CAS TOPICS > Gunsmithing

1873 rifle headspace measurement

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Hi all! First post here, I've been wanting to get into CAS for years, my big hold up was getting a rifle, they were always out if my budget. However at the start of February we were on a trip to Tuscon and I found an Cimarron 1873 trapper used for a price I couldn't pass up. I've been going through it and learning about it, from what I can tell it's already had a lot of work done to it for CAS, it has an aluminum carrier, extended firing pin, a super short stroke kit (I think), and a mag tube with the right internal diameter for 357/38 shells, as well has some nice engraving on the receiver.

I took it to the range and it was deadly accurate at 100 yards with 357 loads, however when going to resize the brass I discovered that some of the brass had a bulge. After doing research, I now believe the headspace is too long. It had zero issues functioning, but it's something I'd like to fix or make sure it's correct for the longevity of the rifle.

With a case in the chamber I can fit a .025 feeler guage between the bolt face and cartridge, without calipers to measure the rim, and knowing that the average 357 rim is .060, my headspace would be ~ .085 correct?

Now where I need help, is I can't find anything that states what the headapace is when it's correct. It could be my fault for not searching correctly. Any advice, input, or information would be greatly appreciated!

Hi Guy, welcome aboard.  I am not a gunsmith, but I think that is pretty excessive.  I'm thinking that gap should be less than 0.010"

If the gun has some of those go-fast parts you mentioned, then it likely has a short stroke it.  Open the lever all the way and if it goes a little past 90 degrees then it is stock.  If it is less than 90, it's a short stroke (some are shorter than others).  Most of those consist of a new set of toggle links, usually a new lifter arm, maybe more, but most that's it.  Now, putting one of those kits in can change headspace.  Depends on the kit and what your gun was like to start with.  When it gives a headspace problem, most of the kit makers have other links available that are longer or shorter to correct it.  So, it's a possibility that a shortstroke kit is the culprit.  You might be able to get a replacement kit with longer links, or possibly returning it to stock would correct it.  If you have to do that, parts should be cheap or free because many have them laying around after putting in SS kits.  But if you are planning to use it for CAS, you might like to keep is short.  Anyway, good luck!


Ghostdevelguy  ;)

Optimum Head Space for a Toggle Link Rifle is .004   Depending on who make the Short Stroke kit, you can measure your head space and the manufacturer of the links can usually provide extended links to correct the head space.  Pictures of the links and Carrier Block Arm would help identify who made it.


I'll get some pictures of the links, carrier block arm, carrier block, of how far the lever opens up, and just general pictures of the rifle later on today. If I can find a set if factory links I'll put it back in factory condition to fix the headspace so I can shoot it for now, and then get another short stroke kit for it later.

When you take the side plate off, look at the links with the lever closed.  They should be in a straight line.  Another possibility for the issue might be that someone had an OOB, out-of-battery firing, which is more common these days with people trying to go so fast, and that can bend some things, like the lever or lifter arm.  I'm not positive if that would affect headspace or not (Coffinmaker?), but something to check.


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