Which barrel profile would act stiffer?

[CharlieNC]

So my understanding in chapter 4 is he balanced his reciever and made it so all his bolt lugs had contact then added a recoil absorption system between the stock and the recoil lug that delayed the return impulse of the stock on the barrel until after the bullet left the barrel.

Is that correct?

That was one modification to address a single impulse, not vibraion. Most interesting is the frequencies associated with load development are high, I recall one around 10 khz. Kolbe also reports high frequencies. I observe 5-20 khz on my rifles during load development.

 

[Rob01]

 

[joshb]

You need to find a hummer. Buy a hundred barrels and one might be in there. One thing I have realized in all these years...... math and science only go so far.......then there’s magic! You can’t put magic on a black board! Read Tony Boyer’s book on rifle accuracy.

 

[darkangel_r2]

That was one modification to address a single impulse, not vibraion.

I think he states that those mods eliminated the development of mode 3 in his rifle until after the bullet was gone.

Most interesting is the frequencies associated with load development are high, I recall one around 10 khz. Kolbe also reports high frequencies. I observe 5-20 khz on my rifles during load development.

I'm confused then as he is stating that mode 3 is dominant in the unmodified rifle which has a max deflection of .004" at the muzzle (sporter profile). Each modes amplitude is significantly less than the mode before it so if mode 3 is .004 for this rifle wouldn't the other modes amplitude be ridiculously small as to irrelevancy?

 

[CharlieNC]

I think he states that those mods eliminated the development of mode 3 in his rifle until after the bullet was gone.

I'm confused then as he is stating that mode 3 is dominant in the unmodified rifle which has a max deflection of .004" at the muzzle (sporter profile). Each modes amplitude is significantly less than the mode before it so if mode 3 is .004 for this rifle wouldn't the other modes amplitude be ridiculously small as to irrelevancy?

Look at the targets he shows which exhibit the sinusoidal vertical response to charge weight. Those are the frequencies actually impacting the poi vs the many which are calculated and measured. These are the same high frequencies reported by Chris Long in OBT. Similar to Kolbes measurements for his barrel tuner work.

 

[darkangel_r2]

Look at the targets he shows which exhibit the sinusoidal vertical response to charge weight. Those are the frequencies actually impacting the poi vs the many which are calculated and measured. These are the same high frequencies reported by Chris Long in OBT. Similar to Kolbes measurements for his barrel tuner work.

That was for a 1.35" strait taper 6ppc rail gun with only 18" in front of the block. That's compared to the other gun which was a 24" sporter 270win. That's going to have a much higher mode frequencies as they decrease by added length squared and increase with stiffness. So a stiff short barrel will have a much higher frequency for modes 3-5.

I bet its the same modes just adjusted to a higher frequency for their stiffer and shorter barrels.

That's why he was able to kill vertical shift in the 6br example with his modified receiver, which should have the largest effect on mode 3.

 

[Rob01]

 

[JFrank]

@joshb Seems to me that when a rifle is in tune the optimum barrel timing has been achieved, so at that stage, barrel profile doesn't really matter.

I could be wrong.

 

[CharlieNC]

That was for a 1.35" strait taper 6ppc rail gun with only 18" in front of the block. That's compared to the other gun which was a 24" sporter 270win. That's going to have a much higher mode frequencies as they decrease by added length squared and increase with stiffness. So a stiff short barrel will have a much higher frequency for modes 3-5.

I bet its the same modes just adjusted to a higher frequency for their stiffer and shorter barrels.

That's why he was able to kill vertical shift in the 6br example with his modified receiver, which should have the largest effect on mode 3.

Like I said I find the same frequencies on my targets. And many find OBT works well. And Kolbe. In other words the targets tell the high frequency story while most calculators are in a different realm. I believe the targets.

 

[darkangel_r2]

@joshb Seems to me that when a rifle is in tune the optimum barrel timing has been achieved, so at that stage, barrel profile doesn't really matter.

I could be wrong.

I think the problem is on lighter barrels if you don't get the few relevant modes to line up they have sufficient amplitude to really screw up your performance.

In other words Good loads would be few and far between, where as with a chubbier barrel good loads should be more common and periodic. I think thats what we are seeing with those heavier barrel profiles where they throw a predictable sine wave pattern on the target. I don't think we would be able to see that with light profile barrels.

 

[joshb]

@joshb Seems to me that when a rifle is in tune the optimum barrel timing has been achieved, so at that stage, barrel profile doesn't really matter.

I could be wrong.

You’re not wrong! The OP is chasing a unicorn with math. Experienced folk have learned that math only goes so far.

 

[Rob01]

An ATS tuner would help make things easier but also add a little weight.

 

[joshb]

Seems the fad is to use fatter barrels free floating on tupperware stocks to get an easy tune.
Myself I like tuning sporting barrels.

My God, the heathens!! Walnut and some other fine woods are the ONLY acceptable materials for a stock! Plastic and composites are spawn of the Devil!!!

 

[Bc'z]

I think the problem is on lighter barrels, where as with a chubbier barrel good loads should be more common and periodic.

Now this is a statement I can get behind!!!

 

[joshb]

Now this is a statement I can get behind!!!

I’m thinking of throwing that stock I started in the trash. I have some “Instrument grade” Tiger Maple on the way to me. I may start over. You set the bar too high!

 

[Bc'z]

I’m thinking of throwing that stock I started in the trash. I have some “Instrument grade” Tiger Maple on the way to me. I may start over. You set the bar too high!

Don't throw it away!
We can finish it and donate to a youngster getting into the game.
Set some pillars, I'll slap a paint job on it, then they can glue a Remington/clone in it.

 

[darkangel_r2]

An ATS tuner would help make things easier but also add a little weight.

View attachment 1289059

Is that the one that threads on but the weight actually hangs over the barrel and not forward of the muzzle?

 

[joshb]

Oops! I just remembered that I picked a couple pieces up before I left Delaware! Out to the Texas shop. Here’s a pic! There is NO contest. Start over!

 

[Bc'z]

Oops! I just remembered that I picked a couple pieces up before I left Delaware! Out to the Texas shop. Here’s a pic! There is NO contest. Start over!
View attachment 1289074

Please don't throw it away,I'll put a rootbeer dye job on it and it'll be super sexy!!
She's got good figure!!
That slab of curly has my head swimming with possibilites

 

[Bc'z]

OK. I’ll finish the one but I’m starting another. The wifey needs better! I’ll send both.

I just got her a 6 pack, she'll be fine.

Editited
And that folks, is how to properly derail a thread!!
Dusty would be proud.