doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Two (2) Shotgun Formulas

2-barrel

If you are saying chamber pressre must be higher there is a difference of powder pressure curves that also must be accounted for. I do not pretend complete knowldge of all the formulas, but I believe if you only consider mass and velocity without accounting for variables in the acceleration due to different powders you may not have the whole picture. You note acceleration in your set-up, but how are you measuring it ? It is a curve not a straightline.

We typically measure peak chamber pressure because that is doable and most powder burns in the first

I do not disagree the smaller bores typically develop greater pressure on average and therefore potentially misshapen more pellets than the larger bore.

The effect is not huge, but definitely definable between gauges. Though the difference when firing the same shot load is not nearly as great as when you use the normally different load weights for a given gauge ( yes I know that is obvious)

I do not think the potentially lower pressure of firing 1oz out of a 12 vs a 28 gets you a greatly different 2D pattern given similar choke profiles, wads, hardness of shot, etc.

The misshapen pellets become the fliers in the pattern, more pronounced as the range gets longer because there is more time for the misshapen pellets to become fliers, on the periphery of the 2d pattern. How significant that is I can't say. Hunting is a poor, poor way to tell. For example, I shoot doves a lot with my .410s, even though I know they pattern poorly in relation to the larger gauges. However, I kill doves handily with them when I'm shooting well. I once killed three sets of doubles, right then left, on one afternoon shoot about four years ago. I cannot remember when I have ever done that with my larger gauge doubles.

SRH

I hate to say this but I went back and looked at WTS's reference to AC Jones book in the patterns thread when I got home from my business trip and while AC did determine larger gauges did better, he mostly held that this was due to average payload size being higher in them.

He specifically looked at overbore barrels and its effect and found them negligible.

Lastly he looked at shotstringing which I believed had a great impact remembering the pictures in Burrards and Bristers books, but in reality the speed of the load and the angle of the target makes shot stringing minorly, not majorly significant.

In that respect WTS was right and I was wrong. I even dug out copies of Lowery's old program and got Jones' and saw it laid out graphically. I have not had the time to put together a posting showing it ngraphically, but hopeto by the end of the summer

You are right hunting is a poor way to tell, the reality is if you put the pattern on the bird you will take it down. You are getting the pattern on the bird. However the difference between the payloads in you 410 and the 12 bore simply creates a better denser pattern with the 12. It is not the flyers from shot deformation that is the major difference, it is the number of pellets

All of this is fine but to what avail?

Mass time acceleration may equal force but speed is a function of the force applied over time.

So in theory a larger force for a short period of time can give the same shot speed as a lesser force over a longer time.

We know that in a 12 ga. PB can produce 1200 ft/sec. at far less pressure than other powders. But I have yet to notice any difference with my heavy 12 ga.

My light weight 20 ga feels quite different with factory shells vs the same speed with my hand loads.

Okay, so what does all that mean?

I have the greatest respect for 2-p's scientific approach and unwavering commitment to truth in shotgunning. His theory and math are good. Chamber pressure is not a factor in this question. We are looking at average pressure. "What average pressure will yield the average acceleration to achieve desired velocity within the barrel time (length)?"

Average pressure and acceleration are theoreticals that are not greatly helpful. "So, what do we really need to know?"

What we need is the pressure vs time history/curve. Unfortunately, the equations used to estimate the pressure vs time curve are more than a little complicated. Fortunately, this data is not all that difficult to establish via test firing.

The problem involves a non-linearly increasing volume for the gas, non-linear energy input from the propellant as its gas generation rate (burn rate) is sensitive to pressure, gas cooling due to barrel heat transfer, and payload friction.

Where do we need to go with this discussion now?

DDA

Actually, the first sentence above is more accurate than the second. It is not the number of pellets, in total, that even matters. It is the number of pellets at any target sized spot in that pattern, which is another way of referring to density. This is partially made up for by tightening choke with the smaller payload. It is conceivable that you could have just as dense a pattern from a full choke .410, with a 11/16 oz. payload, as you do with a 7/8 oz. 12 ga. load and a very open choke. The skill of the shooter then comes into play in a big way. The importance of fliers going to the fringe of the pattern is that they lessen the density.

Given sufficient pellet energy, density ........ is what kills birds and breaks targets. Period.

SRH

It means that there will be more misshapen pellets in the small gauge load, as was states in Miller' original post. There are still some on this board who poo-poo that science. I even posted a link a couple months ago mentioning that I had spoken to Tom Roster about this and he told me about research he had done absolutely proving it. It's easy to find with a search. Misshapen pellets degrade the pattern, all else being equal.

SRH

Most retired Colonels (Full Bird or Light grade) that can afford a 20 something mistress and keep her in shoes, and hidden from the "Old Battle Axe" can afford better flooring for their homes and kitchens that vinyl-- hardwood tongue and groove real flooring over a 1/2" cork underlay-at least we know said mistress is not "barefooted and pregnant", right??

Just a metaphor Fox.
Much like my posting of the O2 cyl video to help people imagine forming barrel blanks from a cross cut chunk of bar stock.

Lead deforms under threshold pressures. Just like a vinyl floor creeps under heel pressure.

Miller and Don are smart guys that can explain things very well. People would be well served to listen to them.