SpudFiles

ok, after getting bored going through 3 pages of searched results, it think it's semi-ok to ask. What are good C:B ratios for hybrids?

use HGDT (hybrid gun design tool, made by D_hall) and experiment around. It depends on just about everything. There is no overall good C:B ratio

linky

As general advice, don't go below (0.8/X):1 where X is your minimum planned mix number for general use - these are still combustion based, so the same ratios apply in similar ways, remembering that hybrid gases are more dense.

So if you're working at 2x and above, stay above 0.4:1, for 4x and above, have at least 0.2:1 - you get the idea.

Extra advice of my own is don't go above about (4/Y):1 either - where Y is your maximum mix number - unless you're either a very long way from it, or being deafened is a hobby of yours.

Ragnarok's advice is quite accurate, including the bit about being deafened. If you think it's just paranoid, overcautious advice from someone with no real experience, consider this: From my experience, for a given mass of propellant, hybrid gas guns without barrels are significantly louder than any pyrotechnic or high explosive I've used - a 150ci volume, 2" porting hybrid at 20x was loud enough to make my ears ring slightly from 100 feet away in a completely open area, and the concussion from it was quite noticeable to everyone present.

The point? If you don't want to end up in a heap of trouble, be extra cautious about where you shooot big hybrids.

And of course, always do extensive fiddling with designs in HGDT before you actually go out and start buying stuff.

my hybrid will be similar in size to big bob's lieutenant johnson; i will be using 2x-6x mixes, what would be a good ratio for that?

my hybrid will be similar in size to big bob's lieutenant johnson; i will be using 2x-6x mixes, what would be a good ratio for that?

Perhaps you should actually read me and Rag's posts in the topic. They'd do you a load of good.

Do you have HGDT yet?

FishBoy wrote:what would be a good ratio for that?

I'm by no means a hybrid expert, but I'd say 0.5:1 would be acceptable for all of those, not have power problems at the low end, and not be uncontrollably noisy at the top end - but still use ear protection regardless!

Like DYI says, it's worth reading posts and working out yourself though, otherwise you won't end up learning!

thanks a lot, I just downloaded HGDT. I like it so far

0.5:1 at 6x shouldn't have any huge problems with noise or power. My ME20H-41 had a ratio of about 1:1, and wasn't even that badly noisy at 20x (although different ranges affect this, it sounded like the end of the world when we set it off at 20x on my friend's farm, but was nearly silent on a windy day at my main shooting range).

The key there is the wind. Wind has a very unexpected effect on noise level. Where I live there is a bike path that goes right along the freeway, right by the bay, so there is a fair amount of wind. On the bike path, the noise from the traffic, not more than 20' away is minimal, but on the other side of the freeway is tremendous.
I would expect it would have similar effects on explosive shock waves.

FishBoy wrote:thanks a lot, I just downloaded HGDT. I like it so far

OK. Then pick either a barrel (length and ID) or a chamber (length and ID). Go to the tools menu and pick "Sensitivity Studies". If you decided on a particular barrel then tell the sensitivity study to vary the length of the chamber. (IF you picked your chamber then tell sensitivity to vary the length of the barrel). Enter starting and stoping values for the study (try 1/3X and perhaps 3X what you think the length should be.) Click the "Calculate" button.

You now have a graph of the affect of the particular variable on performance. You'll probably see that there is no optimal chamber size for a fixed barrel. Bigger chamber gives better performance. You'll also notice that after a certain point you have to make large changes to get even a small increase in performance. Double the chamber size and the performance only goes up by 10% in velocity.

Bottom line for hybrids, for a fixed barrel there usually isn't an optimal chamber, bigger is almost always better. For a fixed chamber there is an optimal barrel but it is often impractically large. You can get very near maximum performance with a chamber (or barrel) much shorter than the optimal.