Barrel vibrations v's crazy stock idea???

DenisA · Post by **DenisA** » Mon Jul 28, 2014 8:29 pm

Seeing as the exit time of the bullet V's muzzle angle due to barrel vibration is the key to grouping potential, what if............ there was a barrel blocked stock that had a barrel block at the muzzle and the rear length of the barrel and action were free floated. In my mind, the barrel would be free to vibrate as much as it wanted rear ward and the critical muzzle end would remain sturdier (with a rigid stock design). The scope would have to be mounted to the stock so that it agreed with the muzzle and not the vibrating action.

And then, what if there was a soft hydraulic mounted barrel block towards the action.

Have there been any known experiments similar to this?

Just a thought......

Longranger · Post by **Longranger** » Mon Jul 28, 2014 9:01 pm

Hell, it might just work! You can only try...

I'd think that unless you can eliminate all vibration and harmonics from the stock very slight position changes would be disastrous. Who knows until it is tried though.

RDavies · Post by **RDavies** » Mon Jul 28, 2014 9:41 pm

Although others who, unlike me, know what they are actually talking about, might prove me wrong, I was thinking there has to be some sort of barrel movement at the muzzle so that we can tune the barrel to regulate any velocity differences out of the load, at least for long range shooting anyway.
Maybe having a hydraulic mounted block at the muzzle end might be better to keep some sort of muzzle movement, but to slow it down a little??????

johnk · Post by **johnk** » Mon Jul 28, 2014 9:58 pm

I've wondered whether the rifles with the tensioned sleeves over the barrel don't achieve that to some degree, immobilize the muzzle, that is.

Post by **AlanF** » Mon Jul 28, 2014 11:14 pm

As Rod says, in order to get the advantage of compensation at long range, you actually need the muzzle to have the freedom to vibrate. This idea might be good for 100m BR but for our game, probably is barking up the wrong tree?

Longranger · Post by **Longranger** » Tue Jul 29, 2014 5:50 am

I think compensation would only be useful to counter velocity spread to reduce vertical dispersion at long ranges as stated. If the sd and es are minimal does compensation really matter that much?
I can't see it, but I am happy to learn more about it.

I like where this discussion is heading.

pjifl · Post by **pjifl** » Tue Jul 29, 2014 7:22 am

People seem to think that compensation is for long range shooting.

BUT need FAR MORE compensation at long range, not less.

Well, we certainly dream about it when V spread really matters giving elevation dispersion on the target. So perhaps this is why compensation is usually associated with long range.

Trouble is that at very long range like 1000y or more, small velocity spread causes an enormous elevation spread and you will need a spaghetti thin barrel to bend enough in vibration for this to be possible. Even if this is possible, it would be badly mis-tuned at closer distances.

The reality is that compensation is not hard to achieve at the shorts but with the stiffer barrels we use for accuracy it is unlikely anything close to full compensation is possible at the longs.

Super accurate loading involving case volume matching and powder weighing is the only realistic alternative in conjunction with measuring V spread and will bring immediate improvement.

By all means, experiment.

This is different from a barrel weight which may induce a wider accuracy node and give other benefits.

Peter Smith.

RDavies · Post by **RDavies** » Tue Jul 29, 2014 7:33 am

If muzzle velocity was identical, there would be no need for regulation.
A muzzle velocity difference of only 15 fps will mean over 3.5" of vertical on top of your rifles accuracy potential in a 284 and 4" with a 308.

DenisA · Post by **DenisA** » Tue Jul 29, 2014 8:17 am

Ahhhh, I thought I'd understood the theory of compensation tuning but had never realised that it was essential to long range precision.

I thought it was another option that could be used in place of nodal tuning.

Basically what's being said here is that nodal tuning is essential for the shorts and mids and compensation is essential in conjunction with nodal for the longs?

Post by **AlanF** » Tue Jul 29, 2014 9:26 am

DenisA wrote:Ahhhh, I thought I'd understood the theory of compensation tuning but had never realised that it was essential to long range precision.

I thought it was another option that could be used in place of nodal tuning.

Basically what's being said here is that nodal tuning is essential for the shorts and mids and compensation is essential in conjunction with nodal for the longs?

Denis,

Compensation and ladder testing for nodes are directly related. For a given distance you get maximum compensation (or over-compensation!) at points of minimum rising slope (or maximum falling slope) on the ladder graph.

Peter,

I agree that stiffer barrels will usually be more accurate, and thicker barrels less vulnerable to heat distortion, and thinner longer barrels would generally have wider amplitude of vibrations. If we concentrate on the normal F-Class long ranges of up to 1000yd, and 10Kg weight limit, there must be an optimum length and profile for accuracy and compensation, which may include a muzzle weight. While I agree that a well compensated tune for the longs is going to be over-compensated at the shorts, that shouldn't be a problem - just a matter of having short and long range barrels. You might have one that goes from 300 out to 800 and another for 900 and 1000.

I now believe that while velocity spread and bullet uniformity are key requirements for LR, the benefits of compensation should be used to further improve vertical dispersion.

Alan

Brad Y · Post by **Brad Y** » Tue Jul 29, 2014 11:15 am

While my first 7mm barrel has proved to be more than a handful and is now retired, I'm going to stay away from the big thick and stiff barrels until I can figure it out. There have been a few well respected shooters that have advised going the opposite route and get a tapered barrel that will "whip" and show me where a node is. More than likely the first barrel wasn't great and it's reinforced the importance of keeping things basic til some results are on the board. Possibly I got lucky with the 260 improved and the thick barrel with only the slightest amount of taper. But I can see merit in the idea of barrels that are easy to identify the node. Then if more weight is required or I wish to use a fixed weight to increase the size of the node.

aaronraad · Post by **aaronraad** » Tue Jul 29, 2014 1:30 pm

Now we just need projectiles that reduce their BC with a shot-to-shot increase in muzzle velocity instead of increasing their BC and putting the shot higher...I think I've got that the right way around...

RDavies · Post by **RDavies** » Tue Jul 29, 2014 3:43 pm

AlanF wrote: While I agree that a well compensated tune for the longs is going to be over-compensated at the shorts, that shouldn't be a problem - just a matter of having short and long range barrels. You might have one that goes from 300 out to 800 and another for 900 and 1000.

Alan

Otherwise you could have 2 loads (or 3) for each barrel.

My 2 Dashers which get used for short range F class and 1000yd BR, works best with .2gns less powder at the long ranges.
My old 284 which gave great vertical out to 1200 and 1500yds preferred an extra .3-.4gns to get best accuracy at 300-500yds. This is the opposite of what some people do who add powder for long ranges.
Now I keep it simple with my 7mms by doing what you said. One barrel for 500-800yds, the other for 900-1200yds.

Tim L · Post by **Tim L** » Tue Jul 29, 2014 8:20 pm

This thread takes me back to a train of thought I had a while ago in relation to indexing the barrel.
In a previous life I used to chase a little white ball around the countryside. During this time I got to know one of UK's master club makers. He used to run all his shafts through an indexing process in order to establish the plane in which they wanted to vibrate. I have no idea how he aligned that plane to the club head, but he made damned fine golf clubs.

I don't know how one would determine the natural vibration plane of a barrel, but I'd bet my left nut every barrel has one. Perhaps those hum-dingers we see from time to time are simply a coincidental aligning of the barrel with the vertical plane. A barrel that WANTS to vibrate vertically would provide a longer dwell at TDC with less lateral drift during it's oscillation cycle.

Just a thought

aaronraad · Post by **aaronraad** » Tue Jul 29, 2014 9:09 pm

PM sent Tim L