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Measurement Question

 
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  #1  
Old 06-23-2010, 09:52 PM
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Join Date: Sep 2009
Posts: 41
Measurement Question

hey guys,

first of all i would like to say this forum is awesome and i'm really enjoying all of the info i can suck up on here. thank you to all of the contributing members

first some data

i've been shooting a remington 700 pss in .300 rum and i've started to reload for it with some 180 grain swift sciroccos that came with the gun, and now that i've found a ton more info i want to do it properly. the rifle has a very low round count, approximately 175 down the tube.

i bought a hornady OAL guage, and spent some time fiddling with the thing until i could get consistent reading within .003"

i used this with a hornady bullet comparator to determine a base to "ogive" max length of 3.084"

hornady recommends starting at about .040" off the lands up to .020" off the lands.

so with some spiffy math i figure i should be seating these bullets to 3.044" (.040 off) and working my way from there

i then took some reloads from a few weeks before i read this great seating depth info and they were seated base to bullet tip at 3.600" and measured the base to "ogive" length to determine the length at 2.928" average

so i took some remington factory ammo with the same swift bullet which measures about 3.570" average from base to bullet tip, and measured it out at 2.900" from base to "ogive"

so if this is all acurate (after many measurements) i'm showing my base to "ogive" length at 3.044" (3.084"-.040") compared to factory at 2.900" giving me a difference of .114" seating depth from factory to what i "should" start at according to hornady instructions

is this right? i know factory ammo has to be made to fit all firearms, and therefore has all kind of room to play for different rifles, i just wanted to make sure this isn't way out of wack.

i'm new to this bullet seating depth measurement stuff so i figured i would run it by some professionals.

so does this measurement seem normal?

Thanks again guys!
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  #2  
Old 06-24-2010, 12:00 AM
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Join Date: Jun 2006
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Posts: 923
Re: Measurement Question

Entirely normal for a factory 300 RUM to have that much jump to the lands. Also common with other calibers such as Weatherby's. It seems that it is becoming more and more common in all factory rifles.

Some Weatherby's and RUM's I have reloaded for have as much jump as .275" jump to the lands. This will vary with the bullet as you can load some bullets closer to the lands and still have the same OAL because of the shape of the bullets. IOW you would be able to load a heavy roundnose bullet (if you wanted to) closer to the lands and still have a OAL that would fit in the magazine.

A large jump to the lands decreases pressure (all other variables being stabilized) and decreased pressure lessens liability. Personally it aggravates the hell out of me to not be able to seat where I want and still fit the magazine and don't own any rifles set up that way. I do own a 338RUM but it is a custom rebarrel without excess freebore but that means that I have to be careful not to shoot factory ammo or load to manual maxes as it will lose the primer pockets.
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Old 06-24-2010, 07:08 AM
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Join Date: Sep 2009
Posts: 41
Re: Measurement Question

awesome, i just wanted to make sure this was the norm for a factory rifle.

tonight i'll measure headspace and do a little more messing with things.

then i'll shoot off the rounds i loaded up and start prepping some more brass for more rounds.

i love it when one hobby feeds another

thanks
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