Barrels and Accuracy

Right...important things barrels.

I realize that shorter, heavier barrels tend to vibrate more consistently during shooting and are probably more accurate on average (sets up a vibration barrel pattern that duplicates well from shot to shot).
These heavy barrels are also better at handling heat expansion/movement.
And they give extra weight to the rifle hence stability to the shooter.

But what I don't understand is why when you sometimes cut a barrel shorter (so 'should' be more accurate), it actually loses accuracy.
Let's assume the barrel is cut from 24" to 18" and the recut crown is as good as the original. Why then can it sometimes be that the barrel is actually less accurate?

I haven't heard of shorter barrels being more accurate.
Heavier barrels, yes, because of less movement/whipping.

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Originally Posted by Cigar

I haven't heard of shorter barrels being more accurate.
Heavier barrels, yes, because of less movement/whipping.

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Barrel shortness = stiffness. A short bbl is stiffer and helps reduce harmonics issues. Sure all barrels whip when the rifle is fired and a thicker, stiffer = shorter barrel will be more forgiving and more accurate on a whole.

Some guesses that could effect accuracy after a barrel chop,
1) Harmonics of the whole system has changed. With the shorter barrel the projectile may be exiting when the barrel is at a different point of "whip" each time.
2) Velocity change, could try and regain that with reloading but again that comes back to the harmonics in a way.
3) Less mass, more felt recoil and more noise. Harder for the operator to shoot accurately.
4) Murphy is a bastard and doesn't like it when people tinker with things?

Even the finest barrelmakers will have variation in the bore and land dimensions, and no barrel is perfectly straight. So when a knowlegable gunsmith seeking the finest accuracy shortens a barrel he/she will take careful measurements to ensure the dimensions at the crown are optimum. Most gunsmiths dont have the skills or equipment to do it so just wack it off at the desired length. Mostly its ok, sometimes a barrel that previously shot well might now not. The same sort of principles also apply to threading barrels for suppressors.

Yeah, some good ideas there. I especially like #1

1 - if the barrel's dimensions change (as when it is shortened), then the vibrating frequency does change. You might then have to change the ammo you use as the barrel harmonics will be different and therefore accuracy will be different.

But then you should be able to get accuracy back with different reloads even after a barrel chop (whereas sometimes you can't... 'your Murphy law').
But maybe harmonics only matter when shooting factory ammunition as handloading allows you to tune a load to a barrel's harmonics?

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Originally Posted by Tentman

Even the finest barrelmakers will have variation in the bore and land dimensions, and no barrel is perfectly straight. So when a knowlegable gunsmith seeking the finest accuracy shortens a barrel he/she will take careful measurements to ensure the dimensions at the crown are optimum. Most gunsmiths dont have the skills or equipment to do it so just wack it off at the desired length. Mostly its ok, sometimes a barrel that previously shot well might now not. The same sort of principles also apply to threading barrels for suppressors.

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Ok, so you are saying there are 'good' and 'bad' / 'loose' and 'tight' variations in the actual barrel's bore/rifling.
So if cut for shortening at the wrong place = worse accuracy.
And I suspect it's no use re-cutting a new crown at that same place.....you would be better getting the barrel cut back another inch and then recrowning (to hopefully get out of the 'loose' variation).... Correct or not?

Shortening it further will be a lottery unless the GS has the measuring equipment and skill to use it.

Accuracy has a degree of alchemy involved. There are rules and exceptions that prove the rule.


Some barrels with twist rates that are theoretically too slow still shoot very accurately with heavy for twist rate projectiles.

Some barrels that are fitted with open sights and a two piece wooden stock can shoot better than the muzzle breaked, carbon fibre stocked
scoped rifle next to them at the bench.

Some barrels shoot well when they haven’t been cleaned in a long time.


All things being equal, variations in accuracy still happen for myriad reasons and that is one of the things that makes the pursuit of accuracy so interesting. Also why it’s a good idea if you end up with something so accurate that the last adjustment at sighting in is one click, don’t muck around and alter that.


