How critical is case length?

Case length isn't very critical to accuracy unless the case is so long it exceeds the neck portion of the chamber. I have a case length gauge good for quite a number of cartridges. I check cases with that and if they don't exceed the maxinum length indicated on the gauge, I don't trim them. You can also use dial calipers to check cases. Many firearms could probably take a case a little longer than the published maximum but you won't really know unless you have measured the chamber in some way like with a chamber cast.

The trim to length has nothing to do with case life. The fit of the cartridge to the chamber after resizing has everything to do with case life. The more closely the cartridge fits the chamber the better will be case life. Some are very compulsive about this and get excellent case life with neck sizing, etc. My practice is to use a standard die and full length size cases and not agonize so much about case life and I still generally get pretty good case life.

The first part of a bottle necked case to fail is usually in the web area, i.e., a head separation. The first part of a straight walled case that fails is usually case mouth splits. There are exceptions to this. In my full house near 65,000 psi 460 S&W Magnum loads, I get incipient head separations before case mouth splits. Some bottle necked brass is a bit brittle and mouths will split first but that can be prevented with annealing.

After resizing your empty .243 brass, put it back in the chamber of your rifle, if the bolt is hard to turn on closing, then there is a good chance the neck is too long. If your dies have worked well all this time, I would suspect your shoulder is fine and the neck needs trimmed.
I ran into this with my .243 and trimming the necks. I never changed my die settings so after reloading them, all of a sudden the bolt got hard to close.
I knocked one apart and put the empty case back in the rifle and same thing.
The necks being to long won't affect anything until they hit the chamber throat, the part the bullet sets in, if you force them you can buckle the case or spring it out of shape and yes, then, it will affect accuracy.
If your bolt is not hard to close then it won't affect accuracy.

You can also pinch the brass between the bullet and the chamber wall/leade area if things get too long then when firing the round the pressure spikes and the bullet swages itself down before clearing the narrow part. If you exceed the max pressure bad things can happen as you already know AND that round is now swaged down to a smaller size and accuracy will be poor at best. You don't have to have them all at minimum trim length----BUT over MAX length and you risk having problems. Just set and lock your calipers to the max length allowed and try to set the brass inside the opening. If it fits or is loose load em up. Too long and you need to trim them. The Lee system is the cheapest to buy, or the hand crank lathe type with pilot bushings from several makers is the next less expensive. Or go full on and get a WFT or the likes. Length trimming is a necessary evil of reloading bottle necked cases just like primer replacement.

You can do an interesting experiment if you are bored. Find a fired 7-08 case, lube it VERY well and size it to .243. This should give you a .243 case with an excessively long neck. Trim it incrementally until the chamber bind goes away. You can also soot the shiny trim line and look for galling. This should give you the absolute max case length in your rifle, but I would still use the SAAMI max for practical purposes.

In general, case length, assuming within the tolerance range for your chamber, can have some effect on internal ballistics. It's another variable you have control of, and consistency in all aspects of your loads matters. For match ammunition, I try to keep the cartridge length as uniform as practical, and in some rifles/loads I have noticed a slight difference between freshly trimmed (uniform) and random but within tolerance length brass. The difference has occurred both in terms of vertical and lateral dispersion, suggesting some mechanism affecting velocity and harmonics or concentricity. Doesn't really show up until 300m or farther though, and it would be quantified in fractions of MOA in my observations. For hunting ammo, so long as I am below the max SAAMI case length, I load and shoot. I do trim the whole batch when even one case gets close to the max.

As was mentioned above, I believe that the most important aspect of neck or case length is that it be consistent across all cases - this is to ensure that the neck tension is also as consistent as possible.

Walkalong said:

Without a chamber cast you don't know how long the neck is in your chamber. At 2.042 you are flirting with being too long, although your chambers neck may be well over 2.045. Problem is a pinched neck from a case that is too long is very bad mojo and there is no point in chancing it if you do not know the measurements of your chamber.

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Back in the day when dial calipers were very expensive, vernier calipers were much cheaper. They also took forever to read. I was lazy and decided not to trim once fired brass under that fallacious idea that brass would not grow much with one firing. I was wrong, brass grows the most on the first firing, it is always over length after full length sizing. On the next firing I had lots of blown primers because the case necks were in the throat, pinching the bullet. Lesson learned, trim brass. I always trim brass and have spent a lot of money on devices that trim bottleneck cases. Straight cases are not as much a problem as bottleneck cases.

I regularly over trim cases when setting up the trimmer. I can also say, I cannot tell a difference on paper. As long as the case neck holds the bullet in place, everything goes bang, the bullet goes where it is aimed, and fears about inconsistent case trim lengths causing accuracy issues are baseless. Maybe a bench rest shooter will see it, but I won't. I pulled targets with several Champ Perry National Champions and they were more concerned about the effect of wind conditions on their score, than trim length.

I do recommend setting up bottleneck rifle case dies with a cartridge headspace gage,



I have a lot of clearance between the case neck and the throat of this SAAMI dimensioned gauge.



And I do recommend trimming bottleneck rifle brass after each firing, but only to keep the case neck from pinching a bullet in the throat. By how much do you trim these cases?

By how much do you trim these cases?

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I trim mine to SSAMI case length spec.
I have to have some constant to go by. It's as good as any.

Lee Precision makes a really easy to use case length gauge/ trimmer that you can hook up to a cordless screwdriver/drill motor. Their case length gauge, cutter, and lock stud checks each case and trims away any excess. This set is third from the top on their web page. Last one I bought was less than $10 and it has trimmed 1000s of cases. I neck size and rarely have to trim cases a second time.
https://leeprecision.com/case-conditioning-tools/case-trimming-tools/

Walkalong said:

And warm and fuzzy never hurts.

