243 or 270 for short barrels?
- Thread starter Grey Morel
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Legionnaire
Contributing Member
Good thread; not much I can add. I have Remington Model 7s in both .243 and .308. I've been playing around some with load development, and thus far can add the following observation: Much easier to approach published velocities with the .308 than the .243 in the 7s' shorter barrels. Don't have my notes in front of me, or I could add specific velocities. But no doubt the .243 is giving up a significant amount in the shorter barrel using the 100 grain PSPs I've been using.
And to the OP's original question, I'd still opt for the .243 over the .308 for varmints at reasonable ranges.
And to the OP's original question, I'd still opt for the .243 over the .308 for varmints at reasonable ranges.
Legionnaire
Contributing Member
I've been thinking about this thread since reading it a couple of days ago. Something was nagging, and that was a sense that the overbore table in krochus' post seemed to be missing something. I'm not a physicist and am only a relatively new reloader. But it seemed to me that the table leaves out some important variables: notably powder bulk and energy (burn rate) and bullet weight. So I did some additional digging on the web and came up with the link below:
http://ninthstage.com/index.php/2008/05/06/overbore/
I'd be interested to hear what some of you others think about the arguments made there. Regardless, I'm thinking that the key shooting .243 Win cartridges in short barrels is to custom build your ammo to the task. I think I suspected this because of knowing that there are special reloading data for T/C Contenders and Encores, with their shorter barrels. Thoughts?
http://ninthstage.com/index.php/2008/05/06/overbore/
I'd be interested to hear what some of you others think about the arguments made there. Regardless, I'm thinking that the key shooting .243 Win cartridges in short barrels is to custom build your ammo to the task. I think I suspected this because of knowing that there are special reloading data for T/C Contenders and Encores, with their shorter barrels. Thoughts?
R.W.Dale
Member
You're putting the chicken before the egg.
My chart does not leave out burnrate because that is completely dictated by bore case ratio and bullet weight. Barrel length is irrelevant. Just look at the cited hodgdon data and you'll note that the top performing propellants are by in large also the top performers in a handgun.
Why is this? It's because guns unlike rockets don't rely on thrust from a continuously burning fuel source. Folks think burn rate is linear with bullet travel down the entire length of the bbl. This is false. But rather burn rate really just relates to the first couple of inches of bullet travel after which the powder is all consumed (that can burn) and pressure is dropping rapidly as the volume in the bore/chamber increses.
To get the highest velocity possible with any given cartridge you want to burn the largest quantity of the slowest propellant (most energy) that the cartridge can just reach max pressure with. Using a lesser quantity of a faster powder will ALWAYS result in a lower MV in all bbl lengths is the same pressure levels are maintained
a very informative discussion we had on this
http://www.thehighroad.org/showthread.php?t=498504&highlight=powder+fast
My chart does not leave out burnrate because that is completely dictated by bore case ratio and bullet weight. Barrel length is irrelevant. Just look at the cited hodgdon data and you'll note that the top performing propellants are by in large also the top performers in a handgun.
Why is this? It's because guns unlike rockets don't rely on thrust from a continuously burning fuel source. Folks think burn rate is linear with bullet travel down the entire length of the bbl. This is false. But rather burn rate really just relates to the first couple of inches of bullet travel after which the powder is all consumed (that can burn) and pressure is dropping rapidly as the volume in the bore/chamber increses.
To get the highest velocity possible with any given cartridge you want to burn the largest quantity of the slowest propellant (most energy) that the cartridge can just reach max pressure with. Using a lesser quantity of a faster powder will ALWAYS result in a lower MV in all bbl lengths is the same pressure levels are maintained
a very informative discussion we had on this
http://www.thehighroad.org/showthread.php?t=498504&highlight=powder+fast
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Legionnaire
Contributing Member
I hear you, but am still wrapping my head around it. I understand that burn rate is not linear, and that there is a peak pressure. But "fast" versus "slow" powders peak at different times, don't they? Don't you want the curve to peak just prior to the projectile leaving the barrel? In the other thread, you said that using a "faster than optimum powder will not provide more velocity in a shorter barrel ..." suggesting that there IS an "optimum." No doubt I'm missing something.
R.W.Dale
Member
From what Ive seen generally speaking pressure peaks right as the bullet hits the rifling or thereabouts. After that point gas pressure is dropping off rapidly because the space inside the bbl it has to fill is increasing as the bullet travels. pressures at the muzzle are a mere fraction of what they were at the chamber.
RcModel has an excellent post here that explains this relationship
http://www.thehighroad.org/showpost.php?p=5974432&postcount=5
Folks get hung up because they relate powder burn to the entire bbl length. When in reality it just relates to that first couple inches before the bullet has a chance to start "getting out of the way"
Legionnaire
Contributing Member
Appreciate your patience ... think I'm almost there. So, in a nutshell, what makes a powder "too fast" or "too slow?" Weight of the projectile?
