Hi all,
I have 2 Winchester/Miroku 1873s in .357 that I've had a few years. I've mostly shot .38 specials in them and only enough .357s to sight in and hunt with, probably less than 30 rounds between them, which were Buffalo Bore 125 grain loads. No problem with those ccx and killed a couple of deer with them. Last week I decided to try some 158 gr less than max handloads in them and got several case separations. I decided to then shoot the BB 125 hrs again to see what would happen.....case separations again. The cases would separate right in the middle. What would cause this? Thanks in advance.

Case head separations usually are caused by excess head space. Can you check the headspace? The 1873 action isn't very strong, but I can't imagine .357 ammo is causing setback. Still, that's what I'd check.

Jip, headspace is the most likely reason.

If it is, check for any wear in the linkage. It may be much easier to correct the issue by fixing that than the usual approach of setting the barrel back, because on lever actions that also requires magazine and stock alterations.

Thanks for the responses. I have no way of checking head space. Someone also suggested that it could be oil in the chambers. I hadn't thought of that one but he could be right. I didn't remember to swab the bores before I shot them and I haven't shot them since last year when I oiled the bores and put them up. Anyway I swabbed the bores last night and hopefully will get to shoot them this weekend. thanks again guys.

If you have a caliper or a depth gauge and a fired case you can check headspace. Punch out the primer from the fired case. Clean the primer pocket. Press the primer back in and leave it around .020 inch proud. Place the case in the chamber. Close the action smartly so that the bolt fully seats. Remove the case. Measure the rim thickness at four opposite points and take the average. Then measure primer protrusion. Add the two numbers and you have your headspace. Compare this to the range that is acceptable for your rifle and cartridge combo.

Thanks Bobster

quote:

Originally posted by Bobster:
If you have a caliper or a depth gauge and a fired case you can check headspace. Punch out the primer from the fired case. Clean the primer pocket. Press the primer back in and leave it around .020 inch proud. Place the case in the chamber. Close the action smartly so that the bolt fully seats. Remove the case. Measure the rim thickness at four opposite points and take the average. Then measure primer protrusion. Add the two numbers and you have your headspace. Compare this to the range that is acceptable for your rifle and cartridge combo.

Bobster, that is so clever and useful! Thanks for posting it.

Do what Bob said. You will quickly see. You can also put some tape on the case head and see if the action closes; it will. Or shims made from pop can material. Glue them to the base of a case; see: you do have methods to check headspace. The actual value is not important unless you are going to make the repairs; you will be able to see how much the primer sticks out, or how much material there is between bolt face and case head. It will be quite noticeable.
Oil will not cause case separations; in fact, it will do the opposite; prevent case separation because the front of the case can't grasp the chamber walls so it all slides back to meet the bolt. Putting more pressure on the bolt, which a 73 doesn't like. So don't oil your chambers.
Your rifle needs help; it has excessive headspace and the 73 is almost the weakest action made. Fitting new links is the only cure, or setting the barrel back.
Having said all that; we routinely shoot revolvers with grossly large headspace and never notice it; maybe your chambers are rough and the brass can't slip back; check that.

I wish I could take credit for that method but alas I learned it from the staff at Midwest Gunworks. Just passing it forward. I was surprised to learn that the .30-30 Win has an acceptable .007 headspace from minimum to maximum! That produces some serious primer protrusion. When you are working with bottle necked rimmed cartridges you need to cut the spent case off behind the shoulder so case elongation won't be a factor. Not really an issue with straight cases. With rimless bottle necked cases use a new un-fired case.

quote:

Originally posted by skl1:

quote:

Originally posted by Bobster:
If you have a caliper or a depth gauge and a fired case you can check headspace. Punch out the primer from the fired case. Clean the primer pocket. Press the primer back in and leave it around .020 inch proud. Place the case in the chamber. Close the action smartly so that the bolt fully seats. Remove the case. Measure the rim thickness at four opposite points and take the average. Then measure primer protrusion. Add the two numbers and you have your headspace. Compare this to the range that is acceptable for your rifle and cartridge combo.

Bobster, that is so clever and useful! Thanks for posting it.

Seven thousandths! That's tight compared to reality:
Problem is; it ain't .007; it is Seventeen!
.053 for minimum brass, all the way up to .070 for a max chamber, so the potential excessive space is 17 thousandths. And that is for new chambers and brass that meet SAAMI specs. Add some wear and the allowance for a rifle made on Monday by a hungover worker, and you get more slop.
The 7 thou is just for the chamber; it is the brass in that chamber that is what matters.
And also, what is the first word in the SAAMI book? VOLUNTARY.

I swabbed the bores of both rifles really good....problem solved. I'd have never thought it. thanks again for all the suggestions.

If you have headspace in a win. lever gun, get a new bolt form Jim Wisner and fit it, It has fixed every old Win. I have and its a cheap fix..as they come in differnt size or can be hand fitted..

Sometimes reloading practices can cause head space through full length resizing..in a larger chamber than factory stats your over working your brass and in each firing as it stretches and then sets back when you run the fired case through the die..I,ve seen this a lot on Savage Marlin and win. lever guns. However the best option is to replace the bolt by whatever the primer protrusion reads..Jim wisner sells those bolts for not a lot of money and its the only reasonable option to fix lever action headspace.