Concerned about shooting

[mowhawky]

Well, since I have finished my cannon and have some powder coming, I am a bit concerned about some of the dimensions and wether or not it is safe to shoot blanks from this cannon. The cannon is made from 8620. The bore is 1 3/8, breech 4" which  is just shy of the 3 times rule I have seen mentioned here. Also the barrel thickness at the breech is just shy of the recommended one caliber thickness by 1/16th. I know the numbers are close but everything I have seen here says that to have a safe barrel, it should meet those requirements. Any comments or ideas on this?

Thanks in advance.

Pat

[Double D]

The rule is written as a general rule of thumb to establish minimum standards for safe shooting.  The steel you are using is ordnance steel and far exceeds the minimum standards for strength.  Your cannon should be safe to shoot.

Shoot your cannon and enjoy!!

. 

[keith44]

The rule is written as a general rule of thumb to establish minimum standards for safe shooting.  The steel you are using is ordnance steel and far exceeds the minimum standards for strength.  Your cannon should be safe to shoot.

Shoot your cannon and enjoy!!

. 

From the description it would not only be safe with the blank loads you are asking about, but safe for live fire drills as well.  That is if you have a good safe back stop.

[Cat Whisperer]

Pat -
You have done well in your research.  You've taken responsibility.  (Most folks don't.)
8620 is one of the toughest steels used - as I said before it is spec'd for M16 bolts because it handles the repetitive abuse without cracking.

I have seen a cannon explode.

I would have no problem with using yours.

Work the charges up from something rediculously small.  At some point you're just adding more powder without adding more boom.

2F will have lower pressure than 3F for the same effect.

[mowhawky]

Pat -
You have done well in your research.  You've taken responsibility.  (Most folks don't.)
8620 is one of the toughest steels used - as I said before it is spec'd for M16 bolts because it handles the repetitive abuse without cracking.

I have seen a cannon explode.

I would have no problem with using yours.

Work the charges up from something rediculously small.  At some point you're just adding more powder without adding more boom.

2F will have lower pressure than 3F for the same effect.

Thanks so much for the information. I am really looking forward to shooting the cannon and have some peace of mind now. I worry too much some times.

Thanks again

Pat

[gunsonwheels]

CW:

2F will have lower pressure than 3F for the same effect.

Something else about powder... if you are buying "A" Blasting or Fireworks powder the fuller designation is to use Fa whereas sporting black powder is designated as with Fg.  4Fa is approximately equivalent to one Fg in formulation, granule size, and density and is usually purchased in 25# or 50# quantities for a few dollars a pound cheaper than the sporting grades and is usually only available from a GOEX powder distributor.  Sporting grades are available in one pound cans and 25# boxed bags and are more redily available from sporting goods stores as well as the distributors.

Here are some fairly close approximations:
4Fa approx. equiv. to Fg
5Fa approx. eqiv. to FFFg
7Fa approx. eqiv. to FFFFg

I have copies of the old "through" vs. "on" sieve specs for the various black powders (sporting, "A" and "B") from DuPont... GOEX is using the same specs but has discontinued the "B" blasting (sodium nitrate oxidizer versus potasium nitrate in "A" and Sporting).  "B" was considerably cheaper but was slower and gave less pressure.  With the expanded use of ammonium nitrate for blasting, "B" demand almost disappeared.