Velocity and pressure

The pressure is due to some barrel factor other than length. Max pressure is obtained way before 30 inch.
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says your theory. My real life experience shooting the same reloads in three different rifles with barrels from 24 - 30 inches says otherwise. I have seen a pair of 26"ers from the same manufacturer behave differently with the same load in the same action and stock. You ever seen a barrel tighten up at around 500 rounds then start to drop off at 1500 - 2000 ?

Now who should I believe your theory or the data I have gathered and observed in real life experiences at the shooting bench ?
 
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hounddawg said:
says your theory. My real life experience shooting the same reloads in three different rifles with barrels from 24 - 30 inches says otherwise. I have seen a pair of 26"ers from the same manufacturer behave differently with the same load in the same action and stock. You ever seen a barrel tighten up at around 500 rounds then start to drop off at 1500 - 2000 ?

Now who should I believe your theory or the data I have gathered and observed in real life experiences at the shooting bench ?
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Peak chamber pressure in a rifle occurs when the bullets has moved only a few inches. It's not theory, it's fact. See this article:

https://gundigest.com/gear-ammo/reloading/bullet-ballistics

By the time the bullet exits, pressure is a fraction of what it was at peak. Again, not theory, but fact.

In handguns, with their much faster powder, peak pressure occurs by the time the bullet has moved even less. See the graph here, and table 3 for peak chamber pressure and gas pressure at the muzzle.

http://www.shootingtimes.com/editorial/compensators-pressure-gas/99170
 
Tell you what. After I do a velocity workup from the bottom on this H4350 load to get a safe and stable performance in that 30 inch I will shoot it three ways over a chrono. First in the 30 inch Shilen 8 twist then in a Criterion 24 inch 8 twist both with and without the muzzle break. Both barrels just north of c. 500 rnds. I will use the Sierra manual data for COL so it will be apples to apples comparison case volume wise.

I have a new chrono coming in to replace the Labradar and my ancient Pro Chrono which has seen better days and drops as many shots as it picks up. I am curious myself to see what happens

It may take me a week or two depending on time, weather and the wife's mood but I will make a thread and we will see how much difference six inches of barrel makes
 
hounddawg said:
Tell you what. After I do a velocity workup from the bottom on this H4350 load to get a safe and stable performance in that 30 inch I will shoot it three ways over a chrono. First in the 30 inch Shilen 8 twist then in a Criterion 24 inch 8 twist both with and without the muzzle break. Both barrels just north of c. 500 rnds. I will use the Sierra manual data for COL so it will be apples to apples comparison case volume wise.

I have a new chrono coming in to replace the Labradar and my ancient Pro Chrono which has seen better days and drops as many shots as it picks up. I am curious myself to see what happens

It may take me a week or two depending on time, weather and the wife's mood but I will make a thread and we will see how much difference six inches of barrel makes
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No need to go to all that work. read post 22.
 
No need to go to all that work. read post 22.
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a article dealing with one cartridge and one powder tells me nothing how my cartridge and my powder acts. Anyway for me it is not work, it is fun.

For my shooting it usually takes 200 to 500 rnds for me to find the load then I chase the throat with it for another 2000 rnds or so depending on the cartridge. If I shoot the exact same load 500 or more times through a barrel you can watch the changes. That is entertainment for me

Feel free to rely on the internet for your shooting knowledge, I prefer to test things first hand at the range
 
says your theory. My real life experience shooting the same reloads in three different rifles with barrels from 24 - 30 inches says otherwise. I have seen a pair of 26"ers from the same manufacturer behave differently with the same load in the same action and stock. You ever seen a barrel tighten up at around 500 rounds then start to drop off at 1500 - 2000 ?

Now who should I believe your theory or the data I have gathered and observed in real life experiences at the shooting bench ?
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I am discussing facts and not theories. The FACT is that within reason, barrel length has absolutely nothing to do with peak pressure. By "in reason" I mean you can't use a 1" barrel. That is a fact. It's not an opinion. It's not a theory.

The ONLY meaningful test you could do would be set your rifle up with pressure testing equipment. Test the load at 30" cut the barrel off and test the load at 22". You will amazingly find the peak pressure to be identical. Even though this is the internet, you do not own a physics defying barrel.
 
There are combinations of cartridge/bullet/powder that can produce two pressure spikes while a bullet is still in the barrel. And in some cases the second pressure spike is higher than the first, as illustrated in this post.

In that post the second pressure spike occurs roughly 1mS after ignition, an approximation of the time a bullet spends in the barrel. So for such a second higher pressure spike to occur, the barrel must be sufficiently long.

In cases where the second pressure peak exceeds the first, it's possible that excessive pressure signs could occur. But if you shoot the same load in a shorter barrel, any second pressure peak could be less and exhibit no excessive pressure signs.
 
you have never considered what effect using a slower powder in a longer barrel would have on velocity and pressure have you? You have also not considered the effect of the applied pressure over time on the brass and primer which would give more velocity up to a point

My issue was bad data from Hogdon, I should have done more research. For H4350 in a 6.5 CM the charge should be from 38.8 - 41.5 for the .260 Rem they list 41.5 to 44.5. The 6.5 CM and .260 Rem cartridges have almost identical case volume with the 6.5 CM a couple of tenths less

I started at 42.5 which I thought was reasonable. The primer blew at 43, but that 142 was getting 6.5 -284 velocity. I figure even dropping down to 41.5 I might get 2900 FPS

oh and as far as velocity vs barrel length goes here is a article which must be true because it is on the internet

http://bulletin.accurateshooter.com...l-length-223-rem-test-results/comment-page-1/
 
Peak chamber pressure in a rifle occurs when the bullets has moved only a few inches. It's not theory, it's fact. See this article:

https://gundigest.com/gear-ammo/relo...let-ballistics

By the time the bullet exits, pressure is a fraction of what it was at peak. Again, not theory, but fact.

