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Joined: 28 Jan 2009 Posts: 107

While reading the posts on the AA wad diameter and thinking that these different components where not all made for the same application, I got to thinking about the dia. slightly being larger than my choke and brought the question to mind; will a larger dia. wad create more preasure going through a tight choke?............or is the combustion area so large by the time it gets to the choke that it has no impact.

I have reloaded for a lot of years but not for the low preasure loads that I nead for my old gun , any help here would be appreciated.

thanks BRUCE

Joined: 01 Oct 2006 Posts: 171 Location: western PA

I have never seen data regarding choke verses pressures. Therefore i assume it dose not matter. Surly the manufactures of wads or amo would have made notes on it if it mattered. I have been told that all of the powder is burnt long befor the payload reaches the barrel end.

Ben

Guest

The 'Pressure' that you are worried about and that might damage your gun is produced in the chamber (peak chamber pressure).

What little radial pressure that a plastic wad might have on the choke area of the barrel is insignificant and can't harm anything.

As far as a larger diameter wad producing anymore pressure, again no. By the time the expanding gases reach the choke area the pressure has dropped quite a lot from the original peak chamber pressure. No matter the wad diameter the pressure is not affected and of no consequence with regards to firearm damage.

dogchaser,

What exactly causes the difference in chamber pressure between loads where the only difference is the wad? Friction, caused by? I see some recipes where the pressure can change as much as 1500 PSI just by using a different wad. I have weighed quite a few wads and the weights do not seem to vary much.

Thanks,

Dennis

Guest

Normally, it has to do with the actual friction area of the wad and the type of plastic used, the larger the friction area the more pressure that a wad produces.

I am really not sure what plastic types change pressures but the plastic has a definite affect.

Anytime you increase the "pull" (resistance) of the shot/wad column, you also will increase pressure to some degree. Outside wad diameter in relation to inside hull diameter is one factor. So is wad OAl, the compressed diameter and obturation of the wad, the relative hardness of the plastic used to mold the wad, it's basic form to some degree, and the firmness and form of the crimp. Another factor is the condition of the surfaces of the internal hull walls.

Any increased resistance increases the burning rate of our modern progressive burning powders. It is the increased burning rate that increases pressure the most. Once the wad/shot column overcomes the initial resistance and starts up the bore, pressures drop off dramatically and so does the speed at which the powder burns.

The fastest burning propellants are more subject to variations in the amount of column pull, but also tend to produce more uniform velocities overall. Slower, more progressive burning powders are less affected initially by slight variations in the amount of pull, but also tend to produce less uniform velocities unless the loads are assembled with a great degree of uniformity.

This why I tend to fall back on my target load recipes for close to medium range hunting loads for smaller to average size game birds. The only change I might make to the basic recipe is the shot size. I assemble these loads on a progressive press and throw all powder and shot charges. I also use only once fired hulls. The loads generally give me excellent, uniform performance without any extraordinary measures on my part.

I assemble heavy, long range hunting loads which use slow burning powders like Blue Dot on a carefully set up single stage press. I use only very carefully selected, once fired hulls, weigh all powder and shot charges, inspect and seat the wads as carefully as possible, and crimp the hulls as perfectly as I can to help ensure uniform and dependable performance out where it really counts--taking bigger, tougher game birds at longer ranges. Since I generally use these loads less often and only under the toughest conditions, the extra time and effort invested to produce them is very well spent IMO.

Joined: 23 Jan 2008 Posts: 224

I don't know about pressure...but I have seen a measurable change in velocity with different chokes. I do a lot of testing and comparing loads using an A-5 barrel with invector chokes. The tighter chokes always give a higher velocity measured using a home chronograph. I think this is due to the venturi effect. I have wondered myself if pressure is effected in the chamber. It is good to know it is not.

Guest

16 Gaugeguy,

Wad diameter has little or to no effect on powder gas pressures, peak chamber pressure or muzzle region pressure.

Peruse any loading data, if you don't believe me.

Overall wad length has nothing to do with it either. It is how much surface area is actually touching the hull and barrel walls. That is why a number of wads have ribbing, which is supposed to cut down on the friction.

You also can't change the burn rate of powders. The coating that is applied to powder determines the burn rate. There are many factors that contribute to chamber pressure, but none of them can change the burning rate of the powder, only the pressure.

And finally, where did you come up with this statement?

"The fastest burning propellants are more subject to variations in the amount of column pull, but also tend to produce more uniform velocities overall. Slower, more progressive burning powders are less affected initially by slight variations in the amount of pull, but also tend to produce less uniform velocities unless the loads are assembled with a great degree of uniformity."

One of the most influental dynamics not even mentioned is the one piece wad "crush" section.....

Is the crush progressive? Or is it regressive? What load (pressure) is required for full collapse?

All this is happening as we approach our maximum chamber and even small differences can affect the time pressure curve of a load.

Initial wad tightness in the hull may have some affect on pressures... But a smaller wad by several thousandths of an inch is expanded and "tight" with 10,000 psi behind it and I think bore friction is there even with a wad that might fall through the barrel if just dropped into the bore.

An oversized wad to bore diameter may open another can of worms pressure-wise as initial compression will alter the pressure dynamics...

Slidehammer

Guest

Slidehammer,

That is just a very tiny part.

I have run loads thru a pressure gun and the length and or resistance in the compression section has very little effect on pressures, it might alter the pressure/time curve. but you will never notice it.

Perfect example:

WAA12L vs WAA12, with an ounce of shot, in some hulls an ounce of shot actually fits better in the WAA12 wad, even though the WAA12L holds the ounce of shot. Load with the same components, there was absolutely no way to differentiate between the 2 loads, by looking at the data sheets. You had to know what hull was loaded with what wad.

That is only one example. If you look into any extensive reloading data I am sure you will find similar results.

Guest

Slidehammer,

I no longer run any tests. Any topic I speak on, is from actual experiece and fact.

In other words if I am not absolutely sure I won't comment!!!

What a lot of folks are looking for are absolutes, in shotshell ballistics there are very few.

The length of the compression section of a wad has very little to do with peak chamber pressure. Now maybe if wads had stiffer and much longer compression sections that wouldn't be true. But 1/8" or so difference doesn't change much. Think about it, you can compress a wad with your fingers. When 9,000 PSI and greater is being applied how much difference will an 1/8 to 1/4" really make?

Now did you get that out of your system?

Go to the Hodgdon look under Federal Gold Medal 2 3/4" data 1 1/8oz. with Titewad powder and Fed 209A primers. all the wads are there, the load with a Federal 12S3 makes less pressure with more powder than, a WAA12.

Now wipe the egg off your face and understand that there are no absolutes and that the stiffer compression section is not the reason for pressure differences, it is how the load reacts as an entire system.

That was the first data that I looked at. There are more examples.

Member Joined: 16 Nov 2006 Posts: 1338

Guest

Mike,

I couldn't agree with you more.

But we were talking about the compression section of a wad and the possible effect on pressure.

Member Joined: 16 Nov 2006 Posts: 1338