R.W.Dale
Member
Amongst a few other things. Remember the bore is a set size so that effects how the pressure drops (through expanding volume) in relation to how it builds from the burnt propellant.
a gross over simplification
Too fast a propellant in relation to the bullet weight, bore size and case capacity and the pressure can spike before moving the bullet uncovers sufficient volume to keep pressure in check.
Too slow a propellant and the bullet and therefore expanding volume outruns the powders ability to turn to gas resulting in low pressures and MV's
The important thing to take from this is that all this occurs just as the bullet starts moving
a gross over simplification
Too fast a propellant in relation to the bullet weight, bore size and case capacity and the pressure can spike before moving the bullet uncovers sufficient volume to keep pressure in check.
Too slow a propellant and the bullet and therefore expanding volume outruns the powders ability to turn to gas resulting in low pressures and MV's
The important thing to take from this is that all this occurs just as the bullet starts moving
Legionnaire
Contributing Member
Thanks! Very helpful! If I understand ...
Again, many thanks.
... with potentially cataclysmic consequences because the pressure has to go somewhere. And as you note, too slow can reduce pressure and velocity.
Again, many thanks.
Art Eatman
Moderator In Memoriam
Somewhere on the Inet is a bunch of graphs of pressure curves for rifles. Been a good number through the years in some of the gunzines. My memory has it that that the peak pressures for rifles seem to occur about one-third of the way through the time of burning--or a probably-standard sort of barrel length, whatever. (The curve won't vary with length, of course, but most barrels are in the 22"-24" range, SFAIK.)
Legionnaire, a generality would be that slower powders require longer barrels for maximum effectiveness. This is particularly true with overbore cartridges. Anyhow, the peak pressure isn't higher; it's that the powder burns longer. More area under the pressure curve.
Fast burn powders work for small "underbore" cartridges such as the .22 Hornet. In my ignorance, I'd think that the Hornet wouldn't gain much from barrels beyond 18 to 20 inches. OTOH, an '06 does very well with barrels of 26" when using slower-burn powders; even 30" barrels for the Very Long Distance shooters.
Legionnaire, a generality would be that slower powders require longer barrels for maximum effectiveness. This is particularly true with overbore cartridges. Anyhow, the peak pressure isn't higher; it's that the powder burns longer. More area under the pressure curve.
Fast burn powders work for small "underbore" cartridges such as the .22 Hornet. In my ignorance, I'd think that the Hornet wouldn't gain much from barrels beyond 18 to 20 inches. OTOH, an '06 does very well with barrels of 26" when using slower-burn powders; even 30" barrels for the Very Long Distance shooters.
Grey Morel
Member
I have a question for Krochus:
How does one determine the "optimum" case capacity for a given bore? Is there some kind of formula? If so is said formula based on empirical data, or the ever popular gun writer style wild guess ? Or is it more of a popular consensus / estimation?
How does one determine the "optimum" case capacity for a given bore? Is there some kind of formula? If so is said formula based on empirical data, or the ever popular gun writer style wild guess ? Or is it more of a popular consensus / estimation?
R.W.Dale
Member
WAG time
I would say it has most to do with the kind of ballistic performance you expect vs the sacrifices you're willing to make. If you shoot 1000yds + your probably a bit more ameiable to burning some extra powder through a long barrel that may wear out faster.
The guy shooting Bambi or steel 75 yds away will likely select a cartridge a that's a bit more fuel efficent that does better in his carbine lenght bbl.
That's why this thread got so hot. The OP's cartridge selection really didn't fit the intended use that well.
I would say it has most to do with the kind of ballistic performance you expect vs the sacrifices you're willing to make. If you shoot 1000yds + your probably a bit more ameiable to burning some extra powder through a long barrel that may wear out faster.
The guy shooting Bambi or steel 75 yds away will likely select a cartridge a that's a bit more fuel efficent that does better in his carbine lenght bbl.
That's why this thread got so hot. The OP's cartridge selection really didn't fit the intended use that well.
Been away for about a week and have not had a chance to respond to the posts on page 3. Will be away for about another week so I won't have a chance to respond again for a while.
You can play around with theoretical math equations all you want. I've seen the chronograph numbers on too many rifles.
There is never a time when a 308 will be faster than the 300 wm. I have never seen a barrel length where a 308 was faster than a 30-06 when they are shot from the same length barrel.
If you WANT a shorter barrel you can make a good argument that the bigger round is the better choice. It may lose a larger percentage of it's velocity, but because it starts faster, it will still be faster even from a shorter barrel. Yes, a 308 is more efficent than a 30-06. The 30-06 may have a 200 fps advantage when both are shot from a 24" barrrel. Go to a 20" barrel in both rifles and the 30-06 will still be faster. Possibly by only 180 fps now. Some of you are over thinking this.
