OK -- In all my years of reloading I have never really been able to determine how many times (cycles) is to many to resize (full length) trim and reload. The cartridges I am concerned with are 416 Rem and 375 H&H -- some of my cases are on their 4th trip through the system. I have been resizing full length (not open to debate -- as I do not want any questions on feed issues for these two calibers) -- trimming after resizing and thence reloading.
I only use this brass for practice and such but got to wondering how many times I can do this before I experience something negative.

That's one of those "how long is a piece of string" questions. A lot depends on how hot your load is; how much difference their is between your chamber and the dims in the die (how much your brass is actually being worked); and some intangibles that I can't bring to mind. Don't know how many times you've trimmed your brass but I assume a bullet will slip readidly into a fired case.
I'd keep on going. If you want to be really anal, use a hacksaw and section a case lengthwise to see if there is any thinning of the case wall forward of the belt (trying to use a bent paperclip sux) and if not, and if the neck isn't too thick, I wouldn't worry about it.
Sooner or later, you'll start getting neck splits and then you can deside what percentage you'll accept before pitching the whole batch.
Now someone can jump in and tell you about annealing cases if you want to get invoved with that sort of stuff.

quote:

.. got to wondering how many times I can do this before I experience something negative.

Given your adherence to FL sizing, you will have to wait and see.

Cases will either work harden until the body or neck splits OR stretch until you have a head seperation. Which occurs first depends mostly on how large your chamber is and how small your sizer die is and how excesively you're resizing the cases. None of us can gage any of those factors for you.

Splits are generally harmless. Head seperations generally are not.

load mild, partial resize, anneal every 3 to 5 times, and you are going to be in for a long life .. i've had over 35 reloads on 257 bob cases.

Full length sizing of belted cases will certainly shorten case life. I get 8-10 easily w/ non belted cases running full speed using partial or neck sizing (depends on caliber).

How many angels can dance on the head of a pin?

Here is the inaccurate premise: FL sizing assures trouble-free chambering and function. Bullshit. I have experienced more chambering difficulties with FL sized brass than with partial or neck-sized brass. This can be due to a number of factors, but simply "FL" sizing is no panacea for feeding and functioning.

All "full length sizing" assures is that you will reduce the cartridge case to the internal dimensions (minus spring back) of the resizing die - diminsions which may or may not match that of your chamber. What repeated FL sizing does do is work-harden your brass and force it to stretch to fit the chamber over and over again. The inevitable result is a radial crack forward of the case head, or more problematic, a complete case head separation. When this occurs depends on just how much the case is worked and stretched at each reloading, as well as the pressure you run in the case.

With cases which are properly sized, there are basically two case life limitations: Head expansion (which loosens primer pockets) and neck splitting. The first problem is purely a function of pressure -- high pressure can render a case unusable in a single firing. Marginally excessive pressures may take two or three firings to expand the primer pocket excessively. "Working maximum" loads will run five or more firings, while backing off of a "working maxium" will allow your brass head to last virtually forever.

Neck splitting: Again, a result of work hardening. You have no control over how much the neck is work hardened on each firing because it will expand to whatever the diameter of the chamber's neck. Conversely, it has to be reduced back to .002" or so less than the diameter of the bullet for the next loading. Other than getting a custom chamber with a minimum neck diameter, controlling the hardness (brittleness) of your neck brass is the only other solution. In other words, annealing the neck to make it last longer. Annealing is, in and of itself, easy to mess up. As a result, most reloaders simply shoot their brass until the necks split then toss it. With "normal" chambers and typical brass, this may be five or so firings. With hard brass or loose chamber necks, it may be fewer. Minimal sizing with collar inserts or collet type dies may help extend brass neck life a little.

Fortunately, the area of the case just forward of the head and rearward of the shoulder usually lasts forever

I've read in my reloading manual that cases that require a fifth trimming should be tossed out.

I am up to 4 reloads in my 375H&H, next time I will cut a case in half length wise to check how thin the web ring is getting.

I have tried using a bent wire feeler to try to detect the thinning ring but that method hasn't been too positive a detection method for me.
Cutting one case in the batch in half and looking and measuring the thinning ring will tell me a better story.

quote:

I've read in my reloading manual that cases that require a fifth trimming should be tossed out.

That's likely a good rule...if you're loading for the manual's rifle and using the manual's dies! But, if your's doesn't match their's it can be an invitation to disaster. There are no such (valid) simplistic rules in this game.

Two things can make your belted mag practice cases last longer:
1. Partial full length resize, so the case headspaces on the shoulder instead of the belt.

2. Anneal the necks that work harden and tend to split.

Also, not overly hard crimping the case mouth into the bullet's cannelure.