Why do Shotguns use fast (pistol) powders?

[Dave R]

Just idle curiosity on my part. Heavy bullets in a rifle with a big case typically like slow powders, right? I'm thinking .30-06 with 220gr. bullets and up.

So why do shotguns, which throw a 1.oz. plus shot cup, and operate at lower pressures, use faster powders? Wouldn't a slow powder give a shotgun payload more velocity with a slower pressure curve?

Just wondering.

[AlaskaMike]

Shotgun shells that use powders like Unique, Red Dot, Green Dot, etc. do so because they have that little plastic wad in them that acts like a shock absorber.

The .410 is different and doesn't use that little plastic 'shock absorber' and so it uses slower pistol powders like 2400 and Lil' Gun.

I'm not a shotshell reloader, so hopefully someone who is can give a better reply.

[Doyle]

I think more than the "shock absorber" wad is the fact that the very large bore size means that pressure doesn't have a chance to build up too quickly. It is the rapid pressure buildup that makes you use a slower powder in a rifle (as opposed to the same diameter ammo being used in a short-barreled pistol).

[BigJimP]

Reloading shotshells - in all gagues / including the .410 ---requires a "wad" that separates the powder from the shot inside the shell. The was is typically a plastic one part item / with a small cup on the bottom - and a larger cup with petals on the top for the shot.

The published recipes for shotshells - are usually relatively low pressure ...( say probably 10,000 - 12,000 psi ) compared to handguns where a 9mm round might be pushing 33,000 psi --- but to say all shotshell powders are fast or slow -- is a little too generic. In shotshells powder like Hodgdon Clays - are pretty fast burning / where powders like Longshot are slower burning .... but powders like Longshot can develop some pretty fast loads / and some pretty high pressures ...

It is true - that there are some powders that work pretty well in handgun calibers - and pretty well in shotshells .... like Hodgdon Clays or Hodgdon Universal ....but usually most of us tend to use powders designed for shotshells vs powders designed for handguns ...

Every combination of shotshell primers and a powder ( and you can't mix and match shotshell primers like you do in "small handgun primers" as an example - will give you different results. In shotshell primers - not all 209 primers are created equal / and changing a primer brand will often result in a change in the recipe - maybe changing the wad, or powder qty, etc ...

As an example - a lot of shooters use Hodgdon Universal in 20ga shotshells....but I find it really dirty / so I shifted all of my 20ga loads to Hodgdon International. In my 28ga shotshells - Hodgdon Universal is a very clean powder ... so its some combination of the primer, the pressure - the ounces of shot in the shell ...the cross section of the area of the hull ...that contributes to all those characteristics. I've tested some handgun loads .45 acp with 230gr bullets - and Hodgdon Universal ...and on the high end of a legal load ...it was pretty clean and acceptable. At the low end of the powder drop allowed / I thought it was really dirty ...

So in my mind - its hard to generalize .....most of us find a published recipe / try it ... and if we like it / we tend to stay with that load for a long time. But to me -- its too hard to generalize ....

[wncchester]

Shotguns have low expansion ratios, pretty much like handguns. If we used a slow powder it would be virtually impossible to build up much chamber pressure in either.

[GeauxTide]

Everything depends on the expansion ratio - the volume of the case versus the size of the hole. The '06 has a low ratio, even with 220gr bullets. No slow powder needed; however, the 257 WBY and the 264 WM take a case full of the slowest powder. Other comments about the pressure apply, too.

[frumious]

I never hear stories or see pictures of shotguns that were destroyed by an incorrect powder charge. Does this happen?

-cls

[Crosshair]

Slow powders don't like burning at low pressures and shotgun loads typically operate at 10,000 PSI or less.

[Sport45]

Low pressure and thin barrels. You want the pressure spike to be over with while everything is still in the thicker part near the chamber.

Why do Shotguns use fast (pistol) powders?

I think you may have it backwards. There are probably more pistols loaded with "shotgun" powders than the other way around. (Although the powder really doesn't care what you put it in.)

[Dave R]

OK, I'm starting to get it. Can someone explain expansion ration (or link to an explanation?)

[zippy13]

I never hear stories or see pictures of shotguns that were destroyed by an incorrect powder charge. Does this happen?

It sure does, I've witnessed two such incidents. The first was an overcharged 20-ga Browning O/U back in 1968. It made a very loud boom, kicked like a mule and them it wouldn't open. The second, in the early 1990s, was a fellow who thought the warnings about not mixing powders didn't apply to him. He was shooting an 1100. As the gun fired, another loud boom, the locking lug failed, the bolt was driven back back deep into the action and the operating handle (normally just snapped in the bolt) was found in the adjacent trap field. In neither case was there a spectacular banana-peeled barrel nor anything else overly dramatic. Yet, both guns suffered ruptured/deformed actions. Thankfully there were no injuries except to the reloader's pride.

[BigJimP]

I see more handguns damaged by sloppy reloading ...than I do shotguns .../ but its always hard to tell if it was a squib round that blocked the barrel / and then the gun blew up as a follow-up round was fired ....or if it was a double charge of powder....

