Hello all. I am new to the forum and new to reloading rifle shells. I have reloade quite a few pistol shells but never rifle.
I am unfamiliar with the use of calipers and case trimmers. Do I really need them for accurate rounds? What are they supposed to do . I would appreciate any info you can give me. Thanks.

The big reason for a trimmer and calipers is case stretching. This isn't a problem with pistol calibres unless you're loading magnums at full snort. High powered rifle cases stretch enough so that the mouth of the case will jam into the chamber throat, pinch the bullet, and jack pressure into the dangerous zone. Some calibres are worse than others, but you'll need to trim after every 3 reloading, on average. The Hornady manuals have a very good discussion about this.

Calipers are a general purpose measuring tool and you'll find lots of work for one away from the reloading bench.

You'll find that you'll get much more uniform crimps on your pistol cartridges if you trim them to the same length. I've used a Forster trimmer for over 30 years. There may be better ones, but mine just keeps going and going.

Bye
Jack

nalgai,
The two main uses for dial calipers are to measure the overall length of loaded rounds and to measure the length of your cartridge casings. There are many more uses but the two listed are the mains ones you need to concern yourself with for general reloading.

The overall length of your cartridges is important to know and be able to repeat for your reloaded ammunition to be consistent. The overall length often has to be kept withing limitations so the cartridges will function in your firearm. Fine tuning of OAL will also enable you to fine tune your loads for best performance.

As far as case length goes, it's something you need to know to prevent creating a dangerous situation with your reloaded ammo. Each cartridge has a maximum length, which must not be exceeded to prevent causing dangerous pressure levels. Your cartridges will grow in length each time they are resized, it may be very little or quite a bit, depending on the cartridge and your resizing method or tools. If the cartridge casing gets too long it can still chamber, but if it is so long that it is forced slightly into the throat of the chamber so that has no room to expand upon firing, it cannot release the bullet properly and will cause pressure to skyrocket. Case length is also important when using cartridges that require a crimp, such as any that will be used in a tubular magazine. If you are crimping into a cannelure on a bullet, your best accuracy will come from cases that are even in length so that they are all crimped into the cannelure uniformly. For the most accurate ammo your case mouths also should be square so that you have the most consistent bullet release.

I would suggest you look in some of the reloading manuals you have been using for your pistol data and read the sections on reloading as they will give you the details, and possibly illustrations, as to why case trimming is needed.