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338 LM Project

 
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  #15  
Old 09-28-2006, 01:08 PM
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Re: 338 LM Project

BD408,

That is what I was curious about, figured it had to be a carbon fiber barrel and not an all steel pipe.

What is your opinion of the stiffness of the carbon fiber barrels at this lenght. I have fitted several of them and all have been extremely good shooting rifles in the end but I will say that when I chuck up the muzzle end of a carbon fiber barrel in the lathe and get ready to chamber it, it is no where near as stiff as an all steel barrel, even a smaller diameter steel barrel.

By this I mean that it takes very little pressure at all to flex the barrel when the lathe chuck is holding the last 4-5" of barrel and the barrel is hanging unsupported at the breech.

A #5 contour all steel barrel seems to have about the same amount of flex at 30" at a carbon fiber barrel, even a 1.250" straight cylinder barrel.

Comparing a #7 or larger all steel barrel to the stiffness of a carbon fiber is not even a comparision, the all steel takes alot more pressure to get it to flex then the carbon barrels.

Now obviously, for the rounds I have chambered in these carbon fiber barrels, they are certainly stiff enough for fine accuracy but I am just curious about when you put the powder to them in a 338 Allen Magnum with a 300 gr SMK loaded to 3450 fps or even more of a strain when you drive a 350 gr ULD RBBT to 3250 fps.

We are playing with the idea of a 400 gr 338 bullet as well and this will add dramatically to the stress on these barrels. Will they take it?

Just wondering what velocity you are loading your personal rifles to and at what barrel length you have on your 338 Sniper Tac.

What gets me is the barrel cost, DAMN!!! They have to have twice the barrel life because they cost more then twice what an all steel barrel runs!!! [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/grin.gif[/img]

From the barrels I have chambered though, the ABS barrels appear to be the real deal. Everyone has been a shooter that I have fitted and for light weight they are nearly impossible to beat. I just wonder if there is a limit to the stress they will handle consistantly.

I know my barrel in the lathe experiment does not tell alot of scientific data but from what I see, as far as stiffness alone is concerned, an all steel barrel of a #7 or higher offers dramatically stiffer barrels then a carbon wrapped barrel.

Does this hurt accuracy, does not seem to so far, at least not in a 30" or shorter barrel in a round the class of a 338 RUM but we are talking alot more snort with our babies!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

Just curious what you have found.

Kirby Allen(50)
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  #16  
Old 09-28-2006, 03:17 PM
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Join Date: Sep 2003
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Re: 338 LM Project

Fifty:

From what Mike has told me, the bbl under the carbon is still a shootable bbl, with out carbon. Unlike the Christianson Arms using the Shilen tube. I have only put on one ABS bbl in the 338 snipe-tac, it shoots just as good as my personal steel barreled rifle, and a lot less weight. Mike said it will take anything we can put into it, i think the brass will go way before any other signs develop, when testing the carbon bbl earlier this summer, i put some really hot loads through it, "proof tests on the action as well" there was no change that i could see in performance. Groups stayed sub .5 moa through out the loads. There was even one load, way to stiff, that put 3 shots into one hole. Bolt lift was very tight. But this is in no way a test of any sort that shows how a bbl is reacting during firing.
400gr bullets sound good too, i dont think it will change any bbl dynamics, your limited to a certain amount of chamber pressure no matter what bullet weight you use. Twist rate on the bbl may be a big factor, will a 10" stabilize the long bullet? or will the 9.2 be a better choice? The 11" tops out at 300grns, 350grn bullets will key hole in my rifle. What kind of speed do you think the 400gr bullet will go? 3100?
My Lawton bbl is 1.350 breech, tapers to 1.200 then straight tapers to .900 muzzel 33" long then add the brake to end up at 35" total. I fluted it my self, big heavy flutes, it removed a lot of weight. I am loading my rifle to 3350 on average with the 300mk, i have pushed it too 3520,with good accuracy, it will give you a good thump with these loads, hard on brass too. I like to say stay around 3400fps or under.
Yea the price is up there, but they have their use in special circumstances, much lighter than steel. I dont push them to customers, but if they ask, what is the lightest rig you can make then, its Ti action and carbon bbl and 100% carbon stock. If a guy wants a Ti action and steel bbl, i allways ask "why"? What is the purpose of a light Ti action on a heavy steel bbl? It takes me twice as long to build a Ti action vs steel, when you start adding the cost of a rifle with a Ti action the carbon bbl should be the only choice along with it.

As far as the flexing, i have no idea, only thing i can go by is the end results. Groups and the stated performance of the carbon bbl. It may be such a thing where the carbon may flex more, but not vibrate or the flex returns faster than steel. Look at it this way, a carbon golf shaft flexes more that steel does, but a steel shafted golf club will ocilate after the flexing occurs, a filiment carbon shaft flexes but, stops abruptly after impact, where the steel shaft vibrates all over the place. Carbon fiber Absorbs vibrations quickly, they are not transfered through the carbon like steel does. This may play a large role in the bbl dynamics as well, im not an expert on the phyisics in the carbon bbls, but do know quite a bit about the golf shaft industry, but that is another story.
Any bbl can be carbon wraped, Mike has a certain profile that has to be met, Lawton, Mike Rock and some others make the bbls to be sent to ABS to be wrapped. They undergo a test inpection before he starts the process, if it dont meet his requirements, the bbl goes back to who ever made it. Lawton makes the 408bbls to ABS specs and they are putting them on the Chey-Tac rifles, i ordered two of these contours for my next two projects.
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