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View Full Version : Overall Length Diiferences with Different Bullet?



jimfinn
02-18-2010, 09:06 PM
I sure hope this isn't a completely stupid question.
I use a StoneyPoint tool and comparator to measure from the base of the case to the ogive. The modified case is one that has been fired in my rifle (a 6MM BR). I get the same distance using different wieght Berger bullets, Hornady, and Sierras. I just got in several flavors of Bart's 68 grain 6MM bullets. When I ease these in to touch the lands using the StoneyPoint tool then measure the length with the comparator, it is about 0.020" shorter than for the other brands of bullets.
I would have thought that for a given chamber that the distance from the base of the case to the lands would be constant, given that the same case is used and it is inserted into the chamber consistently. If that is so, wouldn't the Length from the base of the case to the ogive be the same for all brands of bullets?
Am I missing something, doing something wrong, or am I just too dense to see something obvious??:confused:
Thanks
Jim

Al Nyhus
02-18-2010, 09:22 PM
Jim, what you're seeing is the result of different bullet profiles. -Al

HovisKM
02-18-2010, 09:23 PM
Yep....if the ogives were the same. The reality is....they are not and are not designed to be the same. The distance from the bolt face and the lands are is of course the same in the same chamber/barrel. It's the bullets that are different. However, if your comparator is reamed with a throating reamer that matches the throat of your rifle, it will be the same, the problem is, it's not. That's why you have to figure it for every bullet you use.

Hovis

jimfinn
02-18-2010, 09:32 PM
Thanks Guys, that makes sense. Yep the comparator is just an off the shelf job. I'll make up some dumby rounds with the bullets set to touch the lands for these new Bart's bullets.
Jim

nhkuehl
02-20-2010, 12:43 PM
When I ease these in to touch the lands using the StoneyPoint tool then measure the length with the comparator, it is about 0.020" shorter than for the other brands of bullets.


Like everyone else said about the ogive of different bullets.

Also the ID of the Stoney Point gage is straight drilled and is probably different than the ID of lands, which taper in the throat. A Sinclair gage is tapered (reamed?) and will give a different reading than Stoney Point. nhk

Cheechako
02-20-2010, 12:53 PM
Guys

Don't overlook the key word here - COMPARATOR. The tools are meant to COMPARE different bullets not to determine the seating depth. You do that by actually loading a bullet in a case and seeing when it touches. Even if the tool is reamed with the same reamer used to chamber the barrel it will only be 100% accurate until you fire the first shot. Think about it.

JMHO

Ray