You don't unscrew the barrel off the model 99 you unscrew the shot-tube inside the barrel. Look closely at the end of the barrel you will see that it has ridges around the end. Grab these and untwist the very end of the barrel. It will come out and you will be able to pull out the shot tube.
See the link below for the Owners guide for the model 25, it uses the exact same barrel and loading system as the model 99.
You just unscrew it off the barrel
you just unscrew the muzzle brake and replace it with the silencer
First, unscrew the magazine tube cap, located at the end of the forearm. Then pull the action back to about half-way, then you should be able to pull and jiggle the barrel and forearm free. To reassemble, slide the barrel and forearm back on, and pull the action back until the barrel slides into place, then rescrew the magazine tube cap.
Unscrew cap from end of plug chamber .Take your barrel off there will be a little tin cap at the end of your plug barrel take it out to get to your plug
well you unscrew the screws and gun off parts of the barrel you should be left with the inner bit where the bullets go threw!
If the co2 cartridge is full unscrew the back slowly until all vapor is gone, then just unscrew the back all the way off and it will slide out.
By designer are you asking what Model it is? If so, the Model can be determined by the serial number, which is located on the barrel flats and the forend. You have to take the barrel off the receiver to see them.
I can't exactly identify this model but I believe I know what it is. Both Daisy air gun and Crosman air company made pellet/BB guns and rifles for Sears under the JC Higgins name. All the Crosman models started with Sears model #126. All the Daisy models started with Sears number 799. Daisy made a 1894 model for Sears and the number was 799.19052 it really was a Daisy commemorative model 1894. It looked like a Winchester 3030 it had an octagon barrel. If this is your rifle, hopefully it is then the standard Daisy model 1894 is worth $50 to $100. If this is the model 799.19052 Commemorative model with gold plated finish it's worth $200 to $250. Because your number is only one digit off, I think it's a standard Daisy model 1894. This is all a best guess it I have the right rifle or not.
It would help if you stated the model.
Pull down on the front of the foreend. It snaps right off. Open the action, and the barrel lifts back and up off the hinge in the receiver.
It is a Savage/Stevens Model 94, and the barrel has been cut off. Value is minimal.
Remove any magazine and ammunition. Loosen the barrel band by loosening its screw and pull the band off. Unscrew the screw under the stock that holds the stock to the barreled receiver. Move the safety to the middle position, then separate the barreled receiver from the stock. Unscrew the 2 hex head bolts that hold the barrel onto the receiver. Pull the barrel out of the receiver. It should go back together in the reverse order that it came apart.