I recently got a Giraud trimmer and trimmed 2 sets of brass in different calibers. Both batches were on their 3rd reloading/sizing cycle. After trimming the brass in the Giraud, I took my calipers to a random bit of brass from each batch. I was surprised that it varied by as much as 10 to even 16 or 17 thousandths.

As the Giraud trims based off of the case shoulder, I took my headspace gauge--measuring from case base to datum point, and discovered that the measurement varied by about 10 to 15 thousandths. I was surprised by this, as I set my dies for these cases to bump the shoulder back by about 3 thousandths, and felt they would be more consistent than this.

I now wonder if I have discovered a shortcoming in the Giraud length gauging style, or have I discovered another spec to sort brass by. I figure that shooting brass that varies by as much as 10 to 18 thousandths in base to case mouth length isn't smart, it would have to give you varying neck tension at least--right??

I am used to using a trimmer that indexes off the base of the case, and therfore yields very consistent overall case trim lengths, so I am concerned that the Giraud might not be for me, or is for someone who can get much more consistent base to datum point measurements than I am getting---or did I just happen to have the dies for these two particlar rifles set up such that they arent really bumping the shoulder back on all the cases????

I have seen that when using the headspace measurement, the distance varies quite a bit, indicating to me that the brass either grows a different amount upon firing/sizing, or springs back quite inconsistently???

Thoughts?? Am I missing something on my sizing setup--sure seems to give consistent results in the rifles, and cycling of the ammo......

Don, I tried a trimmer similar to the Giraud in that it trims based on the shoulder datum. I didn't like having to hold the cases in hand while trimming and went back to my trusty old RCBS power trim-pro. Do you have to hold the cases while trimming with the Giraud? If so that would give me one more reason not to try one, though if you don't like it that would be good enough reason for me.....................DJ

DJ, you do have to hold the case. It inserts into a fixture that is cut with a chamber reamer, and is spring loaded, you push the case in far enough to compress the spring and the trim is based on the length from the shoulder.
It trims very cleanly and efficiently, both inside chamfers (vld taper) and outside deburs as well as to length simultaneously.

I'm not sure if I like it or not yet--it has revealed that my cases are not as consistent as I thought in terms of base to datum measurement after sizing--I didn't measure all my cases after getting my die set up for a particular rifle, PFLRS being my goal.

I was actually between this and the RCBS trim pro power trimmer--schools still out....

What you have found is your resizing technique could use some refinement.
First things I would look into would be the press. Is the linkage getting loose? Die lock up to the frame tight? Erratic lube film on the cases. Dirty dies. Is the frame of the press strong enough to not flex? Is your "stroke" constant? I am sure there are others I can't think of now.

Yes this is a short coming of the case trimmers that index off the case shoulder/datum line. However with a little practice you may be surprised at how close you will be able to hold the case length. Provided you have consistent length cases to begin with. Not likely to ever be as accurate as a Wilson or other that indexes off the case head though. But the Giraud is designed for large volume trimming with good results. The Wilsons et al are slower but much more accurate.
The Giraud is great for trimming several hundred to a couple thousand cases in a batch. But unless you reload at those volumes its is a rather expensive toy. IMHO

muck

Don, I think that the RCBS is slower but I like that the lever to insert the cases is easy and you don't have to hold the case while the motor is running.
I usually set up batches to where while it's trimming one case I'm deburring the flash-hole or some other chore on the other cases while it's waiting.
My hands tend to cramp up after holding a few hundred small object for long so I probably couldn't use the Giraud as effectively....................DJ

Rimless cartridges headspace on the shoulder. In the chamber that shoulder determines how far the bullet starts in the throat. So why are you worrying about taking measurements from the base?

When the firing pin hits that primer, the front of the case sticks to the chamber walls and the back of the case stretches to the bolt face. Seems to me the more exact way of controlling trim length and bullet jump is off the shoulder. Not the base.

Slamfire, that is in fact one of my questions, but isn't having 10 thou or thereabouts more neck than the next or last cartridge varying neck tension? I'm used to having that spec very precise with my Wilson, but don't profess to know that it matters, I just would surmise that it does. Intuitively the neck tension would have to vary???

DJ, I hear you about the holding a bunch of cases....The RCBS power trim pro is back on the radar, I'm gonna talk to Doug, but maybe like Muck said, this trimmer is for big volumes and a hair less precision???

Muck, I do intend to investigate my sizing in more minute detail--It was definitely a discovery, I truly thought that the case head to datum would be way more consistent than I am finding so far. My presses are in superlative condition, and very 'tight'--I'm confident they're not the issue.
I've found that even fireformed brass from anywhere from 1st to 5th, 10th and 13th reloading (all I had on hand) varies quite a bit. I had wrongly thought that it would be very consistent at these intervals--especially the stuff in the 3rd or 4th iteration......

Doug Giraud was absolutely super to deal with, but I do not trim so many cases that this trimmer is a necessity, I had assumed greater precision....I was just wanting to go to the best, that was powered, and a cordless drill in a Wilson is not it for me.

Still ciphering