blast chamber length

[clark4283]

How long should the blast chamber be for a 10" x 1.75" 338lm can? I was thinking 3" but I not sure. Any advice would be helpful.

[cal50]

I would calculate the barrel volume and start there or larger.........

[clark4283]

I would calculate the barrel volume and start there or larger.........

How would I calculate the barrel volume?

[Historian]

I would calculate the barrel volume and start there or larger.........

How would I calculate the barrel volume?

V=πr^2h


As an example:

For S&W 41 with 5.5" barrel, .22 diameter:

V = 3.14159 x .11^2 x 5.5.

Additionally, if you look up from pressure table
of bullet you can calculate pressure of expansion tube
by Boyle's Law:

P_1 V_1 = P_2 V_2.

[EXPERIMENTAL]

I am not disagreeing with Boyle's law P1*V1=P2*V2

But I am also not sure that barrel volume will be the best starting point for blast chamber volume, just by using the following example (obviously please let me know if I have something incorrect)

Example: 16" .223 caliber

Pi=3.14 (simplified)
L=16"
r=.224"/2=.112"

Barr. V=Pi*L*r^2 = (3.14)(16")(.112"^2)
Barr. V=0.6305 inches^3

So, in my case, assuming inner ID 1.350" (r=.675) (SDTA Carbon D-Cell), if you want blast chamber to match barrel volume....

0.6305 inches^3=Pi*L*r^2
0.6305 inches^3=(3.14)(L")(.675"^2)
0.201 inches^3=(L)(.456 inches^2)
L=0.441"


Just not seeing how this, this could be. I am waiting on Form 1, and this is something that I have been trying to figure out for myself (blast chamber size). Seems the normal blast chamber for .223/5.56 and 300 BLK is around 1.5" to 3.0" length.


Please help, this would be something I would be very interested to have explained.

[partsguy22]

Using barrel volume gets even more screwed up when you start calculating short barrels (10.5" .223) you start getting impossibly small blast chambers

Also keep in mind if you use a muzzle devise you need to factor it into the volume of your blast chamber

[delta9mda]

too much over thinking this. why does the blast chamber need to be "larger" or 1/3 of can volume/ length?

just as an example the distance from muzzle to cone apex in a cyclone is less than an inch. i know this is for a bolt gun typically and is just an example.

look at how the new sig cans are set up. really not a lot of space in the first chamber. the saker doesnt have much volume either.

[partsguy22]

I agree with delta...my 8" Ti 5.56 can is 1.25 from end cap to baffle it probably would've been shorter but my brake is 1.125" in the can . The reason I did it that way was to fit more baffles

[Dr.K]

For a closed action, super sonic, there are no worries about blast chamber volume. If you're shooting subs, chamber volume, and design have a direct effect on frp. For gas operated firearms, blast chamber volume determines the amount of back gassing. That's it in a nutshell.

[clark4283]

too much over thinking this. why does the blast chamber need to be "larger" or 1/3 of can volume/ length?

just as an example the distance from muzzle to cone apex in a cyclone is less than an inch. i know this is for a bolt gun typically and is just an example.

look at how the new sig cans are set up. really not a lot of space in the first chamber. the saker doesnt have much volume either.

I was thinking 3" from the back of the first cone to the front of the end cap. That would mean my spacer for the blast chamber would be 3". I'm not real familiar with the 338lm but plan on getting one in the future. I was hoping some one would know what is typical for 338 can. I'll use it on my .30 cals till I get a 338.

[cal50]

Excellent point on blast chamber volume and gas gun blow back.
Something to factor in if you are putting it on a gasser.

[clark4283]

For a closed action, super sonic, there are no worries about blast chamber volume. If you're shooting subs, chamber volume, and design have a direct effect on frp. For gas operated firearms, blast chamber volume determines the amount of back gassing. That's it in a nutshell.

It will be bolt action and supers. I'm not a fan of gas guns.

[Samson104]

If the first baffle is gonna be a cone then I'd say make it 2" , the cone will protrude down into his space some taking up some volume but you'll still have plenty enough and the front baffle will be far enough away from the crown so as not to cause any heat related issues there.
If you are running a flat baffle then shorten it down some.
note here , the "blast chamber" or lack there of on the AAC Cyclone , that can is designed for precision rifles.

[Historian]

too much over thinking this. why does the blast chamber need to be "larger" or 1/3 of can volume/ length?

just as an example the distance from muzzle to cone apex in a cyclone is less than an inch. i know this is for a bolt gun typically and is just an example.

look at how the new sig cans are set up. really not a lot of space in the first chamber. the saker doesnt have much volume either.

