Gordons reloading tool over pressure?

[national86]

I using the Data from Hornady 11th edition and was curious what Gordon reloading would give me. I'm using a Hornady 87gn A Max, Starline brass once fired and measured water volume 34.6gn. Powder is Vihtavuori N133 with a 10 shot and .20 grain ladder. Why is it showing over pressure for Hornadys max load. If someone can look at it and see if there is something I inputted wrong. Also it is a 26 inch bolt action. Thank You    

[BD1]

This is the main reason I spend time on this forum. I am not familiar with Gordons Reloading tool, but I am very familiar with Quickload, (I've been using it since 2009), and QL also shows Hornady's max load data to be well over the Sammi upper limit for the 6MM ARC.
IMHO the 6mm ARC data is all over the map. I am using Starline brass. Quickload's default case capacity is 34.5 grains of H2O at overflow, my twice fired Starline brass trimmed to 1.480 holds 35.4 grains.  I emailed Berger for their data, and what I was sent is so conservative that their loads won't even lock my bolt back until I get near max. Hodgon's loads are sort of the middle ground, but they list loads as "compressed" that don't fill my cases to the shoulder, so you're left wondering if the loads are limited by pressure, or by case capacity.  I'm curious where all the variation comes from. Having separate data for bolt guns vs gas guns sure doesn't make it simpler. And, whether all of this data was in fact developed in a lab using a pressure transducer, or maybe just computer predictions?  With Quickload adjusted to my barrels particular dimensions, my particular load parameters and my fired brass case capacity, it tracks my results using Varget pretty closely. It also tracked the lower level loads using LVR pretty closely with the 105 Bergers, but the real world velocities and QL's predictions start to diverge as I advance up the load latter.  And the 107SMKs on top of LVR don't track at all.
Does anyone have the latest version of Sierra's load manual? I'm not seeing their data online. I have the 5th edition, but I'm too much of a Yankee to pay $50 just to see the 6mm ARC pages in the 6th edition. Why can't they just sell me the pages with new data? I already have the three ring binger with their logo on it, and the other 1,000 pages that didn't get changed for this edition

[national86]

I have the Sierra 6th edition first printing and does not list the 6mm ARC. The 51st edition of the Lyman reloading manual has 6mm Arc and they list the Hornady 75gn Vmax, 90gn Nosler E-Tip, 103gn Hornady ELD-X, 105gn BTHP, Sierra 107 jacketed MatchKing. I Emailed Sierra about load data for the 6 ARC about 3 mounts ago and have not heard back.

[national86]

Ok, after my reply I decided to check my spam folder and there it was, Sierra did respond and sent me some data for my bolt gun.
  Sierra 6MM ARC Bolt Gun 62,000 psi.pdf (Size: 234.8 KB / Downloads: 17)

[grayfox]

Y'all are running into the same issues that have confronted me. First, note that Hornady's data is with their brass, which differs from Starline capacity. But (not being patient enough to get into QL) I've developed a workaround for me in Grt, that works, although truth be told it is not perfect and won't cover all the bases.
First caveat, this is info only, and use at your own risk. It works for me in a limited way, but beats not having anything to go on as well. YMMV.
Even with Grendel there was talk somewhere that these short powder-column cartridges, with small diameter bullets, needs some tweaking to even come close. One thing is that (theory) the primer firing can unseat the bullet enough to make the chamber effectively more "room" than just measured cc capacity, until the bullet obturates and seals the gas behind it. Another is that the Sebert factor differs for these cartridges from the default of 0.50... due supposedly to some of the powder "following" the bullet farther down the barrel more than the more standard, 308-style cartridges. I can't prove or disprove these, but I did put them together for my workaround...
1. For 6Arc and 6.5 grendel, I change the Sebert to 0.45, a factor that I played with a bit to find something that works pretty well. ie, more powder follows down-barrel when Sebert is below 0.5.
2. I use the hornady data (or hodgdon for that matter), and develop a "calibrated" round for a Hornady bullet, using bullet, oal, and powder charge, then adjust the case capacity until I get the Hornady book value. From that cal value I can find 1 or 2-off load data that pretty much tracks with my results.

For bolt action I use the 62ksi limits and Hornady bolt action data. Hodgdon sticks to 52 ksi for its data.

So if you do this, you would start with the 87 gr Vmax as your bullet, at the book oal of 2.140 (iirc, going from memory) and stock 6Arc case data, then add the powder and charge weight, 18" barrel, 52ksi limit, then change the case capacity to get a "calibrated" load sheet. Save this as "18-AR-87Vmax-powderxx-cal.grt" (example load sheet name), then you can do 1-offs from it, sometimes 2-off deltas. like swap in the 87 gr Amax, and move its seating depth to your load to get a feel for it, and your barrel length. Save your 1-offs under a different sheet name. I store each rifle, each barrel length, basically in its own sub folder. Organizing helps you retrieve load data.

I don't know in Grt how to "calibrate" powder burn rates or energy which can vary up to 10% lot to lot, so this case cc delta is my workaround (I've seen 1-2% but never 10, but there you go). You won't be able to always tell exactly what % load you're at, maybe in general, but from your loading bench you can develop a feel for it.

Anyway it has worked for me as a usable guide. I'm sure there are better ways to do it, but this is one I've found for me.

Edit to add: once you have chrony data you can tweak your specific load sheet to match your actuals, I usually use case capacity again, along with the other real world data from that cartridge load. I then save it and add "chron" to the file name.

[dfosland]

To add info regarding differences from the Hornady info an GRT, if you are using the Bolt Action load info, as Grayfox confirmed at 62K PSI, look at what GRT has set for max pressure, 52K. If you manually adjust the max pressure to 62K (I set it to 61K just because), things will start to look closer to what the Hornady app/book lists.

[BD1]

Does anyone have a good idea of the case capacity of the Hornady brass in overflow grains of H2O as compared to a Starline case? The comparison is necessary as this will vary rifle to rifle. IMO the best way to measure this is to fire a new cases, resize with minimal shoulder setback, trim it and fire it a second time before measuring. This process will provide a valid answer on a relatively small sample like five cases averaged.

---

Ok, after my reply I decided to check my spam folder and there it was, Sierra did respond and sent me some data for my bolt gun.

I have to wonder why they are seating that 110 grain SMK so Short? 2.245 in a bolt gun?

[GRH]

I use N140 and my preliminary GRT load file was within 20fps of my chrono results, but I see no mention of running OBT.

In order for GRT to most accurately reflect what's happening you must run OBT. N133 is well represented so I would tend to believe the results after running OBT. Otherwise you're just getting generic data that does not reflect the individual set of circumstances.

In case anyone is wondering... (I did my best here)

Add your chrono results into the "Measurements" tab, save, and then run OBT. The first window to open will show you what it's calculating, and provided everything was previously input correctly, the only thing need doing is check/change the distance to chrono and click compute.

After that it will show a OBT file that is an accurate representation based on your chrono numbers and data. Then if desired, you click "compute node charge adjustment" and it will create a OBT file targeting the next nearest lower (theoretical) charge node.

The OBT file can be saved before computing a node charge adjustment or after. Either way, the only way you should move forward with any certainty, is to stop using or discard your preliminary un-calibrated file, and use your now calibrated OBT file.