In handguns, with their much faster powder, peak pressure occurs by the time the bullet has moved even less. See the graph here, and table 3 for peak chamber pressure and gas pressure at the muzzle.
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Correct in every statement. What you must understand is that in shooting forums, there are always a few who own physics defying firearms. The "laws" of physics become the "myths of physics" in internet discussion. Anecdotal evidence, that makes no sense, is always used to demonstrate why established physics has it wrong.
 
you have never considered what effect using a slower powder in a longer barrel would have on velocity and pressure have you? You have also not considered the effect of the applied pressure over time on the brass and primer which would give more velocity up to a point

My issue was bad data from Hogdon, I should have done more research. For H4350 in a 6.5 CM the charge should be from 38.8 - 41.5 for the .260 Rem they list 41.5 to 44.5. The 6.5 CM and .260 Rem cartridges have almost identical case volume with the 6.5 CM a couple of tenths less

I started at 42.5 which I thought was reasonable. The primer blew at 43, but that 142 was getting 6.5 -284 velocity. I figure even dropping down to 41.5 I might get 2900 FPS

oh and as far as velocity vs barrel length goes here is a article which must be true because it is on the internet
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Man, you are schooling me. I always thought you could just pack any powder in any case and it all worked the same. You mean my 300 Rum would shoot better with RL25 than it does with Zip?
. Go dig up some real books about pressure and read them. Talk to some real people who have used pressure testing equipment.
 
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Once had a book tell me that I did not need a line filter for a piece of equipment, engineers who sold us the equipment backed that up. After a week of head scratching and running new wire twice the equipment still was non functional. We installed a line filter and it ran.

Bottom line is I could care less what the books say, I care about real world results

you seem to be pretty hostile about me actually testing my loads, if you have a a problem with that how about we just add each other to the ignore list. I'll go first, just go to your control panel and type my name into the ignore list and you no longer have to read my posts just like I no longer will see yours
 
The only thing Reynolds357 said that I didn't think applied was his hydraulic analogy. It is true the bigger chamber has more area, but at any given pressure that just means more total force is applied to its walls (force=pressure×area). The cross-sectional area of the bullet is the same in both guns mentioned in the example, so the peak force accelerating the bullet is the same.

In the case of matching peak pressures, the fact a larger quantity of powder is needed to reach that same pressure in a larger capacity case means more total gas is made. As Reynolds357 said originally, the pressure then is sustained better in the large chamber’s barrel past the peak and all the way to the muzzle¹. That adds to the total acceleration the bullet undergoes.

You can think of the bore as representing a gas “leak” that is smaller relative to the volume of the larger capacity chamber. Therefore, it bleeds that pressure down more slowly from the large chamber. In turn, that means an even slower powder may be used in the bigger case without it failing to keep up with the “leak” rate. As a result, you can use a still larger total charge weight (of slower powder) in the big case that makes even more gas. The end result is more bullet acceleration after the pressure peak, and therefore higher final velocity.

It is true that pressure is not caused by barrel length. It is caused by burning powder. But even if you use the same chambering and load in two different lengths of identically chambered barrels, the pressure impulse that launches the bullet is changed by barrel length because the bullet needs more time to get out of a longer barrel. It remains under some amount of acceleration all the way to the end. The only place that doesn’t hold up is in really large expansion ratios, such as you have in a rifle chambered for 22 Long Rifle. There the bullet can actually start to slow down before it reaches the muzzle, though not by much.

The pressure impulse driving the bullet is force times the length of time the force is applied. So if you had two, truly identical guns with truly identical chambers (good luck finding those; even SAAMI standard test barrels in universal receivers fail to match perfectly) and truly identical cartridges with the only difference being the previously mentioned barrel lengths, up to the moment a bullet’s base reached the muzzle of the 22 inch barrel as well as for the first 22 inches of a bullet traveling down a 30-inch barrel, the pressure impulse for both would be the same. But the last 8-inches portion of the 30-inch barrel also has an average pressure and a bullet transit time, and product of those two comprise additional impulse to be added to the impulse over the first 22 inches to get the final impulse acting on the bullet in the 30-inch barrel.
 
you seem to be pretty hostile about me actually testing my loads, if you have a a problem with that how about we just add each other to the ignore list. I'll go first, just go to your control panel and type my name into the ignore list and you no longer have to read my posts just like I no longer will see yours
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The problem I have is you have no idea why you got your results. You derive false conclusions based on improper interpretation of your data. You have a 30 inch barrel that showed pressure signs. You assumed it was caused by barrel length. It was not caused by barrel length. Simple.
 
The problem I have is you have no idea why you got your results. You derive false conclusions based on improper interpretation of your data. You have a 30 inch barrel that showed pressure signs. You assumed it was caused by barrel length. It was not caused by barrel length. Simple.
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better go back and reread my replies

I found the culprit, bad load data on the Hogdon site. It is was way too high.
But that was the only source I could find using that appx weight bullet and that powder so I ran with it. In retrospect I should have checked the data against the 6.5 CM which has just slightly less case capacity

Now you assumed that was the the first and only possibility I had researched, it wasn't. The first was pulling bullets weighing powder and second checking the Hogdon data on the .260 Rem.

Once the obvious was eliminated I started looking at less likely causes the barrel length being one of those possibilities. When I looked at the Creedmore data I knew what the issue was.

At any rate I have at least 100 spreadsheets on load testing various bullets and powders. I have no idea how many you have. But I know for a fact that velocity data does not fit into any mold I can see. The most minute things will effect how much energy that powder produces and transfers to that bullet.

To me it looks like you are the one attempting to simplify
 
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