Re: Hand loading for Long range 1: brass case prep
The question has been asked a few times but no answer has yet been given & I'll try and walk through it to see if it makes sense;
First, let's assume we have our shoulders bumped to .003 under our chambers headspace measurement.
Now, after determining your total chamber length, how many thousandths under do your trim your case length to? I would think you would want your cases as long as possible for the neck to support the bullet without it exceeding your chamber length so .003 under? .004 under? I understand consistency is the goal here and as long as possible the better, but I suppose it all depends on if your cases even approach that chamber length.
Let's say your chamber length measures to 3.000 just as a round number. Out of 50 cases, your longest is 2.998 & your shortest is 2.993. I would assume you just cut them all to 2.993 for consistency but unfortunately, you're losing .005 of neck support. If you could cull out your 10 shortest, maybe then your shortest now is 2.996. Now you could cut the 40 to 2.996 thus gaining .003 more neck support.
Also, since the case expands upon firing, I would assume it expands lengthwise also to a certain degree but is also limited by restricting the shoulder from expanding only that .003 forward. Let's say you were somehow able to get 40 cases to 2.996. When that round fires, I'm thinking it will it expand lengthwise .003 until the shoulder makes contact within the chamber. This should keep the end of your case from going past your chamber length measurement with it coming up .001 short. I couldn't imagine the neck alone lengthening much if any at all if the shoulder couldn't get past the headspace.
I will personally keep the length of my .338 LM cases to exactly .004 under my chamber length. But, I will always ensure my headspace never exceeds that .003 thus preventing excess expansion and the end of the case going beyond my chamber measurement.
I hope I described this in a way that makes sense. I had to pretty much talk my way through it for it to make sense to me.
<span style="font-style: italic"><span style="font-weight: bold">Now here's something that'll challenge y</span>ou;</span> I own 4 Weatherby Mag guns (.240, .257, .300, & 30-378) and in those cartridges the headspace is determined to be at the top of the "belt" near the base of the cartridge & NOT the shoulder if I understand correctly. Thus it's referred to as a "belted magnum". Here's where it gets tricky; Because in our standard non-belted rounds the shoulder is what stops the lengthwise expansion of the case forward, in the Weatherby Mag brass, there is more chance for forward expansion of those cases because you have the entire case body expanding forward. But wait, can we still restrict that forward expansion by knowing the distance to where the shoulder would rest in the chamber or not? Weatherby has the "double radius" shoulders and are they even meant to rest against a shoulder "rest" within the chamber since the top of the belt is actually the "headspace"???
Now, when "fireforming" a case, will the fact that the top of the belt being way down by the base of the cartridge and it being the "headspace", prevent the shoulder from ever reaching the area in the chamber where the shoulder would rest against? If the shoulder never reaches this area, why would you even have a reason to bump the shoulder back .003?
But, in the picture examples for this thread, it looks like he's using a .300 Win Mag case which is also a "belted magnum" case.
Here's two paragraphs from the below link that talks about the 3 different types of headspace & about headspace and the belted magnums;
"On a rimless cartridge such as the .308, the stopping surface is the shoulder. On a rimmed cartridge like the .30-30 or .303 British, the headspace is the gap for the rim. On a belted magnum, headspace is the gap for the belt."
"And the rimmed and belted magnum rifles? Dealing with the rim or belt and the shoulder at the same time is a reloading problem, involving expanding the neck and resizing it down to create a false shoulder, then fire-forming the brass to your chamber. On a .303, I wouldn’t waste time. When I tried it, I got one extra loading out of my brass. On a .300 magnum, it is definitely worth the extra effort."
So, it states it's a "reloading problem". Great. When he talked of fireforming being worth it for the .300, I take that as you can form the case to make contact with the shoulder then? If anyone knows how to specifically deal with the belted magnums, please let me know how to incorporate the detailed brass prep that works so well with the unbelted cartridges. Thanks.
Sorry if this was too confusing but I tried to explain it as plainly as possible.
Link:
http://www.rifleshootermag.com/2010/09/23/gunsmithing_headspace_0612/#ixzz1ySNgGbx9
