I've been following your work with great interest. You are taking loading the nitro expresses out of the dark ages.

Can you distill what you've learned into advice on fillers. If fillers are needed or desired, do you lean towards dacron, foam plug (like Kynoch) or foam backer rod?

How about 450-400 for your next project? Tropical vs regular loadings, Woodleigh & Hornady, RL-15 & 4831, filler or not.

Thanks, Bob

Bob,

I hope you don't mind me chimming in first since your question was to Michael.
We have done quite a bit of filler testing with full nitro loads and in the 470NE types of fillers made a big difference. In the 500NE the case is 1/4 inch shorter so not as much filler has been needed. We saw very littler difference in type of filler in it. We have not tested the 500NE much with fillers. We did find that loose powder verses the same charge with filler had a big difference in pressure. My thoughts are if you have airspace you need a filler and I like foam backer rod. I think you should find a powder and load that fills the case and forget the filler if possible. We will be testing lower pressure nitro for black loads with slow powders that fill the case. Fast powders and lots of airspace in big cases I think could cause a lot of problems.

Sam

quote:

Originally posted by srose:
Bob,

I hope you don't mind me chimming in first since your question was to Michael.
We have done quite a bit of filler testing with full nitro loads and in the 470NE types of fillers made a big difference. In the 500NE the case is 1/4 inch shorter so not as much filler has been needed. We saw very littler difference in type of filler in it. We have not tested the 500NE much with fillers. We did find that loose powder verses the same charge with filler had a big difference in pressure. My thoughts are if you have airspace you need a filler and I like foam backer rod. I think you should find a powder and load that fills the case and forget the filler if possible. We will be testing lower pressure nitro for black loads with slow powders that fill the case. Fast powders and lots of airspace in big cases I think could cause a lot of problems.

Sam

I think that is what I,ve found in over fifty years of loading large NE cases! Fast powders, and Air space in large cases is a volatile combination!

........................................................................................

Sam, if I read you right, the 450-400 would resemble the 470 more than the 500 in space needed to fill with a filler?

Bob,

If you use RL-15 in the 450-400 it will require a filler. You can use a slower powder like IMR 4831 to fill the case and still get regulating velocity. I shoot a 450-400 3 1/4 and have used both powders in it. I prefer filling the case and not using a filler.

Sam

Hi Bob

I think Sam has pretty much chimed in with nearly exactly my thoughts as well! At least for the most part. Personally I hate Fillers! What I have found over the many years of loading, that in smaller cases, 45/70 a good example, you really don't need fillers. However, these big Nitro cartridges are a bit of a different story I believe, and I think that light loads of faster powders need that filler. I suspect also that with some slower powders and smaller air spaces may not need fillers at all. And what I mean is, if there is just a few grains short of the base of the bullet, do you really need that filler? I think not, but that is ONLY OPINION right now, not fact.

It is my opinion also, all cartridges/bore size are not created equal. Sam and I found horrible and some scary results using fillers in 470 Nitro. Dacron filler was a bit scary in some of the wild pressures it gave over the exact same load in the foam rod. No doubt about it, the foam rod is far superior in that cartridge and bore size. We tested fairly extensively on that. So far, our tests in 500 Nitro don't seem to bear that out, which was only one test as I recall, and the Dacron won out with consistency of the rounds tested. But, that in not conclusive either, that was only one small test with one powder. So there is work that could be and will be done on that front over the coming months as well.

I don't shoot the Nitros on a regular basis, and my experience is increasing as we move forward with them. I don't like to introduce foreign matter into the mix, a filler is nothing but foreign matter. With the equipment hooked up to the barrels, it is very evident and easy for Sam and I to see these issues plain as day, but most of the time they do not show on the chronographs or other common equipment used, and therefore, you don't see this in you loading and testing. While in some cases you may think you are just fine with the super duper load you just tried, but in reality it may be far from fine. There are lot's of variables to contend with, add filler, that is another variable you have introduced into the mix. Now for shooting light loads in in a Nitro gun, where pressures are down from 15000 to 30000 PSI, no problems, if you have a spike, then it's not going to be dangerous anyway, under most circumstances. But if you are up into Nitro pressures, 40000 to 45000 PSI--then a continuous spike there might be a problem!

I am with Sam all the way, choose a powder that fills the case and gets you to Nitro velocity and pressures without a filler.

