best signs of "overpressure"

[denton]

4. I know some of you are absolutely wild about using velocity as a pressure sign. There was a test done some time ago on, as I recall, around 10 "identical" rifles. Muzzle velocities with "the same" load varied by about 200 fps. There are fast barrels and there are slow barrels. In my opinion, muzzle velocity is one of the least dependable so called pressure signs. Remember that published muzzle velocities in may cases were obtained from longer pressure barrels.

It's actually one of the best indicators, as long as you're only varying powder charge.

A firearm with geometry on the maximum side will produce lower pressure and correspondingly lower muzzle velocity than one with minimum geometry. If you measure pressure in that "slow barrel", it will be lower, along with the lower MV. So the slower MV correctly predicts lower pressure, and higher MV predicts higher pressure.

The forces acting on a bullet in the barrel are propellant force (pressure x cross sectional area of the bullet), friction, torque (small loss of energy to spinning up the bullet), and engraving force. MV is a result of these, and not anything else I can think of. Friction is pretty constant, as are torque and engraving force for any given bullet. That leaves just the area under the pressure curve. So for any given type of bullet and type and batch of powder powder, the pressure curve tells the entire tale.

 

[noylj]

Signs of over pressure
The first sign is recoil above factory rounds. At the same time, you can trace the case diameter, about 1/4" above the extractor groove, as you go up in charge weight and compare to factory rounds.
Standard pistol primers may show signs with pressure above 35-40ksi. Magnum may not show pressure until above 40-50ksi. Rifle primers will usually not show anything until above 55ksi. Any time you see flattened primers, back off.
Here is a clear case of over pressure from a Winchester .40 S&W NT case:

 

[Trent]

Great read, Slamfire, appreciate it.

Just a side note (lack of time), wikipedia is not accurate on one count. 5.7x28 has a slightly tapered case (quite visibly, if you stack 30 rounds side by side on a flat surface). Early reloading dies were straight walled, and cause malfunctions in the magazine. So they DO have a taper... just a very, very slight one.

Tumbling (and subsequently stripping the lube from) a 5.7x28mm case will cause nasty problems with extraction, and has been (potentially) linked to more than one kaboom (due to cases stretching on previous fires from hard extractions, weakening the walls).

Chemically cleaned 5.7x28mm cases leave the the dry lube intact.

What Slamfire is saying makes sense, on a number of levels.

 

[Slamfire]

I am certain if teflon was available to Schwarlose and Nambu, they would have coated their cartridges with teflon instead of installing an oiling mechanism.

Teflon came post WWII. The US Army tested teflon and wax coated cartridges, must have been in the early 60's. Neither the mechanisms of the time and cartridges needed teflon, teflon added cost, so the results went in the dust bin.

However AMCP 706-260 has a summary, which is in itself an interesting read.


From Army Material Command Pamphlet AMCP 706-260 Engineering Design Handbook, Guns Series Automatic Weapons. Feb 1970

Chapter 8 Lubrication of Machine Guns

8-3 Case Lubricant


Although the gun designer is not directly involved with ammunition design, he is directly concerned with handling, loading, and extracting during firing. A smooth chamber is essential for extraction and a properly lubricated case is a decided asset. The lubricant should be a dry lubricant and should be applied at the factory. Considerable effort has been made to find suitable lubricants for this purpose. Some success has been achieved but continued search is still being advised, especially since two independent facilities are not in total agreement.

The Naval Research Laboratories conducted test of brass and steel cartridge cases coated with films of polytetrafluoroethylene (Teflon). Results were outstanding in meeting required protection and lubrication properties. Laboratory results, later confirmed by firing tests, showed low friction and consequently less wear in gun barrels. Other desirable features include freedom from cartridge malfunction, no chamber deposits, decreased ice adhesion, and less chance of thermal “cook-off”. Teflon can be applied to steel and brass ammunition by mass production methods. Its protective ability permits pre belting and packaging of ammunition since no further handling prior to use necessary. Its supply is abundant and its cost reasonable. Thus the use of Teflon in this capacity seems ideal.

