Biggest factor in shotshell pressure?

[GaryM]

Of course powder charge/shot charge is the biggest factor but those are adjustable by the loader. Other than that is it which primer, hull, crimp or the wad?

[Budzilla 19]

Primers and wads, I would have to say, in my opinion. Numerous tests have shown wads can change a load from safe, although close to max pressure, to a gun killing load! Same goes for primer changes. May not burst the gun itself, but, accelerated wear on parts, head space issues, and probably punishing recoil! Crimps? Need to be firm and tight to promote good powder burn. I hope this helps.

[dverna]

Primers can alter pressure by about 3000 psi in some testing I saw a long time ago.

So can crimp:

https://hodgdon.com/faq-items/effect...on-shotshells/

Your crimps should look like a factory shell. Learn to adjust your dies as even a cheap MEC will make a good crimp. If your hulls are junk or worn out, you will get a poor crimp but that will be safe...just lower pressure.

I am not going to wade through a bunch of data to prove wads matter...that is your homework assignment...LOL

DO NOT substitute components and you will be safe. There are people who do stupid things and get away with it.

The Lyman manual is a good one. Hodgdon and Alliant both have good on-line resources. More data from Downrange Wads. Those are what I use. No reason to dink around as there is plenty of data.

Beware of loads posted on forums. Some guys know what they are doing, and some do not. If you have a specific load you are looking at, send me a PM and I will comment.

[megasupermagnum]

Primers and wads, I would have to say, in my opinion. Numerous tests have shown wads can change a load from safe, although close to max pressure, to a gun killing load! Same goes for primer changes. May not burst the gun itself, but, accelerated wear on parts, head space issues, and probably punishing recoil! Crimps? Need to be firm and tight to promote good powder burn. I hope this helps.

Wads is such a broad subject, since there are so many of them. I think most people can make reasonable judgements. I'm not suggesting you swap things willy nilly, but changing a Winchester AA for a Remington RPX 12 does effectively nothing. Going to a BPI Ranger Elite would probably do bad things.

[jim 44-40]

Lyman Shotshell Handbook says Shotshell pressure is substantially affected by any component change.

[shootinfox2]

The total composition of hull, primer, powder, wad, shot weight, and crimp determine the final pressure. Use proven data with no substitution, unless you work up the load carefully. Under charge can be as dangerous as over charge.

[Cap'n Morgan]

The biggest factor is no doubt the wad. The wad controls the size of "the boiler room" so to speak, and it has a huge impact on the pressure.
All wads will compress during launch, but some more than others. Plastic wads for light loads has a high compression zone between seal and shot cup, meant to take up space in the hull.
Wads for heavy hunting loads have a much shorter compression zone - some none at all. Felt wads will compress, but some are denser than others, and nitro cards are denser yet.

It is almost impossible to calculate the effect of swapping one type of wad for another, and that goes for other shotshell components as well, but I will try to demonstrate how much
two different components can affect pressure: the volume (boiler room) the powder gases has to fill, and the weight of the payload.

I designed a non-existent cartridge in the QuickLoad program, based on the .700 Nitro Express, and modified the case volume to somehow resemble a 12 gauge shotshell.
The beauty of QuickLoad is that you can fiddle with almost every thing and get instant feedback on various stuff, like chamber pressure and muzzle velocity.
In this case, I just changed the seating depth 0.2 (5mm) and the weight of of the payload (from 500 grains to 750 grains) I tried two different powders from both ends of the
shotgun powder range: Red Dot and Blue Dot.

(THE FOLLOWING DATA IS JUST FOR COMPARISON - DON'T TRY THIS AT HOME; FOLKS!)

I decided to tweak the loads so the pressure for the 500 grains payload would be approx. 10.000 psi. This was the "basic load"

It took 31 grains of Blue Dot to reach 10.000 psi, but only 13 grains of Red Dot to reach the same pressure.

The numbers were as follow,
Red Dot:
Increasing the payload with 50% to 750 grains raised the pressure with 29% to 12.900 psi.
Lowering the seating depth with 0.2 raised the pressure with 39% to 13.900 psi.

Blue Dot:
Increasing the payload with 50% to 750 grains raised the pressure with 33% to 13.250 psi.
Lowering the seating depth with 0.2 raised the pressure with 38% to 13.850 psi.

As you can see from the numbers, swapping a compressible wad for another wad with 0.2 less compression will increase
the pressure MORE than adding 50% extra shot to the load. Bet you didn't see that one coming..!

There's a reason the reloading manuals tell you NOT to substitute any parts of their recommended loads!

[longbow]

What Cap'n Morgan said!!

I've raised the same issue regarding slug loads where people are subbing a full bore slug or ball replacing equal weight birdshot load but using hard card wads under the slug instead of cushion leg wads.

Another issue is those making shorty rounds. You can't just remove the cushion leg and replace with a plastic gas seal and shorten the hull. That cushion leg compresses at ignition producing much more combustion chamber volume at ignition than with no cushion leg.

More volume = less pressure
Less volume = more pressure... quite a bit more pressure!

Play but play safe!

Longbow

[Petander]

Now here is something new!

Thank you Captain Morgan, I'm a longtime Quick Load user but simulating a shotshell load in QL never occurred to me!

Of course it's not Pressure Trace but...

[Blood Trail]

As Cap’N Morgan stated, seating pressure is the most overlooked and the most important factor that can affect chamber pressure. It’s the equivalent of seating a bullet’s OAL too deep.

However, I know I’m gonna get some backlash from this, but here goes:

You will never blow a shotgun up by subbing primers. You will never blow a shotgun up by subbing wads or hulls. I’m talking modern shotguns in good working order.

As many of you know I do a lot of pressure testing. Highest pressure I’ve purposely recorded was 28.7k psi with a double charge of a certain powder with a 1 oz shot payload.

Wanna know what happened to that Mossberg? Nothing. Absolutely nothing. I still use it.

Shotguns can take a lot more pressure than people think. Tom Roster hit over 55k psi. Wrote he was able to an 870 barre up and while strong, they aren’t the strongest in the market.

So what exactly am I saying?

I’m saying to still be smart and pay attention when reloading. Don’t venture off the unpublished data path if you don’t have the knowledge or experience to do so.

The main jest of this is don’t tear down your loads because you mistakenly used a magnum primer when data called for a standard primer or you used a FED 12S4 when you should of used a WAA12. You’ll be just fine.


Sent from my iPhone using Tapatalk

[Baltimoreed]

Very interesting thread as I’m currently loading 12 ga shells. Guess you would call me off the reservation as I’ve been building cas loads with the intent of using the lightest amount of powder possible and 3/4 -7/8 oz of # 9s. Yes I’ve looked in my antique Lyman shotshell manuals and nothing listed is light enough. I’ve even loaded 1/2 oz loads for my 20 ga Marlin Model 30. These loads work for me and my firearms YMMV. If so inclined use at your own risk. Currently I’m using a#408 powder bushing/7/8 oz #9 shot/CB1138-12 red wads in a 2 inch WW AA cut down shell. My powder is Extra-Lite but I’ve used Red Dot, Clay Dot or Clays pretty much interchangeably. My standard sized shell WW AA load is the same except for a CB0175-12 pink wad. They work just fine for my cas shoots. The shorter shells give me one more in my mag for Wild Bunch shoots. I did increase the powder bushing from a #398 bushing to the #408 to give me a little more power.

[Cap'n Morgan]

However, I know I’m gonna get some backlash from this, but here goes:

You will never blow a shotgun up by subbing primers. You will never blow a shotgun up by subbing wads or hulls. I’m talking modern shotguns in good working order.

Blood Trail, you're not gonna get any backlash from me!

I've been reloading shotshell by the seat of my pants forever, and (crossing my fingers) never had any worries - using common sense goes a long way.
At one point I cut up several hundreds shells of various brands, too rusty to chamber and retract reliably (hunting at sea takes a heavy toll on both guns and ammo). I mixed all the powder into a "Special Blend" and reused both shot & powder in once-fired target hulls.

As you noticed, shotguns can take an awful amount of pressure. Some guns have even survived a twelve gauge shell on top of a twenty gauge shell without splitting the barrel, yet shotguns still, sometimes inexplicable, blow up.

I have an old 16 gauge Spanish s/s lying around somewhere. One of these days I'm gonna test a theory of mine: cut a shotshell in half, plug the barrel halfway towards the muzzle with the front part of the shell, and shoot the powder/wad part, hopefully creating a disastrously "bicycle pump effect" when the speeding wad meet up with the stationary front part. I may have to use black powder to get a proper ignition, but I certainly will use a VERY long string when firing the gun.

[longbow]

Having blown up one shotgun in my hands I can say for sure they can and do blow up!