Michael

As far as vintage doubles regulated with Cordite, I still go with the Article by Ross Seyfried in the December/January 2000 Handloader Magazine.

RL-15/Norma203B with Dacron/foam plug will give you excellent performance in the old Nitro Cases.
Held against the primer by the filler RL-15/Norma 203B will give uniform velocity and a reduction in felt recoil.

In modern doubles you ought to use the powder/bullet combination that give you the best regulation.

Rusty

Be it far from me to dispute anything that either you or Ross might have to say on the matter. As all of you know, my experience is limited. On this double rifle work, I look at what the science is telling me and I have no influence beyond that. And in truth, with all the variables involved the science has not matured as of yet with either for, against, and differences in between. At some point the science will be far enough along to be able to make some certain conclusions about this, that or the other, but it is not there yet.

We know that in some cartridges that there are HUGE differences in the type of filler used. We know that in other cartridges there are still differences, however it can be reversed at to what type worked better, with what powder!

We know that each cartridge--powder--filler that can be used may show different results, for example, in Cartridge A--Foam Filler may show up far superior to Dacron with Powder A. Cartridge B can be totally opposite. Cartridge C may work best with NO Filler at all? While Cartridge D may have to have a filler. Cartridge A and B may be best one way or the other, with or without filler. What do we know to be fact? Very little, and not enough to draw 100% conclusions.

The Science behind this will mature, but it will take time and lot's of work, and it is not there yet. Stated above is my opinion on what I have seen thus far. Stated as such. There is much you can see that will give excellent and consistent velocity, but that might not show up well in the pressure traces, which is far far more sensitive than the chronograph that can only tell you the speed of the bullet and relationship of several rounds. Many times the chrono looks great, but the rest of the info looks either dangerous or rather ugly, and the chronograph does not tell the story all the time. It does assist many times with correlating and confirming the data, but it's story is short and limited.

Regulation? Sure, a double that is not regulated is not much good is it? But for the sake of longevity one best know the other factors involved in getting to that point. Does not do much good to be regulated and over the next 100 rounds the barrels come unglued! I have duct tape for that if it happens however-HEH.. But of course my experience is limited in this area and I am speaking as an outsider in this area of expertise. Maybe it's much ado about nothing? I don't know? I am along for the ride to take a look at putting some science behind the myths, and that is all.

Enjoy

Michael

Michaels (and now Sam's) work bears out the truth and not old dogma. It is only cold hard facts. Having been in involved with strain gauges in medical orthopedic implant research...all I can is this: "strain gauges do NOT lie"! They are the reason we have joint replacement implants that can now withstand the cycles of 40 years vs. the old 20 years.

Thank you Michael and Sam!!!

There was another filler test done by a well known writer. Those tests show very similar results with most fillers as the tests Michael and I did. Our tests were with full power nitro loads and the other test was with nitro for black low pressure loads. I'm sure there could be some major differences in results because of the pressures involved. Also two totally different cartridges could show different results. I still feel that fillers of any kind are as Michael says "Foreign material" are a problem or could cause a problem.

quote:

Originally posted by michael458:
It is my opinion also, all cartridges/bore size are not created equal. Sam and I found horrible and some scary results using fillers in 470 Nitro. Dacron filler was a bit scary in some of the wild pressures it gave over the exact same load in the foam rod. No doubt about it, the foam rod is far superior in that cartridge and bore size. We tested fairly extensively on that. So far, our tests in 500 Nitro don't seem to bear that out, which was only one test as I recall, and the Dacron won out with consistency of the rounds tested. But, that in not conclusive either, that was only one small test with one powder. So there is work that could be and will be done on that front over the coming months as well.

I am with Sam all the way, choose a powder that fills the case and gets you to Nitro velocity and pressures without filler.

Michael

Michael, and Sam, first let me say that I for one am impressed with your experiments with the large Nitro express cases are among very few published for the end user to benefit from. I believe this lack of scientific experimenting being readily available to the guys who actually depend on this type of firearm to actually defend their lives. That lack of information ,IMO, is one reason so many people simply do not understand double rifles.

Having said that, I would agree with everything you guys have found with your work, and I’d like to make one comment on the quote above. In regard to the difference between the results in a 470NE being far different than what was found with the 500NE in the use or need for filler. I think you will find this difference in like capacity in all bottlenecked cases, and straight sided cases.

