The winter was getting long.
A little Beretta .380 (12.6) ejected empties straight up to land on my hat - making them hard to collect, so I changed it over to a .22 LR.
This required :
a new barrel
changes to the magazine
work to bottom side of the slide
changing the firing pin
changing the bolt face from centre fire to rim fire
changing the hammer spring
changing recoil spring
work to the extractor
other stuff
The results were not so impressive. The slide was too heavy, requiring that the hammer spring be as light as possible and the recoil spring very light also. Everything had to be very slick - perfectly polished on all contact surfaces. It worked, but .22 LR just doesn't have the horsepower to throw the heavy slide like it should. It never felt far from the point of not working.
I learned:
That a .22 slide should be about 2 oz lighter than a .380 slide.
That a magazine has more engineering in it than I ever thought. It is tricky to get those rimfire cases which are bigger at the base than at the front to stack up in a magazine with the nose of the bullet at the right attitude. After five in a stack, they start to level out and nose down.
That the case head needs to be supported on the opposite side from the extractor, to keep the case rim under the extractor.
That the chamber must be polished smooth to allow the blowback to actuate the action dependably.
Other stuff.
Well winter wasn't over yet - so what about a .17 Mach 2? That required:
another barrel - chambered and installed.
minor magazine changes
reinstalling the .380 hammer spring
a heavier recoil spring
other stuff
Now this .17 Mach 2 Beretta starts getting silly :
It blows the head off some cases, leaving the case in the chamber. Oiling the chamber only partially fixes that.
All case heads are bulged - no longer flat.
Some cases rupture as they extract/blowback - spraying fine brass particles.
The cases have every sign of extreme pressure - the case head etc is pounded thin like as if struck with a hammer - paper thin. The case is abraded from blowing out of the chamber while under peak pressure.
Unburned powder is lying about.
Other stuff!
From this I suppose:
These little Mach 2 bullets operate at very very high pressure compared to .22 LR.
The Mach 2 cases are thin - they weigh 10% less than a .22 LR case, even though they are longer. ( The COL is the same as .22 LR.)
They may use a slower burning powder.
I conclude:
That .17 Mach 2 is not suitable for a blowback operated gun. I think that if I used a locked action that delayed the opening of the breech until the pressure was down, that it could work better.
That safety equipment is good.
I also learned that if an extractor spring is too strong, that the extractor can slamfire when it hits on the rim of a rimfire case and that:
It is good to point the muzzle in a safe direction while loading.
A little Beretta .380 (12.6) ejected empties straight up to land on my hat - making them hard to collect, so I changed it over to a .22 LR.
This required :
a new barrel
changes to the magazine
work to bottom side of the slide
changing the firing pin
changing the bolt face from centre fire to rim fire
changing the hammer spring
changing recoil spring
work to the extractor
other stuff
The results were not so impressive. The slide was too heavy, requiring that the hammer spring be as light as possible and the recoil spring very light also. Everything had to be very slick - perfectly polished on all contact surfaces. It worked, but .22 LR just doesn't have the horsepower to throw the heavy slide like it should. It never felt far from the point of not working.
I learned:
That a .22 slide should be about 2 oz lighter than a .380 slide.
That a magazine has more engineering in it than I ever thought. It is tricky to get those rimfire cases which are bigger at the base than at the front to stack up in a magazine with the nose of the bullet at the right attitude. After five in a stack, they start to level out and nose down.
That the case head needs to be supported on the opposite side from the extractor, to keep the case rim under the extractor.
That the chamber must be polished smooth to allow the blowback to actuate the action dependably.
Other stuff.
Well winter wasn't over yet - so what about a .17 Mach 2? That required:
another barrel - chambered and installed.
minor magazine changes
reinstalling the .380 hammer spring
a heavier recoil spring
other stuff
Now this .17 Mach 2 Beretta starts getting silly :
It blows the head off some cases, leaving the case in the chamber. Oiling the chamber only partially fixes that.
All case heads are bulged - no longer flat.
Some cases rupture as they extract/blowback - spraying fine brass particles.
The cases have every sign of extreme pressure - the case head etc is pounded thin like as if struck with a hammer - paper thin. The case is abraded from blowing out of the chamber while under peak pressure.
Unburned powder is lying about.
Other stuff!
From this I suppose:
These little Mach 2 bullets operate at very very high pressure compared to .22 LR.
The Mach 2 cases are thin - they weigh 10% less than a .22 LR case, even though they are longer. ( The COL is the same as .22 LR.)
They may use a slower burning powder.
I conclude:
That .17 Mach 2 is not suitable for a blowback operated gun. I think that if I used a locked action that delayed the opening of the breech until the pressure was down, that it could work better.
That safety equipment is good.
I also learned that if an extractor spring is too strong, that the extractor can slamfire when it hits on the rim of a rimfire case and that:
It is good to point the muzzle in a safe direction while loading.
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