pressure question

[Clem Bronkoski]

I was thinking and searching about this and found different answers on it. What I was wondering is if barrel length has an effect on chamber pressure?
One side says that although barrel length effects velocity it does not effect chamber pressure. The other side of the coin say that it can if the powder used is too slow and can cause a spike. Another which I totally disagree with was that there will be a spike if the barrel is too short! That sounds just illogical.
I do know from experience that a safe load in one rifle may not necessarily be safe in another which is why you always start low and work up. Now is this due to barrel length, chamber dimensions, or both?
Sorry but being down here in FL without any guns to shoot I have nothing to do but think about crap like this!!!

 

[HSmithTX]

Peak chamber pressure is the same whether it's a 16" barrel or a 26" barrel.

 

[Ace Quackhunter]

I was thinking and searching about this and found different answers on it. What I was wondering is if barrel length has an effect on chamber pressure?
One side says that although barrel length effects velocity it does not effect chamber pressure. The other side of the coin say that it can if the powder used is too slow and can cause a spike. Another which I totally disagree with was that there will be a spike if the barrel is too short! That sounds just illogical.
I do know from experience that a safe load in one rifle may not necessarily be safe in another which is why you always start low and work up. Now is this due to barrel length, chamber dimensions, or both?
Sorry but being down here in FL without any guns to shoot I have nothing to do but think about crap like this!!!

My understanding is barrel length & powder will affect velocity. Magnum rifle loads are usually slow powder for longer barrels to get a complete burn. Fast powders for short barrel handgun or subsonic loads in rifles. I use Red Dot for my 308 for reduced loads and almost no recoil or sound. Were powder charge, type and primers will affect chamber pressure. I started reading ever reloading book when I began and still reread them 30 years later. It's always better to start with a moderate load and see if your firearm likes it. My 308 load will work well in my Remington 700 but not some much in the savage and starts to show pressure signs. Be cautions, if you can find a local in your area that loads you can always pick their brain. They will talk about the time they used the wrong powder, wrong primer or looked up the wrong load info for the for their firearm. So, after having blown a few primers and locked up the bolt in a match or two I still don't much.

 

[Hugger-4641]

I don't think theres one final answer here, too many variables, except I agree with you that a short barrel is not going to create a spike.
As to the other two scenarios you mentioned, there are some things to consider here:
Peak pressure usually occurs within the first one to three inches of bullet travel, so barrel length is not going to change peak pressure in a rifle, maybe it could in a snubby pistol.
However, a longer barrel may allow more time for the pressure to accelerate the bullet, so velocity will increase, but not because of increased pressure, it's because the gas pedal stayed on the floor longer.

 

[Mike Matteson]

Well I give it ago. Not just one. Barrel length does help on velocity. Powders, and primers are two of the biggest increaces of pressure, and velocity. Case volume can also come into play.
I findly looked you up and you have been around for a long time. Velocity increase from a few fps to 25 fps per inch or so, depending on powders, primers. I don't know if you have a chronograph or not. I would think you do have one.
Me I generally use a 26" or longer barrel. I started using a chronograph about 30+ years I generally don't go to the range without one. If you have different barrel length in the same chamber you can check it out.

 

[Tiny Tim]

Alot goes into all this. Longer barrels generally give higher velocities due to bullet having longer time being pushed. It also oftentimes allows for benefits of the use of slightly slower burning powders which are better able to utilizethe additionallength. .

The powder that produces the highest velocities will generally do so regardless of barrel length. People oftentimes use faster burning propellant in shorter barrels to reduce muzzle flash, rather than to gain speed.

In the case of rimfire 22, if the barrel becomes too long, velocity begins to reduce due to bullet drag in the barrel lasting longer than the propellant's push on the projectile.

 

[WA Coyote]

Sorry but being down here in FL without any guns to shoot I have nothing to do but think about crap like this!!!

You need a fishing rod my friend…..

 

[Clem Bronkoski]

I don't think theres one final answer here, too many variables, except I agree with you that a short barrel is not going to create a spike.
As to the other two scenarios you mentioned, there are some things to consider here:
Peak pressure usually occurs within the first one to three inches of bullet travel, so barrel length is not going to change peak pressure in a rifle, maybe it could in a snubby pistol.
However, a longer barrel may allow more time for the pressure to accelerate the bullet, so velocity will increase, but not because of increased pressure, it's because the gas pedal stayed on the floor longer.

This seems to be the most logical answer. I believe you are correct.

You need a fishing rod my friend…..

Thought about it Coyote and I must have 25 outfits back in PA for everything from crappie to light saltwater. I used to live in Port St Lucie, FL for a while and was only 20 mins from a public boat launch. I had a nice Aquasport center console boat and went out to the Atlantic almost every Saturday. It was nice but I missed the mountains and seasons in PA.

 

[akmtnhnt]

Both QL and GRT have higher peak chamber pressure if you change the barrel from say 30in to 20in leaving everything else the same. Higher pressure in the shorter barrel. It's only a few hundred psi though.
The Pmax also doesn't occur a the same length down the barrel/time when you change the barrel length. In the shorter barrel it occurs before the longer, which would make sense why it's a little bit higher, there's less volume to expand into at that point.
Just thinking about why that is, I'm thinking it's probably about compressing the air in front of the bullet and the drag/opposite reaction that creates. The bullet is already over Mach 1 at Pmax.

 

[Hugger-4641]

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Both QL and GRT have higher peak chamber pressure if you change the barrel from say 30in to 20in leaving everything else the same. Higher pressure in the shorter barrel. It's only a few hundred psi though.
The Pmax also doesn't occur a the same length down the barrel/time when you change the barrel length. In the shorter barrel it occurs before the longer, which would make sense why it's a little bit higher, there's less volume to expand into at that point.
Just thinking about why that is, I'm thinking it's probably about compressing the air in front of the bullet and the drag/opposite reaction that creates. The bullet is already over Mach 1 at Pmax.

This is because the software is trying to simulate the entire pressue curve of the burn cycle. If you use a longer barrel, it likely will show an increased velocity and the software back references this velocity to a pressure.
In reality, there is no difference in the actual "peak pressure", but this is useful for staying within safe parameters.

 

[charlie 7]

Just look at the pressure curve in gun barrel. You will see that, the peal pressure is within first few inches of the projectile travel.

 

[std7mag]

@Clem Bronkoski,

The pressure will drop some as the bullet goes down the barrel.

The issue with longer barrels is the tendency to use slower burning powder to help squeeze more velocity than just the added barrel length.
The whole reason for a longer barrel is velocity.