Author Topic: Finishing a Hern Coehorn Mortar (Read 3370 times)

CrufflerSteve · « **on:** March 26, 2005, 01:49:31 PM »

I'm using some of my tax refund for a Coeharn mortar from Hern iron works. The hardware kit arrived today. This is going to be pretty hefty when done. The barrel is 80 pounds, the kit was listed at 30 ponds. The base is 31" long by 15" wide by 9" high. That is going to be a lot of oak,
or whatever hardwood I use.

I've never built one of these beasts before. It looks like the 45 degree angle is just from how it is inset to lay in the base. Is that true? Its going to take a bit of shaping for that. I might laminate the wood together and leave the exact middle unglued to make it easier to get in there.

The hardware is substantial but the handles are a little rough from the casting. I just wondered if people who do these grind and polish or leave the sand cast look?

Steve

Cat Whisperer · « **Reply #1 on:** March 26, 2005, 04:10:00 PM »

45 degrees is a very typical angle for fixed mortars. Range was adjusted by varying the powder charge.

Double D · « **Reply #2 on:** March 26, 2005, 04:41:40 PM »

Grinder will work but be careful, best is the gunsmiths favorite "Nicholson milling Machine"

Cat Whisperer · « **Reply #3 on:** March 26, 2005, 11:21:24 PM »

Also consider strongly using strips of abrasive paper - comes on a roll of way-to-long by 1/2 or 3/4" wide. It will flow smoothly around the small diameters of the handles.

Blaster · « **Reply #4 on:** March 27, 2005, 03:36:11 AM »

CrufflerSteve, Hey Steve, since you and I are only about 135 miles apart, and in the same State, would you mind telling what the shipping charges were on the mortar tube from Hern Iron Works and the separate shipping charges for the kit?? I am already aware of the price for the tubes and kits themselves...... Many thanks, Blaster (Bob in CO)

CrufflerSteve · « **Reply #5 on:** March 27, 2005, 10:30:43 AM »

Quote from: blaster

CrufflerSteve, Hey Steve, since you and I are only about 135 miles apart, and in the same State, would you mind telling what the shipping charges were on the mortar tube from Hern Iron Works and the separate shipping charges for the kit?? I am already aware of the price for the tubes and kits themselves...... Many thanks, Blaster (Bob in CO)

It wasn't cheap. The price worked out to being slightly less than $1 a pound. I did get the harware kit and the mortar which are shipped seperately. I hope it is cheaper for the large tubes.

Steve

Evil Dog · « **Reply #6 on:** March 27, 2005, 01:06:24 PM »

A buck a pound sounds about right. Their half scale Napoleon weighs right at 150 pounds..... $187.00 shipping to the Left Coast.

CU_Cannon · « **Reply #7 on:** March 28, 2005, 08:08:56 AM »

I found that is quite easy to carve out the recess. With a mallet and a sharp gouge it doesnÂ’t take long. A forester bit that is the same or just under the size of the trunnion will help to remove material for the trunnion recess. The rest is carve, test and carve some more.

If you don't try to rush things you will end up with a very well finished coehorn. Just remember that it is much easer to take material off that to put it back on.

CrufflerSteve · « **Reply #8 on:** March 28, 2005, 01:04:42 PM »

The barrel arrived today. It is a solid little thing! One surprising thing is that the bore is rough. I don't mean off in any way. Its just rough metal. I thought Hern used tubing. Wonder if some metal got in from the casting. I should be able to clean that up with sandpaper on a dowel rod in a drill.

It is a kind of rough on the outside. I would prefer a smoother finish. I know some people has cautioned me not to go nuts with a grinder. I agree. I'd rather spend a lot of time with sandpaper and files to avoid a whoops. Looking at the roughness I had a thought - car body filler. Is this an off the wall idea? If I sanded it smooth, filled, sanded and painted would it work? I have pictures of the shock of firing making it all fall out. (I can tell stories about orange dayglo paint, tennis ballls and a Lee Enfield greanade lancher sometimes.)

CU_Cannon is right about how to carve it out. Rough it out small and then vewry carefully complete it. One useful tool is carbon paper. When it is getting close, stick carbon paper to the barrel and see where it touches. sand & continue until done.

Steve

GGaskill · « **Reply #9 on:** March 28, 2005, 01:13:13 PM »

Bondo! If it works on cars, it should work on cast iron.

