Powder v. Bullet v. Barrel Relationship

[Rockdoc173]

Does this sound right?

Powder
Faster powder, lighter bullet. Slower powder, heavier bullet

Bullet
Heavier bullet, longer barrel. Lighter bullet, shorter barrel.

Barrel
Shorter barrel, faster powder. Longer barrel, slower power

Yes, there are a million variables that could affect the situation. But, in general, if you were talking to a new reloader at the range, is this the kind of generality with which you would agree ? If you agree, please explain. If you do not agree, please explain that too.

 

[spife7980]

The lighter bullet faster powder is the only one that really jives.

The others are just compromises.

 

[Rockdoc173]

The lighter bullet faster powder is the only one that really jives.

The others are just compromises.

I'm exploring the relationship between all of them so, for example, if you have a little 16" shorty 308 you'd want to go with a lighter bullet and faster powder, right? And, if you had a 30" 300NM, you'd want to run a heavier bullet for maximum ballistic efficiency. To run the heavier bullet, you'll typically run a slower power, yes? And, the reverse is true.

 

[spife7980]

if you have a little 16" shorty 308 you'd want to go with a lighter bullet and faster powder, right?

That depends on whether you value flat elevation up close vs wind bucking abilities at distance. Which would depend on distance and amount of unknown variables.

And, if you had a 30" 300NM, you'd want to run a heavier bullet for maximum ballistic efficiency.

Probably since that’s what people mainly use the chambering for. If you wanted to completely unzip a coyote at 300 yards you wouldn’t.

To run the heavier bullet, you'll typically run a slower power, yes? And, the reverse is true.

Correct, heavier bullets use slower powders. They accelerate more slowly and create volume in the bore behind the bullet more slowly so a powder that burns slower and fills that volume behind the bullet proportionally is the best choice.

 

[MediumSpeed]

add to the list magnum vs standard primers...

I've played this game a little bit, made some nice sub sonic 147gr 9mm for a 10" PCC (but then is wouldn't cycle a handgun reliable) I have had some interesting insights with Gordons Reloading Tool, I think it is worth running your hypothetical loads through it to see how they compare though as folks here will point out, it is just a tool, work up your actual loads responsibly etc

 

[Rockdoc173]

add to the list magnum vs standard primers...

Let's put primers on hold a bit and consider twist. What would be our assumptions here?

Lighter bullet, slower twist (think 155gr 308 w/ a 11.25tw over a 215 with a 9tw)
Faster velocity, slower twist (so you don't spin the bullet apart)
Longer barrel, slower twist

 

[spife7980]

The heavier a bullet for a caliber the longer it gets by necessity, can’t get wider. The longer something is the faster it has to spin to maintain gyroscopic stability and continue to fall over itself and fly true. If it’s not spinning fast enough when it falls it will catch the wind like a sail and tumble.

Spinning too fast is only dependent on bullet construction. It can’t tear itself apart and still fly true. The faster it spins the better it will go through the transonic region of flight.

 

[MediumSpeed]

interesting enough with regard to 308, I have a couple different uppers for my LMT gasser. the LMT upper barrel is 1 in 11.25 The Criterion barrel is 1 in 10. The Criterion is more accurate with the 155s I run through them (both are stainless steel 18" barrels, 155s are going about 2740-2760 fps)

 

[Rockdoc173]

Okay, now here's the interesting part...

1. Longer barrel, heavier bullet, slower powder, faster tw?
2. Shorter barrel, heavier bullet, faster powder, slower twist ?
3. Longer barrel, lighter bullet, faster powder, slower twist?
4. Shorter barrel, lighter bullet, even faster powder, even slower twist?

 

[Rockdoc173]

interesting enough with regard to 308, I have a couple different uppers for my LMT gasser. the LMT upper barrel is 1 in 11.25 The Criterion barrel is 1 in 10. The Criterion is more accurate with the 155s I run through them (both are stainless steel 18" barrels, 155s are going about 2740-2760 fps)

We've all had those guns that seem to defy what's 'normal.' lol

 

[clcustom1911]

Okay, now here's the interesting part...

1. Longer barrel, heavier bullet, slower powder, faster tw?
2. Shorter barrel, heavier bullet, faster powder, slower twist ?
3. Longer barrel, lighter bullet, faster powder, slower twist?
4. Shorter barrel, lighter bullet, even faster powder, even slower twist?

