Case Shortening with Light Loads

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  • Last Post 06 July 2012
John Alexander posted this 10 June 2012

For sixty years I have been reading about the dangers of using rimless cases that have been used for light loads for full charge loads. The story goes that the primer blast forces the case into the chamber and shortens it (excessively FL sizes it.) In full charge loads the pressure of the powder charge burning then expands the case back up to fit the chamber and everything is hunky dory. But if the powder charge is very light (many CB loads) the case isn't expanded enough and the case is now undersized creating excessive head clearance -- a dangerous condition that can lead to case head separation and other bad things.

Yet, I have loaded tens of thousands of light loads in rimless cases and have never seen any cases shorten. Most of this shooting has been with the 222 and 223 cases in production chambers. But I have also used the 22-250 and 30-06.

I have loaded both cast and jacketed bullets down to 22 long rifle velocities and reloaded sets of cases dozens of times by neck sizing only (by either backing off the FL die or neck size dies both old type and Redding S type before collet dies.)

I have NEVER had one of these cases become loose so you didn't feel a slight resistance as the bolt was closed on an empty case. I don't think they had excessive head clearance. This is true even for cases I reloaded over 200 times using the collet die.

Is case shortening another one of the myths about cast bullet shooting that is repeated generation after generation?

Have any of you ever experienced case shortening? If so under what conditions.

Maybe it takes a large rifle primer or very small sloping shoulders.

John

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Reg Lingle posted this 10 June 2012

John: Yes, using MO's head space  gage from my hi-power days and Mil match cases, - I have .004” in shortening. I remedy this by expanding with a 32 cal. expanding bushing and then partial neck sizing, leaving a “bulge” just in front of the neck. Zero's out any head space and works great. Reg Lingle

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nimrod posted this 10 June 2012

I had a problem like that way back when I was a young'un. Ended up with a case seperation after loading 30-06 brass many times with a very light cast bullet load and then loading a high pressure jacket bullet load. To this day I always keep cast bullet brass seperate form high pressure loads.

I don't recall the loads that were used too many years ago but it was in a 1917 Enfield so may have had a oversized chamber anyway? I have read of some people that drill out the primer flash hole to relieve the primer pressure. I would definetly keep that brass seperate maybe even paint the bases red or something very visable.

Richard

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Vassal posted this 11 June 2012

Another good Argument for the Big Old Russian,! Or the Modestly Hefty Ol' American,,! Or the Bulky British,,,!

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nimrod posted this 11 June 2012

Now we're talking Vassel big ole rims load'm any way you want and go enjoy!

Richard

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runfiverun posted this 11 June 2012

it's from the firing pin driving the case into the chamber.

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cityboy posted this 11 June 2012

I shot light loads in a 30-06 for several years, and the problem I encountered was the shoulder being set back causing excessive headspace. I got around this by spraying the cases with a light coating of silicone lube. Head-to-cone distance was checked with an RCBS gauge and it stayed in normal tolerences.

The lube never stuck around very long and was done every the cases were loaded. I got the lube in the automotive dept at WALMART.

Jim

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LWesthoff posted this 12 June 2012

I'd be a little nervous about that silicone lube - or ANY lube on my cases unless I was very sure I had cleaned every trace of it from my chamber before I fired any regular (higher pressure) loads. That being said, I have salvaged shortened cases by coating them with sizing lube and firing them with very light loads. However, even if you are religeous about cleaning the lube out of your chamber, if you shorten cases with light loads and then blow them back out very often, you are probably going to shorten case life.

Wes

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joeb33050 posted this 12 June 2012

runfiverun wrote: it's from the firing pin driving the case into the chamber.

I have twice fired one case with ~20 oiled = new dead primers in rifles with the extractor removed, and have not yet had the headspace increase. The firing pin didn't drive the case forward. On 11/16/06, I did this test for the third time on the third gun, a Win M70 Target 30/06 Post 64 rifle. I “killed” 26 CCI 250 Magnum primers with marvel mystery oil. (I did this test at home, in the condo.) Put an empty fired case in the gun. Removed the firing pin from the bolt. The bolt closed easily on the case. Made a .004” copier paper patch to fit the bolt face, put it on the bolt face, the bolt would not close with a little pressure. After testing and fiddling and firing 26 primers in that one case, the bolt closed easily on the fired case-wouldn't close with a little pressure with the paper patch on the bolt face. Others, including Tom Gray, have increased headspace with the firing pin striking the primer, but I can't and this is the third time I've done this test. JOE B.