Cat Whisperer · « **Reply #10 on:** March 28, 2005, 01:16:14 PM »

CrufflerSteve -

Body filler and painting over is a common method of finishing castings, not necessarily cannons, but look at any milling machine or lathe that has been scratched up a bit and there it is - body filler used to make a good looking finish.

CrufflerSteve · « **Reply #11 on:** March 28, 2005, 04:30:21 PM »

I'll try the Bondo but you're all in trouble if it all falls off when I fire it.

I do have one further question. This has no vent hole drilled. I believe the vent hole is 3/16"? Also how far from the base of the chamber is standard. Its a 10" deep bore.

Steve

Double D · « **Reply #12 on:** March 28, 2005, 05:56:58 PM »

Make the vent come out just ahead of the wall rear of the powder chamber.

C2ND · « **Reply #13 on:** March 28, 2005, 06:01:23 PM »

Steve,
I bought my Hern coehorn through Dixie Gun Works several years ago, it came with the vent already drilled. 1/4" diam. 5/8" from the bottom of the bore.

Evil Dog · « **Reply #14 on:** March 29, 2005, 12:04:41 PM »

Hey Steve..... I talked with Joel Brown over at Hern Iron Works for quite a while this morning as I am starting to get the hots for their Coehorn mortar myself... would be the same bore size as my half scale Napoleon so could use the same zinc balls. Going to have to seriously consider selling my golfball mortar to buy one.

I mentioned your post where you indicated that the bore seemed a bit rough... Joel had a very logical explanation and an easy cure. The bore is indeed lined with seamless tubing. Evidently for the casting process, the liner is packed with sand. During casting some of the sand might melt and cause the bore to appear rough. Real easy to fix. Just go down to the local auto parts store and get an appropriate size cylinder hone. Chuck it up in a drill motor and make a few passes through the bore.... should slick it right up.

CrufflerSteve · « **Reply #15 on:** March 29, 2005, 05:39:58 PM »

Quote from: Evil Dog

I mentioned your post where you indicated that the bore seemed a bit rough... Joel had a very logical explanation and an easy cure. The bore is indeed lined with seamless tubing. Evidently for the casting process, the liner is packed with sand. During casting some of the sand might melt and cause the bore to appear rough. Real easy to fix. Just go down to the local auto parts store and get an appropriate size cylinder hone. Chuck it up in a drill motor and make a few passes through the bore.... should slick it right up.

That would make sense that its melted sand. It didn't feel like a metal casting and the bore is dead straight. How much are cylinder hones? I'm trying to keep costs under control. I'd been thinking about sandpaper on wood dowels in a drill but a hone would do a better job. I want it smooth so it cleans up well. That grit would just invite BP residue to accumulate. I hone would also keep it straight.

I think you'll be happy with yours. You can get better barrels than Hern. Just get ready to pay lots of $'s. I've looked over the barrel and the hardware and they show good quality. I wouldn'ty be surprised if Hern gets more of my money in the future.

Steve

C2ND · « **Reply #16 on:** March 29, 2005, 05:41:39 PM »

Steve,
Mine has a "dimple" about 3/4"wide and 1/4" deep where the vent is drilled.

[/img]
Looks like the vent is off center in the photo but is just from camera angle.

C2ND · « **Reply #17 on:** March 29, 2005, 05:50:42 PM »

Couple more photos. Details still need finishing, replace hex nuts with square, add a couple tie down rings, maybe carry handles, and paint metal.

Evil Dog · « **Reply #18 on:** March 29, 2005, 06:23:58 PM »

Yup, no doubt about it now...... gotta sell my golfball gun and buy Hern's Coehorn. Whimper, whimper, whine, whine.

Cat Whisperer · « **Reply #19 on:** March 30, 2005, 12:34:11 AM »

Quote from: Evil Dog

Yup, no doubt about it now...... gotta sell my golfball gun and buy Hern's Coehorn. Whimper, whimper, whine, whine.

NO! Keep yours and get another!

Guns are meant to be bought (PERIOD).

Ok, I know, like the rest of us limited resources, but somedays its guns or butter. I can always stand to be a little thinner!

CU_Cannon · « **Reply #20 on:** March 30, 2005, 10:30:08 AM »

Quote

...somedays its guns or butter.

Seriously, how much do you really NEED to eat?

