Unusual case separation?


October 18, 2011, 06:58 PM
100% of my brass that has reached it's final loading has failed just above the web, that place where the sizing die stops. This batch was in need of shoulder bumping, but it still chambered, just a little bit tight, but none of the brass was on it's last leg though. I don't usually load brass that chambers that tight without having first bumped it, so I am now thinking that was why it did, what it did.

I was shooting a 700 SPS 7mm RM loaded with 120 gr. V-Max and 69.0 grs. of RL22, a well worked up and tested load I've been shooting for some time now. The few rounds that didn't chamber as tight against the shoulders didn't fracture. Nothing leaked and no gases blew through at all, and everything functioned normal with no pressures issues or stiff extraction.

Is this typical of shoulders that need bumping?

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October 18, 2011, 07:08 PM
I have never had a belted case round but I always thought that for long case life that you should size the shoulder and ignore the belt.

October 18, 2011, 08:09 PM
that place where the sizing die stops.It has nothing to do with where the sizing die stops.

It has all to do with where the tapered case web stops, and the thinner case wall starts.

That is where all the stretching that leads to case separation always happens.

I agree that for maximum case life, you should size belted cases to headspace off the shoulder, not the belt.


October 18, 2011, 09:36 PM
I don't FL size my rifle brass, I was only using the stopping point of FL die marks as refrence point. What I am refering to is that the brass is almost cut clean straight across the very edge of the belt, not the usual spot where brass commonly separates within the top edge of the web where it tends to start thinning. Having never seen this point of separation in over 30 years of loading, and since it's not like me to ever run my shoulders up that tight, I'm just wondering if anyone else has ever seen a case separate right on the belt edge on brass that was in need of bumping, and was no where near it last loading.

October 18, 2011, 10:47 PM
Most case stretching occurs on the first firing unless you take pains to fireform your brass.

Take a new unfired case and seat a fired spent primer in the primer pocket and chamber and eject this test round. The amount the primer is protruding from the rear of the case is your head clearance or the "air space" between the bolt face and the rear of the case.

Below on the left, the primer protrushion is "head clearance" and the amount of case stretch you will have on the first firing.


Your case can stretch a little further than the head clearance due to the diameter of the chamber and the diameter of the case. (it will stretch in two directions at once when fired)

It does not matter what type cartridge case you have, rimless, rimmed or belted, headspace is the distance from the bolt face to a datum point in the chamber. (thats the long and the short of it) :D


Below is a .303 British commercial case being fired in a long fat Enfield military chamber and shows what the "head clearance" is going to do to your case on the first firing.


If you seat your bullets long and jam them into the rifling when fire forming your cases the long seated bullet will hold the case against the bolt face and your cases will not stretch in the web on the first firing.

Below from Reloader Magazine on case head seperations.
(NOTE: A properly fireformed case will last twice as long as these abused full length resized cases were)



October 19, 2011, 01:22 AM
Bigdp51, the brass that had the unusual separation was on it's 7th or 8th reloading and still had a good 7 or 8 loadings left in it, if not for the premature separation problem. It was very well fire formed and should have had the shoulders bumped back before loading it. On that particular rifle my head space was under .003", pretty tight. But I ran the same load in another rifle and of course with brass fire formed for that specific rifle as well, but the shoulder's had been maintained and were not up against the wall. Those cases didn't separate, and they were in fact near the end of their life span and probably had been reloaded a good 13 or 14 times. That rifle also has marginal head space, at just under 005" which brings me to my point and question. But since I form my brass off the chamber, head space doesn't really have a lot of significance in that regard.

Does the fact that my brass was in need of bumping have anything to do with the unusual point of separation with brass that is still quite young?

October 19, 2011, 02:28 AM
Your asking if you had made your cases "shorter" would they have had a case head separation.

My answer is simple, if your brass is a perfect fit or a tight fit in your chamber how is it going stretch and cause a case head separation.

Your cases were either fireformed incorrectly or "OVER" resized in length "AND" diameter. "AND" headspace/head clearance does matter because it allows your cases to stretch. Your cases should be headspaceing off the shoulder and "NOT" the belt for longer case life.

If you had a RCBS Case Mastering Gage you would be able to "SEE" how much your cases stretch and thin in the web area or above your belt. (it will tell you if your doing something wrong a lot faster than a paper clip) ;)


The factory loaded Winchester .303 British case on the left below stretched and thinned .009 on its first firing in the web area and only lasted three reloadings. The military .303 case on the right only stretched .002 when fired in the same Enfield, so case construction plays a big factor. And this is why military cases are thicker in the base web area to with stand longer military headspace standards.


