Hot Barrel and Accuracy
- Thread starter bsekf
- Start date
Heavy barrel is more rigid
D-4297
Gold $$ Contributor
Physics . The "light" barrel is smaller in outer diameter , thus heats up faster , initally gets smaller in the I.D. of the barrel as it heats up , but then the Bore begins to expand , as the barrel temps get greater , and the whole barrel expands , increasing in diameter . So the Bore expands , along with the total diameter of the tube . Saw this same issue when making 20ft. sections of Pump shafts for deep water wells , from thick wall tubing . You could only thread the ends when it was cooled down , or the threads were over-sized due to heat expansion of the tube .
My understanding has been that the harmonics change with heat, an old timer called it barrel whip, but I'm not testing in any scientific way.
All of my medium, heavy and dangerous game rifles have pressure points on the barrel.
I have a heavy barreled 358 magnum with the barrel completely bedded. It shoots, 1 1/16" at 300 yards.
My one varmint rig is free floated, it shoots 1 1/8" at 300 yards the other has a pressure point, it shoots 1 1/16" at 300 yards both with varmint weight barrels.
I simply shoot how the barrel works, a thin barrel heats up quickly so working loads is more time consuming and shot strings in the field are short.
The heavy barrels heat up more slowly, however with that said in my experiance rate of fire, operating pressure and cartridge capacity dictate how much fire you can get before you screw up your bore and accuracy.
My 223 with moly bullets and coating, running at 63,000 PSI can fire 2 rounds a minute on a summer day with a 50 shot string and has no loss in accuracy without excessive heat, not uncomfortably warm to touch. A 45MM case
My 6MM Remington with the same moly, running 65,000 PSI needs to slow the fire to 3 rounds in 2 minutes and with a 50 shot string has no loss in accuracy without excessive heat, not uncomfortably warm to the touch. A 57MM case.
My 358 magnum with moly, running 64,000 PSI requires a much slower rate of fire, 1 round about in about 75 seconds and I've never shot more than 15 round but there was no loss in accuracy, heat is not uncomfortableto touch. A 63MM case.
All of these rifles can make aimed accurate 5 shot groups in short time, maybe in a minute, without any serious heat issues, not uncomfortableto touch.
My medium game light barreld rifles, generally running around 60,000 PSI, withn57 and 63 MM cases, cannot maintain accuracy with with any rate of fire near my heavy barreld rifles. They cannot produce more than 3 shots in rapid succession with any accuracy, most only 2 shots. Barrel heat for a quickly fired 5 shot is significantly high, uncomfortable to touch and the 100 yard groups are awful.
The old timer said the heat on the thin barrels increased the whip. I have no scientific explanation but only experience of the effects. It may be BS but the effect is real.
dgeesaman
Gold $$ Contributor
The heavy barrels simply have more metal to absorb the heat of firing, so they warm and cool much more gradually. If you're trying to run a quality string of 10 shots, that's essential to holding a good group.
A hot barrel changes shape because of the cooling. The lower half of the barrel is bathed in cool air and that air warms, rises, and keeps the upper half surrounded by warmed air. In theory that will push POI down. Then that hot air rolling off the barrel forms mirage you have to see through. Mirage shields work, but they work better when they don't have to work hard.
Pencil barrels can be just as accurate if the thermal effects are thoroughly controlled. Thats hard to do outside of a shooting tunnel.
Also in match rifles you have a weight allowance, and the barrel is an awfully good place to put much of that weight.
Much is discussed about barrel whip. Barrels vibrate in all directions and forms simultaneously during a shot. But some barrel profiles will have their natural frequencies spread out more, which should make tune windows a bit broader and easier to hold. I'd have to do math or research to see which profiles have their natural frequencies spread out more.
A hot barrel changes shape because of the cooling. The lower half of the barrel is bathed in cool air and that air warms, rises, and keeps the upper half surrounded by warmed air. In theory that will push POI down. Then that hot air rolling off the barrel forms mirage you have to see through. Mirage shields work, but they work better when they don't have to work hard.
Pencil barrels can be just as accurate if the thermal effects are thoroughly controlled. Thats hard to do outside of a shooting tunnel.
Also in match rifles you have a weight allowance, and the barrel is an awfully good place to put much of that weight.
Much is discussed about barrel whip. Barrels vibrate in all directions and forms simultaneously during a shot. But some barrel profiles will have their natural frequencies spread out more, which should make tune windows a bit broader and easier to hold. I'd have to do math or research to see which profiles have their natural frequencies spread out more.
Comment of the free-floating aspects since the difference in barrel weights has already been addressed.
First, I'm not a gunsmith but my gunsmith who's has been building custom rifles for 30 years told me that the pressure points were devised to provide increase barrel support / stability for factory rifles which had cheap stocks with no substantial bedding. This was especially applicable to light weight barrels.
Remington, to my knowledge, had pressure points on all their sporter weight barrel models. Kind of proving the point, their heavy varmint rifles with aluminum bedding block stocks were free floated. Not sure about the heavy varmint models with wooden stocks.
Removing the pressure points on some of these models without adding bedding can cause the accuracy to go haywire. After market Bell and Carlson Medalists stocks with bedding blocks for the sporter weight Rem barrels are free floated.
Note that Tikka's are free floated and all the one's I've had shoot terrific including the sporter weight barrel models. While the stocks are stiffer than most factory synthetic stocks, there doesn't seem to be any special provision for bedding. They also have that slotted recoil lug design which puzzled me why the Tikka's still shoot so good.
The Browning sporter weight barrel models I have are also free floated, but they have factory installed bedding.
