Hornady OAL Gauge

hybridspecies

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Hi all, I'm looking for guidance on the correct usage of the Hornady tool after using it to load some rounds recently that ended up with flattened primers:

I used the OAL gauge with a generic 6.5 CM modified case to measure the CBTO in my Savage 12 LRP rifle. I inserted the body into the chamber until it rested against the shoulder and then pushed in the plunger stopping at the first sign of resistance. The CBTO measured 2.0000" on average using my mitutoyo digital caliper. On my 5th measurement (using the same bullet) I wiggled the plunger a little after initial resistance and the bullet slid in an additional 0.25" before stopping again. I did not force the plunger, just rotated it and the bullet slid in further without any pressure. I repeated this another several times with the same results. The CBTO measurements afyer wiggling were an astonishingly consistent 2.2500."

I loaded 100 rounds using new Lapua LR brass, Berger 140 hybrid target bullets, H4350 powder, and CCI BR-2 primers seated at 2.2300" (0.020 less than measured CBTO) and cycled a number of the rounds without feeling any resistance or seeing markings on the bullets. I measure COAL before and after cycling and it did not change.

I took the rounds to the range and had very good accuracy with reasonably low SD measurements (8.6 fps at 41.5 gn and 9.0 fps at 42.5 gr of H4350). The issue was that all of the primers were flattened which makes me wonder if I had seated into the lands of the rifling using the 2.2300 CBTO length?

Should I have used 2.000" CBTO as my seating reference? COAL for my loaded rounds was 2.9375" on average using the 2.2300" CBTO seatinng depth.

The online Hodgden reloading resource lists 40 gr of H4350 as max with a Hornady 140 gr bullet, but Hornady ammo boxes indicate (or at least they used to indicate) that their 140 gr A-Max rounds were loaded with 41.5 gr of H4350. I had heard that earflier versions of the Savage 12 LRP CM rifles had tight chambers resulting in popped primers, but my gun is new production so I wouldn't suspect that this is the problem either.

Thanks for your thoughts.
 

MagnumManiac

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Feb 25, 2008
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3,628
Take a case, cut 2 slits in the neck opposite each other, clean up any burrs on the inside and outside, size it, place a bullet in the neck and chamber it gently. Close the bolt, open and close the the bolt gently and slowly a few times, then carefully remove it from the chamber. If the rifle has a plunger ejector, place a finger on the side of the case as you withdraw it so that the bullet makes no contact with the action.
Measure the COAL/CBTO and compare with the Hornady measurement.
It won’t be exactly the same, but definitely won’t be .250” different.
This measurement should be your ‘touching’ measurement which will be .003-.005” into the taper cut on the start of the rifling.
If you do this several times, you will get a feel for doing this very accurately, I no longer bother with Hornady measuring tools, they are clumsy and often not accurate enough.
My Stoney Point Headspace Gauge set are the only tools I use these days.
I have found the Sinclair Nut for bullet measuring, RCBS Precision Mic and a few other doodads work perfectly for me in my F-class pursuits. The RCBS Precision Mic is the most accurate headspace measuring tools you can buy, and it covers several cases if based on a parent family, like 30-06 will cover ALL 30-06 based cartridges, as does a 308 etc, etc
I have actually sold or given away at least half of my doodads I used a few times and found unnecessary. I am now a minimalist with my loading gear. Although every barrel/rifle has it’s own set of dies and combinations of dies and mandrels.

Cheers.
 

hybridspecies

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Messages
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Did you ladder up to 41.5gn? My initial reaction was "that's not a starting load", and it's over book max from Hornady and Nosler from the get go.
Berger lists 42.3 gr H4350 as max with their 140 grain elite hunter bullet so I laddered up to 42.3 gr in 0.1 gr increments starting at 40.4 gr. The primer pockets looked the same after firing for each load. No signs of ejector marks, piercings, or gas leakage, just more flattening than I'm used to with CCI primers. I found an accurate node at 41.8 gr with average muzzle velocity of 2842 fps and SD 5.0. Below is a photo of the Hornady ammo box specifying 41.5 gr of H4350 under a 140 gr Hornady A-MAX bullet.
140 gn Hornady AMAX 6.5-Creedmoor-1.jpg
 

