he can try pushing the pellet as far into the tap as it will go. That controls where the pellet is in relation to the breech when the air blast hit it. I’ve had some noticeable gains in accuracy with some pellets in some guns when I do this. But I don’t want people to think it’s a fix, because it isn’t. I’ve also had guns that exhibited no difference when I did this. Try it and see. And shoot 10-shot groups when you do — it will save you a lot of time and guessing.
In contrast to a breakbarrel, a taploader is far more intricate. That tap has to be lapped perfectly with the receiver of the gun it fits into to prevent air loss around the outside of the tap when the airgun fires. And the chamber in the tap has to align exactly with the barrel’s breech when it rotates closed. That’s why you will probably never see a cheaply made spring gun that has a loading tap.
But the fact that the pellet is not in the breech when the gun fires is also a detriment to ultimate accuracy. The jump it must make when the gun fires is a little too much for the pellet. So taploaders are accurate, but they are not the absolute best, and nothing you can do will change that.
Pick your pellets
I saw some readers giving Brad advice about which pellets to use, and I think I saw some errors. For example, I have often mentioned that RWS Superpoints have very thin skirts that work well in many guns with loading taps. Readers see RWS and the word “Super” and they immediately think Superdomes instead of Superpoints. Superdomes are accurate, but they have thick skirts and don’t work well in taploaders.
The .22 caliber RWS Superpoint on the left has a thin skirt that works well in a taploader (in any caliber). The .22 caliber RWS Superdome on the right has a thick skirt that doesn’t expand as readily. Please disregard the damaged skirt of the Superdome. I may have done that while setting up this photo.
Brad was concerned that his piston might be slamming into the end of the compression chamber, because the pellet doesn’t stop the air as effectively as it would in a breechloader. This is why I say to use pellets with thin skirts. They will deform more readily when the compressed air hits them. But there is more.
This is also the reason that taploaders are never magnum airguns — or they shouldn’t be. They should be moderately powered guns whose pistons will decelerate properly when they encounter the compressed air that a thin-skirted pellet can generate in a loading tap.
Don’t do this often!
Years ago I wondered if I was right about the thin skirts and soft lead doing what I said they do in a loading tap, so I did an experiment. Brad, if you wonder too, this experiment will show you exactly what I’m talking about. Try Superpoints in your rifle. Then contrast them with pellets that are the exact opposite. I tried Crosman Premiers in a Hakim. All it took was one shot to tell me Premiers are not right for that rifle! In contrast to a smooth firing cycle with the Superdomes, the Premiers gave me a jarring cycle that I knew instantly was the piston bottoming out. Brad, that is the answer to your question.
Right now you don’t really know whether the pellets you use are good or not. You need to try a pellet that the rifle seems very calm shooting. It doesn’t have to be a Superpoint. Plenty of other pellets will give the same results. Superpoints are simply a good place to start. Your goal is to find the most accurate pellet with the smoothest firing cycle.
My thanks to Brad for giving us a subject I have wanted to write about for years. I probably have said all of these things over the years, but this may be the first time they have all been in one place.