Brent,
Here's some clarification for you on the fire-forming techniques I use.
First a little background for anyone else reading this. When fire-forming Ackley Improved chambers the original parent case technically is suppose to headspace properly in an Ackley chamber and only the angle of the shoulder and body taper of the case gets pushed out. This was one of the design principles of Mr. Ackley. There is always tolerences in everything so the heaspace may not be a crush fit per say but should be within a couple thousands. About the same as firing a factory round in a factory chamber. If it's a custom chamber normally they are setup at minimum spec and that is how my custom chambers are cut. Mine are headspaced to where the bolt of my action just gets resistance about 1/2-3/4 down it's bolt throw and will lock up on a "go" gauge. That's it. The "no-go" gauge is never even used. This sets the chamber at minimum headspace and helps with case life.
Now with that said:
Brent,
Here the details of the cornmeal method I use.
Cornmeal method for Ackley Improved cases
When blowing out my Ackley Improved cases, I've used Green Dot and Unique powders. I reload and shoot shotguns also so it's simply the powder I have laying around. I use whatever I have handy at the time. BUT, you do run pressure with this method, so it's not as simple as just dumping a little powder, it goes pop, and your done. Could you "blow up" a rifle... I don't know and never tried. I doubt it though. But you would be surprised at the sound and some recoil you get when firing one of these cases. Wear ear protection. And your barrel will get hot if you run a batch of cases through one after another.
In my 6.5x55AI case for instance I used 14gr of Green Dot back against some old CCI 200 primers (junkers that are old and questionable for firing). Then I take cornmeal (cheap and not course grained like some other fillers used by others) until the cornmeal is heaping out of the case mouth. Then I take an ink pen and tap on the case. This will settle the cornmeal most of the time until it's about at the shoulder level down inside the case. Then it's a matter of getting the right amount of wadding (another shotgun term there Brent!!
) or TP and pushing it down on top of the cornmeal until the whole thing is tight. The TP should go in with some resistance. I use the same ink pen to "seat" the TP tight on top of the cornmeal. If done properly you can turn the case upside down and nothing moves or spills. So you don't have to worry about spilling cornmeal and junk in your chamber if you don't hold the rifle straightup all the time. I also very lightly lube these cases with Imperial sizing die wax to make sure upon firing, the case sets back against the boltface. Done this for years without a problem. And it does blow it out so it headspaces properly after the fire-forming load. The only reason I said 98% above is the shoulder and neck junctions are normally a little rounded. But after the first full house load they sharpen right up. But no, the shoulder placement doesn't move after the first fire-forming load to answer your questions directly. I use this method for forming 300 H&H brass into 6.5-300 WWH brass also because that case has a belt on it so it doesn't headspace on the shoulder until after it fired. Works the same. I used Green Do for forming that brass also.
One other thing I do while "shooting" these fire-forming blanks is I setup my whole bench, setup with rests, bags, stops..... the whole 9yds. I practice actually firing my bench guns aligning the scope, gun hold, developing good bench technique, watching to see what direction my cross-hairs move after firing etc, etc,etc. This is great practice without the expense and wear/tear on your barrel. This is a great way to tell you if your bags are packed properly. If you rifles walks using these rounds it's going to be a lot worse during actual live fire. This is more for competition type shooting but regular bench techniques can be used and observed. Just thought I would throw that in.
Moving a shoulder forward method
Now if I'm blowing a shoulder forward while fire-forming like I do for the 338 Yogi(approx .050" the shoulder moves forward) then I use my regular load minus 2 grs of whatever powder your using and lightly lube the outside of the case body and neck with Imperial Sizing-Die Wax. Normally jsut enough wax so that your finger tips look shiny is all. Then EVENLY spread the wax over the entire circumference of the case body and neck. Seat the bullets long to hold during intial chambering. What this does is allow the brass to expand against the case walls but not stick for those few milli-seconds and allow the case as a whole to slide back against the bolt face and not stretch the brass. Yes this does create more thrust on the bolt during firing. I've never done this on anything but good commercial and custom actions. Would I do this with a 30-40 Krag rifle with an improved chamber for example?..... no! I've had guys argue with me tooth and nail that this is dangerous and I'll blow my head off. I've also talked with many others that have used it for many years and some are prominent gunsmiths. So it's up to you. Just realize what you are doing and be willing to accept the risk if there is any. NOTE: remember that it is important to keep your locking lugs lubed while doing this or you take a big chance of galling them. Especially in SS actions.
Here's is a perfect example of how this work and that it really does work. 2 or 3 yrs ago, during a competition I normally fire my first 2 or 3 sighters with my fire-forming load that has lubed cases. Due to the oily bore and such the first 1 or 2 sighters are very course sighters anyway so the accuracy/drop isn't that important. It will hit lower so I jsut don't click down that much. In this particular match I was fire-forming all 10 sighters and my match load was 2 gr hotter. I needed those case fire-formed for an upcoming aggregate match. But in the confusion of getting everything setup and my other duties during this match, I forgot to lube all 10 of my sighter(fire-forming) cases. Well, I fired all the sighters and record rounds without a problem. They all fire-formed fine by the naked eye and nothing unusual.
Then a couple days later I resized all of the cases I fired in this match and the sighter cases felt different during sizing. Then I put them in the case trimmer and after the first case realized something was different. It was cutting off .010-.012" off the OAL. Normally this is only a cleanup cut to make sure they are square. At most I might get some shavings. But noramlly just barely a skim cut. This happened to all 10 of those sighter cases. So the wheels were turning in my head as to what is different. Then I realized what happened really by accident a little later on. I ran out of sizing wax that I keep on my loading bench. I went to my shooting box to get my "traveling" can that I take to the matches. I couldn't find it in my box. I found it on my shooting table and I hadn't opened my shooting box after returning from the match until then. So the "traveling" can of wax never went ot the match with me and because of that I never remembered to lube my cases.
So that extra .010-.012" is case stretch from within the case from the brass "holding" against the chamber walls during firing and pushing the shoulder forward and/or the case head backward. The real kicker happened a couple ofweeks later during another match when I had my first case retire out of the original 100 Lapua 338 Lapua cases I purchased. Then another. Within a 2 week period I had 3 case failures (cracked cases around the shoulder/body junction) on 5 firings or less. I number my cases with a majic marker and keep track of the them in a spreadsheet so that I know what cases were used and at what match. Well, those 3 failed case came out of that batch of 10 unlubed cases!
To this day of the original 100 cases I bought, I've fired them many times (wore out one throat and had it setback and rechambered and started firing again on the same cases) with over 20 loading on some of those cases. I've lost 5 cases out of that batch since 1999 in my 338 Yogi chamber. 4 of them were case body/shoulder cracks out of that batch of 10 unlubed case. The 5th is a cracked neck from fatigue that wasn't in that batch.
Hope this answered your questions Brent. If not let know and I'll try again. My fingers are tired right now.
Steve
