How much barrel/stock gap?

[LoonWulf]

So I've just finished fitting a Eurobolt stock to my Abolt. I'm curious how much gap you guys would be comfortable with between the stock and the barrel on a floated rifle?
I've sanded it in so that the gaps even all the way around and a piece of sand paper touches but doesn't hang up.

I like the way it looks now so I'd probably try a pressure point at the forend before sanding out anymore.

 

[RecoilRob]

I always thought the 'traditional' method of checking to see if it's free-floated was to slide a dollar bill down the barrel. If it clears..it's free enough.

 

[jmr40]

I wouldn't use a pressure point, except as a last resort. Most rifles shoot better without them. You are at the minimum. It looks good, but with a wood stock I prefer a little more generous gap in case you get some swelling in the wood. Try it like it is. It is a lot easier to remove more later than replace wood if you remove too much.

 

[LoonWulf]

Rob, I had issues with the dollar bill method or checking. My .243s channel would allow a dollar bill to go thru freely but the stock was still interfering with the barrel. I didn't catch it till I changed stocks and the groups went down. After that I started using a large gap, which I would do on this gun except it would look weird with the thin forend. Thanks guys, I'll try get out and shoot it before modifying any more. I was planning on trying it unless I got a decisive no that's not enough.

 

[Art Eatman]

Both my pet rifles improved with free-float and a shim. Clearance of maybe 1/16". I then waxed the channel against any changes from humidity. I used a folded strip of kitchen waxed-paper just thick enough for a very light pressure between the forearm tip and the barrel. I'd fold the 3/4" strip back and forth until it took about a five-pound pull to insert it. The heat from shooting shrinks it a bit, so I'm guessing maybe two or three pounds of force against the barrel.

My theory is that it acts as a damper on barrel vibrations, giving better shot-to-shot consistency.

.243 and '06: Sub-MOA, reliably and regularly. Beaucoup shots over some thirty-five years.

 

[LoonWulf]

I've never thought about wax paper as a shim, I've always used epoxy or plastic, I'll have to try that one.

 

[Bart B.]

1/16th inch clearance from barrel to stock is good.

Anything between barrel and fore end transfers fore end bending to inconsistent pressure on the barrel. All fore ends bend from external forces. It's tip bends an amount more than a 1, 10 or 100 dollar bill's thickness; measure it then you'll see. The objective is to have a constant force of zero on the barrel in all shooting positions. That's the only way it'll whip, bend and wiggle exactly the same for every shot fired.

Surely, this ain't too hard to figure out and understand. Is it?

Benchrest folks figured that out in the 1950's.

Besides, for those wanting their barrels to cool faster, 1/16 inch clearance makes a lot more room for hot air to get out than 6/1000th inch does.

 

[LoonWulf]

Bart I totally agree in principle, my experience is that in practice with factory rifles floating isn't always the best option. It's always the option I try first (usually it's factory default), but SOMETIMES I think having that pressure on the tip can help compensate for factory bedding, inconsistency (and some guns are just weird). My Abolts glassed into its stock so I'm fairly confident floating the barrel will result in the accuracy I'm looking for, and again my standards are 1.5moa or better. I usually shoot of sand bags with the forend sitting in my palm (same or similar to how I would hold the gun when hunting), I've found that I'm more consistent this way, tho I don't produce as small groups usually.

 

[Dr T]

If I have accuracy problems, I will float the barrel using a dollar bill as a feeler gauge. But, it depends on the amount of flex in the stock. If the stock is very flexible, you may need more gap (like the 1/16" mentioned).

My current hunting rifle is a Ruger Frontier that had the factory bedded laminated stock (not floated). It general it was an accurate rifle off the bench or with a solid rest from the blind. However, I found that If I put any substantial pressure on the stock from a handy sling or holding the fore end with my left hand, my point of impact would shift about 6 inches to the left at 100 yards. I floated it with the dollar bill method, sealed the barrel channel with Watco tung oil, and it seems to work.

 

[Bart B.]

If I have accuracy problems, I will float the barrel using a dollar bill as a feeler gauge. But, it depends on the amount of flex in the stock. If the stock is very flexible, you may need more gap (like the 1/16" mentioned).

All stock fore ends bend. Measure how much they bend from their own weight; stock toe on bench, fore end on support. Use calipers to measure from barrel top to fore end tip bottom; before with the rifle vertical and after its on the bench horizontal.

How much wiggle in thousandths of an inch do your barrels span before their bullets leave? Does it bounce off the fore end tip?

 

[mshootnit]

How far back do you float? I have a gun where the entire 1.5" shank is contacting the stock but free floated from there. OK or float it?

 

[Bart B.]

How far back do you float? I have a gun where the entire 1.5" shank is contacting the stock but free floated from there. OK or float it?

Yes, all the barrel's length from receiver to fore end. Free floated barrels do not touch anything forward of the receiver; they're free of any contact with the stock. If they do, they're partially bedded or floated.

I used to think the chamber area should be bedded. But I learned to shoot well enough to see vertical shot stringing as the barrel and epoxy heated up and expanded increasing more pressure on the barrel. Removed that bedding under the chamber. Starting with a cold barrel, fired 30 shots 20 to 30 seconds apart. No vertical shot stringing as things heated up.

 

[LoonWulf]

Yes, all the barrel's length from receiver to fore end. Free floated barrels do not touch anything forward of the receiver; they're free of any contact with the stock. If they do, they're partially bedded or floated.

