# Custom Barrel Question



## RutCrazed10 (Dec 19, 2009)

I have a Thompson Center Pro hunter and I want to have a custom barrel built in 300 wsm since Thompson does not offer that. Anybody got any advice or references on who to talk to? I thought about getting a 223 barrel and having it custom bored out to the 300 short but not real sure if that would work. Any help would be greatly appreciated.


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## Cknerr (Dec 20, 2009)

sent you a PM.

Chris


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## Hammack (Dec 21, 2009)

You aren't gonna find anyone who can bore a .223 barrel to another caliber without it costing you more than a new barrel will cost.  What you want is to purchase a barrel that can be re-chambered.  Purchase a barrel in 308 for your rifle and then have a qualified smith re-chamber the barrel to 300WSM.  The key is to buy a barrel that has a smaller case than the cartridge that you want to end up with, but still has the same caliber.  Another thing to consider is that I believe the short mags run at a slightly higher pressure than standard cartridges so that might be an issue with the Thompson since it only uses the barrel to hold the cartridge.  Can't say for sure, but it is something to keep in mind.


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## deadend (Dec 21, 2009)

I thought that most good 'smiths wouldn't chamber an Encore barrel to a WSM caliber because of the lack of adequate material that would be left in the chamber.  There were several threads on the net about exploded Encore WSM barrels.  

Just a question?  Why would you want a WSM in a single shot?  I understand having one in a bolt gun for a more compact gun but it makes no sense to me in a single shot.


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## deadend (Dec 21, 2009)

http://forum.gon.com/showthread.php?t=12918

http://forum.gon.com/showthread.php?t=382276&highlight=encore


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## Cknerr (Dec 21, 2009)

short mags where developed for accuracy. Initially had nothing to do with changing performance, ie. higher muzzle velocity, bigger bullet weight, etc. The fat short case burns almost all the powder in the case. This allows a very consistent muzzle velocity from round to round. A standard cartridge blows a lot of powder down the bore to be burned in there. Throwing powder around like that creates a slightly inconsistent burn from round to round. When people where having so much trouble telling any difference between the two cartridges (standard vs wsm), they had to come up with more ways to sell them... short cartridge = shorter magazine= shorter rifle=easier to handle. 

There is not much difference  between groups. If you are not an accomplished shooter who can take advantage of that small, but definite edge in accuracy, you are wasting time and money shooting one. Expecting a miracle to happen isn't in your future. Sorry, you do need some trigger time to take advantage.  Don't know if a pistol is accurate enough to "see" the difference. I would really like to find. Definitely curious about this one!

You are correct in mentioning the pressures can be higher in a wsm type cartridge. Burning all the powder in one unchanging volume tends to create high pressures.  Throwing powder out of the case to be burned in the barrel creates lower pressure because of the increase in volume AND with the lower pressure, the powder usually burns slower which also decreases pressure even more. That is why muzzle velocity is so hard to control with long slender cartridge styles. My standard cartridge 270 Winchester rifle average spread is about 45fps. The WSM is around 12-18fps. Benchrest rifles (just for comparison) try to keep the spread below 5fps.


Hope this helps,
Chris


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## germag (Dec 21, 2009)

Hmmm...I would think that the object would be to have the burn complete JUST before the bullet exits the bore. That way, you are using the entire tube to generate velocity. If you burn all the powder before the bullet gets to the end of the tube, then you are fighting friction for the remainder of the bullet travel through the bore, therefore are _loosing_ velocity.

Consistency of velocity is definitely key to accuracy and a short powder column will definitely burn more consistently than a long one of the same diameter. That's (one of the reasons) why the .308 Winchester shows more inherent accuracy than the .30-06 Springfield cartridge from which it evolved.


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## RutCrazed10 (Dec 21, 2009)

Well my reasoning for going to short mag is that I have had great success in the past with the 300 wsm. I loved the feel of the T/C Pro hunter and decided to purchase one but still had my heart set on the short mag. I have a .308 barrel and just wanted to know what options i had.


