Contra-Testing Free Floating

[davidjoe]

I don’t know exactly what to expect, here, but I’ve been curious about this subject for at least a decade. I’m wondering if anyone has tried this, or has any hunches, as I have just assembled it and not tried it yet.




This is a 40-X with a fast twist straight 6mm chambered in .243 Win. It is not the .243 40-X that is shooting well in the Manners F-Class stock, that gun is undisturbed.

Along the lines of pre-stressed concrete beams, I have carefully filled an opened barrel channel with the correct amount of semi-compressible fill, such that once compressed initially with C-clamps, and finally with strap clamps, the action is flat (or will be after heat cycles), and the barrel is being pressed very tightly into the stock, contacted and semi-surrounded by dampening material. This is tricky.



Plenty of times I’ve padded the channel for heavy barrels, but I have never pulled the barrel down from the top, and it is under significant pressure.




Like action screws, these hose clamp straps can be tightened and loosened as desired.

The rifle is as “dead” as any I have handled. The goal, as always, is to shoot small, but I don’t know if it is a step forward or backward. It’s certainly a step toward my old Crosman.22 pump pellet gun, but I can’t say they were wrong regarding the strap.

 

[K22]

Without exception, all rifles I have owned have shot tighter and more consistently with the barrel free floated.

However, the bedding is critical. In my experience, in most cases, a free floated barrel without adequate bedding will shoot worse. I learned this the hard way with Remington rifles that have that pressure point at the end of the stock. If that pressure point is removed on their cheap stocks without pillar bedding or using bedding compound on the action, the rifles shoot worse. The exception is the Remington's varmint models with free floated barrels that have those aluminum bedding blocks.

The Weatherby Vanguards are similar to the Remington's at least the one that I owned. If you remove that pressure point without bedding the action, the accuracy goes to hell.

What I can't figure out is why the Tikka's shoot so well with factory stocks, free floated barrels, and no special bedding. Then there is that "floating" recoil lug. Defiles logical understanding at least in my small brain. But all my Tikka's shoot exceptional well, out of the box.

Be interested in how your experiment works out.

 

[john 800]

There is a lot going on there…
Keep us posted

 

[Tommie]

Can’t wait to see the results. Thanks for undertaking this experiment.

 

[ClayM]

Veeeery interesting...

 

[JMayo]

I'm sure the free floating barrel millions use & much time and effort r&d to float a barrel is proven better than tying one to a stick.

but hey, go for it. Keep us posted.

 

[Gary in MD]

Did you establish what accuracy that the rifle was capable of before this new work so there is something to compare to?

 

[alchemist]

The barrel is not free floated.

 

[farmerjohn]

Watching... John

 

[Dimner]

I'm all for going against the grain and outside of the box thinking. Seems like this might become a low dough anti float barrel tuner.

Sometimes the projects like these keep one excited in the shooting sports rather than just having a rifle made in the newest greatest 6brxyza.

There is a video I watched with a very high regarded gunsmith who puts together competition service rifles for CMP high power shooting. He has a method for determining where to put a pressure point on the barrel from the handguard. His rifles win.

 

[davidjoe]

Good or bad, there will be a batch of honest results coming today. Wind is terrible. 100/200 only.

 

[davidjoe]

So far so good. 100 wasn’t showing me much. I walked in a rough zero, then went to the upper left for a 5 shot group. In four shots, I started getting a bit too happy and yanked the 5th.




That told me enough to tack up a 200 yard target, and come up 1/2 moa.





The wind presently is very uneven, strong and disruptive (affects the body), and what appears at 200 is basically drift. I know there is a lack of comparison to judge these by, but I believe the gun is shooting as tight with ammo I pulled off the shelf, in these conditions as my most elaborate rigs would do, except that it is rather primitive, and still settling in.

 

[davidjoe]

I'm sure the free floating barrel millions use & much time and effort r&d to float a barrel is proven better than tying one to a stick.

but hey, go for it. Keep us posted.

The action is tied to the stick, though, and most shooters would say that if any more of the action could be in contact with the stick, they would do it, some of the most accurate are glued to it.

We turn a 180 at the recoil lug. Behind the recoil lug, we want them anatomically connected, fused, molecularly, and in front of the recoil lug it’s diving board time. Two of them, really, free to resonate at will. And man do we spend a lot of time talking about the ostensibly solved issue of harmonics and resonance.

The logical difficulty for me is that the stock is strong enough to marry the action to, but where it is even thicker and more rigid, the fore end, which is exactly where the cantilevered barreled action is at its least rigid, well that would be a big “nah” on any contact, we’ll “pass”.

But boxing out structures that exists next to each other anyway, kind of like my car window is at its weakest, just before it’s all the way up into the frame, just hits me as mechanically sound, but at minimum, certainly not crazy.

