Range Report Optimum Barrel Time and barrel length

[Notso]

I'm a big believer in The OBT theory of barrel harmonics and such. All the charts for the nodes reference barrel length. My question however is: do barrel attachments such as brakes, flash hiders or suppressors affect barrel harmonics and if so, how do I determine which barrel length chart to choose?

I have a hard time believing a big hunk of steel screwed on the end of the barrel isn't going to affect harmonics. But since the attachment is NOT the same material, thickness, weight, etc of the barrel - can you just pick the barrel length from the chart by just measuring the barrel plus the length of the attachment?

 

[bohem]

Re: Optimum Barrel Time and barrel length

My testing with the OBT has shown a trend that attachments to the barrel do not affect the OBT. The barrel still likes the same load whether the can is on or off, the POI is affected by the attachments.

 

[damoncali]

Re: Optimum Barrel Time and barrel length

Anything you add to a barrel will change the way it vibrates, both the frequency and the amplitude of the vibrations will be different. In some cases, you may even be able to change the shape of the barrel vibration. The bigger the weight at the end, the more it will change it. This is exactly how the Browning BOSS works, and how benchrest tuners work.

But my understanding is that OBT is the idea that the minimizing the rate of change of the bore diameter at the muzzle at the time of bullet exit will minimize dispersion. Frankly, I think it's a bit of a logical leap, but whatever - I'm all for people digging around in this stuff and it's at least an attempt to explain some of the voodoo that we see.

In any case, I would expect that there might be change, but maybe not. I would guess that the interface between the two components would introduce some sort of complication at the very least.

But honestly, I'm just not sure I buy the theory in the first place.

 

[sharac]

Re: Optimum Barrel Time and barrel length

The end of the barrel whips and forms "a line in time" so for a given amount of time a barrel will draw a pattern. So if you'd put a pencil (<span style="font-weight: bold">don't</span>

) inside a barrel and produce the same vibration as when firing a result would be a pattern on the paper. What you are looking for is a "time" where pattern covers the least area on paper - usually a swing which will create either an U or an A or something similar. So for a given exit time lapse the barrel swing will be as close as possible and this gives you a window where you can:

- be inaccurate in loading
- be inaccurate in quality of components
- be inaccurate in position/rear support

Basically for a load that is on the node you can have a small amount of error and still be pretty close to the POI of ideal load.

OR in short OBT node will give you certain range of speeds (usually around 60fps window - depending on caliber, bullet etc...) which will still produce close groups on target.