Bedding of Barrel in a Rifle

[aadhaulya]

Hi all Members,

I want to know about bedding of a barrel as I have heard a lot about 'Free floating', 'glass bedding' etc.

I did some research and I found the following.

1. Bedding of the barrel means how it rests and/ or connects to the action and stock.
2. There are different types of bedding i.e. how the gap between the barrel and the stock including minor irregularities in the manufacture of the stock, is filled to take care of the movement/ vibration of the barrel on each or a series of shots fired, so that it remains accurate. For this purpose a suitable epoxy compound is used or fiber glass for 'Glass Floating' barrels.
3. There are also 'Free Floating' barrels where the action is firmly mounted in the stock and the barrel is free and is not resting on the stock.
4. High powered sniper rifles barrels are rested on the stock using a suitable material and normally where accuracy is recuired the barrels are 'Free Floating'.

My primary source of information is as follows.
http://en.wikipedia.org/wiki/Rifle_bedding
http://en.wikipedia.org/wiki/Free-floating_barrel

Now my doubts and questions.

1. I suppose sniper rifles should be very accurate then why the difference in the bedding of long range sniper and accurate (competition rifles I presume)??
2. People open up there rifles for maintenance/ bluing as and when required, do they need to bed it down every time it is disassembled??
3. Does any one have an idea if the IOF rifles (my interest is only in 30.06 at this time) a 'Free Floating' or a bedded barrel??

Regards

[timmy]

The way an action and/or barrel is bedded has a lot to do with the design of the action and the thickness of the barrel.

Another major factor is the material used to make the stock, which you might very roughly divide into synthetic/composite materials and, to a certain extent, wood laminate on one hand and wood on the other.

Regarding wood, it is important to remember that no amount of fiberglass bedding material or pillar bedding techniques will stop wood from changing bedding when the weather changes. If there is humidity and the wood swells and then shrinks, for instance, the bedding of the receiver and barrel will change. If epoxy bedding and/or some sort of metal insert is used with the wood, none of these techniques will stop this from happening, although they may offer some help in this regard.

Composite and synthetic material, like carbon fiber, fiberglass, or other such materials molded around a metal armature won't usually change when temperature and humidity changes.

The receiver needs to be bedded firmly in the stock and the action screws torqued to a constant torque, so that the "squeeze" applied to the receiver and magazine cover is constant. Because wood swells and shrinks, "pillar bedding" is one way to moderate this problem. The idea is that the receiver should be bonded to the stock so that they vibrate as one. This way, each time the gun is fired, the bullet will leave the barrel at the same point of vibration of the assembly and the point of impact is both predictable and repeatable.

However, on many commercial rifles, the receiver is made to be used in a rifle that's carried in the field. This is why the torque of the receiver screws is important, especially when using a wood stock. Commercial receivers, especially, flex and bend, so that the torque of the screws will affect both point of aim and the resonance of the stock/receiver assembly, affecting point of aim. Receivers with a broad, flat base or tubular receivers, like the Remington 700 series, are relatively easy to bed. Sometimes, it is best if the sides of a flat-bottomed receiver don't touch the stock on the sides, only the bottom. If you look at the way the Finns bedded the M39 bolt action rifle, you will see a gap between the receiver and stock all the way around, including the rear tang. This reduces the number of ways that the changing wood stock can affect the action and helps the rifle to act the same way at all times and conditions.

Having the recoil lug firmly bedded against the stock is also important. This is why Ruger uses an angled front receiver screw on their M77 rifles: this screw both tensions the action against the stock and ensures that the recoil lug is pulled against the stock at the same time.

Rifles that use a two piece stock, like both of the IOF rifles, are a whole different matter. The .315 is based on the Lee Enfield action, and the issues and techniques the British developed for target and sniper rifles would apply to these rifles. The .30-'06 rifle is another matter.

The barrels bed in various ways, as well, depending on whether they are thick or thin. Generally, if the barrel is thick and heavy, and if the receiver is strong enough to hold the heavy barrel, it will probably be free floating. The common test for this is to use a bank note to run down the barrel between it and the fore end to ensure they are not touching. A sporting rifle barrel may profit from having a pressure point. This could be a place where the fore end touches the bottom of the barrel near the tip. A thin barrel will vibrate in a larger pattern, usually, and this pressure point dampens these vibrations. Again, the goal here is to make the vibration of the barrel consistent, so that it is predictable each time a bullet leaves the barrel. When the barrel is heavy and the action is not rigid, say, like an M98 Mauser with a heavy barrel, sometimes good results can be obtained by bedding the rear-most, thick part of the barrel for 25 to 50 mm.

Another example regarding the barrel bedding is the SMLE, which halfway down the barrel has a tensioning screw and spring. The SMLE uses a relatively thin, long barrel and this is what the British have determined best for the rifle and the way it is used.

