What's the future of .40 S&W?

[Monac]

Look, with old, non-expanding bullets, kinetic energy did not matter very much. A 9mm FMJ would usually go straight through people, and as long as you were doing that, what difference did muzzle energy make? A 45 ACP FMJ might have been a little less likely to go straight on through, and that may account for its better reputation for stopping power back then - it was punching people harder.

But nowadays we have bullets that expand on impact, and it turns out that once you design a good bullet, one of the key qualities that determines how much it expands is its kinetic energy (when it hits the target, obviously, but that depends on what it started out with).

(Quick flashback to high school: Momentum = mass times velocity. Force = mass times acceleration. Kinetic energy = 1/2 mass times velocity squared.)

If you think expanding bullets don't work, well, then you've got an argument with every police department that has adopted them since the 1970's and has found out that they DO work. Don't talk to me, talk to them.

And thus we circle back to the whole reason this conversation started: Law enforcement agencies have decided they can get adequate stopping power from 9mm guns using the right bullets. They are therefore dropping the 40 S&W because 9mm is more pleasant to shoot and easier for their officers to qualify with.

So does 40 S&W have a future? My opinion would yes, because it does offer somewhat more power than 9mm, and there will always be people who want that. The analogy I think of is that back before 1945, when 32 ACP was what most people wanted in pocket autos, there were enough people who wanted pistols in 380 to make it worthwhile for Colt and Savage and Remington to make guns for them.

A better question might be about the future of 45 ACP, because it requires guns that are either bulky or low-capacity, without - in the day of expanding bullets - offering better stopping power. But I am not worried about it, because it is a quintessentially American cartridge, like 45 Colt, and THAT is still around 140 years after it was new. Cartridges take a LONG time to die, if there are a lot of guns around for them, or if people just really like them - 32 S&W Long is another classic example.

 

[cdk8]

I'm sure it will stick around. From a ballistics standpoint, I don't feel there are any shortcomings with the round that are much greater than the same shortcomings of all handgun calibers in respect to their ability to incapacitate.

With that said, I consider the energy differences among most man-stopping handgun calibers to be a largely moot point, and so I strongly prefer 9mm because the capacity is higher and I can shoot it faster. I do not expect any handgun caliber to reliability incapacitate with a single shot to center mass, and that is why I train to keep shooting until the target goes down. In my opinion, the person who can shoot faster & more accurately is the most likely person to survive, where as which specific calibers are being used play a drastically lesser role in outcome.

.40 came into effect after there was a perceived lack of 'stopping power' of 9mm, but a realization that the larger frame sizes and higher recoil of the 10mm were problematic, in many cases not providing any gain while increasing the risk of collateral damage. Since then, bullet technology has changed. The biggest single incident I know of, the Miami shootout, likely would have ended differently had the 9mm's used been loaded with a modern JHP, such as the Speer Gold Dot. In my personal opinion, a "lack of stopping power" is more perceived than actual in regards to the LE-grade calibers loaded with modern ammunition.

 

[ColoradoShooter77]

You forgot the 155 grain 40 loads that clock 1200 fps and 500 ft lbs of energy. That's the most powerful 40 caliber load.

 

[Monac]

True, ColoradoShooter, but I wanted to use the standard loads for each caliber. I wasn't entirely sure what the "standard" bullet weight for 40 S&W is; since it's a modern round, hollow points of various weights are as common for it as FMJ loads, AFAIK. All of these cartridges can develop greater muzzle energies than the ones I quoted by using lighter bullets.

Muzzle energy isn't the end-all and be-all of cartridges; you need a well designed bullet of adequate weight for good penetration too, which is why 380 still isn't the equal of 9mm Parabellum.

 

[justin22885]

i dont know about you guys.. but i think im going to say forget what military and LEO use.. im going to go against the grain, ignore the status quo and just pack a .38 super for self defense.. more power than a .40S&W, 17 rounds like a 9mm.. why? because it surpasses both 40S&W and 9mm and i dont need some agency bureaucrat to tell me to think otherwise

 

[Girodin]

just don't buy it you can say and believe what you want but mass × speed = force
saying that a 9mm equals a 40 or a 45 is simply untrue in the real world

The problem with that line of thinking is that terminal ballistics involves more than force or kinetic energy. You have to look at how handgun bullet wounding characteristics. Long story short none of the common service pistol calibers have enough velocity to wound they way a rifle round does. Basically pistol rounds just poke holes. The extra energy isn't in and of itself causing any additional damage.