I can understand that in the past, wood warped, small manufacturing variations would exert different amounts of pressure into sporter weight barrels that would give them different zeros, pressure screws and adjustable tensioning bands were patented at different times by at least Winchester, if not also Remington, and so forth.

There is certainly no easier manufacturing spec than “have a generous, non critical space between them” - but is is better? From the barreled action’s standpoint, there may as well be no forend.

 

[clowdis]

I'd think this would be along the same principle as a barrel bedding block, except you don't have the action floating. Should work well.

 

[RegionRat]

TLDR: There is another important structural concept to keep in mind, that is just as important as stiffness. That is, the damping.

There are no doubts about the basics of static structural concepts like section thickness, truss work, etc..

A stiff barrel section certainly has benefits to group shooting and that is tied to both the mass and the stiffness.

That said, we need to keep in mind that there is more to this than just stiffness or section thickness.

The first big dynamic mode of this system is basic action-reaction straight back along the barrel line and the CG if the rifle while supported on the bench by the rests and the shooter.

While we can certainly machine mount rifles and show how adjusting things like stock stiffness, bedding, barrel sections, etc., all have an effect on the target, there is a practical aspect to keep in mind that affects the size of the change on the groups. We as drivers are not as stiff and repeatable as a gun trunnion or a machine mount, so the shooter matters.

With this kind of gun, your bench manners have the biggest effects. Choosing to allow the barrel line to pivot on the rests, versus move straight back, will be the largest contributor regardless of the barrel straps.

The experiment needs to be baselined the same way with and without the straps, or the change/effects can be swamped by bench technique.

When we consider stiffness, it is easy to imagine the frequency moving up with stiffness but we also need to keep in mind that there is damping on each mode shape.

The damping makes it difficult to predict when moving a particular structural resonance up or down will decrease or increase the amplitude (damping). The frequencies are much easier to model and calculate, but the damping is very hard to predict and usually ends up in testing over analysis.

In so many words, if the horizontal axis is frequency, those modes are easier to predict based on basic concepts like structural stiffness. This looks like the F~(K/M)^0.5 where K is stiffness and M is mass.

However, folks need to remember that to learn if this is important, we really want to know the amplitude and how the change in using the straps versus not using the straps might change the outcome, and that requires knowing (or really testing) the damping. We can't really predict the outcome without testing.

Since the connections are like having a crack in the system that dissipates energy rather than creating an efficient rebound, it may turn out that the real benefit of such an experiment is the damping effect of those soft parts that damp the high frequency mode shapes. In so many words, they may kill the ringing.

It probably explains why OP says he feels the rifle is "dead" and doesn't ring. It could turn out that the change is negligible at the target, or that it damps one or more of the secondary mode shapes.

Only a careful test will tell. Good Luck.

 

[dave@aDave]

Mark Penrod re-barreled my FN Browning Safari.
He bedded it from the tang to a tad back from the front of the stock.
Something about the weight of the barrel and the thickness of the sides of the action.
He didn't want anything to move around.
The rifle shoots very well.

 

[davidjoe]

I’m at 100 letting the barrel cool. Results so far this morning. Target is two bullet types and keyed and sequence labeled. Group 5 was more me than anything else, the first shot was low left and I knew that and gave up on it.

Region Rat is right about holding the rifle the same way on a bipod / pinch bag setup. Also, the factory trigger is pretty heavy, and both of these bullets are high BC heavies and thus not ideal for small 100 yard groups.

Starting the remainder.

 

[davidjoe]

The finish out was far better for the DTACs than the first set was for them. The A-Tiips want to shoot flat and next to each other.




The bold green lines are 1 inch.



I think it’s pretty decent for what it is. The straps are a standard three inch to two inch rubber joint I cut with a pocket knife after the two inch section.

I plan to add another or two just to see what happens. 12 mph this morning and too hot these days to shoot a .243 with stout loads very many times.

 

[Ned Ludd]

I'm thinking that somehow, somewhere, there has to be a "Gorilla Glue" commercial in all of this.

It might go something like this: David, you would be at the range with your rifle, having a somewhat "loose" barrel/stock arrangement. Obviously, the groups would be poor, and you would be complaining about how big they were to a friend. Suddenly, the Gorilla Glue gorilla would appear behind your shooting bench. You and the friend would both let out girlish squeals of surprise, then say, "Gorilla Glue...now why didn't I think of that?". Of course, after gluing the barrel into the stock the groups would all become one ragged hole. You should contact the Gorilla Glue people and suggest this as a new advertisement. I'll settle for 5% of the net. You're welcome.

 

[davidjoe]

Their tape is the main part of what’s inside the channel. No joke ).