PCC Chamber Pressure

[Sarge]

PCC chamber pressure should be lower than a pistol correct?

I have a bunch of the stepped brass I was getting ready to pitch but it seems guys are doing ok with it holding together in minor loading. If I load it to high end minor(140ish)it would still be low enough pressure in a long barreled carbine no?

Will stepped brass hold together at 140PF out of a PCC?

[Steve RA]

Save those - along with used primers - and sell for scrap.

[Flatland Shooter]

What barrel are you running Sarge?  Seems like a lot of them require we load short and that may be a problem in stepped cases.

I'm loading 147 gr X-treme plated RN bullets at 1.085".  That's close to the max for my barrel.  That puts the bottom of the bullet 0.290" into the 9mm case.  For my load, if the step is 0.300" from the case mouth, i'm OK.  Any less and we are looking at problems.

And I would think that 140 PF in a pistol and 140 PF in 16" barrel would generate similar pressures. But I could be wrong.

[Hi-Power Jack]

12 minutes ago, Flatland Shooter said:

 I would think that 140 PF in a pistol and 140 PF in 16" barrel would generate similar pressures.

I could also be wrong, but I'd bet 140 PF in a 16" barrel would be LESS.   

[Sarge]

It's in a STAG 9 so not sure if they turn their own bbls. I don't load anything heavier than 124's so depth should be less of an issue. I'll probably shoot the Xtremes 124 HP I bought through it since it's just for a fun change of pace from Open.

[Flatland Shooter]

I don't know about the shape of the Xtreme 124 HP bullets, but in my PSA barrel I actually need to load 124 gr MG JHP's 0.050" shorter than the 147 Xtreme RN bullets.

Probably not the most scientific method but I measured the distance from the face of the bolt to the muzzle.  Then I put a bullet (just the bullet, no brass) into the chamber.  I held it up to the rifling with short cleaning rod and then measured the distance from the muzzle to the bullet with a longer cleaning rod.  I would do this for 5 or 6 bullets from the same box to see how consistent the measurements would be.

I then loaded bullets several thousands of an inch shorter than the max measurement and did the "plunk and rotate" test.

Again, not all that scientific but the best I could do with what I had on hand,

Bill

[Sarge]

here is 124 Xtreme HP loaded to 1.097. Drops in and out freely. I zoomed waay in to show the distance from base of bullet to the ledge.

[Flatland Shooter]

Looks like that will work.  

Now all the folks that were scrapping their stepped brass can send it to you.  

[Flatland Shooter]

1 hour ago, Hi-Power Jack said:

I could also be wrong, but I'd bet 140 PF in a 16" barrel would be LESS.   

Are you thinking the longer barrel allows lower peak pressure since it can be spread out over more that just 4 or 5 inches in a pistol barrel?  That would make sense.  

That would also explain why we need less powder in 16" barrel to make a certain PF compared to a pistol barrel.

Now my brain hurts.

Edited January 21, 2017 by Flatland Shooter

[dauntedfuture]

I think that you'll get more velocity in that carbine barrel.  Pressure in a rifle vs. pistol should be about the same.  I should think that variations in pressure would be due to the chamber and throat of the given barrel. 

[superdude]

Sarge, what is your reasoning behind why the PCC chamber pressure should be lower than a pistol?????

[Flatland Shooter]

You will get more velocity in a carbine barrel using the same loads in the carbine and the pistol, but we are downloading our pistol ammo to get the same velocity (PF) out of the carbine.  

This is where the smart guy in the room needs to step up.  Will the pressure be greater in the pistol due to the increased amount of powder used or will the pressure in the carbine be greater due to increased friction between the bullet and the barrel due to the barrel length.  Or would there be an argument that not all the powder has burnt within the pistol barrel where the longer carbine barrel allow more efficient burning of the powder.

[superdude]

According to the pressure curve output in Quickload software, peak chamber pressure in a pistol cartridge occurs shortly after the bullet has started to move.  See the figure below. Pressure drops as the bullet continues down the barrel even though bullet velocity increases. 

More (of the same) powder means more pressure (all else being equal).

The same load should produce the same peak pressure in two different barrels regardless of barrel length (if chamber/bore dimensions are the same and the short barrel is longer than an inch or so). 

Longer barrels provide more velocity because the gas pressure has more time to accelerate the bullet. This figure illustrates the pressure (red line) and the velocity (blue line): (figure from: http://firearmsdesigner.com/?p=234)

 

 

 

[Flatland Shooter]

So Superdude, less powder in the PCC means lower pressure, right?

[superdude]

1 minute ago, Flatland Shooter said:

So Superdude, less powder in the PCC means lower pressure, right?

Yes, less peak chamber pressure. 

[Sarge]

1 hour ago, superdude said:

Sarge, what is your reasoning behind why the PCC chamber pressure should be lower than a pistol?????

Lack of education...

[Sarge]

So it sounds like these stepped cases should be fine?

Edited January 21, 2017 by Sarge

[superdude]

2 minutes ago, Sarge said:

Lack of education...

We're all members of that club. 

1 minute ago, Sarge said:

So it sounds like these strapped  ASEAN should be fine?

Now I have to show my ignorance. What is ASEAN?

[Sarge]

8 minutes ago, Sarge said:

So it sounds like these strapped  ASEAN should be fine?

Damned if I know! 

 

5 minutes ago, superdude said:

We're all members of that club. 

Now I have to show my ignorance. What is ASEAN?

Hilarious

[kneelingatlas]

Does anyone know how a blowback action effects pressure/velocity vs a locked lug setup like a pistol?

[cecil]

Sarge.... I got a Stag Arms 9mm carbine in Oct.. had a world of problems with it stove piping ... I tried some hand loads.. some Blazer factory loads.. and Winchester white box factory... they all stove piped.. finally found out from a gun smith friend of mine.. I had to load my cartridges using Precision Delta 124 HP bullets to 1.045 max .... one would think a Stag 9mm carbine would shoot Winchester white box ammo..

 

[Sarge]

33 minutes ago, cecil said:

Sarge.... I got a Stag Arms 9mm carbine in Oct.. had a world of problems with it stove piping ... I tried some hand loads.. some Blazer factory loads.. and Winchester white box factory... they all stove piped.. finally found out from a gun smith friend of mine.. I had to load my cartridges using Precision Delta 124 HP bullets to 1.045 max .... one would think a Stag 9mm carbine would shoot Winchester white box ammo..

 

That's odd. Mine runs everything with no issues so far.

[jhgtyre]

Hodgdon has a nice little article discussing this: http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/does-my-shorter-barreled-rifle-require-different-reload-data

[sitw]

Length of barrel affecting chamber pressure doesn't make any sense.  I have to believe a chambers dimensions is the  primary factor affecting pressure, using identical ammo.  Unless the barrel is worn, the bullet is creating a gas seal as soon as it leaves the chamber so what is after the chamber would have little if any impact.

edit: just looked closer at the graph superdude posted, it supports what I believe to be the case.

My JP GMR-13 runs flawless right out of the box, full power loads all the way down to powder puff loads out to 1.15 OAL.

Edited January 23, 2017 by sitw

[sitw]

Reading how short everyone has to load had me wondering.  For the heck of it I went and did a plunk test with my open ammo.  Montana Gold 124 JHP 1.17 OAL.  It more or less plunked but didn't spin freely.  The JP barrel lets you load long.