October 19, 2011, 12:42 PM
100% of my brass that has reached it's final loading has failed just above the web,

Sounds like you are moving the shoulder back and relying on the belt for headspace.

Use the shoulder, and only bump it back about0.001-0.002 at each reloading unless it has fit problems in the chamber.

THEN move the shoulder around 0.004

October 19, 2011, 02:42 PM
Your cases were either fireformed incorrectly or "OVER" resized in length "AND" diameter. "AND" headspace/head clearance does matter because it allows your cases to stretch. Your cases should be headspaceing off the shoulder and "NOT" the belt for longer case life.

I agree 100%.

I purchased one of those expensive Sinclair belted magnum cartridge headspace gages. I had set up my die following the best practices found in print. This was before the internet. After I got a gage I found that my shoulder set back was way off.

I have no doubt you are pushing your shoulders back too far, without gages to measure what you are doing, you are only one step from reading tea leaves to divine the future.

I really dislike belted magnums. One reason is headspace. The only dimension that is controlled is the head space off the belt. Between manufacturers the distance from base to shoulder can be all different, probably is all different, and probably varies quite a bit from production lots.

October 19, 2011, 03:22 PM
Is it possible that your case length had stretched to the point where the neck was too long and when you forced it into the chamber it caused way more tension on the bullet not allowing it to escape from the case like normal? If that is what happened then the pressures would be way higher than you would normally get with the same load, and possibly be enough to cause a ruptured case. Just a thought... Anyone else think this is a possibility?

October 19, 2011, 03:56 PM
Belted magnum handloads need to headspace on the shoulder - not the belt. I believe that it's always best to use a FL die. However, the FL die height MUST be adjusted accurately.

Case head separation is totally avoidable with any caliber IF you reduce chamber clearance (at the shoulder) to -.001" and this requires measuring.

Your tight fitting cases have bulged too much above the belt. This is caused by stretched cases that have thinned your brass. The bulge occurs during the reloading process - not when your case is in your chamber. There are jillions of wild theories about reloading belted magnum calibers.

Read my website, and you'll see how thousands of shooters are now handloading belted calibers. There's no need to resort to smoked cases, scotch tape and paperclips. Handloading technoloy has come a long way.

October 19, 2011, 07:50 PM
The bulge occurs during the reloading process - not when your case is in your chamber.

No disrespect intended Sir but I have a question because I don't have a rifle that shoots belted cases.

My cases bulge when fired and my full length resizing process squeezes the body of the case and makes it smaller. During this squeezing process the brass has no where to go but upward in the die.

Why would resizing a belted case make it fatter when the die is smaller in diameter than the expanded cartridge, what am I miss here.

By the way I like your Digital Headspace Gauge and the price ain't bad either.

October 19, 2011, 08:40 PM
bigedp51 .....

When your brass is allowed to get paper thin, it's thin enough to crack. Before it gets quite that thin, it becomes thin enough to easily bulge. This picture (from my website) shows what a fired belted case looks like from the inside.


Every handloading operation pushes downward on the case, and unlike a non-belted caliber, there's limited support at the web of the case.

When a fired round is extracted, it will rechamber. However, after resizing they often fail to chamber because of the slight bulge. It doesn't take much.

The reason cases get more bulged than non-belted calibers is the first firing (with new brass) often has .020" (or more) shoulder clearance. That stretches the case considerably on the FIRST firing. However, this can be managed very well with modern reloading techniques.

October 20, 2011, 01:20 AM
Nope, I don't head space off the belts. This particluar brass has never seen a FL die since it was virgin, about 7 or 8 loadings. All of my brass is sized on a neck die until it gets too tight to chamber, then I carefully push the shoulders back just far enough to chamber, adjusting the FL die in increments of .001".

This is how I've been doing it for over 30 yrs., but the first time I've seen separation in this particular spot.

October 20, 2011, 01:57 PM

Forgive me I don’t have a belted 7mm Remington magnum because I already have the worlds best non-belted magnum cartridge in the world, it’s called the .270 Winchester. :D

I would check the diameter of new unfired cases (pleural) and see which brands have the largest base diameter just above the belt and then check for case expansion after firing.

Below are two factory loaded once fired .303 British cases, the one on the left is the Serbian made Prvi Partizan and the one on the right is the Greek made HXP case. Both of these cases were fired in the same Enfield rifle and as you can see there is a big difference in the base diameter in these cases.