I used to think the chamber area should be bedded. But I learned to shoot well enough to see vertical shot stringing as the barrel and epoxy heated up and expanded increasing more pressure on the barrel. Removed that bedding under the chamber. Starting with a cold barrel, fired 30 shots 20 to 30 seconds apart. No vertical shot stringing as things heated up.

excellent info. Id never thought about it, and always bedded the chamber area of a barrel. that right there makes a bunch of sense tho.

 

[Art Eatman]

Both my pets have rather dense walnut stocks. Both are 1971 vintage. A Sako Forester 19" carbine .243 and a Wby Mk V 26" in '06. When sighting in or load-testing, I always locate the front sandbag under the forearm in the same place as my hand will be when in the field. Consistency.

 

[243winxb]

If a rifle was built with bedding under the chamber , when remove , a bull barrel will droop. Requiring more forearm material needing to be removed.

 

[Bart B.]

There's nothing preventing a barrel forward of that bedding under the chamber from drooping. Removing that bedding lets it droop a little more. If the pad is 2 inches long, take it out then reshank and rechamber the barrel 2 inches shorter at its back end. It's then supported like it was at original length forward of the bedding under it.

All barrels droop when held horizontally and fixed at one end. See Table 1 about barrel sag (droop) in:

http://www.varmintal.com/aflut.htm

I've zeroed scopes on an optical collimator with a 30" and 26" long 1.2" X .9" 30 caliber barrels pointing straight up, turned them horizontal then counted 1/4' clicks back to zero.

How many MOA did the barrel axis at the muzzle droop when horizontal?

Better yet, measure yours.

 

[Varminterror]

Most bench rest gun builders will recommend 15-20 thousandths of clearance around the barrel channel. That's 4-5 dollar bills. The old "slide a dollar under the barrel trick," doesn't cut it.

 

[Bart B.]

Winchester once made their post '64 Model 70 stock fore ends' barrel channels 1/8th inch wider than barrel diameter to guarantee the barrels would be free floating with lots of external pressure on it. They knew stock fore ends bend; more so with slender sporter ones.

Too many complaints from potential customers about that ugly wide gap between barrel and stock; custom stocks had virtually no clearance showing a "perfect fit" to the fore end just like the action has to its part of the stock. Sales dropped. They quit making their rifle stocks best for accuracy.

For the 1976 World Palma Matches at Camp Perry, Winchester built a few hundred M70 match rifles for all the teams to use. Rules at the time stated everyone used the same rifle make/model rifle without modification and issued ammo all the same lot. M118 match ammo was used. Some people checked barrel clearance to stock with a folded dollar bill or thin cardboard. A few rifles' fore ends didn't have enough clearance. Those didn't shoot to accurate. Wasn't legal to fix them. A carryover from Great Britian's Commonwealth rules for their fullbore long range matches and most members of the Int'l Palma Committee were from that Commonwealth based on their many decades-old reasoning that the playing field was level with such rules to see who was the best marksman.

 

[MCMXI]

Most bench rest gun builders will recommend 15-20 thousandths of clearance around the barrel channel. That's 4-5 dollar bills. The old "slide a dollar under the barrel trick," doesn't cut it.

Exactly. A $ bill is only .004" thick. I like a minimum of .030".

 

[Welding Rod]

Depends on the rigidity of the stock, but generalIy I would go an 1/8". That way when you sling up it is very unlikely the stock will and barrel will contact, and allows for cooling.

 

[Bart B.]

I would go an 1/8". That way when you sling up it is very unlikely the stock will and barrel will contact, and allows for cooling.

Yes, there's a small amount of cooling, but not much. That heat also warms up the fore end next to the barrel that some say slows down barrel cooling.

Well built rifles won't change point of impact as their barrels heat up. The vast majority of causes is the barrel's fit to a receiver whose face ain't square with the barrel tenon thread and chamber axis. The high point puts more stress on the barrel when it and the receiver heat up. That causes the barrel to whip more in that point's direction from bore center.

Once the receiver's squared up, a dozen shots per minute can be fired and group center stays in the same place.

 

[MCMXI]

That way when you sling up it is very unlikely the stock will and barrel will contact, and allows for cooling.

Doesn't using a sling pull the stock away from the barrel? I've always thought that more barrel channel clearance helps when shooting off a bipod since the stock can move closer to the barrel in that situation.

This is a hunting rifle, not a match rifle, so heat shouldn't be an issue. I expect my hunting rifles to put five shots into 0.7 moa or better at 100 yards within a minute and a half from a cold, clean barrel. My Kimber rifles do this with a #1 Light Sporter barrel (84M/84L) using my handloads which always meet or slightly exceed published maximum velocities. They also do this with the heavier 8400 barrels too, such as the Talkeetna. I inletted the barrel channel on that rifle a little after I removed the barrel band.

 

[Bart B.]

Doesn't using a sling pull the stock away from the barrel?

Sometimes, but only if the force on the fore end is straight down under the barrel.

Depending on the position one is slung up in, the stock fore end can be pulled to the side. If there's not enough clearance to the barrel channel at the tip, then the fore end puts pressure on the barrel at its tip.

There's often some upward bending of the fore end when the shooter's bagged the rifle on a bench and bears down on the rifle held against his shoulder.

Best way to see how fore end pressure ends up bending the barrel is to put an optical collimator in the muzzle, zero your scope reticule on it with the rifle resting untouched on bags atop a bench. Then shoulder the rifle and bag it like you shoot from a bench. Note where the scope reticule now is relative to the collimator. Many people cannot believe they're putting that much down force on the stock as the scope reticule moves away from its centering on the collimator.