How to match powder to barrel length?

[Mikecr]

What has been working great for me:
Using QuickLoad, I run what-ifs to find fastest powder that fills the case, right at SAAMI max pressure, causing no more than 8Kpsi muzzle pressure, with a given case/bullet/barrel length. I tweak barrel length where that's under my control to nail this.
Cartridge design also plays a big role in this, as it can hold powder back to burn in/near chamber, or it can add a slug of unburned powder to bullet mass, burning way down the barrel or on muzzle release, if at all. The latter in extreme can cause a secondary pressure spike exceeding 1st pressure peak, to a dangerous level. And it's opposite of clean bullet release..

A competitive 6PPC sees ~6,600Kpsi at the muzzle, efficient mid-hunting capacity ~8Kpsi, a good magnum ~12Kpsi.
Barrel lengths follow.

 

[Philward]

Maybe the more important question would be why install a longer barrel?

 

[QuietTexan]

People put on longer barrels because it's very easy to show consistent, substantial, and repeatable gains in velocity by increasing barrel length holding other features (chambering, bullet weight, powder, etc) constant. This is all a balancing game. You can also gain velocity holding everything thing else constant by increasing case capacity. But that introduces variability of efficiency, and changes recoil profiles significantly.

Do you want fast and soft? Go longer barrel, which typically ends up with heavier rifle. Do you want light and fast? It's going to kick. Do you want absolute precision? Choose an efficient design that isn't necessarily practical for reliable feeding. So many variables to fit so many goals.

Also impacts load tuning. Since longer barrels nearly always gain velocity in a sane range, it's an expedient way of finding a faster velocity node.

If you absolutely need to get a certain bullet to 3000 FPS, your options could be - 300 RUM in 18", 300 WM in 22", 30-06AIN in 26", 308 in 28". Stack a weight limit or barrel length preference on the velocity target, and one guy might want an 18" 300 RUM when another guy shooting off a bench would be happy with a 30" 30-06AI. The 18" RUM is undoubtedly going to be significantly less pleasant to shoot than a 30-06, doubly so if it weighs 6# compared to 18#.

But to be fair you've tumbled in to asking one the most important questions when it comes to picking a chambering - pick something designed to do what you want? Or beat a square peg into a round hole? Longer barrel is round peg/round hole stuff, works pretty much every time, tradeoffs in most cases are limited increased length and weight, not a lot that can go wrong with adding barrel length, and if it does it's easy to rectify by chopping and crowing the barrel.

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[Veteran]

X10 on Quick Load

What I like to do is build a file for your bullet, your volume measured brass, input your bbl length, and then there is a button in quick load that will generate all the various powder combinations that will result in a certain velocity or pressure. It spits out a table you can review of powders that work for the specs you enter. Be careful as it will give a warning on pressure and danger if you did not select a pressure limit that works. Then you can select a powder from list based on your desired velocity and of course these days powder availability........

If all it spits out are H1000, Retumbo, and Varget, or N570,
all your science may be to naught.

 

[Justice1327]

I know Gordon has passed on, but GRT is an excellent software for load work up that is free.

 

[Mike Matteson]

Trying to match you reloading components to the rifle. That a daunting question. It's what you want, and will that rifle you have do what you are trying to get out of it. So you have to have an idea as to what you want. I start with the reloading manuals, with their velocity, bullet weight. to get to somewhere in the range of what I want. I start at the low end of the powder being stated. I use there primers suggestions. You have ladder tests, that will kind of show where to go. The whole point is to get ES & ED down lowest numbers possible. Achieving what velocity you are wanting to achieve, and getting the groups as tight as possible, and within reason. Staying within safe chamber pressures. Again it's, what you want to do with that rifle.
Here a place to read and learn. Not all is correct, but it's enlightening but stay tuned in here.
Me: I hunt in weather that ranges from -20 to 115+. So I have to be very careful on what powders I use. I have to know the path the bullet is taking down range in the different temps. So you have open pandoura box.
Now down the rabbit hole. There is, Primers, Powders, Brass, bullets of all different types. There is reloading equipment from all prices ranges and what they will do. I use RCBS mostly for a great many years. Now changing to other types of equipment. It's how deep your pockets are and what you are trying to achieve. Now I have been reloading for 60 years now. I load for rifles, pistol, and shotguns, in several different caliber, and shotgun gauges. Now I was and do achieve groups in the 1/2" areas of less by using RCBS Eq. That's by being careful on how I put together the round. There is a lot of equipment out there that's good or better. One item I would go to if you haven't purchase much in reloading dies is bushing dies, and FL too. Hopefully this help some, and it doesn't tell you what to use. You Will Have To Figure That Out.