The length of your bullet determines the twist. The longer the bullet, the faster the twist is needed to spin faster to maintain optimal gyroscopic stability for that longer object.

 

[GreenGO Juan]

Barrel
Shorter barrel, faster powder. Longer barrel, slower power

No, most of the bullets acceleration from combustion pressure occurs in the first few inches of bullet travel. The slower powder adds more energy over time causing higher velocity in this critical first few inches with out “blowing up”. A faster powder has a quicker energy spike, but lower average pressure in this critical area.

Basically a powder that produces more or less velocity for a given bullet weight will give similar results in commonly used barrel lengths. At the extremes of lengths, say you cut your 20” down to 2” this might change but at that point, a different cartridge would be the answer.

A faster powder when using the same bullet is not giving you increased velocity, say going from a 24” to a 16”, compared to a slower powder, At similar peak pressure.

 

[Frank Green]

In my opinion it's got more to do with the actual bullet diameter vs the bore/groove size.

A fatter bullet in Marks terms here you don't have to spank it as hard to get it to shoot good. A smaller diameter bullet and you have to spank it harder to upset the bullet jacket more to drive the bullet. This is assuming the same chamber reamer and that the barrels bore/groove sizes are at the same spec.

I've asked this same question to a couple of bullet/ammo makers.

I've also asked the question, "how much does the bullet obturate when it slams into the bore of the barrel?" I've been told no exact way to measure it but the opinion is from what they see...the bullet will expand as much as a full .001" and then form down to the rifling.

Now if you have a bore of a barrel that is loose or where on button or hammer forged barrels where the bore opened up say another .0005" to a .001" over min spec tolerances and it affects the bullet even more in terms of a negative on accuracy.

The powder and load is another variable. Pressure generated etc...

Also look at solid bullets...they don't obturate as much as a jacketed/lead core bullet. So it's even more critical to the relationship to the bullet and bore/groove sizes are. This makes the solid bullets even more temperamental. Three or four different bullet makers when I've asked the question all agree on this as well.

Later, Frank
Bartlein barrels

 

[Rockdoc173]

No, most of the bullets acceleration from combustion pressure occurs in the first few inches of bullet travel. The slower powder adds more energy over time causing higher velocity in this critical first few inches with out “blowing up”. A faster powder has a quicker energy spike, but lower average pressure in this critical area.

Basically a powder that produces more or less velocity for a given bullet weight will give similar results in commonly used barrel lengths. At the extremes of lengths, say you cut your 20” down to 2” this might change but at that point, a different cartridge would be the answer.

A faster powder when using the same bullet is not giving you increased velocity, say going from a 24” to a 16”, compared to a slower powder, At similar peak pressure.

So, you're saying the majority of the velocity a bullet is going to achieve as a function of the powder used occurs within the first few inches? Then why do we have ≥30" barrels? I've always heard that you typically use a slower powder for a heavier bullet because 1. the heavier a bullet, the longer it takes to get going. Using the slower powder allows the gas volume to continue to expand all the way down the bore (accept on an AR where some of the gas bleeds off through the gas port) increasing velocity as it goes. 2. Using a faster power means it's more of 'poof' of gas volume expansion which is insufficient to continue to expand down the bore, the net result being sub-optimal velocity. Is the extra length of barrel solely for the purpose of imparting spin and thereby gyroscopic stability? The slower powder adds no more velocity, but rather maintains the velocity the was created as the barrel gets the bullet spinning appropriately? For the big 34" + ELR barrels, are they long solely for getting the big bullet spinning without having to run a super fast twist thereby maintaining forward velocity which would have been slowed by rotational energy? My peanut is working overtime, I apologize if my dialup is slow. lol

In my opinion it's got more to do with the actual bullet diameter vs the bore/groove size.

A fatter bullet in Marks terms here you don't have to spank it as hard to get it to shoot good. A smaller diameter bullet and you have to spank it harder to upset the bullet jacket more to drive the bullet. This is assuming the same chamber reamer and that the barrels bore/groove sizes are at the same spec.

You mean wider or narrower in terms of tolerance like +/- 0.0005, or in the context of caliber like 30cal vs. 24cal?

 

[GreenGO Juan]

So, you're saying the majority of the velocity a bullet is going to achieve as a function of the powder used occurs within the first few inches?

Most of the velocity is gained in the first few inches when pressure is highest

Slower powders maintain a higher average pressure.

