| Posted: Wed Nov 4th, 2009 08:27 PM |
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KY Hunter
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Ok - here is my basic question.
When a round is loaded to accepted pressures and fired, the brass expands to the inside wall of the chamber and then relaxes a little which makes the bolt open easily.
When a round is loaded to very high pressures and fired, the brass expands to the inside wall of the chamber and then what happens to make the bolt hard to open?
Does it not relax or return to just under the chamber ID? or why with the chamber determining the maximum expansion, would the round cause the bolt to be hard to open or extract?
Looks like the millisecond the pressure is present, the extreame pressure or the normal pressure would expand the brass to the same dimension inside the chamber and the chamber see the pressure, not the brass?
I know something is different or the brass reacts different, but what exactly?
KY
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| Posted: Thu Nov 5th, 2009 01:17 AM |
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fryboy
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the case head expands more and being thicker it doesnt contract like the walls and neck does ,on a real hot load even the chamber steel stretches and after enough hot loads kinda stays that way ( IMO )it also expands against the bolt thus helping make it harder to open/close , when u see extractor marks on ur case head ur getting into the area of courting with disaster
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| Posted: Thu Nov 5th, 2009 01:41 AM |
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MontanaShooter
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It is always better to be safe then sorry and high pressure is pretty hard on the brass, the gun, and can be dangerous to the user. If a chambers good and loads good atleast in my opinion the primers should not be flattening and brass should reform fairly easy when resizing without requiring both hands and the back of your bench coming off the ground. I have a friend that loads 308s to the point of "hot" and they swell ahead of the case head approx a 1/4 inch or less in anyone of his 308s. I asked him if he could back them off a little bit, in fact not long ago one of his cases separated in the chamber (which by the way wasnt the first time). Im sure this wasnt due to natural wear and tear but excessive pressure and prob quite premature. Hes been loading prob since the 1960s! I dont know why people try and cram as much powder as they can in a caliber, if you wanna make a 308 shoot like a 30 06 or a 300 win mag shoot a 30 06 or a 300 win mag. By the way that wasnt a bash on 308s there i dont even wanna go down that road been there done that will never surrender:) Also if your lubing your cases properly and still getting them stuck frequently in your sizing die your prob bulging your cases. Last edited on Thu Nov 5th, 2009 01:49 AM by
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| Posted: Thu Nov 5th, 2009 02:06 AM |
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OldManMontgomery
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Ky Hunter;
Normally a cartridge expands against the case walls and then shrinks back somewhat. When pressure is excessive, the head (or web) of the cartridge is crushed and expands in diameter. Conventional wisdom is .002" over what it was. PLEASE NOTE: This is only for rifle cartridges running at the 55,000 to 60,000 psi range. If your .38 Special case expands .002" at the case head - thank God or your Fairy Godmother or somebody.
Other signs of excessive pressure in full rifle rounds are loose primer pockets and a smudge ring around the primer. (It means propellant gas is leaking around the primer. Bad juju.)
If, as Fryboy mentions, the load expands the chamber; give all your reloading stuff to someone else and buy ammo from there on out. That is a monstrous overload.
The expansion about a quarter inch in front of the rim is another matter. That is about where the head (web) ends and the case walls begin - the combustion chamber part. Expansion there is quite common and comes from either brass a little on the small size in the manufacturing process, or an oversize chamber. This occurs in surplus military rifles more than commercial rifles. The condition can result in premature failure of the case. For a first or second loading, it is not in and of itself dangerous, but can be a pain in the yarmoosh. Full length resizing simply speeds up the process of case failure.
Case head separations are another matter. Sometimes the case body expansion is caused by excessive head space. Excessive head space can be caused not by an over long chamber, but by excessive resizing, setting the shoulder back. If this continues, the case will separate, usually at the junction of the head and the case wall. Sounds like Montana's friend with the .308 has this problem. Simple over loads will usually beat the headstamp flat and emboss the ejector slot or hole into the face of the case.
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| Posted: Thu Nov 5th, 2009 02:22 AM |
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MontanaShooter
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Actually this happens on three rifles, a FAL, Fairly new built sporter, and a M1A, both civilian and military cases. Of course his brass is mixed and what not from one to the other. Once i fired one of his rounds, when i opened the bolt the primer fell out. Perhaps theres a few problems then huh? Of course never have again. I had a imported sharps that they didnt get the falling block guide slot (sorry dont know how to call it proper) milled out true, the pressure egged the chamber do to the uneven block behind the case head over time (20 thousandts). I rebarreled it and with some help fixed the unsquare part. In 30 carbine i got a few loads a little on the higher end once, and they were a bitch to resize, but cycled the carbine, i backed off some and and its never been a problem since. To 12 grains of 2400 the max load recommended in a 30 year old speer book, which goes to show that modern loading manuals with modern technology can still be unsafe even when staying within there specs or rather high, i was using a modern lyman book by the way as others appear to have found some high pressure loads in other threads here. The carbine thing though there never was a really a swell so to speak like i mentioned before pertaining to the guys 308s. Anyone else ever experienced this? Like the carbine? Last edited on Thu Nov 5th, 2009 03:15 AM by
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| Posted: Thu Nov 5th, 2009 03:26 PM |
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KY Hunter
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This is a very interesting internal ballistic topic. I do need to clear up one aspect of the topic - I am not having this problem currently ( not that I haven't seen a few in the past ) but have wondered why with the chamber constricting all brass expansion, high pressure and normal pressure alike, what was different. I would believe what happens in the "head half" of the casing after ignition is causing much of the bolt tightening??
