Case tweaking.........

[oneokie]

Is there any need for case neck clearance when shooting cast?

Am loading boolits sized to fit groove(+.0015"). These cartridges chamber snugly. Accuracy is good to a point.

Is there a minimum to neck wall thickness? Am at .007" now. If I go to a bigger dia. boolit, am thinking about turning the neck area of some cases. Would .006" be too thin?

What is the nominal diameter of the flash hole for use with large rifle primers?

[Doc Highwall]

The trouble with going too thin is the necks get work harden easier. Also you did not say what caliber it is. In my gun 30-30, the groove diameter is .30875" I size my boolite .3095", and the expander M die that I made is .3097" giving a very lite press fit good enough for a single shot rifle. The cases are sized with a LEE neck sizing die with enough force that the expander will not enter and no more. When I prepare my cases for reloading I use a 30cal bore brush in a cordless drill and clean the inside of the necks and wipe off the outside of the necks as best as I can before they get sized. This makes it easier to load the gun and make shure their is clearance in the neck of the chamber to release the boolit. I thing this will give me the longest case life with annealing. And YES you do need clearance in the neck of the chamber to release the boolit or the chamber pressures will raise dramatically.

[shooter93]

Hard bullets like linotype....jammed into the lands and fired for higher velocities can actually spike pressures quite high...higher than most people think.

[felix]

80-100K psi with condoms using jam seating using military sized cases close to max loads. Neck clearance should be 0.0008 with a bench rifle. More when chamber not pristine in dimensions. Best accuracy across the board will be when there is no jam, about 0.010-0.015 off from jam with most factory leade dimensions. If using a bore rider, don't allow the meat of the boolit jam, and seat as instructed. OK for witness on bore riding nose, but nowhere else. Change powder speeds and primer ignition to make that work, and accuracy will be good throughout the weather conditions. Jammed projectiles are unreliable and shoot differently day-to-day. ... felix

[oneokie]

Cartridge is 38-55. Using commercial cast, 92-6-2. Moderate thumb pressure will chamber the case rim against the breech face. Light engraving of lands on nose of boolit.

[runfiverun]

with a bit of polishing and some work hardening to the necks
you might get away with not sizing the necks at all.
andstill have near .001neck tension, but your loads have to be fairly light to do it.
and you gotta play with your alloy to get that "happy size".

[oneokie]

with a bit of polishing and some work hardening to the necks
you might get away with not sizing the necks at all.

Do not have to resize cases now.

andstill have near .001neck tension,

Have to use the seater die to seat boolits into a flared case. Boolit will not go deeper in case with thumb pressure, and will not rotate in case before crimp is applied.

but your loads have to be fairly light to do it.

Would you elaborate on the light load? What am I missing here?

and you gotta play with your alloy to get that "happy size".

"happy size"??? I thought that size is directly related to groove diameter. Boolit size can be adjusted with a boolit sizer die, and case to chamber fit can be adjusted with neck turning. Is there another reason I have all this equipment to do these things with?

What I am having trouble understanding, is the need for neck clearance as it relates to accuracy. At this point in time, my boolit is sized close to optimum diameter for the groove diameter. The transition from case to bore is smooth, a precise straight line IMO. No chance for the boolit to get sideways entering the bore.

[leftiye]

If you are not having pressure symptoms, then you are in the range that R5R was alluding to as the Happy size (as relates to fit in the chamber neck). However, if you are not sizing at all, and are having to use a seater die, then your case neck to chamber clearance is borderline, or maybe a little too tight. A little dirt could send pressures skyrocketing. Anything that pinches the case neck/mouth to the boolit can even cause blown primers. If your boolits are sized groove diameter plus one thou. and you cannot seat in the case with only minimal pressure in a die, then you're probly pretty tight in the chamber neck with the finished cartridge. Try sizing boolits only .001" over groove diameter. Reducing neck thickness would be good also.

[Doc Highwall]

You also have to watch how the case is crimped. Some times with a roll crimp it makes a slight bulge just below the case mouth and this will cause drag on the chamber wall when loading. By the way what kind of accuracy are you getting and what is your load? I want to learn more, makes life interesting.

[oneokie]

My most accurate load to date is shown in my avatar.
Measured c-c.
Load consisted of Starline 2.125" cases, WLR primers, 5744 powder, and commercial cast boolits sized at .380". Boolit is a 246 gr. bevel base similar to the Lee 379-250, lubed with an unknown hard lube, red in color.
Charge weight was determined after talking to the head ballistican at Accurate powders. (Western Powder, Miles City, MT.)

Other components used in testing were:

Cases; all were annealed prior to use.

WRA 38-55 @ 2.112", circa 1964, neck thickness is close to .007" used in second most accurate load
Rem-Umc 38-55 @ 2.112" circa before 1960
Win 38-55 @ 2.080"
Win 375 win

Primers:
CCI 200
CCI 250
Fed 210
Fed 215

Powders:

IMR 4895, worst accuracy
IMR 3031
IMR 4198
IMR 4227, used in second most accurate load
IMR Trail Boss

Alliant 2400

Same boolit was used for all loads. This boolit is said to be 92-6-2, equilavent to Tarracorp Magnum alloy, BHN listed as 16.
No charge weights listed for the reason that what works in my rifle may not work or be safe in another firearm.

[runfiverun]

nolan: that boolit is a magma engineering mold and the lube is theirs also.
i have that mold.
in my 375 win cast from ww+2% i can only go up to about 1500 fps
before major problems.
and leftiye is correct about what i was saying, however the case expanding upon firing and contracting back to size and then not having to resize is dependant on your load,
the flame temp, pressure, and when it peaks.
as the temps will tend to harden the case some,not as much as sizing.....IMO.
but will harden them over time.
you didn't say if your cases are staying clean or blackining any.
you can tell some about what is happening by that also.