PRESSURE QUSTIONS

[chance_livewire]

ok fellas i need some help i have a 6x284 im reloading for, and im fairly new at it. so heres my question?

 im using 49 grains of imr4350  100 grain power point
 6.5x284 lapua brass necked down to 6mmx284
 
  i dont know the formula for figuring out the cup pressure of this round?and the fps. and knockdown

 all this is thru a 22'' standard contour single shot nef. with muzzlebreak.

[Graybeard]

Wal geewhiz Chance no one else does either cuz it can't be done. You don't "figure out pressure" you MEASURE it. Iffen you ain't got the measurement equipment and 99.9% of us don't then you are really working in unknown territory once you leave the loading manuals and their pressure tested loads. Sure there is the Powley computer and some other computer programs that purport to guess at pressures but they can be off by enough to blow up you and your gun so are at best wild guesses. All the "old tried and true" methods have been proven to be nothing more than hogwash by folks using pressure measuring equipment.

You can look to book loads for rounds with similar case volume or hunt down whatever pressure tested data there is. In your case the 6-284 is almost a twin of the 6-06 aka .240 Wheatherby so some decent pressure tested data is out there and can be used carefully in working up loads. But without measuring equipment you'll never KNOW but only guess.

[303Guy]

 Greybeard is quite right!  (Of course).  But there are a few tricks to help with the guesswork.  One is to compare a given fired primer with a known pressure, to your loads.  That helps little until you have a reference in your own rifle.  That means firing a primer in an empty case.  That gives you some idea of the firing pin indent.  The primer flattening inward onto the firing pin indent and reduction of the indent depth give some indication.  (So does flattening toward the outer edge).  Another trick is to make a small indent in the case wall, somewhere near the neck and see how it pushes out on firing.  This too only helps if the indent is consistent and is done with each powder increment.  At some point in the pressure curve, that indent will start to push out.  If the strength and thickness of the brass is known, a guess can be made.  If that indent disappears on the first firing then run!  Your pressures have exceeded the strength of the brass!  Well, maybe.  My indents take about three firings to disappear, in a thin walled low pressure hornet.  I use that indicator when changing powders or bullets, to compare the new pressures with the 'standard' load.  But it is guesswork and no values can be deduced.

303Guy :

[Lone Star]

Greybeard is quite right!  (Of course).  But there are a few tricks to help with the guesswork.  One is to compare a given fired primer with a known pressure, to your loads.  That helps little until you have a reference in your own rifle....

As GB states, this method has been proven to be BS.  Hornady even devotes a page in their manuals to showing how it is misleading and not reliable.  The same can be said about case head expansion - it is a "too late" measurement.  The average handloader can obtain dependable pressure measuring instruments like the Oehler M43, but expect to spend the cost of a top-quality rifle setup - ca. $1450.


.

[R.W.Dale]

 Unless you're looking at a primer that's fallen out, any estimations of pressure based on examination of a fired case is little more than a wild guess

[303Guy]

Quite so.  No estimation of pressure can be be made - I thought I made that one clear!  But we repeatedly hear about working up a load.  Standard practice actually.  But no-one use pressure measuring equipment to do so.  So what does a person do?  Well, I make dings in my cases, I look at loading tables, I look at primers, I measure case dimension changes, and then I guess.  Hopefully I err on the low pressure side.  In the case of the hornet, any case deformation would indeed be too late!  In the pictures, kindly posted by krochus, I read excess pressure signs on all the primers!  That would make me  run!  But if you know what you are doing, you can  get some ball park idea  of the pressure.  But only if you know what you are doing.  The answer to  chance_livewire's question is no.

By the way, hornet load data gives certain loads and pressures.  BUT, not the bullet make!  Well, by using my methods, I determined that I had to keep to a much lower powder charge than the tables would otherwise indicate, with the bullet of my choice.  I could have been wrong, of course.  But I am still in one piece (for now).

But please note:   I am not suggesting flaunting the safety rules and procedures.  (And I'm not disclosing my load data, just in case it is wrong).

303Guy

[Siskiyou]

The 6mm-284 is a great round.

I just checked two recent reloading manuals, Hornady 7th Edition which shows a maximum of 43.9 grains of IMR4350 with a 100 grain bullet.

And the Sierra Edition V which shows a maximum of 43.5 grains of IMR 4350 with a 100 grain bullet.

I am sure that the maximum recommended by Hornady and Sierra was developed using expensive pressure measuring instruments.  As a reloader I would have to use their data as my measuring device because I cannot duplicate it.  I find the near consistency between the two-recommend loads in two different rifles reassuring that the data is on the mark.  I believe that your load is approximately 12 percent over the published loads. 