The ventury effect of a bottle necked case will always act differently than a straight sided case, because the combustion chamber the suddenly reduces in size will automatically increase pressure, and adding a plug of inert substance at that juncture can’t help but increase it further. In the case of NE cases the key is how much it increases! These cases with max loads are still fairly mild, but when loading any of these cases one needs to not go above max with powder only, or powder plus filler. As long as that is abided by no problems will arise. IOM, where your experiments are valuable is in the scientific differences in the type of filler used in the two different types of cases!

All good stuff Michael!

I find this discussion very informative,I have been using fillers for quite some time,
in my 470 NE,I use Rl 15 with a foam plug as a filler for the airspace,my question goes out to Micheal and Sam,I would like to know,shooting a load with the same powder,one with and one without foam filler,did you get different speeds? Was the no filler load slower?I am just curios as to how the pressure would affect the speed,and secondly regulation in a DR?
BTW,it was a pleasure to meet both of you at DSC.

I'll be more than happy to send a PDF of the article to anyone requesting it. Just email me directly. rkmojo@aol.com

I might add, that as a personal preference, I do not shoot monolithic solids in my vintage British double rifle.

Hi guys, I fully admit you guys have forgotten more than I'll never know about the art & science of loading for doubles, but in my experience those rod fillers caused significant velocity excursions when I used RL-15 in my 450NE. I took great pains to ensure I was doing it right and consistent and it just didn't work for me. I'm just using H-4831 which eliminates the use of a filler and it is an "Extreme" powder. Cheers, jorge

From what I have seen in the 470 and 500 using a powder that doesn't fill the case you can get a false idea of a safe load. When the powder is loose it may not fully ignite. You might get a load that shoots well and gives you proper velocity. OK that seems fine. Now you add a filler and the powder ignites fully giving you much higher pressures. My thoughts are if you are using no filler and you have worked up a load that seems fine, what happens if all the powder ignites. You might just have a bomb or at least pressures higher than you want. If you look at the filler tests Michael and I did you can see lower velocities and pressures with foam type fillers. Other fillers have higher pressures and velocities. This may be fine as long as the load is in the safe pressure range. In the 470 why use any powder that doesn't fill the case? With IMR 4831 we have a good regulating load that fills the case and give good velocity and pressure.

Mac

Thank you! Coming from you that means a lot to me. The support for these projects has been incredible here, and there seems to be a great deal of "darkness" on the many subjects we are trying to cover, and bring "light" to. Some of the things we are doing, we are still in the dark as well, some of the things such as actual barrel strain, I think we have taken that out of the dark and shed light on that subject for all to see. Fillers--still a rather dark subject.

quote:

The ventury effect of a bottle necked case will always act differently than a straight sided case, because the combustion chamber the suddenly reduces in size will automatically increase pressure, and adding a plug of inert substance at that juncture can’t help but increase it further.

That Hits the Nail on the Head! Absolutely correct in every way. This also helps explain how some powders react different with various fillers as well, change of combustion rate from one powder to the next.

Who knows what happens as we go down in caliber with these same questions. Just so happens we have gone up in caliber from our start with the 470 to 500.

As we gather more data on this, and it is compiled I am hoping that we begin a move to some more positive conclusions on the matter. Right now, there is just a lot of work to be done on it to see if we can get to that point.

I have it here, somewhere, Sam and I tested a load that was in the reduced loads, one with no filler gave 15000 PSI, but very ugly up and down, inconsistent trace. Foam Filler, same powder, the pressure went to over 30000 PSI, perfect trace lines, even combustion, even pressures, perfect load, but pressure doubled with the same powder charge.

Jorge, I think a very good choice you have made myself!

Fillers???

Honestly, I think that use of fillers can be like Sam says, a bomb waiting to happen. Now I know that many of you have used them for the last 100 yrs (some old guys here LOL) and never had a problem. But I also bet good money you are not looking at them like we are seeing them either! If you have, it will scare your britches down when you are shooting that $10000 to $50000 rifle or more! If I was doing it in a bolt gun, it would give me no concerns, you should see some of the things I have done to bolt guns! But doing it in a very expensive, and not easy to fix double, that is not all that strong to begin with? Gives me pause, and not many things do that. If there was enough real science and data to look at, maybe it would shed light on it some more, but the 1000s of combinations that can be contrived is a bit much, and it's going to be different in each and every cartridge and bore size, that is evident right now early on.

