question about using an OAL guage

[jimborock]

I have a Tikka .243 caliber. I recently purchased a Hornady OAL gauge and bullet comparator. I used them today on my .243. It seems that when the bullet is set to touch the lands, the OAL is about .07 longer than if the bullet was seated so the mouth was in the cannelure.

I use almost no pressure at all, when moving the bullet to the lands. So I know I did not push it past the lands. In fact, I retried it several times with the same results everytime.

Does this seem right? I would have expected the mouth to be somewhere within the cannelure or maybe just slightly below it, but not that much.

 

[10 Spot Terminator]

Of cannelures and bullet oal it goes like this ,,,
The purpose of a cannelure is to be a crimping groove to help put a consitant pull on the bullet when the powder is ignited for bullets that are sure to be seated well off of the lands in any given weapon. As all wepon manufacturers chamber dimensions vary there is no "one size fits all" rule that applies therefore the bullet manufactures set their crimping grooves short enough so "one bullet fits all" . The trade off here is you may get an extreme amount of bullet jump to the point where the bullets contact the lands of the rifling when fired . The point here is what is trying to be accomplished by seating your bullets to the lands is to create that consistant breakaway pressure where the bullet starts to move upon firing AND not have the bullet jump as with crimping. You dont need to crimp using the "touch the lands" seating method, you do need though to be more carefuls as to powder selection as some powders can tend to have erratic pressure jumps when loaded at or near max loads. For loading cartridges where trying to touch the lands creates cartriges too long for use in the magazine then cannelured bullets can help here. If having to use cannelures and crimping you are trying to reduce the bullet jump as much as possible all you can do is this,,, get your hands on as many samples of cannelured bullets over an acceptable grain weight range as you can without having to buy a full box and do the following,,, get a bullet comparator tool such as that made by Stoney Point that will measure the length of the bullet from the base to the ogive ( point where the bullet starts to taper ) and subtract the distance from the base of the bullet to the middle of the cannelure . This will give you a good idea before you start the tedious load work up scenario of the few bullets that will best tend to reach out closest to the lands for the jump length you are looking for. Rule of thumb here is .0015 to .0020 per most all published load data. Do note as well using the cannelure requires crimping the brass at the cannelure and you may want to consider seperate crimping dies such as those made by Lee as crimping when bullet seating can be a bit tricky and do more harm than good . Hope this hasnt confused you on this issue,,,, will answer questions as best I can .

 

[10 Spot Terminator]

Of cannelures and bullet oal it goes like this ,,,
The purpose of a cannelure is to be a crimping groove to help put a consitant pull on the bullet when the powder is ignited for bullets that are sure to be seated well off of the lands in any given weapon. As all wepon manufacturers chamber dimensions vary there is no "one size fits all" rule that applies therefore the bullet manufactures set their crimping grooves short enough so "one bullet fits all" . The trade off here is you may get an extreme amount of bullet jump to the point where the bullets contact the lands of the rifling when fired . The point here is what is trying to be accomplished by seating your bullets to the lands is to create that consistant breakaway pressure where the bullet starts to move upon firing AND not have the bullet jump as with crimping. You dont need to crimp using the "touch the lands" seating method, you do need though to be more carefuls as to powder selection as some powders can tend to have erratic pressure jumps when loaded at or near max loads. For loading cartridges where trying to touch the lands creates cartriges too long for use in the magazine then cannelured bullets can help here. If having to use cannelures and crimping you are trying to reduce the bullet jump as much as possible all you can do is this,,, get your hands on as many samples of cannelured bullets over an acceptable grain weight range as you can without having to buy a full box and do the following,,, get a bullet comparator tool such as that made by Stoney Point that will measure the length of the bullet from the base to the ogive ( point where the bullet starts to taper ) and subtract the distance from the base of the bullet to the middle of the cannelure . This will give you a good idea before you start the tedious load work up scenario of the few bullets that will best tend to reach out closest to the lands for the jump length you are looking for. Rule of thumb here is .0015 to .0020 per most all published load data. Do note as well using the cannelure requires crimping the brass at the cannelure and you may want to consider seperate crimping dies such as those made by Lee as crimping when bullet seating can be a bit tricky and do more harm than good . Hope this hasnt confused you on this issue,,,, will answer questions as best I can .

 

[10 Spot Terminator]

Of cannelures and bullet oal it goes like this ,,,
The purpose of a cannelure is to be a crimping groove to help put a consitant pull on the bullet when the powder is ignited for bullets that are sure to be seated well off of the lands in any given weapon. As all wepon manufacturers chamber dimensions vary there is no "one size fits all" rule that applies therefore the bullet manufactures set their crimping grooves short enough so "one bullet fits all" . The trade off here is you may get an extreme amount of bullet jump to the point where the bullets contact the lands of the rifling when fired . The point here is what is trying to be accomplished by seating your bullets to the lands is to create that consistant breakaway pressure where the bullet starts to move upon firing AND not have the bullet jump as with crimping. You dont need to crimp using the "touch the lands" seating method, you do need though to be more carefuls as to powder selection as some powders can tend to have erratic pressure jumps when loaded at or near max loads. For loading cartridges where trying to touch the lands creates cartriges too long for use in the magazine then cannelured bullets can help here. If having to use cannelures and crimping you are trying to reduce the bullet jump as much as possible all you can do is this,,, get your hands on as many samples of cannelured bullets over an acceptable grain weight range as you can without having to buy a full box and do the following,,, get a bullet comparator tool such as that made by Stoney Point that will measure the length of the bullet from the base to the ogive ( point where the bullet starts to taper ) and subtract the distance from the base of the bullet to the middle of the cannelure . This will give you a good idea before you start the tedious load work up scenario of the few bullets that will best tend to reach out closest to the lands for the jump length you are looking for. Rule of thumb here is .0015 to .0020 per most all published load data. Do note as well using the cannelure requires crimping the brass at the cannelure and you may want to consider seperate crimping dies such as those made by Lee as crimping when bullet seating can be a bit tricky and do more harm than good . Hope this hasnt confused you on this issue,,,, will answer questions as best I can .

 

[Ol` Joe]

The OAL is almost never at the same lenght even if the chambers are in the same brand of firearm. Tooling wears and is resharpened causing the chambers to vary. This is the reason we need a tool to find the leade, otherwise it would be at the same place every time.
The canalure also is in a position to fit the most cartridges in the most chambers. Seating a specific bullet in one cartridge you may be deeper in the case then seating it in another to keep the round within SAAMI COL. Everything is a compromise.