My Wildcatter brother shot a deer a few years ago with his 6mm-284.  He was very impressed with the results.  The deer was on the ground at the sound of the shot.

[303Guy]

A 12 percent increase in powder will produce a more than 12 percent increase in pressure - the increase is exponential.  The difference between a 'normal' looking pressure and an 'excess' looking pressure is very small.  Just look at those primer pictures.

303Guy

[SHOOTALL]

one way to stay out of trouble is measure the expansion ring above the base of a new ( unfired ) case as you work up in power use a new case each time and record the expansion , it should never get as large as case size , i don't like to see it get to where it is all to one side ! there is a not to exceed measurement i want to say .04 but not sure , i will try to locate it or you may find it in a reloading guide ! the reason to use a new case each time is that's the only way to get a good reading on the true expansion not the collective expansion of more than one firring .

[SHOOTALL]

looked on line and the only measurement was .02 for factory new ammo , i don't have a manual handy will look later !

[Graybeard]

NO-NO-NO!


The myth of pressure ring expansion as a valid measure or guide to pressures has been debunked by almost every magazine writer in the business. Pressure testing has shown it to have little to no validity and the way it is described here and in most places is not and never was the suggested way to use it. I will not detail how it was to be used as it's been proven invalid too many times to continue discussing it here. I am not going to let this unsafe practice continue to be pushed here at GBO. No further discussion of that invalid method will be allowed to stand and all such posts on it will be deleted henceforth.

[SHOOTALL]

sorry it was in a magazine i just got !

[Questor]

Now this is the scariest reloading post I've seen in years! The terms "6x284" and "farily new at [reloading]" are incredibly incompatible. The 6x284 is a rare wildcat for which there may be no data published from a reliable ballistics laboratory. If you can't find good data that you can trust, discard the barrel. My recommendation is to go to some of the varmint shooting sites and see if you can find someone that can give you a lead on reliable, professionally developed data.

[Graybeard]

sorry it was in a magazine i just got !

Me too and I think he is the ONLY major magazine writer who has not yet come out publicly against the use of that method and he put some serious limitations on it but even what he said wasn't the way it was supposed to be used.

My concern is that people with inadequate knowledge will try to use it and get themselves in trouble and say they read it here. I was a bit amazed when I read the article you mention myself. Some folks just have their head in the sand and clearly he is one of them. I've seen it in that same magazine several times already debunking the use of that method and yet he then comes up and more or less says it's still valid. Quite amazing really.

[Questor]

I dunno, GB, but it seems like it's more common than just one guy. I recall recently reading a variety of articles citing loads that were worked up by the author, or some other unreliable source. It's as if we're supposed to trust some rancher who writes for gun rags as much as we trust professional ballistics engineers who do load testing for a living. Maybe it's just one or two that still claim to read pressure signs from the debunked indicators.

Then there are the reliable indicators, like wrecking the gun, being blinded, losing a hand, and having the top of one's head blown off. Those are definite signs of high pressure that nobody has yet debunked.

[Siskiyou]

A quote from my earlier post:

“I just checked two recent reloading manuals, Hornady 7th Edition which shows a maximum of 43.9 grains of IMR4350 with a 100-grain bullet.

And the Sierra Edition V which shows a maximum of 43.5 grains of IMR 4350 with a 100 grain bullet.”

A quote from Questor,

“The 6x284 is a rare wildcat for which there may be no data published from a reliable ballistics laboratory. If you can't find good data that you can trust, discard the barrel. My recommendation is to go to some of the varmint shooting sites and see if you can find someone that can give you a lead on reliable, professionally developed data.”

Now Hornaday has been in the bullet business for a lot of years and I recall buying Hornaday ammunition over 20-years ago, and bullets over 40-years ago. 

Sierra has been in the bullet and ballistics business for over 55 years.  They provide free of charge technical support to shooters.  They can be reached toll-free at 1-800-223-8799 or e-mail sierra@sierrabullets.com


Do you think in this day of litigation these two sources do not use their own ballistic laboratories to develop the loads they publish in their manuals?  I believe these two noted data sources in the reloading/ballistics world chose to add the 6mm-284 to their manual because the following for the round is on the increase.

Another popular wildcat round is the 6.5-284.    Commercial cases are available for this round and again Sierra and Hornaday have chosen to publish data for these to rounds.  Will commercial brass be next for the 6mm-284?  Commercial cases are available for the 6mm-06, so the day is coming. 