If you really wanted to put it down to something though, and this is assuming all things being equal.
The most likely contributor to accuracy loss will be the shooter, due to flinch from increased muzzle blast and/or recoil.

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Originally Posted by Tentman

Shortening it further will be a lottery unless the GS has the measuring equipment and skill to use it.

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Yeah, but I'd take the gamble....if accuracy is crap then I would play the 'shorten the barrel until it's accurate' lottery.

This explanation of yours @Tentman seems to tell me that if you really like the rifle and want to get the best results, you don't shorten it to the shortest length you might want initially. For example, if you think that 18 is probably what you want, start by shortening it to 20 inches and having it recrowned properly. Then shoot it for accuracy. If you're happy with the accuracy, you're done. If not, take off an inch, recrown and try again, etc (down to the legal limit if necessary).

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Originally Posted by longshot

Accuracy has a degree of alchemy involved.

If you really wanted to put it down to something though, and this is assuming all things being equal.
The most likely contributor to accuracy loss will be the shooter, due to flinch from increased muzzle blast and/or recoil.

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Yes...the 'unknown ingredient.

I'm well aware that other variables like the shooter, the ammunition quality, rifle setup, stock fit, trigger, etc are far more important for practical accuracy than barrel length. I was just after the reason why accuracy can go south after a shorten and recrown. Tentman supplied what I think would be the correct answer.

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Originally Posted by Hermitage

Yeah, but I'd take the gamble....if accuracy is crap then I would play the 'shorten the barrel until it's accurate' lottery.

This explanation of yours @Tentman seems to tell me that if you really like the rifle and want to get the best results, you don't shorten it to the shortest length you might want initially. For example, if you think that 18 is probably what you want, start by shortening it to 20 inches and having it recrowned properly. Then shoot it for accuracy. If you're happy with the accuracy, you're done. If not, take off an inch, recrown and try again, etc (down to the legal limit if necessary).

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yes . . . .

Best practice would be to ‘slug’ a barrel to check the best place to cut it if shortening it - especially for a rimfire i.e. seem to remember Calfee writing at length about this…

This is quite interesting, I've never heard of a barrel being less accurate due to being shorter than it previously was. It's not something I've come across before. My current hunting rifle has been shortened 3 times and accuracy has never been an issue. Actually I was at the range recently and there was a new rifle being tested that had been accidentally shortened to 16 inches instead of 18, the owner was seriously conflicted, he couldn't decide whether to be pissed off by the screw up or over the moon that it shot like a laser beam.

Differing lengths could have differing harmonics that could affect accuracy.
You might not notice the difference as it could be small, but it could be large.
It might also be within your tolerance - the accuracy you're comfortable with - whereas someone else might notice the difference.

I'd recommend starting longer and gradually reducing.
It is easier to cut more off than put some back.

If you subscribe to barrel timing theory it’s likely due to the mv not being optimal for the barrel length. I use quickload and the barrel timing calculator for working up new loads. So far it has worked well every time. As someone else commented basically the barrel is not in a stable point in its movement when the projectile exits.

Joe90 has accurately summed it up, and Longshot's suggestion of alchemy pretty much matches my own thoughts. I have often said that successful gunsmiths are also alchemists! The ability to 'create honey out of dogshit' as one of my mates was fond of saying. My opinion on the current subject is that the 6" barrel shortening has reduced the velocity below the 'sweet spot' for the particular projectile. Find a load with a slightly faster powder to boost the velocity by 150-250 fps in the shorter barrel.

i had one cut that must have had a bulge in it

it would stack bullets at what ever the factory sako 75 barrel length was

nipped it shorter and it went to a4 size groups at 100

could have been a bulge but gunworks (robbie) offered to put a new barrel on it
I was a very broke student so im probably never going to stop being appreciative for that

all other ones Iv cut shorter have been perfect and as accurate as when they were long or better and thats at least half a dozen
you always remember your first tho and mine was horrible but im over that now, short tubes are the best when you cant shoot over 300m in any direction and have a suppressor