excessive pressure signs - shotshell loads

[wmitty]

What are the signs of excess pressure when handloading shotshells? Do primer pockets become loose as with metallic cartridges? Could the case head be measured with a mike to determine if pressures are becoming unacceptably high?

[lancem]

There are none, follow printed load data.

[longbow]

Well, if you get sticky extraction you are running high pressure. Ask me how I know!

Yes, best to follow published load data. Substitutions of equal weight payload are generally acceptable as are some wad column substitutions but one must be very careful regarding hulls and primers. As is published in more than one reference, a simple change of brand of 209 primer can affect pressure by up to 3000 PSI. 209 primers are not created equal!

Hull design also affects pressure dramatically. Small capacity pressure formed hulls tend to run significantly higher pressures than straight walled hulls.

In short, it is difficult for the home tinkerer to "work up" shotgun loads of any kind. Not impossible but difficult to the point of dangerous.

Play but play safe!

Longbow

[wmitty]

I am using data from Lyman shotshell manual and working up charge in half grain increments. I'm not interested in having a spontaneous dis-assembly or damaging the shotguns the loads are used in (recoil operated autos). I'm just trying to get an idea of what an over-pressure round would exhibit when fired.

[Dhammer]

With as much info is out there, I have never seen or found a need to do anything but what's published. You can search the early days of ballistics products and find plenty of complaints about early data and issues it caused for some. Was it really BP's data or operator error? Dont know but, people were saying be careful. I've used there data for years amongst a host of other sources.

[too many things]

best way is look at primer. That will tell more. If it has a burn ring around the cup, either the hull is bad or you loaded it too heavy
on a auto gun look at the back of where the bolt slides in the slot. if there is any note of a hit. its too hot.Last if the gun blows up it TOO hot

[longbow]

Get yourself as many shotgun reloading references as you can. I have three editions of the Lyman Shotshell Reloading Handbook. Reloading For Shotgunners. The BPI Shotshell reloading manual, BPI Slug Reloading Manual, BPI Buckshot Reloading manual, Alliant Shotshell Reloading manual, Federal Shotshell Reloading manual, Winchester Shotshell Reloading Manual, downloaded reloading info from every powder manufacturer (or most anyway) and I have copied every relevant "Load For The Week" BPI has posted. I also save posted info from trusted sources and posted pressure tested loads.

I find discrepancies between manuals and some not minor so it makes a guy wonder.

The only shotshell reloading manual I have that lists more than one powder charge for a given set of components is Reloading For Shotgunners. For most loads the recipes have 2 or 3 levels of charge with pressures listed.

I do substitute payloads and wads but not without cross referencing and knowing the pressure of the recipe. I would not hesitate to substitute a wad or primer in a recipe that was running 8500 PSI but would certainly think twice before substituting something in a recipe that is running 10,500 PSI. You never know which way things will go and adding 2000 to 3000 PSI to an 8500 PSI load is not a problem but it could be with a 10,500 PSI load.

If I had access to a variety of hulls, powder, primers and wads I would have no valid reason to do any substituting but I live in a reloading component desert... almost anyway. There is very little available here so i very carefully research and choose what substitutions I think will be safe and knowing the starting pressure is essential.

Yes I have had sticky extraction and brass heads bulging into the extractor groove and yes I have blown up a shotgun. Not fun and I do not recommend it.

Stick to published data and be safe.

Longbow

[Ballistics in Scotland]

There are numerous signs, mostly described above, that may indicate excessive pressure. The trouble is, I don't believe their absence necessarily indictes acceptable pressure.

Gough Thomas, a British writer of the sixties, was very interested in an idea of someone's I don't remember. If a shotgun wasn't tightly headspaced there would be room for a disc of thick foil, embossed with concentric lines. A good idea of pressure would be given by how close they came to being squeezed out of existence. It would only be a comparative measurement, but that comparison could be made with a commercial load you know is safe. I don't see why the discs couldn't be embossed with parallel lines, such as you could press between two pieces of metal engraved with a fine checkering file.

[longbow]

I think the biggest problems in reading or interpreting pressure in shotshell reloading is that hulls and primers are not made to a standard where they all deform the same no matter the brand.

It has been stated that mic'ing the metal case head can be used to determine pressure relative to a load of known pressure shot in the same hull ~ more expansion than the known pressure load = more pressure.

Some say flattened primers are a good indication but again if the primers are not made all the same the brand makes a difference and I have had sticky extraction where the primer looked fine, and no signs of gas escape around the primer either.

I had had a thought similar to the foil idea which may be workable. I was thinking of Plastigauges (http://www.plastigaugeusa.com/) or similar where the material would be squeezed thinner by higher pressure. Again, it would be a relative thing unless calibrated against known pressure loads.

In short, if you don't have pressure testing equipment it is not a good idea to stray far from published load recipes.

Longbow

[wmitty]

Thanks for the thoughtful comments. Specifically I am using the Remington 2 3/4" case with yellow plastic basewad as shown on p.384 of Lyman 5th edt. manual. Load calls for Federal 12S4 wad. I have the 12S3 (1-1/8 oz.) wad available, but not the 12S4 (1-1/4 oz) wad. I'm using the shorter wad, as it encloses the Lyman Sabot slug fully. The 12S3 has a longer compression section below the shot cup portion of the wad than does the 12S4, which leads me to believe the 12S3 would produce lower chamber pressure if substituted for the larger capacity wad. I am curious as to why Lyman chose the 12S4 for this load rather than the 12S3. Regardless, I realize I am on my own if I attempt this substitution; which I am still debating. If I proceed, I will back off the charge weight a considerable amount and creep forward very slowly.

[bikerbeans]

Positive excessive pressure signs.

BB

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