Cartridge length question

[Reformedcitykid]

Hey all, I have what is, I’m sure, a really dumb beginner question. I’ve just started reloading, am reading and watching all that I can, but am otherwise on my own. No father to look at me when I ask this question and say, “are you fuckin’ kidding me?”

When measuring cartridge length, how accurate should you be? The manual I’m reading now (Speer Reloading Manual 12), it lists the cartridge length for 308 as 2.0150”. The first 5 I measured are 2.0195”, 2.0240”, 2.0140”, 2.0175”, and 2.0195”. Is this an acceptable variation, or do I need to try to size them all on the button?

Thanks in advance, and feel free to make fun of the dumb new guy!

 

[Franko]

A few thousands variance in OAL isn't going to be an issue. Odds it's a combo of slight inconsistencies in your measuring technique, the projectiles, and your measuring tool. What I do suggest is that you buy the Hornady bullet comparator so you can measure CBTO (Cartridge Base to Ogive) as there is going to be less variance there and you will get more consistent measurements.

Edit:
It's late and I missed the point brought up by @KnowNothing256 about this being case OAL and not a completed round so my answer is only partially on point.

 

[KnowNothing256]

I’m not sure what you mean by “on the button,” and I suspect we need to clarify a couple other things too. So, a few items:

1) Based on the numbers you provided, you’re not asking about cartridge length, you’re asking about max case length. Cartridge refers to the assembled round, and if you wanted to talk about that length the bottom line is you need to measure from the base to the ogive using a caliber-specific comparator. But, you seem to be taking case length.
2) Most of us would be happy measuring to the nearest thousandth. Looks like you’re using digital calipers that mostly report in the thousandths, and sometimes give a half a thou. That’s fine.
3) It’s not clear if you’ve trimmed those cases or if they came that way. If you trimmed them to those lengths, you have some issues with your trimming setup; you should expect maybe +/-0.001” results, definitely no more than +/-0.002”. If those are virgin brass, or once-fired from factory ammo, that makes more sense.
4) It’s not clear if these cases have been resized or not. The case length should only be measured after sizing, since most centerfire bottleneck cases will grow from the sizing step.

I have a few other thoughts, but that should help you provide us a bit more info. That said, the answer to your original question is: you’re being accurate enough.

And a bonus piece of info is that all of your cases are over max length per the book, so as a new reloader, you should size them if they aren’t already, then trim them to the book trim length, which I expect is 2.005” in your manual.

 

[mullmann]

You should be accurate. You need to trim to the trim length. If the brass gets too long it won’t chamber correctly. I think trim length is 2.005 for .308, but check a manual. Every rifle is different and some might not be as tolerant to cases that are too long.

 

[alamo5000]

No one will make fun of you for a good question.

First thing is what you are measuring. Some measure base to tip and others measure base to ogive.

As for how accurate you need/want to be is going to be determined by a lot of things. The primary one (in my opinion) will be the nature of the ammo. For example if I am loading bulk .223 ammo then it won't matter that much (within reason).

If however I am trying to get a 'precise' or 'precision' load then it becomes much more critical.

As for reloading manuals in general, they are 'guidelines' rather than rules. In my opinion, as long as you are using basic safety principles you are ok to test out various cartridge lengths.

 

[DAMNKID]

2.015 is max case length not COAL

 

[pabrousseau]

Get a case length gage from sinclare. Only a couple bucks and you will know your true chamber length. Most are longer than than you would expect.

 

[918v]

Hey all, I have what is, I’m sure, a really dumb beginner question. I’ve just started reloading, am reading and watching all that I can, but am otherwise on my own. No father to look at me when I ask this question and say, “are you fuckin’ kidding me?”

When measuring cartridge length, how accurate should you be? The manual I’m reading now (Speer Reloading Manual 12), it lists the cartridge length for 308 as 2.0150”. The first 5 I measured are 2.0195”, 2.0240”, 2.0140”, 2.0175”, and 2.0195”. Is this an acceptable variation, or do I need to try to size them all on the button?

Thanks in advance, and feel free to make fun of the dumb new guy!

Please get your terminology right so we can all be on the same page. Sizing is different from trimming. Case length is different from cartridge length. These are important words if you want to stay healthy while participating in this hobby.

With that said, most factory 308 chambers are ok with cases growing past 2.040”. The shortest 308 match reamer out there cuts a chamber that will accept a 2.025” case.

