Measuring Cartridge O.A.L.

Josh1978

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In March I purchased a Ruger RPR in 6.5 PRC. I have recently purchased the Hornady O.A.L. Gauge and a 6.5 PRC modified case so I could measure the bullet jump. The Hornady reloading data states that cartridge max O.A.L. should be 2.955 when using the 147gr ELD match bullets. The longest measurement I could get when measuring my chamber is 2.835. When comparing ogive measurements, a factory cartridge measured .104” longer than my modified case and bullet setup.
I am having a hard time believing that this gun is forcing a factory load into the lands .104”. I have to be missing something simple but I can’t figure it out. Any help would be appreciated.
Thanks,
 

918v

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It’s not just you that is having a problem with this. Another guy found out that if he shoved the bullet into the throat real hard he was able to get a better more accurate reading.
 

Josh1978

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I will try to apply more pressure when measuring and I will update with my results.
Thanks for the advice.
 
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Snuby642

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You are confusing base to ogive measurements with cartridge overall lenght.

Your hornady gauge and modified case measure distance to the lands at the point your bullets ogive touches it.

Do not cram it in there it should just touch.

Use a bullet comparitor to measure a loaded case to see how far to the ogive.

Oal is base to tip of bullet, and is good for mag lenth loading.
Hornady has videos.
 
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Josh1978

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I went downstairs and set everything up again and remeasured my chamber as well as a factory load.
I measured O.A.L. on a factory round (2.950”) and compared it to the O.A.L. of my modified case setup. (2.835) A difference of .115” I them measured case head to ogive on a factory cartridge and got (2.358) Then I measured case head to ogive on my modified case set up. (2.256) My measurements tell me that a factory round is being forced into the lands .102”. I am having a hard time believing this. Below are pictures I took when taking measurements.
5D6D33C1-F463-4EAA-AF8A-157662017E43.jpeg256F4E1F-5B71-4C9A-8F8D-1D36B440EBBD.jpeg8FA3015E-7B9D-4447-81B3-A479324788E1.jpeg89C4D921-8A96-4D9E-98E0-CF0273BB4A58.jpeg
 

Snuby642

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You have to use the same bullet.

Different bullet vary greatly in ogive location.
 

Snuby642

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I remember some thing about hornady messing up a factory load.

Check thier website. I could not find a press release on it but several websites said hornady screwed up.

I think there is a post on the hide, looking.
 

918v

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If your factory load chambers at 2.950” and you can close the bolt easily, then the Hornady tool is wrong. You cannot possibly jam a bullet that much.
 

918v

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Do this: Size a case and seat the bullet to something where the bullet is barely in the neck. See if it chambers and you can close the bolt. You won’t be able to. Then start seating that bullet deeper in .005” increments until you can close the bolt easily. That will be your working max coal.

A FL sized case has a lot of grip on the bullet and can overcome geometry problems during chambering.
 

Snuby642

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His tool, a starret caliper is off by 0.100, not likely.
 
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Josh1978

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Do this: Size a case and seat the bullet to something where the bullet is barely in the neck. See if it chambers and you can close the bolt. You won’t be able to. Then start seating that bullet deeper in .005” increments until you can close the bolt easily. That will be your working max coal.

A FL sized case has a lot of grip on the bullet and can overcome geometry problems during chambering.
I have sized case ready to go. I will go through the operations you have listed and report back my findings.
Thanks, Josh
 

Snuby642

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Which hornady ogive tool datum size are you using? Mine is not near so cant check.
 

Josh1978

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I have sized case ready to go. I will go through the operations you have listed and report back my findings.
Thanks, Josh
I did as you suggested. The bolt finally closed on an O.A.L. of 2.968. Measuring from case head to ogive was 2.383. This tells me that a factory load, (using the same 147gr Hornady bullet sets off the lands by .025”. This is a number that I feel better about. Thank you all for your comments and help. 😁
 
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Snuby642

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I print the page from saami for each caliber I reload and put it in my loading binder.

In case I get a wierd measurement I can look it up for a reference quickly.

Let us know how your load works out.
 

DownhillFromHere

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I also found the Hornady tool to be problematic. Over time, I've evolved this approach which gives repeatable measurements within a thousandth.
  1. Using a Dremel cutting wheel or similar, cut a slot in the neck of a resized case (both sides) down as far as barely into the shoulder (photo). This case will hold a bullet firmly for purpose but allow it to slip.
  2. Push the bullet of choice into the neck. If desired, use your seating die to start it as straight as possible.
  3. Push it into the chamber with your fingers (not the bolt). You should feel the cartridge stop cleanly when it reaches headspace depth.
  4. Push the cartridge out with a cleaning rod. This will be more consistent than pulling out a Hornady modified case.
  5. Repeat steps 3 and 4 a couple of times until very, very little pressure on the rod is required to start pushing the cartridge out. You now have a cartridge whose bullet is touching but not jammed into the lands. Repeating the insert/push-out process three times or so will yield a high level of concentricity.
  6. Take the CBTO reading with your comparator tool and record it. Record the COAL if you want it.
I "resize" my split cases every so often to get the most consistent pressure on the bullet pressed into the lands.

