ojive and OAL?????

[steelersfan]

Hello Reloading folks,

Reloaded my first 20 rounds of .270 Win. yesterday. I have been reloading for my .38 special and .40 S&W for a while and this was my first attempt at bottle neck cases. The ojive on bullets and using that to determine OAL measurement is new to me.

I understand that the purpose of a comperator is to measure OAL not from the bullet tip but instead from the ojive, which is a more precise way to measure OAL and determine bullet seating depth keeping the ojive a consistent .02 " away from the lands of the barrel. Is this correct?

So if I used an OAL gauge in my particular .270 rifle and found the OAL is 3.802 (hornady comparator inculded in this measurement), will the OAL for any bullet I choose be 3.802 with the comparator??

I understand that depending on bullet the OAL from bullet tip to bottom of case will be different due to differnt types of bullet, but the OAL from the ojive should be consistent no matter what bullet I use??? Is this thinking correct? Or will I need to use an OAL gauge everytime I try a new bullet to determine proper seating depth?

Thanks folks and I hope these questions make sense.

 

[OKFC05]

will the OAL for any bullet I choose be 3.802 with the comparator??

Wow, I love it when you talk technical.
Right up to the "any bullet" you have me convinced. Not all bullets are secant ogive, so it is possible to find one that is a little off. Don't ask me to name one offhand.
Been loading for .270 since 1973, and doubt you are going to see much difference unless you have one teriffic test-bed rifle you are shooting. I just use a seater that contacts the bullet near the rifling diameter, and load them all the same. Still do a quick check to be sure the rifling misses the bullet.

P.S. Never got anything lighter than 130gr to shoot worth a flip in mine.

 

[s&wchad]

Or will I need to use an OAL gauge everytime I try a new bullet to determine proper seating depth?

You should. There's no magic depth, you need to develop loads for each gun. You should also reduce your charge and work your way up looking for signs of excess pressure.

OAL can be important if you want to feed from a magazine. I seat bullets for my Rem 700 .22-250 at 2.52" OAL with Nosler 50gr Ballistic Tips, which is about .010 off the rifling on that gun. 2.35" is the listed max cartridge length and my loads don't fit in the magazine, but I single load only. Seating to that depth cut my group size in half. The same loads engage the rifling in my 40X and opening the bolt on a live cartridge results in a mess, so I'll never try that again. My bench rifle, a 40X in 6mm PPC USA (.262" neck) shoots best when I push the bullet into the rifling.


Some of the hot magnum cartridges have substantial free bore for a reason and I load them to spec.

 

[Ron H.]

Hello Reloading folks,

Reloaded my first 20 rounds of .270 Win. yesterday. I have been reloading for my .38 special and .40 S&W for a while and this was my first attempt at bottle neck cases. The ojive on bullets and using that to determine OAL measurement is new to me.

I understand that the purpose of a comperator is to measure OAL not from the bullet tip but instead from the ojive, which is a more precise way to measure OAL and determine bullet seating depth keeping the ojive a consistent .02 " away from the lands of the barrel. Is this correct?

So if I used an OAL gauge in my particular .270 rifle and found the OAL is 3.802 (hornady comparator inculded in this measurement), will the OAL for any bullet I choose be 3.802 with the comparator??

I understand that depending on bullet the OAL from bullet tip to bottom of case will be different due to differnt types of bullet, but the OAL from the ojive should be consistent no matter what bullet I use??? Is this thinking correct? Or will I need to use an OAL gauge everytime I try a new bullet to determine proper seating depth?

Thanks folks and I hope these questions make sense.

Sir, different bullets' ogives differ, even with bullets of the same weight, and sometimes even bullets of the same weight from the same manufacturer. For example, a Sierra .30 caliber 150-grain GameKing has a different ogive than a Sierra .30-caliber 150-grain Match King.

To get a consistent distance from the lands, you'll need to re-measure with each bullet. It also helps to have something like a Stoney Point OAL gauge so you'll know where each bullet type touches the lands. Continuing with the example of .30-cal Sierra 150s, the Game King will have a different measurement than the Match King.

BTW, there's no hard-and-fast rule about accuracy and distance from the lands. You'll just have to try different seating depths until you find the combination that your gun likes.

Hope this helps, and Semper Fi.

Ron H.

 

[Big Cholla]

steelersfan: If you are loading to achieve minute-of-angle of deer then load to make your cartridge feed reliably thru the magazine. If you are loading to achieve the utmost in accuracy then you must determine by experimentation the optimum loaded cartridge length for each bullet and each powder loading. The easy way is to use a pencil to push your bullet selection into the leade of the barrel. Don't use excess force. Take a cleaning rod with a blunt end and push it in to just touch the nose of the bullet. Carefully put a fine mark on the rod at the muzzle. Load a brass with no primer or powder with that same bullet to a 'normal' depth. Chamber that test round. Do the cleaning rod thing again and mark the new length. Carefully use a vernier caliper to measure the distance between the marks. That measurement plus the collimator measurement of the test round is your maximum seating depth. Save the test round for later use in setting your bullet seating die.

Over the years I have found that a good place to start experimenting at is to use this rule of thumb; If it is a .30 caliber use .030" back from maximum. If it is a .25 caliber use .025" back, you get the idea. Most often I have found that the optimum seating depth will be between this start point and .005" to .010" of maximum. Start your test shooting with three rounds loaded to the start point; three more at that minus .005", three more at that minus .010", and so on to maximum minus .005". Let your rifle cool between the sets of three. Someplace in the series will be the optimum seating depth for accuracy. Be aware that point moves forward with lots of rounds thru that rifle because the throat of the rifling is being eroded away as you shoot. Also, be aware that all rifles with box magazines or removable magazines have a maximum seating depth that will feed from that magazine. That length may be considerable shorter than optimum seating measurement.

It is true that benchrest competitors usually seat bullets to just make contact with the lands of the barrel. They are shooting single shot and have actions built to take greater pressures than most sporting rifles. I would not advise seating any bullet for a sporting rifle out far enough to touch the lands.

One last Bon Mot; Every rifle/cartridge/bullet combo is a law unto itself. Once, I ran across a Remington 760 that developed its best accuracy with the bullet jumping a full .125". And all revolver bullets have to jump at least that far before engaging the rifling. Some of them give amazing accuracy. Those are the things that make this game so interesting. ...... Big Cholla