Does anybody have any insight on chamber pressure and barrel length? Where is the bullet at the point of maximum pressure? at the end of the barrel, the beginning, or is it variable? i see that contenders shooting 35 rem are loading differently than 336's with longer barrels. should i be shooting a faster powder like varget in my 18.5" barreled 336? or could i use varget without increasing pressure beyond the pressure generated by 4895 in a 20" barrel? has anybody done any pressure work with the 336 in the 18.5" barrel? just curious, not about to do anything crazy!

Usually the peak is within an inch or two of the chamber. The fastest loads in a long barrel are generally the fastest loads in short barrel, although slower powders will give more muzzle blast.

Varget works great in my 20" 336 in .35 Rem.... in fact, it's about the slowest powder you can use and still get enough in the case.

Welcome to the forum....

Well Z, you may have to re-think your "burning" question.

According to Hodgdons powder co. and Western powder co. in seperate papers:

Powder in a correctly matched powder cartridge combo., is completely burned within a couple of inches of the case mouth. Exact distance depends upon powder burn rate. Something like Unique would be burned before the bullet leaves the case. So chamber pressure would have nothing to do with barrel lenght and vice versa. Shorter barrels requiring a faster burning powder is a myth. For example, H-4831 is an excellent powder in a 270 with 24 inch barrel.
But, the same powder works well in a 270 with an 18 inch barrel, also. You may lose some velocity in the short barrel but the best powder is still the best powder.

So what is the fire ball we see with short barrels? More gas escapes at the muzzle of short barreled arms. When the escaping gas hits the outside air we see a brief re-ignition or flash. The shorter the barrel the higher the muzzle pressure is and the greater the flash. Do not confuse muzzle pressure with chamber pressure, chamber pressure is many times higher.

You haven't told us what caliber you are using so we don't know what powder you can use. Use a couple of good reloading manuals to determine type and quantity of powder. Approach maximum loads with caution and DO NOT exceed the max. The people who do the manuals have lots of equipment to test the loads and know what they are doing. Don't try to second guess them.


Jim

Going to a faster power like 3031, not Varget, might get you a slight reduction in muzzle blast. To tell you the truth I don't think I could tell the difference between 3031 and 4320 in my 20" .35 Remington, although I haven't shot them both at the same bench session.

3031 is pretty well optimal in the .35 Remington.
http://www.imrpowder.com/data/rifle/35rem.php

Bye
Jack

Going to a faster power like 3031, not Varget, might get you a slight reduction in muzzle blast. To tell you the truth I don't think I could tell the difference between 3031 and 4320 in my 20" .35 Remington, although I haven't shot them both at the same bench session.

3031 is pretty well optimal in the .35 Remington.
http://www.imrpowder.com/data/rifle/35rem.php

Bye
Jack


I agree, 3031 is the best all around powder that I have found. Benchmark show promise, also.

Thanks to all who replied! It's fascinating to me that all the powder is burnt so quickly... That means that all the gas used to propel the bullet is already present, albeit in a VERY compressed state, as the bullet leaves the chamber.... I'd have to dig back into my university chemistry or thermodynamics texts to figure out if it's even possible, or if the combustion products exist partly in a liquid state until the volume of the available space increases as the bullet travels down the barrel. of course, who really cares as long as the monster buck falls down, right?

zen...

I've done quite a bit of pressure work with the 35 Rem but I don't think it is every really done. I've got a "D" with the 18 1/2" barrel and several other rifles with a 20" (336SC) and 22" (Sav 170B) barrels.

With published data, you will almost always see the data shot in a barrel that is about the longest barrel available for the caliber or longer. The long barrel generates more pressure for a given powder charge. In other words, if the 18 1/2" barrel of my "D" was used to generate the max load data of "BOOM1234", when you shot that max load out of the 22" barrel of my Sav 170B there is a good chance it would go BOOM!