 

[Mikecr]

Maybe the more important question would be why install a longer barrel?

QuietTexan well covered a lot, and then there is the counter consideration; why go with a shorter barrel?

Shorter barrels are more forgiving to barrel tune because they're stiffer for weight.
Desiring this attribute while adding barrel length, also means moving up in profile weight to keep stiffness.
This changes gun balance and could force you to add weight to the butt stock to regain good balance.

A good LR big boomer is likely heavy, and for stalking hunting, less field practical.
So then you're considering fluting or carbon barrel enhancements.
It always begins with a bullet, then cartridge to push it, then barrel to cover, and overall system to reach all needs.

 

[biff's reloading]

Theres a ton of gun math out there. Google cartridge overbore ratio and start reading all the forum threads on the subject.
Case capacity in h20 divided by bore area gets you a basic expansion ratio, then work in the length of the tube (volume) to start understanding how many "case capacities" there are in the bore volume that need to be filled by the gasses produced, then work in the payload (bullet weight x speed =work) to your equation and you will have It. Basically, this is how quick load works. It comes up with a dynamic working number to apply to the known burn rates of all the available powders, which spits out load data in a form we simple humans can understand

This chart should list bore AREA, not diameter. You have to do that math yourself to get good results. Pi x r2

 

[Mikecr]

Theres a ton of gun math out there.

Ok Biff, how long should a 6.5x47L barrel be for a 140gr bullet at 3kfps?
And how did you get from the table to your conclusion?
Thanks

 

[biff's reloading]

Ok Biff, how long should a 6.5x47L barrel be for a 140gr bullet at 3kfps?
And how did you get from the table to your conclusion?
Thanks

That's not really how it works, But I'd build it at least 24" if it were mine. Speed will be determined by your load and chamber/throat. Longer tubes are more efficient, giving you the 3k u want with less inputs, but you gotta haul the fence post around too so the compromise is needed.

 

[MagnumManiac]

In reality there is no formula for barrel length and powder burn rate that works until extremes in both long and short come into play.
A 22rf works most efficiently at 18", the pressure at the muzzle at bullet release is highest. Move to a 24" barrel and pressure and velocity has dropped. Now we can't change the powder used in a 22rf, but we can tune with barrel length.
Unfortunately, due to the nature of the PROGRESSIVE nature of the powders we use mostly, except ball powder which is DIGRESSIVE, barrel length plays almost no role in the outcome.
@QuietTexan summed it up very well with his description.
It is the cartridge size, bore size and the Expansion Ratio that determines what powders work efficiently, not the barrel lengths because the same powder in a short barrel will also give the highest velocities as used in a long barrel.
Every reloading manual will show you this.
Those powders listed at the top with the highest velocities are the same one's across the board that burn at the most efficient utilising that Expansion Ratio regardless of barrel length, short or long.

Cheers.

 

[Tommo64]

tagging in. I know Quick load is a easy solution for a price. It has a % burn rate, based on barrel lenght, powder, etc. So there is probably a math formula out there somewhere?

Gordons Reloading Tool is another option. And it's free!

 

[hydehunter]

I'm 100% with Cohunt on this one.

Just for fun, go over to Hodgdon's reloading site and look at the 308 Win data under both rifle and pistol. They list data for both 15" and 24" barrels; it's the same data for both lengths. You'll see the same thing when you compare rifle and pistol data from other sources.

I just looked up 150 Nosler bullets for the 15" and 24" barrels in 308. using IMR8208 powder the 15" lists a max if 2655 fps and in the 24" lists almost 2900. in my 30.06 with an 18" barrel I get 2864 with a 152 Hammer Hunter Bullet using IMR8208 powder and when it was a 24" using H4350 I was getting 2924 so the IMR is a faster powder and got me close to the 24" barrel load worked good

 

[yorke-1]

I just looked up 150 Nosler bullets for the 15" and 24" barrels in 308. using IMR8208 powder the 15" lists a max if 2655 fps and in the 24" lists almost 2900. in my 30.06 with an 18" barrel I get 2864 with a 152 Hammer Hunter Bullet using IMR8208 powder and when it was a 24" using H4350 I was getting 2924 so the IMR is a faster powder and got me close to the 24" barrel load worked good

You're comparing the listed data for a 308 to your results from a 30-06?

What are the velocities when you shoot the same loads in the 18" barrel compared to the 24" barrel?