Is it safe to headspace on bullet instead of case mouth?

[IndyGunworks]

40 loaded this long would keep it from slipping past the extractor and going off unrestrained in the chamber would it not?

Your onto something. 40 loaded like that WOULD probably go bang, and would properly cycle the gun, however you will see a HUGE unpredictable increase in pressure and in no way is it something I would every try. Perhaps its been done w/ success because in theory, in my head, I can understand how it would work, but there are ALOT more variables at play here. Pressures, variances in seating depths, the force in which it chambers, ect ect. If you try this be sure to come back here and report, but I don't think you would find very many people to recommend it.

 

[giovani]

Autos headspace on the mouth

water is wet

sharks have a water tight bung hole

bears do s$&t in the woods

and the sky is blue

all facts

 

[IndyGunworks]

.755 is deeper than .745 what is sticking out??

Nothing, your hole is deeper than your casing. but there would still be pressure of the breech face pressing the bullet in. Not sure I grasp your question completely, perhaps ask it differently and I will try to answer it better.

And I thought the max case length of .40 was .850 not .755?

 

[shawnba67]

Autos headspace on the mouth

water is wet

sharks have a water tight bung hole

bears do s$&t in the woods

and the sky is blue

all facts

Measure one of yours, I just did one of mine. Conclusion; they are held for ignition by the extractor and the case mouth is backup to control jump to rifling and control pressure spikes. You ever check a sharks butt? I have given data, real actual data. Do some research measure your own. Explain to me how .745 case is held tight at the end in a .755 hole?

 

[shawnba67]

Nothing, your hole is deeper than your casing. but there would still be pressure of the breech face pressing the bullet in. Not sure I grasp your question completely, perhaps ask it differently and I will try to answer it better.

And I thought the max case length of .40 was .850 not .755?

I measured my 9mm, they are .755 max sammi. Picture your .745 case standing straight up vertically in your .755 tall chamber. Is it touching the top shoulder? If not how is the breech pushing on the case mouth? Now where is your headfspace being controlled.?

 

[sloughfoot]

It is not safe to fire a cartridge in a chamber marked and designed for another cartridge.

If the shooter next to you, the RO behind you, or you, get hurt you are totally on your own. Legally and morally. It could even be criminal.

Fer petes sake, don't bring your contraption to any match I am at.

I won't discuss the technical aspects of what you are attempting. There are rules that need to be followed. One of the gun rules is to only shoot cartridges out of firearms that are chambered for that cartridge.

 

[IndyGunworks]

Are you assuming that the chamber is .755 from the breech face when the slide is fully in battery just because that's what the SAMMI max case length is?

 

[IndyGunworks]

see here, the case is sticking out just a bit? There is margin for error with different case lengths w/in a set tolerance ie Min and Max case lengths... that's why they give both min and max lengths.

 

[shawnba67]

I am just feeding an arguement here not recomending or even doing anything unsafe, just challenging common belief's. Or at least begging for why it isn't safe as opposed to it isn't and thats that. At the end of this we might all have a better understanding of things.

 

[giovani]

If you are sure it head spaces on something other than the case mouth why dosen't a case with no bullet just fall 1/4 in or so into the chamber.

got my shark info on wikipedia and they never lie.

 

[giovani]

I think I know someone that just learned a lot about headspace.

 

[shawnba67]

Thinking out loud here ande I might try this tommorrow. I'm going to put some thin modleing clay or something on the back of a 380 case and chamber it in my 9mm and measure the squish of the clay without any case mouth input. Then again with a .745 piece of 9mm brass should get more squish out of the 9mm shouldn't I. The picture doesn't show the lock up of barrel to breach bieng controlled by the locking lugs though, the breach can only get so close tom the barrel before it runs into mechanical interference. Perhaps my pistol is different in its tloerance than some other common types. Yours looks like a glock, mines a cz variant. No I'm assuming my chamber is .755 because .760 wouldn't chamber and .755 would but slightly harder than normal and .753 went like clock work.

 

[IndyGunworks]

Your .380 case will probably just fall into the 9mm chamber... I don't believe they are the same diameter, nor the same taper. The better test would be to take 9mm casings of various lengths and measure the difference (or lack of) squish. BUT, I doubt it will work to well as adding not much at all would essentially be making a NO GO guage and it wont go into battery anyways.

 

[shawnba67]

It is not safe to fire a cartridge in a chamber marked and designed for another cartridge.

If the shooter next to you, the RO behind you, or you, get hurt you are totally on your own. Legally and morally. It could even be criminal.