I pulled the trigger and was instantly covered by a cloud of smoke, felt a spray of debris in my face and felt the gun go "limp".

When the smoke cleared and I composed myself my wife was screaming having witnessed the blow up and I found myself holding the forearm in my left hand and buttstock with receiver in my right hand and the barrel on the ground about 10' in front of me.

This was an inexpensive single shot with Remington's name on it, bought new.

The same loads had been previously shot through my Browning BPS with Buck and Slug barrel on it.

Recoil in the Browning was punishing with some sticky extraction but I wasn't smart enough to recognize the signs!

This was a Lyman manual load except likely a different primer and with shortened hull with a soft lead filled Lyman Foster slug and fold crimp.

I was lucky! The entire top of the chamber was missing but no other bulges or damage. I kept the pieces for show and tell until we moved at which point I tossed it all but wish I had kept it!

My injuries were relatively minor...I had a cut above my right eye and powder debris all over my face and I lost some hearing in my right ear.

Again, this was a book load possibly with different primer, shortened hull and filled Foster slug.

Indications are that the slug obturated to fill the chamber at the case mouth then hit the forcing cone and couldn't squeeze down fast enough.

Powder was PB and no mistake because I only had one powder. Couldn't be double loaded because the was no room in the shortened hull.

There was no barrel obstruction... 1st shot out of the single shot.

My guess is pressure spike caused by no cushion leg and obturated filled slug squeezing down from chamber diameter to bore diameter. Primer may have contributed to high pressure too.

To reinforce above comments by Cap'n Morgan and BT...

Removing the cushion leg can increase pressure.

Primer change can change pressure by up to 3000 PSI.

Deep crimp can raise pressure by up to 3000 PSI.

And I believe soft HB slugs can obturate to fill the chamber, at least under certain circumstances, leading to increased pressure due to squeeze down to bore diameter.

Any one of these may not lead to a blow up but combine them at your own risk!

I was lucky!

These days I don't stray far from published load data. I do substitute wads for similar wad and I do substitute slug for equal weight shot.

I do not remove cushion legs without reducing powder charge.

I do not use HB slugs in short hulls!

As I said before... play but play safe!

Longbow

[Dieselhorses]

Recently landed a "never-used" MEC Sizemaster (12 ga) from a coworker (SM82) along with 25 lbs. chilled 7.5 shot, 250 AA wads, 4 lbs Red Dot, 200+ hulls, 200 Winchester primers-all for 100.00. Now after reading this thread, it has wondering if I even want to get into shotshell reloading! Obviously, there are more variables than rifle and pistol reloading. It was fun giving the ole press a "facelift" and reassembling it though!


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[farmbif]

as far as the original question, I'm not so sure there is any one main factor that would change or determine shotshell pressure. all the components that can be changed can greatly change the pressure curve. this I guess is why there are exact formulas for specific components in shotshell reloading manuals. reloading shotshells is very different than reloading center fire brass cartridges. nowhere in any shotshell reloading manual I have ever seen does it say to start low with the powder charge and work up a load.

[dverna]

Recently landed a "never-used" MEC Sizemaster (12 ga) from a coworker (SM82) along with 25 lbs. chilled 7.5 shot, 250 AA wads, 4 lbs Red Dot, 200+ hulls, 200 Winchester primers-all for 100.00. Now after reading this thread, it has wondering if I even want to get into shotshell reloading! Obviously, there are more variables than rifle and pistol reloading. It was fun giving the ole press a "facelift" and reassembling it though!






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There are thousands of published recipes. Use them and you are completely safe. Ignore loads on this or any other forum not found in a manual or the powder manufactures web site.

[megasupermagnum]

There are thousands of published recipes. Use them and you are completely safe. Ignore loads on this or any other forum not found in a manual or the powder manufactures web site.

dverna, we get it. You load nothing but published target loads. There are not thousands of published loads for anything except basic target loads, and really that only applies to 12 and 20 gauges. If you are wanting to load any kind of hunting load, especially buckshot or slugs, more often than not you can look through half a dozen books, and all of them will have at least one component that is either unobtanium, or discontinued. Ballistic Products is a big turnover factory, and over the last 10 years, they have rarely had a component more than a year or two before being changed or discontinued. Other than that, the next newest shotgun reloading manual is the Lyman 5th, and that came out in 2007. Half the stuff in that book is discontinued now. This isn't the 1980's and 1990's anymore where there is a billion different loads for a Federal gold medal hull, and everyone and their brother is making shotgun wads. We are at a time now where we are left with bare bones choices in a lot of cases, components are changing year-to-year, and no new data is coming out for this stuff.

