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Why start at 10% below maximum?

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Unread 08-14-2011, 08:27 AM
Bronze Member
Join Date: Mar 2011
Posts: 48
Why start at 10% below maximum?

Everything I read says that we should always start at 10% below the maximum listed in the manuals and work up.

Using the IMR loading sight as a reference and using their standard 270 Winchester, 130 grain Hornady bullet, they list maximum velocities of from 2884 to 3085. The typical commercial round is about 3060. The "standard" load of H4831 lists 3019 fps.

Taking the "standard" H4831 as a reference they list starting load at 56.0 and maximum at 60.0C. Actually the 90% starting load would be 54.0. This is with a maximum pressure (60.0C load) at 51,000 CUP.

Going to the Hornady website and checking their 130 grain Interlock ammunition, it is listed at a velocity of 3060 fps.

Unless they have some magical powder, that means that they are running their pressure at about 50,000 CUP plus. When I check primers of fired brass in standard hunting rounds the primers are flattend a great deal more than any I have seen from my handloads at what I use as "max" loads. And I typically load at the max loads listed in the manuals. That means they are running their pressures up there close to max.

So, why wouldn't I have to buy some factory loads that start at 90% (velocity in the 2850 fps range) and work up slowly to be sure it is safe in my rifle to shoot a standard commercial round that is obviously loaded at near, or over, the max listed in the reloading manuals?

I understand that the companies are all lawyered up, and everyone wants to be safe in what they recommend. But has anyone ever experienced an actual case, themsleves, of a load reaching maximum pressure indications in a load that was more than 2% below the maximum listed in the manuals? In 40 years of reloading, I never have.
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Unread 08-14-2011, 09:06 AM
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Join Date: Aug 2011
Location: Pueblo, CO
Posts: 371
Re: Why start at 10% below maximum?

I am 19. When i started reloading on grandpas old RockChucker RCBS press i wanted to make the best ammo i could make. I wanted a 44 mag round that would throw the gun out of your hand, i wanted a .223 round that would blow a hole in a 6" tree.

I know about powder charges and exceeding the max range. I also know after having lots of cases fracture and primers flatten that there is a limit to how much explosives you can fit into the weapon.

With that being said i am convinced that your statement of
"I understand that the companies are all lawyered up, and everyone wants to be safe in what they recommend."
is true.

Now here is some good news. I shoot my .270 Win religiously and love my handloads. My load was worked up in 1/10th grain increments for accuracy at 100M using my 700 ADL (i was one of the lucky ones with a really accurate one). Here is my load:
150 gn Sierra Boat Tail Spire Point
56.0 gn H4831 Powder weghed with a balance scale (i can see individual grains and get it perfect).

Look into the 150's i love them. If you are still going to use the 130 then i reccomend starting right in the middle of the suggested powder charge (I use all the manuals as well so i kinda average them all out), and work up to the max in 1/2 gn increments. If you look at loading data for the 150 56.0gn is towards the upper part of the load and its the most accurate.
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Unread 08-14-2011, 09:17 AM
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Join Date: Jun 2007
Location: Wilmington NC
Posts: 4,777
Re: Why start at 10% below maximum?

There are several reasons for what you are seeing.

1. The data in the manual is ONLY accurate in that particular gun chamber, with that throat, etc that they tested the loads and listed in the manual. Want to blow your mind, compare different manuals from different sources and even previous editions.

2. Component variation will cause pressue to go up or down. Pressure testing has shown that changing primers alone can raise pressures over 5000 psi. Plus with many powders you have lot to lot pressure variations. Did they test a slow or fast lot? That is also why they tell you when you change components to start over.

That why I love the Quick Load "experts" that jump out and say this load is over pressure or not based on their doodling with QL. If you talk to QL techs, they will tell you it is an average and cannot be applied to specfic guns that are outside their test parameters they used to determine their data. You can go into QL afterwards and adjust certain parameters to equal what you are showing in testing. When someone posts a QL chart, you do not know what the internal parameters are set and and you can vary pressue printouts by over 7000 psi by that alone for the exact same load if you do not watch it. Done it and seen it erroneously done on this board. It is just another tool to give you starting indicatores that can ONLY be validated as accurate by pressure testing with a strain gauge. No one outside of labs is using copper CUPS anymore.

3. Lot of old guns out there that are weaker in action strength than modern guns, yet they are chambered in most of the modern calibers. ie 98 mausers for example.

4. Flattened primers by themselves is not a reliable indicator of pressure or absence of pressure. Primer cup hardness greatly varies between brands. Good example is everyone has learned to use the CCI 450 primer in the BR cases because of that to prevent primer piercing and flow.

5. Using just visual indicators of pressure, it is difficult to actually determine what is under max SAAMI pressure. Without an accurate pressure guage it is a guessing game where you have to rely on the total sum of indicators not just one. You cannot say, load until the bolt locks and then back off two grains for example as some say. You have to look at all of them and understand when you see the totality of pressure indicators, you know you are over but not how far or in their absence, how far you are under.

6. Load manuals are based soley off rounds loaded to no more than max COAL for hunting purposes. Put a bullet into the lands, as many do here and pressures jump with the same load.

