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Author Topic: Barrel length vs. accuracy  (Read 9494 times)

Thernlund

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Barrel length vs. accuracy
« on: September 14, 2009, 08:24:49 AM »
I remember a nice little debate that went on a while back about barrel length vs. accuracy.  I believe it was in one of Harm's threads.  I took the position that a short barrel (18", even 16" bull) was just fine for .308 accuracy, while others suggested that a short barrel would degrade accuracy.  While certainly a respectable debate on everybody's part, it did actually began to derail the thread some from the intended topic.

So in this new thread, I offer this for your consideration...

Quote
Appropriate barrel length for sniper rifles has been debated at length in tactical communities and online forums alike. In the spirit of GPS Defense’s teaching principle of deciphering the truth out of the piles of opinions by testing a theory and seeing the results first hand, we decided to put the barrel length issue to rest.

As our previous students can attest, and as you will experience in any of our classes, we often choose to prompt our students to figure out the answer to a question or previously held belief on their own. Chances are, we have encountered their question or opinion many times before and we have learned that the reason they are led to believe a certain point is simply because somebody else told them it was so. If we do the easy thing by simply telling them the correct answer, the truth we tell them will have no more weight in their mind than the possibly incorrect information that has been unquestioned and passed down from person to person.

Simply put, barrel length (within reason) does not affect accuracy within a manner many people believe. My personal rifle, based off of a Remington 700 action, has an 18? .308 barrel. When people see my rifle, they often ask, “How much does that affect the accuracy?”

Their question, although a valid one, is usually asked in such a way that assumes accuracy must have been compromised in order for the barrel to be so short. The exact opposite is true.

My rifle came from the factory with acceptable sub minute of angle (less than 1? group per 100yds) accuracy out of a 26? barrel. I had my barrel cut down to 18?, took it out to the range and was pleasantly surprised to see the accuracy improve to a 1/2 minute of angle. Yes, you just read that right… the shorter barrel was more accurate.

When I dropped off the rifle to have it cut and re-crowned from its factory length, the gunsmith asked how short I wanted the barrel to be, and when I told him 18?, he tried his best to talk me out of it. He explained to me that 20? is a “safe” length and about as short as he has seen people go while maintaining accuracy. I decided that since I was cutting the barrel to create a more manageable and compact shooting platform and partly to prove a point, I shouldn’t go to a “safe” length…. I should go shorter.

A common argument I hear from disbelievers revolves around some sort of belief that the twist rate must relate to the barrel length. This fallacy tries to say that since the twist rate of my .308 700 PSS is 1 in 12?, the barrel must be cut to a length in multiples of 12 inches in order for the bullet to spin properly. This is absurd. If this was true, Remington would never ship the PSS from the factory with a 26 inch barrel. And for that matter, a 1911 style .45 with a twist rate of 1in 16? would have a 16? barrel in order to be able to hit the target.

So, if a bullet from my barrel is spinning at a 1 in 12? rate regardless of the length, why did cutting it down increase the accuracy? The answer lies in the effect of barrel stiffness. We all understand that a thicker bull barrel will provide better accuracy than a thin sportster style barrel. From this we know that a stiffer barrel helps increase accuracy by negating excessive barrel flex and vibration. The only way to stiffen an already stiff bull barrel from the factory is to shorten it. Let me explain….

Inch per inch, the barrel’s stiffness has not changed. But when taking the entire length into account, the overall effect is a stiffer barrel. Think about a 2 inch stick that is just stiff enough to be unbreakable. Now, take a stick of the same diameter with a length of 12 inches…. it would be much easier to break. Each individual inch of the two sticks share the same rigidity, but the longer stick allows more leverage to be imparted on the stick and therefore nets less overall stiffness and more leverage.

So, by cutting the barrel, the twist rate was not affected and the barrel was relatively stiffer. The only other concern lies in whether or not the powder has enough time to burn before the bullet leaves the barrel. This should not affect accuracy since it should burn consistently whether or not it burns completely. The only problem will in fact lie in the change in velocity of the bullet.

At 100 yards, I found absolutely no change in the point of impact of the bullet from the longer 26? original length to the new shorter 18? length. I did, however find a significant difference at longer distances.

At our 920 yard target on our range, school rifles with standard length barrels are able to hit the target with a 34 minute of angle adjustment above their 100 yard zero. When I first shot my rifle to compare the bullet drop from my rifle with the short barrel to the school rifles, I was using 168 grain Federal Gold Match ammunition and recorded hits at 39 1/2 minutes up from my 100 yard zero. That translates into a little over 50 inches of difference between the barrel lengths at 920 yards!

