Headspacing Pistols?

[Muddawg900]

We've all heard how important it is to make sure your rifle (or M2HB for you military folk) is headspaced. Usually after some sort of major barrel or receiver work is done. Everyone raves over it, and for good reason due to a safety concern. Over the course of the day I flipped through 40+ pages of threads in the General Gunsmithing section, looking for information and doing research on building my first 2011 limited gun, and other general 2011 gunsmithing knowledge. Of the 6-8 or so threads (and lots of youtube videos) I read specifically on building a gun from the ground up, no one mentioned headspace gauging their pistols. 

 

Is headspacing a pistol not as prevalent as it is for rifles? Is it still a concern, but heavily overlooked? Or is it just not a thing at all? 

 

Insight and knowledge is greatly appreciated! Thanks for stopping in.

[Yondering]

Maybe I'm being picky about terminology, but "headspace" is not a verb. It is not a thing that we do; it's something we can check, and that should have been set correctly when the chamber was reamed in the barrel. Checking headspace can be important in rifle cartridges, but is not as critical in most pistols.

 

It's important to understand that headspace is the relationship between the cartridge brass and the barrel's chamber, specifically at the controlling feature in the chamber. That controlling feature is usually the shoulder in bottleneck cases, and the front lip of the chamber in straight wall pistols. Why is this important? - because changing the brass changes headspace; it's not an attribute of only the gun itself. A bottleneck case with the shoulder bumped back or a straight wall case trimmed to short can cause excess headspace, while the correct brass dimensions in the same gun would have correct headspace.

 

Straight wall pistol cartridges are very tolerant of a wide range of headspace, so it's really not that important to check in most pistols. In fact, many don't realize this but a lot of pistol case lengths vary enough that the extractor ends up controlling headspace some of the time with shorter cases. This is perfectly acceptable. 

Edited August 15, 2019 by Yondering

[Muddawg900]

Yondering,

 

Thanks for the clarification. I certainly appreciate you explaining things out as it definitely helped me understand better what I was trying to ask. It makes more sense in that it's not a verb but rather a spec being checked. 

 

I'll even go so far as to say that I'm overthinking this in terms of pistols. I understand it's more important for rifles as they aren't quite as tolerant to a wider range of dimensions unlike pistols. 

[Yondering]

Glad to help. Nothing wrong with asking the question and learning about it; I respect that, unlike the guys who make up their mind without doing either one. 

 

One example of loose headspace that works OK is when firing 40 S&W in a 10mm Glock. (Glock ONLY, but that's a different topic) When doing this, the extractor itself controls headspace, not the chamber, but it works flawlessly. The exception is when doing the same in a 1911 or Tanfoglio, when the round falls in front of the extractor; in that case the extreme headspace causes the case head to slam into the breech face and can be a problem, but we still don't normally see case head separations from it.

 

The main effect of excess headspace in a straight wall pistol cartridge is that fired primers can appear more flattened than if the same load were fired with the correct headspace. This happens because the primer is pushed back against the breech face when it ignites and the case is pushed forward, but then the case moves backwards against the breech face under pressure. The small amount of primer protrusion from the case during that time allows it to bulge slightly, resulting in a flatter appearance when pressure forces the case back over it. 

Edited August 22, 2019 by Yondering

[RaylanGivens]

I case gauge all my 9mm ammo in a match hundo gauge...  I notice that some cases are longer than others...  some almost 0.040 or so...  I pull them and put them in my practice ammo box...  and they always shoot in my PCC.

 

Always seems odd.