Canadian Airgun Forum

That is a fine looking piece of engineering.

Bob? Is that a steel breech or Aluminum? If so what kinda material?
Thanks! My aluminum one is 6061. But Imagine being the .30 will generate higher pressures you'd want steel?

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-Rick

Brocock Concept .22
3 Crosman MK 1 pistol .22

6061-T6.... The pressure is contained within the barrel and the transfer port, the breech only has to hold those items and make sure the bolt can't blow back.... The breech on my Hayabusa .357 cal is aluminum, and when I built the .45 cal and the .410 shotgun, they will be as well.... However, Sean plans on using steel as he can blue them himself instead of having to send aluminum out to be anodized.... I never worry about the natural finish, it's kind of my "signature", as in "all the aluminum parts I made myself".... Take a look at my other projects and you'll see what I mean....

The only pressure related failure I've had was the Carbon Fibre sleeved barrel on my .22 cal Hayabusa which flew through the Chrony on the first shot because the setscrews ripped along the surface of the CF.... It didn't have sufficient shear strength to withstand the end load, which was only 112 lbs at 3000 psi.... Drilling through the carbon so that the setscrews got a bite into the steel barrel solved that, and the same system works on my .357 at 300 lbs. of load with no signs of loosening or wear on the screws or barrel.... The momentary end force on the .457 barrel on firing will be nearly 500 lbs, so yes, I'll make sure it's well anchored....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Thanks for that Bob! I figured end thrust on he bolt would be almost equal to the FPE of the projectile going out the barrel. Will a .30 Cal discovery have a recoil to it? I have never fired an airgun bigger then a .22 magnum Springer.

_________________
-Rick

Brocock Concept .22
3 Crosman MK 1 pistol .22

The recoil will be less than a .22 rimfire....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Over the last couple of days I made the two bolts (.25 and .30 cal), the bolt handle, and machined the bolt slot in the breech.... The bolt design is quite unique, thanks to Sean.... at least I have never seen it before.... It is probeless.... The sealing O-ring is in a groove in the end of the barrel and the bolt slides through it....



Rather than have either a hollow probe (which loads the pellet by pushing on the base, and the air flows through it).... or a thin extended probe (which loads the pellet by pushing inside the skirt and the air flows around it).... this bolt simply has a flat end.... The key is in the bolt slot.... The bolt pushes on the base of the pellet (or bullet) to load it, and stops with the base or skirt past the barrel port.... It is then withdrawn to clear the barrel port completely, leaving no obstruction to the airflow once in the firing position....



Sean's original bolt slot design was "T" shaped, the bolt moved past the battery position, was withdrawn and turned down to lock.... We then modified it to a triangular shape, where the bolt handle was pulled down and back on an angle to the locking position.... I then saw a photo of the Crosman Rogue which has a slot shaped like the one in the above photo, and uses the retraction of the bolt to the firing position as a safety interlock (as I understand it).... I adopted that rectangular slot design and Sean's probeless bolt for this rifle.... In addition to having no obstruction to the airflow in the barrel, the bolt handle, once in the firing position, can't pop up on firing.... The bolt in the second photo is shown in the firing position....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Good thoughts into Engineering that!

_________________
-Rick

Brocock Concept .22
3 Crosman MK 1 pistol .22

Brilliant idea!

Actually the idea of a probe less bolt came out of the Philippines, with their big bores.... The hooked J look is different, does have an aesthetically pleasing look about it. The Philippine was a straight feed in, then back down into a T slot. The design goes back to the late 70s believe it was.

There was also another Philippine design of the port coming thru the center of the bolt. The exhaust port was positioned half way down the length of the bolt, with orings to seal either side. The bolt end was oringed to seal against the barrel end. This design was done when Ron Sauls(Bryan and Assoc) built Crooked Barn their .32 and Cr1100 pistols back around 2002. I've used this type, the port is directly behind the pellet, which has in turn increased power. It does however make for a longer breech. Believe Gipetto has the same design upon his 32 pistol.