After realizing that the powders used by Federal (ammo I used) and Black Hills (ammo the students use) may burn at different rates, I decided to re-test my rifle with the 175 grain Black Hills Match ammunition that our students use. When using the same ammo, my rifle only needed 36 minutes of elevation in order to hit the target. Based on changing the ammo, I had a 3 1/2 minute change at 920 yards! Using consistent ammo and consistent environments, my 18 inch barrel only requires two additional minutes of elevation to engage a target 920 yards away!

With a more manageable, compact, lighter, and more accurate rifle only requiring only 2 more minutes of angle at 920 yards, I see no reason to not cut down a barrel on a sniper rifle. Still don’t believe me? Enroll in a class and I will shoot my short barrel rifle next to yours and you can learn what happens in the manner we suggest the most… you can see for yourself.

–Ryan Cleckner


SOURCE:  http://www.sniperschool.com/sniper-rifle-barrel-length/

Discuss.


-T.
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Coronach

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Re: Barrel length vs. accuracy
« Reply #1 on: September 14, 2009, 09:35:25 AM »
The usual accuacry degradation due to shorter barrel length is experienced on iron-sight rifles where shortening the barrel reduces the sight radius. Even then, the rifles aren't mechanically less accurate, the sight system is just less precise in practical use (think full-length M16 vs M4). Naturally, muzzle velocity suffers as well, which means that the bullet will stay supersonic for a shorter distance. It could have stability issues when it goes subsonic. It will go subsonic eventually from either a long- or short- barreled rifle, of course, but the transition occurs sooner if your rifle barrel is short.

Mike
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only1asterisk

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Re: Barrel length vs. accuracy
« Reply #2 on: September 14, 2009, 11:50:29 AM »
The usual accuacry degradation due to shorter barrel length is experienced on iron-sight rifles where shortening the barrel reduces the sight radius. Even then, the rifles aren't mechanically less accurate, the sight system is just less precise in practical use (think full-length M16 vs M4). Naturally, muzzle velocity suffers as well, which means that the bullet will stay supersonic for a shorter distance. It could have stability issues when it goes subsonic. It will go subsonic eventually from either a long- or short- barreled rifle, of course, but the transition occurs sooner if your rifle barrel is short.

Mike

Right.  A shorter barrel is stiffer, all else being equal.  When you cut take 6" or 8" of barrel off the attendant velocity loss reduces your potential for downrange accuracy.  An 18" or 20"  is going enter the transonic range at just over 500 yards +/- depending on the bullet.  The reduced velocity means more time for wind to act on your bullet.  Using 175 SMK for example netted about 15% more drift in a standard 10mph crosswind. 

I notice that the author of the blurb that Thernlund posts doesn't shoot for groups at the longer range, but instead records "hits".   I don't consider "hits" as a useful measure of accuracy. 

An 18-20" .308 might be able to hold it's own to 300 yards or so maybe a bit more on targets of known range in ideal conditions.  When you start talking about 400 yards or so, the loss in velocity is really going to amplify all range estimation and wind reading reading error.  Past the point where the bullet goes transonic you have to add that variability in as a well. 

Shorter barrels don't inhibit excellent mechanical accuracy.  They do give up significant velocity which will invariably inhibit practical accuracy downrange.  The real question is this:  Do the advantages in weight and handling outweigh the loss of precision as range to the target increases? 


Thernlund

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Re: Barrel length vs. accuracy
« Reply #3 on: September 14, 2009, 12:44:23 PM »
.308 will get (average based on found examples) 2550fps out of an 18" barrel.

A 168gr .308 BTHP Matchking has a BC of .447 as per Sierra.

The speed of sound is what?  About 1100fps?

By my math, a 168gr SMK is still moving faster than 1100fps at 1000 yards.

Recalculated for a 16" barrel (2550 - 100 = 2450fps), the same bullet is still barely supersonic at 1000 yards.

Taking into account a reasonable margin of error, you're still comfortably supersonic at 800, and pushing 900+.  Hotter ammo will get you to 1000 consistently.

No?

Powder is a big factor of course.

There's also this...

http://www.tacticaloperations.com/SWATbarrel/


-T.
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only1asterisk

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Re: Barrel length vs. accuracy
« Reply #4 on: September 14, 2009, 12:58:27 PM »
.308 will get (average based on found examples) 2550fps out of an 18" barrel.