In a defensive shooting you want to stop the person. How do you do that? Well there are essentially three/four ways (depending on how you want to count them):

First: CNS shots. Shots that effective damage the CNS can be instant fight stoppers

Second: Physiological stops (and I divide this into two categories)

A) Bleeding until the person is disabled through blood loss

B) Destroying physical structures to the extent the person is physically incapable of being a threat.

Third: Psychological stops. This is basically the threat simply deciding to stop fighting.

For the first two it is hard to argue that additional energy of .40 makes it perform any better than a 9x19 or offers any real advantage.

What is critical in each is penetration and shot placement. What matters, in short, is hitting the right parts of body. That is why shot placement and penetration are key. Shot placement is obvious. Penetration matters because if you don't reach the right parts you wont have the desired effect. If a bullet punches through the brain stem and cerebellum it really doesn't matter one bit whether is an expanded .68 40 cal or a .62 9mm

View attachment 734797

If the bullet goes through the heart, lungs, etc. it similarly is very unlikely to matter in any significant way by being .06" wider. There just isn't enough difference to make a significant difference in the wound channel.

Expanding bullets from 9x19 typically will give adequate penetration. The same is not true of expanding 9x17 bullets. Penetration of comparable loads is similar between 40 and 9x19 and both reliably meet acceptable standards.

View attachment 734798

Since you get similar penetration from 40 and 9x19, since the difference in expanded diameter and frontal area doesn't get you a significantly larger wound channel and since neither had the velocity to have the temporary wound channel create any real wounding effect, what does that extra energy get you? What does it accomplish in terms of terminal ballistics or stopping a threat?

In short the energy difference between those two does not mean the 40 has better terminal ballistics.

It does mean that there is more recoil. The fact is most people can shoot a 9x19 better than they can a 40 S&W in a similar gun. That is why you have power fact and categories in competition shooting. I would hypothesis that as guns get smaller this is probably even more true. It also costs more to shoot. Dollar for dollar you can practice more with a 9x19 (hand loading may affect this to some degree). Both of those are notable because shot placement is a seriously significant factor.

So once you reach the conclusion that the 40 does not have any advantage in terminal ballistics, then how do you justify having fewer round and greater recoil in the same gun.

Where your argument also goes astray is in claiming that it is accepted that .380 with modern bullets is the equivalent of 9x19. Its not. Expanded 380 tends to be around .45" give or take a couple hundredths given the load in question. So the difference in expanded diameter between a similar 9x19 and 9x17 is about 4x the difference between 9x19 and 40 S&W. More importantly though, is the difference in penetration. From what I have seen, .380 projectiles that get any kind of real expansion tend to come up short on penetration. Inadequate penetration is a serious problem. Some people advocate carrying for FMJ in a .380 for that reason. Thus modern projectiles have not resulted in 380 being the equivalent of 9x19. In sum, 9x19 arguable does have an advantage vis-a-vis .380 whereas 40 S&W does not have any advantage vis-a-vis 9x19.

I have 40s and 45s, but the above is why I believe a 9x19 makes the most sense for a defensive or duty weapon. If other people want to look at the evidence and reach a different conclusion and carry something else, more power to them.

 

[ljnowell]

The problem with that line of thinking is that terminal ballistics involves more than force or kinetic energy. You have to look at how handgun bullet wounding characteristics. Long story short none of the common service pistol calibers have enough velocity to wound they way a rifle round does. Basically pistol rounds just poke holes. The extra energy isn't in and of itself causing any additional damage.

In a defensive shooting you want to stop the person. How do you do that? Well there are essentially three/four ways (depending on how you want to count them):

First: CNS shots. Shots that effective damage the CNS can be instant fight stoppers

Second: Physiological stops (and I divide this into two categories)

A) Bleeding until the person is disabled through blood loss

B) Destroying physical structures to the extent the person is physically incapable of being a threat.

Third: Psychological stops. This is basically the threat simply deciding to stop fighting.

For the first two it is hard to argue that additional energy of .40 makes it perform any better than a 9x19 or offers any real advantage.

