Progress on the AR-pattern blunderbus

[command_liner]

More new pictures.
The business end is about finished and still mounted on the lathe.

Another shot shows the 80% lower lined up on the barrel with a DPMS
adjustable stock.

[command_liner]

pictures?

Pictures are in the flickr link a bit earlier in the thread.
There will be a great many pictures, so I do not want to link them all
into the thread. I am using a flickr set operator. One link leads
to a growing group of related images. The link should remain valid
for a long while.

http://www.flickr.com/photos/command...7623583216070/

[command_liner]

After good machining success, I have my first minor failure, or at least a
reason to stop and think.

As when making my cannons, I want to have a welded in breech plug
with a welded cap. The cannons required a 20 ton press to put in the
breech plug. Then the plug was welded, then capped with 1" plate and
welded. The blunderbuss is much smaller.

The breech plug was a loose press fit -- no strength there. So I
cut like the end of a chisel so it could be welded on 2 sides in the
bore. The idea being that after a 50% weld, then the plug could
be brazed in. The weld went OK, but the braze was short. On
the outside the braze is good. But I cleaned and alcohol washed
the inside of the barrel so I could see the golden ring of a good
braze joint when I looked down the bore. No golden ring.

I do not want a circular crack down there. So what to do?
1) Re-heat and continue the braze. Problematic because my oxy-propane
torch is not quite big enough to braze 1 3/4" stock.

2) Point the muzzle to the sky, and add tin/lead solder and rosin. Heat and
flow. Easy, but low strength.

3) Like 2, but with silver solder. My tools should have enough heat.

4) Chuck it up in the lathe, cut it all out and start over.

Send in your votes. Choice 3 looks good to me since the steel is very
clean.

[DougJ]

Your project is far beyond anything I have attempted. With that disclaimer I would go for option #4.

Do it over with a good press fit and welds that you are sure of. Unlike your cannons you will have your face directly behind the breech on this one correct?

Make it right and you'll feel much better about shooting it.

[command_liner]

Breech plug re-braze

Votes were pretty light. I decided to try and re-braze the breech plug.
If it fails, I can always chuck it up and cut it all out.

After making a small jig to position the barrel above my Victor Turbo Torch (propane), I added a ring of brazing rod to the inside of the breech and
tossed in some flux.

Then the torch went on for a while for preheat. After 10 minutes, I
hit it with the oxy-propane torch. It got hot enough so brazing rod
would melt and stick to the outside, so I expect the ring of braze flowed
on the inside.

The pictures show the heat quite well. It will take a few hours to
cool and tomorrow I can try and check to see the braze at the bottom
of the barrel. Cleaning out the flux might be difficult.

[command_liner]

Brazing inside the breech

The barrel is now cool. I fractured off some of the brazing flux and
can see that the braze operation was a success. Good stuff.

[command_liner]

General layout of finished parts

Check out the layout of the finished product. It is not finished
yet, just laying on the bench.

http://www.flickr.com/photos/command_liner/4444911894/

[command_liner]

Dealing with the breech face is not quite so simple.
The barrel is shaved 0.045" to make a flat. The inside of the buffer
tube is offset 0.125" from the top surface of the lower.

But now that the cuts are made, the path is committed. As the
Chinese say, 'the tree is a boat'. There will be a breech plate which
also slips into the buffer tube, a rear lug, a front lug and a huge
lug in the mag well.

More metalwork pictures loading now.
Pictures up.

http://www.flickr.com/photos/command_liner/sets/72157623583216070/

[77bawls]

You're going to upload video to youtube right??

[command_liner]

Progress continues!
Slowly, though. Looking for a job is taking up too much of my time.

I have designed a lug system to hold the barrel and machined that up and welded it
to the barrel. Also I needed a breech plug cap first, so that needed design, machining, welding and such.

The result is something that looks like a firearm. LOTS of tedious filing will be needed
to get the upper to drop onto the lower, but some is done already. The rear lug needs
to be machined and then welded in place. The the front and rear lugs need to be
drilled to accept standard AR pins. Yes, I have a basic design for the trigger and
hammer assembly, but all this is groundbreaking "research", so some trial and error
is needed.

You can check the Flickr set for progress.

http://www.flickr.com/photos/command_liner/sets/72157623583216070/

If you are feeling charitable, send along a few T/C super musket nipples and
a gross of #11 magnum caps.

[motorhead]

i don't know if i'd trust brazing the breech plug. i think i would opt for welding. really cool project, btw. add a spike folding bayo.

[command_liner]

Assuming a 40,000 PSI in shear for the braze, it should be good for 120,000 lbs.
That was before the weld of the plug, probably good for another 10,000 lbs. Then
there is a welded-on breech plug cap. Assuming 70,000 psi for the weld, that gives
about another 100,000 lbs. So call it a quarter million pounds of hold for the breech
plug. Plus, since it is sealed front and back, it should have no corrosion cracks.

A quarter-million pounds is enough for a 1" breech plug for black powder.

The breech plugs I use in my 1.75" cannons are press fit, then welded. This
adds the extra step of braze, which should be much stronger than a 20-ton
press fit.

My hands hurt from filing! Fit-up is progressing well.

[motorhead]

ah, i stand corrected. i thought you were depending only on brazing for the plug.
a spike bayo would add that extra touch of evil. who'd a thunk it, zombie coach gun.

[command_liner]

After hours and hours of filing, we have a good fit-up between the 80% lower and the
front lug (using front take-down), and center lug.

Tonight I turned stock for the rear lug, which fits into the rear take-down slot. Not
a pretty operation on the lathe -- straight brute force.

New pictures loading at the same URL.

[command_liner]

The rear lug is now ready for welding onto the barrel. I started with 1" by 1/2"
hot rolled, bar stock and turned it in the lathe to 0.90". A slight cleanup on the
belt grinder and it fits right in.

Odd AR15 note: The rear lug depth is the same width as the magazine well.

To facilitate positioning, I am making the rear lug way too long. After welding the
lug on, it will need to be trimmed to fit, an easy hand operation. Yesterday and
today I took some good photos of the brute-force nature of the build.

http://www.flickr.com/photos/command_liner/sets/72157623583216070/

NOTE: URL corrected