Assuming both are loaded to the same peak pressure, the slower powder should achieve more velocity. As it has a higher average pressure.

People use long barrels to maximize performance.

That is what I am saying.

 

[Frank Green]

You mean wider or narrower in terms of tolerance like +/- 0.0005, or in the context of caliber like 30cal vs. 24cal?

caliber doesn't matter. 6mm or 30cal. The bigger the bore/groove size is and the smaller in tolerance the bullet is....you will see less accuracy and I'll say velocity will suffer as well.

I know one manufacturer of they're one set of match bullets has a size of .3082" +.0002"/-.0000" for tolerance.

But another maker if I understood them right has a dimensions of size +.0007" tolerance.

So a couple years back JJ in the shop built a back up F open gun. Same caliber and reamer we've used in our other guns. He was checking seating depth.....and his bullets where going .050" deeper in the case. He asked me to double check his measurements. I was getting the same thing. Then I asked him... is the same lot of bullets you had before as what I had? He said no....he ran out and it was a new lot. So I went and measured the bullet diameters as I still had a bunch of the old lot and I could compare to the new lot. Sure enough the old lot measured right at .2840". The new lot measured .2844"/.2845". Plus the variance in the ogive length made the new bullets go +.050" deeper into the case.

As they make the bullets the bullet dies wear and typically the bullets will get fat (bigger on the diameter over the course of running the die). Other variables like how much lube is being used on the bullets has an affect as well and I don't know all the variables. Just naming a couple of them here.

What this bullet maker vs that bullet maker and what tolerances they hold on the bullets and when they decide to replace the dies during manufacturing...I don't know all of the specs but bullets are a variable. Just like everything else has a tolerance in manufacturing.

We hold our barrels to size +.0005" tolerance (which is saami min spec.) on the bore and groove size. So a .30cal barrel is .3000" x .3080" is min spec. and max spec is .3005" x .3085" is max. What other barrel makers or gun manufacturers hold they're tolerances to is up to them.

Same with chamber reamers... you have custom, you have saami min spec and you have production spec...I've seen production spec chambers for example that are +.002" bigger on diameters as one example. I never order a production spec type reamers. It's either custom to our spec or saami min spec.

Now imagine your barrel actually measures .3010" x .3092" and the bullet your loading is at .3080".

Or worse yet you have a .3010" bore back at the breech but your muzzle end where it is threaded measures .3015"!

So when we make a ammunition test barrel and the customer tells me 300WM saami min spec. I know exactly what to make them but what chamber is on your production gun or custom barrel you had made by someone or what tolerance the barrel was made to.....at times your guess is as good as mine!

Variables!

Later, Frank

 

[spife7980]

So, you're saying the majority of the velocity a bullet is going to achieve as a function of the powder used occurs within the first few inches? Then why do we have ≥30" barrels?

They use longer barrels so the expanding gases push on it for a longer period of time making it go faster. Longer barrels are just free velocity and thats true with a slow or a fast burn rate powder. The longer the bullet is acted upon in the bore the more work is being done to it and thus the faster it will be going. Period.
Just because a short barrel ends the process of acceleration sooner doesnt mean its not still the optimal combination for the bullet weight in that caliber.

In 5" that bullet in this quick load graph google image is already going 1500 fps, it takes another 10" (3x the distance traveled) just to make another 1k fps. The difference between a 15" and a 20" is only 150 fps or so in this example which is 10% of what the first 5" got you. Going from a 20" to a 30" will an even slower nfactor on that curve flattening the acceleration and top velocity, but it will still gain speed, just not at the same rate it did to start with.

Sure, some people may go with a faster powder in a sbr to avoid flash etc but thats just compromising efficiency for secondary reasons, not ballistics.

 

[Frank Green]

They use longer bullets so the expanding gases push on it for longer making it go faster. Longer barrels are just free velovity.
Just becsue a short barrel stops the process sooner doesnt mean its not still the optimal combination.

I'll butt in here for a second....

Usually because the barrels are longer the individual is trying to get as much velocity out of his gun for a reason.

Also depends on caliber.... a 6BR up to 28" finish length you have your biggest velocity gains but going to 30" or 32" the gain is minimal per inch of barrel length. Kind of the same thing for a 308w.

But now make the caliber a 300wm. You have doubled your case capacity over the 308w. The longer barrel can give you more velocity gain up to X amount of barrel length but take that 300wm and cut the barrel down to 20" and your giving up a lot in terms of velocity.