What is critical in each is penetration and shot placement. What matters, in short, is hitting the right parts of body. That is why shot placement and penetration are key. Shot placement is obvious. Penetration matters because if you don't reach the right parts you wont have the desired effect. If a bullet punches through the brain stem and cerebellum it really doesn't matter one bit whether is an expanded .68 40 cal or a .62 9mm



If the bullet goes through the heart, lungs, etc. it similarly is very unlikely to matter in any significant way by being .06" wider. There just isn't enough difference to make a significant difference in the wound channel.

Expanding bullets from 9x19 typically will give adequate penetration. The same is not true of expanding 9x17 bullets. Penetration of comparable loads is similar between 40 and 9x19 and both reliably meet acceptable standards.



Since you get similar penetration from 40 and 9x19, since the difference in expanded diameter and frontal area doesn't get you a significantly larger wound channel and since neither had the velocity to have the temporary wound channel create any real wounding effect, what does that extra energy get you? What does it accomplish in terms of terminal ballistics or stopping a threat?

In short the energy difference between those two does not mean the 40 has better terminal ballistics.

It does mean that there is more recoil. The fact is most people can shoot a 9x19 better than they can a 40 S&W in a similar gun. That is why you have power fact and categories in competition shooting. I would hypothesis that as guns get smaller this is probably even more true. It also costs more to shoot. Dollar for dollar you can practice more with a 9x19 (hand loading may affect this to some degree). Both of those are notable because shot placement is a seriously significant factor.

So once you reach the conclusion that the 40 does not have any advantage in terminal ballistics, then how do you justify having fewer round and greater recoil in the same gun.

Where your argument also goes astray is in claiming that it is accepted that .380 with modern bullets is the equivalent of 9x19. Its not. Expanded 380 tends to be around .45" give or take a couple hundredths given the load in question. So the difference in expanded diameter between a similar 9x19 and 9x17 is about 4x the difference between 9x19 and 40 S&W. More importantly though, is the difference in penetration. From what I have seen, .380 projectiles that get any kind of real expansion tend to come up short on penetration. Inadequate penetration is a serious problem. Some people advocate carrying for FMJ in a .380 for that reason. Thus modern projectiles have not resulted in 380 being the equivalent of 9x19. In sum, 9x19 arguable does have an advantage vis-a-vis .380 whereas 40 S&W does not have any advantage vis-a-vis 9x19.

I have 40s and 45s, but the above is why I believe a 9x19 makes the most sense for a defensive or duty weapon. If other people want to look at the evidence and reach a different conclusion and carry something else, more power to them.

Well said, good post!

 

[USAF_Vet]

I don't own a .40, but considering all the .40 S&W range brass I pick up, I'm a minority.

I've seriously considered getting into .40S&W, eyeballing the police trade in S&W M&P .40 at Bud's and other places. I'm more or less invested in 9mm, both casting and reloading.

It's not going anywhere. It's quite popular, and the gubmint still stockpiled millions upon millions of rounds.

 

[Casefull]

Shoot through clothing, leather, metal, heavy bone, thick muscle and all of the gelatin tests mean very little. Gelatin is soft consistent material. If you hunt you have a better appreciation of bullet performance and has been said pistol rounds suck at tissure damage.
Velocity and bullet weight and the penetration it offers are much overlooked when it comes to real world performance. A 10mm 155 g at 1500 fps would be a good man stopper but not very easy to shoot.

 

[mavracer]

Since you get similar penetration from 40 and 9x19, since the difference in expanded diameter and frontal area doesn't get you a significantly larger wound channel and since neither had the velocity to have the temporary wound channel create any real wounding effect, what does that extra energy get you? What does it accomplish in terms of terminal ballistics or stopping a threat?

Both actually have enough energy for the temporary cavity to have some effects, it only takes 500psi to have a possibility according to Dr Courtneys BPW research the problem for the 9mm is it has to give up adequate penatration to get there 40 and 45 don't.

What does it accomplish in terms of terminal ballistics or stopping a threat?

All depends on what he's doing while he's bleeding out.
There are two kinds of wounds timers and switches larger holes turns some timers to switches and shortens some timers.

The 40 has a terminal ballistics advantage no matter how much 9mm fans want to ignore it.

 

[SC Shooter]

Walk down the ammo aisle of any big box sporting goods store and look at the multitude of various calibers. Some are big sellers, some not so much, but hardly do any ever go completely off the chart. The .40 caliber will be around long after we are all gone.

