i thought i felt something as i opened the bolt of the 6.5-.270 that i've had so much appearant pressure problems with, so....
i made a 24 inch long, 1/4 dia. brass rod with the ends radiused to use as a push rod in the bore sitting on the bolt face, barrel in vice held verticle. i then clamped my indicator bracket to the muzzle so that it held the dial on the end of the rod. opening and closing the bolt would gave readings of face travel parallel to the bore on the dial. with the bolt closed and the dial zeroed,pulling back on the bolt as i opened it,the dial never showed a positive reading, only negative as the lugs started off their seats after about 30 degrees of bolt rotation. test repeated several times. dial and bracket were starrett indicator test set #196A5Z.
would you consider that a legit test for back set.

Merlinron,

If you're checking to see if the lugs have set back, you need an original measurement with the same setup and clamp location to compare it to.

Does your 6.5-.270 have the same shoulder/datum line as the rest of the 30-06 cartridges? If so, I'd just check it with a 30-06-based cartridge no-go gauge. If not, I'd make one/have one made based on the original drawing or reamer.

The setback that I have observed in a receiver was at the area of contact when the bolt was in battery. The area that is not in contact does not get setback, obviously, since there is no contact at the moment of high pressure.
So, when the bolt is first starting to be rotated into battery, the lugs are contacting an area that has not been violated. When in battery, the lugs can move rearward, increasing headspace.
I don't think that this can be measured accuratly by simply using go/no-go headspace gages.
That is just my opinion, I may be way off on this, tell me if you think that I am.

merlinron,

I think you have a clever way to determine that you may have setback, but often you can feel possible setback just by closing the bolt, pulling back on the bolt handle gently and opening the bolt. You'll feel the bolt pull forward as it rides over a little hump on the lug seats, and you can feel the edge of that hump through the bolt handle, but not always. That little hump is what often locks the bolt closed on a fired case. The only way to tell for sure and get an accurate measurement is to unscrew the barrel which is easy, usually.

Pull the barrel and look.

hi john,
thanks, i thought it would be good enough to initially confirm or negate what i thought i felt.i realize ultimately the barel should come off, but i don't have that basic equipment and fool with barell work. i do have plans to build/get a barrel vise and action wrench though, and drool over someday, getting a lathe.
i did innitially notice it when i had a fired, well-formed (good, sharp shoulders, etc.) case in the chamber. it is an AI chambered rifle and i only neck size the cases.
as said, no positive readings as the bolt was turned, so i guess it's ok.
i've spent many years as a milwright, doing precision machine installation and set-up and quite a bit of fabrication. i'm "old-school", doing most of my work when you used a dial and math to align shafts... not a lazer, like they do now...most of the "kids"( milwright apprentices) now-a-days, barely know what a dial indicator is.

skl1,
regaurdless of measurement, setback is independant of headspace specs. granted, it's result is assuredly excessive head, but a go-no- go guage won't necessarily tell you it it exsiste. a no-go guage indicates excessive headspace. if it exhistsin the rifle being checked for setback, the bolt will still close on the guage, because the distance from bolt face to shoulder is to long in either condition. if you put a go-guage in the chamber and the headspace is good innitially, the bolt will close and you will feel the friction, as you should, as the lugs passe over the seats. the only indicator will be a sudden lose of that feel of friction as the lugs seat in the "setback" area. but it doesn't actually tell you how much actual setback is there vrs. just a well lapped in lug/seat fit. the method i described gives you a visual picture of how much the bolt face is moving laterally as the lugs seat. with the dial set to zero and the bolt closed(in battery) the lugs are down in the setback on the seats. when you open the bolt, the lugs have to climb out of the setback are and the dial will indicate that as positive travel by reading a cuople thousanths or so, it will then level off maintainng the positive value for several degrees of bolt rotation, before before diving into the negative as the bolt backs away from the barrel following the extraction ramp. it is that jump into the positive value just as you start opening the bolt that indicates setback. 1 or 2 thousanths would be ok, but any more is a problem. even at 1 or 2 thousanths, set back has probably happened and is an indicator that it will probably continue to get worse.
my gun is basicly the same as a 6.5-.270. the reamer was made with the longer neck of the .270 so i can use .270 cases without trimming them back to '06 length and make use of that longer neck for holding the bullet. just something a little different than the standard 6.5-'06.

Merlinron,

Sorry if it appeared I was correcting you without understanding your setup.

Neat wildcat.