Brass sizing issue w/ reduced loads

[Busterman]

Last year a few of you helped me with reduced loads and I hope you can assist on a sizing issue. I am using 25gr load of IMR 4759 in my 03A3 with excellent accuracy. Starting with once fired LC68 brass sized to 2.036" on my Hornady gage the fired reduced load cases measure 2.030". I realize that reduced loads don't normally stretch a case much and that the case is probably stretched to fill the chamber and would size back fine. That isn't what happened. I set my sizer die and sized a couple once fired cases to 2.036" just fine but the reduced load cases sized down to 2.022"?
I have no idea of what the science is here or whether or not the cases can be salvaged as they are now too short to risk fire forming I think.
Any suggestions on how to save the cases?

Thanks in advance,
Don

[tmark]

Full length resizing is what stretches the brass. The brass expands when fired to fit the chamber diameter but full length resizing will lengthen the brass. What kind of brass are you using, commercial, military. How many times have your reloaded and thus, resized the brass?

I have only neck sized one piece of brass to see how many times I could reload it. After about 10 reloads, the neck split.

[k arga]

I would just neck size, no need to work the whole case.

[Busterman]

Thanks for the replies I appreciate the advice. I'm starting with once fired LC68 brass so its not been overworked or reloaded before. I have neck size only dies and will try that suggestion. I'm still trying to sort out why the die shortened the brass fired with a reduced load so much but not a once fired case which sized normally. I measured the fired cases at the shoulder, mid cartridge and base and the results were the same as an unfired case. So, reduced loads expand the case but case length is reduced? And, when resizing, the case is further reduced, at least thats what I am finding. The mystery is, where does the brass flow? I don't know how to better explain what's happening but its a conundrum for sure.

[Parashooter]

First off, you need to know exactly what you're measuring. Here are the SAAMI cartridge and chamber specs for .30/06 -



Note the measurements from base of case and chamber (bolt face) to the .375" datum on the shoulder. Case = .2.0526" to 2.0456"; chamber min. 2.0487", max 2.0587". Since none of the dimensions you're quoting are within these specs, we have to conclude that either your measuring tool isn't providing an accurate reading at the .375" point on the shoulder or all of the cases you've measured (2.022" to 2.036") are significantly short.

This leaves us with information that is useful only in relative terms and is missing the critical dimension of a case fired at normal pressure (which will reflect the chamber dimension fairly closely.) All we know is that the head/shoulder measurement of your fired reduced-load cases shows a .006" reduction from the original sized dimension and is reduced a further .008" on sizing.

Perhaps what you're missing is really some critical dynamics -

1. When a rimless case is chambered forcefully, its head/shoulder dimension can be reduced significantly simply by the chamber acting as a sizing die. Furthermore, the primer's force acts to push the case farther into the chamber - "sizing" it some more. Under normal pressure, the case expands fully, re-seating the primer and stretching to fill the available space in the case. At significantly reduced pressure (as is generated by your 4759 loads), the case doesn't expand fully and/or completely re-seat the primer - leaving the head/shoulder dimension more or less reduced from what it was before chambering and firing.


2. When sizing a case in a full-length die, the resulting head/shoulder dimension varies depending on (among multiple other factors) the dimensions of the fired case. Larger/longer cases produce more strain on the press and die, resulting in significant flex and a sized case of longer head/shoulder dimension than when a smaller/shorter case is sized in the same die. The press and die are, after all, made of somewhat elastic materials that stretch and compress less when lighter resistance is encountered.

It's not uncommon for F.L. sizing dies to be made with a significantly shorter head/shoulder dimension than is appropriate for most chambers. (This reduces the number of customer complaints from novice reloaders who don't well understand press/die flex dynamics.) Experienced reloaders often adust sizers to produce cases that will just fit in the intended chamber. This is best judged not with an imprecise gauge but with the actual rifle in which the loaded ammunition will be fired (feeling for resistance when chambering a sized case with a stripped bolt).