My $0.02
KY
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| Posted: Thu Nov 5th, 2009 04:44 PM |
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Paul B
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KY Hunter wrote: This is a very interesting internal ballistic topic. I do need to clear up one aspect of the topic - I am not having this problem currently ( not that I haven't seen a few in the past ) but have wondered why with the chamber constricting all brass expansion, high pressure and normal pressure alike, what was different. I would believe what happens in the "head half" of the casing after ignition is causing much of the bolt tightening??
My $0.02
KY I think you're right.   What happens is when pressure gets too high, the brass begins to flow, It can flow into things like the ejector hole which, when you open the bolt, the brass inside the hole is sheared off. This is where the tight feeling in the bolt when attempting to open the action comes from. Have enough high pressure and primers can actually fall out.  I don't get too excited over somewhat flattened primers as the cause can be other than high pressure. I believe that every time you reload a cartridge case, the primer pocket gets just a hair looser. I shoot a lot of cast bullets in my rifles and those loads are nowhere near being called high pressure loads, yet after multiple loadings, even with those light charges, primer pockets do loosen up and primers get flatter. Maybe someday, I should set up at the range and use just one piece of brass and see just how many times that shell can be loaded using 25.0 gr. of IMR-4895 and a 180 gr. cast bullet (my standard cast bullet load fo both the .308 Win. and 30-06) and see just how long before primer pockets loosen up and flattened primers show up. I do know that one box of .375 H&H brass I have has been loaded over 20 times with my pet cast bullet load and primers are much flatter than when I started out. Still, with only 49.0 gr. of IMR-4895 under a 270 gr. cast bullet and velocity arounf 1900/2000 FPS, the load is a relatively mild one for the cartridge. Primer pockets, while still tight enough to hold primers are much looser that when I first started working with that load. Paul B.
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| Posted: Thu Nov 5th, 2009 05:06 PM |
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Hunter76
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As has been said the case is plastically deforming in all directions. With the lengthing of a particular dimension you will have a reduction (necking) in a another. For instance as the case diameter increase due to radial pressure there is a corresponding reduction in case thickness. This happens after each firing and typically the case will return to a size about 2% greater than it was. When a "hot" load is discharged the pressure cause a lot more plastic deformation and cause the case to stick. Think of a keystone in an arch. The residual friction force prevents/hinders extraction.
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| Posted: Thu Nov 5th, 2009 05:54 PM |
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swampshooter
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Montanashooter, I have some of the old manuals, including Speer's. I've been reloading since 1962. Many of the maximum loads listed can't be duplicated by myself, nor could they back in the 60's and 70's. It was common knowledge back then amongst reloaders to start low and work up. Today's shooters want to skip the formalities and start at maximum, forgetting about normal variations in individual rifles and lots numbers of components. Subsequently modern manuals are more conservative.
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miestro_jerry
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I have always found that with rifles cases, especially the magnum one, the neck expands forward in to the chamber/barrel. This is why we have to check the length of the cartridge before reloading, if it is too long then you have to trim it back to spec.
Everything else every one has said is true. If the cartridge is hard to extract, then it has expanded too hard. If the primer is flat or blown out, way too hot of a load.
Jerry
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fryboy
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Paul B wrote:
KY Hunter wrote: This is a very interesting internal ballistic topic. I do need to clear up one aspect of the topic - I am not having this problem currently ( not that I haven't seen a few in the past ) but have wondered why with the chamber constricting all brass expansion, high pressure and normal pressure alike, what was different. I would believe what happens in the "head half" of the casing after ignition is causing much of the bolt tightening??
