Point of no return. .308 cal barrel length?

As the load combos in FTR start to stabilize, we will get a better feel for where the bullet likes to be. My suspicion is that popular bullets like the Berger 185BT and 200gr H are going to be shot within a 75fps window regardless of the ingredients.

The combo I am using matches shooters from 3 countries that merged to the same conclusion in different ways. Ultimately, a bullet and barrel will only shoot in a narrow window... we just need to figure out what that is.

One of the big unknowns on any barrel is what is the ACCURATE speed it will produce for you. I have had super long pipes that shot like crap and actually produced accurate velocities LOWER then shorter barrels. So barrel length equalling more accurate speed is not always a given.

My present combo seems to be very stable and tuning has been a breeze. Over 4 barrels all chambered to the same spec, loads are within 0.1gr and grouping is near identical. The last barrel I tested took 9 bullets to confirm the node after I sighted in the barrel.

No barn burner load but with that level of simplicity, I'll take it.... Now for the snow to melt and get out longer distance to confirm all this goodness.

FTR will be very interesting in the coming years as shooters try all manner of tech to push more performance out of this case. A lot of stuff will not amount to much but nothing ventured, nothing learnt.

Then you show up at a windy match and have your "you know what" handed to you by a shooter using a Palma load - beat a bunch of shooter using the latest greatest. When I quizzed him on his choice, his answer was simple. .... Been shooting this combo for over 20yrs, I KNOW where it is going to go.

Interesting.....

Jerry
 
WG300 said:
to cook a 308 win barrel in 1500 rounds, you need a smack load, read stupid dangerous, of either N550 or N540 as they are really warm burning powders. Those shooters are UK guys and throw their brass to garbage after 1 firing. If a brass is cooked by then, mean they are runing dangerous pressure for sure. As for the load i stated above, my barrel life was estimated at 2900 rounds...and was done just before that.
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Oh the silliness was not limited to 1 country :)

A bit luck, a bit of design, I am working on a new stock that will try a few very different ideas to try and take strengths from rail guns and suspensions. Maybe push the fence posts forward. Maybe crash in a big flaming heap.

We shall see...

Jerry
 
RIFLEF said:
There is no sight radius in F-Class.
I realize that, but the question is IDEAL length for F-Class? Or beyond what length do you stop gaining velocity?
To take it to the absurd could we see 50" barrels on the firing line?
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There are no ideal lengths (that anyone has come up with yet?), due to what compromise you may need to make in the build. The first decision is what can you get? I've always approached my FTR built in that the three heaviest components you have are the barrel, the scope and the bipod and one of the three gets compromised due to weight. I run a tube gun on a Remington 700 - my bipod is a Rempel (yes, there are lighter but this is my preference) and a Nightforce scope (yes there are lighter scopes, again my preference). With the NSX, my barrel length was limited to 26.5" and it worked well to 1000 yds. The Competition is letting me go to 28.5" and while testing needs to be done, I'm sure it will work. My barrel blanks are the Rock Creek MTU profiles and a heavy Palma profile might gain another inch or two.
 
I agree with WG300. we come to the same conclusions but using different methods. the longest barrel you can possibly get to work with your F/TR rig which will still make weight.

longer barrels have two main factors going for them, the gain more speed (lose less) and they provide better ES/SD numbers (complete burn of powder and spike anomalies).
My current rifle has a 32" heavy palm. you can ask robertii how much fun it was making sure I made weight.

here is some more numbers
http://www.accurateshooter.com/cartridge-guides/308win/

and if you really want to wrap your head around some of this stuff look up the writing of Geoffrey Kolbe
http://geoffrey-kolbe.com/
 
the post is about "barrel lenght"...but what about contour, and flutes ??!! I figured out that a 7 pounds barrel is optimal for a FTR rig, whatever lenght you choose. The need for a straith 1 1/4" is essential when shooting heavy's to help manage torque and vibrations. I'm always looking for a straith of a minimum of 4 inch after recoil lug. My last year barrel was too skinny and was shifting P.O.I. with temperature raise,,,,,specially at Raton of 20 shots strings ! This year gonna be a fluted barrel, at 7 pounds and 34 long, but will finish at 1in and have a straith 1 1/4 for 6 inch :) cant wait to put that beast on my action.
 
WG300 said:
the post is about "barrel lenght"...but what about contour, and flutes ??!! I figured out that a 7 pounds barrel is optimal for a FTR rig, whatever lenght you choose. The need for a straith 1 1/4" is essential when shooting heavy's to help manage torque and vibrations. I'm always looking for a straith of a minimum of 4 inch after recoil lug. My last year barrel was too skinny and was shifting P.O.I. with temperature raise,,,,,specially at Raton of 20 shots strings ! This year gonna be a fluted barrel, at 7 pounds and 34 long, but will finish at 1in and have a straith 1 1/4 for 6 inch :) cant wait to put that beast on my action.
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My guess is If your POI was changing while the barrel was warming up it means your barrel either has stress in it and no amount of fluting will help that ,or the bore is crooked to the point where one side of the bore is thicker than the other and the thin side gets hot faster so the barrel warps a bit .
 
Coyote, i confirm that it was shifting while warming up. Trying to identify the exact reason is more complex but your statement is right. As for fluted barrels, they are stiffer within the same weight of a barrel that dont have flutes so i figured out that it can only help, and it will.
 