Aberdeen Proving Ground is more reserved in its appraisal of Teflon coating. Whether or not the techniques of applying the coatings were similar, those used at APG were not free of coating defects; a high cull rate existed. When tested with cartridges coated with microcrystalline wax, ceresin wax, and uncoated ammunition; the Teflon-coated wax showed many advantages but was also found wanting in some respects. Teflon and micro-wax had better extraction properties and Teflon left a much cleaner chamber than the others; micro-wax was second best. About 50 percent of the Teflon-coated cases had slight bulges after extraction; other types also were similarly damaged but with no apparent significance attached to a definite choice. For dusted ammunition, the Teflon and micro-wax were far superior to the other two types with Teflon having a slight advantage, although when fired in a comparatively rough chamber, Teflon was outperformed by all. Reiterating, the gun designer, aside from providing smooth sliding surfaces, is almost totally dependent on the physical properties of the lubricant to make his gun perform satisfactorily under all assigned conditions.

The last sentence is a summary of the chapter; not a comment on case lubrication alone. A copy of AMCP 706-260 and other out of print AMCP pamphlets can be ordered from NTIS at 703-605-6000.

 

[Doug b]

"What Slamfire is saying makes sense, on a number of levels."
Yep. Aren't all of us that tumble with Nu Finish using a lubed case? Thanks Slamfire1.

 

[W.E.G.]

how do you tell if it's too hot?

This load was accurate, but it was hell on firing pins and boltfaces.

23.0 grains N135, SMK 80 (moly), CCI 400 (non-magnum) primer, Remington case

We switched to CCI 450 (magnum) primers and all these primer-failure issues disappeared.

 

[Sport45]

I'm a firm believer in using clean dry brass in my guns. I think it stays cleaner and reduces bolt thrust a bit.

That said, I cannot see that little ring of brass having enough tensile strength to make the difference between damaging or not the massive (by comparison) bolt lugs.

So even though I'm in the clean/dry brass camp I do not think the folks that lubricate theirs are hurting anything.

 

[armarsh]

...
...

What am I seeing on the 1978 bullet? Is it grease covered with paper, or just a really waxy grease?

 

[Slamfire]

What am I seeing on the 1978 bullet? Is it grease covered with paper, or just a really waxy grease?

I stole the picture from a poster who uses the name "parashooter". I only have Norma Swiss and my reloads.

Looks to me like a grease with a high percentage of beeswax. Like a toilet ring. But that is appearances only.


From Gunforms.com, this is old and the links are bust.

Date: Mar 17, 2002 on 03:29 p.m.
Gren16
2. Re:Wax on GP11 cartridge


The "grease band" on the GP-11 was adopted as early as May 9, 1913 in form of a 7 mm band. 1942 the band was reduced to 4 mm. There are well over 30 variations of the GP-11. Some with, others without lubrication. The grease band was not welcomed by the troops operating in cold weather as the grease accumulated in the chamber and finally made proper feeding impossible. The grease ring had to be removed with a rag - a tedious job. The use of solvents such as diesel fuel was strictly prohibited as it tended to enter the cartridge and made the round unusable.
Date: Mar 17, 2002 on 04:13 p.m.

Big L.E.E.
Normal member
in Gunboards.Com Members

posts: 169
since: Jul 16, 2001
3. Re:Wax on GP11 cartridge

I'm told many Swiss believe the grease ring improves the accuracy of the round. Independent testing by the German Gun Magzine Calibers would suggest this is the case. The found the grease ring improved accuracy by about 1cm at 300m.
In addition, it is believed the grease ring improves the life of the barrel. Around 1981, the Swiss stopped putting the grease ring on GP11 ammo.uch to the dismay of many target shooters. As a result, it is now possible to by tools to add the grease ring to ammunition manufactured without it. See http://www.swissrifles.com/~swissdagger/bullet_greaser.html for an example.

 

[45crittergitter]

Short of a strain gage or other lab type pressure device, by far the best indicator of pressure levels is a chronograph along with the reloading manual.

 

[Sport45]

Posted in wrong thread...

 

[p5200]

I started using BR4 primers lately haven't had any trouble with the CCI 400's but just feel a little safer.

