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  #1  
Old 08-06-2009, 08:00 AM
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Pressure Signs


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Load manuals and experienced reloaders frequently advise working a load up in small charge increments while watching for pressure signs. Many beginners are unaware of all the signs. Below is a partial list of them, along with alternate causes of the same signs where I am aware of them. No one particular sign can be counted on to become apparent in all guns, nor even to be consistent with any particular set of load components. There is also no way to tell which sign will show up first in your gun and with your load and component combination, so you need to learn to watch for them all. The standard recommendation, if you get a clear pressure sign, is to back the charge weight of the load down 5%. In most instances, persistent pressure signs do not occur until your pressures are already well above SAAMI MAP.
  1. Case bulging excessively. (This is most often at an unsupported part of the case head.)
  2. Case cracks along its side. (May mean excess pressure, but may mean brittle, defective, draw mark scored, or worn out brass.)
  3. Case head expansion. (A.k.a., CHE. It most often means pressure too high for the lot of brass used, but an isolated example from a lot may mean nothing, as brass is often imprecise, so CHE can occur at pressures that differ by 2:1 within a brass lot.)
  4. Case head separation. (May mean high pressure, but may mean excess headspace or worn out brass.)
  5. Case splits in body in fewer than 10 reloads. Back powder charge down at least 2%; 5% if in the first two or three reloads. (May also be due to excess headspace, a once-fired case from another gun that was highly stretched at first firing (use paperclip probe to feel for pressure ring inside case and reject any where you can feel one), or is less commonly due ammonia vapor exposure or to a brass defect in an individual case.)
  6. Case mouth split in fewer than 6 reloads. (May mean high pressure or ammonia vapor exposure, but more often simply means case needed neck annealing.)
  7. Case mouth split in fewer than 4 reloads (May mean high pressure or ammonia vapor exposure, but more often means case got too hot during annealing.)
  8. Case pressure ring expansion (A.k.a., PRE; not much more reliable than case head expansion but may mean pressure is excessive for the particular piece of brass or lot of brass it occurs with. It can, for example, happen with Federal commercial brass, but not with Lapua brass or with military brass at the same pressure.)
  9. Case primer pockets getting loose in five reloads or fewer. (This is a version of CHE, but may be apparent earlier in pressure. Lowering charge, as in the introductory paragraph, may fix it. However, if the load seems reasonable or is an old standard, same as in 3 and 8, switching make of brass can fix it.)
  10. Case stretching excessively. (This is usually visible as pressure ring area stretching which may be due to excess pressure or to excess headspace. Use a bent paperclip or other probe to feel for thinning at the pressure ring. In rear bolt lug guns, the whole case may lengthen before resizing and be impossible to rechamber without sizing.)
  11. Case, extractor or ejector marks on head, especially after increasing powder charge to next higher increment. (Most common in semi-auto rifles, but can happen with any extractor and ejector. May be due to high pressure, bad timing in a semi-auto action, or may be due to an improperly fit extractor standing proud on the bolt face.)
  12. Case, won’t fit back into chamber after firing. (May mean high pressure, but can also result from a chamber cut at an angle off the bore axis or by an out-of square bolt face. Test for the latter two possibilities by noting head stamp orientation at firing. If case fits back in at that same orientation but no other, then one of these two conditions obtain.)
  13. Gas leak. (See Primer Leaking, below.)
  14. Groups start to open up at or beyond a published maximum load.
  15. Hard bolt lift. (This often indicates excess pressure, but can also result from only one bolt lug making contact until peak pressure is reached (lugs need lapping).)
  16. Incipient case head separation (Starting or partial case head separation or signs of it. Can also be a problem with excess headspace.)
  17. Increase in powder charge achieves unexpected velocity. (Average velocity will tend to increase by the same number of feet per second per grain of additional powder over the normal operating pressure range. If your next charge increment fails to produce the expected additional velocity or produces too much additional velocity, pressure may be high. Poor grouping usually accompanies this symptom. It is also caused at reasonable pressures by uneven bolt lug contact (lugs need lapping), in which case still further charge increments go back to producing orderly velocity increases and grouping improves. Suspect this last situation if the charge at which the velocity anomaly occurs is in the middle of a published load range. Otherwise, back the charge off 5% from where the issue started.)
  18. Primer blown loose. (Primer falls out when gun is opened; same as loose primer pocket, #9, above.)
  19. Primer cratering. (May mean high pressure, or it may mean a worn firing pin or firing pin tunnel, or may mean you have a new production Remington bolt with chamfered firing pin tunnel.)
  20. Primer flattening. (May mean high pressure, or may mean long headspace; some loads always make flat primers; softer primer cups (Federal) flatten more easily than harder ones (CCI), so it may mean nothing at all.)
  21. Primer mushrooming; i.e., primer cup fills out radius at primer pocket perimeter. (May mean high pressure, or may mean excess headspace.)
  22. Primer piercing. (May mean high pressure or may mean incorrect firing pin protrusion or incorrect firing pin nose shape.)
  23. Primer leaking gas around edges of primer pocket. (May mean high pressure, may mean loose primer pocket in case, may mean damaged primer was inserted, may mean excessive chamber headspace.)
  24. Case, short life - back load off at least 2% (under 10 reloads in non-self-loaders, or under 5 loads total in self-loaders before pressure ring is detected with paperclip probe.)
  25. Case, sticky or hard extraction. (Especially in revolvers, this is a positive sign to knock the powder charge down at least 5%. In rifles also look for chamber ringing.)
  26. Case, torn or bent rim. (Caused by hard extraction, see #24 & #25, above).
  27. Case, primer pocket expanded. (A.k.a., PPE; this is the same, in principle, as #9 above, but can be made apparent by measuring with gauges before primers actually are loose. It is a somewhat more sensitive measure than O.D. CHE measurements.)
  28. Primer loose or falls out when opening the action or after seating. (See #9 & #27, above).
  29. Case, increase in required trimming frequency. (This refers to a sudden increase in case length growth per load cycle. It is actually a less acute version of #10. It can be caused by excess pressure, but can also be a sign of increasing head space due to some other problem. It is especially common as a pressure sign in lever action guns because the greater span from bolt face to rear lug allows more steel stretch when pressure gets excessive.)
  30. Case, increase in apparent headspace. (This means the cases are coming out longer, including between the casehead and shoulder. It can mean bolt lug setback, which is usually an extreme pressure sign. It can also mean a loose barrel or an improperly set up Savage barrel. Whatever the cause, the gun should go straight to the gunsmith for inspection.)
  31. Gas or Flame Cutting of revolver top strap. (Can also be due to excessive barrel/cylinder gap that needs correction.)
  32. Gas or Flame cutting of rifle bolt face by gas leaks around primer pocket or at bolt face perimeter. (Can also be result of occasional leaks from normal rounds firing, as is observed in many military gun bolts.)
  33. Velocity higher than manual maximum load velocity reported for same powder charge and barrel length. (May mean excess pressure or a “fast” barrel, but often is actually a chronograph error due to screens being too close to the muzzle blast, bad lighting conditions (watch for ground reflection), or a low battery. In one instance, though, a fellow loading a .243 Win load in the Speer manual and still one grain below the manual maximum was getting velocity readings 200 fps higher than the manual claimed for the higher maximum load. His single-shot action was also popping open at every shot. With QuickLOAD, we were able to calculate he had about 77,000 psi.)
  34. Flash hole diameter growing. (This is a more sensitive version of case head expansion. See #3, #9, and #27, above. It can be checked with pin gauges in the form of numbered drill bits or by special gauge.)
Please contribute any additional signs I've missed.

