Is my chronograph having issues?

[High-PSI]

Hey Guys,

I have been doing a bit of velocity testing lately and I have a question for you (those who understand the math far better than I).

I have gotten some odd readings from my Chrony. The gun I am firing is a 1 and 1/4 inch (nearly 1 and 3/8 inch bore) barrel, 4 feet long with a 2 to 1 tank to barrel ratio. The gun uses a 1 and 1/4 inch brass Granzow diaphram valve pilotted with a 1/2 inch bore diaphram valve. It is a very fast acting valve with a good flow rate. Firing a 25 gram slug (hollow plastic bottle wrapped with black duct tape) at 210 psi, my Chrony recorded a 1,179 fps reading, the next shot showed only 162 fps. I know the 162 fps was incorrect. However, I am not sure the 1,179 fps reading was right either. Honestly, the recoil was freakin VIOLENT! HOLY COW! Also, the stop I was using (carboard box with a couple loose towels inside) could not stop the slug. It went right through. So, I know my velocity is high, but from a previous thread, it has become clear my Chrony numbers may be off a bit.

So, who can crunch some numbers for me on this?

Oh, by the way, this stuff is ADDICTING!

Matt

[jackssmirkingrevenge]

What model is your chrony, and how far away is it from the muzzle? Sometimes muzzle blast can interfere with the ready if it's too close.

Oh, and videos please!

[jimmy101]

Like jack said. Not only can the concussion affect a normally operating chrony it can really mess with one that has a bad solder joint, or wimpy battery connections, or ...

[High-PSI]

Gotcha.

I guess what I am looking for is the engergy I have available versus the slug weight and barrel diameter. I am not a physics major. I have no clue how to calculate that. I used to have the link to a spreadsheet that would give rough data like this.

Matt

[jackssmirkingrevenge]

These are the online calculators I use:

This one gives you instant results in Imperial/metric etc.

This one allows you to plot a graph of velocity vs muzzle energy for a given projectile.