Max OAL using 168gr TTSX in 2.5" Brass

300magman · April 14, 2011, 09:06 AM

Just like the title says, What is the Maximum over all Length of a seated 168gr Barnes TTSX in a 2.5" case (like the 300 Norma Mag, or very similar to the old favorite 30.06)

Actually, if anyone has the tool to measure this, the length to the ogive would be more helpful, as I am trying to use this information to determine how to throat a new barrel.

I don't have any of these bullets on hand yet, so I can't check this out myself. A big thanks to anyone who can help me get the # I need.

**Unclenick** · April 14, 2011, 09:10 AM

Since different manufacturers use reamers with different freebore lengths and, even when they use a standard reamer, the headspace differs from one chamber to the next, there is no single correct answer to that. You'll have to measure it for yourself for your guns individually.

You don't need fancy equipment to get a pretty good idea of what the number will be:

Take an unloaded bullet and drop it into the chamber. Push it to the throat with a pencil or other convenient rod. Slide a brass rod from Lowe's or a cleaning rod in from the muzzle until it stops on the bullet. Watch that a cleaning rod centers over the bullet; the flat end of the brass is easier as it stops on the bullet tip, regardless of position. Watch that the rod didn't push the bullet back from the throat. Use the pencil to test that.

Mark the rod flush with the muzzle. You can put Magic Marker on the rod before you put in into place, then lay a single-edge razor blade or a box cutter blade flat on the muzzle to mark the Magic Marker. The blade thickness creates an offset, but that's not relevant in this case as long as it's consistent.

Remove the rod and bullet.

Use the same bullet to make up a dummy round to the bullet manufacturer's recommended COL or to below SAAMI max using a case you were ready to retire (resize it same as you would for your other loads). Chamber the dummy round. (NO! Don't do this with a live round or you can blow the gun up and yourself with an AD.) By using the same bullet, any small difference in nose shape or length is taken out of the equation. You can later use an inertial puller if you want to pull the bullet to load and shoot or if you want to redo the measurements in another chambering with it.

Use the brass rod or cleaning rod through the muzzle and mark it as before, but this time with the dummy in the chamber. You now have two marks on the rod. Add the distance between the marks to the COL or of the base to ogive length of the dummy. That will be the length of a loaded round that touches the lands.

Now the only job is to find what length (COL or base to ogive length) gives you the best accuracy below the length of the throat touching round. A description of how Berger does it for their VLD's is here. I like to use Dan Newberry's round robin method, but using a starting load and substituting seating depth increments for charge weight increments.

wncchester · April 14, 2011, 09:14 AM

As Nick says, max seated lenght to the ogive varies by the reamer.

Max OAL is usually dependant on the magazine length.

Doodlebugger45 · April 14, 2011, 10:15 AM

Nick's method certainly works and I have done it before. But that is for when you already have a rifle built and you can measure it. Maybe I misunderstood the question, but isn't the OP in the process of builing a rifle? So he doesn't have a chamber to measure at this point. He wants to build the chamber to match a specific OAL, not the other way around.

wncchester · April 14, 2011, 11:07 AM

Well, yeah. That's why Nick and I both point out that...

"max seated lenght to the ogive varies by the reamer."

Adjust the throating reamer and make the OAL whatever you want. ??

300magman · April 14, 2011, 11:31 AM

That is good information guys, but Doodlebugger45 seems to be the guy who understood me the best.

I'm using a slightly extended long action/magazine that allows for rounds to extend slightly past 3.9" if necessary. And I do not have a barrel yet, I am in the process of having one made with a custom reamer, and I can have it set up pretty much however I want.

I do not know if the maximum length of 3.9xxx would limit the extension of the 168gr ttsx from the case or not...but I was assuming that in all probability the max OAL would be limited by how long the combination of bullet + brass turned out to be, with the bullet seated the minimum acceptable depth into the brass.

