One for the techies

[CharlesP]

Well said, bigman.

Three words!

[TIGHTCHOKE]

10 hours ago, buze said:

"redundant gas" would push forward if it wasn't used backward. There's no such thing as redundant gas. Perhaps the loss is 'insignificant' compared to the total velocity, but you can't claim it 'groundless' -- especially when the original discussion is about a very edge effect of 5fps

And if the cases expanded enough to be a full block, you'd have problems removing the cartridge afterward, so there MUST be a loss there.

Also, more generally I hoped we could have a fun argument here, you know, pull interesting whacky theories together, before the usual PW brigade arrived.

It is redundant as it has got the payload up to speed and with the lengthening barrel it has done its job and the pressure is dropping, it is only there because it has to be and is spent.

The case does expand and seal and once the payload and wad has left the barrel the pressure returns to atmospheric pressure and the case returns to its previous dimensions and can be removed easily.

You really are being a rude little boy today aren't you?

Edited January 24, 2018 by TIGHTCHOKE

[buze]

It's my new style of replying to the PW brigade: in kind.

I'm still not agreeing with you on the technical bit, because you are still not replying *in context* of the original article. Technically, I agree that "up to speed" makes sense as they are specced for a speed, however here the claims are that with longer barrels, the pellets will exit at a higher speed. Marginally. 

And my point is that it's going to be even more marginal because some of that 'extra length' no longer has as much pressure as it's assumed.

[timps]

Just to answer the physics side of it, due to inertia the amount of force (pressure) needed to accelerate 28g of wad and shot from rest to 1350 fps in let’s say 11” is massive. To accelerate from 1350 to 1375 in the remaining 21” not so massive so even if the pressure is dropping it is exerting a force and continuing to accelerating the wad and shot down the barrel just at a greatly reduced acceleration.  

The figure of 5 fps is a complete guestimate there are so many variables in bore diameter, burn rate etc. that no one can qualify that figure at all in every case.

I have seen countless chronograph videos and reports on the net (including semi autos) indicating that longer barrels do give an average higher velocity, I don’t think the testing regime of all the videos stands up to the precision and bias that is required to categorically state it’s a fact. However, I haven’t seen any videos the other way around (I do stand to be corrected if there are) but it does tend to support the theory that the force of the pressure is still greater than the friction even up to 32” and on semi autos.

Regarding chokes again I’ve seen, albeit just one, chronograph report that tighter chokes increase velocity, the principle is based on the venture effect and Bernoulli’s principle on the expanding gas behind the shot causing it to drop in pressure and increase in velocity at the choke.

But any increase here would be negligible.

I have seen one choke manufacturer claim his chokes regardless of constriction do increase velocity over standard chokes backed up by his own chronograph evidence, however I am EXTREMELY sceptical to say the least.

Obviously, the caveat is there will be a longer barrel length and tighter choke constriction which would have a negative effect on velocity.

What does this all mean to the shooter?

Answer: absolutely sod all.

If you shot at a crossing target (depending on its own velocity) it will have only moved less than an inch towards the intercept point between shot travelling at 1300 fps and shot travelling 1400 fps (100 fps should cover any claimed increase easily). Nothing in the world of scatter gun shooting is that accurate or consistent to worry about an inch or less at 30 yards or more.

Regarding impact energy, again any difference is completely academic, a 28” gun can hit any target just as hard as a 32” can out in the filed I’ve own both at the same time and cannot tell any difference.

It is like all good theories in shooting, it’s provable in the lab and by physics and formulas but it means sod all out in the field.

Just my view on it anyway and yes I do work in a lab.

[buze]

Ahh, thank you so much @timps for a nice, literate, documented argument. Very refreshing.

For your note on choke, it makes perfect sense to me, as the Pressure versus the Force is proportional to the Aperture. Basically, it's the good old trick of putting your finger on the end of a hose to have the water go further. The *pressure and force* is the same, but the *aperture* is reduced, so the velocity augments.

Of course, by 'tight choke' on a 12 bore we imply we know the basic bore diameter, and the fraction of reduction -- that will be the key.

And also, tighter chokes will also produce more flyers by deformation, so you might gain on velocity, but lose out on the pattern...

[AYA117]

How have you all managed to get this far without someone mentioning bc or shot strings ?   

[Wb123]

6 minutes ago, AYA117 said:

How have you all managed to get this far without someone mentioning bc or shot strings ?   

Because those are subjects for threads about plated shot coatings and extra superdoopha highspeed 1450fps cartridges, not these super soft recoil 1350fps ones...

[AYA117]

4 minutes ago, Wb123 said:

Because those are subjects for threads about plated shot coatings and extra superdoopha highspeed 1450fps cartridges, not these super soft recoil 1350fps ones...

Thanks for clearing that one up for me. Still bet it will happen !

[Ultrastu]

Pretty sure I mentioned bc in post  8 .

 

Just saying