Credits:
Expansion of 23 based on F. Guffy's comments.
Addition of 5 and 24 based on Kanuck's comments in another thread.
Addition of 27 based on Wm. Iorg's link content.
Addition of 26 based on Precision Shooting Reloading Guide, Chapter 1.
Modification to #10 based on Purpledragon's experience with hot .38-55 load plus the writing of M.L. McPherson.
Addition of 30 inspired by modification of #10.
Addition of 31 based on Tac_driver's suggestion.
Addition of 32 inspired by 30.
Addition of 33 based on a thread I participated in at another forum.
Revision of 17 based on Denton Bramwell's recommendation.
Addition of 34 based on F. Guffey's suggestion for a more sensitive indicator than case head expansion. He made a tool for this at one time that he gave me a copy of, but I don't know if he has any more available as I write this?
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Last edited by unclenick; 06-26-2014 at 04:22 PM. Reason: Updating the list
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Old 08-07-2009, 01:56 PM
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Pressure signs 11, could be yes, could be no

Gas escaping from around primer can happen when the primer drives the case forward causing the primer to unseat, the case is driven back and re-seats the primmer when pressure builds. Caution: when this happens the gas escaping is hot high pressure metal cutting gas, the gas will first show on the bolt face as a black ring, if nothing is done about it the gas will cut a circle in the bolt face around the firing pin, and a pierced primer can be caused by a weak firing pin spring, the pressure inside the primer can exceed the weak springs ability to hold the firing pin forward.