The Prvi case has a larger base diameter by .006, the case walls are .010 thicker and the rims are also thicker which means less headspace. The Prvi Partizan case when fired had “NO” stretching in the base web area, “BUT” a Winchester case fired in the same rifle had .009 stretching and thinning in the web area. The Winchester case had .007 head clearance or air space between the bolt face and the rear of the case “BUT” it stretched and thinned .003 more due to radial expansion and expanding outward to meet the chamber walls.



The bottom line here is I think you had cases with smallish base diameters and thinner case walls which caused your case head separations. You need to check and measure your base diameters and case wall thickness between your cases to determine the true cause.

Also from reading other postings on belted magnums there appears to be differences in full length dies and how far down above the belt they size and some are leaving a bulge where the case remains “untouched” and these cases have a “pot belly”. :eek:

October 20, 2011, 02:29 PM
Ah yes, the .270 win. was my first high powered rifle and the one I've killed most of my big game with. Indeed one of the worlds best high power's, and certainly a lot easier cartridge to read.

I'm not going to worry to much about the 7 mags. separation issue, after all it's the first unexplained issue I've encountered with this cartridge. And I'm about 99.9% certain of why it did, what it did. In short the brass was cut because it had no where else to flow or expand other than at the top edge of the belt. I learned something about running it that tight.

October 20, 2011, 02:31 PM
bigedp51 ......

I understand what you are showing here. However, most tapered cases need to be forced .100" into a FL sizing die just to remove .001" from case diameter.

This is due to a shallow case angle and the springy nature of brass when it's under high pressure.

Full length resizing requires die travel to go slightly beyond any given area to be resized, and when the belt (on a belted case) stops the travel of a die, only limited resizing above the web is possible.

October 20, 2011, 04:40 PM

And American made cases are notorious for being undersized in diameter at the base. These cases stretched on firing and they didn't stretch because they were too long or too fat in diameter. These cases stretched because the brass case had room to stretch on firing, these cases in this posting were not full length resized so what you are saying does not apply. A full length resizing die never touched these cases so the fault lies with case construction and how far the brass dislikes being stretched beyond its limits.

The Winchester cases below were neck sized only and only lasted three reloadings due to stretching in length and radially in diameter. A case can't stretch and fail unless it has somewhere to go. ;)

Below, left to right, a new unfired case, once fired, third firing and were neck sized only.


Does the American case in the bottom of the photo in this Wilson Case Gage look like it was made correctly compared to the military case at the top?


Any cartridge case on the small side in base diameter will have almost twice as far to stretch when fired. The OP needs to measure his cases and find the problem and your reloading die will not fix poorly made brass cartridge cases.

Or are competitive shooters buying Finnish made Lupua brass for the fun of it. ;)


Please do not take what I'm say the wrong way, I have noted many, many times the forum member at AccurateShooter.com praising your reloading equipment. I just believe that the brass case is at fault here and nothing more.

October 20, 2011, 08:51 PM

I understand exactly what you are describing with British 303 cases. (well illustrated) More than almost any other rifle, British 303 chambers were made with extremely wild variation in tolerances and uniformity. This formerly military cartridge required ammo to ALWAYS chamber, and with little or no regard for handloading. Therefore ammo was often made to fit the smallest possible chamber.

However, your experience with belted magnum calibers is a bit limited.

October 21, 2011, 09:00 AM
However, your experience with belted magnum calibers is a bit limited.

The OP cases had case head separations and were "NEVER" full length resized, how is your full length resizing die going to solve case stretching in the web area above the belt verses neck sizing only. Your die is going to make the base smaller and it can expand outward again and stretch "MORE" than if it was just necked sized.

Lets switch to standard cases, case head separations are based on headspace, chamber diameter and case diameter and how "far" the case can stretch. The cases below were full length resized and longevity was based on case "quality" which is the most likely cause of the OP case head separations. Remember he had other cases that lasted much longer and they were also just necked sized.

Below from Reloader Magazine



The above cases are not .303 British cases and they were not fired in a over sized military chamber. It is also clear that some brands of cases lasted twice as long as the ones at the top of the list. This shows that case construction and quality have a lot to do with case head separations and some things can't be fixed with a specialty made full length resizing die.

The OP case life was cut in half and you think your reloading die is going to fix poor quality cartridge cases? I do not think my experience is "limited" Sir, and if anything of late our American made cartridge cases leave a little to be desired in quality. Or did you forget the Wall Street bean counters are running the show at these ammunition companies.