My $0.02
KY I think you're right. What happens is when pressure gets too high, the brass begins to flow, It can flow into things like the ejector hole which, when you open the bolt, the brass inside the hole is sheared off. This is where the tight feeling in the bolt when attempting to open the action comes from. Have enough high pressure and primers can actually fall out. I don't get too excited over somewhat flattened primers as the cause can be other than high pressure. I believe that every time you reload a cartridge case, the primer pocket gets just a hair looser. I shoot a lot of cast bullets in my rifles and those loads are nowhere near being called high pressure loads, yet after multiple loadings, even with those light charges, primer pockets do loosen up and primers get flatter. Maybe someday, I should set up at the range and use just one piece of brass and see just how many times that shell can be loaded using 25.0 gr. of IMR-4895 and a 180 gr. cast bullet (my standard cast bullet load fo both the .308 Win. and 30-06) and see just how long before primer pockets loosen up and flattened primers show up. I do know that one box of .375 H&H brass I have has been loaded over 20 times with my pet cast bullet load and primers are much flatter than when I started out. Still, with only 49.0 gr. of IMR-4895 under a 270 gr. cast bullet and velocity arounf 1900/2000 FPS, the load is a relatively mild one for the cartridge. Primer pockets, while still tight enough to hold primers are much looser that when I first started working with that load. Paul B.
have u checked ur necks for thickness / a thick neck will dramatically increase pressure ( also including flatter primers and blown pockets )
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MontanaShooter
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Actually fryboy, the correct carbine load was in the old manual, the higher pressure loads were from the recent 48th add lyman book. I usually start loads mid to below mid in half grain increments. I started at 12 (load data showed 11-13) with no pressure problems and increased half a grain to get the slightly expanded cases then reversed procedure immediately and it wasnt really noticable till you ran it thru a sizer die. Very few things even in the modern manuals have i ever used the highest load given. I wouldnt say that all loads in modern books are atcorrect or reasonable pressures though, every once in awhile one pops up atleast in Lymans books. I usually bounce thru both my books and see how much they agree or disagree and if one is higher then other. Loads that have 7 grain windows versus ones that have 3 grain windows to work within are much more tolerant of course to deviations.
Last edited on Fri Nov 6th, 2009 01:02 AM by
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fryboy
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the carbine is a cat of it's own critter just as the obsolete round it was derived from ,actually two powders worked great in it ( in fact i think one was designed for it ) h110 and ww 296 ..both are two powders that have as u call it small operating windows (also both are/were made by st marks and except for lot variance are the same powder )i've typed it before but it stands to be repeated ... i bought a gun ...bought two boxes of factory loads ( for reference) bought brass etc etc mounted a scope worked up some loads( yup from the start point ) took it to the range slipped in my first 2 rounds of factory and settled in to 2 shot zero it...sounds like happiness doesnt it ? gently squeezed the trigger ... holy smokes that dude kicks like a mule on steroids and dynamite ummm ok eject the brass ..i should of paid more attention right there (hindsight is always so clear but i was alot younger then )jacked the second round in slipped the safety on realigned my rifle to where i had it before the world got rearranged referenced the hole in the target counted the clicks( 5 up 7 right) to align my crosshairs to the hole and touched the satan spawn off again ...when the world quite reverbertratin i looked thru the scope dang thaz close enough for a bull's eye for me jacked out the empty picked them both up and slipped them back into the box and noticed that for factory ammo that primer was about as flat as a fritter ,thought to myself dang the factory loads them dudes a mite warm but thaz why it's called a mag grabbed my box of brand new reloads slid 3 in the chamber settled in in and squeezed again ..holy cow batman for a starting load that round is about as bad as the factory ,jacked it out and looked at the brass another very flat primer pulled out the calipers whoah wait a minute summin aint right ,what wasnt right was starting loads were very hot in this barrel and factory once fired was trashed ...my ending max load ( 4 scopes and much frustration later) was just about 1 1/2 grain below starting load ...from the factory this gun has a very tite chamber had i started in the middle ...well i dont like to think of it ,it could of been much worse thank heavens situations like that are the rarity as opposed to the norm but it really adds to the logic -start low and work up ( or in this barrels case start low and work lower lolz )
the fact that h110 and 296 have small operating windows is both good and bad , for their application there is no equal but it is up to the reloader in the end ,if u want top performance in several types of mag rounds there is less choices than say for light load plinking
necks grow longer and also thicker ..either one will raise pressure with a otherwise normal and safe load add both together and well... plz dont shoot beside me at a range i have a aversion to flying shrapnel in fact i'd be tempted to shoot back , i have some old 38/357 brass that was well used when i got it being as i mostly shoot wadcutters at mid velocity this brass will last forever including the primer pocket in fact when it finally wears out it will be because the neck starts splitting from belling crimping , these i try to do in a minimal ,i trust no manual explicitly and often over analyze before i ever drop that first charge of powder and even then with a new load i have certain trepidations as i pull the trigger thankfully it eases as i fire more of the round i have also found that as i grow older ( and wiser i hope ) that some factory ammo is loaded hotter than i ever would load,some because of like in my case the rifle it's self ,i used to shoot more at public ranges but i've seen too many accidents that were preventable, i know a guy who wanted to reload and had no scale so he made one ( sort of )my brother and i and a few other's all chipped in and bought this guy a real scale ( and other assorted stuff)brass that is toasted after one firing and beating the bolt open in my opinion isnt the proper way to go about things but some see no problem with those concepts ....
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