My recommendations is that chance_livewire purchase one or both manuals that I referred to.  Check his health insurance and make sure he has good liability insurance to cover claims from those injured from fly debris.  Twelve percent over published maximum is scary.  I also commend him for asking questions, at the risk of taking some heat. 

[SHOOTALL]

GB , took you comments as  good advice , now with regard to the round in question , I believe SHOOTING TIMES or SHOOTING  has an article on it this mo. with some of the imfo requested .

[Graybeard]

Clearly I don't subscribe to or read nearly ALL the magazines put out these days. But I have seen articles in I "think" all those I do read and from most all the major name writers these days debunking most all the older and formerly accepted methods to check for pressure using "signs and portents" in lieu of pressure testing equipment.

Now knowing how rag writers are I'd not put it passed some of them to say one thing once and then revert back to the "old line" in yet another article as most of them do seem doomed to relive history many times over and are hard pressed to break from the traditional story line on most anything. But most at least seem to have at least at some point in the last few years admitted that there are no reliable and safe methods to guesstimate pressure. Trying is a dangerous business.

If like me you've had a gun come apart in your hands from high pressure you'll know first hand just how little fun it is. We've all these days seen the photos of the results of high pressures on guns even if we've not experienced it ourselves but having it happen to YOU like it did to me is a real eye opening experience that leaves a lasting impression on you and is a real wake up call. It is for that reason that I keep harping so long and loudly on this issue.

The 6-284, 6-06 and .240 Weatherby all have roughly the same case capacity. It's not exactly the same by any means and two of them are mostly if not completely wildcat rounds at this time so there is but little pressure tested data for them. Magazine articles most of the time do not contain pressure tested data so even if it was "safe in their rifles" as they so love to state that doesn't necessarily mean pressures weren't in the 80,000 range as opposed to in the 65,000 range that is generally taken as max for all the more modern rounds these days. Those same loads in your rifle could give up to 100,000 or more pressure just as easily or drop to under 60,000. The problem is you have no way to know without pressure testing equipment on hand to test the load using YOUR components in YOUR rifle. Still there is some data out there and when working with such a round it is wise to get your hands on as much of it as you can. Read it all and compare what different sources offer and then you must make up your own mind as to where you begin and ultimately where you STOP in your load development.

Working without a chrono is sheer foolishness in the case of such wildcats. Velocity and pressure do have a lot of correlation even tho it's not a direct straight line correlation. But if in your barrel you reach what the sources (any of the sources) say was max velocity and I'd use the lowest of them in this then STOP and consider it max in your gun. Don't try to exceed what they got and if one was significantly higher than the others by all means don't try to match that velocity as there is for sure some reason why it was the stand out velocity and that is likely because it had the stand out pressure which in your gun might be a grenade ready to explode.

[Siskiyou]

It is rather difficult to compare pressures in different custom rifles.  As I recall the Mark V Weatherby barrel had a 5% free bore.  This was to drop the pressure in the Weatherby rounds.  The same chambering in rifles without the free bore locked up the actions using Weatherby ammunition.  Typically the family wildcatter has his barrels free bored or chambered for the heavier bullets in a given caliber which theoretically provides a slight free bore when shorter, lighter weight bullets are load.

I remember when a one of our neighbor’s, Tom, bought a new barrel for his Model 70, it was for a rare, unknown wildcat, that offered high velocity, light recoil, and offered maximum velocity with surplus 4831.  Tom hunting group would not stoop to owning a .270, but this new miracle round had them in awe.  I should note that Tom was a cracked shot and always left the pre-Thanksgiving Turkey shoot with a couple of birds in a crate.

At about the same time I was hearing about another “rare” cartridge.  A number of rock chuck hunters in my area were having rifles chambered for it.  It was almost as flat shooting as the .220 Swift.  And barrel life was supposedly better.

A few years later I read a couple of articles about these two cartridges.  Like every article in a gun magazines the cartridges produced outstanding results.  Around 1965 Remington made chuck hunters happy when Remington started chambering the model 700 in the .22-250 Remington.  In 1970 Remington chambered the Model 700 in .25-06.  I suspect that Tom tried some of the new factory in his old, rare, custom barreled 25-06.

In the marketing world it is difficult for me to predict the next miracle cartridge.  But an indicator is one starts seeing publish data from major firms.

One source that I failed to mention regarding the 6MM-.284 was the Hodgdon, IMR, and Winchester site with reloading data for numerous cartridges.  It also provides pressure measurements for its loads.

 http://www.hodgdon.com/

A sample of 6mm-284 loads from the Hodgdon site, along with pressure.


