Quote from: Ethang on December 16 2021 10:14:42 PM MST
I will argue that the only way a 10mm headspaces on the case mouth is if EVERY case is the exact same length as the available chamber. If any cases are shorter then the chamber spec, the cartridge is not headspacing on the mouth, it is being held by the extractor. This is not a bottle neck rifle round. Given that short cases are held by the extractor, then a 40 case is also held by the extractor and is headspacing on it.... you make your own decisions.

I am with you Ethang on this issue.  Most of my 10mm cases run .985 average.  Saami chamber spec is .992 minimum-1.004 maximum.  I would not think it ever headspaces on the case mouth and whether it is .007 or .019 short of the end of chamber that means it would never touch.  Is there a difference between .010 and .500?  My G20SF has handled some .40's without a hiccup but I only did it to test the theory as I have more 10mm cases than I will ever use.  Yes, scrub the chamber clean after doing so.

Quote from: jazzsax8 on February 04 2022 11:05:25 AM MST

Quote from: Ethang on December 16 2021 10:14:42 PM MST
I will argue that the only way a 10mm headspaces on the case mouth is if EVERY case is the exact same length as the available chamber. If any cases are shorter then the chamber spec, the cartridge is not headspacing on the mouth, it is being held by the extractor. This is not a bottle neck rifle round. Given that short cases are held by the extractor, then a 40 case is also held by the extractor and is headspacing on it.... you make your own decisions.

I am with you Ethang on this issue.  Most of my 10mm cases run .985 average.  Saami chamber spec is .992 minimum-1.004 maximum.  I would not think it ever headspaces on the case mouth and whether it is .007 or .019 short of the end of chamber that means it would never touch.  Is there a difference between .010 and .500?  My G20SF has handled some .40's without a hiccup but I only did it to test the theory as I have more 10mm cases than I will ever use.  Yes, scrub the chamber clean after doing so.

yup...it either touches or it doesn't ..if it's not touching with every case it is not headspacing on the case mouth, it's headspacing on the extractor.

Given the inertia of a 180 or 200 grain bullet, I suspect that it might be enough for the f.p. to ignite the primer even if the extractor isn't retaining the case toward the breech face. At any rate, that inertia will definitely help keep the case rearward on striking.  It would be interesting to see if primers will ignite reliably without an extractor to see if this happens. It might be hit and miss.  Given how fast the slide can come back upon firing and the ejection process, it seems questionable if a firing pin strike moving a case forward is going to damage the extractor.  If it did, why doesn't normal firing and ejection operation damage it?

I would feel uncomfortable using 40 S&W in the 10mm. It would be fine with a conversion barrel, but I would NEVER risk my life or pistol just to try it out. Like someone said, in a SHTF time I might give it a try, but that is all.

There is a very simple experiment you can do, which I was inspired to do by the old trick of putting a pencil down the barrel of a 1911 to see how much force the  firing pin exerts. In the case of the 1911, it may surprise you.  Anyway...

I took my Glock 20 ensuring that it was not loaded and  put an EMPTY once fired resized 40 S&W case with a fired primer reinstalled, into the chamber.  I dropped a pencil, eraser end first, down into  the barrel.  Holding the barrel up, I squeezed the trigger.  The pencil barely moved and did not jump upward noticeably.  This tells me that that case is held pretty tightly to the breech face wall by extractor tension (which it is confirmed by putting a dummy round in the breech face with the slide off) and it barely moves on impact.  Now an unfired primer will get a more solid hit, but I don't want to try this with a live primer as it would not tell me anything anyway.  Maybe fill the primer dent with glue or epoxy and that would be a more reliable indicator.

Thinking that the bullet inertia will no doubt somewhat resist forward movement of the cartridge by impact of the f.p., I tried a 40 S&W DUMMY round, resized with a 175 gr SWC bullet and again a reinserted, fired primer.  The pencil did not even move upward and I could barely feel the hit with my finger on the pencil end.  This seems to confirm my theory that the extractor tension combined with bullet & case inertia are sufficient to hold the case in place on firing with perhaps only a slight force against the extractor on striking.  It may be arguable that new, shorter than maximal length cases of 10mm will exhibit this same minimal force against the extractor on striking by the f.p.

Quote from: RickShooster on March 26 2022 01:38:19 PM MDT
There is a very simple experiment you can do, which I was inspired to do by the old trick of putting a pencil down the barrel of a 1911 to see how much force the  firing pin exerts. In the case of the 1911, it may surprise you.  Anyway...

I took my Glock 20 ensuring that it was not loaded and  put an EMPTY once fired resized 40 S&W case with a fired primer reinstalled, into the chamber.  I dropped a pencil, eraser end first, down into  the barrel.  Holding the barrel up, I squeezed the trigger.  The pencil barely moved and did not jump upward noticeably.  This tells me that that case is held pretty tightly to the breech face wall by extractor tension (which it is confirmed by putting a dummy round in the breech face with the slide off) and it barely moves on impact.  Now an unfired primer will get a more solid hit, but I don't want to try this with a live primer as it would not tell me anything anyway.  Maybe fill the primer dent with glue or epoxy and that would be a more reliable indicator.

Thinking that the bullet inertia will no doubt somewhat resist forward movement of the cartridge by impact of the f.p., I tried a 40 S&W DUMMY round, resized with a 175 gr SWC bullet and again a reinserted, fired primer.  The pencil did not even move upward and I could barely feel the hit with my finger on the pencil end.  This seems to confirm my theory that the extractor tension combined with bullet & case inertia are sufficient to hold the case in place on firing with perhaps only a slight force against the extractor on striking.  It may be arguable that new, shorter than maximal length cases of 10mm will exhibit this same minimal force against the extractor on striking by the f.p.

Try the same experiment with a 10mm round and see if there is a difference. I don't think there will be.

 OK, I actually  did this, I repeated the pencil test with a 10mm dummy round with the same bullet and another fired primer.  Honestly, the result was different.  I felt no impact on the pencil and the pencil did not move that I could see, so evidently this dummy round case was headspacing on the mouth or bullet ledge and it could not move appreciably.   It also made a seriously deep dent in the primer after a couple of tries, so no doubt the primer gets a much more substantial blow when the  case is not able to move forward much or at all.  Whether or not 40 S&W cases fired in a 10mm pistol are causing any damage to the extractor is still debatable.  For ultimate reliability, you would definitely want to use the designated cartridge with the designated primers