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Ken Campbell Iowa posted this 13 June 2012

GREAT STUFF, JOE ....I HATE IT WHEN MYSTERIES ARE EASILY SOLVED   (G) KEN   ooops caps were stuck on

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joeb33050 posted this 13 June 2012

Some claim that the primer explosion pushes the case forward, driving the shoulder back. The primer and primer pocket act as a piston and cylinder, with the primer gas acting on the forward surface of the primer pocket, around the flash hole. These folks tell us that the problem can be solved by drilling out the flash holes to a larger diameter, and keeping these cases for light loads only. On 18 Nov. 2006 I took the Win M70 30/06 Post 64 rifle and taped a 2 liter Pepsi bottle on the muzzle to hold the noise down. (TRK points out that taping a Pepsi bottle to the muzzle of a rifle is against the law, that the BATFE considers this “making a silencer” So don't do it, or you could end up in jail. Or in hell. If any BATFE guy is reading this, it's all a lie, I never did it. Don't drink Pepsi. Had no tape.)

Put an empty fired case in the gun. Removed the firing pin from the bolt. The bolt closed easily on the case. Made a .004” copier paper patch to fit the bolt face, put it on the bolt face, the bolt would not close with a little pressure. Firing pin in, CCI 250 Magnum primer in the pocket, in the gun, fired, a little pop. Tried again with the paper shim, no firing pin in the bolt. The bolt closed with no resistance. The primer drove the case forward. Fired four more primers, made another .004” shim, both shims on the bolt face and the bolt closed on the (primerless) case with a little resistance. In my guns, with my tests, it's the primer driving the case forward, not the firing pin. Mike in CO was kind enough to give me a reference to “Handloading", NRA, 1981, William C. Davis Jr. After the testing, another reader scanned and sent “Reduced Loads", pages 113-115, by Mr. Davis. On page 114 he states clearly that it is the primer firing that moves the case forward and moves the shoulder back. My experiments agree with this. joe b.

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John Alexander posted this 13 June 2012

Thanks Joe,

Two nice small reports on actual logical testing. I wish more people would take this approach. We have lots of “facts” circulating around that have never been proved by actual tests instead of just seeming “only reasonable that it's true.” As a result, progress if slow.

I am still mystified as to how I could have reloaded for sixty years mostly with light cast loads in a variety of rimless calibers in about all the common types and makes of actions using both standard and magnum primers and have never had a much loaded case that didn't give slight resistance upon chambering. I have also never had a case head separation although I often load full charge jacketed loads in the cases I have been using for the light loads. Charmed life??

At least after reading this thread I do believe it happens and will be on the lookout for it.

John

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onondaga posted this 13 June 2012

http://www.castbulletassoc.org/view_user.php?id=6375>John Alexander:

John, I have been waiting for my brass to get shorter with my experimenting in light loads for the 7.62X39. I really expect it to happen but it has not yet materialized.

There is a particular reason I am  watching for the problem with my particular rifle. The extractor on my rifle grabs the case head well but only has a very small protrusion that is spring loaded and sets in the extractor groove.

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joeb33050 posted this 14 June 2012

John A. I think I know that it is the primer and not the firing pin that drives an empty case forward, moving the shoulder back. As I wrote to you, my set of low velocity cases, set aside to avoid danger of loading them with hv loads, do not have ant case shortening/shoulder set back. I don't know if or when lv loads cause shoulder set back = reduced case headspace. I'd like to know, and it seems to me that the testing could be done easily and quickly. joe b.

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cityboy posted this 14 June 2012

LWesthoff wrote: I'd be a little nervous about that silicone lube - or ANY lube on my cases unless I was very sure I had cleaned every trace of it from my chamber before

I used silicone spray for several years and never had a problem; it is not very durable and wears off easily.

Jim

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John Alexander posted this 14 June 2012

"John A. I think I know that it is the primer and not the firing pin that drives an empty case forward, moving the shoulder back. As I wrote to you, my set of low velocity cases, set aside to avoid danger of loading them with hv loads, do not have ant case shortening/shoulder set back. I don't know if or when lv loads cause shoulder set back = reduced case headspace. I'd like to know, and it seems to me that the testing could be done easily and quickly."

Joe, What kind of test would you suggest? Your test with primed cases and without using the Pepsi bottle was cunning and got shortening right away so I am convinced. But as I noted earlier, I have been running a very similar test (except for the light load of powder and a CB) with a variety of calibers and rifles for a long time and never seem to get shortening.

John

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joeb33050 posted this 14 June 2012

John Alexander wrote: Joe, What kind of test would you suggest? Your test with primed cases and without using the Pepsi bottle was cunning and got shortening right away so I am convinced. But as I noted earlier, I have been running a very similar test (except for the light load of powder and a CB) with a variety of calibers and rifles for a long time and never seem to get shortening.