 

[JR47]

Interesting, in a watching a train-wreck kind of way. Has anyone actually bothered to make any attempt to verify all of these claims for improved wounding, or killing, since the 1990's? Nobody liked Marshall's protocols, and Fackler's minions self-destructed when he retired. So, WHERE are these "facts" coming from?

Face it, short of the hype provided by the manufacturers, by what yard-stick do we determine just how effective a caliber is?

The FBI, which has become the poster-child of "diversity" in law enforcement, had trouble qualifying it's recruits with firearms. Rather than bring them up to the standards of the older agents when they went through the Academy, they've decided to reduce the standards via the use of a less energetic round. An added bonus to this reduction in skill is that the gun now gives you more shots to try for a meaningful hit. Perfect.

There's been mention of the 10mm, as well. How many people remember the ORIGINAL specifications for the 10mm? Like the .41 Magnum, they were markedly reduced from what the ammo companies settled upon. Might be considered a clue of where the issues lie.

Glock's problems with the .40 S&W seem to have been concentrated in their barrel chamber design, not in anything more basic.

I would also point out that "worn out" guns seem to be hard to find. After all, those "worn out" guns are sold to distributors, resold to shooters, and have been operating safely for decades. Not bad for "worn out".

I own a S&W 4006, a Sig P229, a Taurus PT101, and a Ruger P944. None of them recoil anywhere near a 4" K-frame revolver in .357 magnum. Yet, nobody seems to think that the .357 mag is hard to shoot. I also shoot the neighbors .40 Shield without a problem.

If the Police, including the FBI, wish to qualify their agents and officers with minimum fuss and expense, they should buy Ruger 22/45 pistols, and let them shoot .22 Long Rifle. Cheap, quick to learn, and intrinsically accurate. Problem solved for the Administration.

.40 S&W is a choice. People really aren't hard to kill, if you do your part. Trying to justify one caliber over another is a fool's game. Especially for CCW holders, who aren't going to be facing armored felons on a routine basis, especially at long range.

Most criminals regard being shot as a ticket to prison, or the grave yard.

 

[ATLDave]

It is interesting to see, once again, the terminal ballistics debate revolve around whether additional mass or velocity or diameter creates marginal benefit along a somewhat steady curve, or if there are absolute "tiers" of effectiveness, within which there is ZERO additional benefit to extra mass/velocity/diameter.

I'm no expert in this, and I think it's a still-unsettled scientific question, but I find it somewhat implausible that there is literally NO marginal incapacitation potential from a projectile with extra mass, velocity, or diameter simply because they're both handgun projectiles. I find it very plausible that the marginal incapacitation potential may be small, and certainly does not offer the kind of quantum leap that rifle velocities or shotgun masses/diameters would offer. But the idea that an extra 100 ft/lbs, or an extra 35% more mass at the same speed, would have NO marginal incapacitation potential seems less likely than not to me.

FWIW, the gun in my bedside safe for home defense is a 9mm.

ETA: Here's one study that would tend to show that there are some small differences in effectiveness between 9/40/45. Not dramatic, and perhaps readily outweighed by other considerations, but some difference. http://www.buckeyefirearms.org/alternate-look-handgun-stopping-power

 

[cdk8]

If you are saying the 9mm is equal to a 45 that follows the same as the folks that say with the new bullets of today that the 380 is on par with 9mm so by this logic you would say 380 is equal to 45. I just don't buy it you can say and believe what you want but mass × speed = force
saying that a 9mm equals a 40 or a 45 is simply untrue in the real world

Is there evidence that establishes significant differences between 9, 40, and 45 in regards to effectiveness when each is loaded with the right type of modern and optimal defensive loadings? From a statistics standpoint, one of the most liked 9mm JHPs, the 127gr +p+ RA9TA Ranger T, isn't all that different from its 165gr .40 counter, and many other 155 and 165gr .40 rounds. Both carry respectable figures on energy, penetration, penetration through fabric, barrier penetration, expansion, and weight retention, and both have a reputation for being very effective as far as handgun calibers go.

http://winchesterle.com/Products/handgun-ammunition/ranger/t-series/Pages/RA9TA.aspx
http://winchesterle.com/Products/handgun-ammunition/ranger/t-series/Pages/RA40TA.aspx

In my opinion, many of the impressions of 9mm's lack of capability has come from various 115gr loadings that have, historically, not worked as consistently and not always penetrated deeply enough. The 9mm debate became heated because the FBI chose a particular 115gr round that was not a strong penetrator. Had the FBI's 9mm firearms in that incident used a round like the RA9TA, the particular 9mm round in question, which was fatal but did not achieve rapid incapacitation because it stopped slightly short of the heart, would have fully penetrated the assailant's heart, with those petals ripping right through it.

