Are bull barrels more accurate

S

splatman

New member
There are differing viewpoints on
whether a bull barrel is inherently
easier to tune for accuracy than
a regular barrel. Here is my take
on the internal ballistics as your
bullet approaches the muzzle. At
this point the bullet is still accelerating but not as much as
when the bullet is say midway down
the bore. The mathematicians
understand this to be the time
derivative of acceleration da/dt.
As an interesting side note, the
human body can feel acceleration,
like when you jump out of an
airplane, but the body can not
detect its time derivative. In other
words the body cannot detect a
change in acceleration. So getting
back to the internal ballistics at the
point when the bullet begins to exit
the muzzle. So as you know the
barrel is somewhere in its whip
dynamic. Now suppose you have
skillfully fine tuned your load and
the tip of the bullet clears the crown
at zero amplitude... ok thats great.
Now here is what makes life interesting. Bullets have length so
what is happening when the tail
of the bullet clears the crown? Well
more than likely the muzzle is no
longer at zero amplitude. The
muzzle is undergoing a net acceleration in some direction
which is not longitudinal with the
static bore. It is as if the crown has slapped the bullet in the butt
right before the bullet is airborne.
Of course this degrades accuracy
to some degree. It is at this point
the bull barrel shines. The whipping
amplitude is impeded by the bull
barrel from is mere mass and stiffness. In other words, bull barrels dont whip around as much at the muzzle. Of course I am talking about two barrels which are the same in
all regards except the diameter. So if you are considering pushing the accuracy envelope, consider the bull barrel.

splatman
 
So if you are considering pushing the accuracy envelope, consider the bull barrel.
Click to expand...

I like bull barrels, but your assumption that they are the only accurate barrels is a false one. Depending on the quality of the carbon steel and workmanship of those drilling the barrel and chamber as well as how sharp the tooling that is used for drawing the rifling, will make a difference in the accuracy of any rifle.

As I said I like bull barrels but they are a pain in the backside to carry around in the field while hunting. The extra weight make them fine for bench rest shooting but not for free hand shooting in the field. Most rifles that need to be transported on foot you will find in a standard profile and not as a bull barrel, including those used by snipers that have to be extremely accurate.

This was shot with a Savage 110 in 270 Winchester with a standard profile barrel on a budget package gun ($450.00) I purchased about 8 years ago for hunting.

100 yards 5 shot group





Your assuming (ass-u-me) that bull barrels are more accurate is totally false.

Jim
 
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Bull barrels work better for long strings of fire. They are more stable with heating. But for some five-shot group with a cool-down interval before the next group, they don't generally work particularly better than an equally-built lighter barrel. I guess that build quality is as important as barrel thickness.

(I'm leaving bench-rest competition rifles out of consideration, since in the grand scheme of rifles, they're few and far between. :))
 
Bulls are good for heat dissipation and slightly less bullet harmonics as the bullet travels down the barrel.
I have a YH stainless 20in fluted bull on my long range AR rifle.
I can run 30 rounds hard and fast and my POI stays very tight and on target.
A lighter barrel will heat up and the POI will start to spread out as the barrel heats up.
 
In other
words the body cannot detect a
change in acceleration
Click to expand...

A change in acceleration is referred to as a "jerk" and can absolutely be felt by the human body.
If you're accelerating your car slowly, and then stomp on the gas the initial surge you feel is the change in acceleration.

As far as bull barrels go, they are generally stiffer and thus would move less, but the movement in a lighter barrel - as long as it's consistent - would be compensated for when it's sighted in.
 
One, I've never heard of any one tuning a load so the "tip" of the bullet leaves the barrel at a certain time.

Two, a human body most certainly can detect a change in acceleration.... although there are limits. That's why flying under instrument conditions can be so dangerous, slow changes are not felt.

Three, loads are normally not tuned to leave at "zero", center position. It is best if the bullet leaves near the top (or bottom) of the vibration, as that is the area where the least amount of movement takes the most time.

Four, the amount of vibration is a lot less important than a consistent exit timing.

Fifth, it has been shown many, many times that neither a barrels profile nor it's length are indicative of it's accuracy potential.
 
Are bull barrels more accurate?
Not necessarily.
As a former barrel maker myself, I have experience with this issue and I know the process and problems well.

When a barrel is made by any cutting machine process (as opposed to hammer forging) there are 2 “secrets” to making it super accurate.

