Need some QL help

[bohem]

I know that there's been a request/mandate from the powers that be for people not to request or provide Quickload data.

I have a request, but for a different reason, and it doesn't involve a projectile, which is the tricky part.


My brother is writing a CFD simulation of a Reflex style suppressor on a 308 Win. with a 24" barrel. He doesn't have the bullet modeled yet, just the gas expansion inside the can itself. His professor has asked that he provide a check that the muzzle velocity of the gasses without the suppressor attached match his simulation without the suppressor. Here's his email to me:
<span style="font-style: italic">
I found out that not as much is due tomorrow for the CFD project as I thought. Tomorrow I just turn in a report on the model and a verification of the model.

Verification being proving that the model will be representative of the actual this.

So, for this essentially all i need is the muzzle velocity of the gases for a rifle firing a blank. Preferably .308 since that is what everything else is already based on. I need it like this since I can't model the bullet into the simulation. Well really it is possible but it's a lot of work.</span>

Can someone give him a hand please? Thanks.

 

[bohem]

Re: Need some QL help

Bump for the morning crowd.

 

[Rafael]

Re: Need some QL help

I am not aware of QL giving gas velocity, which only has a relationship to bullet velocity ranges when there is a bullet.
I would imagine that gas velocities in a blank are a heck of alot faster than any bullet.

I don't have the skills to come up with such a number.

 

[bohem]

Re: Need some QL help

Is it possible to feed it a really light bullet like 5 grains and get a bullet velocity from that? I figured a blank would be extremely fast compared to a bullet, but maybe someone around here would know for sure.

Just off a momentum balance and PVT calculation I think we could get in the ballpark, but instead of going through that work I thought QL might be able to do it easily.

 

[Rafael]

Re: Need some QL help

Will contact you tonight via PM.

 

[bohem]

Re: Need some QL help

Cool, thank you.

 

[Rafael]

Re: Need some QL help

Here's the problem:
When a bullet like a 175 MK is fired, the pressures behind the bullet can reach 56,693 psi in the load I use in my 308. The pressure in front of the bullet is likely less than 200 psi and more like a few atmospheres at the most.

This means a pressure wave reaches the supressor all at once, as the bullet passes it.

If you use a blank loaded with the same components, the presure never builds, and the model says it never rises above 10,474 psi.....though that is with a 1 grain bullet since the software will not go below this. The actual pressure should be alot less with these same components and the pressure curve would be more of a sine wave rather than the early peaking sawtooth wave of a bullet exiting rifling. In fact it would be extra low because with a 1 grain bullet the percentage of propellant burn drops to less than 25 percent from the 99+ percent of the normal load. Another problem is that a blank is likely powered by a very fast powder, much faster than a rifle powder, and more likely an explosive such as black powder rather than a propellant like a 308 would normally use. This throws off the data once again and we have no software to predict this.

In my opinion, trying to use a blank to prove a supressor is rediculous. No offense intended.

 

[bohem]

Re: Need some QL help

I completely agree with you, however, the professor that's assigning a grade wants to see some sort of proof. My brother asked for the information if possible, and since I have no way to measure velocities of only gases, this was the only thing I could think of.

A 5 grain lump of wax is what I've made blanks from though so I thought it might work. I appreciate you taking the time to try it out for me. I'll forward the information and your reply to him and he can show the professor just the same thing you suggested too.

 

[Rafael]

Re: Need some QL help

No problem. If I had the know-how to solve this for you I would.
I love problem solving, but I lack many of the tools needed for this....like a good mind.