Differences between the loading "bibles"

[hdwhit]

hmonnier asked:
"...'should I take the lowest of the max across the different books' as the max load?"

No.

You should follow proper load development procedures and begin with the Starting Load (if there's a difference between manuals, use the lowest or take a consensus) and then work up incrementally until you get a load that 1) functions the gun reliably and 2) is accurate. Once you achieve this, stop. That's your load.

If you reach the Maximum Load and still haven't achieved reliable function and accuracy, then look to a different powder, bullet or primer and start developing the load again.

[44 AMP]

I think it is kinda weird though how all the 120 and 130 load data mirrors the 6.5 CM yet the Hogdon number for the 142 compared to the CM jumps 7 or 8 percent. To me that is a red flag

I understand how the sudden dis-continuity for no apparent reason, gives one pause and makes you go "hmmm I wonder why that is???"

But I think that, rather than just saying "its got to be bad data", I think the key is apparent reason.
There is always a reason. In this case, we don't know what it was that caused the difference, and Hodgon didn't say. It's even possible the members of the test staff don't know the reason, but there is a reason.

Why do two guns as identical in all aspects as we can make them shoot the same ammo and show differing muzzle velocities? There are reasons, even if we can't pin them down, exactly.

they report what they got. Sometimes they say why they got what they got, often not. It doesn't have to make sense or be in line with all the rest of the data, if that's what they got, its what they got. It MIGHT be what you or I get, it might not.

years ago I had a rifle that loved a load that was a full grain over the highest listed max I could find in anyone's book. It shot well (which is usually NOT the case with max loads), there were no pressure signs on the case or primer, case life was normal, everything was as good as it ever got with anything. And yet, it was well over book max. For that rifle, and ONLY that rifle, that load wasn't "max".

Had another rifle, cratered primers with everything you put in it, low starting load, factory load, everything showed excessive pressure. And no, it wasn't the firing pin or the hole or any of those parts. It was the chamber. Just a little too tight in the throat, so the case mouth didn't have the usual amount of clearance to release the bullet, which raised the pressure on every load fired. in that case it was something that could be, and was, fixed. But it was just a tiny bit of not quite enough, and within the acceptable tolerance specs (though at the extreme end of the range).


Different things in different guns can cause different results, with different bullets. Apparently there was something just enough different between the rifle and the 142gr bullet and the rifle and the 120 nd 13gr bullets to cause a "weird" result. What it was, they didn't say.

[hounddawg]

you know I have a pair of .260's don't ya ? One a 24 inch Criterion and the other a 30 inch Shilen. You know what when I try this load in that rifle I am going to treat the the same way I am treating the Shilen. That 6.5 CM data is working just fine for me. Common sense just ain't common it seems

https://i.imgur.com/JlvAgEU.jpg

https://i.imgur.com/S3cHsw4.jpg

[Rimfire5]

Overall bullet length isn't the key measurement in making this comparison.
Given identical cases, seating depth and shank seating depth would be more important when determining pressure differences and where PMax might be.
Incidentally, no one knows if the specs of the cases tested were the same so the volume of the cases can't be compared.

For a 6.5mm Creedmoor according to QuickLOAD, using IMR4350 powder at identical seating depths (2.810) and cartridge trim lengths (1.910)

Hornady 140 grain A-Max #26332 (bullet length = 1.375) would yield 63,060 psi at 44.1 grains of IMR4350 at 59 deg. F. The seating depth would be .475 and shank seating depth would be .325.

Sierra 142 grain SMK #1742 (bullet length = 1.380) would yield 63,501 psi at 44.1 grains of IMR4350 at 59 deg. F. (That is over the 63,091 psi PMax.) The seating depth would be .480 and shank seating depth would be .290. Notice the difference in the shank seating depth between the two bullets.

Just for comparison,
A Sierra 140 grain SMK #1740 (Bullet length = 1.320) would yield 60,416 psi at 44.1 grains of IMR4350 powder at 59 deg. F. The seating depth would be 0.420 and the shank seating depth would 0.230.