My 300PRC open class gun has a 32" long barrel on it but the next one I put on is only going to be 30". The extra 2" I don't feel is giving me anything extra unless I really want to try and step on it.

Make sense?

 

[straightshooter1]

So, you're saying the majority of the velocity a bullet is going to achieve as a function of the powder used occurs within the first few inches?

Maybe the pic below will give you some idea regarding the velocity through a barrel as it relates to distance and pressure (note the red dot on the curve indicating the 50% of total velocity as indicated in the box at top right and the distance distance the projectile has traveled in the box at the bottom:

 

[spife7980]

I'll butt in here for a second....

Usually because the barrels are longer the individual is trying to get as much velocity out of his gun for a reason.

Also depends on caliber.... a 6BR up to 28" finish length you have your biggest velocity gains but going to 30" or 32" the gain is minimal per inch of barrel length. Kind of the same thing for a 308w.

But now make the caliber a 300wm. You have doubled your case capacity over the 308w. The longer barrel can give you more velocity gain up to X amount of barrel length but take that 300wm and cut the barrel down to 20" and your giving up a lot in terms of velocity.

My 300PRC open class gun has a 32" long barrel on it but the next one I put on is only going to be 30". The extra 2" I don't feel is giving me anything extra unless I really want to try and step on it.

Make sense?

But would you sacrifice and choose a suboptimal powder just to take advantage of those otherwise meaningless inches for less performance? Thats what Im trying to get across to the op

 

[Frank Green]

But would you sacrifice and choose a suboptimal powder just to take advantage of those otherwise meaningless inches for less performance? Thats what Im trying to get across to the op

Define suboptimal powder?

Now I get what your asking to the OP.

 

[spife7980]

Define suboptimal powder?

Ex: going with a fast powder like varget and a 200gr bullet in that 300wm just because its only 20"
Its going to hit max pressure sooner and leave you with less velocity as a result, a lose-lose proposition.

 

[GreenGO Juan]

Another reason to consider powder burn rate is port pressure on a semi auto/gas gun.

For example I have started shooting a 110grain load in .308 gas guns using IMR 4198, loading 39.7 grains. Its one of the fastest powders listed for 110 loads.

I tried IMR4895 I had on hand, a slower powder that requires nearly 10 more grains (inefficient)to achieve similar velocities, and was producing way to much port pressure. In working the load up I stopped, because I couldn’t tame the cycle down and never got close to the velocity I achieved with 4198 which runs the bolt much happier.

Btw- 4198 behind a 110grain bullet in a gas gun is tits! Getting around a little of 2900 fps with a 16” barrel. At closer ranges its very flat and low recoil. My Zombie load…

 

[Frank Green]

Ex: going with a fast powder like varget and a 200gr bullet in that 300wm just because its only 20"
Its going to hit max pressure sooner and leave you with less velocity as a result, a lose-lose proposition.

That's where I thought you where going with that. For that example even with a short barrel length Varget isn't a suitable powder for 300wm. Your asking for trouble as the burn rate is to fast for case capacity/volume.

Imagine using a fast burning powder like a pistol powder in 308w (ok might be an extreme comparison) but doing something like that....and KABOOM is what will happen.

 

[brianf]

caliber doesn't matter. 6mm or 30cal. The bigger the bore/groove size is and the smaller in tolerance the bullet is....you will see less accuracy and I'll say velocity will suffer as well.

I know one manufacturer of they're one set of match bullets has a size of .3082" +.0002"/-.0000" for tolerance.

But another maker if I understood them right has a dimensions of size +.0007" tolerance.

So a couple years back JJ in the shop built a back up F open gun. Same caliber and reamer we've used in our other guns. He was checking seating depth.....and his bullets where going .050" deeper in the case. He asked me to double check his measurements. I was getting the same thing. Then I asked him... is the same lot of bullets you had before as what I had? He said no....he ran out and it was a new lot. So I went and measured the bullet diameters as I still had a bunch of the old lot and I could compare to the new lot. Sure enough the old lot measured right at .2840". The new lot measured .2844"/.2845". Plus the variance in the ogive length made the new bullets go +.050" deeper into the case.

As they make the bullets the bullet dies wear and typically the bullets will get fat (bigger on the diameter over the course of running the die). Other variables like how much lube is being used on the bullets has an affect as well and I don't know all the variables. Just naming a couple of them here.

