Canadian Airgun Forum

Some of you will remember my ongoing project gun which I dubbed the "Hayabusa".... It has been through three versions, the Mark I was a regulated repeater shooting pellets in .22 and .25 cal, the Mark II was an unregulated version built for bullets in four calibers, .224, .257, .308, and .357, and the Mark III, completed a few months ago, was also unregulated, in .410 shotgun and .458 rifle versions.... I decided some time ago that the 7mm (.284) caliber had some advantages in long range ballistics over the .257 and .308 as a varmint rifle, and finally got a .284 liner with a 14" twist from TJ's and I have on order a 94 gr. Bob's Boattail bullet mold from Veral at LBT which will be sent to Erik at HollowPoint Service to have two of the four cavities converted to HP.... I have been collecting the parts for a while now, and today was the day to start making chips.... Here is the beginnings of the new breech, with the bottom rebate for the main tube machined....



The rifle will be built on the Mark II version, using the larger valve which was designed for the .308 and .357.... The valve has a 9/32" exhaust port and the throat is over 5/16", so the porting when used with the 7mm barrel will be full bore area to maximize the power possible.... I will even be using a probeless, retracting bolt to avoid any restriction to the airflow, the idea borrowed from my Disco Double which was the first gun I built to utilize that feature.... I originally planned to use the .308/.357 breech, but with the change to the retracting bolt, and some other changes I have planned for this build, a new breech became necessary....

Bob

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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!

Spent another day on the breech.... got it drilled and the boss for the shroud turned, threaded the front for the ferrule which will retain the barrel (shown), machined out the loading port, the notch for the front mounting band, and drilled all the mounting holes and the transfer port hole....



Not a huge amount of major work left on the breech, just the dovetails on the top, the bolt slot, and the slot to clear the cocking handle on hammer.... Another good day should see the breech pretty much done....

Bob

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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!

Bob I see the compression nut but I dont see the conical ferrel

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

Whitewolf

No conical ferrule.... There will be a sleeve silver soldered on the barrel just ahead of where the front breech band mounts.... The barrel is 9\16" OD, the compression nut (what I called the ferrule, me bad) the same size ID, and the 3/4"-16 NF threads are 11/16" ID.... The sleeve will therefore be 11/16" OD and about 1/2" long, almost 1 sq.in. of area silver soldered.... At ~ 10,000 psi shear, that should be plenty to stand 1000 lbs. of pull on the barrel from the Bellevilles at the muzzle....

Bob

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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!

What's the small hole in the breech just forward of the loading tray?

I like your solution for mounting the barrel, that should be rock solid.

That will be tapped for a set-screw to hold the thimble in place.... The plan is to have the barrel able to rotate in the breech to index it where it groups the best.... There will be an additional setscrew to keep the barrel from rotating as well, once the best location is determined.... At the muzzle will be Belleville washers putting the barrel in tension and the shroud in compression like this....



Instead of a nut as shown above in purple, I will be using a Hatsan Air Stripper to compress the Bellevilles.... Expected load is 800-1000 lbs....

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!

Bob, wondering if you've ever silver soldered a sleeve onto a barrel before?

Did it once...shrinking caused a "significant" tight spot in the barrel.

Would suggest a machined recess on the barrel and a split sleeve (along the lines of valve spring retainers) set into that recess...no heat needed.

As ever, YMMV.

Al

Interesting, this was suggested by Sean Pero who has done it many times.... I asked him about shrinking, and he said not an issue.... Thanks for the warning, however, I'll keep it in mind.... I will do the chambering after installing the sleeve anyway.... the leade will go nearly to the sleeve.... and you can bet I'll check for a tight spot and report here the results, one way or the other....

Bob

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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 had thought the same upon the shrinking. But maybe the chromoly liner is forgiving. I know some firearm bbls arent.

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

Whitewolf

Just an idea but for securing the bbl what would be wrong with turning a groove into the bbl and using a thick spring retainer to secure the bbl? I'm thinking the same way a punch press or iron worker holds its punch in place? It would be a very strong and simple method.

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Be safe and have fun!

Don't know how a spring retainer works, but bear in mind there isn't a lot of room inside the breech, and you only have access to the retaining collar from the front.... I'm going to proceed with the soldered collar, it's only 0.060" thick, compared to the barrel wall which is 0.140".... besides, if it screws up, I'll just blame Sean....

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!

Lol I will send you a drawing, for future reference.

_________________
Be safe and have fun!

Long boring bar between centres Bob for radius, used to do the first 7 that way.
Old Daystate lock up only done number 3 like that.

I wouldn't silver solder a sleeve it will alter the grain structure of barrel and probably shrink the bore plus usual scaling. Soft solder should be ok, quality shotguns are still done this way but tinned or coppered first, however it wont take hot blacking without coming apart.
Better solution locktite the sleeve on assuming sufficient clearance, works every time.

No, Jon, I used a 1" Ball End Mill for the radius for the reservoir.... Loads to be applied to the sleeve may be a bit much for Loctite with only 1 sq.in. of area in shear....

Anyway, I finished the breech today.... Machined the "J" slot for the retracting bolt, the slot for the side cocking lever on the hammer, the dovetail for the scope mounts, and tapped the holes for the setscrews.... Oh, and prettied it up with a bevel on the top corners....



Now that this major chunk of work is done, I can get on with the small but interesting bits that I haven't done before, the thimble for the transfer port, machining the overlapping portion of the barrel, and install the retaining sleeve on the barrel....

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!

Splendid! I'm waiting for a chamfering bit to arrive so that I can finish up my breech with some bevels