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## Cknerr (Dec 21, 2009)

RutCrazed10, why not?! If it works, more power to you. If you call T/C and talk to a tech, they might give you some reasons why they decided not to go with that cartridge. I am going to guess there was not enough interest to warrant production costs.  They can also tell you if the their barrel will take the abuse/pressure. I think it will, but would have to do some research. 

Germag, you are thinking along the correct lines...just not far enough.

The pressure is so high in  the chamber and bore, the bullet is going to continue accelerating after the powder has burned up. There is plenty of energy left!  End of powder doesn't mean the brakes get hit. As far as I know, and have to admit I haven't looked into it very much, the time to burn the powder in a 270 WSM and a standard 270 are approximately the same. The difference between burns might be better explained by looking at pressure curves. WSM is smooth and consistent from shot to shot.  The standard cartridge will have just a few small random spikes and dips impressed onto the curve. Those anomalies will change,  by a small amount,  where and how much max pressure is reached. That is how the muzzle velocity gets varied. 

Like you said, that is why the 308 Winny is so hard to beat. 

Take care,
Chris


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## Hammack (Dec 21, 2009)

Chris, I am curious about the idea of the WSM case being designed to burn the powder in the case?  I guess I am asking what is so special about the case that "keeps" the powder burning in the case that any other case doesn't have?  I understand that it burns more uniformly which translates to more consistent velocities and better accuracy.  

I do agree that you don't stop gaining velocity as soon as the powder is burned.  A guy ran my 264 win mag load thru his ballistic program over on BR central for me when i was deciding on how long of a barrel I wanted to use for my rebuild.  If I remember right powder was burned in less than 20" of barrel, but it would keep gaining velocity all the way out past 34 inches of barrel.


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## germag (Dec 21, 2009)

Cknerr said:


> RutCrazed10, why not?! If it works, more power to you. If you call T/C and talk to a tech, they might give you some reasons why they decided not to go with that cartridge. I am going to guess there was not enough interest to warrant production costs.  They can also tell you if the their barrel will take the abuse/pressure. I think it will, but would have to do some research.
> 
> Germag, you are thinking along the correct lines...just not far enough.
> 
> ...



Hi Chris,

Yeah, I'm going to try to find a good source for pressure curve charts for different cartridges that indicate the point of ignition and the point of bullet exit. This is something that I've been wondering about for some time. It seems to me that the physics would dictate that you're building pressure as long as powder is burning and producing expanding gasses, but the microsecond that powder stops burning, you stop building pressure and the curve starts on it's downward slope. As the bullet travels down the tube fighting friction, then that pressure is used pushing the bullet through the bore. It defies logic to me that you could possibly still be building pressure when the powder is all spent and you're not producing gasses any more. Do you know of any good sources for information on the finer points of internal ballistics?

I'll tell you what, Rutcrazed10, if I had a good .308 Win barrel, I'm not sure I'd really look too much further. That cartridge, as Chris pointed out, is hard to beat. For whitetails, it's just the ticket. Of course, if you just want the .300 WSM, then certainly you should go for it. I can see no reason why a barrel couldn't be chambered for it.


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## germag (Dec 21, 2009)

Hammack said:


> Chris, I am curious about the idea of the WSM case being designed to burn the powder in the case?  I guess I am asking what is so special about the case that "keeps" the powder burning in the case that any other case doesn't have?  I understand that it burns more uniformly which translates to more consistent velocities and better accuracy.
> 
> I do agree that you don't stop gaining velocity as soon as the powder is burned.  A guy ran my 264 win mag load thru his ballistic program over on BR central for me when i was deciding on how long of a barrel I wanted to use for my rebuild.  If I remember right powder was burned in less than 20" of barrel, but it would keep gaining velocity all the way out past 34 inches of barrel.



Do you know where I can locate a source of pressure curve charts and internal ballistics for different cartridges?


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## Cknerr (Dec 21, 2009)

Might have found out why they don't offer your desired cartridge. 

Here is the first article I read about it:http://www.eabco.com/WSM01.htm

I'll keep looking after dinner.
Chris


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## germag (Dec 21, 2009)

Cknerr said:


> Might have found out why they don't offer your desired cartridge.
> 
> Here is the first article I read about it:http://www.eabco.com/WSM01.htm
> 
> ...



