Google has failed me

[Diamondhitch]

I can usually find any manner of good info (as well as plenty of bad info) on google. However after discovering that the max pressure for a 12ga 3" load is 2500psi lower tha the max for 3 1/2" shells, I can find nothing definitive about why this is? Makes no sense to me, pressure is pressure is pressure. If this is because 3 1/2" shells are only available in modern rifles, that is one thing, similarly if there us a difference in hull construction.

I have learned there is no difference in hull construction save for the additional length. As to the elevate pressure max of 3 1/2", I have only found that SAAMI decided to raise the max press for 3 1/2" shells??? Someone help me out here, Im not getting it. If it wasn't safe for 3" shells, how come the advent of 3 1/2" shells suddenly make those pressures OK in a 12ga???

 

[BRICKBURN]

I have noticed a couple of things in my reloading for the shotgun. Wads can make a difference in the pressure along with the type of powder and the amount shot.

Hulls have been irrelevant.

Not sure what the deal is with the specs you are talking about.

What is the powder and shot load differences?

 

[Diamondhitch]

No actual loads to compare Wayne, just SAAMI specs for max pressure. Struck me odd that 3" and 3 1/2" shells fired from the exact same gun have different SAAMI max chamber pressures.

 

[BRICKBURN]

Where are you getting your info?


Partial table:


All fired out of Skeet Chokes

I have attached the file I obtained this info from.

 

[Diamondhitch]

That chart concurs Wayne. 11500psi for 3" and 14000psi for 3 1/2" 12 ga. Really strange that 3" and 2 3/4" have one pressure standard and 3 1/2" has another.

 

[rookhawk]

Gotta be honest with you, I don't trust SAAMI at all so I take their standards as dubious. They are an honor system group of MODERN American gun and ammo companies.

I'd really suggest you look to CIP and the two English proof houses for their take. The Euros take definitive proof and proper proof testing a lot more seriously.

I am surprised that 3.5" is such a nominal pressure increase because the additional shot weight should cause a greater pressure spike. As a for example, a 1oz 2-3/4" load is 1/3 less pressure and recoil than the 1-1/8 ounce load. Put another way, adding 1/8 ounce results in almost 50% more pressure and recoil. (And gun wear)

I can only guess that they compensate with 3.5" shells by using slower burning powders to flatten the pressure curve to propel up to 2-1/4 ounce of lead than the 1-3/4 ounce from a 3" shell?

 

[rookhawk]

I just figured out why the pressure is so low at 3.5" she'll length. The velocity in the above referenced is a very low 1150fps. Really shocking how slow that is compared to the 3" example. That's how you get the low 14,000 pressure, you're not pushing a hot load because you can't, because the weight of the shot is too great to move it any faster without insane pressure.