OAL or Ogive

flstfi · April 27, 2006, 09:51 PM

Case= 6mm Remington
Projectile= Hornady 75gr hp

Using an O.A.L guage and a comparter I determined the maximum overall length to minimize freebore travel. I then deducted .030 from that figure. I then made up a dummy round and chambered it. It went in smooth and there were no marks on brass or copper to indicate any contact.

However the new length does not work well for the magazine in my model 700 Remington.

Is This Normal?????????

garryc · April 27, 2006, 10:10 PM

same gig with my 243 remmy.
http://hometown.aol.com/garrywoodsma...age/index.html

rwilson452 · April 27, 2006, 10:18 PM

In a word, Yes. Often a cartridge long enough to work properly in the bore will be too long for the magazine. Sad, isn't it. So you need to make a choice. Use your rifle as a single shot to use the most accurate load you can build, or a less accurate load that will fit in your mag. Many factors go into that choice. In my varmint rifles, a singe shot is just fine.

Case= 6mm Remington
Projectile= Hornady 75gr hp

Using an O.A.L guage and a comparter I determined the maximum overall length to minimize freebore travel. I then deducted .030 from that figure. I then made up a dummy round and chambered it. It went in smooth and there were no marks on brass or copper to indicate any contact.

However the new length does not work well for the magazine in my model 700 Remington.

Is This Normal?????????

kingudaroad · April 29, 2006, 06:10 PM

Sounds like a hunting situation where you will need the magazine. Even though your chamber will accomodate a longer bullet, your magazine will not. So now you need to determine what the longest oal will fit in your magazine and that length is now the max oal that will function in your rifle. Chances are it will still be over saami reccomended max length and chances are it will still be more accurate as it is still closer to the lands.

I'm kind of surprised though as my remington adl in 270 will accomodate a cartridge that touches the lands.

If you make one that barely fits in the magazine and then make them shorter in increments you can still likely find a sweet spot for your rifle.

**Unclenick** · April 30, 2006, 02:39 PM

Yes to Kingudaroad's point. Not all rifles have a sweet spot .03" off the lands, and it may not be the only one. Pick a load on the light side (a starting load) and fire groups in a round-robin progression in 0.005" depth increments. See if you don't find one around the place where the neck begins to get hold of the most bullet bearing surface?

Nick

918v · April 30, 2006, 03:14 PM

Why is it that certain factory loads shoot sub MOA from the magazine? Because freebore is not an accuracyrobber at all, unless your chamber is not concentric with the bore centerline.

**Unclenick** · April 30, 2006, 04:01 PM

918v,

Ahh, now you've opened a can of worms. Check Dan Newberry's Optimal Charge Weight theory out. Also look at his instructions for firing 3-shot round robins instead of Audette ladders. Interesting stuff.

Freebore has no reason to affect accuracy if it isn't loose. If it is loose enough to allow a bullet to cant, it will cause trouble, or if your bullet's side bearing surfaces aren't a true cylinder, it will allow canting. Touching the lands is just a way of using the taper and hole centering principle to be certain there is no cant. The conflict is the deeper seating tends to improve start pressure consistency, and improves accuracy for that reason. Seating a little off the lands lets the start pressure improve but also lets the bullet hit the lands at a low enough velocity that it still centers rather than ploughing onto the lead so fast it remains canted. The exact best point of compromise varies with powder burning characteristics.

Harold Vaughn reported that sizing Noslers down half a thousandth improved 300 yard groups from 3.5" to 2.5" in a .270 just by forcing the sides parallel.

In addition, if you have fixed your powder charge, seating depth affects accuracy by changing barrel time. Newberry blames the whole effect on this, but I don't agree. There are cases of the optimum seating depth being found first, then the powder charge afterward. So it is a mix of things. Newberry's ideas are here and fit will with Chris Long's optimum barrel time theory.

Nick

kingudaroad · May 1, 2006, 01:20 PM

Thanks for the links Nick. Great reading and great information.

