Author Topic: 4" 4340 for Beer Can Launcher (Read 1563 times)

NOSMO · « **on:** April 29, 2005, 03:48:48 AM »

Hello to everyone, and thanks for all of the great information. I'm a beginner in machining, a very much NEWBIE, but have acquired Shoptask and trying to get started. I'm going to try and tackle a golf ball mortar for one of my first real projects. I have found several 8" long x 4" pieces of 4340 and one 12" piece. I have several questions. Is the 4" 4340 safe for beer can size mortars? Will I gain any performance leaving the lenght at 8" vs. the other lengths shown in drawing on the forum for the gb mortar? Does anyone have ideas for a steady or fixed rest that I could fabricate? Any hints, directions, etc., will be appreciated. Again thanks!

Double D · « **Reply #1 on:** April 29, 2005, 06:19:34 AM »

General speaking the bore in a coehorn style mortar should be 2 calibers long.

4340 should work just fine. You might want to look at it's welding characteristics for attaching trunnions. 4 inch diameter might work for beer cans. It would give you roughly .700 inch thick walls in the bore, bit thin. You need all you strength in the powder chamber any way.

Cat Whisperer · « **Reply #2 on:** April 29, 2005, 07:23:47 AM »

NOSMO -
Welcome to the board!

I'll look up what I can tonight on 4340 and report back, but 4" diameter with a powder chamber doesn't give me any pause. I just want to verify the characteristics of the steel - strength, hardness/brittleness.

Glad to have you on board.

CAV Trooper · « **Reply #3 on:** April 29, 2005, 08:19:33 AM »

CW,

Got it for you. 4340 is tough stuff. According to the specs I found, it has a yield strength that runs from 69,000psi up to 238,000psi depending on the hardness of the steel (ie: how it was heat treated). While there's no way, without testing, to know what the hardness of the steel is that NOSMO has, he should be OK with it. After all, we use 1018 steel for barrels and that had a yield strength of 54,000psi.

As to welding, it's like 4140:
"The alloy can be fusion or resistance welded. Preheat and post heat weld procedures should be followed when welding this alloy by established methods."

Oh yeah, I also found that a foot long piece of 4" diameter 4340 sells for about $300 (from one supplier anyway). If you got yours for free (or real cheap) you did REAL good NOSMO. :-D :-D

NOSMO · « **Reply #4 on:** April 29, 2005, 09:10:46 AM »

Thanks for the replies. I guess I did ok on the purchase... all 5 pieces for $50.00.

I would appreciate it if anybody has any drawings for a simple mortar or cannon that will meet my minimal machining abilities that they email them to me. Thanks again.

GGaskill · « **Reply #5 on:** April 29, 2005, 09:37:18 AM »

I would not waste the 4340 on a golf ball mortar as golf balls are so low density that the extra strength of the 4340 will be wasted. Find a piece of 3" 1018 scrap for the golf ball mortar and save the 4340 for a more serious piece.

Also, since you are new to machining, I suggest you make some practice projects to gain familiarity with your machine before starting your first artillery piece.

Cat Whisperer · « **Reply #6 on:** April 29, 2005, 11:50:22 AM »

Quote from: NOSMO

Thanks for the replies. I guess I did ok on the purchase... all 5 pieces for $50.00. I would appreciate it if anybody has any drawings for a simple mortar or cannon that will meet my minimal machining abilities that they email them to me. Thanks again.

Look through the last 5 or 10 threads and you'll see some ideas (of drawing and of designs). It's easy enough for us (there are several of us with cad that could put something together for you). Pick what you think looks good and is within your abilities.

You've gotten some very good advice and good information in the last several posts - thanks guys!

Your 4340 is probably in what's called pre-hardened state - at the low end of hardness and strength (so it can be machined) - probably scrap ends. It's a great way of getting quality steel for a steal (couldn't resist).

Drill as big a hole as possible - boring takes time. There are some shortcuts, so ask before you setup.

Cat Whisperer · « **Reply #7 on:** April 29, 2005, 04:29:06 PM »

George & I have be exchanging PM's back and forth on steel, hardness thereof, machineability and the term pre-hardened. I'll start a new topic.

NOSMO · « **Reply #8 on:** May 04, 2005, 03:34:07 AM »

Many thanks to all for the information. CW you mention to decide what my first piece will be and then ask for information. I purchased a couple of 8" pieces of 3 1/2" solid shaft and have decided to build a simple golf ball mortar that doesn't tax my minimal machining experience. I welcome drawings, setup proceedure, any info on machining sequence or other suggestions that any of you may have. Also, what granular size and how many grains of BP do you use for initial firings and what load do you work your way up to for optimal performance of the GB mortar. I handload for my rifles so know that there may be reluctance about loads, so I acknowledge that any information is your opinion only and may not be safe in my mortar.

