Why the big discrepancy with published load data?

[HighnDry]

So, I'm reloading for a 7mm Rem Mag with H1000 and 150 gr Barnes TTSX.

Barnes' reloading data from their website for 24" 1:9.5" twist:

Minimum 61.0/2758 fps

Maximum 67.7/2998 fps

Hodgdon's reloading data (same bullet) from their website for 24" 1:9.5" twist:

Minimum 67.2/2847 fps/49,200 psi

Maximum 73.8/3083fps/59,100 psi



Why the big discrepancy? Does anyone have a recommended load for this combination?

 

[A382DWDZQ]

Nearly same thread here. But, not a definitive answer to the question. Might be worth checking with one or both manufacturers.

 

[Grassymike]

Start low and work up slowly. Stop when you see signs of too much pressure. A primer that shows signs of being "flatened" is the signal to back off .

 

[Wyobohunter]

I’ve found the same thing. Still don’t know why. Make 100% sure Hodgdon is using the same exact bullet. Those mono metal bullets cause higher pressure.

Once you are positive, begin with the Barnes start load. Consider the Hodgdon data to be max and work toward it.

Use a chronograph as well as inspect your fired cases/primers. The chronograph is an important tool. If your ES & SD aren’t good and your V is significantly higher than expected it’s time to back down.

If in doubt stick to the Barnes data. The extra 85 fps isn’t a big enough gain to risk anything. You’ll never notice a significant ballistic advantage.

That’s how I’d do it anyway.

H1000 is slow burning, slow burning is somewhat forgiving so the difference may just be accuracy results from each manufacturers test barrel.

 

[Wyobohunter]

Also, if you are fairly new to reloading and/or new to reloading belted magnums…

Belted magnums headspace off of the belt. Either FL size or do some research before neck sizing.

 

[Pickettpuncher]

Lawyers….

 

[Bull_n_heat]

Pay attention to your rifle when working up in loads too. A heavy bolt lift should appear before the flattened primer and might be a more reliable indication of pressure going to high (at flattened primer it might be too late).

 

[Wyobohunter]

100%

 

[35WhelenAI]

It's common knowledge in experienced reloading circles that different powder lots, different case brands, different primers, different chambers and barrels all contribute to varying results. I've seen 100 to 150 FPS variation between two lots of powder from major manufacturers when bought at different times. It's just a fact. Then a magnum versus non-magnum primer, a case with more capacity or less capacity, was the chamber cut with the same reamer. Think about it. It is what it is, start low and work up.

 

[Bull_n_heat]

It's common knowledge in experienced reloading circles that different powder lots, different case brands, different primers, different chambers and barrels all contribute to varying results. I've seen 100 to 150 FPS variation between two lots of powder from major manufacturers when bought at different times. It's just a fact. Then a magnum versus non-magnum primer, a case with more capacity or less capacity, was the chamber cut with the same reamer. Think about it. It is what it is, start low and work up.

I've actually seen 50-100 fps variation in muzzle velocity out of a rifle of mine that is shooting sub-MOA loads. Hard to explain how that works in physics land, but where the bullet lands is consistent as little sense as that makes from the numbers.

And the velocity numbers from the gun were close to 200 FPS below the book estimates. It's become my expectation to come in well lower than the book numbers.

 

[moose375]

Hi , my name is Tim and I just joined this group . I'm interested in buying your Barnes 190 x 308 bullets but I'm unable to respond to your add. For details could you e-mail me at "[email protected]" Thanks Tim

 

[35WhelenAI]

I've actually seen 50-100 fps variation in muzzle velocity out of a rifle of mine that is shooting sub-MOA loads. Hard to explain how that works in physics land, but where the bullet lands is consistent as little sense as that makes from the numbers.

And the velocity numbers from the gun were close to 200 FPS below the book estimates. It's become my expectation to come in well lower than the book numbers.

The shot to shot variation makes more of a difference at really long range. At 100 yards a load with a high(ish) extreme spread or standard deviation can still group really well, but that velocity gap opens up groups down range.

I was looking at my reloading notes and I've had different lots of H1000, IMR3031, IMR4064, RL 22, H4350, IMR4350, H870 that had enough difference in velocity that the final load (charge weight) was not the same as the lot before.

 

[wyosam]

I’ve been faster than book values, lower than expected book values, and everywhere in between. Remember that every barrel and every chamber is a little different, just as there are variances from lot to lot of powder, primers, and bullets. Those numbers in the book represent what they found with their test barrel, more and more with a little left on the table for the lawyers.


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[wind gypsy]

Just remember folks, "it's dangerous to deviate from book loads"