#1 is to drill and ream a super straight hole and then ream and polish it well. Next the rifling is cut into the bore and those cuts should be smooth and of the same depth. At this point my barrels were all heavy and large. I used 1- 3/8” bars.

#2 is to turn the barrel down to final dimensions and never put undue stress or heat on it as its being brought down to final size. If you have a flowing bath of coolant you can cut more off the barrel then if you have only a brush and coolant, but the speed of the cutting, the tool geometry and tool sharpening all come into play. A barrel held between centers will expand as it heats, and it heats only at the exact point the tool is putting pressure on it. You never want it to “grow” much as you turn it. I used to make my barrels slow enough to be able to touch the barrel within 1 inch of the cutting action with a finger and never have it be hot enough to make me want to draw back. I never make a cut of more than .015" at a time. And I run my lathe at only 190 RPM when I am contouring a barrel. For those that have no experience with running a lathe, I’ll just say 190 is pretty slow.

So, if we look at factories that make guns by the hundreds or even thousands every week it’s obvious they cannot slow the manufacture down to cut a barrel that slowly. If the round stock is thick and if it’s run in flowing coolant you can cut them fast and heat is not a problem The thinner the barrel gets the more stress can be a factor however.

A thicker piece of steel is stronger than a light one, and can be cut faster without distorting it.
That is the biggest reason heavy barrels often shoot better than light barrels on factory rifles. It’s the old “time is money” reason. It’s totally understandable too, when you need to keep the doors open and the crew working.

But in a custom shop where a rifle can be made the old slow way, taking a high quality heavy barrel and turning it down to a “pencil weight” on a good lathe is not a difficult thing to do. When it’s done it will shoot just as well as it did when it was a bull barrel. It will heat up a lot faster, and therefore it will sometimes not last as long as it would have if there was more steel to soak up the heat, but for a rifle that fires 1-2 shots at a time and doesn’t get rapid fire use it will last almost as long as it would have in its heavy form.

Another way to lighten a heavy barrel is fluting. This retains much of the stiffness of the larger diameter, but gives the consumer less weight and more air surface for cooling.

I have built many hunting rifles for customers using barrels that started out at large diameters and when they were done the muzzles are often at or below .500” and they were still sub MOA shooters with the loads they like.

As an example my 25-06 has a 25” long barrel and its muzzle is .475”. The barrel is only .780 5” in front of the breach. It’s a very light rifle, and it will put 3 rounds into a clover leaf group every time at 100 yards. But I took about 8 hours to turn that barrel down and polish it up before I installed it into the rifle for the last time.
It’s unreasonable for customers to expect a factory to take even 4 hours to contour each barrel for its rifles unless you want to pay for that time.

We are used to being able to buy very accurate rifles and get them for under $1000. I can tell you without a doubt that getting a sub-MOA rifle with a long barrel at $1000 or less (sometimes a lot less) and having it come in at 6 to 6.25 pounds from a major factory is not likely to happen with a lot of regularity. Such rifle barrels have to be made slowly to retain their accuracy and that has to go into the production cost.

Yes it’s very possible to make a light barrel shoot into one ragged hole. But those barrels can’t be made fast, and therefore can’t be made cheap.
You can buy very accurate short light rifles. Shortening the barrel is a way to keep it stiffer. That is one way the industry gives us good performance at a good price.

All in all when we look at the performance we can buy today for not much money, it’s amazing to me that Ruger, Savage, Weatherby, HOWA and Winchester can do what they do. My hat is off to their engineers.
 
Nothing to detract from the above, all true, but I'll add. While it is possible for a lighter, thinner barrel to be almost as accurate as a heavy bull barrel, (at least until they get too hot) most people find it easier shoot heavier guns more accurately.

A lot of weight can be lost, or gained in the barrel. Put a 10 lb rifle on a bench next to a 6 lb rifle and most people will shoot the 10 lb gun more accurately. Minor imperfections in technique are less likely to pull the sights off target with the heavier gun.

But those differences are not huge, especially for a skilled shooter. For a target shooter the difference between a gun that shoots .2 MOA vs .3 MOA is a big deal. As a hunter anything under 1 MOA is just fine. From shooting positions encountered in the field you can't really take advantage of much more accuracy. It is simply not worth carrying around a 10 lb rifle that shoots .2 MOA when a 6 lb rifle will shoot .7 MOA.
 
