24hourcampfire.com
24hourcampfire.com
Previous Thread
Next Thread
Print Thread
Hop To
Joined: Mar 2001
Posts: 1,766
SeanD Offline OP
Campfire Regular
OP Offline
Campfire Regular
Joined: Mar 2001
Posts: 1,766
Ok, after several discussions with friends about the new short mags and "effeicency" and all that usual stuff, i started wondering about how the barrel length effects optimum powder burn rates. One the common views is that the short mags can get away with shorter barrels because they use faster powders. Is this true?

One buddy of mine is convinced that the 300 wsm can get away with a shorter barrel than his 300 win mag and still be as effiecent. Some of the loads i have seen for the wsm use the same powder, like rl 22, so why would one need a longer barrel than the other? Maybe because the wsm burns less powder? Not that i am convinced that there is an "optimum" or necessary length after reading Charlie Sisk's thread on barrel length and velocity. It just seems the logic that the wsm doesnt need as long of a barrel as the regular mags doesnt add up. <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

My thought was that case and bore dimensions are the factors that decide what burn rates are ideal. If the powder is mostly burned in the first few inches of the barrel anyway, does the same cartridge with a shorter barrel need a faster powder than the standard length barrel? I have a 30-06 with a 20 inch barrel, and with IMR4831 i was getting a significant flash out the end of the barrel at dusk, with 4064 the flash went away. I figured it was unburned powder that caused the flash, so i assumed with faster powder i was getting less flash, thus more velocity (this was a few years ago before i had access to a chronograph). After all my recent "internet schooling" now im not so sure. Dad and i also wrongly figured that the short barrel would allow us to load to higher than listed charges and the pressure would be lower due to a shorter barrel. Now i realize the pressure peak is past before the bullet leaves the gun, so barrel length should have no effect on chamber pressure. At least i think this is the case.

Dad recently aquired a model 7 in 7mm-08 with a 20 inch barrel, and he pretty sure he needs to load it up with some faster than normal powder to compensate for the short barrel (like we did with my 30-06). I dont know if i agree with him. Especially after reading Charlie Sisk's thread on barrel length and velocity.

What do you guys think-- Does barrel length effect optimum burn rates? Or is it case size or case dimensions that effect it?


Sean
BP-B6

Joined: Feb 2001
Posts: 710
Campfire Regular
Offline
Campfire Regular
Joined: Feb 2001
Posts: 710
I don't think you need a faster powder in a shorter barrel. Look at load data for the 7-08 in a rifle compared to the load data for a handgun. Powders that give the highest velocity in a Rifle still give higher velocities (within what I assume would be normal deviation between two different barrels) in a handgun. Sean


"You shouldn't say it is not good. You should say you do not like it; and then, you know, you're perfectly safe." James Whistler
Joined: Jul 2001
Posts: 57,468
M
Campfire Kahuna
Offline
Campfire Kahuna
M
Joined: Jul 2001
Posts: 57,468
Case dimension mostly determines optimum burn rate. I have experimented with cutting rifle barrels off down to 20" and the same powders that provide maximum velocities with a certain cartridge at 24-26" also provide maximum velocities at 20". (And no, cutting a .300 Winchester Magnum down to 22" doesn't turn it into a .30-06. I cut a .300 WM to 22" one time and standard manual loads still got 3000 fps with 180's and 2850 with 200's, both of which are impossible in a .30-06.)

Just about any modern bottleneck cartridge gains something from a longer barrel and loses velocity in a shorter barrel. You gain quite a bit with a 26" barrel on a .270, 7mm-08 or .30-06 as well as the "magnums."

Muxxle flash is caused by hot gases reigniting when they hit the atmosphere, but unburned powder. At least 99% of the powder is burned in the first few inches of any centerfire rifle barrel.


“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck
Joined: Mar 2003
Posts: 2,167
C
Campfire Regular
Offline
Campfire Regular
C
Joined: Mar 2003
Posts: 2,167
Hallaluyah (sp?) finally an answer that makes some sense and has some tested truth to it!