John John; I got shortening with no powder or bullet-doesn't mean that WITH powder and bullet there's shortening. 5 cases, 50 bullets, a light load that just gets the bullet out of the barrel reliably. Measure case headspace Shoot them Measure case headspace Reload them Shoot them Measure case headspace and so on I have RCBS case headspace measuring micrometers for 223 Rem, 308 Win/243 Win that they loaned me for this project. Happy to mail it/them. I've measured and sized and measured every piece of brass in sight. I'm thinking that an hour and we'd know. joe b.

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delmarskid1 posted this 15 June 2012

Most of us load our cast bullets out far enough in the throat to constitute a datum. This could be the reason that the cases are not driven back by the primer in the chamber. Bullet seating depth may be another variable in the experiments. Thanks for doing the work Joe.

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joeb33050 posted this 21 June 2012

DOES THE PUSH FEED EXTRACTOR DECREASE CASE HEADSPACE? (INCREASE HEAD CLEARANCE?) 223 REM, M10 SAVAGE, 6-20-12

I chambered the same case 35 times with the extractor pushing and then snapping over the extractor groove. I measured case headspace using the RCBS Precision Mic, graduated in .001” intervals. Case Headspace is the feature with the 1.4666” -.007” dimension on the SAAMI CARTRIDGE drawing. Zero on the RCBS Precision Mic is the minimum SAAMI CHAMBER headspace dimension, 1.4636". A reading on the Mic of -2 is 1.4636” - .002” - 1.4616" Case headspace each time was in the interval between -1 to -.2 and -.2 to -.3. All measurements were -2, except the 18th, 24th, 28th, 30th and 31st; which were -3. The last four measurements were -2. It looks like the extractor is not pushing the case into the chamber and decreasing case headspace = increasing head clearance.

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TRKakaCatWhisperer posted this 21 June 2012

joeb33050 wrote: DOES THE PUSH FEED EXTRACTOR DECREASE CASE HEADSPACE? (INCREASE HEAD CLEARANCE?) 223 REM, M10 SAVAGE, 6-20-12

I chambered the same case 35 times with the extractor pushing and then snapping over the extractor groove. I measured case headspace using the RCBS Precision Mic, graduated in .001” intervals. Case Headspace is the feature with the 1.4666” -.007” dimension on the SAAMI CARTRIDGE drawing. Zero on the RCBS Precision Mic is the minimum SAAMI CHAMBER headspace dimension, 1.4636". A reading on the Mic of -2 is 1.4636” - .002” - 1.4616" Case headspace each time was in the interval between -1 to -.2 and -.2 to -.3. All measurements were -2, except the 18th, 24th, 28th, 30th and 31st; which were -3. The last four measurements were -2. It looks like the extractor is not pushing the case into the chamber and decreasing case headspace = increasing head clearance.

Might could be that the extractor held it from being pushed forward (hence shortening).  Therefore it could be that the behavior of being shortened would be limited to a type of action?

 

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joeb33050 posted this 22 June 2012

TRK wrote: joeb33050 wrote: DOES THE PUSH FEED EXTRACTOR DECREASE CASE HEADSPACE? (INCREASE HEAD CLEARANCE?) 223 REM, M10 SAVAGE, 6-20-12

I chambered the same case 35 times with the extractor pushing and then snapping over the extractor groove. I measured case headspace using the RCBS Precision Mic, graduated in .001” intervals. Case Headspace is the feature with the 1.4666” -.007” dimension on the SAAMI CARTRIDGE drawing. Zero on the RCBS Precision Mic is the minimum SAAMI CHAMBER headspace dimension, 1.4636". A reading on the Mic of -2 is 1.4636” - .002” - 1.4616" Case headspace each time was in the interval between -1 to -.2 and -.2 to -.3. All measurements were -2, except the 18th, 24th, 28th, 30th and 31st; which were -3. The last four measurements were -2. It looks like the extractor is not pushing the case into the chamber and decreasing case headspace = increasing head clearance.

Might could be that the extractor held it from being pushed forward (hence shortening).  Therefore it could be that the behavior of being shortened would be limited to a type of action?

 

I don't know. There's space between the case head and bolt face with the case held by the extractor. I haven't figured out how to measure the space.

The question was:"Do cases shorten?" Your implied question is: “Would cases shorten absent the extractor?"

I'm preparing to do the test due to lack of volunteers. joe b.