hybridspecies

Active Member
Joined
Jul 9, 2021
Messages
26
Location
California
Take a case, cut 2 slits in the neck opposite each other, clean up any burrs on the inside and outside, size it, place a bullet in the neck and chamber it gently. Close the bolt, open and close the the bolt gently and slowly a few times, then carefully remove it from the chamber. If the rifle has a plunger ejector, place a finger on the side of the case as you withdraw it so that the bullet makes no contact with the action.
Measure the COAL/CBTO and compare with the Hornady measurement.
It won’t be exactly the same, but definitely won’t be .250” different.
This measurement should be your ‘touching’ measurement which will be .003-.005” into the taper cut on the start of the rifling.
If you do this several times, you will get a feel for doing this very accurately, I no longer bother with Hornady measuring tools, they are clumsy and often not accurate enough.
My Stoney Point Headspace Gauge set are the only tools I use these days.
I have found the Sinclair Nut for bullet measuring, RCBS Precision Mic and a few other doodads work perfectly for me in my F-class pursuits. The RCBS Precision Mic is the most accurate headspace measuring tools you can buy, and it covers several cases if based on a parent family, like 30-06 will cover ALL 30-06 based cartridges, as does a 308 etc, etc
I have actually sold or given away at least half of my doodads I used a few times and found unnecessary. I am now a minimalist with my loading gear. Although every barrel/rifle has it’s own set of dies and combinations of dies and mandrels.

Cheers.
Thanks. I'm intrigued by the RCBS Precision Mic. Does it use an actual bullet or a simulated bullet for measuring seating depth? Hornady says that using the actual bullet is necesary for accurate measurements? My understanding is that the Hornady OAL gauge is the same as the Stoney Point Gauge (maybe Hornady bought the rights??). When I use the Hornady gauge my bullet usually sticks in the rifling so I'm not sure that chambering a dummy round with a slit neck would have enough tension to allow the bullet to be withdrawn without shifting position or remaining in the case altogether in my rifle.
 

hybridspecies

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Messages
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Sounds like you've found your cbto. Now need to back off your over pressure powder charge
So the longer CBTO (2.2500") is the correct measure? I was wondering if maybe the higher pressures were coming from the bullet being jammed into the rifling at ignition. This is a long range shooter (1000 yards plus) so I was hoping to maintain 2800 fps muzzle velocity, which I wouldn't be able to do with H4350 below 41.5 gr out of my 26" barrel. Bummer if this is the problem because accuracy was under .5 MOA at a MV of 2842 fps using 41.87 gr of powder. Thanks.
 

MagnumManiac

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As I stated, the case needs to be sized prior to doing this.
There is sufficient grip for me when I do this.
The Precision Mic uses a generic bullet, but if you then use a bullet nut comparator, the distance to touching is the same, the only difference is where the ogive touches on different bullet profiles.
Anyway, I think you have found your CBTO.

Cheers.
 

QuietTexan

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Nov 16, 2020
Messages
511
Location
Texas
Do you have any other primers to try? A flattened primer is not always a pressure sign - absent carbon leakage, pin cratering, ejector wipe, or other signs it could mean excessive headspace. I don't thing you were hard jammed into the lands at -0.020" using the tools how you did. Reshooting with once-fired brass that has not been minimum-FL sized could change the primer signs. Shoulder measurements on new versus fired brass?

COAL-wise I have two 6.5CMs that shoot fine sat out around 2.900" depending on the bullet (Hornady 140 ELD-M and Berger 153.5 Hybrid), just can't use the mag that long - neither is jammed at that length. The BTO measurement is dependent on your tools vs mine, but sounds reasonable based on your COAL.
 

hybridspecies

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Messages
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Location
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Do you have any other primers to try?
The only other large rifle primers I currently posses are Winchester 8 1/2 magnums and I don't see much for sale at the moment either. I haven't deprimed yet, but assumming the primer pockets are still in good shape I plan to reload the spent brass shortly with the same bullet and powder combination. I usually full length size setting the shoulder back 0.001, but I think I'll just neck size per your advice to see how that affects the primers. Thans for the confirmation on OAL.
 

hybridspecies

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Messages
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Location
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A couple other thoughts as I work through this, first, Berger 6.5 mm Creedmoor 140gr Hybrid Target Rifle Ammunition uses Lapua brass and their stated muzzle velocity of 2850 fps is very close to what I was getting with 41.8 grains of H4350 (2842 fps) using the exact same bullet and brass, so I'm leaning towards ruling out the brass and my charge as the source of overpressure (if any). COAL length of the Berger ammo is much less at 2.810" than I was using (2.9375") so seating depth is still a potential area of concern. Second, the Lapua brass has the Palma sized flashhole (0.059" vs the standard 0.080") and I'm wondering if that might be contributing to the primer flattening that I'm seeing? If anyone reading this has used this factory Berger ammo did you also notice primer flattening? Thanks.
 

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