Ogive Length

[Pirate-69]

I finally bought the Hornady device for measuring ogive length. I think I need a little education. If I understand correctly, the ogive length is the distance from the bolt face to the point that the bullet touches the lands. If so, should the ogive length be the same regardless of the bullet measured? I compared a Sierra 180 grain .308 and a Hornady 168 grain .308 and the ogive lengths were exceptional close.

I also selected 5 rounds of each and measured the ogive lengths. For each weight, I did not always get the same ogive length, even remeasuring the ones that were odd. The maximum variation was 0.0025". Am I seeing operator problems or is this to be expected? Thanks for any advice.

 

[Pirate-69]

Re: Ogive Length

Found a 5/23/09 post that is helpful. If I read it enough, it may answer all my questions and more!!

 

[Fuzzball]

Re: Ogive Length

"If I understand correctly, the ogive length is the distance from the bolt face to the point that the bullet touches the lands."

That's not quite correct. The "ogive", as such, of <span style="text-decoration: underline">bullet</span> is the full length of the bullets nose curve, from the tip (meplat) to the point of the full body diameter. It does not directly relate to seating depth.

It's good to measure seating depth to the point on the ogive where the rifling contacts the bullet tho. It matters not how much the bullets nose extends into the bore, all that really makes any difference is how much the bullet travels before contacting the lands so the OAL, of its self, isn't the real issue.

Consider that a .308 bullet sits in a <span style="text-decoration: underline">bore diameter</span> that's .300" and the <span style="text-decoration: underline">groove diameter</span> is (typically) .308". If we measure the cartridge length from head of the case to the .300" diameter of the ogive we can seat the specific distance off contact that provides best accuracy. (And, contrary to popular myth, factory rifles shooting standard cases with off the self bullets, best accuracy is rarely with bullets in contact with the lands.)

That's a part of why agonizing over any <span style="font-style: italic"><span style="text-decoration: underline">book</span></span> OAL is virtually pointless. The book cannot possibly accomidate the contact point of more than one bullet seated for one specific weapon, and it ain't yours! You need to find the best OAL, head to ogive contact, for YOUR LOAD and each BULLET you use. Then you will be seated correctly for YOUR RIFLE! Your Hornady "device" will help you do that.

 

[FNuser]

Re: Ogive Length

If you understand that o.a.l. is over all length for that cartridge then there is some knowledge to be gained but it pressure related, the capacity of the case with the bullet seated to this depth. so if you extrapolate this to meaning "if I seat the bullet out a little more I have at least this much volume to work with safely." This only works if the brass is listed by manufacturer, and the exact bullet is used. However chamber dimensions do vary but usually the manuals are written in a conservative manner. But yes most bullets jump better then they jam with of course the exception of Bergers.

 

[Pirate-69]

Re: Ogive Length

Education obtained as requested. Thanks Guys.

 

[hershey]

Re: Ogive Length

thanx fuzzball... that was the way i always pictured it to work in my mind, but could not put it to words. i have to seat 168's long because my chamber is cut for 180's.

 

[LNO1]

Re: Ogive Length

Forget that! The ogive is what usually contacts and stops the lands. It's lengtht is yet another measure to consider for sure but the Hornady OAL guage (with a bit of tapping) will fine tune your rifle to the OAL that is effective +/- a few thousandths (vs. many from ogive to tip) maybe. So many bullets vary in size from the ogive to the tip (which I measure to) so I go for the OAL and +/- from there. Oh BTW, tightest group in FN SPR's is 2.856!

 

[LNO1]

Re: Ogive Length

check this..

http://www.cabelas.com/prod-1/0044519216354a.shtml