Thanks,

Nosmo

Cat Whisperer · « **Reply #9 on:** May 04, 2005, 06:48:07 AM »

Let me put some things together in the next several days.

This should be open to others as well, that way you can make some choices.

I've been using 15 to 30 gr. of fffg in a powder chamber 1/2" diameter and about 1" deep. That will give you about 100 to just under 200 yards, depending on bore length (2 calibers long) and windage (golf balls are about 1.68 and bore of 1.72 or so) with a golf ball.

Cat Whisperer · « **Reply #10 on:** May 05, 2005, 04:19:23 PM »

Here's about as basic a design as can be done.

Nothing special, rounded corner on the inside to eliminate a stress point, could use rounding of the bottom of the powder chamber.

3/4' trunion - could be bigger or smaller. Could move it to the end.

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NOSMO · « **Reply #11 on:** May 06, 2005, 05:59:20 AM »

Thanks to all of you for the great information. I'm going to get started this weekend. I hope in the future I have something to add to the forum, meanwhile I'm soaking up all of the information I can!

Nosmo

Cat Whisperer · « **Reply #12 on:** May 06, 2005, 02:58:21 PM »

NOSMO -

Cool handle! Could that be as in Nosmo King?

NOSMO · « **Reply #13 on:** May 17, 2005, 04:19:48 AM »

I finished up my barrel last week, made a temporary base, and was able to get out and fire my golf ball mortar over the weekend. It was made pretty much to the specs on CW's plans, with the exception that the powder chamber is .75" x 1.00". Firing with 30 grains of fffg put the ball about 100 yds high and 200 yds horizontally. What would your suggestions be for maximum safe load based on the dimensions for ffg and fffg powder. I would like suggestions for both blank and golf ball load. I will post some pictures soon, not anything fancy as most of them on this forum, but one heck of a lot of fun to shoot and it got me started using my new machine. I'm also really enjoying learning the history of the various pieces. Thanks to all for the info.

Nosmo

Cat Whisperer · « **Reply #14 on:** May 17, 2005, 11:24:46 AM »

You'll find that as you increase the charge you'll increase distance. Up to a point. Then it's just more powder, bigger bang, brighter flash and more smoke (and more crud to clean out of the tube). Take note of that point and back off. Unless you're trying to put a golf ball in orbit, you'll find some very comfortable loads that will reach out to reasonable ranges and not burn up huge amounts of powder.

Cat Whisperer · « **Reply #15 on:** May 17, 2005, 11:27:39 AM »

Quote from: NOSMO

... not anything fancy as most of them on this forum, but one heck of a lot of fun to shoot and it got me started using my new machine. ...

THAT'S WHAT THIS FORUM IS ALL ABOUT!

The elegant one's are ok too.

NOSMO · « **Reply #16 on:** May 17, 2005, 12:16:08 PM »

I was not very clear in my last post. I'm not too interested in launching a golf ball much over 250-300 yds., my eyes won't see it anyway, what I'm asking about is getting the most boom out of the mortar for blank shots without overtaxing it structurally. Maybe this isn't the best design for a noise maker, but I and my nephew like a big boom once in a while. 250 yds. is fine for the golf ball.

Nosmo

John N · « **Reply #17 on:** May 17, 2005, 01:25:11 PM »

I've always produced a lot more "boom" firing a projectile in a mortar. In my experience, blank loads make for more of a "thud" than a boom, even with with a heavy foil wrapped powder charge and newspaper wadding. I think the resistance offered by the projectile is needed in order to obtain decent peak pressure (and associated boom) in a mortar's short barrel.

Has anyone created big "booms" shooting blank loads in mortars?

CAV Trooper · « **Reply #18 on:** May 17, 2005, 06:08:01 PM »

My experience has been that in order to get a nice a boom with a blank load, short barrels, like a mortar, really need some wadding. I have the same problem with my SBR King howitzer which has a 1.5" bore that's only 12" deep.

When I shoot blank shots (which is most of the time), if I don't use any wadding, I'll occasionally get a boom but most of the time it's more of a "cough". It appears that without anything in the tube, the powder doesn't completely burn up before some of it gets pushed out the end. You get a nice flash and a lot of smoke but no boom (which is what the crowd wants). Something is needed to raise the pressure in the tube and insure that all of the powder burns before it reaches the muzzle.

I've had great success ramming a hotdog bun down the muzzle as wadding and without fail get a really good BOOM on every shot.

(In case anybody is worried about a hotdog bun cannonball going down range, it doesn't happen. We ran some tests and found that the bun turns into toast crumbs and doesn't travel more than 20 to 25 feet)

GGaskill · « **Reply #19 on:** May 17, 2005, 07:56:17 PM »

I agree completely. I watched a guy try to fire a blank load with 8 oz of cannon grade powder from a bowling ball mortar; just a big whoosh and cloud of smoke. Don't believe those who say black powder burns the same rate confined vs. unconfined.