 

[Gtscotty]

Girodin,

By my calculations, based on the example bullets you posted, the expanded .40 diameter is 10% larger than the expanded 9mm diameter, but the frontal area is about 20% larger. Given two same length wound tracks, that is 20% more crushed tissue, why is that an immaterial difference? At what % increase would the two wound tracks cease to be counted as pretty much the same? Also, its plainly visible in the dyed gel tests you posted that all of the other rounds in the frame have noticeably larger total disrupted tissue paths than 9mm.

When selecting a defensive round, its important to weigh all factors and find what you think is the best balance. Now i can understand many people deciding that .40 doesn't strike the right balance for them, but that's totally different from claiming that .40 and .45 do not produce a larger wound channel with modern bullets than a 9mm with modern bullets.

The most logical conclusion I can draw from the tests I've seen and read about is that, when it comes to causing damage to a human, the .40 is probably more effective than the 9mm, and the .45 is probably more effective than both, but that both of those steps up in performance come with other costs that may or may not be worth accepting.

 

[sheephearder]

I don't think the 40 is going away soon. I like it for a woods gun with 180 gr bullets. It is more the man behind the gun than the caliber. so a 9mm or 38 sp is a good couch for most. Me I like all of them and now am not into mag calibers. I don't think the 40 will disappear soon. There are still a lot of city and state agencies using the 40 so we will see if they go to the 9mm or stay with the 40.

I am old and like slow and heavy over light and fast. The 45 will always be my first chose. How ever the 38/ 9mm are not bad and the 40 is just a little better IMHO.

 

[Bama Drifter]

Girodin, fantastic post. You deftly articulated what I wanted to say & included excellent visual aides. JR47, hahaha! I think you're definitely on to something w/ .22LR as a train & qual round for the Bureau.

Other guys talking temporary wound cavity, % greater efficacy, etc.... From my readings of Ayoob and other experts, the pistol rounds don't really matter as much as the rifle rounds in quickly putting down a bad guy. Our argument shouldn't be .38/9mm vs .40 vs .45 but instead Pistol Caliber vs minimum Rifle Caliber. Per the conventional wisdom, "A pistol is what you use to fight your way to a rifle." Considering rifles are difficult to wear, even SBRs aren't easy to conceal, we are stuck debating the merits of sidearms. All 3 aforementioned calibers are a weak runner-up to the Queen of personal weapons. YMMV

 

[kennedy]

I have two 40`s, a sig 226 and witness silver team and love them. I reload for both, I found a very accurate load with 155 gr bullets and universal powder. Just found a 15 rd mag for the sig. no intention of ever owning a 9mm or 45 acp. I might try a 357 sig barrel in the 226 if I find one cheap.

 

[cougar1717]

This thread is hilarious.

I absolutely believe there will be time when the 40S&W is no more. By the advent of energy weapons, only a luddite would use such a disgustingly dirty and archaic smokeless powder firearm. Our great-grandchildren will be discussing the pros and cons of Magnatec's pocket rail-gun vs the Gauss pistol vs the Tesla portable force field generator! Good times!

 

[TarDevil]

It is interesting to see, once again, the terminal ballistics debate revolve around whether additional mass or velocity or diameter creates marginal benefit along a somewhat steady curve, or if there are absolute "tiers" of effectiveness, within which there is ZERO additional benefit to extra mass/velocity/diameter.

I'm no expert in this, and I think it's a still-unsettled scientific question, but I find it somewhat implausible that there is literally NO marginal incapacitation potential from a projectile with extra mass, velocity, or diameter simply because they're both handgun projectiles. I find it very plausible that the marginal incapacitation potential may be small, and certainly does not offer the kind of quantum leap that rifle velocities or shotgun masses/diameters would offer. But the idea that an extra 100 ft/lbs, or an extra 35% more mass at the same speed, would have NO marginal incapacitation potential seems less likely than not to me.

Well put. But I can understand the rationale... having spent some time at the triggers of my sons' (including in-laws) .40s and .45s, I know I can empty the magazine of my 9 mm much quicker and more accurately than I can from their guns (none of these boys can hit a barn with their guns!).

