Harmonics and OBT in a barrel blocked rifle

[APGE]

Hi Folks,

I will have all the parts ready to assemble a barrel blocked ftr rifle I've been working on this weekend. The whole thing is a bit of an experiment.

I have always used quickload to get me a starting load close to an OBT node and then tweaked from there. I've used this technique for probably 20 barrels and it has served me quite well, saving a lot of time and components.

Question for the gurus - will the nodes still be where they would usually be in a conventional stock?

Let's say that I have 20" of barrel protruding from muzzle end of the block and the barrel is 30" total length. Would I expect a node based on a 30" barrel length or one on a 20" barrel length? I'm expecting it should be a node based on the total barrel length, but maybe someone here has first hand experience that suggests otherwise or confirms my suspicions.

Alex

 

[RDavies]

I only have experience with 3 barrels block set ups and strangely enough, they seemed to tune in at about the same speed as my regular non blocked barrels.
ie. My 300WSM heavy gun with a 30" long 1.45" diameter barrel glued into a 9" bedding cylinder, with 20" of barrel protruding runs best at 2830 fps (Though I am going to try it at the higher 2950-2960 area soon)
My clamp in blocked 284 (with approx. 24" protruding) ran best around 2830 fps and my clamp in blocked short mag (With approx 24" protruding) ran best around 2960 fps which is spot on where my regular guns ran. Personally I think there is a fair bit of coincidence involved as they realistically shouldn't have come into tune at the same speeds.
Im keen to get a muzzle brake on one or more of these barrels and am interested in whether or not a brake really will affect the OBT.

 

[mikecr]

Barrel vibrations opening/closing bore, traveling back & forth, doesn't represent an attribute of tune, but instead a factor of detriment. So while results may take a hit at a 'bad' OBT, actual tune is unaffected.

It's similar with seating depth. While in or out of lands affects the pressure curve as a step change, adjustments otherwise (window to window) are not affecting tune. We're merely identifying and clearing a factor of detriment to results.
So ideally you would not be in bad seating, nor in bad OBT.
And clear of this, ideally, you would find a powder node(lowest SD) -that also releases bullets into tight grouping.
But we know that these things don't always line up for us. That's the challenge in it.

There is no doubt in my mind that a barrel block, or any other pressure point, affects barrel vibrations.
Keep in mind though that there are different types, or modes of vibrations.
Many focus on the muzzle whipping kind, and with that they're watching mostly vertical at distance. This cycle is influenced from muzzle to barrel support.
OBT is based on a bore changing wave from end to end (breach to muzzle). That is, right through any support -end to end back & forth.
Then there are surface vibrations, and system interference waves, that throw every abstract in the world into the mix.
A barrel block would affect whip, and surface,, should not affect OBT. If I were to wonder, it would be about a barrel block's affect to best seating(how affected).