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Reg posted this 22 June 2012

John, Am glad you brought this one up. I too have been loading for more than fifty years and have shot loads of all description and a lot of them were light loads. Always tried to keep the cases for any cast load and higher power jacketed loads separate but there were some cases where they got mixed. Never have I seen where the shortening , if it took place at all, was due to primers, firing pin strike or any of the other normal excuses but rather when we really checked things out it was often due to the loading die itself. They are a man made, mass produced product and subject to tolerances and simple error. How many of you have cleaned the FL die then dropped ( carefully!!) in a quality headspace gage. Now it does take different gages to make dies than it does to chamber a rifle but it will give a base dimension. Check several different brands, sometimes it is amazing. In short I have learned to check every round in a Wilson gage as part of final inspection and just use the brass for whatever it would be needed for and not worry about keeping things separate. This is for normal shooting ammo, of course. For the target work, target procedures apply but then again, the final inspection includes the Wilson gage.

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TRKakaCatWhisperer posted this 22 June 2012

Yup. Love the Wilson case-length gauges!

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joeb33050 posted this 27 June 2012

Case shoulder setback with LV loads

In February 2010, M10 Savage 308 Win, loads of 314299 and IMR4227 from 10 gr down to 6 gr showed no bullet tipping-the question at that time. For this test I felt safer from stuck bullets with 7/IMR4227, which shot, (Feb 2010), 16” below 20/IMR4227 at 100 yards. Savage Striker, 308 Win. Two cases were used, loaded at the bench. Headspace was measured with the RCBS Precision Mic, that has ZERO at minimum headspace dimension = 1.630". Then a -7 below = 1.630” - .007” = 1.623". The shoulders were pushed back, SAAMI “headspace” decreased = head clearance increased. The extractor was not in the bolt. I attempted to put the extractor back and shoot some more, the extractor ball bearing is in low earth orbit now, and I didn't bring a spare. Both misfires fired the second try. I would have bet the ranch at 9:00 AM that the case shoulders wouldn't set back.

6/27/12 311299 no gc, 203 gr, WLR, 7/IMR4227, 1 FC case, 1 BHA MATCH case BHA Match FC Headspace (.000") Headspace (.000") -7 start -7 start -8 -7 -10 -8 -9 -9 -11 -9 -14 -10 -13 -11 -15 -9 -15 -9 -17 -10 -20 -12 -23 -11 -22 misfire -11 -23 -11 -25 -11 -25 -11 -25 -12 -28 -12 -27 -11 -27 misfire -12 -27 -11 -26 -12

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pat i. posted this 27 June 2012

Joe if you're not still pissed at me and don't mind me adding to YOUR topic.......... Below is a picture of the two cases that I used yesterday at the range. Both have been fired about 15 times. Initially both primers where seated flush with the case head when fired and proceeded to back out as I reloaded them for a total of about 15 shots each.

From what I've been able to gather FC cases are noted for being soft which might explain why they shortened so much more than the BHA case which I think I heard Winchester makes. Obviously the Lapua are similar because the case I used before this one shortened enough that the extractor wouldn't pick it up and I had to push it out of the chamber with a cleaning rod the last two times before the neck split (waste not want not is my motto). 

P.S. I just thought of something I'd like to run by you guys. If the shoulder is being pushed back the brass has to be going somewhere and the only somewhere I can think of would be into the length of the neck. As a test I measured one of the cases I shot with the primer sticking out .020 and came up with a length of 2.498 including the primer. PTG's chamber print book lists the chamber length up to the 72 degree incl angle transition point from the chamber mouth to the throat at 2.502 for the 30-06. Would you think it possible that as the shoulder got pushed back even more it would get to the point where the steep angle up at the front of the chamber would put a crimp on the case pinching the bullet when it was shot? I think I'll have to dig for my chamber length guages and see just how long my chamber is. I'd imagine it would be a bit longer that 2.502 but you never know.

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John Alexander posted this 30 June 2012

Pat,

That's pretty dramatic visual evidence of gross case shortening. The mystery remains. Why in a lifetime of shooting reduced loads in several calibers, often very reduced loads, I have never had a case shorten. I have never seen a primer backed out like yours. I have never had a case that went into the chamber without causing resistance on closing the bolt after firing many light loads.

What are other people doing that I'm not or what am I doing that others aren't?

Apparently Joe has had a similar experience to mine at least with some cases.

John

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joeb33050 posted this 05 July 2012

While I can't get the table onto this reply space, the whole article is attached. Cases shorten with light loads. joe b.

CASE SHOULDERS SET BACK = HEADSPACE DECREASES = HEAD CLEARANCE INCREASES WHEN CASES ARE FIRED WITH LOW VELOCITY CAST BULLET LOADS. EXTRACTOR INSTALLED!

