Saturday, June 18, 2016

Electromagnetic firing pin

What happens if we use an electromagnetic tubular push solenoid as a firing pin?

No, I'm not going to explain specific forces required.  I am not exactly sure what I used or of the legality of this exactly or the liability if some idiot tries this at home.

It is a home made gun and that much is legal.  I used a 24 inch long pipe so the barrel would be legal.  The gun couldn't be carried since it required a car battery and I dissembled it years ago.  I built it from junk I had in the garage one night about twenty five years ago, just something to do.  I showed a couple of friends, but, it was fricking LOUD!  and reasonably useless, so just an experiment.  Motorcycle backfire can be a excellent excuse for loud noises.  Just make sure your neighbors know that you work on cars or motorcycles so they aren't surprised at loud bangs.

There is discussion about this on the web and there are a lot if idiots suggesting that anyone who tries this should be nominated for the Darwin awards.  People have done this.  I've done this.  No trouble, just be smart about it, or you could blow yourself up, so, don't do this at home.

The force required to activate a primer is a funny thing, it is actually pressure, not really force.  Pressure is force distributed over an area.  We call it force, 21psi of force, 15 newtons of force, etc, but, really, pressure is force distributed over area.

Most firing pins, centerfire, are rounded at the end.  If you look at solenoids you might discover that they have different ratings based on the diameter of the rod the solenoid is moving.  A "1000" gram solenoid becomes "2000" grams when the diameter of the rod is smaller.  454 grams are roughly a pound of force.  A 2000 gram solenoid is roughly, 4 pounds.

If you get a double head nail, double head nails are the "McGyver" home gunsmithing "easy peasy" firing pins, cut the head off and round it or just round the point of a normal nail.  Put it in an electric drill, have someone hold the drill and file the point round.  That makes a fair firing pin for any zip gun

By reducing the area of the force, you have increased the mechanical advantage.  Truthfully, a 2000 gram solenoid will probably punch right through some primers once it is attached to a firing pin.

Now, depending on what someone is firing the rest of the rig is important.  Shotgun shells are not really high pressure, smooth bore, all that.  Still, they need something strong enough to absorb the recoil.  3/4 inch black pipe with a pipe cap will do, but, make sure the rounded point reaches the primer.  I've filled the pipe cap with different things.  I like rubber hose washers, make sure the cap threads on securely and the pipe washer pushes the shotgun shell firmly into the barrel.

If you attach the nail to the solenoid it will move in and out of the hole drilled in the pipe cap.  Use a fired shell to set the distance from the pipe to the solenoid.  I used U clamps for pipe into a 2x4 for the pipe.  The solenoid was square.  I had to notch the 2x4 for it and I used a simple C clamp to hold the solenoid in place.

I C clamped the thing to my work bench and I used shotgun shells I had pulled the shot from.  Getting the alignment and the stroke right was the hardest part.  I only fired it a couple of times and it did work.

I also considered drilling a couple of holes in the primers on fired shot gun shells and using nicrome wire or Estes rocket igniters to set off the reloaded shot gun shell, but, I never did do that.

Doing stuff is fun, building stuff is fun.  Messing with guns can be dangerous, so if you ever do any home gun smithing or reloading remember that it's dangerous and be careful.  Shove a hunk of 1 1/4 pipe over the 3/4 pipe if you are worried about the breech pressure.  Some epoxy will keep it in place.

Now, some idiot is going to claim I "encouraged" some other idiot to do something stupid.  I'm not encouraging anyone to do this, I'm just explaining how I did it and how it can be done.  So, don't try this at home.

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