Most of the accidents I see on shotguns / is when the barrel is obstructed by a wad on a squib shell ( again a reloader error ) .... / or an improper shell dropped into a barrel ( like a 20ga shell dropped into the forcing cone on a 12ga - and then a 12ga shell will still fit in behind it ... / and then the 2nd shell is fired behind the first causing a catastrophic failure.

But there are too many reloaders that think the rules don't apply to them about using published recipes ....or they get incredibly careless ...and don't keep their loaders clean or tuned up ...or they mix powders, or they mix wads ...or whatever ....

[Mike Irwin]

"I never hear stories or see pictures of shotguns that were destroyed by an incorrect powder charge. Does this happen?"

Good lord yes.

Kid in my high school decided to make some super special dove loads for his double barrel.

First shot blew the barrel out and a chunk of it removed a very large piece of muscle and bone from his forearm.

He and his brother both were Darwin Award candidates of first order. They knew EVERYTHING about EVERYTHING. The wages of being spoiled by a very rich grandmother who bought them everything they wanted...

[smokem]

Hey all;
Shotgun powders have to burn all powder in 20 inches of barrel. That's way ammo companies design them, because some people like to hunt birds with a riot shotgun!
Here'a scenario....
My young 18 yr. old bud, pulls trap and skeet at alocal shooting place, sees a sweet young thing, with miniskirt and halter top and a 12 ga. 870 Remington walking up to him. She asks him to pull a round for her, and stand behind her to see where she is shooting. He stood foirmly behind her at her request.
She told him her Dad encourages her and her broyther to load their own shotgun and rifle shells; and that she had just loaded up25 shells that am.
She calls for the bird, pulls the trigger....large BOOM, and last thing my young bud remembers is her on top of him, shotgun about 10 feet away, and her screaming!
He helped her up...no blood or damage, but upon inspection the Rem 870 was blown out at chamber(Remember shotguns are only rated for about 20-25, 000 PSI). But, they are made of STEEL, and good steel at that since all blast was away from shooter! He asked girl what powder did she used...she mumbled something about Bullseye... (That's one of the FASTEST pistol powders they is!).
Girl hurriedly gathered up herself, ammo and drove away, leaving shotgun at facility. Management still has that shotgun on display to warn reloaders about OVERLOADS! (Remington has offered up to 4x the value of the shotgun, and has offered a new 870 to them. I guess to avoid bad publicity.
They declined. Steel is great!
Thought you all would find this interesting!
smokem

[wncchester]

". Can someone explain expansion ration"

I know of no link nor will I post an indepth explaination but I'll do a brief one.

Expansion ratio relates to how far the projectile (or shot column) has to travel down the bore to double or tripple the powder burn space. Shotguns typically double that space when the shot has moved down the bore less than an inch, ditto a .45 ACP, etc. That's a low ratio, effectively 1:1. A .22-250 bullet has to move perhaps 5-6 inches down the bore to double the burn space, 1:5 or 1:6 is a high expansion ratio.

If a shotgun powder was a slow burner the burn space would expand so fast the powder wouldn't have the needee resistance or confined space to achieve the proper pressure needed for a good burn. But, try loading a .22-250 with a shotgun powder and the powder burn rate would go outta sight before the bullet could move enough to keep pressure under control.

[Brian Pfleuger]

Another factor is probably "start pressure" and acceleration resistance.

Shotguns loads are pretty heavy, 300-600grs generally, but a smoothbore barrel and a plastic wad offers very little resistance to acceleration compared to the need to engrave rifling into a metal bullet and continue to force it forward.

That, coupled with the enormous (or tiny, depending on how it's expressed) expansion ratio, makes for the need of a powder that can keep up with the easily accelerated projectile and the rapidly expanding area behind it.

[Clark]

If there were an over bore shotgun, like a 10 ga necked down to .410, it could use a slower powder.

The term "expansion ratio" has been mis used several times in the above posts.

Over bore cartridges with slow powder, like the 7mmRemMag, has low expansion ratios.

Shotguns and hand gun cartridges, like the 32 S&W, have high expansion ratios.

The way I am able to get 400 fps 145 gr button bullet with one grain of Bullseye in a 45/70 was by highly modifying a cartridge to get a higher expansion ratio as well as a higher peak pressure.

This gun, with the sound of a pellet gun, will kill large varmints with a body shot.

In order to get an intuitive feel for expansion ratio, do some compression ratio calculations for internal combustion engines.

[wncchester]

"The term "expansion ratio" has been mis used several times in the above posts."

Don't stop now, explain how it has been mis used. ??

[Clark]

wncchester
Senior Member

Join Date: December 1, 2002
Posts: 1,717
"The term "expansion ratio" has been mis used several times in the above posts."

Don't stop now, explain how it has been mis used. ??

Uh oh, it looks like I misused it

Compression ratio is greater than one.
Expansion ratio is less than one.

I think I made that mistake once before.
.