April 27, 2006, 09:51 PM	#1
flstfi Member Join Date: March 28, 2005 Location: California Posts: 44	OAL or Ogive Case= 6mm Remington Projectile= Hornady 75gr hp Using an O.A.L guage and a comparter I determined the maximum overall length to minimize freebore travel. I then deducted .030 from that figure. I then made up a dummy round and chambered it. It went in smooth and there were no marks on brass or copper to indicate any contact. However the new length does not work well for the magazine in my model 700 Remington. Is This Normal?????????

April 27, 2006, 10:18 PM	#3
rwilson452 Senior Member Join Date: June 10, 2004 Location: Tioga co. PA Posts: 2,647	OAL and magazines In a word, Yes. Often a cartridge long enough to work properly in the bore will be too long for the magazine. Sad, isn't it. So you need to make a choice. Use your rifle as a single shot to use the most accurate load you can build, or a less accurate load that will fit in your mag. Many factors go into that choice. In my varmint rifles, a singe shot is just fine. Case= 6mm Remington Projectile= Hornady 75gr hp Using an O.A.L guage and a comparter I determined the maximum overall length to minimize freebore travel. I then deducted .030 from that figure. I then made up a dummy round and chambered it. It went in smooth and there were no marks on brass or copper to indicate any contact. However the new length does not work well for the magazine in my model 700 Remington. Is This Normal?????????

April 30, 2006, 02:39 PM	#5
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Yes to Kingudaroad's point. Not all rifles have a sweet spot .03" off the lands, and it may not be the only one. Pick a load on the light side (a starting load) and fire groups in a round-robin progression in 0.005" depth increments. See if you don't find one around the place where the neck begins to get hold of the most bullet bearing surface? Nick __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

April 30, 2006, 04:01 PM	#7
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	918v, Ahh, now you've opened a can of worms. Check Dan Newberry's Optimal Charge Weight theory out. Also look at his instructions for firing 3-shot round robins instead of Audette ladders. Interesting stuff. Freebore has no reason to affect accuracy if it isn't loose. If it is loose enough to allow a bullet to cant, it will cause trouble, or if your bullet's side bearing surfaces aren't a true cylinder, it will allow canting. Touching the lands is just a way of using the taper and hole centering principle to be certain there is no cant. The conflict is the deeper seating tends to improve start pressure consistency, and improves accuracy for that reason. Seating a little off the lands lets the start pressure improve but also lets the bullet hit the lands at a low enough velocity that it still centers rather than ploughing onto the lead so fast it remains canted. The exact best point of compromise varies with powder burning characteristics. Harold Vaughn reported that sizing Noslers down half a thousandth improved 300 yard groups from 3.5" to 2.5" in a .270 just by forcing the sides parallel. In addition, if you have fixed your powder charge, seating depth affects accuracy by changing barrel time. Newberry blames the whole effect on this, but I don't agree. There are cases of the optimum seating depth being found first, then the powder charge afterward. So it is a mix of things. Newberry's ideas are here and fit will with Chris Long's optimum barrel time theory. Nick __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

April 27, 2006, 10:10 PM	#2
garryc Senior Member Join Date: November 12, 2005 Posts: 2,536	same gig with my 243 remmy. http://hometown.aol.com/garrywoodsma...age/index.html

April 29, 2006, 06:10 PM	#4
kingudaroad Senior Member Join Date: March 11, 2005 Location: austin Posts: 735	Sounds like a hunting situation where you will need the magazine. Even though your chamber will accomodate a longer bullet, your magazine will not. So now you need to determine what the longest oal will fit in your magazine and that length is now the max oal that will function in your rifle. Chances are it will still be over saami reccomended max length and chances are it will still be more accurate as it is still closer to the lands. I'm kind of surprised though as my remington adl in 270 will accomodate a cartridge that touches the lands. If you make one that barely fits in the magazine and then make them shorter in increments you can still likely find a sweet spot for your rifle.

April 30, 2006, 03:14 PM	#6
918v Junior member Join Date: September 25, 2005 Posts: 1,372	Why is it that certain factory loads shoot sub MOA from the magazine? Because freebore is not an accuracyrobber at all, unless your chamber is not concentric with the bore centerline.

May 1, 2006, 01:20 PM	#8
kingudaroad Senior Member Join Date: March 11, 2005 Location: austin Posts: 735	Thanks for the links Nick. Great reading and great information.