Load Development -- Seating Depth First?

[BeeTee]

I load for acceptable velocity within acceptable pressure. Once I get that I go for accuracy.

Call me crazy but I will not use a 300 rum with a 180 gr bullet at 2900 fps even if it shoots in the .1's.

I'll second that... If I buy a race horse, I want it to run... I shoot a magnum because of the range it provides. I always begin load development with a combination of components that should deliver the velocity I'm looking for, and bullets are loaded a few thou off the lands. Once a reasonable combo is discovered, I may tinker some to fine tune. You can't shoot a magnum hundreds of rounds looking for the perfect load or to get that last tenth of an inch accuracy. By the time you get there, it may be time to rebarrel.

Some of the different mind sets to load development may be attributable to the intended use of the rifle - a precision benchrest rifle versus a hunting rifle, for example. With a bench gun, a tenth of an inch reduction in group size is far more important than that last 100-fps. And, the accuracy life potential for a bench gun is usually measured in the thousands of rounds range. BT

 

[SJB358]

On page 147 in an article by Bryan Litz, chief ballistician at Berger, talks about seating depth during load development: "In general, the seating depth of a particular bullet in a particular rifle tends to be more static than what powder charge will work best. In other words, it's probably best to start with a low to medium powder charge and find the best seating depth. Then, using that estabilished seating depth, start working on changes in powder charge."

IMO he is not saying the seating depth will always be the same he is just saying that it will effect group size less than varying the powder charge.

For me I like to find a velocity I am expecting and am comfortable with no pressure signs and then do a seating depth test.

To find the velocity with the least work and components used you can't beat the Audette ladder which uses ONE load at each powder charge going up. Each of these loads I will shoot at .20" off the lands.

For instance recently I wanted to try a new bullet in my 6.5 rem mag (130 gr SSII) using RL17. With no data I wanted to start low at 48.3 gr and loaded one round at .3 gr increments up to 55 gr. That is 23 different powder weights but only one shot each. Then settled on the powder weight of 54.5 gr at a respectable velocity.

To do a seating depth test I load 4 or 5 shot groups at .015", .030", .045", .060", .075" & .090". The best group, best standard deviation and best extreme spread was at .060" off

Notice how velocity decreases with increased seating depth.

Perhaps it is a matter of fine tuning the exact millisecond of the bullet exit from the muzzle or the best combination of bullet jump/powder combustion/case expansion et al in the chamber who knows but IMO finding the lowest SD and ES will make that load more consistant through several loadings

But I suppose the question would be: If I did a seating depth test at 50.0 gr, would it have shown the best seating depth to be .060"? And if it had shown .045", wouldn't I have had to do another seating depth test to find the .060" seating depth at the 54.5 gr powder charge?

Nuff said, sorry to ramble

Great info right there. Thank you for posting it. It really helps to put it all together for us knuckle draggers.

 

[Oldtrader3]

Interesting but! The groups all have a degrees of freedom problems and are, IMHO, mosty statistically identical as far as grouping size and velocity to a great extent (Std. Dev. and with some high correlation, velocity as well). The sample size indicates a reduction in velocity as the COAL is increased except, the three middle groups are statistically identical in velocity and may indicate a totally different distribution curve for groups at different COAL than you are assuming. The curve may not be linear but linear part way integrating to some first or second degree curve at longer lengths.

I would need to see closer increments or length and many more shots per group (>30) to form a postulate on this data. Not nipicking, just not ready to assume anything statistically from this work so far.

 

[woods]

The sample size indicates a reduction in velocity as the COAL is increased

Probably you meant to say a reduction in velocity as the COAL is DECREASED

except, the three middle groups are statistically identical in velocity and may indicate a totally different distribution curve for groups at different COAL than you are assuming.

The reductions in velocity are:

.015" to .030" - -9 fps
.030" to .045" - -14 fps
.045" to .060" - -10 fps
.060" to .075" - -6 fps
.075" to .090" - -14 fps

for an average of 10.6 fps. The 3 middle groups have a variation of 30 fps for an average of 10 fps. Perhaps you see a different distribution but it seems extremely linear to me for such a small sample.

The velocities actually were:

.015" off - 3197+3205+3228+3205+3212
.030" off - 3197+3197+3189+3197+3220
.045" off - 3189+3197+3182+3174
.060" off - 3174+3174+3174+3182
.075" off - 3155+3174+3182+3167
.090" off - 3159+3122+3174+3167

I would need to see closer increments or length and many more shots per group (>30) to form a postulate on this data.

It would depend upont what kind of postulate you wish to form. Certainly it is the beginning and I too would like to see much more data, please furnish some.

Could we at least begin a "postulation" that certain seating depth groups "may" yield a better velocity standard deviation and extreme spread than others?

Could we at least begin a "postulation" that velocity "may" decrease with greater distance from the lands and that positively the opposite is not indicated at all?

Waiting on your data

 

[Oldtrader3]

I was hoping that you would not take this wrong but I guess you did? It is your path, not mine and I am not going to carry your monkey on my back. If you wish to postulate, prove it!

When I was working, all of the immature engineers reporting to me, who did not want to do the work to prove what they stated as fact always tried to get me to do their work! It is called "flipping the monkey off my back"! I am not going to carry your monkey, sorry!

BTW, you are most likely on to something, because of the Avogadro's, Universal Gas Laws, just prove it with more data. Pressures diminish with larger volumes, all things being equal with gas laws, because of increased capacity!

 

[woods]

You misunderstood. I never said I had "proved" anything, only gave my method as everyone else was doing. Even asked several questions showing that the reasons were unknown. I am only wanting to prove things to myself, others are free to draw their own conclusions from the facts (data) provided.

I wouldn't think Avogadros would apply since that assumes equal pressure and seating depth affects pressure. There are other factors that affect pressure other than volume such as resistance to bullet engraving. If you want my information on that I will provide.

First you made a erroneous statement about velocity/COAL and then you stated that the 3 middle groups were statiscally identical in velocity (in error). I brought that up and now it is time for you to carry that monkey yourself and answer the reasons for your statements.

 

[Oldtrader3]

This is a friendly place and I am not going there! Lets's keep it that way. Your means are so close that your SD 's overlap. Intuitively what you say is true but you are just looking to pick a fight so go find a bar!

 

[woods]

No, not wanting to start a fight. It just seems that you want me to be responsible and prove every iota of my data but you don't want to answer for your own statements. I look forward to discussions on my posts but fair is fair and you should not post what you are not willing to discuss.

But if you don't want to discuss your statements, fine with me, just don't expect me to let statements about my posts that I consider to be in error go totally unchallenged.

 

[Oldtrader3]

Look, I just said that you do not have enough data points to prove what you are saying, mostly because of degrees of freedom. I was as not trying to wind your stem and get you all bothered. You still have a degrees of freedom issue and I am NOT running your data. Besides, intuitively, everyone who handloads already knows that if you lengthen your COAL, your pressure decreases, given everything else being the same. I just wonder why you are plowing, plowed ground? I'd rather read Harold Vaughn than argue with you!

Running sd's on 4 shot groups is a waste of paper, or board in your case.

 

[woods]

Besides, intuitively, everyone who handloads already knows that if you lengthen your COAL, your pressure decreases, given everything else being the same.

Ehhhh (buzzer sound), wrong again

If you lengthen your COAL you are loading closer and closer to the lands which will increase pressure, all else equal. That is within the normal range of distance from the lands handloaders normally use, from into the lands out to .250" or so

http://www.hornady.com/ballistics-resource/internal

Bottom of the page if you want to look at illustrations

To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).

When the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low (E); and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gases now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive (F). Velocity is high at 3650 fps - but at the expense of rather dangerous pressure. Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.

I can provide others and even quote someone even you might believe if you feel it is necessary

Again, I am not trying to prove anything, reread my original post. Just posted what my chronograph said, what my calculator told me was the SD & ES of the admittedly skimpy data and posted a pic of group sizes for verification. I did say that the velocities had decreased with progressive deeper seating, that was an observation, did not say that proves anything.

If you will stop making statements that are in error or that you don't want to back up, we can end this (and a cheer went up from the crowd!)

 

[HomerOz]

G'Day Fella's,

Joel, I haven't read any of what the other blokes have written but this is how I do it!

I start by finding the maximum length of the rifles magazine.
I then confirm the maximum OAL of a seated bullet (when the bullet is touching the lands), with a particular bullet in that same rifle.
Hopefully, this later measurement is less than or the same as, the magazine length!
I then generally seat the bullet to be 0.020" or 0.5mm off the lands and then start my ladder test with slightly increased powder charges, until I find a tight group or a Maximum Safe Working Load (MSWL), with that combination. I may then make some small seating depth adjustments if I'm onto something special, otherwise I just load up some amount of ammo, and Go HUNTING!!!

Hope that helps

Doh!
Homer

 

[Oldtrader3]

You are something! An idiot who will show me numbers which are more than .250 off the lands to prove some stupid point. What are you shooting a 20mm cannon? Your relevant curve is between .000 and .250 and looks just like I said it would in terms of not being completely linear. So you get a "B" for being a wise guy and incomplete. Nobody loads .250 back from lands except in a Weatherby and its curve would be completely different! What else do you want from me any further? Can I go now?

I just love people who will calculate all the way out to the the rediculous or the sublime to make themselves look good, get a life! Your numbers over .250 are meaningless! Your pressures over .250 just show the lengths that you will go to to be "right" whatever the hell that means! They are empirical and stupid!

 

[woods]

You are something! An idiot who will show me numbers which are more than .250 off the lands to prove some stupid point. What are you shooting a 20mm cannon? Your relevant curve is between .000 and .250 and looks just like I said it would in terms of not being completely linear. So you get a "B" for being a wise guy and incomplete. Nobody loads .250 back from lands except in a Weatherby and its curve would be completely different! What else do you want from me any further? Can I go now?

I just love people who will calculate all the way out to the the rediculous or the sublime to make themselves look good, get a life! Your numbers over .250 are meaningless! Your pressures over .250 just show the lengths that you will go to to be "right" whatever the hell that means! They are empirical and stupid!

Well, I misjudged you completely Oldtoddler. You have a reading comprehension problem or an intelligence problem.

I specifically said the relevant numbers were between .000" and .250" and would show pressure decreasing with increased seating depth. You never said anything about the pressure curve not being linear you were talking about the velocities on my target.

The charts prove this statement wrong

Besides, intuitively, everyone who handloads already knows that if you lengthen your COAL, your pressure decreases, given everything else being the same.

Not my charts and actually the values OVER .250" AGREE WITH YOUR STATEMENT and don't agree with mine. Perhaps you need me to interpret the graph or explain how graphs work; draw a horizontal line from the values on the left and a vertical line from the values on the bottom and interpolate the value at their intersection

I would suggest you stop reading Vaughn and take some classes on rudimentary reading skills and perhaps math.

So far you have been using words like "immature", "monkey" & "idiot" and I have not. Name calling and attacking are signs of a weak argument. I had hopes that you would see the error in you statements and recant or offer knowledgeable arguments to support them but it doesn't seem to happen

So yes you may go now

 

[Oldtrader3]

What are you, twelve years old? I did not call you anything and the Monkey reference was one on passing the buck and did not refer to you personally as one!

I am 70 years old, retired and you are very annoying! Go away!

 

[caribouhunter]

i've only been reloading for 4 years and for 3 rifles. so my opinion is not worth much
but for me, in all 3 rifles, the longer the COL the higher the velocity.
in my 7WSM for example, three 5 shot groups have an average of 3085 fps @ 2.865" (.085" from the land)
the exact same load at 2.920" (.030 from the land) gives 3140 fps. average. this trend have also been experienced in different conditions on different days.
from what i've read, starting at the land, pressure will drop as you shorten COL. up to a certain point where the pressure will start rising again when the bullet start to take more room in the case.

 

[Oldtrader3]

That is true according to the gas laws. All other things being equal, the pressure will go down with greater case volume.

 

[caribouhunter]

ok!?
but my 2.920" load has more case volume than my 2.865" loads. and it has more velocity/pressure... no?

 

[Oldtrader3]

It shouldn't? The 2.920 COL should be slower than the 2.865 loads. Is everything else the same? There is a theory that powder separates more and burns faster with a longer load but as far as I know, no one has dupicated it in the ballistics lab. It is just book theory.

 

[woods]

but for me, in all 3 rifles, the longer the COL the higher the velocity.

caribou hunter, your observations are correct and entirely normal

The longer the "jump" the bullet gets the less engraving force it will take to start the bullet down the barrel. That is up to a certain point that is approximately 1/4" off and then the reverse may happen.

The volume inside the case is of little consequence since it takes very little force to break the bullet free and move it to the lands. Anything we can do at the loading bench such as sizing or pulling bullets, pales in comparison to the forces and pressure inside the chamber during firing. Once at the lands where the pressure significantly builds, the volume of the "combustion chamber" will be the same no matter what your seating depth is or was. That is why pressures and velocities will remain very close whether you are using new brass or fire formed brass, expanding the brass case to the walls of your chamber takes a very very small percentage of the pressure that will be generated by the expanding gases during combustion.

Hence

the pressure will go down with greater case volume

that effect has no measureable correlation to pressures or velocities

Edited to add: It would be true to say that the pressure will go down with greater combustion chamber volume. Case volume has little to do with it

 

[woods]

Ran across this thread

http://forums.accuratereloading.com/eve ... 5901078581

and this guy explains it simply enough

4. Regardless of whether the brass holding the load is standard or fireformed, with identical powder charges it will perform the same. The pressure vessel is not the case, but the chamber; and it is the capacity of the chamber which determines the constriction of the powder charge. The brass case simply fills and conforms to the chamber like a plastic trash can liner conforms to the trash can when you fill it with water.