Chuck

Joined: Mar 2002
Posts: 4,208
J
Campfire Tracker
Offline
Campfire Tracker
J
Joined: Mar 2002
Posts: 4,208
I think another thing that strengthens John 's statments but is often forgotten in an explanation is simply that the longer barrel exposes the bullet to the pressure curve longer, giving it time to build up more velocity. Those gases will continue to expand and increase velocity of the bullet until extending barrel length is no longer practical. Dan Lilja has experimented with barrels in 46"-50" range producing extremely high velocity, but not very practical...
So the question is --How long do you want your barrel to be? OR How much velocity do you want? Barrel weight increases exponentially with its length to keep the same stiffness, so most of our factory barrels are the best of nothing--only a comprimise of several factors to make them manageable on hunting weight rifles...
For example:
Benchrest barrels are typically heavy contour, but short, aiding in extreme accuracy, but giving up a little velocity.

Factory sporter barrels are thinner and lighter, giving up accuracy and stiffness, but picking up a little velocity in the process.

Long range hunting rifles and Varmint rifles are usually very heavy, as they use stiff, long, thick(heavy contour) barrels and are after the most accuracy and highest velocity, mostly to help with with bucking the wind.

The differences between 20 inches, 22 inches and even sometimes 24 inches, will probably never be felt by whatever you hit with that bullet- <img src="/ubbthreads/images/graemlins/smirk.gif" alt="" />-You might notice that the rifle is much easier to carry in the field, though.
I have a couple of guns with 28-32" barrels, though, and I'll take them anyday in a velocity shootout......

IC B2

Joined: Dec 2000
Posts: 29,348
Campfire Ranger
Offline
Campfire Ranger
Joined: Dec 2000
Posts: 29,348
By "burn rate," I assume, you mean quickness. (Burn rate is a property of the powder substance and varies with the pressure it's burning under -- expressed as so much of an inch per second at such and such a pressure.)

The length of the barrel has nothing whatever to do with either the linear burning rate of the powder substance nor the quickness of its granulation. Let's look at how an expert determines the optimum powder for a brand-new cartridge, which should give you some idea of how powder quickness comes into consideration. Let's say that you (an expert) have created a new cartridge and now want to determine which powder will be its best.

Your first premise is that the powder charge will just fill the case to the base of the bullet (or nearly so -- not less than, say, 90% to 95% of the space behind the seated bullet).

First, you decide on the maximum peak chamber pressure that you want your new cartridge to develop with the one chosen bullet seated to a specified depth -- leaving, IOW, a known space to be filled.

Then the powder to be chosen (or created) is the one that meets both basic criteria -- a caseful of powder that produces no more than the desired maximum peak pressure.

The goal of the handloader is to find the canister powder that exactly or most nearly meets these criteria. Notice that there's no mention of barrel length. Barrel length does not produce or influence peak chamber pressure, therefore does not bear on the optimum burning rate or quickness.

In general, (a) a powder that's slower than the optimum can fill the case 100% and not produce the specified maximum peak pressure, and (b) a powder that's faster than the optimum produces the specified maximum peak pressure with somewhat less than a 100% case fill. The former is safe, the latter dangerously susceptible to overloading.


"Good enough" isn't.

Always take your responsibilities seriously but never yourself.



















Joined: Jan 2002
Posts: 1,195
Campfire Regular
Offline
Campfire Regular
Joined: Jan 2002
Posts: 1,195
Here's another place where the S/W Program Quick-Load can answer questions for the Internal-Ballistically challenged (or just the curious), by presenting graphs and numbers that attempt to model the process.

I plugged in a generic .300 Win mag, 24 inch barrel, COAL=3.340"
and Nosler #4 book-safe load of 75grs RL-22.

Even though the barrel is 24 inches long, that includes the chamber, so the bullet actually starts at about the 3 inch point. The peak pressure occurs just about the time the bullet clears the case mouth (ie: has moved only .6 inches forward ... its seated depth).

Barrel position " - Psi (rounded) -- % of powder burnt by this position -- Velocity

3.5--- 61K -- 52 -- like a snail
5 --- 60 K -- 57 -- 1400
10--- 38 K -- 86 -- 2200
15--- 26 K -- 95 -- 2650
20--- 19 K -- 98 -- 2900
24--- 15 K -- 99 -- 3050

As you can see, with 95% of the powder burnt by the time the bullet has reached the 15 inch point in the barrels length, most of the additional velocity gained is from the existing pressure (behind the bullet), not from the last couple percent of unburned powder being burned. Hope this helps visualize it ..

... Silver Bullet

Joined: Mar 2002
Posts: 4,208
J
Campfire Tracker
Offline
Campfire Tracker
J
Joined: Mar 2002
Posts: 4,208
Excellent point---
The rapidly expanding gases(created by burning powder) do the velocity work. The longer the barrel, up to a certain point, allow the gases to push on the bullet for a longer period of time, hence an increase in velocity with the same max pressure.

