I've had my 7 STW for about 2 years now. To this point have only used CT ballistic ST. Anyway with any new barrel I insert a bullet just barely into the case then insert it in the action. I then use my Sinclair bullet comparator to find the OAL for the bullet ogive. This way no matter what bullet I am measuring off the ogive so the distance off the lands will be the same. Well here is my current status. I loaded up some Barnes XBTs. To be .05 off the lands like is suggested by Barnes. Well I tried to fit one of the rounds in the chamber by hand and it wouldn't go all the way in. I had to close the action then remove the shell to find it had shrank in length. Well thinking I had made an error I inserted some CTBST's in cases then closed the action to get another reading with my sinclair comparator. These numbers came out the same as always 4.155" off of the ogive. I then did the same with the XBT's and they came out at 4.059" off the ogive. Basically my question is since these are all new cases, shouldn't matter but don't know, and the lengths are gotten off of the ogive why is there such a difference? I mean I will seat the bullets to 4.009" now to make them work but what gives. All help is greatly appreciated. Like I stated earlier these are all new cases that have been FL sized, trimed to length and chamfered. Thanks in advance for the help.

This is completely normal.You must determine the overall length for each bullet that will be used in this rifle separately.Every bullet may result in a different overall length even if seated the same distance off the lands.

Seems like since I wasn't measuring the loaded OAL but the length from the ogive then it shouldn't matter what bullet I'm using. The length from the ogive to the base of the cartridge would be the same for any bullet loaded.

The shape of the ogive on the new bullet may not follow the lead angle the same as the old bullet. I doubt that is the cause for almost .10" difference in variation though.

I suspect the OAL you were useing with the CT BT in your old loads acually has the bullet in the lands a bit. Try smoking or color a seated CT BT bullet with a magic marker and chamber it in your rifle. (use a uncharged dummy round) I`d bet there will be marks where the lands contact the ogive.

I`ve found chambering a round with the bullet seated in a case doesn`t give a true "just touching" OAL. The bullet sticks in the lands as it reseats and depending on how far it jammed in the lands seating can acually be pulled back out some or stay seated in the lands a hair.

The X bullet is not as sleek as the BT and the ogive will touch at a shallower depth due to the sharper angle of attack. It may not slip into the lead as easily as the BT and cause the variation you`ve found between the two.

Ogive shapes vary dramatically.I just went through some of my own numbers and my loads vary by .050" or so among the different bullets.I don't use a comparator myself.I take a fired case and flatten the case neck a bit so it will hold the bullet in place.I then leave the bullet barely started into the case and chamber it and close the bolt.When I remove the cartridge I measure the overall length to the lands for that bullet.I repeat this several times with a few bullets(due to tip variations) until I get very similar readings several times to be sure of a correct measurement.I find this method is very consistant once you have done it a few times.

[ 07-14-2003, 06:07: Message edited by: stubblejumper ]

Using a comparator corrects for different ogives.

I had similar problems for years until purchasing a OAL guage (Mines a Sinclair).

By trying to guage seating depth without such a tool it is very easy to induce a 0.020+ error.

Wally

Due to the differance of tip taper by various
manufacturers the seating die must be set seperately for each manufacturer.

You should get the Stoney Point tool for measuring the distance to the lands, your method is far to crude to get a reliable reading. The bullet could stick then pull when you remove the case or just plain slip a hair while your fiddleing with the calipers. You are on the right track with your method but need better tools.

I take any and all advice seriously. So agreeing that seating the bullet in the case then craming it in the chamber was kind of crude I devised a little experiement. I enlarged the primer hole on one of my cases, opened up the neck and proceeded to try a setup like the stoney point with some enlighting results. After seating the case I pushed the bullet forward into the lands and found that it was .2 shorter than any previous depth. I did this several more times measuring after each and am now conviced that my old technique was indeed pushing the bullet in the lands. I will set about tomorrow making a proper stoney point oal length tool. Anyway thanks for the help and advice. Can always count on help from knowledgeable people. Thanks again.