7. Always start testing from one of two points: IF it is a magazine gun, start at max COAL. If it is a single shot, start into the lands. You only have one way to go; back!!!

Build a load that is accurate as you want and need, and as fast as you think is reasonable and be happy. Is 50 fps going to make or break a LR shot? Doubt it.


Last edited by BountyHunter; 08-14-2011 at 10:12 AM.
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Unread 08-14-2011, 09:44 AM
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Join Date: Aug 2011
Location: Pueblo, CO
Posts: 371
Re: Why start at 10% below maximum?

I see your points. I have no experiance with the pressures other than as you say looking for indicators. Many times on my .357 mag brass i see lateral rips in the brass from my uber hot loads i used to do. Now i just load for accuracy.
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Unread 08-14-2011, 10:39 AM
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Join Date: Oct 2007
Location: Patagonia Mountains, Arizona
Posts: 770
Re: Why start at 10% below maximum?

Originally Posted by ballistx View Post
(snip)I understand that the companies are all lawyered up, and everyone wants to be safe in what they recommend. But has anyone ever experienced an actual case, themsleves, of a load reaching maximum pressure indications in a load that was more than 2% below the maximum listed in the manuals? In 40 years of reloading, I never have.
You have the choice of starting where you want when reloading. I choose to start with 10% reduced loads when I change components or change the firearm the ammo will be used in. While it is a safety precaution it's also the first step of a "ladder test" to determine where the firearm will have accuracy nodes. The lower pressure loads are not "wasted" They are part of achieving accuracy. Best accuracy may or may not be found at "factory" pressure or SAAMI max levels. That's the main reason I handload, to achieve better accuracy than I get using factory ammo. For some firearms factory ammo works just fine. Factory loads however are nearly always limited to SAAMI dimensions which are often not optimum.

Pressure signs are not the same for all cartridges or for all firearms using the same cartridge.. Primer flattening and case head growth may work fine for modern high pressure rifles but it may not be good for low pressure firearms like AR-15s with large diameter cartridges or antique rifles or some pistol designs. An example is the 6.5 Grendel where bolt or barrel extension breakage is likely if you use the same pressure signs as are suitable for a 223 AR-15.

There are lots of factors which affect the peak chamber pressure. Many are obvious like powder selection, charge weight, and bullet weight. Some are not so obvious like seating depth, seating space from the lands, leade angle of the throat, bullet engraving forces, bullet volume dependence on core material, brass case volume vs manufacturer, etc.. If several of those variables come together on a "first load" pressures can go high enough to be dangerous. There is more than just the danger of blowing up and injuring yourself. Hot loads will damage most firearms long before they blow up.

Obviously you don't have to start 10% low every time you sit down at the loading bench and make more cartridges using the same components you used previously with that cartridge for that firearm. There is no guarantee that if you screw up by using the wrong powder a 10 % reduced starting charge will keep you safe. Using VV N310 instead of VV N130 powder will llikely become a bomb even with the reduced charge weight.

Ultimately how you handload is your choice. There are a lot of things in life which are dangerous. Driving a car far more likely to kill you than handloading. But like driving a car it only takes screwing up once by you or someone else to make you dead. Rules are important. Thinking about what you're doing and understanding the consequences are even more important.

Last edited by LouBoyd; 08-14-2011 at 10:51 AM.
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Unread 08-14-2011, 02:18 PM
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Join Date: Sep 2008
Location: Las Cruces, NM
Posts: 156
Re: Why start at 10% below maximum?

Commercial ammo manufacturers do often use propellants that are not available to you and me. I am not saying they don't use off the shelf powders, but they have a few more offerings than we get. They also have pressure testing equipment that the majority of average Joes do not. They have mechanical and chemical engineers that calculate and analyze data to see that Bubba does not blow his gun up when be buys their ammo.

There are a lot of variables when crafting a load, component selection, chamber size, throat length and angle, bore diameter, barrel length, bullet bearing length, distance from bullet ogive to lands, etc., so telling someone it's ok to load starting at or near max would be negligent and reckless. Even though a load that is worked up in February and is perfectly safe not be safe in July. Test over a variety of temps and conditions (like the factories do) to be sure you have a safe and well performing load under most or all conditions. I would take a load that shoots 3/4 MOA all year over a load that shoots 3/8 MOA for 4 months.

As you look at your loading data and results (using commercially recommended recipes), you will learn what to look for, when you can take short cuts, and how to develop a load quickly and safely without asking for pet loads, or if something is ok to do. Many of the same people you may be asking have similar knowledge or are only keyboard experts.

Last edited by Hntbambi; 08-14-2011 at 02:23 PM.
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Unread 08-14-2011, 03:45 PM
Bronze Member
Join Date: May 2011
Posts: 49
Re: Why start at 10% below maximum?

I've had ejector marks and flattened primers on 300 rum managed recoil I use for barrel break in. That's the 150gr at 2750 fps. I have no ejector marks on 300 rum or flat primers with my 200gr nab load at 3165fps. So not sure what to make of that.
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