Another interesting note, the Bell and Carlson Medalists stock stocks for Vanguard rifles have both an aluminum bedding block and a pressure point. I questioned Weatherby about this and they told me that their testing shows that their 24" sporter barrels shoot more consistent with a pressure point regardless of the bedding. It seems Bell and Carlson agrees. Perhaps it's due to the longer thin barrel.
Personally, I like free floated barrels. It just seems logical that as the barrel temperature changes and expands or contracts, that this could change point of impact due to a pressure point in contact with the barrel.
First, I'm not a gunsmith but my gunsmith who's has been building custom rifles for 30 years told me that the pressure points were devised to provide increase barrel support / stability for factory rifles which had cheap stocks with no substantial bedding. This was especially applicable to light weight barrels.
Remington, to my knowledge, had pressure points on all their sporter weight barrel models. Kind of proving the point, their heavy varmint rifles with aluminum bedding block stocks were free floated. Not sure about the heavy varmint models with wooden stocks.
Removing the pressure points on some of these models without adding bedding can cause the accuracy to go haywire. After market Bell and Carlson Medalists stocks with bedding blocks for the sporter weight Rem barrels are free floated.
Note that Tikka's are free floated and all the one's I've had shoot terrific including the sporter weight barrel models. While the stocks are stiffer than most factory synthetic stocks, there doesn't seem to be any special provision for bedding. They also have that slotted recoil lug design which puzzled me why the Tikka's still shoot so good.
The Browning sporter weight barrel models I have are also free floated, but they have factory installed bedding.
Another interesting note, the Bell and Carlson Medalists stock stocks for Vanguard rifles have both an aluminum bedding block and a pressure point. I questioned Weatherby about this and they told me that their testing shows that their 24" sporter barrels shoot more consistent with a pressure point regardless of the bedding. It seems Bell and Carlson agrees. Perhaps it's due to the longer thin barrel.
Personally, I like free floated barrels. It just seems logical that as the barrel temperature changes and expands or contracts, that this could change point of impact due to a pressure point in contact with the barrel.
If the barrel is heating and moving point of impact shifts. Free floated or not. Harry McGowan built my heavy 358 and recommended bedding the barrel because of barrel weight, 30" and 1.2" diameter no taper.
I ask him about there not being free floating on my factory Remington. He ask about the length and diameter and I said 26" heavy varmint. He said the long heavy barrel was more likely to be less stable without a pressure point.
So I ask if the long thin barrels had pressure point because of stability and he said they many times simply had low accuracy results without a pressure point.
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drop_point
Silver $$ Contributor
Interesting because I have 4 Lite Models, and 1 Varmint Model - all are free floated from the factory. There are mix of T3's and T3X's.
There is no stock forearm contact until near the recoil lug area.
drop_point
Silver $$ Contributor
I certainly am in no position to dispute your trained gunsmith since I have no professional gunsmith training. I guess there is a difference of opinions between gunsmiths. All my heavy varmint rifles are 24 to 26" in length. Whether that would make a difference or not compared to your 30" length I don't know. But mine are all free floated and shoot sub 1/2 moa with tailored reloads.
There is a renowned gunmaker in Adamstown, PA who make high end custom rifles. He's been published in the American Hunter magazine in articles by celebrity hunters. I don't use him because I can't afford his rifles, but I occasionally see him at the range testing his custom rifles. He makes his own stocks, and all his rifles are free floated. He espouses a similar philosophy as my rifle smith, that the pressure points at the tip of the forearm are designed to provided increase stability for cheap factory stocks with no bedding.
I forgot to mention in my original post that I have a Weatherby Supervarmint Master - one of the most "out of the box" accurate rifles I've ever owned. It has a heavy 26" barrel. There is a pressure point back at the 3/4 point in the forearm but not at the tip. So go figure.
Wow, that's interesting because I can run a dollar bill down the forearm of all of mine without contact until I near the recoil lug area.
drop_point
Silver $$ Contributor
Wow, I just did a google search and found out there is a wide variety of stocks making it out there. Some have a V-block section 3" or so in front of the action, some have one a few inches from the tip, some have both, and some actually float. Very strange. I grinded that surface away on mine. Not sure how much it gained me, but mine shot well.
All I know is that all my Tikka's shoot great - especially the varmint model and all are free floated.
Mine were purchased from 2014 to 2019.
drop_point
Silver $$ Contributor
After 55 years of shooting I'm interested in the results more than what it takes to achieve them. As I said I have 1 varmint free floated and one not floated both shoot well.
I will agree that the stock bedding is important however I'm not qualified to claim that a good stock and bedding is all that's required to use a free floated barrel. I have a 102 year old Remington Model 17 that was sporterized that shot poorly. I relieved some stress points in the stock and that helped but not enough. I then added a pressure point and now it shoots 3" at 300 yards, not bad for an old WW1 battle rifle.
I think McGowan bedded my 358 because he said a 1.2" diameter (no taper) 30" barrel would sag over time and stress the receiver. At the time and now I am not at a point with my mechanical knowledge to argue, especially given the fact that having a 358 Norma Magnum that pushes a 250 grain Hornady SP at 3,200 FPS and averages 1 1/16" groups has proven the man right with this one.
Don't ask why that type of barrel, suffice that 600 yard cold bore shots work fine, I sent along 3 dummy rounds to cut the throat and to test feeding.
Mike Burns built me a custom dangerous game rifle in 450 Marlin on a Mauser 98 with a 22" Shilen air guage medium weight barrel that is also bedded. Accuracy is awesome for this type of rifle but a 500 grain projectile at 2,000 FPS is unhealthy as a bench rest rifle.
My thinking as well. If I can't get it done in 3 shots I don't need to be out there in the first place.
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