You cannot assume that free floating the barrel works best in all cases or none. Again, whether it is used depends on the stiffness of the receiver, the stiffness of the barrel, and the properties of the stock. Because each rifle is unique, even among examples coming off of the assembly line right next to another, each rifle will respond the same way as its neighbor in some ways, but differently in others. Therefore, sometimes applying techniques will work or won't work, depending on the individual rifle. General bedding principles usually work for all rifles of a certain type, but other techniques may or may not work, and must be evaluated by trial and error for a particular rifle.

[xl_target]

1. I suppose sniper rifles should be very accurate then why the difference in the bedding of long range sniper and accurate (competition rifles I presume)??

While benchrest shooters shoot tiny bullseyes, the sniper shoots man sized targets. Many competition rifles are very specialized and would fare poorly in the field.
Not surprisingly, most competition rifles will make the average Sniper Rifle look pretty bad, accuracywise.

Sniper rifles, however, must be consistent in all conditions. The legendary marine Sniper Carlos Hathcock used a 2 moa rifle that never changed zero, no matter the conditions.
2 moa means a two inch group at 100 yards which is considered pretty horrible for many precision rifle shooting events.

Today however, there are some specialized Sniper rifles that are very good.

[aadhaulya]

Thanks Tim & Xl_target, I think I have understood there is no perfect bedding as such and is to be adapted according to the characteristics of each rifle and the purpose it is to be used for.
Now I would like to know that a rifle for normal use would have an existing bedding (or free floating), when one disassembles the barrel for some reason does it fit back into the original bedding or does the bedding needs to be redone every time the barrel and/ or action is removed?

Regards

[dr.jayakumar]

Thanks Tim & Xl_target, I think I have understood there is no perfect bedding as such and is to be adapted according to the characteristics of each rifle and the purpose it is to be used for.
Now I would like to know that a rifle for normal use would have an existing bedding (or free floating), when one disassembles the barrel for some reason does it fit back into the original bedding or does the bedding needs to be redone every time the barrel and/ or action is removed?

Regards

when you use epoxy you don't redo i believe.i think you are planning on your iof.post some pics of the original bedding before you try anything.

one question for timmy and xl_target,will bedding effect a .177 or .22 firearm as there is hardly any recoil?

regards
dr.jk

[timmy]

Disassembling and reassembling the gun should not require rebedding. As long as everything is reassembled properly, and the receiver screws tightened correctly, all should be well.

[aadhaulya]

Thanks Tim,
Dr. JK, I have still not figured out how to remove the stock of my IOF 30.06. But I will surely post pics of the process as soon as I figure out how to remove it.

Regards

[timmy]

Remember that the IOF rifles -- both of them -- use two piece stocks, which are entirely different than one piece stocks normally found on bolt action rifles.

Being unfamiliar with the IOF 30-06, I don't want to make any comment about it for fear of saying something unhelpful.

The SMLE-based IOF 315 rifle requires a very different approach to bedding, as the fore end part of the stock has a number of critical bedding points around the trigger area and against the buttstock socket.

[aadhaulya]

Tim,

Just share your thought, as I plan to open it up anyway and install it back without bedding, hoping the original one will work reasonably well, as I have no requirement of any sort of precision. But it would be a good learning experience.

Regards

[Vikram]

Re the IOF .30-06

http://indiansforguns.com/viewtopic.php?f=13&t=7379

[aadhaulya]

Thanks Vikram, this is exactly what I was looking for.I am going to try once I am back home the next weekend.

Regards

[timmy]

A gunsmith might use soot from fat wood or a dirty candle to find where the barrel or actin is making contact with the stock. We're you playing with a one piece stock, you might try shims of paper or a matchbook cover to vary the stock tip pressure against the barrel. Or, you might use shims of pop can aluminum under the receiver to lift it out of the stock slightly.

On my Ruger #1, a single shot with a two piece stock, I cured my floating zero by shimming the fore end away from the barrel, which free-floated it. When the weather changed, the zero would move up and down considerably as the swelling and shrinking fore end changed the upward pressure on the barrel.

On my Finn M39, I've shimmed the sides of the recoil lug to center the barrel in the stock all the way to the tip. Now I can slide a dollar bill under the barrel (with the handguard removed, of course!) from the tip of the stock to the rear sight hardware. I used shims cut from aluminum pop cans.

The thing about doing this is that you need to spend some time at the range and test each change by shooting groups (I used 10 shot groups) to see what my changes actually accomplished. Tuning.a rifle can be a time and labor consuming task!

[aadhaulya]

I would like to know that shooting at 50 mtrs using a 30.06 rifle how many rounds should be fired to get a grouping that will give reasonable results?
I will be following steps as listed.

1. I will fire some rounds and see the grouping.
2. Remove the stock and see if any additional bedding is noticed or if pieces of bedding fall off.
3. If, as expected nothing falls off, I clean up the barrel and re fix it.
4..Test another round of shots and see the grouping.
5. If the grouping is similar then all is well.

Next step would be experimenting with bedding to tune the rifle.
Kindly correct me if there is a better option or someone feels that I am going about the wrong way.

Regards