If readjusting dies for minimal sizing isn't sufficient, cases previously used in reduced loads that have experienced a reduction of less than about .015" in head/shoulder length can be "salvaged" simply by firing with a normal load. If the reduction and resultant cartridge end-play is greater than ~.020", it can be worthwhile to fireform them at moderate pressure (~40Kpsi for .30/06) with a thin lubricant film to prevent chamber adhesion and consequent stretching at the web/wall transition. (Few well-made classic military rifles are threatened by the ~10-20% increase in "bolt thrust" resulting from carefully lubed cases, but care should be taken to avoid excess lubricant and consequent hydraulic neck lock.).


(Chamber cast was used to extract broken case #1, too tightly stuck for conventional tool.)

[Busterman]

Parashooter, you've provided some really great information and convinced me that I should review my reloading procedure and tools. Just to clarify though, I sized the cases that were once fired after inserting one into my 03A3 and reducing the size until the slightest resistance was felt. I use RCBS competition dies and while well used they seem fine but, I'll check everything.
Thanks,
Don

[joem]

Double check your dims. All my .30-06 are trimmed to 2.484/ 2.285. Why are your trimmed that short? I only use 4895 in .30-06 but some of my reduced loads were 35 gr of 4895. Had to use my m1's like bolt action rifles as not enough pressure to operate the bolt.

[Sunray]

"...sized down to 2.022"..." In length? That's way under the trim-to length of 2.484". Make drawer pulls and pitch the rest.
That'd be SR4759 and a reduced load means a lighter bullet. Where's the 25gr load of IMR4759 data coming from?

[Parashooter]

I use RCBS competition dies and while well used they seem fine but, I'll check everything.

Please appreciate the difference between elastic deformation (temporary under load) and plastic deformation (permanent, after stress). It is highly unlikely your dies would experience plastic deformation even with abnormally high stress (they are thoroughly hardened and normally will fracture if severely overstressed) but they do have enough elasticity to stretch a little more when sizing a fully-expanded case than one that isn't.

A more frequent contributor to variable sizing is press and linkage flex, particularly when we have adjusted the die so it doesn't contact the shellholder under load. Sometimes we can demonstrate this effect by sizing a case three or four times and measuring the head/shoulder dimension after each pass. Much depends on brass hardness and lubricant quality, too.

This effect can be reduced or eliminated by using oversize shellholders (Redding makes sets) that allow both firm contact and precise end-play reduction. See a decent discussion at http://www.saubier.com/forum/showpos...77&postcount=1.

A less-costly alternative is to use a little sticky grease (or bullet lube) to affix one or more thin washers to the base of the sizing die. (An air-cooled VW distributor shim is about perfect diameter and can be stoned for thickness as necessary, but see http://www.amazon.com/dp/B004K1FF7I/ref=biss_dp_t_asn for an alternative.)

[Parashooter]

"...sized down to 2.022"..." In length? That's way under the trim-to length of 2.484". Make drawer pulls and pitch the rest. . .

Guys, he's measuring the head/shoulder dimension, not the total case length -


Hornady "Headspace" gauge.*

. . . Where's the 25gr load of IMR4759 data coming from?

. . . For the bolt gun, you can get acceptable 200-yard performance and still lower recoil with lighter charges of faster powder. 25 grains of SR4759 or AA5744, for example, produce about 4 ft. lb. of recoil with the 110 Sierra, while the old standby of 12 gr. Red Dot gives just 2.4 ft. lb. - which is slightly less recoil than a 9 lb. mousegun delivers with normal loads.

That 4759 charge data ultimately comes from IMR's old Handloader's Guide -



25 grains of 4759 is normally good for '06 with any jacketed bullet up to 220 grains, bulky enough to help avoid double charges, good accuracy, low recoil. (17.5 grains is my pet load for gas-check cast bullets in the 170-220 grain range.)

*Hornady's gauge isn't really measuring headspace - or is it?