What this bullet maker vs that bullet maker and what tolerances they hold on the bullets and when they decide to replace the dies during manufacturing...I don't know all of the specs but bullets are a variable. Just like everything else has a tolerance in manufacturing.

We hold our barrels to size +.0005" tolerance (which is saami min spec.) on the bore and groove size. So a .30cal barrel is .3000" x .3080" is min spec. and max spec is .3005" x .3085" is max. What other barrel makers or gun manufacturers hold they're tolerances to is up to them.

Same with chamber reamers... you have custom, you have saami min spec and you have production spec...I've seen production spec chambers for example that are +.002" bigger on diameters as one example. I never order a production spec type reamers. It's either custom to our spec or saami min spec.

Now imagine your barrel actually measures .3010" x .3092" and the bullet your loading is at .3080".

Or worse yet you have a .3010" bore back at the breech but your muzzle end where it is threaded measures .3015"!

So when we make a ammunition test barrel and the customer tells me 300WM saami min spec. I know exactly what to make them but what chamber is on your production gun or custom barrel you had made by someone or what tolerance the barrel was made to.....at times your guess is as good as mine!

Variables!

Later, Frank

i guess we know why "jamming" the lands usually shoots best

before the starts moving it is "swelling" for a better fit to the lands

 

[Frank Green]

Also don't grind your powder up in a blender so it meters better thru your powder measure...that' blows up guns also! Yep it's been done!

Doing this even though it's the same powder... you have now just changed the burning characteristics of the powder.

OK getting off base here...sorry!

 

[brianf]

i mix powder for a living

i cringe every time someone posts a pic of a chaffing tray full of different powders

the amount of testing we do to make sure its a homogenous mix is a little more involved than putting your hand in a bowl

 

[Rockdoc173]

They use longer barrels so the expanding gases push on it for a longer period of time making it go faster. Longer barrels are just free velocity and thats true with a slow or a fast burn rate powder. The longer the bullet is acted upon in the bore the more work is being done to it and thus the faster it will be going. Period.
Just because a short barrel ends the process of acceleration sooner doesnt mean its not still the optimal combination for the bullet weight in that caliber.

In 5" that bullet in this quick load graph google image is already going 1500 fps, it takes another 10" (3x the distance traveled) just to make another 1k fps. The difference between a 15" and a 20" is only 150 fps or so in this example which is 10% of what the first 5" got you. Going from a 20" to a 30" will an even slower nfactor on that curve flattening the acceleration and top velocity, but it will still gain speed, just not at the same rate it did to start with.

Sure, some people may go with a faster powder in a sbr to avoid flash etc but thats just compromising efficiency for secondary reasons, not ballistics.

Now I'm tracking. For illustrative purposes imagine a tank filled with water. If you suddenly expand the tank size without effecting the volume of water, the level of water will decrease relative to, say, the side of the tank. Now, if you continuously add water at the rate the tank is expanding, the level of water remains constant. This is what you're saying, as the gas (water) is traveling down the barrel (tank) the slow powder is acting to maintain the average level of gas (water) in the barrel (tank) thereby increasing pressure? Yea???

 

[Rockdoc173]

Also depends on caliber.... a 6BR up to 28" finish length you have your biggest velocity gains but going to 30" or 32" the gain is minimal per inch of barrel length. Kind of the same thing for a 308w.

But now make the caliber a 300wm. You have doubled your case capacity over the 308w. The longer barrel can give you more velocity gain up to X amount of barrel length but take that 300wm and cut the barrel down to 20" and your giving up a lot in terms of velocity.

Make sense?

Actually it does. I've never heard it explained like that, but now I'm sitting here with that 'duh' feeling you get when you just learned something you intuitively knew all along but didn't realize it. lol

So that's why 22LR (small powder volume relative to big bore cals) barrels are typically no longer than about 18"/20" and 50BMB barrels (and other ELR-types) are nearing 2x4 stud length, it's all about the amount of powered that has to get burned.

 

[spife7980]

Now I'm tracking. For illustrative purposes imagine a tank filled with water. If you suddenly expand the tank size without effecting the volume of water, the level of water will decrease relative to, say, the side of the tank. Now, if you continuously add water at the rate the tank is expanding, the level of water remains constant. This is what you're saying, as the gas (water) is traveling down the barrel (tank) the slow powder is acting to maintain the average level of gas (water) in the barrel (tank) thereby increasing pressure? Yea???