If I were you I would trim them to 2.010” to square off the case mouths. Then I would shoot/reload them without trimming enough times until they get so long they won’t chamber. You can establish that by trying to close the bolt on an empty sized case. The bolt won’t close if the case is too long.

Once you know the max case length for your chamber you can decide on the trim length.

 

[spife7980]

Here is where your speer manual got their numbers
The case max length per saami is 2.015-.020 meaning anywhere from 1.995-2.015 are within the min-max spec.

But also notice that the chamber neck ends and begins its sloped transition to the bore at 2.025-2.0488 and thats where it pinches. So you can go a bit longer.
But I dont and dont suggest you do. Its so easy to trim to spec and never have to worry about any danger resulting from the practice. After you size them I would trim them all uniform to middle of the spec at 2.005 +/- .002 or so depending on how accurate and repeatable your trimming and case prep is. Then chamfer and deburr the mouths.

 

[acudaowner]

you could take a factory round apart and measure it while short so it fits in pretty much every 308 you can always play with the lengths when you get more comfortable with reloading keeping it as simple as you can while your getting more familiar with reloading compared to jumping in blind .
best of luck to you it's fun but laden with rabbit holes that never end .

 

[Greg Langelius *]

I use the Little Crow Case Trimmer 2 and the associated chambers for my case trimming. Once set, the adjustment is the same for each case trimmed. This removes the tendency to use an incorrect setting; consistency is ideal.

My sequence is to resize/decap, trim, prime, then charge the case with propellant. Final step is to seat. My press is a Dillon RL550b, bought used n the mid-1990's. My powder measure is the RCBS Chargemaster Lite.

I load my ammo to only a single criterion, as close to match spec as possible. I have no good reason to load it to inferior specs. Do it right, or don't do it at all. I try to keep my deviations to .005" (.308 absolute max case length 2.015"/max overall cartridge length 2.815")/+-.1gr or less.

Being a Marine is not always the most fun.... Some things are like religion, and being a Marine is one of them.

Greg

PS, in addition to .308, I also load .260. I make my brass from .243, and (preferably) 7mm-08, as well as using cases which originate as .260. The .308 trim chamber also works for the .260, since I use the same shoulder and neck lengths for each.

 

[Greg Langelius *]

The reason for case stretch is that chambers usually stretch while firing. As the chamber relaxes, it shrinks back to initial dimensions. The case gets released somewhere before complete relaxation, and that's where the variations come from.

Excess pressure may exceed the elastic limit and result in some degree of permanent chamber stretch, or even complete chamber failure. Any permanent stretch is cumulative.

That, for me, is the main reason why I avoid hot loads.

Greg

 

[db2000]

I’m not sure what you mean by “on the button,” and I suspect we need to clarify a couple other things too. So, a few items:

1) Based on the numbers you provided, you’re not asking about cartridge length, you’re asking about max case length. Cartridge refers to the assembled round, and if you wanted to talk about that length the bottom line is you need to measure from the base to the ogive using a caliber-specific comparator. But, you seem to be taking case length.
2) Most of us would be happy measuring to the nearest thousandth. Looks like you’re using digital calipers that mostly report in the thousandths, and sometimes give a half a thou. That’s fine.
3) It’s not clear if you’ve trimmed those cases or if they came that way. If you trimmed them to those lengths, you have some issues with your trimming setup; you should expect maybe +/-0.001” results, definitely no more than +/-0.002”. If those are virgin brass, or once-fired from factory ammo, that makes more sense.
4) It’s not clear if these cases have been resized or not. The case length should only be measured after sizing, since most centerfire bottleneck cases will grow from the sizing step.

I have a few other thoughts, but that should help you provide us a bit more info. That said, the answer to your original question is: you’re being accurate enough.

And a bonus piece of info is that all of your cases are over max length per the book, so as a new reloader, you should size them if they aren’t already, then trim them to the book trim length, which I expect is 2.005” in your manual.

To expand on this regarding measuring the overall cartridge length.
You should be using a caliber specific Ogive (pronounced O-Jive) comparator to measure BTO (base to ogive) or CBTO (cartridge/case base to ogive). BTO and CBTO are the same thing. This will give you more consistent readings on a loaded round since measuring the base of the cartridge/case to the tip of the seated bullet can vary a fair amount due to polymer tips being bent, shaped differently from bullet to bullet, hollow points deforming from one to the next, etc.
Look up ogive and read on this. It will make sense. The comparators are relatively inexpensive.
Good luck. Pay attention to detail. Lots of room for mistakes if you get distracted while loading.