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Have been thinking about getting the Mjöllnir piston hybrid back out this winter (or summer for many of you) but it's been about 20 months since I last fired the thing so I'm a bit curious about whether it has loss structural integrity over that time. The cannon has been stored inside a garage where max temp is about 30°C on hot summer days and min temp is about 0° C on cold winter nights and humidity is often above 75% year-round.
Rust is the primary concern but I opened it up and didn't see much. There's some surface rust on a few fittings but no obvious pitting (rust is mainly around the marks left by pipe wrenches). Inside, is mainly black soot with light coloured specks here and there and no rust visible.
So I don't think rust is a concern. Is there perhaps anything else I should be looking for? I'd like to clean the soot out but flushing the chamber with water doesn't usually work in my experience. Has anyone tried a cocktail of detergents or such?
Not sure if I'll even get to shoot the damn thing, I think going to my old local hotspots is a thing of the past.
Have you tried engine degreaser?
Here in the States, we can use any common gun or black powder solvents. In fact I would highly recommend lubing Mjöllnir with some micro lubricant before you store her again.
You may want to clean your electrical contacts with some electrical cleaner before you attempt to fire though.
I love the name by the way. I named my first big bore .58 cal muzzleloader Mjöllnir at around age 9. It's now my medium sized muzzleloader, but to this day it still hits like the hammer of Thor.
That's where I got my name by the way. I was the only 9 year old in the competition shooting a big bore or anything over 36 caliber for that matter.
I'm just hesitant about using anything that is hydrophobic and may produce fumes or interfere with fuel mixing. Perhaps I can unthread some more fittings and stick a toilet brush on a long stick or something
Electrics should be fine (good point, though) as I replaced the circuitry and electrodes shortly before I last fired the cannon and I've kept them in good nick since.
When the cannon was in its early days, the long heavy chamber with double tees at one end reminded me of Thor's hammer.
If you haven't seen her, this is what she looks like:
Was yours a musket?
Piston...nice. I'm holding off on making the leap to hybrids for now. I want to make sure I know what I'm doing first. I under stand the math, but my know how on metal pipe is still limited. Maybe next year.
Toilet brush... Why not. I'd use a air compressor to blow it out afterwards.
Yes. Musket, well technically it's a Hawken Mountain rifle. I shot competition and did American Civil war reenactments for about 13 years. I miss the bowling ball cannons. We would shoot bowling balls at 8'x8' targets at 1/2 a mile.
Why didn't you use all galvanised fittings and pipes?
Children are the future
unless we stop them now
I believe I did but some was stripped from using pipe wrenches multiple times. That's why the only surface rust is really around those locations. I've used a wire brush to scrap it off and put some CRC on it overnight.
Seeing as rust wasn't really an issue, I don't think the pipe or fittings have been compromised since I last fired the cannon. Just wanted to see if there was anything I might overlook.
I have always been taught that if its metal lubricate it. Nearly all metals rust or corrode eventually. It does not matter if its stainless, galvanized or parkerized, it will rust eventually. Its called preventative maintenance
It just occurred to me, if you are worried about using lubricants in the chamber that may combust, you should try using some of the silicon based lubricant used in break barrel air rifles. They are specifically designed to be used in high pressure environment without causing dieseling.
Re: Deterioration of Iron Pipe and Fittings
Took a few things apart today to have a peak inside. Gave it a bit of a clean with detergent. One chamber fitting has noticeable surface rust on the inside, doesn't look too bad but I will probably replace it anyway. The chamber fittings below this one don't appear to be bad at all, they just have some soot and white specks on the surface.
This other section of chamber (the half closest to the valve) is spotted entirely on the inside with these white specks. I suspect it is the result of combustion and whatever galvanised coating was on the inside of these fittings. What does everyone else think? The white specks come off with a wire brush and turn to a fine powder. Doesn't seem to be anything to worry about.
Some other pics. The piston is looking fine, though it hasn't been used a helluva lot. I also put an epoxy plug in the 1" diameter pipe coming off the chamber. Never had an issue with mixing in this gun but leaving the 1" pipe open in the chamber just complicates things and doesn't really add to the overall chamber volume.
Damn crowley, how heavy is that piston?
The white areas are zinc oxide, which is just the galv coating rusting.
Rust around the threaded areas is your primary concern, since you're only playing with maybe 0.06" (1.5mm) wall thickness in some areas.
Unfortunately you have a lot of internal threads and other fiddly bits. I'd recommend scrubbing it with CLR (or whatever rust remover your stores carry), then spray it out thoroughly with some non-chlorinated brake cleaner. You can then paint it with BBQ grill paint which should work with hybrid operating temperatures.
Just take your spark plug out first obviously.
Can't recall! 750g comes to mind, though. I looked at getting it turned down to reduce weight but everywhere was looking for $80/h. Probably only take an hour, but still it's $80
Good point. Is it rust on the threads that are covered by another fitting or the rust on the exposed external threads that are more of a concern? Except for that one pipe nipple that has acted as a sacrifice, most of the rust on the threads of fittings are probably on the exposed portions.
Interesting. Has anyone else tried this before? Would be a PITA if it didn't work and started to deteriorate but if it's good enough for BBQ temperatures it should be fine.
And leave it be or flush it out with water? I was hesitant about using CRC (like WD-40) because if I can't wipe away all the excess, it will continue to produce fumes inside the chamber until it all evaporates. Even the external pieces I sprayed and cleaned still smell and leave residue on my hands. Though I guess it won't mess with the mixes if I'm venting the chamber after each shot.
I was testing out my ignition system the other day and noticed that it will only jump the spark plug if I hold the second wire (the wire not attached to the top of the spark plug) slightly off the cannon chamber. If I hold the wire against the chamber, it won't jump the spark plug at all or create any sparks anywhere. I'm thinking I need to either change the batteries or the electrodes of my spark plug aren't isolated.
Exposed threads on the outside are at the highest risk, so is rust on the interior surface that is directly below the threads.
Rinse the CLR/rust remover off with some water, it's a weak acid and will eventually make things worse if it sits for too long.
Non-chlorinated brake cleaner is mostly just acetone in a spray can, and will evaporate quickly. It's used to remove any traces of oil or dirt and will give your paint a clean surface to adhere to. For a good paint job this is a necessary last step, as even fingerprints can keep paint from sticking.
WD-40 and the like are lubricants; brake cleaner is used for removing lubricants.
BBQ paint is usually rated to 1200F. It may gum up your spark gap. It might also be conductive but I haven't tested this.
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