Savage Striker, 308 Win. Two cases were used, loaded at the bench. Headspace was measured with the RCBS Precision Mic, that has ZERO at minimum headspace dimension = 1.630". Then a -7 below = 1.630” - .007” = 1.623". Case length was measured with a 6” dial caliper. The extractor was in the bolt. For both cases, case length didn't change much, or in any meaningful direction. FC case headspace did not change much. BHA Match case headspace decreased = head clearance increased enough to cause concern.

7/4/12 311299 no gc, 203 gr, WLR, 7/IMR4227, 1 FC case, 1 BHA MATCH case. These were not the same cases used in the “no extractor” test. FC BHA Match Headspace (.000") Length (") Headspace (.000") Length (") -7 start 2.025 -7 start 2.019 -7 2.025 -8 2.021 -6 2.025 -8 2.022 -6 2.025 -7 2.018 -6 2.025 -6 2.016 -4 2.023 -10 2.017 -4 2.023 -8 2.016 -4 2.025 -10 2.017 -2 2.023 -9 2.016 -3 2.024 -11 2.016 -4 2.022 -11 2.016 -4 2.022 -11 2.016 -5 2.024 -10 2.016 -5 2.024 -12 2.017 -5 2.022 -12 2.018 -5 2.024 -11 2.017 -5 2.025 -12 2.025 -7 2.022 -12 2.019 -8 2.022 -13 2.015

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nimrod posted this 05 July 2012

Just a thought a lot of people are saying that they have never had this problem while a few others have. Maybe it has to something to do with case length pat i. is showing some with a 30-06 the case that I had a problem with was a 30-06. I don't recall ever having a problem with the .308 case or the .223, 22-250, or .222 Mag and I have shot a lot of those reduced. About all the other reduced loads that I have used were in rimmed cases so would not expect any problems there and haven't noticed any.

Richard

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pat i. posted this 05 July 2012

I had the same thought as you.

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TRKakaCatWhisperer posted this 06 July 2012

nimrod wrote: Just a thought a lot of people are saying that they have never had this problem while a few others have. Maybe it has to something to do with case length pat i. is showing some with a 30-06 the case that I had a problem with was a 30-06. I don't recall ever having a problem with the .308 case or the .223, 22-250, or .222 Mag and I have shot a lot of those reduced. About all the other reduced loads that I have used were in rimmed cases so would not expect any problems there and haven't noticed any.

Richard

Hmmmm. Shoulder angle?

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joeb33050 posted this 06 July 2012

As the test shows, 308 Win case decreased headspace = increased head clearance by .025", then with the extractor .005". Some 308 win cases decrease headspace. The different results with different cases shows that the effect differs. Probably one could ultimately test enough to show that headspace shortening is determined by case hardness, case thickness, chamber finish, case finish, powder charge and so on. I see it this way: Some cases shorten headspace with light loads. Some wizards tell us that excessive headspace causes brass stretch and head separations. Other wizards show pictures of 308 cases fired in 30/06 guns with no ill effects and no shoulders. The question seems to be: will a short headspace ctg head separate, or will it expand and become a correct-headspace case?
My Lyman dies FL size to case headspace = min chamber headspace - .007"/.008” = 1.622"/1.623". Max chamber headspace = 1.640". Then max head clearance with my dies = .018". Yet the guns ain't blowing up. Maybe fire LV load, decrease headspace. fire full pressure load and headspace increases and case is now fine. Maybe fire LV load FL size, load to full pressure and fire fire lv load FL size, load to full pressure and fire etc is what gives head separation. It's all about safety with cases that were fired with lv loads, then fired with full pressure loads. And in the background is the fact that I've never seen a head separation in 62 years. joe b.

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TRKakaCatWhisperer posted this 06 July 2012

Seperation is generally about 1/2” above the base. The process is:

Firing pin pushes whole round forward.

Primer goes off & pressure holds front of case rigidly in chamber (if it's a sufficiently large charge).

Internal pressure pushes base back, stretching the case between the base and where it's stuck in the chamber at the neck.

The result can be seen in sectioned cases (as in Lyman reloading books), can be seen by the burnished ring where it will break just above the base, and can be detected by using a wire to feel inside the case for the thinned-section just above the base.

Separations occur much more often in semi-auto's where there is much more of a jerk - yanking the case from the chamber. I've expereinced on in a 223 and several others that were partials (caught it before full separation) in other calibers.

When I can I have rifles done with a minumum chamber and size for minimum head clearance. That, obviously, allows for minimum stretching and requires minimum sizing.

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