Joined: Dec 2002
Posts: 32
Campfire Greenhorn
Offline
Campfire Greenhorn
Joined: Dec 2002
Posts: 32
A lot of noise is made about how a "long" barrel helps the velocity with standard cartridges like the .243, .270 and .30-06, but the reality is somewhat different. Data published in the November 1981 issue of G&A indicated that barrel lengths over 24" are not a practical advantage:

6mmRem 100-grain handload:
26" 3162 fps
24" 3127
22" 3077

Same source:
.30-06 165-grain handload:
26" 2896 fps
24" 2850
22" 2820

Even the Magnums aren't always crippled by shorter barrels...
7mm Rem Mag 150-grain handload:
26" 3185 fps
24" 3131
22" 3035

That extra 35 to 54 fps with the 26" barrel is of course meaningless in any practical sense, but that extra 2" of barrel length can effect the handling and weight of the rifle. Nothing wrong with long barrels, but their advantages are usually substantially overstated...for standard cartridges at least. Most factory actions will not tolerate 28-32" barrels without some bending ( which effects the potential accuracy ) unless they are reinforced or the barrels are relatively light in weight. My .257 Weatherbys carry 26" tubes, but most all the others are 24" or less.




Joined: Dec 2000
Posts: 29,348
Campfire Ranger
Offline
Campfire Ranger
Joined: Dec 2000
Posts: 29,348
Also check the "difference" in down-range performance. There virtually isn't any practical difference that you can tell. Both the velocity loss and the increase in drop are infinitesimal at close range, minuscule at even several hundred yards. Often, the difference is less than one scope click, less than the spread of the ten-shot group. OTOH, the shorter barrel is generally stiffer, more likely to print smaller groups.


"Good enough" isn't.

Always take your responsibilities seriously but never yourself.



















IC B3

Joined: Feb 2002
Posts: 13,374
Campfire Outfitter
Offline
Campfire Outfitter
Joined: Feb 2002
Posts: 13,374
Man, more practical statements. You guys are starting to make me wonder if you are 'gun-nuts'!! <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Joined: Jan 2001
Posts: 9,034
Campfire Outfitter
Offline
Campfire Outfitter
Joined: Jan 2001
Posts: 9,034
I do prefer heavier longer barrels on some rifles that will see use for long range or high volume shooting. I'm concerned about the barrel weight stressing the action so I bed the stock out to the point of ballance of the barreled action. I hope this will relieve any stress on the action from that heavy barrel hanging out there. I know it won't keep a long barrel from saging, which is why i like heavier barrels if I am going to have them cut long. Any barrel 24 inches long is going to be at least a #4 contour, 26 inch barrels are at least a #5.

Heavier barrels seem to have more stable harmonics under the heat of high volume shooting. Longer barrels seem to be easier for me to hold steady from a sand bag rest for long range bean field deer shooting or prairie dog shooting in the next zip code.

I don't really choose a long barrel because it will give me an additional 50 fps per inch, but it's a nice extra that I won't turn down. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Those are just my observations and opinions bassed on my experience. If anyone has a more educated or experienced theory please share it with us.


"The only thing necessary for the triumph of evil is for good men to do nothing."
Edmund Burke 1795

"Give me liberty or give me death"
Patrick Henry 1775

Moderated by  RickBin 

Link Copied to Clipboard
CTV
Who's Online Now
586 members (19rabbit52, 163bc, 10ring1, 10Glocks, 1234, 1beaver_shooter, 66 invisible), 1,583 guests, and 1,009 robots.
Key: Admin, Global Mod, Mod
RR2/3-22



 







Fish & Game Departments | Solunar Tables | Mission Statement | Privacy Policy | Contact Us | DMCA
Hunting | Fishing | Camping | Backpacking | Reloading | Campfire Forums | Gear Shop
Copyright © 2000-2023 24hourcampfire.com, Inc. All Rights Reserved.
 
Powered by UBB.threads™ PHP Forum Software 7.7.5
(Release build 20201027)
Responsive Width:

PHP: 7.3.33 Page Time: 0.048s Queries: 13 (0.003s) Memory: 0.8818 MB (Peak: 1.0122 MB) Data Comp: Zlib Server Time: 2023-06-01 16:50:43 UTC
Valid HTML 5 and Valid CSS