Fer petes sake, don't bring your contraption to any match I am at.

I won't discuss the technical aspects of what you are attempting. There are rules that need to be followed. One of the gun rules is to only shoot cartridges out of firearms that are chambered for that cartridge.

What contraption? I am having discussion, not action. There is no contraption.

 

[shawnba67]

Your .380 case will probably just fall into the 9mm chamber... I don't believe they are the same diameter, nor the same taper. The better test would be to take 9mm casings of various lengths and measure the difference (or lack of) squish. BUT, I doubt it will work to well as adding not much at all would essentially be making a NO GO guage and it wont go into battery anyways.

How about remove my extractor and feed in a case of known length then use a brush or something to see if moved back and forth in the chamber any while in battery? That might be a better test of it.

 

[IndyGunworks]

How about remove the extractor from your glock and fire a mag of various length 9mm rounds? I bet it will still function fairly well.... esp if cleaned and oiled.

 

[T4rdV4rk]

I am just feeding an arguement here not recomending or even doing anything unsafe, just challenging common belief's. Or at least begging for why it isn't safe as opposed to it isn't and thats that. At the end of this we might all have a better understanding of things.

I can appreciate playing devil's advocate. Having said that, these are not just common beliefs. It is how the components are engineered to function.

IndyGunworks posts contain good information here. Go ahead and experiment if you want man. Just be very careful how you do it.

 

[IndyGunworks]

Here you go




Having your case to short, or you chamber to long is an unsafe condition.


Lets also add to the picture on the right, that it also leaves the case unsupported which is also dangerous w/ higher pressure loads.

 

[Broom_jm]

IGW's drawing illustrates a key part of Shawn's question/argument: In the 2nd picture, the case mouth is clearly not touching the end of the chamber and exhibits a proper/safe headspace. The third picture illustrates a condition where a cast lead bullet is right on the lands, holding the case flush against the breech.

In other words, Shawn is absolutely correct in his observations, but then draws erroneous conclusions, based on what he's seeing. How does a 9mm case that is just .945" actually headspace on the mouth of a chamber cut to .955"? Well, from a precise standpoint, it doesn't. The fact of the matter is that the extractor hold the rim of the case, the firing pin hits the primer, and the case goes off. One of two things might happen at this point: The primer drives the case forward until the mouth does, in fact, headspace at the end of the chamber, or the other common event is that the case expands under pressure, moves back very slightly until it's flush with the breech, and seals off the chamber to complete the firing sequence. In this example, the case mouth might be as much as .015" from the end of the chamber.

A lot of folks focus on the terms "headspace" as determining how far forward a case will be during the shot, but it is far more common for a semi-auto pistol case to be set back quite a bit during this process. What positive headspace does, when a case is too long, is prevent a round from being fired out of battery. The vast majority of fired SA cases are, in fact, fired from brass that is too short to ever see the mouth reach the end of the chamber.

So, to Shawn's original question: Yes, what he's proposing "could" work. In fact, it would work quite well...right up until that point in time where it went horribly wrong! In the first of Unclenick's illustrations (above) the case is too far into the chamber. The strike from the firing pin drove it there and the pressure of the burning powder has stuck the sides of the case to the chamber walls. As the pressure spikes, the head of the case now has excessive space to move back (excessive headspace) so the potential exists for the case to rip itself in half. Shawn is proposing that the bullet would be seated to a precise length and prevent this condition from occurring. In a perfect world, where case OAL never varies by more than 1 or 2 thousandths, he's actually correct. However, in the real world bullets are not so uniform and neither is neck tension. All it would take is for one work-hardened piece of brass to have very little neck tension, such that when the firing pin strikes the primer, the bullet sets back into the case 5-10 thousandths. Now, you not only have a case with excessive headspace, but increased pressure during the firing sequence; a perfect storm for a headcase separation.

As with most things in life, there is a reason folks don't do something that seems like it would work. Oftentimes the explanation for why they don't is complicated, but unless you KNOW what you're doing...you don't. When it comes to reloading, it's fine to ask "what if", but the potential dangers mandate that if you don't know exactly what the outcome is going to be, stick to what conventional wisdom dictates.

ETA: I hope you got Unclenick's permission to post this drawing, as it IS copyrighted! He frequents Shooters Forum, so maybe ask his permission ex post facto?

 

[IndyGunworks]

Broom... You have a way of words about yourself. You were able to put into words what I simply could just not get across. Rep coming your way.