Sporter build, need help

[Taavetti]

Hi Bill,

I started to build a new sporter.
I have the barrell profiled as reverse taper, but
originally it was 0,9" straight. As my experiences
are limited to bigger profiles, I would like to ask for
an estimation for the counterbore depth.
As the weight head is only 0.9" dia, so I believe the
counterbore must be as small as 0.4", but how deep?
Just an educated guess is good enough.
I´ve had success with bigger diameters, this is the first
of this small I´ve tried. I figure it must be at least 2 1/4"
deep. What is your opinion?

BR Tomi

 

[Bill Calfee]

Friend Taavetti

Hi Bill,

I started to build a new sporter.
I have the barrell profiled as reverse taper, but
originally it was 0,9" straight. As my experiences
are limited to bigger profiles, I would like to ask for
an estimation for the counterbore depth.
As the weight head is only 0.9" dia, so I believe the
counterbore must be as small as 0.4", but how deep?
Just an educated guess is good enough.
I´ve had success with bigger diameters, this is the first
of this small I´ve tried. I figure it must be at least 2 1/4"
deep. What is your opinion?

BR Tomi

Friend Taavetti:

Here's where you're at with trying to turn a .900" into a sporta....

To stop the muzzle, we need about 5 ounces of down force at X distance in front of the exit of the crown....

X distance being determined by the stiffness of the barrel......

But, just putting 5 ounces of weight past the exit of the crown will not cause 5 ounces of down force where it is needed, to stop the muzzle.

So to get the 5 ounces of actual down force, we need more than 5 ounces past the exit of the crown...

Also keep in mind, that the stiffer the barrel the closer the exact center of the parallel node is to the crown...

The more flexible the barrel, the exact center of the parallel node is located further back from the crown, which is why some smaller, more flexible barrels, require more weight than a stiff barrel....

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Here's what we need to do:

We need someone who can figure steel tube diameter weight...

Then, how deep will the back bore need to be, with .900" OD and .400" ID, to give about 6 ounces of weight past the crown?

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Something else; it will help your case if you can place the exit of the crown behind (toward the breech end) where the barrel steps down from .900" to the reduced diameter.........

Also, I don't think I would simply reverse taper the barrel from the ,900" point where the actual MD starts....

I would drop the diameter down smartly, with a nice little radius, to something like .800", then reverse taper back to the breech, leaving enough for threading, barrel shoulder, etc......

Then try to get the exit of the crown in this .800" diameter part, if at all possible...

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Now, does anyone know what one inch length of barrel .900" in diameter with a .400" hole through it weigh?

Your friend, Bill Calfee

 

[Timo]

Hi Bill & Tomi!

Remember that I was fishing & hunting many times when others were on mathematic lesson..

I used 0,9 " barrel and 0,4 " hole.

I used 7900 kg / m3.It is stainless steel.

I got 66,06 g / 25,4 mm --> 2,33 ounce / 1 inch.

--> (6,0 ounce / 2,33 ounce) x 1,0 " = 2,58 " = 65,53 mm.

We have nice "lapping day" with Tomi on Saturday.

BR, Timo

 

[Bill Calfee]

Friend Timo

Hi Bill & Tomi!

Remember that I was fishing & hunting many times when others were on mathematic lesson..

I used 0,9 " barrel and 0,4 " hole.

I used 7900 kg / m3.It is stainless steel.

I got 66,06 g / 25,4 mm --> 2,33 ounce / 1 inch.

--> (6,0 ounce / 2,33 ounce) x 1,0 " = 2,58 " = 65,53 mm.

We have nice "lapping day" with Tomi on Saturday.

BR, Timo

Friend Timo:

Thanks..........

Now, how does one put a perfect crown back in a hole 2.58" deep and only .400" in diameter?

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How does one set a MD to stop the muzzle, that is machined as part of the barrel?

When I designed the original Calfee sporta profile, it took some doing to figure out the correct back bore depth and the length and OD of the MD itself....

But, once I figured that first one out, as long as my profiles were pretty much duplication's, the back bore was the same, to stop the muzzle..

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But, there is a very simple way to figure the depth of the back bore.....

I made up a 1 ounce ring weight that clamped to the MD part of the barrel....

Back when I built sporta's, I always back bored a few thousandths deeper than my known, repeatable distance....

I took the gun to the range with my 1 ounce ring weight........

If the muzzle was stopped, as is, without the ring weight, then cool.......I'm done..

But, if I had vertical, then I clamped on my 1 ounce ring weight........

If my vertical got worse, then I knew my weight head was too heavy......so I machined a few thousandths off and re-tested..

If my vertical got better, then I knew my weight head was too light........which means I had to deepen the back bore a few thousandths and re-test....

( I solved this problem for the last few sporta's I built by going to a double lobe weight head.....which you can't do with a .900" diameter weight head, of course)

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Nine times out of ten, since I back bored a little deeper than my repeating standard, I wound up simply facing the weight head to the length that stopped the muzzle...

Every great once-in-a-while, I'd have to deepen the back bore to get the muzzle stopped...

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So setting a fixed MD is really simple using the 1 ounce, clamp on ring weight....

Your friend, Bill Calfee

PS:

Here's a picture of my double lobe weight head..........I still used the ring weight, if the muzzle wasn't stopped, but I no longer had to deepen the back bore to correct a too light weight head.......course this wouldn't work on a .900" diameter weight head....bc)

 

[Bill Calfee]

Could the stopped muzzle weight be within the 1 ounce ring weight


I took the gun to the range with my 1 ounce ring weight........

If the muzzle was stopped, as is, without the ring weight, then cool.......I'm done..

But, if I had vertical, then I clamped on my 1 ounce ring weight........

If my vertical got worse, then I knew my weight head was too heavy......so I machined a few thousandths off and re-tested..

If my vertical got better, then I knew my weight head was too light........which means I had to deepen the back bore a few thousandths and re-test....
Could the stopped muzzle weight be within the 1 ounce ring weight


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CYA friends: (I've quoted from my last post, above)

Let's say I just tested a new sporta build and had excessive vertical......

So I added my 1 ounce ring weight.........and the vertical got worse, indicating the weight head was too heavy...

Question:

Is it possible that the actual stopped muzzle weight could be within that 1 ounce of extra weight?

In other words, within that 1 ounce, could I have moved the exact center of the parallel node to the exit of the crown, then went on past it back to vertical again?

(Put another way, could say 1/2 ounce have stopped the muzzle, then the extra half ounce moved the exact center of the parallel node away from the exit of the crown again, causing worse vertical than the weight head without the 1 ounce ring weight attached)

The answer:

Hypothetically, yes, but in all the years that I built sportas, I never had that happen....

Your friend, Bill Calfee