One of the things we saw consistently in 470 was the increased pressures just from using Dacron vs foam. It was an incredible increase in pressures in the same powder charges. Some that could have been a real problem. In the 500 so far, not seeing much difference between dacron and foam, but there has not been but one or two tests of that specifically now.

Maybe over time we can bring some light to the subject and some conclusions. That will be our goal anyway!

Right now, today, I would say like Sam does, find a powder that fills the case with some compression from the bullet so you don't need that filler, at least until we can put some proper science to the subject.

Michael

quote:

Originally posted by srose:
From what I have seen in the 470 and 500 using a powder that doesn't fill the case you can get a false idea of a safe load. When the powder is loose it may not fully ignite. You might get a load that shoots well and gives you proper velocity. OK that seems fine. Now you add a filler and the powder ignites fully giving you much higher pressures. My thoughts are if you are using no filler and you have worked up a load that seems fine, what happens if all the powder ignites. You might just have a bomb or at least pressures higher than you want. If you look at the filler tests Michael and I did you can see lower velocities and pressures with foam type fillers. Other fillers have higher pressures and velocities. This may be fine as long as the load is in the safe pressure range. In the 470 why use any powder that doesn't fill the case? With IMR 4831 we have a good regulating load that fills the case and give good velocity and pressure.

srose, when the powder is loose and doesn’t come close to filling the case it is MORE likely to fully ignite, especially if it is a fast burning powder. This because when the rifle is held level to shoot at a target the powder tends to lay along the bottom side of the case, and the primer fires a larger surface of the powder charge. This causes a very high spike in pressure, and negates the progressive burn of the powder that is supposed to burn the powder from the back of the powder column as it pushes the bullet down the bore. This is why fillers are needed in large capacity cases that were designed for cordite with fast burn modern powders. The flash-over effect described above causes the spike in the chamber area, even before the bullet starts to move.

The use of filler is not just any way you might want to use it, no matter the type. There is a proper way to use any filler, and there is definitely a WRONG way to use any type of filler . It is my guess that a full 80 percent of the damage done when using filler is because it was improperly applied!

Lets take a look at Dacron fiber fill for instance!

This a complex operation and is not to be toyed with. Packed too tightly it forms a plug, formed too loosely is is ineffective. The proper way to use this filler is to place just enough in the charged case so the when the bullet is seated it very slightly compresses the filler, because it is only there to hold the powder column against the primer, no matter the position of the rifle when fired, nothing more. The use of any filler starts with a careful weighing of brass to match it for weight. What does it matter what the brass weighs you ask!

Since the outside measurements are the same once sized, if one case is heavier than the other to any great degree that means the case capacity is smaller in the heavy case. This alone creates a higher pressure than the same load and amount of filler in the lighter case. It also means the filler is more compressd in the heavy case. This may seem a little drastic but if you are getting close to max load, some of your rounds may be OVER MAX. That is not good in any firearm, but in a break top double rifle it becomes very important to a rifle though new is still 19th century technology, and doesn’t tolerate pressure spike well.
........................................... ..............................

Thanks Michael, I'm glad I could contribute what appears to be a valid contribution to your large volume of work! jorge

MacD37,

I agree with just about everything you said in your above post. I've used about every filler you can imagine at one time or another. I never had access to such wonderful equipment that Michael has. I have learned so much working with him. I have seen things I would have never believed before. Some of the fillers I have used for years showed me scarey things.

The flash over effect you mentioned I agree with but I also disagree that it happens when powder is loose but more than half case full. I noticed the other day when we were shooting everything with no fillers that we had unburnt powder all over the place. I was glad I didn't get cussed out about it! I left Michael's range in a mess. There was powder all over a table off to the side of the range and the floor had it bad to. Most of the loads we were shooting were 75% or more of the case capacity. Poor ignition for sure. One load that we did try with and without filler almost doubled the pressure when we added the filler meaning the powder finnaly ignited fully.
We still have a lot to learn with the filler issue. I like is less and less.
Thanks for your input and it is always welcome!

Sam

quote:

Originally posted by srose:
MacD37,

I've used about every filler you can imagine at one time or another. I never had access to such wonderful equipment that Michael has. I have learned so much working with him. I have seen things I would have never believed before. Some of the fillers I have used for years showed me scarey things.

