Qb free flight hammer, not quite an ssg

[mackeral5]

I really like what I've seen with the ssg thread, however I don't care for the rod protruding from the rear on a qb.  I have very limited fabrication capabilities, but I was determined to try and make a similar device.

Bear in mind my qb's are converted to use a 2240 style rva, so no offset is required for the adjustment screw.  In this setup you must disassemble to adjust preload, the rva now adjusts gap or hammer free flight distance.  But, no moving parts hanging out the back of the gun.  The qb cocking block/spring guide is no longer used and the spring no longer enters the hammer.

I don't yet have a chrony, so I can't really post any scientific data.  However I did want to share the concept.  Initially I set it up with about 1/16 gap and a fairly stiff spring with a decent amount of preload.  Cocking effort is increased, but not to the point of being uncomfortable.  The first shot sent a 22 FTT supersonic, which I have never done with my qb.  Scared my dogs pretty good and the warden demanded there not be any recurrence of that event, lol.  I ended up with about 3/16 of free flight which slowed things down a bit, the sound now is just a sharp crack, with zero sound of hammer bounce.

Here is a pic that is representative of the concept, but a close eye will see this would never work in a qb due to the spring guide being too short.  Again, this was just a mockup for the sole purpose of illustrating the concept, which I am sure I didn't adequately describe.

[rsterne]

3/16" is a large gap, I would try reducing the preload, or better yet using a slightly weaker spring.... Otherwise, no reason your arrangement won't work just fine.... It is one of the variations shown in post #356 on page 18.... (one from the bottom, IIRC)....

Bob

[mackeral5]

Thanks for the reply Bob.  I played with some different springs today, but my selection is limited to either too heavy or too light.  I tried a 2240 spring that came with an rva kit, but it was so light that it would barely open the valve at coil bind.  Over the next week or so I'll experiment with different springs.  Once I figure out the right spring I'll refine my design to allow for external preload and gap adjustment. 

My tanks are regulated between 1350 and 1450 psi.  I'm thinking a spring slightly weaker than a stock qb spring, with a decent amount of preload will be the next one to try.  I just need to search through mcmaster carr's sing selection and order another assortment.

Here is a pic of the first attempt, making use of what materials I had on hand.  With this spring I needed 3/16-1/4 of gap to not waste air. 

[rsterne]

Yeah, that spring looks pretty beefy, judging from the wire size.... The next stiffest Crosman spring, up from a 22XX, is for the 13XX pumpers... Then next is for the Disco....

Bob

[Kailua]

I like that design.  I hope it works.  Is there a way to sleeve the threads or use a bolt with a straight section without threads being exposed to spring binding?

[rsterne]

Use a piece of K&S brass hobby tubing over the bolt.... 7/32" OD tube fits over a 10-32 bolt....

Bob

[mackeral5]

I ordered some supplies from McMaster carr, I should be able to have a more refined version by next weekend.  BTW, the threads are ground off the screw, except for about 1/2 which left room for preload adjustment.

This all started when I was trying to piece together another qb from my parts stash.  all I was missing was cocking blocks and hammer springs.   for cock on opening all that was needed was a long bolt through the rva, with a nut to act as a spring seat.  Then Bob posted the SSG thread and over the course of the past few weeks my gears were turning about how to convert my simple rva to function similar to an ssg.

The "ahaa" moment was when I realized the spring didn't HAVE to go inside the hammer- once the cocking block was out of the way there was plenty of room to compress a spring behind the hammer.  This resulted in no additional mass added to the hammer strike, no drag from spring/hammer contact inside the hammer, and nothing but the rva adjustment knob protruding from the rear cap. 

The next version will allow for both preload and gap adjustments with no dissassembly required.

[mackeral5]

duplicate post...

[mackeral5]

I made a somewhat crude version of an ssg.  The requirements were for externally and fully independent preload and gap adjustment,  made from off the shelf components from McMaster carr and a Crossman end cap.  no moving parts sticking out the end other than the preload adjustment knob which only turns.  The only fabrication tools required were a drill press and a bench grinder.  The average person with decent mechanical and fabrication skills/tools should be able to build a similar version.

the Crossman end cap was chosen as it already has a 5/16 hole centered, and almost all the way through the cap.  no problem drilling the gap adjustment screw hole straight and on center as you already have a guide and are only drilling so far.  you will have to drill a hole through the breech to attach the new upper breech to crossman tube cap/ssg carrier.  this hole can be drilled with the breech attached to the tube with the screw under the loading tray, leaving out the rear qb trigger/tube/breech screw.  having the tube/breech partially assembled in this manner will effectively serve as a jig locating the new hole you will be drilling through the breech.

the gap adjustment Bolt was a rifle drilled 3/8-16 bolt, 1 inch long.  I used a vent type cap screw, which already has a small hole drilled on center, through the bolt.  this served as a pilot, allowing me to increase the size of the hole for the 10/32×4" machine screw to pass.  I did this operation in a drill press, using a drill vice.  the bolt was screwed into a stack of nuts, the nuts were clamped in the vice head up, and I used a couple of different sized bits, increasing the "vent" hole large enough for the 10/32 to pass through.  take your time, slow speed and lube will allow you to complete this operation pretty close to perfectly on-center.

the 10/32x4" machine screw I purchased was threaded half it's length, this is critical to have enough threads for preload adjustment.  you could use threaded rod and a brass sleeve epoxied over the threads that the spring will ride on.  that isn't required with the machine screw I bought, but I added some anyway, if only to have a tighter spring guide.

there is one piece that wasn't purchased from McMaster carr, I just happened to have it in scrap.  it is the crudely ground piece that attaches to the forward side of the gap adjustment bolt.  this is one of the key components in the fully independent gap and preload adjustment.

here are a couple of pics, one with minimum preload, maximum gap.  another with max preload, and zero gap.

this is again a very crudely made, prototype so to speak.  Mainly I'm trying to show another design  of a QB SSG that meets the requirements of externally adjustable, fully independent preload and gap adjustment, no spring guides sticking out the back and moving with the shot, etc.  no additional strike mass was an unintended but welcome feature of this design.


Again, I am not a machinist, this is a very crude representation of what I think is a unique design.

[mackeral5]

 Turning the preload knob clockwise decreases preload, clockwise increases preload.  turning the gap adjustment bolt clockwise decreases gap, counter clockwise increases gap.  the spring guide (10/32x4 machine screw is located front to rear in the gap adjustment bolt by lock nuts on each end.  a square 10/32 nut is what preloads the spring when turning the preload adjustment knob.  the funky looking u-shaped aluminum piece is static to the gap adjustment bolt.  the square 10/32 nut loosely engages the aluminium piece, providing preload adjustment when turning the preload knob.

[Austringer]

So on a QB with a SSG type devise, how is the aft end of the breach attached to the gun? Is it normally held in place by the rear trigger screw which passes through the tube (hammer housing and end plug) and threads into the breach plug?

Bob. It there an advantage of such a devise in a regulated QB?

Troy

[rsterne]

Yep, if you look back early in the SSG thread you will find info on the one I did.... I gained a lot of shots.... I used separate screws to locate the breech and trigger group.... and that is what the OP has done here....

Bob