Establishing maximum load?

[RichCoyle]

For you folks who spent a lot of time in statistics class, how do you establish a maximum load? Say your book says maximum is 72.0 grains.

Do you start at 65.0 and go up till the bolt is sticky, or ejector swipe shows, or primers craters or some other criteria? Do you do this thirty times to make sure it is repeatable? Do you do the same for every powder and bullet and primer combination so you are satisfied statistically you didn't miss something?

 

[Dmagna]

Start 2-3 grains below max and load 1gr over. Then, pew pew. If no pressure during pew pew, then I keep going until I reach pressure during pew pew

 

[RichCoyle]

Start 2-3 grains below max and load 1gr over. Then, pew pew. If no pressure during pew pew, then I keep going until I reach pressure during pew pew

How many times to you verify?

 

[Dirtrax]

It depends on the severity of the signs. Some combos will spike suddenly and others are more linear/predictable. Temperature has a lot to do with it too. Personally I won't spend too much time there if it's ejector swipe or a clicker. Primers are not necessarily a good indicator imo. That is unless they are being blown out of the case!

 

[MagnumManiac]

For you folks who spent a lot of time in statistics class, how do you establish a maximum load? Say your book says maximum is 72.0 grains.

Do you start at 65.0 and go up till the bolt is sticky, or ejector swipe shows, or primers craters or some other criteria? Do you do this thirty times to make sure it is repeatable? Do you do the same for every powder and bullet and primer combination so you are satisfied statistically you didn't miss something?

I run my loads over the Pressure Trace II software…
If I don't have a sensor for a new firearm/cartridge, like I don't for my 300RUM and 257 Weatherby, I run loads until I see excessive pressure signs. It must be understood that some rifle types show excess pressure differently. Such as, stiff bolt lift without other signs, or ejector swipes only, flattened AND cratered primers without ejector marks or even stiff bolt lift. My Win Model 70's will show flattened primers AND cratering without stiff bolt lift or ejector swipes and those loads have been north of 70,000psi, stiff bolt lift doesn't show up until a blown primer is reached. My REM 700's will have all 3 signs at 70,000psi, stiff bolt lift, ejector swipes and flattened primers. My Kimber's will not show ANY signs until way over 70,000psi, and I have never seen a fully flattened primer in any of them, but do get ejector swipes at proof load levels. Still no stiff bolt lift. My Rugers always show stiff bolt lift just as max pressure is passed, sometimes with ejector swipes, but not all brass brands do this. My switch barrel Model 70 in 300/340/375 Weatherby, in all 3 shows cratered primers just as max is surpassed without any other signs. This is my point where I stop and reduce the load by 1%.
I think you have to know 3 things, what primers look like at excessive pressure, although this is not 100% reliable, what your brass does, or doesn't do and what your rifle does or doesn't do. If I went with book numbers when using my custom chambers, without knowing these signs to look for, I wouldn't even be in the ball park with most of them running custom throat lengths and tapers etc, etc.

Cheers.

 

[Barrelnut]

As far as the "flat primer" part of the equation goes. Broz once said that he didn't get concerned with flat primers until they were flattened to the point of mushrooming. That is when, after decapping, the primer shows a mushroom type pattern on the head of the primer. You can usually feel it with your fingernail, and see it with a magnifing glass.
I always though that made sense and tend to watch for it.

 

[Mike6158]

Kind of along the same lines as the OP's question, I did my first round of load testing on my .20 PPC (again, it's been sitting a while) last weekend. I used the load data for a .204 Ruger and worked down from max. The .20PPC case will hold more powder and predictably the velocity was way down. So now I'm about to do a second load test. I'm not sure what the spike at 23gr (RE15) is but I suspect I loaded about a grain over the 23.

In spite of the non-linear increase in charge weight the rise in velocity was linear. I'm looking for 3,500 fps. The red line is average but that is skewed by the large velocity jump. I haven't put much effort into the calculation but, assuming I don't reach max before I get to 3,500, it seems like I could linear interpolate the velocity and charge weight and get a charge weight that should be close to 3,500 fps. Obviously I wouldn't start there. I'd go backwards 0.2 gr 10 steps and start at the bottom. Example: If 25.0gr is the 3,500fps calculated powder charge then I'd load 23.2, increment 0.2gr, and see what the LabRadar tells me, load another, shoot, check data, etc. Or I could start at 23.6 and increment 0.2. That would give me some overlap with the top part of the first load test.