At some point you either need to make the choice to either stop loading shotguns, or learn how to safely make substitutions.

[W.R.Buchanan]

In my opinion the biggest contributor to pressure spikes is the substitution of a Federal Primer which as others have said can contribute a 3000 psi increase in pressure. However as BT said the newer guns we commonly use are up to the task, and a 3000 psi spike on top of a 10,000 psi load is not going to kill you as long as the gun is solid. If it would, then how would the gun swallow 3" Magnum loads and live to tell about it?

I substitute wads as needed, and I don't have any Federal Primers (I don't even know which ones are the hot ones!) Payloads are all in the 1-1.25 oz range, and my loads are always close to book published loads, and I'm gonna use the exact same loads for Rem STS hulls as I use for Win AA's as well as Rio Hulls and Win Universals which are both strait wall hulls. And yet when I look I find the same loads for both styles of hulls in different manuals..

But here's where I don't venture. I don't hotrod loads looking for the most powerful load I can shoot . I see no point in it.

All my loads are on the bottom end of the velocity and pressure charts to begin with. I'm in the 11-1300 fps range, IE: Target Loads with different slugs or buckshot. I have no need for hot loads as nothing I shoot at will know the difference. If by chance I got to shoot at some pigs, my relatively mild Slug Loads would be more than up to the task. And lets say for the sake of conversation I got an invite to shoot a Polar Bear, or the 600 lb + Russian Boar I jsut saw on TV, I'd probably go buy some Brenneke Slugs and not use any of my handloaded ammo. I know that even the bottom end Brenneke Slugs are not as powerful as a Federal 1 oz slug at 1600 fps! And the fact that I still have 28 of those Federals in their original boxes is the reason why I shoot Low Recoil Slugs in the first place.

A Low Recoil 1 oz Slug at 1300 fps has a TKO of 60 when a .45-70 400 gr boolit at 1800 fps is only a TKO of 47. I doubt anyone here would not be willing to shoot jsut about anything in N/A form their .45-70. A .458 Win Mag 500 gr at 2150 fps is only TKO 70, where as those Federals I have a bunch of are TKO 73 and I can sure suffer thru a few of those if I had to.

I actually have bought some Brenneke Slugs and some Lightfield Slugs just to see how they'd perform?

Out of my guns the Brenneke's shoot around the point of aim, and I'm sure I could hit a Paper Plate at 25 or so yards, and even though the slugs I bought are on the low end of what Brenneke sells (1oz slugs at 1300 fps versus 1.5 oz Slugs at 1600 fps!)) I'm pretty sure they'd suffice for my intended use. I also won't have to worry about blowing myself up! Because these loads are similar to what I shoot in my Handloads, and they are Tested Factory loaded ammo that are loaded in to Rio Hulls exactly like I use! In fact my Crimps look a little better than theirs!

As far as those top end Brenneke slugs are concerned I think one 5 round box will last an entire lifetime as I doubt anyone will pull the trigger twice on one of those in a Mossberg 500 that weighs a hair over 7 lbs.!!! Shoulder damage should be expected! They have a TKO of 110! A .460 Weatherby Mag is only TKO 81 !

So in closing with my .02, I maintain that there is alot of room for experimentation at the lower end of the power curve. Being able to think clearly and not engage in Stupid Reloading Practices, and being able to look at a loaded cartridge and decide if it is safe to shoot, will go along way towards keeping you safe.

I am not a fan of the 'Never Deviate from a Book Load' crowd. I feel that they don't understand what they are doing, and the people who compile all those book loads think that too, and have to cover their butts. Plus that since there is only about 8 million different recipes for loading shotshells published over the last 100 years,,, I am pretty sure that if you look long enough you can find about any combination of components you might wish to try in some book somewhere.

Randy.

[Dieselhorses]

There are thousands of published recipes. Use them and you are completely safe. Ignore loads on this or any other forum not found in a manual or the powder manufactures web site.

Appreciate it Don!

[Baltimoreed]

Started back reloading 00 buck loads and am curious about using a filler between the pellets. I’m loading WW AA 12ga with a plastic wad that holds 8 pieces. Is filler even needed?