As far as where the pressure peak takes place, the max is usually at the point represented in the screen shot I've attached. In this example, you are looking at the bullet being in the barrel 1.25 milliseconds (exit represented by the "+" symbols on the trace). The peak is taking place about .3 milliseconds from the "pop".

Most of my work in my "D" has been with cast boolits and I've only worked with Hodgdon powders. The best powders I've found for the short barreled Marlin's (Not compressed, over 85% of the case density, and highest velocities) have been H322, H335, and H4198 & H4895. It depends on the bullet and individual gun. For instance, my "D" will do best with H4895 and the Speer 180-grain FP. With a 180-grain cast boolit is will do it's best work with H335.

There is a bunch to this... but nothing like blind luck for hitting a load!

Been following along....though i knew the answer...so will let others check my logic.

Believe the pressure max. is set by the peak pressure...this peak pressure is happening very early in the bullet's travel...after the "peak" it's a declining pressure situation...so longer barrels don't increse peak pressure, just offer a longer "push" (so long as the force pushing a bullet is greater than the friction acting on that bullet, will gain velocity).

Still sounds right to me....but am open to corection.

Slower powders do delay that peak slightly...but more importatly, they supply more gas VOLUME (becasue they generally are loaded with a heavier charge weight). Peak pressure is the same...the difference in when that peak happens is minimal...but the larger volume of gas after the peak offers greater acceleration...a less drastic reduction of pressure after the peak (at the cost of higher gas exit pressure at the muzzle...which translates to a big-loud-boom).

Still with me? or have i run off the tracks somewhere along this spur line?

The higher vel. with slower powders (at least until you go so slow that max. peak pressure can't be reached) is LESS evident in shorter barrels, but islow powders do still seem to crank the chronograph higher than fast ones. BUT once muzzle pressure (gas exit) gets high enough, seems like some truely bad things happen to accuracy.

Pretty much pure speculation past this point.

For a very short distance out of the barrel, the un-corked gas does blast ahead (...well..around and ahead) of the bullet. High speed photos do show a cloud of gas that hides the exiting bullet for a few inches ahead of the muzzle. Being buffed about in the center of that gas-storm shouldn't foul up accuracy so long as it is uniform buffeting. BUT what I suspect is that any small irregularities of the bullet base/ rifling engravment on that base, muzzle crown, etc. are going to be magnified by the stronger exit gas pressure.

.

Ranch Dog

Why does the second highest pressure "T2" have the longest barrel time?

Jim

.

Ribbonstone,

I agree with your explaination, however, I 'm not quite clear on you thinking about slower powders in short barrels. If a rifle with a long barrel likes slow powder it would like slow powder with a short barrel, too. Barrel length has nothing to do with burn rate. Phil Sharpe proved that many years ago.

Fast burn rate powders will display a sharper parabolic curve indicating that although peak pressure is the same as slow powders, the after peak pressure drops much faster and thus bullet acceleration drop off more rapidly. Therefore, barrel length does not affect peak pressure but it has a very definate affect on muzzle pressure.

I think that is what YOU said, but I was not quit sure.

Good discussion, thanks to all of you.

Jim

You just said it bettter/faster.

Slow powders still seem to give a vel. increase over fast powders (both run at the same peak pressure) even in short barrels. It is just that the increase isn't as great as with longer barrles and the exit pressure is much higher.

.

Ranch Dog

Why does the second highest pressure "T2" have the longest barrel time?

Jim

Who knows Jim. All the charges where fired from the same rifle using identical brass, primers and charges. Each shot has a boom all it's own. Like a chronograph, it is best to look at the statistical data provided from these shots and not the individual shots.

Who knows Jim. All the charges where fired from the same rifle using identical brass, primers and charges. Each shot has a boom all it's own. Like a chronograph, it is best to look at the statistical data provided from these shots and not the individual shots.


Hi Ranch Dog

I think it interesting that higher pressure/velocity does not always mean shorter barrel time. "Barrel time" is somewhat of a buzz word with the gun writers. Barrel time is much ado about nothing.

Keep your powder dry,

Jim