2 3/4", 3" and 3.5" shells...powder charge difference...

[saturno_v]

2 3/4", 3" and 3.5" shells...pressure rating difference...

Question for the experts....

Someone told me that between the 2 3/4" and 3" shells there is an actual difference in the pressure rating, but the 3.5" were designed only to increase the amount of pellets, especially because of the lead ban for waterfowling, but there is no max allowable pressure difference between the 3" and the 3.5"....they just launch the heavier load at slower speed.

Is that true??

 

[slabuda]

Not always, some do shoot heavier loads at the same speed as lighter loads.

Go to cabelas and look at the different boxes they sell

Kent fast steel has two loads @ 1550 fps #4 steel loads
3" 1 1/8 oz
3.5" 1 3/8 oz

 

[Virginian]

Not only the weight but the type of powder varies greatly. The 3-1/2" also has a higher allowable pressure rating. Taking apart shells and weighing powder charges doesn't really tell you a thing.

 

[oneounceload]

In slabuda's example, to achieve the same speed with a heavier payload, they would need to use more propellant to achieve the pressure needed.

 

[saturno_v]

Not only the weight but the type of powder varies greatly. The 3-1/2" also has a higher allowable pressure rating. Taking apart shells and weighing powder charges doesn't really tell you a thing.

I apologize but that is exactly what I mean (my mistake, I corrected the original post)
That person told me that the 3" and 3.5" have the same pressure rating....evidently that is not true then...

 

[Jon_Snow]

FWIW, even with the exact same amount of powder of the same brand, the heavier loads will have a higher peak pressure. As the powder burns and releases gas, the heavier load does not move as much as a light load. This means that the volume of the gas does not increase as quickly, which in turn causes higher pressure. Look at a rifle or pistol reloading book and you'll see that heavier bullets call out lower maximum powder charges.

From Hodgdon's reloading site for 204 using IMR 8208 XBR:

For 26 gr bullets the max load is 29.5 gr with 54,900 psi peak pressure.
For 40 gr bullets the max load is 27.3 gr with 56,300 psi peak pressure.

 

[saturno_v]

FWIW, even with the exact same amount of powder of the same brand, the heavier loads will have a higher peak pressure. As the powder burns and releases gas, the heavier load does not move as much as a light load. This means that the volume of the gas does not increase as quickly, which in turn causes higher pressure. Look at a rifle or pistol reloading book and you'll see that heavier bullets call out lower maximum powder charges.

From Hodgdon's reloading site for 204 using IMR 8208 XBR:

For 26 gr bullets the max load is 29.5 gr with 54,900 psi peak pressure.
For 40 gr bullets the max load is 27.3 gr with 56,300 psi peak pressure.

You are right.

 

[rcmodel]

Not exactly right.
More of a slower burning powder is normally used with heavier shot charges or heavier bullets.
Peak pressure is set in stone by SAAMI and cannot be exceeded.

From the Alliant reloading handbook:

2 3/4" - 1 oz HV load = 21.0 grains Red Dot powder = 1,310 FPS at 10,700 PSI.
3" - 1 3/8 oz = 42.0 grains Blue Dot powder = 1,350 FPS at 8,000 PSI.
3 1/2" - 2 oz = 39.0 grains Blue Dot powder = 1,220 FPSat 10,700 PSI.

It is very possible to have a 7/8 or 1 oz target load generate the same or more pressure then a 3 1/2" Magnum.
It all depends on the burn rate of the powder used in each.

And the factorys always use more of a slower burning powder in the 3" & 3 1/2" magnums to reach the expected velocity while maintaining allowable SAAMI pressure specs.

rc

 

[saturno_v]

Ok but what are the max nominal chamber pressures for the three different shell length??

 

[rcmodel]

SAAMI Shotgun Pressure Specifications (Maximum Average Pressure in PSI)
All Piezo measurements unless specified)

10 gauge 11,000 (all)
12 gauge 11,5000 (all but 3 1/2" mag)
12 gauge 3 1/2" mag 14,000
16 gauge 11,500 (all)
20 Gauge 12,000 (all)
28 gauge 12,500 (all)
.410 Bore 2 1/2" 12,500
.410 Bore 3" 13,500

rc