While a bull (read thick for its length) barrel will have lower amplitudes of whip and at higher frequencies than slimmer ones, so they may direct bullet from their muzzles in a smaller angle of fire. To do that, the barrel time (initial shock of primer and powder pressure building time to muzzle exit; around 1.1 to 1.2 milliseconds for most centerfire rifles) has to be exactly the same for every shot. Otherwise, even bullets leaving at the same muzzle velocity with different shaped pressure curves will exit at different angles of departure; small spread, but it's there.

What about barrels that bend their muzzle axes off the intended direction as they warp from heat stress? A thicker barrel will warp less and it may compensate for some of that muzzle-axis bending. But this is the normal compensation issue when two variables cancel each other out. Why not just square up the receiver's face so the barrel's properly fit and all barrels will then shoot to the same point of impact for dozens of shots fired quickly.

Oft times, the "accurate" rifle is said to be one whose bullets exit when the barrel's straight; mid point in all of its whipping and vibrating cycles. That 'place you have skillfully fine tuned your load and the tip of the bullet clears the crown at zero amplitude.." and the barrel's perfectly straight This is where the anglular rate of change is the fastest. Two bullets leaving 10 fps on each side of the average muzzle velocity you've tuned that load for will leave at the greatest angular separation. What happens to the bullets' trajectories if both have exactly the same in-flight BC and they leave on the muzzle axis down swing; which bullet will strike higher on the target? What happens if they leave on the muzzle axis up swing.

http://www.varmintal.com/amode.htm

http://www.varmintal.com/aeste.htm

The Brits proved over a century ago that their whippy-barreled SMLE's shooting cordite charged .303 ammo with huge muzzle velocity spreads, that when they left on the up swing just before the muzzle axis reached its upper limit, the slower ones going out at a greater angle had their increased bullet drop compensated for way down range. The reverse happens as faster ones leave sooner at lesser muzzle axis angles. The Mauser 98 actions with the same barrel type shot better at the shorter ranges with that same ammo. When they started using 7.62 NATO arsenal ammo for their matches, 'twas soon evident that its lower muzzle velocity spread help short range groups but the long range ones suffered. They got permission in the early '70's from the British NRA to use a commercial, stiffer, front locking Swing action for the same barrel weights and lengths; those barrels whipped less and shot the NATO ammo better at all ranges

https://archive.org/details/philtrans05900167

Smallbore rifle shooters often put tuners on their barrel muzzles so the ammo shoots faster ones out a bit later on the ideal part of the barrel whip cycle on its way up to compensate for its muzzle velocity spread. A happy medium is often used that works well for both 50 and 100 yard use. Others have a tuner setting for each range. A mechanical engineer at the Olympic Training Center's shooting range put some accelerometers on rifle barrels and timed whip versus bullet exit; proved this works very well indeed.

So, 99.99% of all bullets fired get their rear end slapped by the crown as it's moving through its normal arc. 1 out of 10,000 may exit in that .0000001 second time frame when the barrel's muzzle axis is either at its upper or lower limit.

There's a way one can compensate for out of square case heads that typically cause horizontal shot dispersion with top and bottom bolt lug postioning, too. Find the heavy side of all your unbalanced bullets then seat them relative to the high point of the case head so when that high point's on the right side, those unbalanced bullets heavy side will make them jump to the left from centrifugal forces as they exit the muzzle.

It's best to have all the variables be at zero in an accurate rifle; every moving part does so the same way and amount for every shot. Accuracy is the reduction of all variables to zero; or as close to it as possible. A barrel that whips exactly the same way for every shot is perfect; doesn't matter how much nor in what direction.
 
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"A change in acceleration is referred to as a "jerk" and can absolutely be felt by the human body.
If you're accelerating your car slowly, and then stomp on the gas the initial surge you feel is the change in acceleration."

If you are at a stop and your
400 horse power motor is ready
for action and you put the pedal
to the metal, and your head jerks
back you are feeling acceleration,
that is you are feeling your
velocity change, you are not
feeling a change in acceleration.
The body can only detect a change
in velocity.

When the space
shuttle reaches it target speed,
say 30 miles per second, and
thrusters are turned off and
acceleration goes to zero, there
is no force on the body, F=MA
(Newtonian mechanics). At this
point you are moving at 30 miles
per second but you cannot
perceive it, you have no idea or
sensation that you are moving.
 
You're making a distinction without a difference.