Nice work Bob.

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May the cry of the pack be with you upon your hunt

Whitewolf

Nothing new under the sun, just new to me....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Very well executed!

_________________
-Rick

Brocock Concept .22
3 Crosman MK 1 pistol .22

The .32 does indeed have the flow through bolt Kim describes....should as it's more or less a copy of one he loaned me.

Saw one of those T slot bolts at the last shoot in Olds too...thought it was a pretty slick idea. Those guys in the Philippines have a few darn good ideas...I like the swinging breech too.

I do like the "J" shaped slot...bit more work to make, but keeping the bolt locked down is a very good thing IMO.

Doing a bang up job on the build Bob.

Al

I was thinking about this as I lay in bad last night (odd, I know). Isn't putting the o-ring on the inside of the barrel more likely to cause trouble than stretching it around a slot in the bolt? An o-ring under compression seems like it might tend to snag more than one under tension. I was wondering what the advantage of putting the o-ring in the barrel was?

The MRod and the Hatsans use an O-ring in the barrel with a smooth bolt nose sliding through it.... I have adopted that design for my Hayabusa and virtually all my new builds now.... A rifle with a magazine seems to have less likelihood of the O-ring being damaged from snagging when sliding through the magazine.... They seal extremely well, I think better than the type with the bolt pressing the O-ring up against a taper like the Crosmans, and the bolt length isn't critical....

Actually, Al, the "J Slot" isn't really any harder to make.... You mill the upper slot on an "up" angle (same setup), set up for the lower end of a standard slot on the "down" angle (same setup), and just mill a short slot (in my case 1/4" CTC) instead of just plunge a hole.... Then you turn the breech on it's side, and with the mill at 90* to the side of the breech, you clean up the vertical part that joins the two (same as usual)....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

I got most of the remaining parts made today.... Here is the front breech mounting band, shown installed on the breech....



It fits over the tube between the trigger and the gauge, and securely clamps the front of the breech to the main tube.... I then made a new hammer and RVA assembly....



The hammer is the same length as a Disco / 22XX hammer, but it is cylindrical and will therefore work with a Disco, MRod, or PRod trigger group.... If an MRod trigger is used, it should be shimmed down 0.030" because it is designed for a thicker main tube.... The hammer is drilled to accept a QB 7X hammer spring, which is longer and larger in diameter, stiffer, and has more travel.... The cocking pin is moved back 0.065", allowing slightly more total hammer travel.... The hammer weighs 58 gr. the same as a Disco hammer, and has a notch to clear the rear breech screw location used on a Disco.... The spring guide is made from a piece of 7/32" drill rod with a nut threaded on, peened, and turned.... It is long enough to protrude through the RVA adjusting screw and serve as a cocking indicator.... It weighs 15 gr., so the total hammer weight with guide is 73 gr., 26% heavier than a Disco hammer....



You will notice that the hammer face is counterbored 0.070" to increase the hammer stroke and limit the valve lift.... In combination with the 0.070" shortened valve stem, the stroke has increased from 0.58" to 0.72" (an increase of 24%), and there is still 0.18" of valve lift available.... I have found that to be more lift than required on all other Disco platforms I have worked on, in fact it is seldom more than 0.12" in a properly tuned gun.... The RVA is made from aluminum, and carries an adjusting screw made from a 3/8"-24 NF bolt.... The spring and guide can be removed through the threaded hole, no need to remove the end plug once installed.... The guide slides easily through the adjusting screw, and protrudes when the gun is cocked, giving a visible cocking indicator.... There are two flats on the adjuster to allow it to be turned with a 5/16" wrench.... and it is locked in place with a thin (jam) nut once adjusted.... I have enough travel on the RVA to go from no preload to coil bind, about 16 turns....

I am now at the point where I can install the breech on the main tube and inlet the stock for the front breech band.... Once that is done, I can get on with sanding and finishing the stock.... Most of the gun should be done by the time the barrels show up....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!