I think?
As the bullet moves down the barrel the volume of space behind it gets filled with expanding gases.
Lighter bullets accelerate quicker and thus require a powder that burns and expands quicker to maintain a nice pressure behind the bullet to get optimum speed.
Heavier bullets accelerate slower and the volume behind the bullet doesn’t increase at the same rate so a slower powder more closest matches that speed in the increase in volume behind the bullet for an ideal pressure gradient.

 

[MarkyMark007]

Powder
Faster powder, lighter bullet. Slower powder, heavier bullet

Bullet
Heavier bullet, longer barrel. Lighter bullet, shorter barrel.

Barrel
Shorter barrel, faster powder. Longer barrel, slower power

1. YES, but people like to run faster powders than slower. look at tables of powders used on some competitions. quite fast powders for the bullet. but NOT too fast ! just fast from all options.

2. NO ?

3. NO! it's a myth that wont die.

 

[Frank Green]

So that's why 22LR (small powder volume relative to big bore cals) barrels are typically no longer than about 18"/20" and 50BMB barrels (and other ELR-types) are nearing 2x4 stud length, it's all about the amount of powered that has to get burned.

If I recall correctly a 22rf burns all of it's powder in a barrel by 16" long. So no real reason to have a longer barrel than 16" in a 22rf. I run mostly 18" barrels.

Some guns like my small bore rifle where I use to shoot iron sights a lot...28" barrels for the sight radius. If scoped only I was around 21" to 22" and it was mostly for balance.

The accuracy isn't better but having that shorter barrel length gets the bullet out of the bore quicker so less time for your position etc...to blow the shot in my opinion.

 

[perttime]

If I recall correctly a 22rf burns all of it's powder in a barrel by 16" long. So no real reason to have a longer barrel than 16" in a 22rf. I run mostly 18" barrels.

Some guns like my small bore rifle where I use to shoot iron sights a lot...28" barrels for the sight radius. If scoped only I was around 21" to 22" and it was mostly for balance.

The accuracy isn't better but having that shorter barrel length gets the bullet out of the bore quicker so less time for your position etc...to blow the shot in my opinion.

Looks like at least some competition 22LR rifles have quite short barrels, and then there's a long sleeve just for sight radius or balance.

---
Recently, I saw somebody proposing ammunition optimized for short barrels. He was thinking .308 or similar.
Is there something that can be done to get more out of a short barrel?

 

[Frank Green]

Looks like at least some competition 22LR rifles have quite short barrels, and then there's a long sleeve just for sight radius or balance.

---
Recently, I saw somebody proposing ammunition optimized for short barrels. He was thinking .308 or similar.
Is there something that can be done to get more out of a short barrel?

That's called a bloop tube! That's what I have on my 22" barrel gun when not using a scope.

 

[Rockdoc173]

Deviating ever so slightly, I mentioned something about horizontal energy eaten up by rotational energy (don't hate me if I'm confusing semantics). So, on average, all else being equal, will a faster twist barrel have less velocity than a slower twist? I guess I'm thinking that an extreme twist like a 1:4 will not be able to push the bullet down the bore as quickly (without skipping over lands/grooves) as another extreme example of a 1: 24. Imagine a drill bit with very aggressive flutes, if you stand it on end and put a ball bearing in the flute at the top and let it roll down, it will take longer for the bearing to reach the bottom of the bit than if it was very elongated flutes? Is this making any sense?

 

[spife7980]

In theory but not in practice.

 

[alamo5000]

Barrel
Shorter barrel, faster powder. Longer barrel, slower power

I have done some limited testing on this. The short answer is no. This is not correct. The nature of the powder is more important than just speed. Of course if you went out to the very edges of available powders your statement might be true, but for the vast majority of those in the middle it's a definite no from me.

 

[brianf]

Deviating ever so slightly, I mentioned something about horizontal energy eaten up by rotational energy (don't hate me if I'm confusing semantics). So, on average, all else being equal, will a faster twist barrel have less velocity than a slower twist? I guess I'm thinking that an extreme twist like a 1:4 will not be able to push the bullet down the bore as quickly (without skipping over lands/grooves) as another extreme example of a 1: 24. Imagine a drill bit with very aggressive flutes, if you stand it on end and put a ball bearing in the flute at the top and let it roll down, it will take longer for the bearing to reach the bottom of the bit than if it was very elongated flutes? Is this making any sense?

negligible when compared to slightly different bore and built specs

also in theory, you can push a bullet fast enough to make a 1:100 twist act like a 1:10 twist, but in reality, the possible increase in velocity before pressure and failures of components doesn't change enough

there is a reason that most cartridges and calibers settle around a certain barre length/ twist/ bullet weight, gains can be made but nothing earth shattering

if there was a magic pill "winchester" would sell it, no one is leaving money on the table

 

[Rockdoc173]

The nature of the powder is more important than just speed.