A 168gr .308 BTHP Matchking has a BC of .447 as per Sierra.

The speed of sound is what?  About 1100fps?

By my math, a 168gr SMK is still moving faster than 1100fps at 1000 yards.

Recalculated for a 16" barrel (2550 - 100 = 2450fps), the same bullet is still barely supersonic at 1000 yards.

Taking into account a reasonable margin of error, you're still comfortably supersonic at 800, and pushing 900+.  Hotter ammo will get you to 1000 consistently.

No?

Powder is a big factor of course.

There's also this...

http://www.tacticaloperations.com/SWATbarrel/


-T.


I didn't say supersonic.  I said transonic.  Big difference.  The transonic range is going to be slightly different for every bullet, but 1600 fps is a pretty good average starting point.  The 175 SMK @ 2557fps from an 18" is what I used as a base for my above examples.



As for the article you post:

Anyone that is telling you that cutting a .300 Win Mag back from 26" to 22" will no lose any velocity is pissing on your leg and telling you it is raining. 

If you read the article carefully, you will that all this "information" comes from a company invested in selling people on shorter barrels.   Their velocity claims are based on instrumental velocities from single barrels and their accuracy claim is based on a single 3 shot group.  This is anecdote, not data. 

« Last Edit: September 14, 2009, 01:37:23 PM by only1asterisk »

Thernlund

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Re: Barrel length vs. accuracy
« Reply #5 on: September 14, 2009, 01:26:04 PM »
I've heard you say that before.  1600 is a bit high isn't it?  Transonic range would be about 800fps to 1350fps (which is still 750 yards+).

I can't read that chart.  Have a bigger one?

I think I can make out that that's a 300 grain bullet.  Not exactly an apples-to-apples comparison of what we were talking about, eh?


-T.
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Re: Barrel length vs. accuracy
« Reply #6 on: September 14, 2009, 01:40:48 PM »
This is why I selected the 20 inch XCR Compact Tactical over the 24 inch XCR Long Range.   I've shot them side by side and the 20 inch groups tighter.  The trade off is velocity.  I give up some 150 FPS to achieve greater accuracy.  I'm fine with that.   You wont feel the difference.
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Re: Barrel length vs. accuracy
« Reply #7 on: September 14, 2009, 02:06:59 PM »
I think it was Clint Smith who took a 26 in heavy barreled .308 and .300WMag and had shot them for grouping at distance and then had them repeatedly cut and reshot in increments of 2 inches all the way down to 18 inches.  I believe the loss was nothing more than FPS but I don't have a link for you.  I'm sorry on that one.  Maybe an old issue of GUNS has it. 
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only1asterisk

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Re: Barrel length vs. accuracy
« Reply #8 on: September 14, 2009, 02:32:55 PM »
I think it was Clint Smith who took a 26 in heavy barreled .308 and .300WMag and had shot them for grouping at distance and then had them repeatedly cut and reshot in increments of 2 inches all the way down to 18 inches.  I believe the loss was nothing more than FPS but I don't have a link for you.  I'm sorry on that one.  Maybe an old issue of GUNS has it.  

Losing velocity is losing practical accuracy.  While a shorter barrel may make no difference or tend toward slight improvement (which is probably the best way of stating it) at 0-200 yards is not really up for debate.  That's pretty much a given.  

The idea that I putting forward here is that there comes a point where that 150-200fps of lost velocity becomes more important than the slight increase in barrel stiffness.  I'm going to call this point 350 yards. Arbitrary?  Maybe... Proving it would require a substantial and I not sure how to remove the human element from testing. 

To me, the bottom line is a .10" better aggregate at 200 isn't as important as reducing the effect of my wind reading error at 600. 







« Last Edit: September 14, 2009, 03:11:55 PM by only1asterisk »

Harm

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Re: Barrel length vs. accuracy
« Reply #9 on: September 14, 2009, 02:43:56 PM »
I think the article T quoted said 900 plus yards actually...  So what exactly are you arguing?   :devillol
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Re: Barrel length vs. accuracy
« Reply #10 on: September 14, 2009, 03:17:02 PM »
I think the article T quoted said 900 plus yards actually...  So what exactly are you arguing?   :devillol

I'm talking about the second article T. linked to in the post I quoted.  Do try to keep up!  ;D

I don't think the first article mentioned shooting groups of any kind.  Just hitting (steel, I assume) targets.

