PVC projectiles?

[carmy53]

I'm trying to come up with a cheap and easy DIY projectile for a 2" bore mortar. I seem to remember posts about using PVC pipe filled with something (concrete/sand/ice/plaster of paris) as a projectile. If you have done this, how did you seal the end of the PVC pipe?

[cannonmn]

We cut a nearly bore-sized circle from plywood using a hole-saw.  This disc must overlap the PVC pipe completely (be same or a bit larger diameter.)  Plywood used in this manner by us is 1/2 inch for small bore cannons and 3/4 for say, 3" bore guns. 
 
We did this to make canister rounds which did not need to stay together after firing, and in that case the PVC pipe section can then be attached to the face of the wood disc however you like, only needs to be strong enough to keep it together while loading etc. since G forces will keep it together after firing it, at least while it is in the bore.  We plugged the pilot hole in the center of the disc (that's left from most hole saws), with a short bolt, bolt head toward the rear of the projectile of course, that way no nut is needed on the front side if the bolt fits tightly.
 
If you want both discs to stay attached to PVC you need to put a bit of thought into that, perhaps a wood disc on either end of PVC, attached by epoxy if you like, and a carriage bolt (or threaded rod) thru both discs with head on one outside end of disc and nut and washer on outside of disc on threaded end, or something.   When we used the bolting method, we never used epoxy as the bolt when tightened held it all together well enough.  We usually used sand for a filler, probably good enough for small guns or mortars and light blackpowder charges.
 
You may want to put some slots or vents in the front disc so powder gas behind it can blow by; you don't want it to seal well enough so pressure in the bore can pressurize your projectile internally which could cause it to pop open outside the muzzle.  The rear disc should fit the bore well but still be easy to load.
 
Remember the "hole size" is how hole saw sets are labelled, not by the disc size, so maybe a 2 1/8-inch hole saw will leave a disc that's about 2 inches, and if too tight for your bore, you can mount a short stack of them on some rotary tool and sand them down a bit.

[Cat Whisperer]

I use the 4" pvc pipe (which is 4.50" Outside diameter) in my mortar.

I just fill them with a good grade of concrete (or add a little cement to the regular sack-crete type).

If you fire it right after casting you will slide the concrete core out of the pvc - therefore give it a week to harden.

I've used the solid and foam core PVC pipe.  The solid is much better.

You can recycle them several times, the plastic will break at some point leaving the odd piece diverting a few degrees from the gun-target line.

A disk under the round might prove useful in ensuring pressure on both the pvc pipe and the concrete core; don't know as I've not tried it.

One can put a piece of wire in the concrete to tie off a caution-tape streamer too.

I just cut them with a jig saw, line 'em up on a board and fill with concrete and let them cure.

[carmy53]

If you fire it right after casting you will slide the concrete core out of the pvc - therefore give it a week to harden.

I was worried about the concrete core separating from the tube. Good to know it won't if I let it cure.
I might try to cap the ends anyway.

[Cat Whisperer]

Safer is ALWAYS better.  Even if they've been set for a week you will get some minor sliding on some of them.  The PVC is slick!  After a season they lock in better, but you will aslo get occasional fracturing inside and may loose a 1/4 of the core somewhere down range.

I've fired these in a 4.55" mortar.  I would NOT do it in a cannon without a base disk.

[Victor3]

 I imagine if one were to put a few drywall screws through the wall and into the ID before adding concrete, it might hold together better(?)

[SHOOTALL]

 1-1/2" PVC Foam core or Sch 40  both mesure 1.90 inch in dia. I don't have a mesurement on the cap for the pipe . You can check Lowe's or such for that mesurement. Keep in mind there are test caps that are thinner . Also some test caps are nothing more than a thin plug that glues in which might make good end caps some can be had that go in 1-1/2 pipe and over 2 inch pipe . Then there are the plastic and sheetmetal test plugs ( not to be confused with the iron long test plugs) that could be used with a longer screw to cover both ends .. Then there is the bushing for 2 to 1-1/2 pipe which when slipped over 1-1/2 inch pipe would give the OD of 2 inch pipe and add strength to the ends . If you look into CPVC or poly pipe you can find differen OD's and combinations of fittings to get to bore size.
I'm a plumber and only offer the sizes and combination of fittings to give ya'll ideas.
Has it been considered to try alum ? Alum flashing could be cut to size , use a PVC cap on one end and a coupling on the other as forms  spray with oil or something to make concrete release the poor. Knock the fitting off for reuse. Same could be done with plywood with nice holes in them and a sheet of paper between concrete and floor when making the pour.

[jamesfrom180]

Don't know if this will help but for caps there is a product called a Knock out Plug, or test cap. 

http://www.cornerhardware.com/index.php?main_page=product_info&cPath=6748_6951_7751&products_id=21308

very useful as it does not increase the OD of the pipe you are using.  The little lip locks over the pipe walls.  I use it for diaphragms on air horns so it will hold relatively low pressures but will hold up to a beating.  I am sure if backed with concrete it would hold nicely.  Attaching a streamer like mentioned above might help you dial in your loads. 

I see SHOOTALL mentioned this already

[SHOOTALL]

Don't know if this will help but for caps there is a product called a Knock out Plug, or test cap. 

http://www.cornerhardware.com/index.php?main_page=product_info&cPath=6748_6951_7751&products_id=21308

very useful as it does not increase the OD of the pipe you are using.  The little lip locks over the pipe walls.  I use it for diaphragms on air horns so it will hold relatively low pressures but will hold up to a beating.  I am sure if backed with concrete it would hold nicely.  Attaching a streamer like mentioned above might help you dial in your loads. 

I see SHOOTALL mentioned this already

Some are better than others , the ones with a post in the middle are stronger as are the red or yellow ones vs milk white ones.

[carmy53]

Don't know if this will help but for caps there is a product called a Knock out Plug, or test cap. 

http://www.cornerhardware.com/index.php?main_page=product_info&cPath=6748_6951_7751&products_id=21308

Thanks but that company doesn't have 1 1/2" plugs and they are "sold out" on the other sizes.
 
I picked up a couple of metal electrical end caps today. They are marked 1 1/4" but they seem to fit pretty good in my 1 1/2" PVC pipe.
 
 

[SHOOTALL]

Try Souix Chief products or the local plumbing supply, Lowes or Home Depot

[jamesfrom180]

Well for 1 1/2" pipe you may try a well supply store.  They are a bit hard to find but its part of my job.  Environmental companies install 1.5 wells all the time and they make well points which might work. 

http://www.envservprod.com/15-Male-Threaded-Point-P257C53.aspx

I don't know if there are any drilling supply houses near you but my thoughts are this would be more expensive than simply filling the pipe with concrete.

[SHOOTALL]

any plumbing supply should carry 1 1/2" PVC test caps.