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Words to live by.

AMEN!!

A couple guys touched on the safety issue. A bolt has a pretty strong camming action when chambering a round. What will seem like a tight fit can put you in an undesirable overpressure situation. Bad things can happen.

Trim your brass. Annealing before trimming is also a good thing.

Two Lee systems work really well. 1) the Case Length Gage and Trimmer, especially with the Lee 3-Jaw Chuck. 2) The Lee Power Quick Trim that Curator provide the link for. I started with 1 and migrated to 2. Lyman makes an upgraded version to 1 that works really well.

You can trim for fairly cheap if need be but there are some out there that cost $$$. You indeed pay for convenience and speed. After trimming do not forget to ream and chamfer the mouth ever so slightly. Your bullet will thank you by being accurate and the round will feed better. Trust me.

Trimming is more about safety and accuracy than case life. A case thats too long will jam up against the end of the chamber and raise the pressure. Like Walkalong posted, accurate loads are all about being consistent. I doubt many of us can shoot the difference between trimmed brass vs untrimmed brass but the accuracy guys believe in it.

As far as measuring cases, I don't measure all of them. If I find a long one I trim all of them. I can trim a case about as fast as I can measure a case. I want to say that one of the older Lyman books recommended trimming a bottleneck case every fifth firing and scrapping them after five trimmings. My memory may not have this exactly right. You probably will have a case failure from a loose primer pocket or a split case neck long before you ever approach this many trimmings.

Curator said:

Lee Precision makes a really easy to use case length gauge/ trimmer that you can hook up to a cordless screwdriver/drill motor. Their case length gauge, cutter, and lock stud checks each case and trims away any excess. This set is third from the top on their web page. Last one I bought was less than $10 and it has trimmed 1000s of cases. I neck size and rarely have to trim cases a second time.
https://leeprecision.com/case-conditioning-tools/case-trimming-tools/

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I've been using one for years. I Chuck up the cutter and use a Lyman case holder though.

lightman said:

I doubt many of us can shoot the difference between trimmed brass vs untrimmed brass but the accuracy guys believe in it.

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Humans are capable of infinite self deceit. We as a species, see patterns where none exist. You would expect that guys, who are so OCD to try to shoot every bullet in one hole, as a group they will always have nutty as fruit cake belief systems, that they swear are true, but have never tested the veracity.

Now I am not a bench rest shooter, but I will say, all the bench rest stuff you read about being necessary for reloading, that never made any difference on the 2 MOA NRA target. I never saw any of that stuff make the slightest difference when shooting standing, sitting, prone rapid fire, or prone slowfire, with a sling. And, I only met a few individuals who ever put all of their bullets in the 2 MOA target, all the way out to 600 yards. In the real world, sight alignment and trigger pull, wind judgement, are far more important in placing the bullet in the middle of the target, than trim length, or a bunch of other factors. Now my F Class buds, they are shooting off bi pods, and they claim they see things, and they may, but until someone actually runs tests, and publishes the results, I remain skeptical.

It is my opinion that bullet concentricity and center of gravity make more of a difference than a host of bench rest reloading technics, but no one is building Juenke bullet test machines to sort out good bullets from bad. You can buy the part for a Juenke machine here: http://www.bulletinspector.com/vern_juenke_history.htm

I love these quotes from the site:

No directions on how to operate the BulletInspector are available. If you know how to operate a Vern Juenke machine, this operates on the same principle.

It is a clone. No one here at BulletInspector has any idea of how this works.

I always trim my brass two or three thousandths shorter than trim length, it eliminates future problems and I usually never trim them again. I have a some rifles that are very picky about case length.

Slamfire said:

Humans are capable of infinite self deceit. We as a species, see patterns where none exist. You would expect that guys, who are so OCD to try to shoot every bullet in one hole, as a group they will always have nutty as fruit cake belief systems, that they swear are true, but have never tested the veracity.

Now I am not a bench rest shooter, but I will say, all the bench rest stuff you read about being necessary for reloading, that never made any difference on the 2 MOA NRA target. I never saw any of that stuff make the slightest difference when shooting standing, sitting, prone rapid fire, or prone slowfire, with a sling. And, I only met a few individuals who ever put all of their bullets in the 2 MOA target, all the way out to 600 yards. In the real world, sight alignment and trigger pull, wind judgement, are far more important in placing the bullet in the middle of the target, than trim length, or a bunch of other factors. Now my F Class buds, they are shooting off bi pods, and they claim they see things, and they may, but until someone actually runs tests, and publishes the results, I remain skeptical.

It is my opinion that bullet concentricity and center of gravity make more of a difference than a host of bench rest reloading technics, but no one is building Juenke bullet test machines to sort out good bullets from bad. You can buy the part for a Juenke machine here: http://www.bulletinspector.com/vern_juenke_history.htm

I love these quotes from the site:

No directions on how to operate the BulletInspector are available. If you know how to operate a Vern Juenke machine, this operates on the same principle.

It is a clone. No one here at BulletInspector has any idea of how this works.

Click to expand...

I agree with you that most of the stuff doesn't make a noticeable difference. My thoughts are do everything I can to make everything as close to identical as I can so I am the reason I missed.

If I don't trim, don't weigh, don't anneal, and don't sort brass, then my extreme spread goes to crap and I have random flyers. It's probably a cumulative effect.