Does changing barrel length change the most accurate loading?

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hardheart

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Reading a little about obt, harmonics, finite element analysis, etc, there seems to be an idea that a specific velocity for a particular length produces the best accuracy. Since muzzle velocity changes with barrel length, even with the cartridge parameters remaining the same - when (or does) an increase/decrease in barrel length require a new load? Like, 16 increased to 18, 26 down to 22, etc. Keeping all else the same - manufacturer, steel, coating/treatment, twist rate.

I'm wondering because factory match doesn't seem to come in carbine/pistol etc varieties. Do they just assume a narrow range of barrel lengths used, or does it not matter since the increase in velocities for longer barrels tracks with the optimum velocities for those lengths? Perhaps a particular round is most accurate at 2600 from an 18 inch barrel, but needs 2750 on a 22 - and it just so happens that those are the average velocities of that one load out of those two lengths without changes to charge weight or seating depth.
 
Well, how about a hypothetical? Take 100 of the same model and barrel length rifle and shoot ten shot groups of some factory match grade ammo ten times on each. Then take another hundred of the same rifle, but with a barrel length 20% longer or shorter than that first hundred. Shoot the same load for ten groups of ten shots each like the first. I suppose my question then is would you expect the average accuracy out of the two groups of one hundred rifles over those ten thousand rounds shot from each group to be appreciably different? Does the load need to be changed to shoot better because of the different barrel lengths?
 
Harmonic vibration is a complex subject. For any given load and barrel, there may be more than one ideal harmonic or "node". This is usually where the barrel harmonics fall in line with the bore axis. It's not unusual to find, as you work a particular powder/bullet up from min to max, that you'll actually have two powder weights that will produce nodes on the bore axis and produce good accuracy. if you're so lucky, then you just have to choose the one that best suits your needs.

Creighton Audette came up with ladder testing, and you can find his work on the internet. I suggest his work as a starting place for those interested in load development. That original ladder test has been modified by several people to make the process a little easier than the original, but the concept is the same.

6mmBR (www.6mmbr.com/laddertest.html) has a good article on Long-Range Load Development for those wanting to know more.

BTW, handgun load development doesn't really benefit from the process - well, I don't think so unless maybe you have a Ransome rest.
 
My impression is that factory loaded match ammo is match ammo because it:
A) is a load that is proven to work consistently well in a variety of firearms, and
B) is loaded to very tight tolerances to enhance it's consistency and accuracy.
 
Every barrel will have it's own node. They may be close so it depends what you are trying to accomplish. Shooting matches or hunting. I have a 6 dasher that I had the barrel reset.(chopped off 1 1/2 inches from the chamber end, 30 inch to 28.5 and re-chambered) The accuracy node changed while comparing a ladder test from the original to the reset.
 
Like, 16 increased to 18,
Click to expand...

How are you going to make a barrel longer? :)

I understand what you're getting at, but as said every barrel is unique. If you cut a barrel shorter you rarely lose any accuracy as long as it is done right and they often prove to be more accurate.

I've found that virtually all of the time the load that is most accurate in one rifle, will be most accurate with all of my rifles in the same cartridge. I have 4 rifles in 308 made by 3 manufacturers with 18", 20" and 22" and 22.7" barrels. Some are a touch more accurate than the others, but it doesn't seem to matter what ammo I use. And the rifle with the 20" barrel is consistently the fastest of the 4.
 
On one hand, it's more or less an academic question. Just to try to understand better when a change in barrel length becomes significant to the system of the firearm and particular cartridge loading. And for different scenarios, (edited - I do not even know what auto correct was thinking here, sorry) How about lopping six inches off and going hunting with the same recipe. Maybe not. When does it become significant or materially measurable. That's the other hand, if I rebarrel and go with an 18 instead of a 16, does load development need to happen because of the length as well as any manufacturing tolerances stacking? How about going to a 26, would anyone expect the same charge weight and seating depth to potentiallyy shoot just as well?

I rarely, if ever (not that I'm an authority on what gets posted), see anyone ask what the barrel length is when someone else asks for a pet load for a semi or bolt gun. It seems most people think all they need is the cartridge, bullet weight, powder choice, and action. So, is an accurate load an accurate load (on average) regardless of barrel length. Or does it need tuning based on barrel length as well as the method of rifling, the tolerance between parts, the intended use, etc.
 
Last edited:
hardheart said:
On one hand, it's more or less an academic question. Just to try to understand better when a change in barrel length becomes significant to the system of the firearm and particular cartridge loading. And for different scenarios, (edited - I do not even know what auto correct was thinking here, sorry) How about lopping six inches off and going hunting with the same recipe. Maybe not. When does it become significant or materially measurable. That's the other hand, if I rebarrel and go with an 18 instead of a 16, does load development need to happen because of the length as well as any manufacturing tolerances stacking? How about going to a 26, would anyone expect the same charge weight and seating depth to potentiallyy shoot just as well?

I rarely, if ever (not that I'm an authority on what gets posted), see anyone ask what the barrel length is when someone else asks for a pet load for a semi or bolt gun. It seems most people think all they need is the cartridge, bullet weight, powder choice, and action. So, is an accurate load an accurate load (on average) regardless of barrel length. Or does it need tuning based on barrel length as well as the method of rifling, the tolerance between parts, the intended use, etc.
Click to expand...
Maybe its easier to think of another way. If your throat erodes a couple thousandths it can change your tune. So will inches of barrel change anything
 
Barrel length has more to do with velocity than accuracy. Theoretically, there is an accurate bullet/powder combination for every barrel (you may have to rub the Budda's belly and hold your mouth just right). That said, I will say I've offloaded a couple of rifles that I never could get to shoot like I wanted, i.e. sub-moa.
 
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