October 21, 2011, 10:33 AM
bigedp51 .....

Neck sizing was popular about 50 years ago. I believe that it's no longer the best way to go. That is . . . . not when a FL die can be adjusted accurately. This requires very simple measuring. What's bad about neck sizing?

Here's what:

When a case body is not resized, it has absolutely no chamber clearance - not even a little bit. Shooters that neck size know that sooner or later they'll need to bump the shoulder back for their handloads to continue chambering. This indicates that their brass is changing size during the reloading process.

That's how even neck sized cases bulge above the web. It's not when a case is being fired, it's during the reloading process. Why are belted cases affected more than non-belted cases?

Here's why:

Brand new belted magnum cartridges always headspace on the belt, and the shoulder clearance is often .020" or more. This causes belted cases to stretch considerably on the very first firing. This unavoidable case stretching has already thinned the case (usually just above the web) on the very first shot. With this thinned brass, ANY downward pressure from handloading will push down against the weakest part of the case. If a cartridge is only .001" too large - it won't fit.

Specialty dies are almost never required now days. The Digital Headspace Gauge is used to measure the shoulder clearance that handloads have in a particular chamber. That helps adjust FL die height to set back the case shoulder -.001" and no more. By setting the die height perfectly, none of those fired cases in your picture would have cracked.

- Larry

October 21, 2011, 11:59 AM
gamestalker, when only neck sizing a belted round, the case body is moved back towards the bolt face. You are moving the belt away from where it is to headspace. This produces an area where the case body is unsupported. This is why the seperation is right tight against the belt & not in the normal place. When you bump the shoulder back, the brass is moving & stretching on firing. The exact same area in not always unsupported as when neck sizing. Study the SAAMI drawing & i think you will see how it can happen. This is my guess. :) http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm%20Remington%20Magnum.pdf

October 21, 2011, 12:09 PM
When a case body is not resized, it has absolutely no chamber clearance - not even a little bit.

Not true.

The brass case shrinks slightly in size after firing, and this is one of the things that makes extraction easier. Brass is elastic.

As the brass work hardens from repeated firings the elasticity and spring back decrease, but it is not going to get to zero, since thermal expansion still comes into play.

If you repeatedly push the shoulder back the brass is stretching on every firing.
The stretch will show up at the weakest spot in the case body, and on a belted case that is right in front of the belt.

October 21, 2011, 12:26 PM
243winxb .....

Look at the picture I put in post #13, and you'll see that if a belted case is going to bulge, it will happen aprox. .070" or more above the belt.


brickeyee ......

In the relm of ten thousandths of an inch - you are correct.
However, for practical purposes the 50,000+ PSI in your chamber makes your fired case fit REAL close.

October 21, 2011, 12:34 PM
Innovative, OP said seperation is at the belt, not above. This is where the case body has become unsupported as its now sitting in the belt area. Looks like the difference between chamber & cartridge belt headspace* is .030" The seperation should not be in the area right against the belt, because the web is very thick, this is true. Very strange seperation. :)

October 21, 2011, 12:49 PM
243winxb .....

I'll bet that if we saw a picture of the OPs fired case, it would show a sign of case head separation a bit farther up the case.

Most manufacturers make their cases with a thick transition to the case web (like in the picture). That prevents a "stress riser" from causing case head separations all the time.


October 21, 2011, 01:08 PM
Innovative, could it be a bad chamber job? Possibly a reamer left a burr in front of the belt area? Yes, a photo would be nice. Owner has found a fix, bump shoulder at each loading. http://www.thehighroad.org/showthread.php?t=621161

October 21, 2011, 01:39 PM
243winxb .......

This is a very common handloading problem with belted magnum calibers. I've never seen this symptom caused by a chambering problem.

The questions from this post have helped me to expand a page on my website. Take a look at the Reloading Questions page on my website.


October 21, 2011, 03:20 PM
This posting is getting way off topic when people think a full length resizing die will take the place of proper fireforming. Innovative your die has nothing to do with fireforming and cases stretching in the web area on the first firing.

Now ask yourself why the OP left this posting and started another.

The problem is headspace/head clearance, fireforming, cartridge case quality, quality meaning maintaining proper case dimensions during manufacturing.

Innovative your reloading die will not correct headspace, small cartridge case base diameters, thin case walls or fireforming techniques on the first firing.

