Inletting a QB78 Thumb-hole Stock for a Discovery (Long Post)

[zaphod621]

Fitting a QB78 thumb-hole stock to a Benjamin Discovery.
Oldnoob has a tread about his mods and the stock he used was the target stock for a QB 78. I liked the idea but think the thumb-hole stock looks nice so I tried it. I am very pleased with the results.



First I ordered the stock from A-R-C-H-E-R for $60. Comparing the Disco stock to the QB you can see the similarities. The trigger cutout is very close but needs to be widened slightly and inlet-ted for the take-down nut to fit and the slot needs to be drilled and the channel in front of the trigger made deeper. The QB has a cut-out for the bolt handle that does not line up with the Disco but the Disco bolt wont need it so its just there.



 I did all my measurements from the action itself instead of the old stock just to be more accurate.  The channel is slightly too narrow and will need to be opened up some with a sandpaper wrapped PVC pipe.



The Disco sits a little deeper into the QB stock than the Discovery stock so a couple of dimples are needed to clear the two valve screws on the side. My Discovery has a second barrel band placed just in front of the gauge so I had to inlet for that. I very carefully used a Dremel with the cable extension to do most of the work in-letting this but it really takes a deft hand and trial fitting the action to not go too far. Be very patient and eggshell careful with a running Dremel, one slip and the damage is done. You are a surgeon not a butcher.



 Of course I had to bore the hole for the pressure gauge and I used 1” boring bit like they use for door hardware in-letting Be sure to drill a 1/4” pilot hole as straight as you can first for the bore to follow unless you have a drill press that would be best. Also don’t go all the way through in one pass, when your almost through reverse the bore and finish from the bottom side to prevent tearing out the hole at the bottom like I butchered mine. I ripped a chunk out between the gauge hole and the nearby take-down screw hole.



I had to glue the tear-out back in place which forced me to have to strip and refinish the whole stock. I also pressed the sides of the stock too much in the vice that left some marks that needed to be steamed out. I was trying to do this without refinishing but it turned out that to repair my mistakes I had to refinish, it turned out so nice that I'm glad it happened this way. I used a hex head cap screw that is a little longer than the Discovery one and J-B Welded a flat washer into the counter sunk hole for the take-down.




After completing the in-letting I stripped off all the old plain looking original finish and sanding with successively finer paper down to 220 grit. I had some leftover Min-wax red oak stain but wanted it a little darker so I mixed it with some dark brown leather dye and this did the trick. As usual with some of these cheaper woods they tend to turn out blotchy when stained. I stumbled upon a technique to even this out some. I heated the darker blotchy areas with a heat gun which caused the stain to boil out of the wood then I rubbed the stain and blended the dark areas to match the lighter ones. This stock has some nice grain to it that was covered by the original finish. Now the grain stands out in all its glory.




This wood is very close grained and took only about 5 coats of Tru-oil to fill in the grain nicely.
I'm happy with the outcome. The gun is 1.5 pounds heavier but that’s OK as I was using on a bench or out the kitchen window anyways. It balances just in front of the trigger guard under the pressure gauge so off hand shooting works well. The thumb-hole and grip are perfectly alined and trigger length is just right with the Marauder trigger and Challenger trigger guard. Length of pull is 3/4” more and the cheek rise puts my eye at the perfect position behind the scope with a real nice cheek weld and a nice plus is the butt plate is adjustable up and down.

I think its an unusually handsome and practical Discovery now and is now keeping the garden protected in style.

[Kailua]

Wow nice job.  I like that you refinished the wood.  Gives the rifle a lot more class compared to original stock.  Some checkering or stippling might be nice also.  JMO

[BigTinBoat]

That looks really nice.
I now have an extra QB Deluxe Stock that I might do the same to and put under my Disco. I like the angle of the pistol grip on the QB's as compared to the Disco.

[Ribbonstone]

Nice job.

Pleased to see the rear barrel band in use...been a believer in that mod.

[zaphod621]

Thanks for the compliments. Checkering is beyond my ability, I tried it once and it was a disaster.
Ribbonstone you were the inspiration behind the barrel band and it does stabilize the barrel there nicely. Since the QB stock is already in-letted for another band at the end of the stock I may add a third band. Don't see it harming anything.

[Outdoorarki]

Nice job. I like the look.

[Ribbonstone]

Not my original idea…soon as I swar how the Challenger PCP was set up, thought if that’s good enough for a “match” gun, then I’ll try it on the Disco.



Probably better to Al. can shim the rear band  at the bottom of the air tube (in order to pull it down tight) and set screw it.  Using just the screw in the pot-metal band  to pull the barrel/breech firmly down just tends to just strip the treads of the set screw; found it more long lived to shim it and just snug the set screw up .

With this band shimmed tight and set screwed, have removed that accursed tiny b3rech screw and not noticed any difference in the rifle (but I do keep it in pace and snugged up, just as a little extra breech fixation).



6-screw front band has fallen way out of favor, but it works for me. Bottom three screws tight to the tube, top 3 screws made to just NOT TOUCH the barrel.  Won’t shift (because the tight tripod of screws to the tube won’t let it)  but sill a little expansion/vibration room for the barrel (the just loose tripod of the top 3 screws).



May be too much work.  From what I can tell, just getting the bottom part of the front band tight to the tube seems to do just as well.  The normal “slack” in the top part of the barrel band isn’t excessive enough to matter.

[zaphod621]

Ribbonstone,
I don't know why the 6 screw bands are out of favor, I used them both front and rear and like you I locked the air tube down and just barely tightened the barrel ones to allow slight movement for air tube expansion. Seems to work for me too. Mine stacks .177 Kodiaks at 20 yards and whacks the heck out of Eurasian ringnecks at 50 yards. I did glue a piece of rubber bicycle tube repair material to the stock  just ahead of the gauge bore to give some upward cushion and free float the rest of the air tube nicely. I am still experimenting with just how much torque is best with the takedown screw but so far its seems to be shooting well.

[AlanB]

Brian

You are another Surprise shooter??
I am near by-@@ 303/ west bell and spend allot of time west of the canal at the end of greenway - or the extreme west end of white tanks.....it's so nice to have desert so close-

Oh I have that crossman stock on my Disco too- hit me up - I've got something cooking up for the disco guns-  Nice job you did there-
My disco came with a similar stock just not the thumbhole version - too bad , the right handed version is made for tiny kids hands.


Alan

[Monkeydad1969]

Very nice. 

[zaphod621]

AlanB
I am near 163rd Ave and Jomax. Have my own rural acre where I can shoot out my back porch anytime I like. I work at Luke and travel the 303 daily so am familiar with that area. I actually am In the county but Surprise or Wittmann is close enough.
Brian.

[AlanB]

Very Nice-
I wanted a place like that but the commute time for my wife was too much-
We'll need to get together- I'll pm you later with contact info-