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Old November 8, 2011, 02:24 AM   #1
bamaranger
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Sizing Question

I typically size all my cases for hunting rifles full length, and, using an RCBS Precision Mic, take the cases (size) down -.003 less than what a fired case measures.

I've told a friend I will load him some .270 ammo for use in his Rem 7400 auto. His fired cases measure +.008 on avg. (same cases, his rifle, same factory load) .

Should I use the same approach, and size his cases down -.003 less (to
.005)? I have heard that the Rem autos are picky, and small base dies are recommended, etc.

Should I take the cases down more to account for this?
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Old November 8, 2011, 08:05 AM   #2
steve4102
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Semi-autos can be a little difficult to find that .003 shoulder bump. Ya see, when a round is fired in a bolt action the brass expands to fit the chamber then springs back just a bit to allow for easy extraction. Measuring the fired case and bumping the shoulder back is simple.
Things are different in an auto-loader. When the round is fired it expands just as it does in a bolt action, the difference is that the case is still under a little bit of pressure when it is extracted from the chamber. This tiny bit of pressure can cause the case to continue to grow after it has left the chamber. The case may be longer or even fatter than the chamber it was fired in. I believe this is why you are seeing a .008 increase.

Basically only two ways to set up an auto-loader for FL sizing. Trial and error, size and check, size and check until an empty case chambers with zero effort. A better way is to get a case gauge and set the die up so the case fits perfectly into the gauge. This will ensure that the sized case will fit and function in his chamber.
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Old November 8, 2011, 08:21 AM   #3
F. Guffey
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The ability to measure the length of the chamber before firing would allow the shooter/reloader/fire former to know the effect the chamber will have on the case when fired and the reloader that can measure the chamber before firing can adjust the die to the shell holder in the press to size case that will chamber, memory, recovery, pop back, jump back (spring back) does not lock me up.

I use the companion tool to the press, the feeler gage, bump sounds like an accident, there is nothing I do when sizing a case for a chamber that resemble an accident, action/reaction, If I move the shoulder back the case diameter increases, so? I move the shoulder back with case body support, and, time is a factor.

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Old November 8, 2011, 08:50 AM   #4
F. Guffey
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“His fired cases measure +.008 on avg. (same cases, his rifle, same factory load)”

You have everything in front of you, I do not know how you are measuring case length, if you are measuring the case length as in from the head of the case to the mouth of the case I would say we are taking about a case trimming issue, however; if you are finding the additional .008 is between the head of the case and the shoulder you may want to consider refraining from full length sizing, I apply the ‘leaver policy’ when the shoulder of my cases mover forward .008 thousands I ‘leaver out there’. I have the advantage, I use the companion tool to the press, the feeler gage, the feeler gage is the reason jump back, snap back or spring back does not lock me up.

As to the .008, or put another way, when the chambers effect on the case when fired results in an increase of .008 thousands additional length between the head of the case and shoulder I adjust the die off the shell holder with the feeler gage, first I would attempt chambering the fired cases, if the violence of being fired and being ripped from the chamber before the case was ready had an adverse effect on the case as in stretching and expanding the case will not chamber in the chamber it was fired in (without effort).

If the case chambers with a crush/interference fit use the feeler gage to adjust the die off the shell holder to prevent excessive sizing, I would start at .005 thousands, after sizing a case with the .005 thousands gap I would again attempt chambering the sized case, if the sized case chambers, I would then increase the gap to .007, I would continue this process until the press, die and shell holder had no effect on sizing the case.

In the prefect world the effect the chamber had on the fired case would be .005 thousands if the case was the prefect minimum length/full length sized, so your friend should consider his chamber is beyond go-gage length and shorter than no go-gage length, and that goes back to the ‘big inning’ M1 Garands used the same ammo as the 1903/A3 and M1917, the M1 Garand chamber had additional clearance, then there is the small base die, something reloader must have? If only they could learn to determine the length of the chamber before firing.

F. Guffey

Last edited by F. Guffey; November 8, 2011 at 09:03 AM. Reason: move ;
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Old November 8, 2011, 10:28 PM   #5
bamaranger
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again

I am not referring to case length. I am trying to describe setting the sizing die as to how it effects headspace.

The tool I use for same is the RCBS precision mic. The cases in question gauge +.008 after firing. For the Rem 740-7400 series, how much is it recommended I size them back?

Typically, I would size them back to +.005 (.003 less)
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Old November 8, 2011, 10:37 PM   #6
bamaranger
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reread

At this point, I may just size the cases back to .000 on the gauge. That, it is my understanding, is SAAMI spec, and let it go at that.
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Old November 9, 2011, 12:04 AM   #7
F. Guffey
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Bamaranger,

I make gages, I start with measuring the length of the case from the head of the case to it’s shoulder. By whatever means I record the measurement, I then fire the case and measure the length of the case from the head of the case to it’s shoulder again, the difference in length of the two is the effect the chamber had on the case when fired. Autos and semi autos are said to be rough of the case when fired and extracted. If any part of the .008 thousands is being caused by the violent extraction the case will not chamber without resistance.

