40 s&w minimum chamber length
- Thread starter target221
- Start date
it is rimless so it headspaces on the case mouth so if your chamber is very long the fireing pin wiil drive the cartrige
forward and if way to long it will not fire. a long chamber
i think will cause a lot of case streach. IMHO it should be the max case lenght????
Louis
Thanks for the answer Louis but my question is not driven by headspacing issues, which are not to say that are not important
. I've looked at a barrel which provides "full" support for the case, meaning the barrel extends all the way to the edge of the extractor groove on the case, this would be a length of 0.710". In order to fit this barrel, some material would have to be removed effectively shortening the chamber and exposing some of the case which would now become "unsupported". The .40 round case seems to have a web area (the part which is made of thicker material) starting at 0.635" into the case. The difference between these two numbers yields 0.065" which is the web area of the case.
Theoretically, the case support in this web area, especially close to the rear of the case, is not hyper critical however, practical considerations dictate that the actual depth of the chamber should not fall bellow 0.710" too much or the non-web area of the case becomes unsupported. This is a dangerous situation especially with ammo reloaded to pressures nearmax SAMMI specifications. So the question is what is the minimum length of the chamber, 0.700", 0.690", ... or some other value?
Failure to observe such a minimum length, interestingly enough, makes some glocks known for malfunctioning with reloaded 40 s&w ammo and blowing cases out exactly because they don't support the case properly in the barrel feed ramp area
.I've come accross some information that might be answering this question. I am posting the info for those who might be interested.
Some fella claims, in a post to another forum, to have measured the case support on several guns including a Glock 22 (40 s&w). He measured the distance from the base of the case to the furthest point, toward the mouth of the case, which is not supported. The longest unsupported length can be found at the bottom of the chamber where the feed ramp ends. He found that on a standard Glock 22 full case support starts at 0.235 and onward. Because these measurements don't mean much by themselves, he sectioned various 40 s&w brass to measure the case "web" and found brass which has a web area that only extends 0.180 from the base of the case.
This leaves the Glock 22 with a -0.055 deficit when it comes to case support
, which might explain why these guns go KB! with such consistent frequency. As an interesting side-note, the 10mm Glock 20 has a case support defficiency of 0.070, even more than the 40 s&w which has a lower pressure rating.
Based on this info, which is yet to be independently verified, I would reason that the absolute fail safe minimum chamber length is, for starters, dictated by the case webbing , as such it should be 0.670, arrived at by subtracting the 0.180 webbing from the 0.850 case length. Any headspacing gap has to be added to this value as well, so if you had a 0.010 headspace your min. chamber length would have to be 0.680 as the case might get pushed towards the breach-face, effectively exposing more case area beyond the case web.
Based on this I would also never buy a glock in the 40s&w or 10mm caliber as these guns have a design flaw, period!
. Now if you are stuck with a Glock and you reload, you can virtually eliminate your headspace by varrying the OAL of your ammo, but this approach guarantees an even higher case support deficit as a longer OAL will push the case base towards the breach face. minimal or 0 headspace in a Glock, as a matter of proper fitting, would seem pretty important as the gun is operating with a significant case support deficiency, which will lead to KB! with reloaded brass or "hot" loads.
Now I was curious if a 1911 outfitted for 40s&w is any better than the Glock. I made some measurements, and can say that the barrel I have provides full case support (assuming the 0.180 webbing) with a +0.020 margin into the case web area, although with these values I would not want my headspace to exceed 0.020. The case support could be further improved by using a ramped barrel and/or reducing head-space to near 0 in a properly fitted frame-slide-barrel.
Any of this makes sense?
P.S. I am editing this because I was in error not to recognize Louis earlier when he did correctly imply headspace being a factor. Thanks Louis.
Some fella claims, in a post to another forum, to have measured the case support on several guns including a Glock 22 (40 s&w). He measured the distance from the base of the case to the furthest point, toward the mouth of the case, which is not supported. The longest unsupported length can be found at the bottom of the chamber where the feed ramp ends. He found that on a standard Glock 22 full case support starts at 0.235 and onward. Because these measurements don't mean much by themselves, he sectioned various 40 s&w brass to measure the case "web" and found brass which has a web area that only extends 0.180 from the base of the case.
This leaves the Glock 22 with a -0.055 deficit when it comes to case support
, which might explain why these guns go KB! with such consistent frequency. As an interesting side-note, the 10mm Glock 20 has a case support defficiency of 0.070, even more than the 40 s&w which has a lower pressure rating.Based on this info, which is yet to be independently verified, I would reason that the absolute fail safe minimum chamber length is, for starters, dictated by the case webbing , as such it should be 0.670, arrived at by subtracting the 0.180 webbing from the 0.850 case length. Any headspacing gap has to be added to this value as well, so if you had a 0.010 headspace your min. chamber length would have to be 0.680 as the case might get pushed towards the breach-face, effectively exposing more case area beyond the case web.
Based on this I would also never buy a glock in the 40s&w or 10mm caliber as these guns have a design flaw, period!
. Now if you are stuck with a Glock and you reload, you can virtually eliminate your headspace by varrying the OAL of your ammo, but this approach guarantees an even higher case support deficit as a longer OAL will push the case base towards the breach face. minimal or 0 headspace in a Glock, as a matter of proper fitting, would seem pretty important as the gun is operating with a significant case support deficiency, which will lead to KB! with reloaded brass or "hot" loads.Now I was curious if a 1911 outfitted for 40s&w is any better than the Glock. I made some measurements, and can say that the barrel I have provides full case support (assuming the 0.180 webbing) with a +0.020 margin into the case web area, although with these values I would not want my headspace to exceed 0.020
. The case support could be further improved by using a ramped barrel and/or reducing head-space to near 0 in a properly fitted frame-slide-barrel.Any of this makes sense?
P.S. I am editing this because I was in error not to recognize Louis earlier when he did correctly imply headspace being a factor. Thanks Louis.
Last edited:
