Powder Position

[joeb33050]

Son of Powder Position Sensitivity

What is it?
Some powders are said to be “position sensitive”.
This seems to mean that velocity varies depending on the powder location in the cartridge case when the fire is lit. So, for example, a given load might exhibit higher velocity when the powder is back against the primer than when the powder is up against the bullet base.
For years I tested the sensitivity of a powder in a load by testing for increased accuracy with a minimum sized Dacron wad tamped down on the powder; and concluded that, for example, SR4759 and Unique are position sensitive in the 45/70 and IMR4227 is not position sensitive in the 32/40 and 30/30. Thus, better accuracy was obtained with the Dacron wad and a certain charge of SR4759 under a certain bullet, than without the wad. And I haven’t yet found that accuracy improves with a wad in IMR4227 loads in 30/30 or 32/40.
Some fixes
Some shooters state that the effect of this sensitivity can be reduced or eliminated by raising the rifle barrel and settling the powder around the primer before shooting. Others suggest lowering the barrel, moving the powder forward. The objections to these solutions are that at some ranges (Mass. Rifle Association, Walnut Hill MA) shooters are not allowed to raise the barrel before shooting; and that for benchrest shooting raising or lowering the barrel isn’t feasible.
Testing
In early 2008 I did some testing with 30/30 and 45/70 and some proven-accurate loads and found that velocity varied somewhat depending on powder position.
Based on this testing it seems that the following are/may be true:
Accuracy variation has to do with the ratio of powder volume to case volume. Small quantities of powder in big cases show big variations in velocities as powder position varies.
The standard deviation of velocity is least when a Dacron wad holds the powder against the primer. (True for 6 of 8 tests.)
Increasing the powder charge allows for eliminating the Dacron wad while maintaining accuracy.
So far, I have not been able to see accuracy variation with small variations in MV due to changes in powder position.

joe b.

[Jim]

In my experimentation with odd ball milsurp powders, min/max charges and powders that just aren't intended for the use I put them to, I've found ALL KINDS of results in letting the powder lay where it lands vs. using a filler to keep it against the primer.
I've landed here: If the density is less than roughly 90%, I use a filler. Might not be the same kind of filler every time and a lot of the time it's not even necessary, but it sure is reassuring to know that I'm not gonna wear my gun to the ER.
"That's my story an' I'm stickin' to it."

[1Shirt]

JoeB, My experiance and opinion is close to yours.
1Shirt!:coffee:

[Bass Ackward]

Based on this testing it seems that the following are/may be true:
1. Accuracy variation has to do with the ratio of powder volume to case volume. Small quantities of powder in big cases show big variations in velocities as powder position varies.
2. The standard deviation of velocity is least when a Dacron wad holds the powder against the primer. (True for 6 of 8 tests.)
3. Increasing the powder charge allows for eliminating the Dacron wad while maintaining accuracy.
4. So far, I have not been able to see accuracy variation with small variations in MV due to changes in powder position.

joe b.

Joe,

I don't know what you are looking for here. Comment in the way of exceptions?

1. Seems logical until one tries to define case volume. How much powder position sensitivity is because the powder column follows the slug down the bore with an ever expanding volume and it never reaches the proper pressure to burn consistently? So it also depends on case shape and bore diameter.

2. 6 of 8 would destroy a truth wouldn't it?

3. Logical since most powder and reloading companies have target fill percentages and warn against going below those amounts. Yet we do it. :grin:

4. Now we have to define small which is more complicated than it seems. As Marshall said, the best accuracy occurs just before leading begins. The farther away you are from this balance point, the truer your statement would be. If you are on the cusp for your hardness / lube / temperature combo, you would see much more. Why some benchrest shooters get better scores in hot weather and some do worse. They are running small cases at higher pressures so the temperature change made a slight change that affected things both ways.

If you understand this effect, then complicate the issue with a larger case to add position sensitivity to that issue, how do you separate what you are observing? So what is seen, or not seen, depends on conditions. Very low pressure applications generally indicate that we run cast too hard for the pressure, so your conclusions here are valid. Just not .... True.

[44man]

Bass, I took my hat off to respond! :mrgreen:
My 45-70 revolver is MUCH more accurate with dacron over 4759 then without it. But the 4227's shoots so bad that I can't tell any difference.

[45 2.1]

Some powders that are considered position sensitive are harder to ignite properly. Use a crimp with them and the position sensitivity dissappears.

[Larry Gibson]

I do not believe Marshall’s statement of; "the best accuracy occurs just before leading begins". Take the '06 for example; I and all of you have found best accuracy to be in the 1800-1950 fps range. Yet we can take that same bullet to 2500+ fps varying only the powder charge without leading. Accuracy is not very good at that high velocity but the reason is not leading.

I also have done a lot of testing with several cartridges of varying capacity and have found that a crimp used in conjunction with fast and medium burning powders very seldom makes position sensitivity "disappear". A heavy crimp can help a little but the position sensitivity will still be there and noticeable.

A simple test with the 30-30 is evidence enough. Use a 150-180 gr bullet over a load of fast or medium powder that gives 1700 -1900 fps. Use any amount of crimp you want. Shoot 10 shot strings for group over a chronograph at 100 yards. Hold the muzzle down and gently raise to shoot. Then raise the muzzle and gently lower to shoot. Then chamber a round and hold the rifle level and gently shake before shooting. I almost always (with any cartridge that the most constant load is the one with the powder positioned in the forward part of the case. That method also usually produces the highest average velocity and the best group. Vertical stringing is often apparent.

To decrease powder position sensitivity with the reduced powder charges we use with cast bullets there are 3 methods that are most successful. First is to choose a fast burning powder that ignites easily. A drilled out flash hole also helps here as it gets the primer flash into the case right now. I prefer Bullseye, Unique and Red Dot for these loads.

Second is to use a filler such as dacron with medium burning powders. This hold the powder back against the primer in a consistent position. The ease of ignition of the powder also comes into play here. Some medium burning powders (ball powders in particular) have a deterrent on them that prevents consistent burning until a certain pressure is achieved. Many times this pressure is too high for the velocity level we want and ES/SDs are not good. If we increase the pressure with these powders to where the powder burns efficiently we most often have increased the velocity level above the RPM threshold and inaccuracy is the result. Some of the best medium burning powders for most rifle cartridges are 4895, 3031 and RL7.

Lastly to decrease powder position sensitivity is to use a slower burning powder that gives 80%+ fill of case capacity. Again ease of ignition can be a problem. I've found RL19, H4895SC and 4350 to be very good powders for this method. Even with this method I've also found a dacron filler to be beneficial many times.

BTW; I'm not looking for an arguement here, I'm just stating an opposing view. Obviously I agree with Joes conclusions.

Larry Gibson

[44man]

Me too! :drinks:

[Bass Ackward]

I do not believe Marshall’s statement of; "the best accuracy occurs just before leading begins". Take the '06 for example; I and all of you have found best accuracy to be in the 1800-1950 fps range. Yet we can take that same bullet to 2500+ fps varying only the powder charge without leading. Accuracy is not very good at that high velocity but the reason is not leading.Larry Gibson


Larry,

I think that you miss the point. Leaving velocity aside. Leaving loads aside. If you pick a load in the zone and play with hardness, your best accuracy should occur with a hardness / lube combination that matches your pressure. Translation: Just before leading begins.

Same as you climb the velocity ladder, no matter where that is, best accuracy will occur when there is a balance so that the lube, any lube, which acts as a fouling is used up. Right before leading begins. In other words again, you can't simply substitute lubes and then credit or blame the lube. You must start the ladder test again and then compare peaks with this lube to peaks with that lube.

That's what it means.

[Larry Gibson]

Bass

Still disagree and did not miss the point.

Been there, done that with the lubes and alloys many times over the years and quite extensively recently. If you are in "the zone" (assuming you are talking accuracy) with a particular alloy using any of the modern lubes then going outside that "zone" should not produce leading. I will concede that if you are using as soft an alloy as possible for hunting then there is validity to Marshall's statement. However, that is the exception to the rule.

Bullets of common WQ'd WWs, #2 alloy, heat treated alloys and the harder alloys can be pushed well above "the zone" with no leading. E.g.; 311041 is one of my bullet of choice for hunting with most .30 cal cartridges from 30-30 up through the '06. When cast of an alloy of 15 BHN or harder I can push it to 2500 fps (assuming the .308 or '06 here) with no leading when using 50/50 alox/beeswax lubes such as Javelina. No leading either with other modern wax type lubes. Accuracy will be a consistent 3-5 moa when velocities are 2400-2500 fps. I can shoot a hundred of these and still have no appreciable leading. However, soften the alloy to say WWs + 2% tin for a hunting bullet and at 2000-2100 fps (10" twist) the first 5 shots usually stay in 2-2.5 moa (decent hunting accuracy) and any shots after that open the group to 3-5 moa with leading appearing at the muzzle.

Thus Marshall's statement is an exception to the rule; it only works with softer alloys and if the velocity is kept in or below "the zone" (I believe that to be an euphanism for the RPM threshold). We see that to exceed a certain level with a certain alloy we are actually doing something wrng and leading is the result. We accept this to get the first 5 usable shots for hunting as more than that should not be needed. We can go home and clean the barrel after the first one or two shots bag the game. For general shooting this type of load is obviously not good.

I also have played for years with different alloys. What I find is that if a proper alloy is used for the velocity level attained, the cast bullet fits the throat to begin with and a good lube such as Javelina is used potential accuracy is dependant on the consistancy of the internal ballistics. Leading should not be an issue at all.

Larry Gibson

[shooter93]

Not to be too contradictory and what has been said holds true most of the time I personaly have had one big exception....Unique in a 45-70 case. This is shooting 500 plus grain bullets at subsonic speeds ...ie...1050 fps...through a suppressor. Ruger number 1 rifle, 16-1/2 inch pipe. Unique was the powder used....no filler...it didn't improve a thing, some bullet weights it was worse.....this was easily a 8-900 round test with match grade bullets. Extreme spreads ran 6 to 10 fps and accuracy has been unbelievable actually...one inch groups to sub inch groups...5 shot minimum and a large number of 10 shot groups and it holds that to 300 yds...the farthest we have tested the load to this point which is the farthest we need to shoot this load really for what it's used for. We may very well test it to 1000 when time allows. I think most of what was posted here is true this possibly being the exception to the rule thing.

[runfiverun]

you are forgetting bore size in this equasion also.
what happens in a 7mm 22" tube isn't the same as a 308 22" tube.
but the case capacities can be similar or equal.
for hunting applications you need either a filler, like i use in my 308 with 4895.
or a non sensitive powder, like 2400. like the wife uses in her walkabout loads.
and in my ackley a case full of either rl-19 or 4831sc, does the trick.

wait......... it looks like i agree also.

the lube thing i take a bit different view on.
as accuracy was lost before the lube failed, i pushed till it [the lube] did fail but the accuracy
didn't worsen.
i would imagine that i hadn't exceeded the boolit strength.
as the groups[ such as they were] were maintained, but the lead star and grey smoke was telling a different story.
will a lube change alone make a difference?? still working back up to those levels.
and re-using old data and targets for comparisons,with two rifles takes time.

[Bass Ackward]

Thus Marshall's statement is an exception to the rule; it only works with softer alloys and if the velocity is kept in or below "the zone" (I believe that to be an euphanism for the RPM threshold). Larry Gibson


Well, interesting. I have been doing this the last week because I have been frustrated with a project lately. :grin: So I had to have a confidence builder and fired 5 shot groups all with 15 BHN and my 154 LBT. These were the peaks with the lubes I have on hand.

LLA alone is 2 MOA around 1900 fps.
A Voodo lube peaks at 2100 fps and is 1 1/2 at the peak.
LBT Blue is 2600 fps for 5/8".
LBT Blue soft is 2500 fps and right at 1".

If you try to hold all lubes to the 2600 fps velocity level:
LLA is about 4 feet and kinda RPMy.
The trial lube is about 5".
And the blue soft opens to about 1 3/4".

Gun was not cleaned until the LLA that was saved for last on a hunch and it is still soaking. :grin: Brought me back to my black powder days.

So obviously these lubes require different hardness to achieve a balance and tweek the peak. When I HTd with LBT Blue lube the same 2600 fps load opened to just around 3" at 2600 fps. So it looks to me like the balance theory applies up here too and I would be required to go on up slightly to bring it back down.

[joeb33050]

Joe,

I don't know what you are looking for here. Comment in the way of exceptions?

4. Now we have to define small which is more complicated than it seems. As Marshall said, the best accuracy occurs just before leading begins. The farther away you are from this balance point, the truer your statement would be. If you are on the cusp for your hardness / lube / temperature combo, you would see much more. Why some benchrest shooters get better scores in hot weather and some do worse. They are running small cases at higher pressures so the temperature change made a slight change that affected things both ways.



Comment? I'm looking to put this chapter of the book to bed. What have I missed?

If "Marshall" is the Fouling Shot writer from the 80's, I don't absolutely find him to be corect every time.
I shoot LV PB and GC bullets, and at accurate charges there's no leading with higher charges.
30/30, 314299 GC, 12-12.5 AA#9, an accurate load. There's no leading up to 14.5 grains.
Leading is caused by too-small bullets. I think.
joe b.

[44man]

Bass IS right about lube changes making or breaking accuracy and velocity peaks. It is hard for me to relate to rifles because I sold all but one. But in my revolvers the lead hardness doesn't seem to effect accuracy as long as I am between 17 and 22 BHN for the velocities I use. I have mixed all of these hardnesses and alloys with no effect on groups but a change in lube has a drastic effect with any of them.
I have never been able to relate boolit hardness with a lube or been able to use a poor lube with other BHN's to make it work. I feel if a lube is bad, it is bad and will never grace my boolits again.
Lube does the same thing for me if I shoot 800 or 1800 fps. A bad one might work at 800 but when a good lube works for all, why would I use a different lube for slow speeds?
Besides that I am just too lazy to work farther then decent groups! :Fire:

[sundog]

I don't know that statement about leading and accuracy to true.

Talk to the single shot boys and many of them will tell you that best accuracy occurs as the boolit is just barely stabilized.

In more than one instance while I have worked up loads my best accuracy has been at a velocity determined by the gun and ammo. As velocity was increased, groups would shrink, then expand. Continuing to increase velocity did not produce leading, but did continue to increase group size. There is more to leading than just velocity (pressure). Bore condition, boolit fit, boolit hardness, quality of the loob, environmental conditions, and the list goes on. To say that best accusracy occurs just before leading ignores all those other things. Kinda like working with blinders on - okay if'n yer an ole plow mule.

[Larry Gibson]

Bass

That is interesting but are those groups 3, 5 or 10 shot?

I've alsso recently concluded a lube test. I shot 6 different commercial lubes up through 2400 fps out of the 10" twist .308W. The bullet was the same one that frustrated you:-) Accuracy for the 10 shot groups with each lube was the same at 3-4 moa with 5 of the lubes. One lube did not perform well above 2100 fps and produced 5+ moa groups at 2400 fps. The 50/50 alox/beeswax (not LLA) performed as consistently as the lube you recommend.

I am also testing the 311466 with those same lubes (thanks for the LBT soft BTW) out of the 14" twist barrel at 2600 FPS. Probably do that on thursday. We shall see what the results are. That 154 gr LBT bullet is very well disigned and offers little room for adverse obturation during accelleration so RPM's adverse effect is minimal. BTW; 3 shot groups prove little unless you shoot 5 consecutive 3 shot groups. Otherwise the random placement of only 3 shots can very easily skew the results. Five shot groups are a little better but don't show much on the lubes ability to hold up over a longer (longer than 5 shots) practice/shooting session without cleaning the barrel every few shots. Even then shooting three 5 shot groups will give a much better idea of expected results. Ten shot groups will show much better the consistency of the load. Ten shot groups also show if the lube is giving out.

I recently shot a 1.75" five shot group at 2500 fps (don't have the exact fps here with me) with your 154 gr LBT out of the 10" twist '06 using the best RL19 load. The first 3 shots went into .95". This is the 5th five shot group I have fired with that load and it also is the best 5 shot group. Maybe because it was very close to your magic 80 degrees? It also is the best group for the first 3 shots. So can I now claim it to be a sub moa load? How about a sub 2 MOA load? Some may say yes but I do not. The reason is the average for the five 5 shot groups is 2.9 moa with average for the first 3 shots of each group being 1.45 moa. BTW; I did not wait for that magic +80 degree day for each group. These groups have been fired on days ranging from 45 to 79 degrees. As you know all my groups are tested at 100 yards so the moa is inches also.

My goal is to see if I can come close to matching the 154 gr LBT's accuracy with the 155 gr 311466. I've been very pleased with the accuracy shown (2-3 moa 10 shot groups) out of the 14" twist barrel at 2600-2800+ fps with 311466. I'm trying to see if I can get consistent 2 moa 10 shot groups at 2600+ fps with it. Then if I can get the same 2 moa 10 shot consistency at 2400+ fps out of the 10" twist I'll be quite happy. If not then I'll buy a LBT mould like yours....I know that would make you happy.

Larry Gibson

[Bass Ackward]

Larry,

I believe that there are many possible high velocity combinations if a slug design can handle it. And there are many things that I believe make it more .... flexible to create more and wider points than other designs. And if your cartridge has a pressure limit, and they all do even with jacketed, what is possible is limited as well.

Some of these combos are not logical and NOT solved with a harder bullet. One fella is now shooting HV with something that is in the early stages of working very well for him and you will scream Bull Crap if I told you. My point is that harder and better lube are NOT always what solves the problem or works. If a combo shoots the first three or five or 8 depending on a persons self imposed requirement into a good group and then opens from there, that is fouling causing the problem regardless if you see leading or not. Lube left in a bore is essentially fouling for the next shot that it has to deal with. In some cases that works well, others it creates hydraulic forces that the bullet must size down to pass over. This is magnified with velocity.

I took your 311291 and sized it down to .308 as my bore would do. The GC groove is reduced to .007 at that measurement. That means that by the time the rifling engraves back, a bridge is built that closes this distance and removes the GCs ability to scrape fouling from the rifling. And this is where the forces create the most friction after the bullet begins accelerating. So exactly where you need it, you don't have it. A slower twist creates less friction and heat, so i works to a higher velocity level.

It also serves to create pockets that are bordered by this lead enclosure that once full, make it susceptible to hydraulic forces to size down. This creates a solid band and give you the same effect as a PB .... but at much higher velocity. The pockets make it vulnerable to fouling as gravity will not keep fouling equally dispersed in a bore. So those areas around the bullet fill at unequal rates and locations depending on where the fouling is in the bore. With an open groove deep enoughto be below the rifling, this fouling is free to equalize around the check space before it fills and fails. (Same with a lube groove too) This is also the problem with some Loverin designs as the grooves are NOT deep enough to allow lube to flow 360 degrees around the slug after it has been engraved. The design performs well and then goes wild very quickly.

How you will know what you have is if the groups slightly open as you increase charge or if they BLOW open. That is design, not lead limitation. Fit causes the same symptoms. So if you want to get into another chicken or egg debate, there it is. It ALL begins with fit as to what you will have to do and what you eventually get.

I can get three shot, 3/4" groups at 2400 fps out of your 311291 at 35 BHN (way TOO hard) using 52.5 grains of AA3100 and then it will open erratically. Two of the 5 shot groups may hold 2" area and the third may be 5" or so. Temperature is also in play here. Shot early in the morning the same load will do 5 shots about 1 1/2" even with the fliers, but by afternoon (80) will be 6". If I paint a little LLA on the front band and nose (bullet diameter in a bottle), I can get 3/4" for the first three in the AM. Afternoon still sucks. The 311291 does not react to lube change as much as my LBT, which is design in that it needs more lube capacity for this design as it has to be shot really hard. (high BHN) Lube will only make a diference if the design or hardness is holding. If the lead let's go, then lube will have no effect there. (a good way to tell)

The wide GC designs I have made, do not do that so much. They hold any performance level much better. Zone or not. Until it freezes. Remember, my best groups with 16-18 grains of 2400 are in the 2" area too and also temperature senstitive, just not so much as this velocity. Accuracy (if you can call it that) remains for longer strings. Fouling is not an issue it can't deal with. It's also tempermental to sizing, to hardness and on and on. That's bullet fit.

This GC issue is the same problem (narrow GC groove) with my 154 grain LBT that was originally designed to be 160 grains, just the shank shortened. Veral said that it was made for a customer who requested it for LV use only. And that is why it is so temperature sensitive as it leaves more lube in the bore for the next shot to have to deal with. I need to break down and buy another mold, but I have very limited use for a spitzer design except for ground hogs (summer) and demonstrations for .... unbelievers. :grin: I designed a 165 grainer for my wife to hunt with. Want to know what one of her loads is? Yep, you guessed it, 40 grains of 4895. :grin:

But that is my opinion why you really have this problem with this mold / design. Your slower twist isn't creating as much force / friction / fouling from the rifling trying to rotate the bullet, so it doesn't foul till father up the velocity scale. In effect, slower twist rate makes a stronger / harder bullet.

Does this mean that your 311291 won't EVER shoot HV in a 10 twist? No, I just haven't found the right combo yet. And if I didn't quit because I was told it was RPMs and I kept trying, I would eventually. When I did, the accuracy window for number of shots, temperature will be very small. And the definition of the load will NEVER meet your definition as you have defined it.

But if someone ever asks you why the 311291 doesn't want to work well at HV, and you want to move beyond the simplified RPM answer, that's my opinion of why.

Why not get a better design to do what you want it to do before Veral passes? Keep it light.

[felix]

When ya'all are testing, take into consideration that lube changes character after being fired. Don't compare strings if more than 15-20 minutes passes between the strings, assuming a hot day. A cold day maybe one or two minutes, surely not more than 5. We are talking close fitting bolt guns here. ... felix

[Bass Ackward]

When ya'all are testing, take into consideration that lube changes character after being fired. ... felix



There are so very many things that happen once I pull the trigger that no body can prove. Only to pontificate and theorize as I have done. And those perameters change all the time based upon the cuircumstances and conditions they are subjected to amplified by lead requirements.

In the end, all I get to go by is a target.

Now you are telling me my lube is a changin too?

Have I ever said how MUCH I hate lube? :grin:

[Bass Ackward]

1. Comment? I'm looking to put this chapter of the book to bed. What have I missed?

2. If "Marshall" is the Fouling Shot writer from the 80's, I don't absolutely find him to be corect every time.joe b.


Joe,

1. I see now. Cause the problem with a book is that it can't possibly cover ever situation. So all it has to do is cover the majority. And for that I would say it is OK.

2. Don't know about the accuracy of what else Marshall said or wrote. Just credit his statement about the lube hardness equation to my HV success. But we all are wrong every once in awhile. Only know of one human that was right about everything he said or wrote and they still crucified him.

[felix]

Join the club. I keep dreaming about a non-lube lube that can be made available for all seasons, for all guns applications, having infinite shelf life before and after firing, and cost no more than a penny per application. What shall we call it? Definitely not lube. Gotta' be more than the thought of using a condom, proverbial and otherwise. ... felix

[runfiverun]

and one that doesn't change poi when it warms up would be nice too.
or one .........