That's interesting.


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## Hammack (Dec 21, 2009)

germag said:


> Do you know where I can locate a source of pressure curve charts and internal ballistics for different cartridges?



germag, I don't off the top of my head, but I will look and see what I can come up with.


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## germag (Dec 21, 2009)

Cool. Thanks. I'll appreciate anything I can learn about the actual burn process and internal ballistics. There's a lot of gray area there for me.


Sorry for hijacking the thread RutCrazed10....


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## Cknerr (Dec 22, 2009)

You are getting a lot more then just -is a certain cartridge doable!

Not sure about powder burn curves. Built into my chrony is a pressure sensor. Have to stand on your head, rub your tubby, and count backwards from 300 by 3's to get the pad glued on correctly. It does give nice results though. Only have looked at firing chambers. The curves did behave as mentioned. Why? 

Hopefully this is not going to be another long winded explanations. (ya right) 

In the early days of smokeless powder there was a huge amount of investigations. One results was noticing the  differant materials deposited in the bore. Not sure what was the cause though.  A lot of people incorrectly attributed it to inproper manufacturing. WWI and WWII provide an opportunity for some great minds to work out some fundamentals. Part of the results of different deposits was where the powder was burned. Later men like Ackley, Townsend, etc. worked out some ideas of getting the powder to burn more efficiently. That started the path to the WSM and others of its ilk. 

What is going on:

The gases exiting the cartridge mouth are super sonic. Because the cartridge neck is about the worse design for a super sonic nozzle, there are "problems". Huge amounts of noise (sound) are built up and large amounts of energy are waisted. It can get noisy enough to restrict the flow down to trans-sonic. If you think about it, the pressure inside the cartridge is 2-1/2 MILLION times the weight of a bullet! (50,000psi vs. 140 grain bullet) Yet the bullet doesn't get accelerated much more then mach 3.  Those sound restrictions, sound of course is vibration,  and supersonic flow produces a shock wave that are put to use by the new cartridge shapes. All the above can make the inside of the brass resemble some of the lower levels of Hades. The geniuses studying ballistics had to figure out how to harness some of the chaos going on. Ackley's work led to a lot of standard cartridges getting their shoulder slope greatly increased, the AI versions are well known. The sonic shockwave off the shoulder attempts to keep the powder shoved against the walls and base of the case. The noise produced at the neck tries to restrict the gases and powder from going down the bore. Others working along the same line led to developments of extreme cartridges like the PPC  and other wildcat cartridges. Their concept was to use the shock wave and sound energy to throttle/control the burn, stir, and retain the powder in the cartridge and not allow it to go into bore unburned. The short fat cartridge gave the shock wave (it is constantly being produced) the "elbow room" to work. Initially a hole is blown through the powder charge by the primer and some of the powder begins to burn. This initial reaction does throw some unburned powder down the bore and sometimes a small amount right behind the bullet does make it out the muzzle unburned. (same thing with standard cartridges btw). With the WSM,PPC, etc.,  after the initial ignition the shock wave builds quickly and the pressure wave/sonic boom keeps most of the unburned powder against the walls. The steeply shaped shoulders reflect/direct the sonic shockwave to do this work. The powder forming  the hole's walls is scraped off and tumbled (no clumping) from the onrush and noise of newly produced gases. It burns and producing a larger diameter hole. Initially it was thought the sonic shockwave tumbled everything in the case, it doesn't. The hole increases in diameter as powder is burned - just as a solid rocket motor is suppose to burn. Back to the tunnel with burning powder in it – at the top of the tunnel through the powder, unburned powder is not allowed to exit thanks to the restrictions of the all the noise produced at the top of the shoulders where the neck to the mouth makes such a terrible rocket nozzle. If it was an efficient nozzle, it would be a whole different story. The bore would become the firing chamber. The large grains are knocked back into the “hole”, powder ash (for lack of better description) is small enough that the noise can not find enough area to push it back. It exists the cartridge and goes down the bore. The combination of powder kept against the walls until burned (throttle control), tumbled so there are no clumps to modify burning rates, and retained in the brass until it is completely burned makes from some smooth and predictable result.  