It is one thing to try and help this poster, it is another thing trying to make money off your product and not say a word about fireforming techniques which would prevent the case stretching in the first place. By simply seating his bullets long and jamming them into the rifling on the first firing the case would have been held against the bolt face and not allowed the case to stretch on the first firing.

Innovative, I'm giving advice away for free, what are you doing?

October 21, 2011, 03:24 PM
However, for practical purposes the 50,000+ PSI in your chamber makes your fired case fit REAL close.

Only till the pressure drops away.

Brass is elastic, and even 0.0001 is enough.

October 21, 2011, 04:41 PM
All good points to ponder, and even some sound seriously discriptive of what I'm experiencing with this.
I took some measurements of fired brass that was bumped when before reaching the limits of the chamber:

At the very top edge of the belt on the brass that failed was .512". On brass with that had been properely maintained at the shoulder it measured in the same spot .508" - .510"

So I'm now thinking that it was an effect of no where else to flow/stretch causing the brass to buldge in the only place left to expand.

Having never experienced this before, I don't feel it is brass quality issue, though I do agree the good stuff is going to probably hold up longer.

So the fault clearly seems to be mine because I didn't set the shoulders back, and instead force fed them into the chamber, they were a super tight fit. My other post shows some comparison loads that probably support this.

October 21, 2011, 05:26 PM
bigedp51 ......

My thought is that the OP originally asked if his tight fitting handloads (that failed above the web) were typical for belted magnum calibers (not a 303).

I replied with a cut-away picture of a belted magnum case, and explained what appears to have happened. Other technical questions (especially yours) were helpful for me to explain things in greater detail. You are right that our collet die doesn't correct headspace, because it was not designed for that purpose. I designed it specifically to only reduce case "diameter" above the belt when needed.

You asked "What have I done for the shooting sports?"

Well, my first goal is to promote the shooting sports, and support shooters. Read my website, and you'll see over 130 pages of technical handloading and shooting info that is designed to help fellow shooters. (Only one page has items for sale.) So far, it has taken almost 10 years to create www.larrywillis.com and it gets visited by well over 800 shooters every day.

I've also worked in the shooting industry for over 10 years, where I designed (and patented) 2 reloading tools that are currently used by more than 5,000 shooters worldwide. In that time, I've kept my prices from going up one dime.

- Larry

P.S. There's really nothing wrong with saving and creating jobs.


October 21, 2011, 05:53 PM

At the very top edge of the belt on the brass that failed was .512". On brass with that had been properely maintained at the shoulder it measured in the same spot .508" - .510"

Your next question you should ask yourself is how thick is the case wall on these two case you measured at this point. If the case wall was thinner it would cause the cases to stretch more at the thinner and weaker point above the belt.

What you are saying is your cases were so tight fitting in the chamber that forcing the bolt closed caused the cases to bulge and forced a case head separation? :confused:

I'm telling you your case stretching,thinning and case head separation started the first time you fired your cases causing your weak spot above the belt.

Without checking and measuring your cases in the web area before and after shooting you are doing nothing more than guessing about your problem.




Below is a greatly exaggerated example of creating a false shoulder on your cases to hold them against the bolt face to fireform them, this will keep the cases from stretching on the first firing and you will NOT have a weak point to compress as you stated that caused your case head separations.

Below the case will headspace on the false shoulder which will hold the case against the bolt face when fireforming. This will prevent the case from stretching and thinning and prevent case head separations. The actual false shoulder location will depend on your chamber headspace and the location of the shoulder of the case


October 21, 2011, 06:10 PM

I didn't ask you "What have you done for the shooting sports?".

I asked you how your reloading die was going to stop the case from stretching on the first firing.

I asked how your die had anything to do with neck sizing only. :confused:

And I asked how your die made up for defective cases and bad quality control.

This is a case stretching posting and not a posting on how to full length resize a 7mm Remington magnum that has been neck sized only. You have side stepped my questions and danced around this problem promoting your product.

My statement to you Innovative is your more concerned with selling your dies than fixing the problem at hand, and that is case stretching on the first firing and creating a weak area on the case. ;)

October 21, 2011, 06:30 PM
I'm sure there are other shooters that understand perfectly well.

October 21, 2011, 07:40 PM

A cartridge case can stretch longitudinally and radially when first fired or in length and width and it doesn't matter what "type" cartridge case it is. If the case doesn't stretch in the base web area when fired it will not have a weak spot at that location to fail. This problem is caused by the upper section of the case gripping the chamber walls and the rear of the case stretching to meet the bolt face.