Copper crush/Brass crush, pressure can be determined either way, convincing some one it can be done is the problem. Determining pressure in the chamber is done with something in the chamber as in CUP, the CUP gage is screwed into the chamber, when fired, the case is also in the chamber,

"Primer piercing (may mean high pressure or may mean incorrect firing pin protrusion or incorrect firing pin nose shape"

"Case head expansion (may mean high pressure, may mean nothing in isolated case"

F. Guffey
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Old 08-07-2009, 02:13 PM
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I moved your post into the pressure sign thread to avoid confusion. I didn't realize it was closed. Not meant to be. I've invited input.

My general point in listing pressure signs I've run into is they can mean something else. I'll add your comment to the exceptions in the list for #21, which 11 refers to, and also add that is most likely when headspace is excessive.

I'll keep trying to add any new ones or new alternative interpretations folks post to the list so a beginner can get the information in that one place.

I went to pick up a new .308 rifle one time whose bolt was blackened and a red ring of sealant deposited around the firing pin hole. Someone had decided to try it out and used some hot surplus load, no doubt. Being out of spec is one reason rounds get surplused out, so caveat emptor. But the headspace checked out OK, so it was definitely an ammo problem.
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Old 08-07-2009, 04:44 PM
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Pressure Sign Photos

A few photos of pressure signs mixed in here. http://www.photobucket.com/joe1944usa
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Old 08-10-2009, 11:41 AM
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Thanks for the photos. I will shamelessly link to them as illustrations where appropriate to do so.
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Old 08-15-2009, 10:12 PM
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Ken Waters used case expansion (above the head) measurements as an indicator of over pressure. I believe he stopped at 0.004 or 0.005" over unfired brass, but I sure could have that wrong. He also compared a reload's expansion to a factory load's expansion.

I would have to look this up as I don't use the method. Does anyone use this method anymore?

Last edited by leverite; 08-15-2009 at 10:18 PM.
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Old 08-16-2009, 02:35 AM
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pressure signs

Very good to see this all put in one spot.
Two ideas. The Speer manual references 0.0005" average case head expansion as an indicator of excessive pressure.
The second idea is that straight walled cases, .38/.357/.44 etc may show none of the signs listed and still be over the top. John Linebaugh has an extensive discussion of this and related ideas in his Gun Notes.
See: http://www.foxwebdesigns.com/Area51/...es.html#bullet
Pete

Edit: Thanks for the note about the extra zero in the Speer data.
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Old 08-16-2009, 09:21 AM
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Watch out! Both the Speer manual and Waters use 0.0005" as the max average case base expansion.

Not 0.005" as reported above by myself and Pete D.!
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Old 08-16-2009, 11:56 AM
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Three and seven cover case head expansion and pressure ring (the junction of the inside forward edge of the case head and the case wall, where the brass thins from stretching) expansion. These are often referred to by their initals, CHE and PRE. They have been shown, despite Water's work, to be very undependable, which is why I put no measurements on them. This article by Denton Bramwell shows the same amount of expansion that is supposed to show a limit may be caused by anywhere from 40 kpsi to 70 kpsi in a cartridge that should tolerate about 56,000 psi (CIP).

From the article:

Quote:
Ken Waters helped popularize PRE with his article, “Developing Pet Loads”i. He called
both the strain gage and the copper crusher systems real measurement systems.
Regarding PRE, he said, “It must be understood that this is only a means of determining
comparative pressures, with nothing more to be expected of it. With the data provided,
the pressures of my handloads can be classified as moderate, normal, near maximum,
maximum, or excessive—which is all that is necessary to ensure the safety of the
shooter.” That’s a fairly modest claim, which many have embellished over the years.
Unfortunately, even the original modest claim of being able to put cartridges into five
categories turns out to be optimistic.
It goes on to prove the last point pretty effectively, IMHO, as it pertains to any particular individual shot fired. On the other hand, if you were to fire a statistically significant sample of each loading (say, 30 rounds), then you could probably legitimately say the average result represents a known pressure, but only if you have a calibration of the particular case lot to compare it to. I say that because, if you section a modern Winchester brand .308 Win case, for example, its semi-balloon head profile is quite different from that of a solid, heavy piece of IMI or other military source brass, both of which are not the same as Remington or Lapua or Hornady/Frontier. Looking at their substantial differences, it would be immediately obvious to a dull pre-schooler that there is just no way they would stretch the same number of thousandths in response to some particular absolute pressure.