The "nature" of the powder, please explain? Are you referring to the burning characteristics? How the curve graphs?

 

[acudaowner]

 

[alamo5000]

The "nature" of the powder, please explain? Are you referring to the burning characteristics? How the curve graphs?

I am not a scientist by any means but I will give it a shot. Some powders are created to work better in certain calibers and even there they might be best suited for light bullets vs heavy ones within a single cartridge.

What specific things cause that difference during powder development is beyond my pay grade.

However my testing down to a 10.5" barrel showed me at least that an appropriate powder for the cartridge in conjunction with (again) an appropriate bullet weight range for that powder makes substantially more difference than sheer burn rate.

If you could say as an example, find a powder that is appropriate for .223, and more specifically heavy bullets in .223...by itself that will perform better than just going with something 'faster' that doesn't meet those first two criteria.

If though you had two powders and both were appropriate for .223 w/heavy bullets and one was faster than the other, that would make for an interesting test in a short barrel. But in this scenario both would need to meet the first two criteria first, above and well beyond just burn rate.

In other words you could use a MUCH faster burning powder (specifically for .223), but it is more 'tuned' to use with light bullets vs heavy ones. You will get substantially slower velocity that way than using a powder (for .223) that is much slower, but better suited for heavy bullets (assuming you are shooting heavy bullets for example).

 

[Rockdoc173]

I have done some limited testing on this. The short answer is no. This is not correct. The nature of the powder is more important than just speed. Of course if you went out to the very edges of available powders your statement might be true, but for the vast majority of those in the middle it's a definite no from me.

So, if I have a little 16" bolt action 308 shorty right next to a 26" competition rig, the 16" wouldn't need a faster powder? Would you use the same powder in both? I'm omitting for a moment the differences in what guns like what powders for the sake of comparing a faster powder to a slower powder.

 

[brianf]

there is more to it but simply;

if the case is already full at 16" there is no other way to create more speed (which would mean increased pressure) for the 16"... would need a faster powder

if the case is not full then by adding more powder/case fill you will increase pressure which will increase velocity but diminishing returns

 

[alamo5000]

So, if I have a little 16" bolt action 308 shorty right next to a 26" competition rig, the 16" wouldn't need a faster powder? Would you use the same powder in both? I'm omitting for a moment the differences in what guns like what powders for the sake of comparing a faster powder to a slower powder.

It depends on a whole lot of factors and if you are just talking velocity alone. If you are shooting a light bullet in one and a heavy bullet in the other, generally speaking you will have better results choosing a powder based on bullet weight rather than barrel length. That said there is no way to know for sure except for testing. The caveat to that is there is a lot of manufacturer's data out there to give you a whole lot of clues.

As an example I have a ton of 75 grain bullets that I will shoot through my 10.5 SBR. So comparing out of that platform, H335 is five spots faster on the burn rate chart vs TAC. On Hodgon's website, with a 75 grain bullet out of a 24" barrel the results are only 6fps difference between the two.

Yet when I shot those two powders side by side in my SBR.... the SLOWER powder (TAC) gave me a net 140 fps faster velocity out of my short barrel. TAC is a slower powder but it produced substantially better results.

Again, the idea that a faster powder for a shorter barrel will give better velocity is definitely debunked, at least in an across the board 'standard concept'. It is all going to depend on the details.

To answer your hypothetical question about the 16" vs 26" the answer is generally speaking absolutely no. Given you might find a faster powder that produces great results out of the shorter barrel, but those differences will come from the nature of the powder vs purely how it falls on a burn rate chart.

 

[alamo5000]

So, if I have a little 16" bolt action 308 shorty right next to a 26" competition rig, the 16" wouldn't need a faster powder? Would you use the same powder in both? I'm omitting for a moment the differences in what guns like what powders for the sake of comparing a faster powder to a slower powder.

It's also worth noting that going from 26" to 16" is a substantially different thing than going from 18" to 10.5". That being said, the general concept of what I posted above is correct.