A full length resizing die no matter how well made can not fix a weak spot in the base web area of a cartridge case that is already damaged from stretching.

If you want people to understand what you are saying then send a free die to gamestalker and see if it solves his problem and stops his cases from stretching on the first firing before his cases even get close to your die. ;)

The key words are "headspace" and "head clearance" when it comes to case stretching in the base web area.


October 21, 2011, 08:54 PM
bigedp51 ......

Your illustration correctly shows how a poorly fitted barrel causes a rimmed case to rupture. That's the same for a belted case. However, when a rifle barrel is correctly fitted, and handloads fit the chamber with near zero shoulder clearance, case head separations are avoided.

No die is designed to fix weak cases. However, when a FL (or a NK die) is used accurately on a belted case, it can reduce the thinning and weakening of cases. Those belted cases that are damaged in the first firing can be "managed" my measuring with the Digital Headspace Gauge to limit shoulder clearance.

I don't send free gifts to anyone, and I'll bet you don't either.

October 21, 2011, 09:35 PM
Why are belted cases affected more than non-belted cases?

Does the sharp corner where the shoulder meets the case body create a stress riser?

October 22, 2011, 02:13 AM
Your illustration correctly shows how a poorly fitted barrel causes a rimmed case to rupture.

Innovative you are incorrect again, my illustration shows what happens when you fire a commercial cartridge case in a long, fat military chamber and a cartridge case that wasn't designed to military specifications.

I also mentioned quality control of cartridge cases Innovative, below Remington can't even meet SAAMI minimum standards for the shoulder location of the .303 cartridge case. This makes me wonder where the OP shoulders were on his 7mm Rem Mag cases and if the belt and web were correctly made and within tolerances. And this is the main thrust of my postings here, case dimensions and quality.

It has nothing to do with the noted and praise of your quality products Innovative. And by this I mean your quality dies will not fix defective cases that split just above the belt line, or cases not properly fireformed. ;)


Again, the top military case is made to design specifications and the bottom Remington case fails.


Our discussion here is useless Innovative, the OP here does not have the gages necessary to even find his problem. My apologies for being a little grumpy in this posting, I think my underwear might be too tight. But it is a two way street Innovative and some of your comments were a "little" irritating. ;)
This posting has gone beyond useful its shelf life.

October 22, 2011, 10:07 AM
bigedp51 .....

Sorry about my comment way back in post #19. I can see how that might have been taken the wrong way. No harm intended. Although I have reloaded since the mid sixties, my experience with belted magnum calibers was "a bit limited". There's nothing wrong with that, because nobody has all the answers. I just never had interest in belted calibers until a good friend gave me a new Browning 300 Win. Mag. back around 1995.

mrbro .......

The sharp edge on a case shoulder could "influence" a stress riser during brass movement, but I've never seen any actual damage in this area. Case problems usually occur farther back on the case as seen in the pictures from bigedp51. However, the early Weatherby magnums were on the leading edge of maximum performance, and that might explain why they rounded the shoulder on their cases - or - it could have had something to do with marketing (product recognition).


October 22, 2011, 11:13 AM
Innovative, thanks. When I replied last night I said shoulder when I meant to say belt. I was thinking of the junction where the belt meets the body. Any thoughts?

October 22, 2011, 02:12 PM
However, when a rifle barrel is correctly fitted, and handloads fit the chamber with near zero shoulder clearance, case head separations are avoided.

Just about every gun has cartridge clearance to allow for manufacturing tolerance of the gun and ammunition.

In weapons with less force available to close the action, more clearance is often required (semi auto, lever, etc) for reliable operation.

If you allow the case clearance to actually get close to zero, you are very likely to have some rounds that will NOT chamber correctly.

Every measurement has an error, and even if you checked 10% of the cases by measuring you need to make sure the error in the measurement is accounted for.

If the measurement error was plus or minus 0.001, some cases would be 0.001 OVER length.

To account fr tolerance issues the clearance is increased.

By setting the clearance at 0.002 in, an error of plus or minus 0.001 in the measurement results in the cases being 0.001 short to 0.003 short of the actual chamber size.
They will all chamber.

If the chamber measurement is plus or minus 0.001, better add some more clearance for that.

The clearances needed for reliable operation are going to cause case stretching with each firing.

There is no practical way to avoids it.

All we can do is try to minimize the effect, and keep it to a reasonable number to ensure brass life.

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