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Internal ballistics

Posted: Fri Sep 06, 2019 7:39 am
by lifeandliberty
What program do you folks use to determine the muzzle pressure of various calibers at different barrel lengths?

I am personally looking for the muzzle pressure on 5.7x28 at a ~5 inch barrel.

Re: Internal ballistics

Posted: Fri Sep 06, 2019 12:35 pm
by gun410
Not sure there is a program for it but this website covers how to calculate it https://www.frfrogspad.com/intballi.htm

Re: Internal ballistics

Posted: Fri Sep 06, 2019 12:52 pm
by ECCO Machine
You don't need a computer program to calculate that. You do have to operate under the assumption of certain chamber pressures, though, whether using a computer or doing the math yourself. Unless you happen to have the equipment for testing that...

Boyle's law is a very simple calculation; for every doubling of volume, pressure drops by half and vice-versa (assuming contant temperature). You just need to know case volume less what space the bullet occupies.

5.7x28 has a case volume of about .05 cubic inches if we take away the neck. A .223 caliber bore, if we approximate for rifling lands, will equal that volume every 1.3". 5.7x28 MAP is 50 KSI. So, the first 1.3" of barrel after the case neck will drop the pressure to 25 KSI. The next 2.6" will halve it again to 12,500 PSI. That's 3.9" of bore, which is probably very close to what you have with a 5" barrel that includes the chamber.

Of course, most commercial ammo is running a bit under MAP, so realistically you're looking at probably 10-12 KSI uncorking pressure.

Now, if you're trying to calculate for the operating of your silencer tube, you have to apply Boyles law again. But that assumes a closed system, which a suppressor certainly isn't. That said, operating under that assumption will give you a solid safety margin. Anyway, if the total volume of your case & bore are ~ .2 cubic inches with an exit pressure of 12 KSI and your blast chamber is, well, let's use a nice, round 1.0 cubic inch figure, you'd have a new total volume of 1.2 cubic inches and a pressure in that chamber of 2,000 PSI (if it were sealed).

https://www.omnicalculator.com/physics/boyles-law

Re: Internal ballistics

Posted: Fri Sep 06, 2019 4:21 pm
by lifeandliberty
Gosh dang that is some great help man thanks

Re: Internal ballistics

Posted: Sat Sep 07, 2019 11:49 am
by garredondojr
Thats pretty impressive. One thing I don't think that factors is burn rate which can influence #'s somewhat.

I cheat.... quickload

Image

It's hard to see the cursor but it's at the muzzle exit to the "chamber pressure" reading is at that point so 13k psi at the exit for a load starting at 49.7k psi.

Re: Internal ballistics

Posted: Mon Sep 09, 2019 11:07 am
by lifeandliberty
Thats a slick program.

Having trouble finding internal volume of 300 blk. Mind running 7 inch for me?

Re: Internal ballistics

Posted: Wed Sep 11, 2019 7:08 pm
by garredondojr
lifeandliberty wrote:
Mon Sep 09, 2019 11:07 am
Thats a slick program.

Having trouble finding internal volume of 300 blk. Mind running 7 inch for me?
110gr supersonic, "AR" subsonic, or fast powder subsonic?

Re: Internal ballistics

Posted: Wed Sep 11, 2019 8:57 pm
by lifeandliberty
Super sonic designing the can for both

Re: Internal ballistics

Posted: Wed Sep 11, 2019 10:15 pm
by ECCO Machine
Unless you're trying to get away with sub par materials or really push the envelope to see how thin & light you can go, don't overthink this. Any Ti or stainless seamless tube you can feasibly thread with 32 pitch or coarser will contain 300 blk. of any flavor

Re: Internal ballistics

Posted: Wed Sep 11, 2019 10:20 pm
by garredondojr
lifeandliberty wrote:
Wed Sep 11, 2019 8:57 pm
Super sonic designing the can for both
Didn't feel like uploading a photo but 110gr super is [email protected]" and [email protected]" in case you want to do a super shorty :wink:

Re: Internal ballistics

Posted: Thu Sep 12, 2019 10:46 am
by lifeandliberty
Thanks brother and yeah i am making a hunting can that is as light as it could possibly be

Re: Internal ballistics

Posted: Thu Sep 12, 2019 11:44 am
by ECCO Machine
lifeandliberty wrote:
Thu Sep 12, 2019 10:46 am
Thanks brother and yeah i am making a hunting can that is as light as it could possibly be
This is my Phantom 8 model, 300 win mag rated. 1.5" x 8", Weighs 9 oz

Image

-.035" wall gr. 9 CWSR tube, threaded 36 pitch

-Gr. 5 Ti mount w/integral helix port brake

-Gr. 5 Ti front cap.

-6061-T6 anodized spacer

-Two 50° 17-4 H900 baffles

-Seven 50° Anodized 7075-T651 baffles

The thing is, running aluminum internals on a centerfire rifle can means your rate of fire is severely restricted, need to keep the can under 350°. That means it needs to cool after 3-5 rounds fired quickly, with a sustained rate of fire only 1 or 2 rounds/min, depending on cartridge & barrel length.

Using Ti in place of the aluminum bits would increase the allowable temps, but you'd gain a couple ounces.

Re: Internal ballistics

Posted: Thu Sep 12, 2019 1:57 pm
by lifeandliberty
That is crazy impressive.



My questions are actually geared towards my tubeless ambitions.
Use would hopfully be one or two shots over a day for deer and hogs

Re: Internal ballistics

Posted: Sat Sep 14, 2019 12:18 pm
by garredondojr
lifeandliberty wrote:
Thu Sep 12, 2019 1:57 pm
That is crazy impressive.



My questions are actually geared towards my tubeless ambitions.
Use would hopfully be one or two shots over a day for deer and hogs
I doubt you could get the weight as light as ECCO's going tubeless unless you did the rest of the stack aluminum and threaded baffles which will add weight. But 1 major consideration in his design is anodizing which is absolute necessary.

Re: Internal ballistics

Posted: Sat Sep 14, 2019 10:33 pm
by lifeandliberty
Hmm without adding weld weight ive got a 1 1/2 added up pretty close. Blast chamber weight is pure estimatiom though.

No doubt his can is light as hell

Re: Internal ballistics

Posted: Sat Sep 14, 2019 10:37 pm
by garredondojr
lifeandliberty wrote:
Sat Sep 14, 2019 10:33 pm
Hmm without adding weld weight ive got a 1 1/2 added up pretty close. Blast chamber weight is pure estimatiom though.

No doubt his can is light as hell
Shouldn't be any "weld weight" Fusion welding should be sufficient if you cut your baffles correctly. but if you can do a tubeless full 17-4 at that length for 9oz that should make for 1 hell of a can.

Re: Internal ballistics

Posted: Tue Sep 17, 2019 4:22 pm
by lifeandliberty
Well weld material adds weight no matter how you shake it.

We will see how it turns out.

Re: Internal ballistics

Posted: Tue Sep 17, 2019 11:20 pm
by 3strucking
If you use no filler you are not adding any extra weight.

Re: Internal ballistics

Posted: Wed Sep 18, 2019 12:30 pm
by garredondojr
3strucking wrote:
Tue Sep 17, 2019 11:20 pm
If you use no filler you are not adding any extra weight.
This. If you add a small register to the baffle so it's a lap weld you won't have to worry about backpurging and just fusion weld the stack together. There are a few on here that have made some nice homemade orbital setups with a variable speed motor and setup the rotation speed, mount the torch and set the amperage to desired setting.

Turn on motor, step on the pedal, weld...move to next joint and repeat till completed.