The flash over effect you mentioned I agree with but I also disagree that it happens when powder is loose but more than half case full. I noticed the other day when we were shooting everything with no fillers that we had unburnt powder all over the place. I was glad I didn't get cussed out about it! I left Michael's range in a mess. There was powder all over a table off to the side of the range and the floor had it bad to. Most of the loads we were shooting were 75% or more of the case capacity. Poor ignition for sure. One load that we did try with and without filler almost doubled the pressure when we added the filler meaning the powder finnaly ignited fully.
We still have a lot to learn with the filler issue. I like is less and less.
Thanks for your input and it is always welcome!

Sam

Sam I'm happy for the work you and Michael are doing being posted on AR! Many will benefit from that work. It is rare that scientific ballistics work are available to so many as in this case.

On the flash-over thing, I don’t think we are in disagreement as much as you think. Even with 75% of case capacity and no filler the flash-over can occur! This causes an initial spike in the chamber area, but tends to leave powder behind, igniting the top of the column burning more of the muzzle end of the powder column than the back.

When using fillers they will give different results depending on how they are used. The amount of pressure applied to the filler by the bullet seating is critical. Too much and it becomes a “PLUG” or obstruction much like mud in a shotgun barrel, too little and it lest the powder migrate. No matter which filler is used the pressure should be no more than enough to sit on top of the powder column and be only held there by the base of the bullet, leaving no airspace.

If you have noticed all light loads without filler will leave unburned powder on the bench if the powder is allowed to slosh around in the case. Modern powders are designed to burn at a progressive rate from behind the column ideally to burn out just as it reaches the muzzle of the barrel. The filler holding the powder in a solid column against the primer only allows the back of the column to be ignited. The 75% capacity is far more dangerous to the firearm without filler, than filler properly used. The filler must always be in contact with the top of the powder column, and the base of the bullet with no more pressure than enough to hold it there. Some things people have used as fillers, and some that were simply misapplied have had disastrous results. One that comes to mind is crème of wheat. That one has cause more ringed chambers than any other medium. That stuff was used to fire-form cases without a bullet, and a light load of bulls-eye in a rifle case. Why in the world would anyone think it wouldn’t be a disaster in a loaded rifle round.

Keep up the good work Sam, and Michael are doing, we can all learn form it!

………………………………………………………................................................................. .

MacD37,

I agree! Think we are both on the same page.

Chream of Wheat and any other filler of this type is bad news. We tried grits in our filler tests and pressures were out the roof compared to others. I don't like loose powder or fillers but sometimes you have no choice. Further testing of slower powders is needed.

Years ago I remember someone selling card board tubes to put in nitro and big Sharps cases to take up space. These reduced case capacity by how ever much you wanted. A good idea I think but I have not been able to find any these days.

Sam

I swept at least 1/4 lb of unburned powder up the other day from the Nitros. 1/4 lb--That is a lot of powder not burning!

I have been fire forming a lot of 375 RUM to 500 MDM the last couple of weeks using 20-21 grs of Bullseye and crammed full of cornmeal! Does a great job! But you would not want to use cornmeal as a filler! Packs up tight! BOOM! But, makes excellent brass good to go right from the start!

Yes, there is much work to be done with fillers and other things as well.

Sam, I spoke with Brian today about a change barrel system. Sounds like a damned Encore is about the easiest way to go, and we can get that in different barrels from 500 Nitro on down to anything we want below that. Still a break open deal, and a pure bitch to deal with from the bench.

FYI--Talking about getting a system set up having all the Nitros chambered and doing test work in several calibers/cartridges. But I am not so excited about an Encore to do that with! I don't know, maybe, who knows what we might do any minute! Wild!

Michael

In my 450 No2 I MUST use filler with any powder.
If I do not I will get hangfires.

With full power loads using IMR 3031, IMR 4831 or RL 15 I have used Dacron Polyester pillow stuffing, and 3 different densities of foam plugs, that I cut from a sheet of foam using a sharpened [with a chamfer tool] 50 BMG case.

In all cases the foam or Poly is COMPRESSED between the powder and the bullet.

I can tell no differences in the different fillers used.

My loads with each of the powders shoot and regulate the same.

Rl 15 shows less pressure and less recoil.

The KEY with any filler is to make sure the filler is compressed between the powder and the bullet and that after travel, hunting and any rough handling the filler IS STILL COMPRESSED.

If, after a hunt, in the rounds you have left over, if you can shake the loaded round, and hear the powder in the case you did not have ENOUGH compression.