I have added the initials CHE and PRE to the line items above.
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Last edited by unclenick; 08-18-2009 at 05:49 AM. Reason: corrected information order
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Old 08-16-2009, 11:57 AM
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Remember that Ken Waters was measuring Pressure Ring Expansion (PRE) and not case head expansion.
Ken Waters gave no hard fast rule on PRE – in other words there were no absolutes such as: "Do not exceed .0005” for all cartridges.”

An easy way to check this is to read his article Developing Pet Loads.
Also an easy comparison is between his original 30-30 Pet Loads article and his much later follow up 30-30 Pet Loads Update. You will also notice he gave allowances to new manufactured rifles for the 30-30.
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Old 08-16-2009, 12:07 PM
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We have to stop meeting like this!
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Old 08-17-2009, 06:04 PM
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You beat me to the enter button that time!

Beartooth forum member Rocky Raab runs the forum board Hunt Chat. Similar in nature to the Beartooth board it is a civil and friendly board.

http://www.huntchat.com/index.php

A few years ago Denton, Rocky and I discussed PRE. I believe there are some very good thoughts in this thread from all sides.

Note that most people still attempt to put some correlation between PRE and pressure. Waters was careful and quite clear in pointing out PRE did not equate to pressure. However you feel about PRE it makes for a good evenings conversation. Here is a link to the thread.

http://www.huntchat.com/showthread.php?t=34643
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Old 08-18-2009, 11:08 AM
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Slim,

Thanks for the link. I note the graph Denton put in at the beginning of that thread is the same one he used in writing the article I linked to. I realize the range I gave for pressures was for CHE, while PRE is better. Still, Denton's experiment used one gun and one lot of brass that all had the exact same load history, and used one powder and bullet, thereby isolating variables. As soon as you mix in cases with different load histories (and therefore different degrees of work hardening), different brands, different calibers, all of the above with different primers and powders and bullet weights and the resulting different pressure dwell, then you can expect Denton's plot boundaries would expand dramatically. Yet, the tale continues to be circulated on the Internet and posted in various web pages and even in magazine articles, that the same numbers of thousandths or ten-thousandth will apply to all cases in any condition, universally resulting in hard estimates of PSI. And this is written by authors who would never dream of posting a load without the details of the case brand and the other components

As you say, Ken Waters never pretended there was a PSI association to particular expansion numbers, but as Denton's project shows, any individual test round's result is a crap shoot in terms of meaning. The methodology easily fools people into thinking the system is working when it is actually randomly presenting expansion at lower pressures than average that stop them from raising the load high enough to get into actual pressures of concern. So they never get into trouble and think the system is working great.

If you invested in 30 rounds of reference ammunition from whatever company is assigned by SAAMI to provide it in your chambering, and enough new case identical to those used to roll the reference loads, you could set up a useful PRE pressure measurement. You would first fire the reference loads to find the PRE of each round after firing at the reference pressure. This would let you establish a reasonably good average PRE. It takes about 30 samples of anything random to have reasonable confidence the bell curve is symmetrical and that its peak (the norm or average value) is a representative average. You could then load 30 copies of every prospective test load into those new identical-to-reference-load cases and determine that the average PRE for each prospective test load did not exceed that of the reference load average. This would give you reasonable confidence in the system as a pressure measure. You need the new cases for your test load so you have the same load history on your test load cases that you did for the reference loads. That is, no previous firings.

I will add a line for PPE to the list.
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Old 08-19-2009, 12:39 PM
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Nick, One thing to consider is that in the days before handloaders had ready access to chronographs and there were no PCs our options were quite limited with regard to developing handloads. Ken Waters and others were working pre Powley computer.
After WWII handloaders were working with powders which were not included in anyone’s reloading tables.
A review of reloading literature from the 1950’s and ‘60’s includes discussion of both CHE and PRE measurements and techniques. Today the Speer 14 manual discusses PRE as a useful tool for the handloader working with wildcat and proprietary cartridges.

Ken Waters, P.O. Ackley and others often wrote that with a lack of reliable pressure information the handloader need not obsess over pressure in terms of specific PSI. Ken Waters wrote several times about loading for the 22-3000, R-2 Lovell and the Maximum Lovell and the widespread practice of overloading the cartridges. Ken Waters loaded the R-2 for many years and wrote the handloader with established handloading goals and using PRE to establish stop points could remain out of trouble while developing loads for wildcat cartridges and when using unknown powders in any cartridge.
I have found these thoughts to be true while working with the 30-30AI and 25-35AI. I have established stop points based on my prior established goals for these cartridges. My stop points allowed me to meet my velocity goals while developing data which is interchangeable between all of my rifles chambered for these cartridges. It is true that my velocities with both cartridges are not quite as high as some have reported and I attribute this to my desire to have ammunition useable in a variety of rifles rather than ammunition developed for a specific rifle.