I can do this test (one load at a time, bench rest style lol ) at home. I honestly don't expect to see pressure signs. If I was POSITIVE that I wouldn't see pressure signs I'd just load em up and shoot em. I'm not going to do that.

Thoughts (after you read and understand what I wrote).

 

[MagnumManiac]

I normally start 5% below listed max, or generated data from Gordon's. I have only ever had an issue doing this once, and that was with my own wildcat development. The issue was actually with the chamber and not the load parameters…my fault totally, but no damage done luckily. CZ 550 Safari Magnum actions are very strong.
(I forgot to mention this above)

Cheers.

 

[Chadp82]

I don't always hit max. I will caveat that it is safest to start at the bottom of the range.

Now I personally start in the middle of the range, load .5 increments up to and 1.5 over max. I look for a grouping node on my way up. If I find a node I write it down.

I will still go all the way to the top of what I loaded unless I see a pressure sign, at that point I stop and will just pull the bullets on the rest. I don't risk pushing it higher as soon as I see one pressure sign, sticky bolt, primer signs, ejector mark, etc.

If I never hit pressure and wasn't happy with a node, I will push it a little higher.

I don't purposely look to see what the max load load can be

 

[shinbone]

For you folks who spent a lot of time in statistics class, how do you establish a maximum load? Say your book says maximum is 72.0 grains.

Do you start at 65.0 and go up till the bolt is sticky, or ejector swipe shows, or primers craters or some other criteria? Do you do this thirty times to make sure it is repeatable? Do you do the same for every powder and bullet and primer combination so you are satisfied statistically you didn't miss something?

What would be the purpose of determining the maximum load to such a level of precision?

 

[VinceMule]

Most of my accuracy loads over the years have been within 2.0-2.5g of the max load for my rifle. So, I want to know what is the max load for safety purposes and as a baseline to back off from when chasing accuracy.

Working up loads in 100* heat....hummm...........where's the thinking? Better to shoot a pistol at steel plates.

 

[Mike6158]

Working up loads in 100* heat....hummm...........where's the thinking? Better to shoot a pistol at steel plates.

Simple, it's hot outside. It does that sometimes. Like 103 to 105. I have rifles, I have powders, I have bullets. Load a test and shoot it. It's not THAT hot. PS - I'm fire forming .220 Russian brass to .20 PPC. The shoulder moves a lot. The heat stability of the powder doesn't matter, today.

The .20PPC surprised me today. It's pretty accurate when fire forming. I dialed up for 300 yards and thumped the 4" plate at 300 every time. I shot all of the loads over a Lab Radar and I had a few loads that had a tight ES. One group had an ES of 1.5. I loaded the fire forming rounds as if I was doing a powder test because I kind of was. We'll call it a low expectation powder test.

The linear interpolation trick would have worked but I took the path of caution and backed the max load down one grain. I didn't quite get to 3,500. I think it was 3,300. Again, that was while fire forming and I'm sure that the case expansion reduced the pressure and velocity. I will set up and shoot a legit ladder test now that I'm done (never really done when you shoot a wildcat) fire forming brass.

I found quite a few loaded rounds (had to be at least 5 years ago when I loaded them) and shot them over the Lab Radar. ES wasn't great but it was in the 20's and that's not horrible. Over 3,500fps which is the velocity that i wanted to reach. They were loaded with 25gr of N133. When I tried to load 26gr of RE15 in the un-fire formed case I didn't like where the powder was sitting. The load would have been lightly compressed. The short version of the story is that I loaded the last three in the series, 25.7, 25.8. and 25.9.

I need to decide whether I want to stay the course with RE15 or work a load up around the 25gr of N133. I think the answer will be yes.

I just got home and I need to download Lab Radar data, put stuff up, anneal brass, etc.

 

[RichCoyle]

What would be the purpose of determining the maximum load to such a level of precision?

What would be the purpose of determining the best primer to such a level of precision?
What would be the purpose of determining the best powder to such a level of precision?
What would be the purpose of determining the best bullet to such a level of precision?

 

[Mike6158]

What would be the purpose of determining the best primer to such a level of precision?
What would be the purpose of determining the best powder to such a level of precision?
What would be the purpose of determining the best bullet to such a level of precision?

Raises hand. I'll take precision for 200 Alex... er... Rich.