Pavomesa

I think the truth is somewhere in between here. Brass that isexcessively long can be dangerous. That's a fact. But just how often you need to trim your cases is a whole different subject. There are scads of variables at play on this subject. First and foremost is the pressure of your loads. Probably next in importance is the cartridge...then your particular chamber and rifle.......followed by the type of brass you are using. And there are probably a few I'm leaving out.

Loading really high pressure loads causes brass to flow/stretch. Backing off a few grains with your load will often greatly reduce any neck growth. Ex. Supposedly the 220 Swift is terrible about lengthening cases. I had one for several years and found my cases hardly ever needed trimming. But I loaded a few grains under max pressure. One of the worst cases I've encountered for necks stretching is the .243.

No two reloaders treat this issue exactly the same but I've found the subject greatly overblown in most instances.

The best thing I've found for case trimming is the RCBS File Trim Die. They are cheap and fast and easy to use. I've got a good crank trimmer and never use the SOB if I can avoid it. When I do decide to use the cursed thing, I generally set it to trim my brass about .002 shorter than factory just to be sure it's a long time before I have to play this game again.

Rather than rush out and spend a bunch of money, I would do some case length checking and find out IF and just how bad a problem you really have. Then and only then would I worry about it. I've been loading for over 50 years and never had a case length problem...and I admit I'm a little sloppy about the subject. But I think this should illustrate just how big a deal it really is.

johnny2

bronko22000

Bullethole - Yes you need a trimmer of some sort as suggested by the replies to your post.
And for your info as to why and the reasoning - when you fire your cartridge the brass will expandagainst the chamber walls forming a pretty good gas seal and'flow' toward the mouth of the case. Successive firing will continue this until the case becomes too long to reload and chamber properly causing the mouth of the case to enter the throat of the barrel. This will cause higher than normal pressures and could be dangerous.
Some cartridge cases need to be trimmed more often than others. There are alot of variables as mentioned such as chamber pressure, cartridge design etc. You would be well advised to check your brass after sizing to be sure the case length meets the dimensions listed in the reloading manual for your particular cartridge. Most manuals give a maximum length and a 'trim to' length.

eldeguello

A case trimmer might not be necessary immediately or with certain cartridges that do not tend to "grow" as they are resized over & over-some are a lot worse than others. For example, the .220 Swift, .270 Win, and the .300 H&H Magnum stretch alot the more often they are reloaded. But IRCC, I never had to trim a .308 Norma Magnum case!

The requirement is that you have to keep the case necks short enough that when the cartridge is chambered, it is not long enough for the case mouth to get jammed into the forcing cone of the chamber. If this happens, the case can get too tight a grip on the bullet, thus driving chamber pressures up, sometimes up enough to cause a serious "accident"! Just be sure never to let your cases get longer than the specified MAX case length, and you will have no troubles.

(Isurvivedwithout a case trimmer for my first 6 years of reloading-I used myRCBS case mouth chamfering tool by hand to keep the cases short enough to be safe- very crude, but it worked! No, they sure weren't all the same length,looked bad, and would not have worked if crimped. Probably had a detrimental effect on accuracy too, but in those days I was too ignorant to notice! But I still don't crimp bottlenecked rifle cartridges.)

SJAdventures

The Lymans Universal Trimmer makes it an easy task and it is a manual. The manuals say tha after a case has been trimmed 3 times it is time to get rid of it.