85 GR. BAR XLC    85    Retumbo    .243"    2.750"    57.0    3131    43,600 CUP    59.0C    3272    48,800 CUP          
85 GR. BAR XLC    85    H1000    .243"    2.750"    57.0    3201    44,400 CUP    59.0    3271    47,400 CUP          
85 GR. BAR XLC    85    H4831    .243"    2.750"    53.0    3170    45,200 CUP    56.5C    3370    51,800 CUP          
85 GR. BAR XLC    85    H4350    .243"    2.750"    49.0    3193    45,500 CUP    52.0    3370    51,800 CUP          
85 GR. BAR XLC    85    H414    .243"    2.750"    49.0    3243    47,300 CUP    51.0    3399    52,100 CUP          
85 GR. BAR XLC    85    760    .243"    2.750"    49.0    3243    47,300 CUP    51.0    3399    52,100 CUP          
90 GR. SPR SP    90    Retumbo    .243"    2.750"    55.5    3185    46,300 CUP    59.0C    3338    51,900 CUP          
90 GR. SPR SP    90    H1000    .243"    2.750"    52.0    3072    45,900 CUP    55.5    3241    51,900 CUP          
90 GR. SPR SP    90    H4831    .243"    2.750"    49.0    3101    47,100 CUP    52.5    3272    52,200 CUP          
90 GR. SPR SP    90    H4350    .243"    2.750"    44.5    3077    46,300 CUP    47.5    3223    51,800 CUP          
90 GR. SPR SP    90    H414    .243"    2.750"    44.0    3046    45,500 CUP    47.0    3193    51,800 CUP          
90 GR. SPR SP    90    760    .243"    2.750"    44.0    3046    45,500 CUP    47.0    3193    51,800 CUP          
100 GR. NOS PART    100    Retumbo    .243"    2.760"    54.0    3018    44,400 CUP    57.5    3219    51,800 CUP          
100 GR. NOS PART    100    H1000    .243"    2.760"    52.0    3007    47,300 CUP    55.0    3145    52,200 CUP          
100 GR. NOS PART    100    H4831    .243"    2.760"    48.0    2960    46,400 CUP    51.0    3108    52,100 CUP          
100 GR. NOS PART    100    H4350    .243"    2.760"    43.0    2925    46,300 CUP    46.0    3066    52,000 CUP          
105 GR. SPR SP    105    Retumbo    .243"    2.800"    51.0    2901    45,700 CUP    54.5C    3070    52,000 CUP          
105 GR. SPR SP    105    H1000    .243"    2.800"    47.0    2794    45,700 CUP    50.0    2913    51,600 CUP          
105 GR. SPR SP    105    H4831    .243"    2.800"    45.0    2804    47,700 CUP    48.0    2978    52,200 CUP          
107 GR. SIE HPBT    107    Retumbo    .243"    2.800"    53.0    2972    45,700 CUP    56.5C    3138    51,800 CUP          
107 GR. SIE HPBT    107    H1000    .243"    2.800"    51.0    2879    45,700 CUP    54.5    3069    52,400 CUP          
107 GR. SIE HPBT    107    H4831    .243"    2.800"    48.0    2946    48,000 CUP    51.0    3049    52,200 CUP          
115 GR. BAR SP    115    Retumbo    .243"    2.650"    50.0    2805    47,500 CUP    53.0C    2934    51,900 CUP          
115 GR. BAR SP    115    H1000    .243"    2.650"    46.0    2682    46,400 CUP    49.0    2805    52,200 CUP          
115 GR. BAR SP    115    H4831    .243"    2.650"    43.0    2670    46,500 CUP    46.0    2797    51,800 CUP          
NEVER EXCEED MAXIMUM LOADS

[demented]

It begins to seem as though rifle cartridge reloading is akin to Voodoo or something else as supernatural.  If I paid attention to primers, half the factory loads I've used in my 7mm mag. would be overpressure. I've loaded handgun ammo over 30 years, the more I read about rifle overpressure, the more I hesitate getting into rifle loading.  I just bought new brass, four pounds of powder, primers and bullets to use in my .308.  After reading how easy it is to blow up a rifle, I begin to think my money was wasted!      I'd like to duplicate factory ballistics, but not if there is a chance of killing myself in the process.  Yes, I can download, but using a .308 at 30-30 velocity ain't much fun!   

[SHOOTALL]

as long as you use a good reloading manual and stick to what it says you should be fine , where people get in trouble is trying to tweak out a little bit more than  the listed load calls for ! Winchester ammo put out a booklet that gave the load to match the factory loads a few years back , check the Winchester site they may list them for 308 win.