Now you can fiddle with seating depths with a reliable baseline.

It's worthy of noting that CBTO will vary with different bullets. This struck me as odd... seemed to me that the distance from the cartridge base to the "point" of the ogive where the bullet touches the lands would be independent of the bullet type. But it isn't; checking four different bullets (140, 147gr Hornady ELD-M, 139gr Lapua Scenar, 140gr Berger Hybrid) yielded four different CBTOs with a spread of 0.028 inches.

Make sure your seating stem is pushing on the bullet well below the meplat. Some of the long VLD bullets are so pointy that older stems engage the bullet right on the point and can yield inconsistent CBTO/COAL measurements.

77D67DF1-65C2-4417-A96B-CA5D41C22547_1_105_c.jpeg
 

Mr Tibbs

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Josh might I recommend that you take a piece of brass that was fired in YOUR rifle, take it to a gunsmith and have it drilled and tapped (9/32nd drill bit) & a 5/16x36 tap. The brass you bought from Hornady wasn’t fired in your rifle. A modified case that has been fired in your chamber will be more consistent.
 
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Gustav7

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Josh might I recommend that you take a piece of brass that was fired in YOUR rifle, take it to a gunsmith and have it drilled and tapped (9/32nd drill bit) & a 5/16 tap. The brass you bought from Hornady wasn’t fired in your rifle. A modified case that has been fired in your chamber will be more consistent.
Whats the TPI on the tap?
 

Josh1978

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Josh might I recommend that you take a piece of brass that was fired in YOUR rifle, take it to a gunsmith and have it drilled and tapped (9/32nd drill bit) & a 5/16x36 tap. The brass you bought from Hornady wasn’t fired in your rifle. A modified case that has been fired in your chamber will be more consistent.
I took a fired casing from my rifle and sent it to Hornady and had a custom modified case built. This is the modified case I am using in the pictures.
Should I have run the modified case through my sizing die before I used it to measure?
 

308pirate

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I did as you suggested. The bolt finally closed on an O.A.L. of 2.968. Measuring from case head to ogive was 2.383. This tells me that a factory load, (using the same 147gr Hornady bullet sets off the lands by .025”. This is a number that I feel better about. Thank you all for your comments and help. 😁
Cartridge overall length (from base to tip) is irrelevant when comparing it to the distance from breechface to start of the rifling. Your references to that number keep confusing you and confusing this thread.

I use a much simpler Sinclair OAL tool and get repeatable results.
 

Mr Tibbs

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I took a fired casing from my rifle and sent it to Hornady and had a custom modified case built. This is the modified case I am using in the pictures.
Should I have run the modified case through my sizing die before I used it to measure?
Josh the modified case should not be ran through your sizing die, that case is snap shot (picture)of your chamber if you will.
 

918v

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Cartridge overall length (from base to tip) is irrelevant when comparing it to the distance from breechface to start of the rifling. Your references to that number keep confusing you and confusing this thread.
It’s relevant if you’re trying to see why your perceived max coal is .120” shorter than SAAMI.
 
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db2000

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FWIW, using the same Hornady OAL tool and factory case (not shot in my rifle) in my Christiansen MPR 6.5 PRC w/ Berger 156 EOL (OG 0.895), I measure 2.408 base to the lands and am limited by the mag loading BTO 2.237. I could probably go to 2.250 but that's about it. That seems like a lot of jump. I've measured this several times. I use firm pressure on the case in the chamber and that with the bullet touching the lands but not sticking in them when I remove the rig. I will try the advice above from 918v and report back later.

With BTO of 2.237 COAL is 2.940 fyi
 

Josh1978

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Josh the modified case should not be ran through your sizing die, that case is snap shot (picture)of your chamber if you will.
I didn’t think that I should size that modified case. I just can’t seem to figure out why I get crazy measurements when I use the Hornady tool.
 

Mr Tibbs

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Josh may I suggest that you go to YouTube, there’s video from Panhandle Precision (Sam) CBTO which may help you
 

Josh1978

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So I decided I would set my rifle back up and check it again. I used the same tools as before. I took multiple measurements and continued to get 2.369” measuring from case head to ogive. Comparing it to a factory bullet that measures 2.359 I figured out that the bullet sets off the lands about .010”. This is something I can live with. I have no idea why I was getting off the wall measurements before.
I am just happy that I am getting better measurements. I want to thank you all for the help and education!
Josh
 
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Snuby642

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A lot of people complain about the hornady tools especially that one.

Once you get the feel for it, works fine.

Good luck on your loads.