Chamber Length

[Theinkman]

While back I read something somewhere about trimming cases, specifically bottle neck, and when they actually need to be trimmed. Being somewhat of a data geek, I decided to measure the chambers in my rifles (7mmRM, 2 different .22-250) so I would know when my brass needed to be trimmed as compared to automatically trimming according to published max case lengths and trim to lengths.

So I got some "chamber length gauges" from Sinclair and proceeded to measure my chambers. The process for creating a round to use these gauges is pretty simple so I won't go into that detail here. Interesting results I got; not what I expected to see.

Knowing that SAAMI chamber specs are minimums I figured I would see the chamber lengths on my rifles close to or slightly longer than these minimums.

For 7mmRM, the published max case length is 2.500; my chamber measure 2.548 checked and verified 3 times. For .22-250, published max case length is 1.912; one rifle measured 1.946 and the other measured 1.949. These were also checked and verified 3 times.

So what do I do with this info? Well, one of the reasons I decided to measure chamber length is because I've got some 7mm brass which after the last sizing had exceeded 2.500 in length. Plus some of my 250 brass is near 1.912 in length. So, I won't be trimming any of this brass soon and not sure if any of it will ever reach max length for my rifle chambers.

I know many if not most handloaders hate trimming their brass. By measuring actual chamber length we are able to find out when we really do need to trim rather than going by published max case lengths.

 

[1RedSoxFan]

I used my stony point (now Hornady) in much the same way.measure to the lands, and then trim & seat to that number less 10 thousands. Works for specific guns, bolt action only.
I used saami for my semi-autos.

The drawbacks are, as I see it:
1. I cannot share my ammo with a friend when in the field, if/when some unforseen circumstance arises. (which it has)
2. I need to keep track of what gun my ammo was shot from (ar-10/.308, or bolt.308 (which I have two of, requiring more tracking)). Getting lazier as I age!
3. the ammo for my guns cannot be shared between my guns. (more tracking)
4. Case cleaning after shooting/before loading must be done in smaller batches, taking more time. (again,see the lazy comment above)

For these reasons, I have been loading to saami lately, so everything fits everywhere. I do not shoot competitively, and have noticed little to no difference at the 300 yard range my club has.

I live in the northeast, so 500 yards is the longest range possible for me to get access to,and 300 yd is the longest at my club. If I ever got into PRS, I could possibly see the benefits of creating the additional work for myself. Just not right now, plinking for fun at my club, or in the field, where 100 yards is probably my longest shot ever, at a deer. I think most of the deer I have harvested have been around 30-65 yards.

You folks out west, where you have "miles and miles of miles and miles" of open desert/prairie (Jealous!) might see more benefit since you can shoot out to 1000 yards plus regularly.

I have a Henderson trimmer. Superfast. Trim,and chamfer in & out in one step. much faster and easier than anything else

 

[Cemetery21]

^^^^ Very nice bench system. Looks like a lot of thought and engineering went into that. Congrats!

 

[Theinkman]

That's a nice trimmer setup. I'm not sure what my trim length is going to be yet but I don't think I need to worry about my ammo fitting in another rifle at this time. With the 2 different .22-250s, I will probably trim to the same length on both, although I do segregate those cases shot from each rifle because of slightly different headspace dimensions.

I'm thinking I will end up trimming to the published max trim length for all cartridges once the cases exceed that measurement.

 

[Cemetery21]

I've been using the Sinclair neck length spuds for maybe 30 years. Yes, all my chambers measure longer than max brass length in the manuals. So, I tolerate a few thousanths over book max and never trim to min. Don't know how much difference it makes, it's just what I do. All my rifle brass stays with it's "parent" rifle.

 

[Theinkman]

I've been using the Sinclair neck length spuds for maybe 30 years. Yes, all my chambers measure longer than max brass length in the manuals. So, I tolerate a few thousanths over book max and never trim to min. Don't know how much difference it makes, it's just what I do. All my rifle brass stays with it's "parent" rifle.

My thoughts exactly.

 

[edwardware]

. . . I figured I would see the chamber lengths on my rifles close to or slightly longer than these minimums.

Why would you expect that? The potential consequence of a case neck jambed past the end of the chamber is really unpleasant; blown cases, damaged actions, medical bills, and lawsuits.

The manufacturer has no reason to make such a chamber, and it contributes nothing to accuracy.

 

[Theinkman]

Why would you expect that? The potential consequence of a case neck jambed past the end of the chamber is really unpleasant; blown cases, damaged actions, medical bills, and lawsuits.

The manufacturer has no reason to make such a chamber, and it contributes nothing to accuracy.

My post said I figured I would see that, not that I banked on seeing that. I am aware of what the possible consequences of a case being too long are. This post was about finding my actual chamber length and by doing so I would then be able to determine at what length I would need to trim my cases. If you took my OP for anything else, maybe I wasn't clear enough in what I was doing and why.

 

[murf]

While back I read something somewhere about trimming cases, specifically bottle neck, and when they actually need to be trimmed. Being somewhat of a data geek, I decided to measure the chambers in my rifles (7mmRM, 2 different .22-250) so I would know when my brass needed to be trimmed as compared to automatically trimming according to published max case lengths and trim to lengths.

So I got some "chamber length gauges" from Sinclair and proceeded to measure my chambers. The process for creating a round to use these gauges is pretty simple so I won't go into that detail here. Interesting results I got; not what I expected to see.

Knowing that SAAMI chamber specs are minimums I figured I would see the chamber lengths on my rifles close to or slightly longer than these minimums.

For 7mmRM, the published max case length is 2.500; my chamber measure 2.548 checked and verified 3 times. For .22-250, published max case length is 1.912; one rifle measured 1.946 and the other measured 1.949. These were also checked and verified 3 times.

So what do I do with this info? Well, one of the reasons I decided to measure chamber length is because I've got some 7mm brass which after the last sizing had exceeded 2.500 in length. Plus some of my 250 brass is near 1.912 in length. So, I won't be trimming any of this brass soon and not sure if any of it will ever reach max length for my rifle chambers.

I know many if not most handloaders hate trimming their brass. By measuring actual chamber length we are able to find out when we really do need to trim rather than going by published max case lengths.

saami chamber length for the 7mm rm is 2.524" + .015". so the max saami chamber length is 2.539". either your measuring method is off, or your chamber is out of spec. i think your measuring method is off and you should not suggest anyone go beyond the saami maximum case length when reloading.

if you want to blow up your gun go right ahead. i suggest everyone else keep all cases trimmed to within the saami spec listed in all reloading manuals.

murf