V=d/t
A=Δv/t

A changing velocity IS an acceleration. In fact, it's the very definition of an acceleration.
 
I have to agree more with Brian Pflueger, but splatman has the concept correct, as recoil is usually measured in foot pounds (ft/lbs) or torque. However, the horsepower reference is misleading because horsepower is actually a derived number; (torque in ft/lbs x RPM)/5252=horsepower. But force over distance is the bottom line here.


Btw, next time you see a dyno sheet in a car magazine (or online) if the tq and hp curves don't meet at 5252 rpm, it's a doctored fake.
 
i have a semi heavy barrel on my custom 6.5,the Cooper pheonix also uses the semi heavy barrell.its thicker than a standard barrel but not quite a varmint style bull barrell.
i like it.being that 125 yards is the longest target i have ever seen never mind hit i cant say i am a match grade barrell expert.it shoots tight groups at 50.i have not used the 100 yd target yet but i will.its a pain to walk all the way out to 100 every 3 shots.many people put up 3 targets at 100 and have a telescope to check the groups but i have that.
plus in vermont 75 yds is long shot anyway and at a 50 yd target i can see the groups through the rifle scope.

semi heavy is a good choice
 
Rimfire internal and external ballistics and accuracy theories are different from higher-velocity centerfire rounds. Most .22LR rounds achieve optimum velocity in about 16 inches of barrel, after which acceleration stops and there is a slight deceleration to the muzzle.

Barrel vibration is mostly vertical, but also in other directions as well. The trick to consistency is to tune the rimfire barrel to have as many rounds exit the muzzle when the barrel is nearly at the uppermost limit of vertical travel, when movement has slowed.

Rimfire ammo has a greater percentage of variation in velocity, due to design and manufacturing tolerances, so it's perhaps more important to achieve a tuned barrel than with centerfire benchrest ammo, which is assembled with more precision.

Rimfire benchresters have found that super-heavy barrels are generally not as accurate as lighter ones that better respond to adjustments of barrel tuners. That fact has been proven by building/testing huge machine rest guns with very heavy barrels that hardly vibrate. In fact, several precision rifle builders have constructed tuned sporters that have turned in scores that are as good or better than some Unlimited rifles.
 
No there not in a nut shell. The ability to shoot more rounds faster with out barrel heat up is it. Heavier may help keeping on target while pulling trigger easier,but that is a shooter problem, not a more accurate barrel.
 
"You're making a distinction without a difference.

V=d/t
A=Δv/t

A changing velocity IS an acceleration. In fact, it's the very definition of an acceleration."

Yes that is correct A=dv/dt. So what
is da/dt ? (the time derivative of
acceleration). Well is has no
special name its just an acceleration
differential. At some point between
the breech and the muzzle the bullet
reaches a maximum acceleration.
This does not mean that the bullet
has reached its maximum velocity.
When the bullet reaches the muzzle
it still has a positive acceleration,
and therefore its velocity is higher
at this point than at the point of
maximum acceleration. From an
earlier post this is not the case for
22 rimfire with long barrels. The
bullet has undergone a deceleration
in the bore so its maximum velocity
is attained prior to its muzzle velocity . This happens when bullet friction
overtakes the pressure from expanding gases due to volume
increases as the bullet travels down
the barrel. The 22 rimfire is a very
interesting little beast for a couple of
reasons. No gas leaks occur from the primer since the primer is internal. The internal ballistics of
the 22 is more like an explosion
compared to the centerfire. I have
a Ruger 77 22 mag with a Basix
custom trigger its one sweet piece.
 
Splatman, are you pressing your [Enter] key after typing a few words?

If you don't, the system will let your typed lines extend to the window's width.
 
splatman said:
Yes that is correct A=dv/dt. So what
is da/dt ? (the time derivative of
acceleration). Well is has no
special name its just an acceleration
differential.
Click to expand...

All the equations and names in the world don't change the simple fact that a human being most certainly can feel an acceleration.

All the gobbledegook about a bullet's maximum acceleration and lesser acceleration and what-not has nothing to do with your original premise.

A bullet reaches maximum acceleration at the point that the pressure behind it is highest. All other points the acceleration is either less and climbing or less and falling. Velocity is increasing constantly (not at a constant rate, at all times) except in specific circumstances, such as longer barreled 22LR.

All of which is irrelevant to "Are Bull Barrels More Accurate?"
 
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