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Re: Barrel length vs. accuracy
« Reply #11 on: September 15, 2009, 11:12:23 PM »
Losing a bit of velocity isn't all that big of a deal if you keep it reasonable.... what it effects negatively is the distance at which the 168 grain .308 projectile goes transonic and hits that aerodynamic speed bump that effects accuracy and further degrades speed and energy.  Normally a .308 does this at about 900 yards or a little further.  Shorter, this happens around 850 from what I can tell - at least in my XCR.  Again - from what I can tell.  I don't have a Chrono that I want to put up out there at that range and try to shoot through to see what the bullet is actually doing.  But the XCR Compact Tactical, while able to hit a 1000 yard target, isn't what I'd call a 1000 yard gun.  I like to keep it to 800 yards.   I can stalk in 200 yards closer.   And you'll never know it. 
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Re: Barrel length vs. accuracy
« Reply #12 on: September 16, 2009, 02:33:56 AM »
I like to keep it to 800 yards.   I can stalk in 200 yards closer.   And you'll never know it. 

Every time George says that I get a chill and this insatiable need to duck for cover and look over my should quickly! 
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Re: Barrel length vs. accuracy
« Reply #13 on: September 16, 2009, 04:17:23 AM »
and isn't a shorter barrel stiffer? which helps to offset any accuracy losses?


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Re: Barrel length vs. accuracy
« Reply #14 on: September 16, 2009, 06:24:48 PM »
At LRI last year we saw an 18" barreled DPMS SASS go transsonic/subsonic between 800 and 900 yards using 168 gr SMK Black Hills Match ammo.  At 800 yards it was ringing steel consistently - suddenly at 900 yards it was all over the place: bouncing in the dirt, skipping into the steel, hitting the steel high or low, rounds flying high.  A 20" barreled Savage 10FP was ringing at 1000 yards with regularity.  Between those two rifles the 2" made a big difference.

I would not be surprised if a given gun managed to hold velocity, and thus accuracy, out to 900 or 1000 yards with an 18" barrel but I would also not be surprised if it fell off.  All the desktop ballistic calculators in the world will not replace the facts of what the rifle will do in the field.  And that is the only time barrel length really affects mechanical accuracy: loss of velocity at range.  This "stiffness" argument is really well within the margin of error of the typical shooter.  If you are winning NRA High Power matches then maybe you are enough of a shooter to see the delta caused by barrel stiffness but I think it would be silly for most shooters to go stampeding to cut inches off their barrel in pursuit of some "stiffness enhancement" for accuracy.  Shorten the barrel to make a handier rifle, if you are not shooting beyond 800 yards then why carry 24" of barrel if you will never need the velocity at range?

Thernlund

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Re: Barrel length vs. accuracy
« Reply #15 on: September 16, 2009, 06:47:08 PM »
I just love this video...



(I am NOT picking a fight or trying to contradict anyone or even making a point.  It's juts a relevant video and I enjoy it.)


-T.
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Re: Barrel length vs. accuracy
« Reply #16 on: September 16, 2009, 06:59:50 PM »
Question does the can act like extra barrel but with out the rifling? so a 18" barrel with a 6" can is actually a 24" barrel theretically because the can allows 6 more inches of gas to push the bullet?

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Re: Barrel length vs. accuracy
« Reply #17 on: September 16, 2009, 07:14:10 PM »
No.  The bullet is free inside the suppressor.


-T.
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Re: Barrel length vs. accuracy
« Reply #18 on: September 16, 2009, 07:25:23 PM »
Aye I get that, my thought is that as it is still traveling through the baffels not all of the gas has escaped thus still pushing it along and giving it an extra boost compared to it coming out of the barrel and thats it?

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Re: Barrel length vs. accuracy
« Reply #19 on: September 16, 2009, 07:41:42 PM »
Pretty much verifies what I first read in "Ultimate in Rifle Accuracy" and verified with my Remington 700 LTR. I have no valid opinion on long range shooting as I my range tops out at 225 yards, but at shorter ranges the LTR is a 1/2"-3/4" MOA rifle and easily the most accurate I've ever owned. I've thought about trimming my XR100 to 20" as well but I can't imagine getting better groups than the 1/4"-1/2" I'm already getting.
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Re: Barrel length vs. accuracy
« Reply #20 on: September 16, 2009, 07:56:17 PM »
Aye I get that, my thought is that as it is still traveling through the baffels not all of the gas has escaped thus still pushing it along and giving it an extra boost compared to it coming out of the barrel and thats it?