April 14, 2011, 09:06 AM	#1
300magman Senior Member Join Date: September 12, 2008 Posts: 714	Max OAL using 168gr TTSX in 2.5" Brass Just like the title says, What is the Maximum over all Length of a seated 168gr Barnes TTSX in a 2.5" case (like the 300 Norma Mag, or very similar to the old favorite 30.06) Actually, if anyone has the tool to measure this, the length to the ogive would be more helpful, as I am trying to use this information to determine how to throat a new barrel. I don't have any of these bullets on hand yet, so I can't check this out myself. A big thanks to anyone who can help me get the # I need.

April 14, 2011, 09:10 AM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Since different manufacturers use reamers with different freebore lengths and, even when they use a standard reamer, the headspace differs from one chamber to the next, there is no single correct answer to that. You'll have to measure it for yourself for your guns individually. You don't need fancy equipment to get a pretty good idea of what the number will be: Take an unloaded bullet and drop it into the chamber. Push it to the throat with a pencil or other convenient rod. Slide a brass rod from Lowe's or a cleaning rod in from the muzzle until it stops on the bullet. Watch that a cleaning rod centers over the bullet; the flat end of the brass is easier as it stops on the bullet tip, regardless of position. Watch that the rod didn't push the bullet back from the throat. Use the pencil to test that. Mark the rod flush with the muzzle. You can put Magic Marker on the rod before you put in into place, then lay a single-edge razor blade or a box cutter blade flat on the muzzle to mark the Magic Marker. The blade thickness creates an offset, but that's not relevant in this case as long as it's consistent. Remove the rod and bullet. Use the same bullet to make up a dummy round to the bullet manufacturer's recommended COL or to below SAAMI max using a case you were ready to retire (resize it same as you would for your other loads). Chamber the dummy round. (NO! Don't do this with a live round or you can blow the gun up and yourself with an AD.) By using the same bullet, any small difference in nose shape or length is taken out of the equation. You can later use an inertial puller if you want to pull the bullet to load and shoot or if you want to redo the measurements in another chambering with it. Use the brass rod or cleaning rod through the muzzle and mark it as before, but this time with the dummy in the chamber. You now have two marks on the rod. Add the distance between the marks to the COL or of the base to ogive length of the dummy. That will be the length of a loaded round that touches the lands. Now the only job is to find what length (COL or base to ogive length) gives you the best accuracy below the length of the throat touching round. A description of how Berger does it for their VLD's is here. I like to use Dan Newberry's round robin method, but using a starting load and substituting seating depth increments for charge weight increments. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; April 14, 2011 at 09:51 AM.

April 14, 2011, 09:14 AM	#3
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	As Nick says, max seated lenght to the ogive varies by the reamer. Max OAL is usually dependant on the magazine length.

April 14, 2011, 10:15 AM	#4
Doodlebugger45 Senior Member Join Date: April 15, 2009 Location: Wyoming Posts: 1,717	Nick's method certainly works and I have done it before. But that is for when you already have a rifle built and you can measure it. Maybe I misunderstood the question, but isn't the OP in the process of builing a rifle? So he doesn't have a chamber to measure at this point. He wants to build the chamber to match a specific OAL, not the other way around.

April 14, 2011, 11:07 AM	#5
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	Well, yeah. That's why Nick and I both point out that... "max seated lenght to the ogive varies by the reamer." Adjust the throating reamer and make the OAL whatever you want. ??

April 14, 2011, 11:31 AM	#6
300magman Senior Member Join Date: September 12, 2008 Posts: 714	That is good information guys, but Doodlebugger45 seems to be the guy who understood me the best. I'm using a slightly extended long action/magazine that allows for rounds to extend slightly past 3.9" if necessary. And I do not have a barrel yet, I am in the process of having one made with a custom reamer, and I can have it set up pretty much however I want. I do not know if the maximum length of 3.9xxx would limit the extension of the 168gr ttsx from the case or not...but I was assuming that in all probability the max OAL would be limited by how long the combination of bullet + brass turned out to be, with the bullet seated the minimum acceptable depth into the brass.