 

[Slamfire]

I opined up a box of Swiss Surplus today and found all the bullets were greased:



Now, does everyone remember that Hatcher said that grease was incompressible, pinched the case neck, and that greasing your bullets "dangerously" raised pressures.

And my God! there is not only grease on the bullet but it is on the case neck in spades!

Now my, my, what where those Swiss thinking? For decades they were using greased bullets and never knew that their rifles were blowing up.

Or else, Hatcher lied.

 

[Trent]

Heh, you already made a believer out of me about 12 posts ago.

 

[Slamfire]

My pictures are an over reaction to finding a box of greased bullets. No question at all about the Swiss and greased bullets.

I learned from your posts and had fun looking up on the 5.57 forums issues with the polymer coating on the cases. Which I will bet is Teflon. I also found a reference in a 1970's American Rifleman magazine that the US tested Teflon on steel cases. The US used steel cases in WWII. These cases were coated in a chromate, the steel cases caused malfunctions because of too much breech friction. So it was in the 50's that the Army ran the Teflon and wax coating tests.

I cannot understand how Hatcher, or any of those Ordnance Officers writing for the NRA were not aware of this, and yet they kept on piping about the dangers of greased bullets, oiled cases, grease cases, even though the magazine later published something on the teflon tests.

The authors of the American Rifleman Dope bag must have been schizophrenics.

On the 5.57 forum I saw pictures of reloaded ammunition that had been fired and the case neck was ripped off. I wonder if those guys would be doing better, on reloaded ammunition, if they simply left the case lube on and fired the rounds that way. I suspect any factory coating on the case neck gets wiped off during sizing and then the reloaded case neck sticks to the chamber and gets torn off.

I think chamber flutes, as in the HK weapons, would fix all that. But that is a factory fix.

 

[quartermaster]

pressure and cratered primers

I check out primers for flattening as I work up loads. I don't depend on this as the primary way of knowing max loads, but it is a good indicator as you add more powder. You can see the difference.

As far a cratering goes. I have a remmy 25-06 which craters the primers on every load that I have shot through it. It stemmed me to take a close look at the bolt face. The face was concaved around the firing pin hole. If you experience cratering, it is worthwhile examining your bolt face for sure.

 

[HankB]

The various signs of overpressure available to handloaders (sticky extraction, cratered/flattened primers, case head expansion, ejector marks on case head, etc.) are not particularly reliable, and in some cases won't appear until you're well over safe levels. But that doesn't mean you should ignore them!

And in some cases - say, if you're handloading for a low pressure cartridge like a .32 ACP, most shotguns, or a .45/70 to be used in a trapdoor Springfield - you'll almost certainly exceed the design levels of the gun before any of the "classical" signs of overpressure occur. (Although firearm shrapnel is a reliable sign of overpressure, it's a one-time kind of thing.)

On the other hand, SOME reloading data out there is quite mild - in a modern bolt action with good modern components (i.e., strong brass) there's really no reason why a .30/06 or 7x57 can't be loaded up to the same pressure levels as a .270 or .308 . . . or for that matter, some of the new short magnums. Yet even SAAMI lists pressure limits that are lower, out of deference to old guns.

I'm not an advocate of making a standard round into a magnum (a .30/06 cannot safely equal a top load in a .300 WSM with any combination of components I'm aware of) I'm just saying that in some cases you can improve on published data - slightly. If you know what you're doing.

I'll close by saying that in virtually all cases, factory ammo, when chronographed from my rifles, does NOT achieve advertised performance. When my handloads DO achieve what the factory advertises, I figure I'm doing well.

 

[918v]

I keep a close check for primer flattening as one of the first signs myself.

Define primer flattening.

When I load a primer into a case, the priming tool flattens the primer. When the round is fired, the pressure flattens the primer. The same mild load will flatten a Federal primer alot more than a CCI primer.

How flat is too much?

Primer flattening, in itself, is not a pressure sign.

 

[243winxb]

Bullet may have steel jacket.