It sometimes can, but not always.  When it does it doesn't amount to much. 

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Re: Barrel length vs. accuracy
« Reply #21 on: September 17, 2009, 12:51:59 AM »
Noobtard question:  If you employ a faster burning powder, will you get more velocity out of a shorter barrel?
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Re: Barrel length vs. accuracy
« Reply #22 on: September 17, 2009, 01:15:38 AM »
Noobtard question:  If you employ a faster burning powder, will you get more velocity out of a shorter barrel?

No, that's a good question.  The noobtarded questions are things like "wut skope can u use 2 maek 5 miles hed shots?"
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Re: Barrel length vs. accuracy
« Reply #23 on: September 17, 2009, 01:30:08 AM »
Noobtard question:  If you employ a faster burning powder, will you get more velocity out of a shorter barrel?

Given the range of appropriate burning rates and pressure limitations we see in the real world, short and long barrels usually react similarly to different powder burn rates - ie the same loads that are faster out of long barrels are also faster out of short barrels.

Here are some QuickLoad tables calculated for 24" and 16" barrels respectively:

Quote
Cartridge           : .308 Win.
Bullet              : .308, 168, HDY BTHP Natl M 30501
Cartridge O.A.L. L6 : 2.800 inch or 71.12 mm
Barrel Length       : 24.0 inch or 609.6 mm

Predicted Data for Indicated Charges of the Following Powders.
Matching Maximum Pressure: 62000 psi or 427 MPa

or
Matching Loading Ratio (Filling, ''Load Density''): 100 %

These calculations refer to your specified settings in QuickLOAD 'Cartridge Dimensions' window.
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load ordering can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !

Powder type          Filling/Loading Ratio  Charge   Vel. Prop.Burnt P max  P muzz  Btime
                                      %     Grains    fps     %       psi     psi    ms
---------------------------------  -------------------------------------------------------
Rottweil R901                       97.3     42.1    2742   100.0    62000    7816   1.153  !DANGEROUS LOAD-DO NOT USE!
SNPE Vectan Sp 7                   100.0     47.6    2713    98.5    54768    8669   1.183  ! HOT LOAD !
Winchester 760                     100.0     48.4    2687    93.8    51116    9095   1.204
Rottweil R907                      100.0     46.4    2687    97.3    50583    8884   1.208
Alliant Reloder- 7                  88.6     38.5    2660   100.0    62000    6800   1.171  !DANGEROUS LOAD-DO NOT USE!


Quote
Cartridge           : .308 Win.
Bullet              : .308, 168, HDY BTHP Natl M 30501
Cartridge O.A.L. L6 : 2.800 inch or 71.12 mm
Barrel Length       : 16.0 inch or 406.4 mm

Predicted Data for Indicated Charges of the Following Powders.
Matching Maximum Pressure: 62000 psi or 427 MPa

or
Matching Loading Ratio (Filling, ''Load Density''): 100 %

These calculations refer to your specified settings in QuickLOAD 'Cartridge Dimensions' window.
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load ordering can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !

Powder type          Filling/Loading Ratio  Charge   Vel. Prop.Burnt P max  P muzz  Btime
                                      %     Grains    fps     %       psi     psi    ms
---------------------------------  -------------------------------------------------------
Rottweil R901                       97.3     42.1    2520    99.8    62000   12991   0.900  !DANGEROUS LOAD-DO NOT USE!
SNPE Vectan Sp 7                   100.0     47.6    2471    95.7    54768   13890   0.926  ! HOT LOAD !
Alliant Reloder- 7                  88.6     38.5    2459   100.0    62000   11294   0.912  !DANGEROUS LOAD-DO NOT USE!
Rottweil R907                      100.0     46.4    2437    93.7    50583   14040   0.949
Winchester 760                     100.0     48.4    2435    89.4    51116   14214   0.945


 :hmm Interesting that although both have peak performance with the same two powders, the order changes slightly after that.
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Re: Barrel length vs. accuracy
« Reply #24 on: September 17, 2009, 08:52:36 AM »
Noobtard question:  If you employ a faster burning powder, will you get more velocity out of a shorter barrel?

I think it might be more of a problem if we were discussing loads for a S&W 686, 8" versus a 2" derringer. Where I believe that the derringer will make slightly better use of the fast powder/heavy ball combo, but I've been wrong before.
Some people call the midwest the heartland, I prefer to think of it as the liver. Not too interesting, and easy to ignore until it quits working.


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