A few other myths.
A powder and load combination that gives the fastest velocity from a long barrel will still be the fastest from a shorter barrel. There is no reason to go to a faster burning powder because you have a shorter than standard barrel length. All the powder, will burn within the first few inches no matter how fast or slow. The longer barrels allow more time for the pressure to increase, thus increasing velocity. I know this is hard for some to accept, but once again I've seen the chronograph results too many times.
Velocity loss is not linear. Most guns do just fine in barrels from 20"-24". With most guns you will probably see the biggest velocity losses/gains between 20" and 24". You can make a good argument that if you are going to go 20", you may as well drop down to the legal minimum of 16" since the velocity loss between 20" and 16" will likely be far less than what you lost between 24" and 20". Same thing if going longer. The gains in velocity will be less and less for each inch you gain over 24".
For a hunting rifle, in any caliber, select the barrel length that feels best to you and stop worrying about velocity. Even if you do lose 200 fps between a 24" barrel and a 20" barrel there is not a game animal in the world that will know the difference when you shoot it. If a bullet at 2900 fps is adequate the same bullet at 2700 fps, even 2500 fps, is not suddenly going to bounce off the hide. At 200-300 yards the trajectory is close enough to not matter, and at longer range we are talking about only 2-3" more drop.
You can play around with theoretical math equations all you want. I've seen the chronograph numbers on too many rifles.
There is never a time when a 308 will be faster than the 300 wm. I have never seen a barrel length where a 308 was faster than a 30-06 when they are shot from the same length barrel.
If you WANT a shorter barrel you can make a good argument that the bigger round is the better choice. It may lose a larger percentage of it's velocity, but because it starts faster, it will still be faster even from a shorter barrel. Yes, a 308 is more efficent than a 30-06. The 30-06 may have a 200 fps advantage when both are shot from a 24" barrrel. Go to a 20" barrel in both rifles and the 30-06 will still be faster. Possibly by only 180 fps now. Some of you are over thinking this.
A few other myths.
A powder and load combination that gives the fastest velocity from a long barrel will still be the fastest from a shorter barrel. There is no reason to go to a faster burning powder because you have a shorter than standard barrel length. All the powder, will burn within the first few inches no matter how fast or slow. The longer barrels allow more time for the pressure to increase, thus increasing velocity. I know this is hard for some to accept, but once again I've seen the chronograph results too many times.
Velocity loss is not linear. Most guns do just fine in barrels from 20"-24". With most guns you will probably see the biggest velocity losses/gains between 20" and 24". You can make a good argument that if you are going to go 20", you may as well drop down to the legal minimum of 16" since the velocity loss between 20" and 16" will likely be far less than what you lost between 24" and 20". Same thing if going longer. The gains in velocity will be less and less for each inch you gain over 24".
For a hunting rifle, in any caliber, select the barrel length that feels best to you and stop worrying about velocity. Even if you do lose 200 fps between a 24" barrel and a 20" barrel there is not a game animal in the world that will know the difference when you shoot it. If a bullet at 2900 fps is adequate the same bullet at 2700 fps, even 2500 fps, is not suddenly going to bounce off the hide. At 200-300 yards the trajectory is close enough to not matter, and at longer range we are talking about only 2-3" more drop.
Grey Morel
Member
Thanks Krochus, I had a feeling that it was more of a popular opinion that an actual fact. Either way it still interests me greatly, as I am firmly in the efficiency camp.
The 30 calibers may be more efficient for use in the rifle I originally envisioned, but the more I think about it the more it seems I need to pick a better rifle for the task.
Thanks again to everyone for the help, and the lively debate.
The 30 calibers may be more efficient for use in the rifle I originally envisioned, but the more I think about it the more it seems I need to pick a better rifle for the task.
Thanks again to everyone for the help, and the lively debate.
Yeah, I've been thinking Legionnaire's point for the last couple of days, too. There would seem to be variables that aren't accounted for in the chart (although the chart really isn't being advocated as a specific answer to the OP's question but, rather, as a general guide regarding case size, bore size, and a general correlation between the two concerning velocity. Legionnaire is thinking more about how different powders might burn (outside of the general overbore/slower burning powder point made by Art), as well as other possible variables like barrel vibration caused by different barrel length, etc..... But we could get ultra nit-picky about a million different variables, couldn't we?
The OP needs two rifles. One for varmints/targets, and one for deer/targets. How's that for a solution?
Maverick223
Member
Yes there is, if the powder burn is not complete (it is not always or even often in the first few inches) then you are pushing unburned powder out the muzzle along with the bullet. It is essentially unused mass, and this additional unwanted mass slows the projectile. Add in the fact that slower burning powder is used for magnum cartridges and this accelerates the deterioration in velocity from magnum cartridges.