CrufflerSteve · « **Reply #21 on:** March 30, 2005, 05:24:50 PM »

Being an old gun collector I'd have to disagree with CU & Cat. Its okay to sell or trade. You just have to end up with more and better stuff in the end.

C2ND, I like the sled you have yours on. I got the traditional hardware so mine will be a platform with handles. Its supposed to just sit at a 45 degreee angle.

Steve

CrufflerSteve · « **Reply #22 on:** June 01, 2005, 05:35:38 PM »

[/img]

I apologize for the bad picturtes but my camera is acting up. I'll try to get some good field pictures when it goes to the range Saturday.

I was going to have the authentic olive paint and make it out of wormy maple which was cheap. When I went to the hardwood store 8/4 ash was on sale and it was almost exactly the width I needed.

I liked the looks of it so it got oiled rather than painted. So much for authenticity.

If you order a Hern barrel and might want to refinish it - get it unpainted! I don't know what they use but that is a serious paint job. I've gotten a couple of other barrels with 'super baked on' finishes that you could take off with a hard look. This took hours in the sandblaster and I was getting tired so I let some stuff slide. I also got lazy with finishing. Next winter I'll fix it up better.

I'm happy but I wish I'd built the sled base. This is a seriously heavy hunk of wood! Heavier than the barrel. 31" long, 15" wide & 9" high.

steve

CrufflerSteve · « **Reply #23 on:** June 02, 2005, 04:11:09 PM »

The pictures are a bit better when I'm not shooting with dead batteries. I should have done a better job removing the glue when finsishing but it will be redone over the winter.
I added another one.

The full pictures are:
http://www.crufflersteve.net/coehorn1.jpg
http://www.crufflersteve.net/coehorn2.jpg
http://www.crufflersteve.net/coehorn3.jpg

Oh boy! I get to try it out Saturday!

Steve

Soot Sucker · « **Reply #24 on:** June 03, 2005, 11:25:28 AM »

Nice looking mortar and base Steve....

May I ask where you got the mortar base plans and the hardware?

Thanks,
Dave

CrufflerSteve · « **Reply #25 on:** June 03, 2005, 01:35:17 PM »

Hern sells the hardware and includes a one page drawing in size 17"x22". Its very easy to work from. That's the reason I made the platform and not the sled. It was very convenient to have everything but the wood. Its nicely done. The bolts all have the 4 sided nuts and it was all ready to use. I just painted all of the hardware with Rustoleum, especially the parts inside the wood.

Keep in mind this a a LOT of wood. Its very heavy and makes this a bear to move with the barrel in place. Also, being hardwood it can cost. OTOH, it looks great.

Steve

CrufflerSteve · « **Reply #26 on:** June 04, 2005, 12:12:01 PM »

I took the mortar to the range today. It was cold with some rain and howling wind so it was a short day. The main thing that got us to quit was the problem of lighting the fuse.

We sent about 8 concrete filled juice cans downrange. Only recovered 3 at about 150 yards so I'm not sure what charges were used. I was trying 1, 1.5 and 2 ounce shots.

The pictures come from a blank shot. I used some paper for wadding and you can see it in the 2nd picture. I was taking a movie with my camera and these are adjacent frames.

I can hardly wait for decent weather.

Steve

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Cat Whisperer · « **Reply #27 on:** June 04, 2005, 01:50:18 PM »

C-steve -

Good pix. 150 yards is respectable for concrete filled juice cans.

You'll find a point where more powder doesn't get you any more range - just more smoke, flame and noise. The long tube mortars get very long ranges efficently with little noise or smoke - burning completely.

More range (looks like you have a little to spare)? Heavier bullet. (More pressure too.)

I still want to go woodchuck hunting with a mortar.

CrufflerSteve · « **Reply #28 on:** June 04, 2005, 03:10:43 PM »

Quote from: Cat Whisperer

I still want to go woodchuck hunting with a mortar.

Unless you're using exploding shells I'd bet on the woodcheck.

Steve

Cat Whisperer · « **Reply #29 on:** June 04, 2005, 03:22:59 PM »

Quote from: CrufflerSteve

Quote from: Cat Whisperer
I still want to go woodchuck hunting with a mortar.

Unless you're using exploding shells I'd bet on the woodchuck.

Steve

THAT'S THE CHALLENGE!!!