I just got done reading a book on accurizing hunting rifles and found a couple of things pretty interesting. One thing was 'pressure bedding'. Pretty much the exact opposite of fully floating a rifle barrel. And that got me thinking...
I have one particular Savage bolt action 30-06 that is sort of a rare find with it's ability to group fairly well with any weight or brand of factory 'off the shelf' ammo. I just got done working up the most accurate handload I could come with using 168gr Nosler ballistic tips. With the right brass,primer, and powder combination I was shooting 1/2" 5 shot groups at 100 yards.
Just for the sake of doing it I took 3 business cards stacked together and slid them under the fully floated barrel around where the front stud is for the sling attachment. Holy Cow!!! The next 2 groups made one big hole in the target at 100yds.
Talk about very cool!
All I have to do now is come up with a permanent form of shim the same thickness and I will be in good shape!
In reality a 30-06 that makes 1/2' groups is more than acceptable in my opinion for a hunting rifle i just tried this for the heck of it and boy was I delighted with the results.
Just thought I would pass this on for some food for thought and maybe someone else will get the same reults as I did.
Kenny



eta:Thank you TaosGlock for steering me in the right direction for some good reading material.

This post has been edited by KENNYOHIOHUNTER: September 15th 2009 4:03 PM

Measure the thickness of the cards you used with a micrometer or caliper. Measure the stock thickness in the area near the swivel stud in the smae manner. Use some bedding compound on the area and file it down wiht a half round file until you have the thickness of the stock plus the thickness of the cards you used.

That is one of the things I was considering, I have some left over accuglass from an older project. I need to see if it is still any good.

It kind of got me thinking about why some of my wooden stocked Remmington's have that little contact point in the same area. Other than that they are fully floated. I actually removed that contact point on my Remmy .243 and the group sizes shrunk quite a bit, maybe I will play with a couple of my rifles in this manner just to see the results.

Just for the sake of doing it I took 3 business cards stacked together and slid them under the fully floated barrel around where the front stud is for the sling attachment.

So if I understand, you changed the fully floated feature by using the business cards as shims?

Exactly.
from what I read some barrels respond quite well to this treatment. The finalized version is called pressure bedding and most rifles that show a sign of improvement are rated at 5-7lbs of pressure. I have no way of measuring the actual pressure but when I used 2 cards it helped, when I used 3 i was speechless!

This particular rifle came from the factory with a floated barrel. A friend and I bedded the action and I was amazed at the difference that it made. Now I am completely amazed at how accurate it is.
It has to do with barrel vibrations at certain points along the bullets path to the muzzle. Using business cards you can add or take away thickness as well as move them up and down the length of the barrel to experiment.

Cool! I'll have to play around with that when I get a chance.

Something to try that does not require messing with your bedding, is a barrel deresonator or barrel damper of some type. It can accomplish the same thing without costing the benefits of a free-floating barrel.

Are you talking about those rubber bushing type "O" rings that slide down the barrel? I have read about those before but never seen or used one before.

Yes, like this. Basically what happens is the barrel whips as it vibrates from the explosion of the cartridge firing. The wider the ellipse described by the muzzle during this vibration, the greater the chance that a bullet will leave the barrel when the muzzle is in a different position than it was when the previous bullet left it.

Preloading the tip of the stock as was done with the cards can dampen the vibration and increase accuracy, but sometimes at the cost of accuracy in another way. As the stock expands and contracts with heat (this happens with composite stocks, too), or yaws or swells as well if it is wood, it can change the harmonics or move the barrel to change point of impact. Additionally, shooting with a sling may cause the rifle to hit in a different spot than resting on the forend does, since the barrel is no longer floated and pressure on the forend could be transfered to the barrel.

That does not mean that preloading is wrong for your rifle - what works well with one may not so well with another.

The deresonator or damper serves a similar purpose in dampening barrel vibration, but leaves the barrel floated. Some dampers are just weights threaded to the end of the barrel. The limbsaver one can be moved forward or backward to find an optimal position. Again, it works well on many barrels, but may make no difference at best on others.

That's a pretty cheap option. I may have to get one and try it on a couple of rifles for some T&E. Thanks for the link.

hm 7.62 u seem to be the kind of guy I been lookin for to run an idea I had by when I first read about barrel whip, what about a sort of shock absorber? Let's say a spring in a cylinder with a ball bearing at the surface contact of the barrel, the barrel whips and the bearing contact moves down in the cylinder and returns to the normal contact point, what ya think? In my mind it could easily be adjusted by having the bearing cylinder be threaded into another cylinder cemented in the stock, and the internal cylinder having a slot cut in it's bottom.

Hmm . . . I'm not sure how that would work, but I would generally try to steer clear of any contact between the forearm and the barrel. Even with a spring tension, changes in the position of the forearm could change the amount of pressure on the barrel.

Sometimes free-floated barrels benefit from having the barrel channel opened up because the barrel vibrates enough to hit the stock.

One of the best ways to settle barrel harmonics is to shorten the barrel. Hacksaws are your friends!

Who makes the rubber donut that fits over the barrel to stop the harmonics ?

LimbSaver

I have never bedded a rifle with preload on the barrel, but I read what sounded like a good way to do it in a gun smithing book. Some rifles do end up shooting better groups with a pressure point on the barrel, but I have no idea why one does and another doesn't. Anyway, if you know how to bed a rifle it's easy to do. Using various layers of your ten-mil tape, set up your contact point with the barrel. Then you just hang the hang the amount of weight you want for pre-load (if you need 4 pounds of pre-load, hang 4-lbs of weight, etc...) from the front swivel stud. With the stock secured in a vise, finish the bedding and torque the barreled action down. After it's said and done, when you remove the weights, the stock is supposed to press against the contact patch with the same amount of pressure. At least it sounds like it would work...


Mike