In Part Two of his series, Doug Wall makes a Barra 1100z caliber change. It’s quite straightforward, as you will see. You can read Part One of Doug’s saga here. Take it away, Doug…
In this part, I will be changing the barrel and bolt from 0.22, to 0.177. That’s essentially what is required to make a Barra 1100z caliber change.
However, this involves a bit more than just changing the barrel and bolt. There are quite a few other steps involved to get there. For those of you out there that have worked on the QB78-79 series of guns, this will all seem quite familiar, as there are strong similarities between the designs.
Safety First!
Even though it may not be really necessary for this modification, I am always very wary about working on anything with pressure in it. So for the first step in this Barra 1100z caliber change, I will degas the gun.
This is done using the degassing screw supplied with the gun. The screw is inserted into the fill adapter on the front of the air tube, and screwed in using the supplied Allen key.
As the screw is screwed in, the air will escape, until there is zero pressure on the gauge. Remember to take the screw out afterwards.
Stock Removal
In my case here, I will also be changing the stock. To do that, the safety must be removed.
Rotate the safety to the safe position, and, from the side opposite the safety lever, tap the safety out with a wooden dowel and a small hammer.
The stock is held on with two screws, one in front of the trigger guard…
…and one in the forend, at the barrel band.
Now The Barrel Shroud
The next step is to remove the barrel shroud. Loosen the set screw in the top of the barrel band (with the stock off, you can slide the barrel band off).
Now unscrew the barrel shroud and pull the shroud off of the barrel.
Inside the shroud, screwed onto the front end of the barrel is an air stripper that directs air from the barrel muzzle back into the shroud. This will unscrew from the “old” barrel, and screw onto the new barrel.
I took this opportunity to open up the holes in the air stripper a little, hoping to get more air to back into the shroud. Here’s my thinking behind this…
The new .177 caliber barrel is 22-In. long. The “old” .22 cal barrel was 19 In. long – this was an early gun and Barra increased the barrel length during the manufacturing run. The longer barrel reduces the air volume inside the shroud, so I’m trying to balance that back up with the larger holes.
Barrel Removal
Now let’s remove the barrel. Remove the barrel shroud back end by loosening the set screw in the shroud fitting, and slide it off. Loosen the two set screws in the top of the receiver enough to let the barrel wiggle loose.
Back To The Breech
Next, we’ll take off the top of the receiver. Cock the bolt so that you can access, and remove the Phillips head screw in the magazine slot.
Remove the straight screw at the top rear of the receiver. This will allow you to take off the receiver to change the bolt and bushing.
Make sure that you keep track of the transfer seal that goes between the receiver and the pressure tube!
Remove the cocking pin/screw on the bottom side of the bolt. Slide the bolt and levers out the back of the receiver.
Next remove the breech bushing from the front of the bolt slot. This bushing is held in by TWO set screws on the underside of the receiver, one on top of the other.
To put in the new bushing, make sure that the dimple in the bushing is aligned with the set screws.
Re-installation
To put in the new bolt, change the cocking linkage and lever to the new bolt, and slide the bolt and linkage back into the receiver. Screw the cocking pin/screw back into the lower side of the bolt.
Next, install the receiver back onto the lower tube with the two screws.
Check to make sure that the action cocks, and operates correctly. If it isn’t operating properly, you may have to play with the position of the bolt in relation to the hammer (in the lower tube) when you place the receiver back on the lower tube.
I would suggest cleaning the new barrel before installing it. It’s much easier than when surrounded by the shroud. Everyone has their own barrel-cleaning method, of course. But I use a brass rod with patches soaked with light oil and run through until they come clean.
Install the new barrel into the receiver, making sure that the transfer port is on the bottom, and the two set screw indents are on the top. When installing the barrel, put a little silicone grease on the O-rings, and be very careful not to cut the O-rings when fitting it into the receiver.
Place the shroud back end piece over the barrel, and secure it with the set screw. Put a little silicone grease on the air stripper O-ring, and place the shroud back over the barrel, screwing it onto the back piece at the rear of the barrel.
As mentioned above, the new barrel is longer than the old one. But this created no issues in re-assembly.
Put the stock back on, securing the two stock screws.
Reinstall the safety by pressing up on the safety plunger with a flat bladed screwdriver, and snapping the safety back in from the other side.
That should about do it!
Check everything for proper operation, and you should be back to shooting again. Our Barra 1100z caliber change is complete and the gun will remain in .177 caliber going forward.
Stay tuned for the next in the series. Doug will be testing the 1100z in its new .177 configuration and comparing the results to the performance of the same gun in .22 caliber.
BUY FROM BARRA AIRGUNS:
Barra 1100z Air Rifle
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