Again, I would suggest making an attempt to chamber the +.008 cases, I would then adjust the gap between bottom of the die and shell holder with a feeler gage starting with .005 thousands. After making the adjustment I would size a case and attempt chambering the case, if the case chambers I would increase the gap and size another case and attempt chambering, again I would continue increasing the gap until the case chambered with resistance.

I have bar dies for 300 Win Mag, 270 W and 30/06, I do not use them, but JIC, I have them JUST IN CASE.

My favorite cases are trashy old cases that have been fired in trashy old chambers, with my press, die, shell holder and the feeler gage I have 8 options when deciding the length of the case from the head of the case to it’s shoulder.

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Old November 9, 2011, 05:22 AM   #8
oneoldsap
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On semis the base of the cartridge just above the web can be a determining factor on whether the case chambers or not . On semis I like to size the case as much as possible without lube dents . Sometimes you need smallbase dies anyways , to get them to chamber reliably .
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Old November 9, 2011, 08:31 AM   #9
Jim243
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Not sure why you offered to make up some rounds for your friend other than trying to be a nice guy (most of my shooting buddies reload). I have a 7600 in 30-06 and I would not make any rounds for it unless they were factory spec. I would full length resize, gauge the case for headspace and shoulder and take it to +/- 0.000. Make up two dummy rounds (no powder or primer) and have him fuction them in his 7400 manually to insure fit and function.

Unless you have the rifle to try the rounds in, it would be a crap shoot to tell if eveything is working right. Once you know that the cases are going to full battery and headspacing correctly you can load away.

Good luck
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Old November 9, 2011, 02:50 PM   #10
Slamfire
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Quote:
I typically size all my cases for hunting rifles full length, and, using an RCBS Precision Mic, take the cases (size) down -.003 less than what a fired case measures.

I've told a friend I will load him some .270 ammo for use in his Rem 7400 auto. His fired cases measure +.008 on avg. (same cases, his rifle, same factory load) .

Should I use the same approach, and size his cases down -.003 less (to
.005)? I have heard that the Rem autos are picky, and small base dies are recommended, etc.

Should I take the cases down more to account for this
You should size his cases with a small base die, there are plenty of those, and you should use a calibrated case gage and size to gage minimum.

I use Wilson gages, they are cheap and the dimensions from the lower ledge and upper ledge correspond exactly with chamber headspace gages.


I don’t know what the RCBS precision mike measures, there are a bunch of “relative” gages that are not calibrated to anything.

Your bud’s cases are long because they were fired and ejected from a semi auto. Cases get stretched because cases are extracted while there is still pressure in the barrel.

So you heard this two times now. Believe it yet?

You size those cases long and your bud may have an out of battery slamfire.

Happens even in commercial rifles.


http://www.thehighroad.org/showthrea...49#post7180249

Browning Automatic Rifle (BAR) Slamfire in 270 Win. Neck sized cases.

It's good to think you had the good common horse sense to ask that question. Some have assumed nothing is any different since the cartridge is what it is, 30-06 or what ever high powered rifle round, and then necked it as with their bolt actions. A man came into the gun shot I worked in with a really nice, well was a really nice Browning semi auto, I think it was chambered in 270 win., no matter. He said he had been necking for a while for that rifle without problems. I doubt he considered now and then chambering issues as problems. Either way, all it took was one slam fire to ruin his day and rifle, and fortunately not his life!
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Last edited by Slamfire; November 9, 2011 at 05:06 PM.
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Old November 9, 2011, 04:37 PM   #11
Unclenick
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Unless you can prove the case wasn't stretched, set it back as far as the dies will do it, or use Mr. Guffey's method and insert a feeler gauge between the head and shell holder to take it down the rest of the way. Per the slamfire warning, you need to be extra careful to get primers seated firmly and below flush with the case head.

The two Precision Mic's I own don't have perfect absolute accuracy. A couple thousandths off on one of them. So just use some new factory ammo as a reference and go for that or use a case gauge as Slamfire showed the photo off.

One thing that can mess with any of the gauges is a bent rim from hard extraction, causing the readings to be high. Just line the cases up on a flat surface and make sure they line up when you sight down them. Tilting is caused by a bent rim.

Last thing, I recommend you teach your buddy to reload on your tools. I know I wouldn't use reloads I hadn't made and wouldn't want the liability of someone else using mine.
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Old November 10, 2011, 01:25 AM   #12
bamaranger
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done

Thanks for all replies. Cases sized to .000 on the RCBS gauge chamber satisfactorily. That will be SAAMI spec and should resolve headspace issue.

Bent rims and high primer warnings duly acknoweldged.

Guffey thanks for your time. I had never heard of using a feeler gauge on the shell holder/die rim but I understand what you are doing.

Slam, not disbelieving, just not completely digesting.

Thanks again
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Old November 10, 2011, 02:08 AM   #13
farmerboy
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If i did make some prob only around 10 at first just to check functioning and accuracy. But i bet you will have to small base size to get reliable functioning
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