Seems i remember lube being use on steel jacketed bullets? Could these be steel jacketed?? Found at Midwayusa "Bullet may have steel jacket." http://www.midwayusa.com/product/1918322995/surplus-ammunition-75x55mm-schmidt-rubin-swiss-174-grain-full-metal-jacket-gp-11

 

[918v]

They are not steel jacketed. These have cupronickel jackets.

 

[fguffey]

W.E.G., Every pierced primer I have found was traced to a weak firing pin spring, something about the .7854 thing, it always starts out as pierced primers then progresses to hot, high pressure metal cutting gas cutting the bolt face and firing pin hole, then to cratered primers forming to the bolt face.

Then there was that group of slide and glide shooters, they were fire formers, they greased their cases, chambered them, then fired, the grease prevented the case from locking onto the chamber and as a results, like magic, the case formed to the chamber and no stretch, then they thought everyone was stupid and or believed everything they read on the Internet was gospel. Well, not all, I do not want anything between my chamber and the case I am firing, I want 100% contact between the case and chamber. And every time someone has an epiphany they leave all the details out, without knowing what receiver, make and model of the receiver the rational is at best describing an event in lofty terms, I have loaded and fired rounds that were overloads and produced cases with signs of excessive pressure, none were iffy, none were subtle, and there was nothing to accomplish by doing it twice.

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

Coefficients of Friction.....

There is a thread on 6mm BR fire forming, 14 pages of nothing but insults and dribble, lube the case, do not lube the case, and fire forming fire formers, purchase a rifle, purchase a box of new ammo, chamber a round, fire then instantly become a fire former, I form first then fire.

Hatcher was correct, .080 thousands head space is beyond the ability/limit of a case to form when fired in some receivers, again, friends built 4 03 Springfield 7mm Gibbs type wildcats, 5 of the first 10 cases had insipient case head separation on the first firing.

F. Guffey

 

[fguffey]

Cupronickel and lube, the lube used on the cupronickel was used to deduce the effect the cupronickel had on the barrel, fowling was not easy to clean, conventional methods did/do not work, lubing the jacket of the bullet aided in preventing fowling, Lubing the case should be avoided, I am not angry at Hatcher or Culver and I have no reason for making myself look good at their expense, that would be vain.

F. Guffey

 

[fguffey]

243Winxb, I have a load of 8mmx57 with cupronickel jacketed bullets, $4.70 for 70 rounds, I pulled the bullets, saved the powder and then stored the Berdan primed cases in ammo cans, Hornady accused me of making too many mistakes because their puller would not hold up to ‘as advertised’ I have the RCBS bullet puller now, the RCBS puller never gets tired.

Cheaper than dirt advertised 8mm57 ammo cheap, I called to make sure the jacket on the bullets would not react to a magnet, they said, not a a problem etc., etc.. I wasted a trip.

http://www.turkmauser.com/ammo.aspx

F. Guffey

 

[7.62X?]

Paranoid war pigs just sean him last winter still sound the same all the little kids freeked when I knew ever word to every song HEHE

 

[Slamfire]

I read a Dope Bag article from the Dec 1978 American Rifleman.

The author had been using very old data on the 45 ACP. I am not even going to repeat the cannon blaster load he used, but it was with 250’s and 2400, and he used more 2400 in the 45 ACP than I have used in a 45 LC with a 250!. And yet, the load was in print at the time the unfortunate used it.

The shooter fired three rounds in his Colt New Service revolver, first couple were fine, the third burst the cylinder and bowed the top strap. Maybe it broke the top strap, I forget.

William Davis, the NRA writer replying in dope bag, said that most of that old data was based on “physical evidence” of pressure, such as case expansion, case sticking, primer examination. Basically Mr Davis said all that physical evidence was “unreliable”.

And I totally agree with Mr Davis. Loads developed without pressure equipment can be extremely high pressure and yet never give the slightest warning until the firearm fails structurally.

Colt New Service revolvers, the early ones I have are not heat treated. The plain carbon steel is dead soft. Fine for period loads, if you did not mind the fact the revolver would probably develop end shake in time, but for hot loads, no.

I'll bet this guy never saw or felt this coming. The rifle was a FN in 264 Win Mag. The factory round was loaded hot, I suspect the reloads were an "improvement".