[303Guy]

It begins to seem as though rifle cartridge reloading is akin to Voodoo or something else as supernatural......

I know what you mean!

I always tried to select a powder that filled the case before overload conditions could arise.  Not really possible, as I like heavy bullets (I'm convinced they work better at the receiving end) but I choose a powder to suite the heavy bullets then live with the results for lighter bullets.  I deviated from that principle with my hornet due to availability.  But at least hornets are less explosive than bigger cartridges .  And I don't like empty space in the case but that's just me.

303Guy   

[Siskiyou]

Hodgdon is now the distributor for Winchester, IMR, and Hodgdon powder.  If you go to the link I provided you will find loads for all three brands.

And I agree with SHOOTALL buy one or more good reloading manuals.  Every few years I update my manuals, I hang on to the old ones.

When you were a kid you went down to the Department of Motor Vehicles and a copy of the vehicle regulations so you could pass the driving test.  You drive but you know there is a risk in driving.  There is a risk in any thing you do.  The other day I was almost run over by a fat lady while I was out walk.  A year ago I was running out of the way when a guy talking on a cellphone drove off the road.  I have never had these close calls reloading ammunition.  There is no doubt in my mind that taking a walk is more dangerous then reloading.

By consulting reloading manuals, and being cautious I have never blown up a firearm.   I wear safety glasses, hearing protection, and light leather gloves when I do load development.  And the first aid kit is in my pickup.  Yes, I have messed up.  When I do I correct the error and move on. 

[GregP42]

Guys,

If you have to know why not just buy the instrumentation? RSI sells the hardware and software at a decent price, I know I am going to get it with my next tax return this winter.
http://www.shootingsoftware.com/pressure.htm

Greg

[Graybeard]

That's pretty cheap compared to the Oehler system but those little things ya glue on sure are expensive and I think you'd need one per gun which if a fellow has a lot of guns would get expensive but still this really does bring pressure measuring equipment into the price range of the average serious shooter. But topping out at 80,000 I suspect it would fail to be adequate for the loads a lot of folks try to pass off as safe on the internet. 

[GregP42]

Bill,

Yes, they are not that cheap, but compared to me buying a new head.... well they are cheap then. I am not sure if you can take them off and put them on another weapon or not, but even if you could I am not sure I would trust  not hurting that sensor somehow.

Greg

[demented]

I agree manuals do give one a starting point. BUT and this is a big but..any and all loads approaching advertised factory loads are at or close to maximum safe pressure in the test rifle.  Sooo, when working up a good load for a particular rifle, there are so many variations from one chamber, one bore size to the next, even those charge weights listed as safe in the books MIGHT not be safe in any given rifle.  All this leads back to square one, how does the average reloader tell  whether this or that load is safe?  You can check three  different manuals and get three entirely different answers to the max load question.  All this does is add even more confusion, especially to someone just getting started. Not arguing that primers are the place to look for pressure signs, but again, I've seen quite a few factory loads that created flattened primers which adds more to the confusion list. Do the factory's  know something or possess information we don't?

[Graybeard]

Yes to both. They possess good pressure measuring equipment and the knowledge of how to use it. They have access to powders we don't as well. They use SAAMI minimum spec chambers and barrels to do the pressure testing in as well knowing that should equal the worst case scenario their ammo will be used in. They are working with brand new never fired cases as well.

[Questor]

demented:

You're kidding, right? In the choice of amateurs vs. professionals, I'll bet on the pros every time.

[SHOOTALL]

if in fact you check 3 different loading manuals you are checking 3 DIFFERENT bullets with different max. loads !
which would tell me each bullet/primer/powder / case has a different max. pressure ! which goes hand in hand with the question ! the books give what was safe , what they are willing to call max.
I feel safe in saying it is not the MAX. pressure for the gun , even proof houses can't tell you that , they only say a certain load is safe and in most if not all cases it is less than the proof load !
the max. SAFE load is in the charts for the average re loader , the expert can go farther but even he would not know max. to know that you would need to blow up the gun and realize your previous load was max. as no two guns are the same ! I offer this as food for thought , in a 7BR i shot in competition i loaded max. in dec. now when i was shooting back a few years you could get charts of ? artrhors , anyway i had this really heavy load i worked up in December , shot it in Jan. , Feb. and Mar. , picked up a new gun and did not shoot the 7BR until Aug. the load was hot , i had a hard time opening the bolt on the first 5 the 6th shoved the primer back into the fireing pin hole and half the case stuck in the chamber ! i offer this to show that max. press is different as the temp. changes .