A D-bit after drilling to something fairly close to the finished size?

Rob

That was my first though too Michael, as any off the shelf reamer won’t get all the way to the bottom, even a machine reamer will stop 1 to 1.5mm short at that diameter.

If it can’t be plugged then I would bore to a reasonable depth 11.7 and use that bored and hopefully true hole to guide a drill the rest of the way in. Ream with a 12mm machine reamer and then make a D bit from 12mm silver steel to do the last couple of mm

Hi,

German engineering.

https://hw100tuning.co.uk/guides-hw100

On 24 December 2024 at 10:45 Vic Said:

100 BAR sounds quite high …

Depends on what the design is intended to do.  Many factors, some conflicting, others overlapping, such as:

• Maximise power output – let her blow, no regulator!  Accuracy and consistency not required when killing rats in a trap.
• Staying within the UK limit so as not to require a Firearms Certificate (12ft lbs).  Doesn’t require a regulator or high-pressure because the valve limits how much air energy drives the pellet.  (Or should!)
• Accuracy and precision: target shooting.   Regulator improves accuracy by ensuring the valve input is always fed much the same pressure; it’s more consistent.  Has to be a good regulator, and consistency can’t make full use of the air charge.  High pressure helps for outdoor long range shooting.
• Maximise number of shots per air charge.   Indoor shooting, where excessive power and velocity are an embarrassment.   For this it’s advantageous to keep the pressure low rather than high.
• Maximise the number of powerful shots in the field.   High pressure required.   Except, I suggest an air-rifle limited to 12ft lbs or less is unsuitable for hunting anything.   The exception is close-range work by a disciplined good shot; vermin control, not pleasure killing.   Unfortunately, many airguns are owned by undisciplined yahoos who take ill-judged pot-shots at anything that moves.    To my mind inflicting painful sub-lethal wounds on wildlife and domestic animals is both cruel and stupid.   Ask any vet.  As it’s xmas, I’ll reduce the punishment to ‘off with their goolies”!    Seriously though, these idiots are doing their best to get a mostly harmless hobby banned.  Responsible air-gunners should hate them!

As always, engineering is about balance.   How good a PHP is perceived to be depends on what the owner needs of it.  Very difficult to make one that performs well in all categories, so some owners swear by them whilst others swear at them.

Just a thought, moonman doesn’t want to plug a through hole because he’s worried about the pressure.  Quite right, it needs some thought.  But 200bar (2800psi) isn’t that scary in a reasonably thick mild-steel container, walls say more than 3mm. Thin walled UK domestic Copper water pipe bursts at about 1500psi, and the Sparklets soda siphon I took apart had Mazak innards and a 900psi CO₂.   Look the formula up and do the sums, and maybe increase the safety factor by going for stronger than mild-steel.  But threaded plugs are remarkably strong, this screw-breech thinks 200bar is a sneeze:

Might also be possible to design a PHP so a failed plug was caught inside the mechanism, making unlikely to escape.

How is the air-bottle fixed to the gun?  That connection has to contain 200bar, bet it’s a thread!  The dimensions and number of threads are a clue.

Dave

A photo of a drawing of the breechblock would greatly help suggestions on how to make one.