Hi Grey,
I'm not big into ballistics so can't help with the technical particulars of velocity loss, etc. with various barrel lengths. However, I can't stand long barrels, so I don't own anything with more than a 20" barrel on it. From my own experience hunting coyotes, the barrel length really doesn't matter. I'd be more concerned with accuracy than the miniscule differences in FPS/LBS between different barrel lengths in either of those calibers.
That said, I'd go with the .243 if I were you, simply because it's a much cooler round to play with - so many options in terms of bullet weights, etc. Not to mention the fact it will be easier on your shoulder and more fun to shoot if you are hunting prairie dogs or just plinking around on a weekend with it. I don't think I'd enjoy walking around plinking at rabbits or prairie dogs with a .270 all that much...
I'm not big into ballistics so can't help with the technical particulars of velocity loss, etc. with various barrel lengths. However, I can't stand long barrels, so I don't own anything with more than a 20" barrel on it. From my own experience hunting coyotes, the barrel length really doesn't matter. I'd be more concerned with accuracy than the miniscule differences in FPS/LBS between different barrel lengths in either of those calibers.
That said, I'd go with the .243 if I were you, simply because it's a much cooler round to play with - so many options in terms of bullet weights, etc. Not to mention the fact it will be easier on your shoulder and more fun to shoot if you are hunting prairie dogs or just plinking around on a weekend with it. I don't think I'd enjoy walking around plinking at rabbits or prairie dogs with a .270 all that much...
Hello gunners, I'm new to this site so please bear with me. I just aquired a mint Remington 788 in .243, carbine - short tube, think it's 1 in 9 twist. Took two antelope Oct. last year in wyoming, both inside of 150 yds. My concern or interest would be any suggestions for a load that will optimize that rig for deer / antelope / coyote for the max. range (inside 300) for me. It wears an old 2x7 Redfield, I'm using a 90 grain bullet...good groups 100, 200 yds., big drop at 300. Heavy rig, even with the short barrel, love shooting it - recoil like a .22.. but would like to go to a heavier slug, if possible...or reasonable. Have not chroned that load, custom through Conley Precision Cartridge...I know I'm probably losing 200 fps. + from a 22 / 24 inch barrel. Any thoughts appreciated. Powder / bullet 100 gr., .....Thanks!
JerryM
Member
I much prefer 22" barrels in standard cartridges for deer and above game.
As far as performance my handloads in my .243 WCF 100 gr and .270 WCF 130
M70 FWT pre 64 rifles with 22" barrels chrono 3150 and 3100 respectively.
I often wonder if those who are so set against 22" barrels have ever owned or chronogrphed one.
I could not say that the .243 and .270 are the best for short barrels. I see no reason why other cartridges like the .308 and 30-06 are not as efficient. Maybe a little more efficient. However, I don't really care about efficiency, but what performance I am getting out of the individual rifle.
Regards,
Jerry
As far as performance my handloads in my .243 WCF 100 gr and .270 WCF 130
M70 FWT pre 64 rifles with 22" barrels chrono 3150 and 3100 respectively.
I often wonder if those who are so set against 22" barrels have ever owned or chronogrphed one.
I could not say that the .243 and .270 are the best for short barrels. I see no reason why other cartridges like the .308 and 30-06 are not as efficient. Maybe a little more efficient. However, I don't really care about efficiency, but what performance I am getting out of the individual rifle.
Regards,
Jerry
I have to agree with some of the people that would choose the 7mm-08. This round is a sleeper which has a flatter trajectory than the 308 and the 30-06. The recoil is less than the 308 and at 300 yds delievers more energy ballistically using a 140 grain bullet vs the 150 grain bullet of the 308 and about the same energy of the 30-06 with the 150 grain remington core-lokt. This caliber would make a great scout rifle.
Of course there is always the venerable 30-30 winchester or the 35 remington. But since you wanted a varmint rifle as well the 7mm-08 makes it a wonderful caliber for varmint as well as big game.
Of course there is always the venerable 30-30 winchester or the 35 remington. But since you wanted a varmint rifle as well the 7mm-08 makes it a wonderful caliber for varmint as well as big game.
Thanks Jerry...no, I agree...I just sort of inherited the carbine. Have a lot of rifles 22" to 26" bbls., I'm just sort of stuck with the 18" (ouch) tube. Fun to shoot though. Makes me wonder why Rem. would produce that rig...given the velocity drop.
unwise11
Member
.338 Federal = .308 case necked up to .338, perfect for a brush gun.
Art Eatman
Moderator In Memoriam
Duckdude, if you still have questions after reading through this year-old thread, feel free to start a new thread.
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