Hope this helps explain some of the “rest of the story”.



Take care,
Chris


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## germag (Dec 22, 2009)

Thanks, Chris. I'll have to read this 10 or 15 times now to let it sort of gel in my brain.


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## Twenty five ought six (Dec 22, 2009)

> That way, you are using the entire tube to generate velocity. If you burn all the powder before the bullet gets to the end of the tube, then you are fighting friction for the remainder of the bullet travel through the bore, therefore are loosing velocity.



That's not exactly true.  Even though the powder is burned, the gas it produces keeps expanding and therefore exerts a force on the bullet.  You are correct that at some point, the force on the base of the bullet will become less than the frictional forces (and air resistance) and the bullet will start to slow down.  

The only common caliber where this can be observe is .22 rimfire.

On a related note, one of the long time questions is why revolvers don't lose more pressure out of the cylinder gap.  Using strain gauges and high speed photography, it's been determined that the powder burns completely (and peak pressure is reached) before the bullet completely crosses the cylinder gap.  Again it can pretty easily be proven that except for very light charges of very fast burning powders, longer barrels on revolvers result in higher velocities, due to the jetting action of the hot expanding gas.


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## germag (Dec 22, 2009)

Hmmm....OK. Seems like the gas would keep expanding up to the point that the peak pressure is reached...I wonder at what point in the internal travel of the bullet peak pressure is reached for (pick a cartridge)....a curve that could be considered a "normal" pressure curve? Just engaging the rifling? Still leaving the cartridge? 1/3 of the way down the tube?


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## Cknerr (Dec 22, 2009)

Peak pressure is reached very quickly. The down slope on the other side is less steep and of course never gets to zero  before the bullets exit the bore. As to just how fast a pressure curve builds....wish I had kept some curves. This is a link to the company I bought mine from. Scroll down the page. They have a sample print out at the bottom which has a few curves. http://www.oehler-research.com/model43.html


Germag,
Studying ballistics is a blast (pun intended). After all these years of study all I have figured out was an awareness of what I don't know. Folks like Ackley, Townsend, etc. are geniuses. Wish I could go back in time and spend a few days just listening to them.....wow, what I could learn!

Chris


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## Eddy M. (Dec 22, 2009)

If Fox Ridge, Bellums and the many other BIG TC Custom Barrel makers don't offer this round then they don't consider it safe in the Encore   sorry


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## Twenty five ought six (Dec 22, 2009)

germag said:


> Hmmm....OK. Seems like the gas would keep expanding up to the point that the peak pressure is reached...I wonder at what point in the internal travel of the bullet peak pressure is reached for (pick a cartridge)....a curve that could be considered a "normal" pressure curve? Just engaging the rifling? Still leaving the cartridge? 1/3 of the way down the tube?



The gas keeps expanding after peak pressure is reached, it just doesn't expand as rapidly. That's the principal that makes gas operated semi and full automatic weapons work.  All of them have ports that are well past the point of peak pressure.

Classic calculus problem, the change in the rate of acceleration.  

Even though the gas will keep expanding quite a bit (in term of a barrel) at some point, the force that it exerts on the bullet is less than the force of friction and air resistance, so the rate of change in acceleration becomes negative, i.e. the bullet starts to slow down.  As far as I know, the .22 rimfire is the only common firearm where this can actually be observed.

As noted, pressure peaks very quickly in a handgun.

I don't know for all rifles, but in shotguns, the point of peak pressure is generally between 12 and 14 inches down the barrel.


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## germag (Dec 22, 2009)

Thanks guys for taking the time and effort to answer my questions. It's all very helpful to me. I really need a better understanding of internal ballistics. I pretty well understand external ballistics and all of the mechanics of putting an accurate rifle together....I think a better grasp of what goes on _before_ the bullet leaves the muzzle would take some of the guesswork and mystery out of working up and fine-tuning loads.