WG300 said:
the post is about "barrel lenght"...but what about contour, and flutes ??!! I figured out that a 7 pounds barrel is optimal for a FTR rig, whatever lenght you choose. The need for a straith 1 1/4" is essential when shooting heavy's to help manage torque and vibrations. I'm always looking for a straith of a minimum of 4 inch after recoil lug. My last year barrel was too skinny and was shifting P.O.I. with temperature raise,,,,,specially at Raton of 20 shots strings ! This year gonna be a fluted barrel, at 7 pounds and 34 long, but will finish at 1in and have a straith 1 1/4 for 6 inch :) cant wait to put that beast on my action.
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if I was a betting man I would look elsewhere, I would concentrate on the wood stock. did you bed the section of barrel just ahead of the recoil lug? I don't suspect it is the barrel touching the (barrel channel) but have you been able to run a dollar bill between the barrel and barrel channel after finishing your string?

Trevor
 
For me, I wonder if barrels can be MADE more temperamental by "insulating" the barrel especially at the heat we run with string fire in the summer???

Guess what, a tight fitting forend is a whole lot of insulation for only PART of the barrel. Why I leave my barrels fully exposed. The thought is that they can heat and cool evenly reducing the chance of "hot spots" increasing issues.

With paired shooting, there is enough time for the heat to radiate and equalise but in machine gun US style string fire, things get very hot very fast. Even well stress relieved steel has to show a degree of warping to the "cold side". Is it much? Does it take much?

World-FCNC005_zpscfc2784d.jpg


The barrel block was another way to support the weight so no stress is put on the receiver. Also makes one heck of a heat sink BUT is a huge PITA to set up and string fire heats things up too fast for the block to really work as intended. It's going into the dumpster however, can work very well in other application.

Bedding is a huge issue with these super big heavy barrels. I have found that supporting under a fair amount infront of the receiver is a very good thing.

I agree with WG300 on the need for a heavy shank. With the #7HV Shilen and #17 Krieger, there is 6" of 1.2". Lots of mass to absorb that heat.

Fluting can be a mixed blessing. If the machining is not precise and even, will you impart stress points in the barrel that can influence heat induced warping????

Is the barrel stress relieved after fluting? Does it matter? Can it matter?

I know it can be done successfully but one more variable so not something I will use at this time. Shilen lists this contour at 7.5lbs wit 28" finished so I am closer to 7 3/4 lbs and I have no issue making weight. In fact, it looks like I will be able to add ballast to the stock.

The quest continues for the "magic" combo..... I don't think we will be deciding on anything for a long time to come.

Jerry
 
Trevor60 said:
if I was a betting man I would look elsewhere, I would concentrate on the wood stock. did you bed the section of barrel just ahead of the recoil lug? I don't suspect it is the barrel touching the (barrel channel) but have you been able to run a dollar bill between the barrel and barrel channel after finishing your string?

Trevor
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there is approximately 0.250" free around the barrel. I beleive that air must circulate around it as much as possible depending on stock design. Also, the only contact point on the recoil lug is in the back, no contact in front and on the sides...and under. I agree that flute have to be made properly. As the barrel is a Bartlein, and flutes made by them, i can only assume it will be done properly on a CNC machine.

time will tell if the decision was good. I ahve a backup gun, that shoot even better than the one i had last year so....no stress :)
 
WG300 said:
there is approximately 0.250" free around the barrel. I beleive that air must circulate around it as much as possible depending on stock design. Also, the only contact point on the recoil lug is in the back, no contact in front and on the sides...and under. I agree that flute have to be made properly. As the barrel is a Bartlein, and flutes made by them, i can only assume it will be done properly on a CNC machine.

time will tell if the decision was good. I ahve a backup gun, that shoot even better than the one i had last year so....no stress :)
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There are many thoughts on how to bed a rifle. For me, I fully encapsulate the recoil lug and under the barrel. Depending on the stock, action, I may even impart some preload on the bedding to ensure all is supported when the action is bedded down.

The reason is that the recoil lug is where ALL recoil forces and bending loads should be transmitted. IF there is room around, then the lug has no support in that direction and forces move upstream.... usually to the action bolts. These are of course, NOT designed as load bearing devices and can cause all manner of headaches.

Square bottom actions offer a lot of benefits to aid in this but I would rather put as little stress on this part as I can.

When hanging that long and heavy a weight off the front unsupported, there is a very real chance to start bending that receiver. And if the loads are concentrated, they will impart bending into the stock.

The whole leg bone connected to the hip bone scenario.

As I said, there are PLENTY of thoughts, ideas and methods with this which have shown positives and negatives over time and many rifles. I just see the loads on parts and want to reduce as many variables as possible.

If you see that you are having stringing issues, try putting a blob of modeling clay under the barrel about 3" infront of the receiver to support the barrel. Maybe it helps....

Jerry
 
i made a lot of testing regarding bedding last year both in the way to do it and even the compound itself. I made all of those test with one rifle, proceding carefully and providing accuracy test with same load between changes. And by then, i can confirm that your flyers problems are coming from the fact that you have contact elsewhere than behind the recoil lug. Remove all of that and you will find repetition like never before with the same load.

The weak spot is wright in front of recoil lug. You need to provide support that goes from under the action until half way in front of the fore hand.
 
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