A Hornady 140 ELD-M #25331 (Bullet length = 1.380) would yield 63248 psi at 44.1 grains of IMR4350 powder at 59 deg. F. (That is also over the 63,091 psi PMax.) The seating depth would be 0.480 and the shank seating depth would be 0.330. Note that the pressure data looks a lot like the data for the 142 SMK doesn't it.

The deeper placement of the bullet in the case increases the pressure.
Also, a heavier bullet should also increase the pressure with the same loads.

Also the temperatures during the testing weren't listed.
If the temperature during the testing of the 142 SMK was 37 degrees instead of 59 degrees, the pressure at 44.1 grains would drop to 61,288 psi.
At 37 degrees, 44.5 grains of IMR4350 would yield 63,051 psi (just below PMax).
Could be it was colder on the day they tested the 142 SMKs than it was when they tested the 140 A-Max bullets..

[hounddawg]

Sierra 142 grain SMK #1742 (bullet length = 1.380) would yield 63,501 psi at 44.1 grains of IMR4350 at 59 deg. F. (That is over the 63,091 psi PMax.) The seating depth would be .480 and shank seating depth would be .290. Notice the difference in the shank seating depth between the two bullets.

computer theory is all well and good however in real life I got initial pressure signs at 42.0 grains and at 42.5 grains blew a primer. The Hogdon data uses a 142 SMK for it's 142 gn load data and I am seating between .040 and .045 off lands and shooting in mid 70's temps

I stopped at 42.1 yesterday and my primers were flush but beginning to show initial pressure signs flattening out and getting minor cratering. Pretty sure if I kept pushing just because the book or Quickload said it is ok I would have been splitting cases, blowing primers and taking a chance on having a emergency room visit.

I stopped a full 2.0 gns below what Quickload and 2.5 gns below the Hogdon calls dangerous because I used this thing called common sense. I know that some here won't believe this but sometimes the book is just wrong. Throw out all the esoteric theory in the world and those primers would still look just the same in real life.

Now who am I supposed to believe, the book, the computer program or my eyes ?

[agtman]

'Pet Loads' by Ken Waters.

None better out there.

[Rimfire5]

Hounddawg,

There are a lot more variables that cause overpressure with lighter loads than just powder charges.
For example, a tight chamber will also cause high pressure indications with loads that are far below PMax.
I had a Savage 12 LRP 6.5mm Creedmoor that would show high pressure indications with loads that were close to minimum on the powder tables.
Savage reamed out the chamber a few thousandths and the high pressure indications went away and I can now shoot loads close to PMax with no high pressure indications.

Even if you don't want to believe it, computer simulations based upon measurement data like QuickLOAD provide individuals who want to understand the relative effects of the variables related to powder type, load charges, seating depth, trim length and temperature with information that leads to understanding. Those relationships are all good to understand, but if you don't also consider all the other reasons for variations as well you are just fooling yourself as much as you would by refusing to use information to that is available to increase your understanding.

[hounddawg]

you are just fooling yourself as much as you would by refusing to use information to that is available to increase your understanding.
Rimfire5 is online now

actually you are the one fooling yourself by believing what the book says over real life results. Books data is not infallible .There is no tight chamber causing over pressure, this was the 4th powder I have tried in that rifle using the same bullet.

Varget, H4831 SC, and IMR 4350 book loads all had normal velocities and no overpressure indications with the same bullet in the same barrel. I tested each one from min to max or near max looking for stable velocity nodes. I never had any pressure issues with any other powder using the book loads until I came to the H4350

baffles me as why anyone is still arguing this other than the sake of saying I am wrong. One poster even went as far as calling me a liar.

[RC20]

I don't think you are wrong so much as taking it out of context.

I suspect Quick Load shows a low load as well?

Given the chance I would cross check with my manuals, but those same manuals also disagree and sometimes by two (maybe upwards of 4) grains, that is a lot.

If you start low and work up like you should with any load, you may find that sooner than Quick Load or the highest Manual load showing there be dragons.

Its a guide not a firm, but then so are the manuals.

That is why we start lower and work up regardless of who says what.

So yes in the end you are right that its the real world that counts but that is true for both sources.