I need to find a good comprehensive text (recent print) on internal ballistics....


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## Twenty five ought six (Dec 23, 2009)

germag said:


> Thanks guys for taking the time and effort to answer my questions. It's all very helpful to me. I really need a better understanding of internal ballistics. I pretty well understand external ballistics and all of the mechanics of putting an accurate rifle together....I think a better grasp of what goes on _before_ the bullet leaves the muzzle would take some of the guesswork and mystery out of working up and fine-tuning loads.
> 
> I need to find a good comprehensive text (recent print) on internal ballistics....



There's still a lot of unanswered questions, simply because no one has come up with a way to observe the firing process.

The development of reliable and inexpensive strain gauges has helped a lot.

The revolver situation is the best example I know.  For decades, everyone assumed that the powder was still burning after the bullet entered the forcing cone. 

My focus is more on shotguns, and there's a lot there that still can't be answered.  For example, the idea of lengthening forcing cones to reduce recoil.  Mathematically that makes no sense, but there are tens of thousands of people who swear by it.


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## WTM45 (Dec 23, 2009)

germag said:


> Hmmm....OK. Seems like the gas would keep expanding up to the point that the peak pressure is reached...I wonder at what point in the internal travel of the bullet peak pressure is reached for (pick a cartridge)....a curve that could be considered a "normal" pressure curve? Just engaging the rifling? Still leaving the cartridge? 1/3 of the way down the tube?



It will not vary only by cartridge, it will vary by tube also.  Rifling specs and measurements matter greatly.

There are multiple "peaks" in barrels.  The bullet even starts and stops at various places during the process of firing a round.  They are very, very, very small in time interval and duration.  But they exist.

The case goes fluid.  It is the shape of the chamber that causes the gas flow pattern, not the case.  The case is only a powder retaining medium that conforms 100% to the chamber shape.


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## deadend (Dec 23, 2009)

The shank of the barrel on an Encore is limited in diameter by the receiver.  The WSM cartridge is too great in diameter to leave a chamber wall thick enough to reliably contain the pressure put out by the WSM.  Just another reason to leave the erector set guns to the kids and get a decent bolt gun!  Besides, if you leave it in the garage you'll get it mixed up with the wand on your pressure washer.


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## jglenn (Dec 23, 2009)

now that's funny right there

BTW Deadend has the answer on the WSMs in the TC


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## HandgunHTR (Dec 24, 2009)

RutCrazed10, 

As has been posted, most custom makers will not chamber an Encore in any of the WSM cartridges.  The one that will states that you must handload for it and keep loads around the minimum, which puts the performance about equal to the 30-06.  So, the point of having the WSM is defeated.  
If you want a 30 caliber "magnum" chambered Encore barrel, get a factory .300 Winchester Mag.

As to the rest of you, if you want to discuss pressures, burn rates and velocity futher, please start another thread in the Firearms forum.


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## Eddy M. (Dec 24, 2009)

HandgunHTR said:


> RutCrazed10,
> 
> As has been posted, most custom makers will not chamber an Encore in any of the WSM cartridges.  The one that will states that you must handload for it and keep loads around the minimum, which puts the performance about equal to the 30-06.  So, the point of having the WSM is defeated.
> If you want a 30 caliber "magnum" chambered Encore barrel, get a factory .300 Winchester Mag.
> ...



 as I stated earlier if that round was safe in the ENCORE barrel  Fox Ridge and Mike Bellum and several others would offer it   --- the pressure - burn rates -ECT are very interesting and I appreciate the information  but doesn't apply to this post- but would be a GREAT NEW post  many would enjoy


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## Turkey Comander (Dec 24, 2009)

RutCrazed10 said:


> I have a Thompson Center Pro hunter and I want to have a custom barrel built in 300 wsm since Thompson does not offer that. Anybody got any advice or references on who to talk to? I thought about getting a 223 barrel and having it custom bored out to the 300 short but not real sure if that would work. Any help would be greatly appreciated.



A Thompson Center action isn't the best platform to put a custom barrel on....I doubt you would never recoup the expense in money or accuracy.


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