Signs of pressure !

[nitro450exp]

Hello All,

I remember someone stating that 12 ga shells do not show signs of pressure.
Since I have little experience with shotshells should I treat them differently from regular loads.

The sign of pressure I am familiar with are :
1. Sticky extraction.
2. Flattened primers.
3. Blown Primers.
4. Excess elongation of the case.

I am using Magtech 2 1/2" brass shells, Winchester Large Pistol Primers (WLP)
and putting a crimp on the brass.

With the loads I have made so far I have observed low velocity and low recoil.
The crimp on the brass remains after the shot.

But they are near the Max of the surrogate data I used.
1 1/4 Oz shot is quoted as ~ 1300 fps, field loads
I am shooting 1 1/4 slugs over 11 ga fibre wads and cards and only get ~ 900 fps
I am planning on stepping it up, but want to watch for pressure.

Should and can I use the convensional sign of pressure, as stated above ?

Thanks for the wisdom.

Nitro

[missionary5155]

Good morning
As I do not have pressure equipment I rely on the BIG BOYS to do that.
I buy the least amount of FULL POWER MAG shotshells of the make I will use to test with and fire 3 per barrel that I plan to load for. The Base of that cartrige will expand. Measure those 3 with a GOOD micrometer and that average is you MAX case expansion for that barrel. All barrels are differnt! I do this for every barrel. Doubles are different side to side. I use a FOX B 12 guage as my double test gun and it has barrels almost exact.
The singles are much easier.. I use Mossburg down here in Peru... BUT from one barrel to the next the expansion is different as all chambers vary.
Primers do flatten. But that I feel is not a safe way to go about max loadings. I have only stuck one case in my Mossy... That primer was as flat as the stae of ILL. It was a RB load with Unique and that load was beyond Uniques safe loading. Probably would have shot through a 3 Toyotas though.

[turbo1889]

What missionary has said so far is pretty much up to par with my knowledge of the subject, I would add a couple notes of my own:

~ Do not trust the primers as indicators of high pressure, especially if you are using Mag-Tech full length brass cases with pistol primers. Pistol primers are used in pistol loads at or above 35-K without any issues which is triple the pressure that a shotgun is rated to withstand. With shotgun primers, yes they will flatten but it is an unreliable indicator in my experience.

~ Case elongation is not an indicator at the low pressure levels shotguns operate at.

~ Sticky extraction is an excellent indicator when using conventional plastic shotgun hulls in a single shot break action gun equipped with a spring action ejector that has had the spring tension adjusted to barely be able to eject factory max./mag. loads. It is a less then reliable indicator for guns that use a mechanical ejection system such as pump action guns or break action guns with a true mechanical extractor instead of a spring action ejector. Also, I don't know how this indicator would play out with the full length Mag-Tech brass shells you are using.

~ Head expansion - or better yet unsupported case expansion is your best pressure indicator short of instrument equipping your gun with a strain gauge system. Missionary has already explained how to do regular head expansion measurements.

Unsupported head expansion is even more pronounced and you don't necessarily need a micro-meter to measure it - a simple cheapo $5 plastic dial caliper or even the naked eye is normally plenty enough. You will, however, need a test gun with a chamber defect such that a portion of the case head is completely unsupported and can freely expand under the firing pressure - some of the cheaper older single shot break action guns do have such a defect at the bottom of the chamber where the ejector/extractor is mounted.

Here is a couple pictures of set of 410 test loads fired in such a gun:

http://forums.handloads.com/uploads/turbo1889/2010-01-13_205130_Pressure_Bulge_1.JPG

http://forums.handloads.com/uploads/turbo1889/2010-01-13_205150_Pressure_Bulge_2.JPG

http://forums.handloads.com/uploads/turbo1889/2010-01-13_205214_Pressure_Bulge3.JPG

Of those five shells the middle shell is a factory loaded max./mag. load. The two shells to the left side are handloads that show under factory load pressure and the two on the right are handloads that show over factory load pressure and the one on the extreme right stuck in the chamber and hand to be tapped out from the muzzle end with a brass rod and hammer. The variations in the bulge size which is directly proportional to the load pressure are clearly visible with the naked eye.