The undecided factor is... are some of those early discharges from the larger caliber sufficient to eliminate the need for my multiple 9mm rounds?

 

[Girodin]

By my calculations, based on the example bullets you posted, the expanded .40 diameter is 10% larger than the expanded 9mm diameter, but the frontal area is about 20% larger. Given two same length wound tracks, that is 20% more crushed tissue, why is that an immaterial difference? At what % increase would the two wound tracks cease to be counted as pretty much the same?

It is going to be a slightly bigger hole. No two ways about that. How much bigger does it need to be before its a difference? Honestly I don't know. We could think of hypotheticals where the slight difference clips something vital and makes all the difference in the world. I'm sure there are other times it makes no difference. If one thinks it is a significant difference then one probably should step up to .45 or maybe the 50 GI. Nothing I have seen in either anecdotal shootings I'm familiar with nor any of the studies seem to suggest that marginally wider wound track of a .40 is significant or a justification for the down sides of the .40. This was essentially the conclusion reached but the recent FBI study. Although I have seen some suggest, with no real evidence to support their contention, that the study was just reached a result to justify what they already wanted to do. You can read the FBI study if it interests you.

Also, its plainly visible in the dyed gel tests you posted that all of the other rounds in the frame have noticeably larger total disrupted tissue paths than 9mm.

Are you talking about the temporary cavity which according to the FBI study, and others, is not a significant factory in wounding with projectiles traveling less than 2000 FPS? I think you may be misinterpreting what you are looking at. The permanent cavity is basically the same size in all of them and that is what is significant.

 

[ATLDave]

Are you talking about the temporary cavity which according to the FBI study, and others, is not a significant factory in wounding with projectiles traveling less than 2000 FPS? I think you may be misinterpreting what you are looking at. The permanent cavity is basically the same size in all of them and that is what is significant.

So, by this line of thinking, a .44 magnum bullet travelling at, say, 1,400 fps offers no additional incapacitation potential over a 9mm? After all, at a mere 1400 fps, we can disregard any hydrostatic shock or ballistic pressure wave effect, right? And if both can reach the vitals, then they both work.

"Hey, good news handgun hunters! You can put down the big bore revolvers and SAAMI-max 10mm's for human-sized animals, like deer and pigs. There's apparently zero marginal benefit to bullet diameter, bullet weight, or velocity. Just pop them with your Glock 26 and they'll fall over just as fast."

This strikes me as implausible.

 

[ljnowell]

So, by this line of thinking, a .44 magnum bullet travelling at, say, 1,400 fps offers no additional incapacitation potential over a 9mm? After all, at a mere 1400 fps, we can disregard any hydrostatic shock or ballistic pressure wave effect, right? And if both can reach the vitals, then they both work.

"Hey, good news handgun hunters! You can put down the big bore revolvers and SAAMI-max 10mm's for human-sized animals, like deer and pigs. There's apparently zero marginal benefit to bullet diameter, bullet weight, or velocity. Just pop them with your Glock 26 and they'll fall over just as fast."

This strikes me as implausible.

That's because you are ignoring the other qualities of the 44 magnum load to suit your needs for the argument.

 

[mavracer]

That's because you are ignoring the other qualities of the 44 magnum load to suit your needs for the argument.

The only quality he's ignoring is the same one Girodin is ignoring saying that "is not a significant factory in wounding with projectiles traveling less than 2000 FPS?"

Which has been proven to be false, temporary cavity and BPW can have a significant effect at well below 2000fps, problem is as Fackler and others state it can't be counted on which is why you don't want to give up penatration to get there.

There is no line in the sand here the higher you can get pressure in the temporary cavity the better you're chances of a timer becoming a switch.

 

[Gtscotty]

The only quality he's ignoring is the same one Girodin is ignoring saying that "is not a significant factory in wounding with projectiles traveling less than 2000 FPS?"

Which has been proven to be false, temporary cavity and BPW can have a significant effect at well below 2000fps, problem is as Fackler and others state it can't be counted on which is why you don't want to give up penatration to get there.

There is no line in the sand here the higher you can get pressure in the temporary cavity the better you're chances of a timer becoming a switch.

Bingo, everyone wants a hard and fast rule at the expense of admitting that these kinds of effects exist on a continuum.