+2!

[clark4283]

If the first baffle is gonna be a cone then I'd say make it 2" , the cone will protrude down into his space some taking up some volume but you'll still have plenty enough and the front baffle will be far enough away from the crown so as not to cause any heat related issues there.
If you are running a flat baffle then shorten it down some.
note here , the "blast chamber" or lack there of on the AAC Cyclone , that can is designed for precision rifles.

Isn't the cyclone only rated for .30 cals that aren't magnums? My concern would be the initial volume of gas that comes from from 338lm. Am I just being paranoid?
I looked for a cross section of a 338 can but couldn't find one. Does anyone have a pic of one they would share?

[Samson104]

no the cyclone is not magnum rated , I posted the pic as a reference , your can being bigger in OD and a slightly larger blast chamber would make a big difference though.
look at the chamber at the left side of the this baffle stack , tat first cmaber is TINY , this is the AAC Titan core

[clark4283]

The Titans first chamber is very small. Does that have anything to do with the first baffle being flat? As I have been researching I thought most folks liked cones for baffles. That is if they aren't using monocores. Would a flat baffle first then cones be better? My plan was just to use all cones.

Thanks for everyones input and the pics.

[noisecatcher]

So for a .30 caliber can that will see 10" barrel 300blk subs and supers,16" or longer barrel .308,18" or longer barrel.30-06, and 14.5" or longer 5.56 does a two inch long blast chamber with a muzzle brake reducing the volume seem appropriate? I don't want excessively high pressures with the .308 and .30-06 but I also don't want a ton of FRP on the 300 blk subs. If it makes a difference my intentions right now are to use a flat blast baffle.
Sorry I forgot to mention the can is 1.360 ID.

[whiterussian1974]

The blast chamber is the place where bore gas initially cools and expands. AT MOST 20% of can length unless you need to prevent backpressure.
The reason that flat blast baffles are sometimes 1st used b/f the remaining stack is that they are typically thicker and possibly a more wear resistant material. (IE. Inconel b/f SS, or SS b/f Al.) And thus tougher to machine. So a flat disc is easier to work than a cone, K, etc.
If the same material and shape are used, then the 1st is usually thicker to be stronger.
.338 LM is a very pressure*volume intense rd. So any design will need to be stronger than .308, but not as much as .50BMG.
ALL variables affect each other variable. So it's tough to comment on 1 w/o discussing them all.
Do you have a drawing of your design to post? That's generally needed b/f we can answer any ?s.

[delta9mda]

Look at the new sig cans. They have a 338 and the blast chamber is not that big. Porting is a good way to lower pressure. Just a hint.

[noisecatcher]

I am a little hesitant to post drawings because 1) my drawings are in crayon 2) someone will play the I.P. card within an hour or so and they are probably right. I saw good ideas I tried to integrate them into my suppressor.

Using a YHM QD mount(YHM's idea) in a 2" blast chamber, (several thousand people doing this) followed by a flatish blast baffle(idk whose idea this was). Then I plan on using two 7 step step/aztec baffles (is the aztec baffle design or the number of steps IP?shall I write the Aztecs?) followed by 60* cones (thousands doing this as well) and possibily a K baffle or two at the exit end ( this is a forum member curtistactical maybe?) Really undecided on the K's seems like alot of work that may be better suited for other calibers.

Spacing is still up in the air. I plan to use a variety of spacers too some the OD will be a slip fit to the tubes I.D., I'm also considering using some 1.000" .039 wall Ti tubing as spacers. The 60* cone prints I found on here include an integrated spacer but i am not sure I can do that on my lathe.

My inspiration for my suppressor design was Eric Carle's book published in 1975. As I read that book for the second time in a half hours time it became clear to me 1) these kids need to go to bed 2) why not mix it up a bit on the suppressor design.

All these internals will be Ti in a SDTA 9.6Ti tube.( I got a lathe after I got a solvent trap and I'm too cheap to throw the parts I paid for out)

I apologize for making light of the I.P. of others but sometimes it just seems like people get carried away.

[clark4283]

I don't have any drawings but I was looking to build something like this viewtopic.php?f=10&t=77309 I not going to use step cones. My plan is to use regular 60° cones. I may add a few more baffles also. I just think the blast chamber is a little long. What do you guys think should I think about a different design? I like this one because it's simple.