Author Topic: Understanding Barrel Harmonics and Oscillation  (Read 7949 times)

Offline ModernSurvival

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Understanding Barrel Harmonics and Oscillation
« on: September 21, 2008, 09:49:42 AM »
The following is mostly an exert from the NEF/H&R Handi Rifle list I posted several years ago in response to a guy asking about a poor shooting superlight 243 Handi Rifle.  That barrel shoots like crap and I think NEF (now part of Marlin) should get rid of it.  The NEF is a two piece stock gun, generally the low pressure rounds are tack drivers (22 hornet, 30-30 win, 45-70, etc) and the stiffer stuff shoots pretty good.

Lots of tricks to partially float the barrel (which is hard in a break barrel gun) and other things are done by NEF freaks (like me  :D ) to make them shoot it is part of their charm.  Anyway there was a lot of confusion on why floating barrels, etc makes a gun shoot better so I wrote the following piece. 

This should be useful to anyone wanting to understand rifle accuracy tactics even if you never shoot, touch or even look at a Handi  Rifle

----start exert from Yahoo----

It is all about two things

1. Barrel Oscillation
2. Barrel Harmonics

First oscillation is the way the barrel moves in a circular motion. When we
look at a barrel we see steel and think of it as solid and rigid but this is
not the case. When you apply 50,000 CUP and shove a round down a barrel at
3000 FPS in a rotational pattern the barrel moves A LOT. It moves in a
circular undulation in the direction of the twist of the rifling. Stick
your arm strait out and make small circles with your whole arm that is
basically what your barrel does when you fire it.

Second Harmonics is really how consistent the oscillation is, in other words
as your barrel oscillates it effects your point of impact. This by itself
is NOT bad so long as you get good harmonics shot to shot. What that means
is the barrel shooting the same round oscillates the same way each shot.
Things that change this are pressure points on the barrel, heat, stiffness
of the steel and other factors.

So now think about this you have a 30-30 pushing a 150 grain pill about 2300
FPS or a 308 pushing the same bullet at 3000 fps which one will oscillate at
a higher rate of speed and power?

Again this is not bad by itself but minor differences in pressure on the
barrel will produce greater differences in harmonics when the oscillation is
more powerful. Another way to think about this is if you strike a rock with
a steel rod it will bounce off and how hard you grip it and where you grip
it will effect how it bounces right? OK now if you strike it gently it is
easy to get a very consistent bounce each time but if you hit it very hard
it becomes more difficult to get the same bounce right?

The effect on a barrel is the same. This is why you "float" a barrel not to
avoid oscillation but to improve shot to shot harmonics. If your stock
touches the barrel it is not bad as long as it touches the same way with the
same pressure each time shot to shot. As a stock expands with heat of the
environment or the barrel or say from humidity the pressure changes and
point of impact is effected.

So if you float a barrel you get consistent harmonics because the barrel is
not touching anything. Likewise a thick heavy barrel is less effected by
pressure points and heat then a skinny one by being more rigid, oscillation is
reduced and the effect of variations is therefore reduced as well. Back
to our steel rod a thick rod slapped on rocks will vibrate less then a thinner one.

Now while a break action rifle can be very accurate it has a limitation in
that you can never float the barrel fully and the two piece design will
always have some inconsistency in shot to shot harmonics. So the higher the
velocity and higher the pressure the more oscillation and the greater the
variance in harmonics.

----start exert from Yahoo----

The above explains things such as

1.  Why a synthetic stock will stay accurate easier then a wood stock if neither is floated.  The synthetic stock changes less due to temps and humidity.  If a wood stock is floated the point is moot.

2.  Why people say lever guns are less accurate then bolts but many 30-30s and 35 Remington drive tacks.  As lower pressure rounds the two piece stocks and shot to shot harmonics are less of an issue.

3.  Why floating and "glass bedding" matter in the first place.

Hope you enjoyed it,

« Last Edit: September 21, 2008, 09:53:11 AM by ModernSurvival »

Offline Patriot:Ex Machina

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Re: Understanding Barrel Harmonics and Oscillation
« Reply #1 on: September 22, 2008, 08:45:20 PM »
Great Post Jack!