Working with new powders such as IMR 4007 in the 307 Winchester is “flying blind” and I am working by the best guess method – backed up by chronograph and PRE established stop points. In this specific situation I found IMR 4007 did not develop expected velocities until heavily compressed. Heavily compressed IMR 4007 appeared to reach its balance point, developing expected velocities – similar to those provided by other powders – while delivering good accuracy. IMR 4007 also proved to be quite flexible with regard to bullet weight and ambient temperatures. It will be a very long wait before the handloader sees pressure tested load data for IMR 4007 and the 307 Winchester cartridge. By establishing a load plan which utilized expected velocities backed up by a firm PRE stop point I have achieved my velocity goals with the added comfort of long case life. I don’t need to know what the actual pressure in PSI or CUP is; my velocity goals have been met with a reasonable feeling of comfort.
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Old 08-19-2009, 05:54 PM
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Nick,

Part of the trouble with lap tops is you are generally working away from you data source!
The Speer manuals do not make reference to PRE but to CHE.
Speer 13 provides a more detailed description of CHE measuring technique on page 53.

Speer 14 describes the calibration of pressure guns on page 58 and provides a simplified description of how the copper crusher pressure gun is “calibrated.” It will shake anyone’s faith in the reliability of the copper crusher method of pressure testing.

I believe one of the best article ever written on pressure measuring equipment was: “Ballistic Breakthrough. A new means of determining true pressure” by: L.E. Brownell and M.W. York, 18th Edition, Handloaders Digest. Page 58 has more than a few eye opening remarks about the copper crusher method of pressure measurement.
Mr. W.F. Jackson wrote a sidebar: “Defense of the Crusher Gauge.” Mr. Jackson was the Assistant Director of Research and Development for du Pont.

As much as I admire Neal Knox I have never liked his article in the September 1973 issue of Handloader titled: How Much Pressure? Approximate CUP can be determined from measuring case expansion and hardness.” I believe this article be very miss-leading.
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Old 08-19-2009, 06:04 PM
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I think Knox fell into the trap Denton Bramwell was talking about.

The other thing Denton did was make a correlation between copper crusher and piezo PSI readings. I took his original data and reordered it monotonically so that Excel's trend solvers could also work on it in non-linear trend functions. Though that gave me a power fit that has a little bit higher R squared test value than Denton's straight line (and which goes to zero for both forms) that data is nonetheless a pretty good demonstration of how inconsistent the crushers are. It simply was never a sound metrological method. But as you pointed out about brass expansion in early days, a century ago the crusher was all they had, so they had to make do with it. Also, I understand that on the same copper crusher unit with the same operator, it is apparently repeatable enough that you can make two different loads match pressure pretty well if the speed of the powders isn't too vastly different. So, it would allow a manufacturer to make loads that were like his other loads measured on that one machine, but would not be too dependable beyond that.
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Old 08-26-2009, 04:06 AM
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Added #27.

To complete the thought in my last post: If the copper crushers, with their calibrated slugs, could never be made consistent enough to measure pressure reliably, the idea a few cling to, that uncalibrated brass can do better, is just absurd.
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Last edited by unclenick; 08-27-2009 at 08:49 AM. Reason: typo
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Old 08-26-2009, 10:39 AM
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great info!

Good to know there's a factor of safety in these matters. Only so much powder can be crammed into the brass before the bullet oozes out the case after seating. Even a heavy crimp won't hold it in.

;>}
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Old 08-27-2009, 08:51 AM
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One of the other fellows on the board pulled the bullet from a round of Hornady Light Magnum ammo. He said the powder just gradually expanded until it overflowed the case. I know the powder is proprietary, but don't know if it is plasticized to be elastic or how they are doing that?
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Old 08-27-2009, 09:22 AM
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Nick

Rick Jamison reported the same thing when the Light Magnum ammo first appeared.

I don’t know if you have worked with IMR 4007 yet or not but it is a very “plastic” type powder and compresses beautifully. In medium capacity cases such as the 308 Winchester IMR 4007 does seem to approach its balance point until it is heavily compressed. A compressed load in the 307 Winchester performs well with regard to velocity and accuracy.
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