If you shoot two or three rounds in the right barrel, leaving a loaded round in the left and you can "hear" the powder in that round then you do not have ENOUGH compression...

Also when I have examined the filler on the ground after firing, either poly or foam, neither shows any signs of melting, burning or charring. Funny thing is the foam will usually be twisted in half.

I use these two types of fillers.
Dacron

Low Density Foam


As Tony states above, the fillers are compressed between the bullet base and the powder. It just simply works for my Vintage British Double.
Again, if your rifle is a modern double you can find a powder that fills the case. As long as your regulation is good, go for it.

So can anybody please address the significant velocity excursions in my 450NE when I used low density foam as described with average to mild loads of RL-15?

For my 450NE I have a consistent RL15 load using 3grns of dacron when I tried going to 4grns of dacron thinking that more would be better, the air filled with dacron after the shot and my consistency when to hell.....since then I have worked up a good H4831 load with out the ned for filler feeling that no filler is one less step and one less variable.

quote:

Originally posted by jorge:
So can anybody please address the significant velocity excursions in my 450NE when I used low density foam as described with average to mild loads of RL-15?

Jorge,

I sent Michael and Sam some actual Kynoch low density .510 foam fillers that look identical to those in Rusty's pic above.

In the trials they will do with them...perhaps they can shed some light on your question.

I will add again...strain gauges do not lie...they tell it like it is irregardless of dogma.

If I had an older double...based on the data that I have seen...I would freely shoot bore-riding driving band type solids such as CEB's or NF's in it. What I would be worried about are the Woodleigh FMJ solids if I were to worry at all.

Thanks, Doc. As you know I shoot a new and very strong action in the Verney and while I don't have a strain guage, my own experience with very divergent velocity excursions whilst using foam and RL 15 was enough for me and I'll not use them again, at leat not in the 450NE, especially when I am getting what I want with H-4831. jorge

quote:

Originally posted by ledvm:

Jorge,

I sent Michael and Sam some actual Kynoch low density .510 foam fillers that look identical to those in Rusty's pic above.

In the trials they will do with them...perhaps they can shed some light on your question.

I will add again...strain gauges do not lie...they tell it like it is irregardless of dogma.

Lane,you are absolutly correct! Strain guages do not lie, they tell you there is a problem, or there is not a problem! However they do not tell you what the problem is.

In the case of filler they tell you how much problem exists, but not why it exists. If you are taking data with a certain filler and a problem occurs that problem could be just the fact that a certain type of filler is the problem, OR it could indicate that that filler was improperly used. So the fact that the strain guage indicates high strain doesn't necessarily mean it is the filler per-se but posibly how much or how it was applied.

So I guess what I'm really saying is in less words the the strain guage only indicates a problem, but not what the problem is!

...............................................

quote:

Originally posted by MacD37:

quote:

Originally posted by ledvm:

Jorge,

I sent Michael and Sam some actual Kynoch low density .510 foam fillers that look identical to those in Rusty's pic above.

In the trials they will do with them...perhaps they can shed some light on your question.

I will add again...strain gauges do not lie...they tell it like it is irregardless of dogma.

Lane,you are absolutly correct! Strain guages do not lie, they tell you there is a problem, or there is not a problem! However they do not tell you what the problem is.

In the case of filler they tell you how much problem exists, but not why it exists. If you are taking data with a certain filler and a problem occurs that problem could be just the fact that a certain type of filler is the problem, OR it could indicate that that filler was improperly used. So the fact that the strain guage indicates high strain doesn't necessarily mean it is the filler per-se but posibly how much or how it was applied.

So I guess what I'm really saying is in less words the the strain guage only indicates a problem, but not what the problem is!

...............................................

Well a strain gauge measures strain obviously and strain is a measurement of deformation...in the case of barrels...elastic deformation hopefully...because plastic deformation would equal failure. So they basically measure how much a chamber stretches on ignition of the powder charge or in reference to the barrel...how much a barrel stretches to accomodate bullet passing through. In my comment...I was mainly addressing the latter in that I believe Michael has conclusively shown that some monolithithic bullet designs are safer for barrels than the dogma of conventional cup and core solids.

In reference to fillers...Michael and Sam are testing the conventional (I think a more relevant term here) use of certain types of fillers used in a conventional way. The strain gauges are bearing out that some conventionally used fillers used in conventional ways actually induce more strain than others in a chamber...therefore...they may be inappropriate.