..too many pictures were no longer attached.
Have to remind you at this point, it is summer and still co2 weather.
Just in case you get the urge to cut up your QB78 tube to make a long tube tanker, Have noticed that the increased air tube size means more on deck air (air that has been pre-regulated) and the faster you can make them shoot.
1. Electric drill and 5/32 drill bit
2. Needle files
3. Larger (8) fine flat file.
4. Emory paper
5. QB79 gas block (comes with screws)
6. Masking tape
7. Hammer and center punch
8. Hack saw
9. Ruler/yard stick
10.Normal take down tools (screw driver/allen keys/etc.)
11.Normal cleaning gear
12.Tin snips or heavy scissors.
13. Vice (padded)
Nice to have:
1. Dremel tool with cut off disks/polishing bits
2. Tubing cutter
Do your lay out, measure, and re-think anything and everything. The more you think this through, the better the results.
1. Want to start with a totally empty gas tube.
2. Tape up the end at the expected cut with masking tape. Figure the length carefullyI wanted the gas block to be inletted into the stocks for end, and something near this works out.
3. Run a TUBING cutter around the masking tape at your chosen length (9 1/8 in this case). You are NOT cutting the tube with the tubing cutter, are scoring a line evenly all around it (the tape is just to keep the tubing cutter's wheels from scratching the blue).
If you dont have a tubing cutter to score a line into the tube, can very carefully and evenly apply two strips of tape, with a small space between the strips that space would act as you guide line.
4. Cut along the scored line. Can use a Dremel and cut off wheels or a hack saw, just STAY ON TOP OF THE LINE ALL THE WAY AROUND and it will be pretty even.
(The project pictured was done on a Crosman tube, added a cut off section of QB tube at the top to give an idea of the amount cut off of a QB78 tube for another project.)
5. FILE the end smooth and even, here a large fine flat file works a lot better than a small file. Nice to vice it up, make it sit level. Do a lot of checking to be sure it is even.
6. DEBURR the inside and outside of the tube. Any lip/burr here and it sill slice the o-rings of the tank block. Needle files will do the job.
7. Cut two 1 1/2" long by 1/4 " to ½ wide strips of Al. beer can (or Coke can).
8. Punch two small holes in one end of each Al. strip. Want the holes to be a reasonably small in size.
9. Lay them so that the punched holes line up with the tube mounting holes on the gas block (can run a nail though the block and through the holes on the Al. strips to hold that end in place I used a close fitting allen wrench) and tape the strips FIMRLY to the gas block.
10.Insert the taped up gas block into the gas tube. Take CARE that the top of the tube is really "up" and the gas block hangs down....won't do to have the gas block at an angle.
11. The two Al. strips are on the outside of the gas tube...the holes are in the right spot for the threaded holes in the gas block...so mark the tube with a punch through those holes in the AL. strips.
12. By using a punch, you get nice starting dimples for the drill.
13. Remove gas block and drill the tube for the mounting screws (want the hole to be close to the screw size). The common size that is a close fit (closer than the factory holes in a QB79) is 5/32.
A drill press would make this pretty easy, but you can do it with an electric hand drill. Need to vice up the tube (PADDED please, and not so tight that you ruin it). Just take a lot of care to be sure you are straight vertical when you drill.
14. Deburr the new holes on the inside of the gas block, they will cut the o-rings of the block unless smooth. A partly round needle file, followed by fine emery cloth does the trick just fine. Dremel and a Curex tip would work faster and smother in this case.
15. STOP! the tube is done. CLEAN IT clean it again really clean it. One metal shaving is enough to shred the valve stem seal, so be sure everything is clean-clean-clean.
15. Take the tape and Al. strips off the gas block. Lube the gas block's o-rings with silicon grease and insert it into the tube. The holes should line up if you took care with steps #9-#12.
16. The mounting screws are there just to keep the gas block from shooting across the room, they don't "seal" anything, so don't crank down on them extra-extra tight our you'll just raise burrs on the inside.
Actually, if you over tighten enough, you can cause a leak. Its a round tube, and if you over tighten, will compress the tube in that direction, which lets it gap open in the other direction.
17. Because of the distance the HPA tanks fill nipple and gauge stick out, will need to attach the gas block and the tank BEFORE putting the breech/barrel back on. OR you can attach the HPA tank to the gas block BEFORE you put the gas block onto the tube. either way.
18. Reassemble and test.
19. I like to use a brass RAP 4 (have a large inventory online) on/off. Its gauged to read the gun side of pressure, so with HPA you can check the out put (and it has a burst disk safety nice to have one more between the tank and the tube).
20. Recommend replacing the stock valve with one with a Delrin valve stem., but have had stock valve stems hold up for quite a long time. As you will not be piercing 12gr., get rid of the piercing parts.
Simple tanker valve (minimal parts and no piercing assembly):