Body Die Sizing

['Freak]

If you’ve been neck sizing only then over a number of firings and allowing the case to continue to grow in length it has finally reached the point where it has become too long for that chamber. Not talking about overall length either, it’s not something that’ll get fixed by trimming. Instead, it has grown too long measuring from the base to the case to the case shoulder datum and what you’ve been feeling whilst closing the bolt on a case that’s too long is the bolt face shoving the base of a case that’s too long in body so whose shoulder is already firmly lodged up against the chamber’s shoulder. With the bolt closed on that piece of brass inside that chamber, headspace is somewhere between none and something less than zero.

You need to push the case shoulder back just enough so that when the case’s shoulder is butted to the chamber’s shoulder there will still be ~ a thousandth or two of clearance between the base of the case and the face of a fully closed bolt (headspace, with that case). You’ll need to, by whatever means, adjust how much of the case’s length enters and so will be acted on by the die once the press ram is peaked at the top of its stroke.

 

[BenPerfected]

I think that is important that you understand why one should avoid pushing case shoulders back (bumping) excessively. When a rimless cartridge is fired, the force of the firing pin strike, and slightly after that of the primer going off push the case forward in the chamber until the chamber shoulder stops it. This creates a momentary gap between the bolt face and the case head. As the pressure rises from the burning of the powder, the sides of the case body grip the chamber holding the case in this forward position, and with normal pressure loads, at some point the pressure is enough that the case stretches, just in front of where the solid head begins, back to the bolt face, very slightly thinning the case in a narrow band in this area. The first time that a case is fired, this may amount to a stretch of say .006 or so, but as a one time event, the loss of thickness is not a problem, unless it is repeated over and over, because the case is sized incorrectly, bumping the shoulder back too far each time. If this happens, the case will be gradually thinned, first showing a bright line in the area that is becoming thinner, and developing an indentation on the inside. This is called incipient separation. Cases that have this condition should be discarded. If the incorrect process is continued beyond that point, cases will crack, and their head separate from the body of the case, leaking gas, and leaving the case in the chamber with its head on the bolt face when the bolt is opened. There is some potential for the shooter being injured in an extreme case, but I have not seen this. Getting back to the incipient separation, the internal groove that accompanies it can be detected by straightening out a paper clip, putting a short right angle bend near one end, and pulling the tip up the inside of the case from the bottom. If a groove has formed it will be felt just off of the bottom.
If on the other hand the FL or body die is set properly, and the shoulder not pushed back (bumped) excessively, the stretching of the brass will be minimal, and cases will not be thinned near their heads excessively, resulting in long case life, usually to the point that necks will start to split from repeated in sizings and firings, but if the chamber is not too big in that area, and the sizing process properly controlled, this may not be an issue for a great number of rounds.

You seem to have gotten the impression that you need to get a bushing FL die. While it will eliminate the need to use two steps (neck and body dies) when you size, beyond that, there is no advantage. You can get the same result with what you have. What you do need is a tool to measure shoulder bump, and to learn how to use that tool properly. Once you have one in hand, I suggest that you return to this forum for some coaching as to how that is best done. There are a few things that may not be obvious to the first time user.

Boyd,
This is very helpful and I really appreciate your detailed response. I just got delivery on some bump gauges, the next step is to learn how to use them. I will play with them some, and then follow back with an update.
Thanks,
Ben

 

[243winxb]

Gun: Savage LRPV 6mm NORMA BR 1 in 8 twist

The firing pin strike from my Savage 223 sets the shoulder back .006" Do use Redding Type S FL sizing bushing die. Size about 1/2 of the neck. But your body die & neck sizer will do the same thing, just in 2 operations.

 

[Patch700]

To the OP , there has been some very helpful info provided in this thread... The important thing to remember with precision loading is that without a good solid foundation in normal reloading a lot of what people say with regards to precision reloading may or not make sense.

When it comes to this stuff it's important to understand the "Why's" of it all , the following is a link to a very successful shooter who shares a wealth of information that can be referred to at your leisure .

http://riflemansjournal.blogspot.ca/p/articles-index.html


Take note that at no point does this gentleman change something in his reloading routine without first conducting a series of measurements and for good reason.

Hope you get as much from it as a lot of others myself included have.

Good luck.

 

[Danattherock]

What you have observed is that cases do not all become tight at the same rate, even if their quality, and the equipment are good, and all of the loads that were fired are the same. In my experience, if one has an accurate rifle that has the potential to shoot small groups mixing cases that have differences in bolt close feel in the same group will degrade accuracy. That is the reason that neck sizing has been largely abandoned by target shooters, in favor of FL dies that are a close match for their rifles' chambers. In the case of someone who wants to have the best possible ammunition for a factory chamber, using cases with unturned case necks, a number of shooters have reported excellent results by sizing necks with a Lee collet die, and sizing the rest of the case with a body die, as a two step process, done every loading. The trick is in setting the body properly for shoulder bump. In order to do this, you can use your tightest fired case that has only been neck sized for the last few firings. After removing its primer, or reseating it well below the case head, you can use it as a reference for setting the die. The other requirement is a tool with which to measure from cases' datum lines on their shoulders to their heads. For this task I prefer what Hornady has mislabeled their headspace gauge. It is quite useful, but rather than being a true headspace gauge, it is a shoulder location comparator.

This is the single most substantial improvement I've made to my loads since I started reloading. Average runout on my 21st Century concentricity gauge dropped from 4.5 to 1.5. And that was while still using the seater from my Redding Deluxe 3 die set. Recently bought Forster Ultra seater which should only help. Thanks again Boyd!


Dan

 

[Danattherock]

So I just got a body die...

do I first need to run them thru a neck sizer to knock out the primer? or can I run them thru the body die with the primer still in place and then neck size?

Thanks in advance!

Below is something very similar to my recent success with the Lee neck collet and body sizing routine Boyd Allen mentions. Boyd's post about that was the single best piece of advice on this four page thread.


"Sizing with the neck die first followed by the full length die produced cases with significantly better neck-to-body concentricity that using the full length die first and the neck die second."


From this article which can be found in the link Patch provided...

http://riflemansjournal.blogspot.com/2010/04/reloading-two-step-sizing-and.html


Dan

 

[welscher663]

Thanks to everyone for the information, I will read it all over again and get to the reload bench and see what I can do. I truly appreciate the wealth of knowledge there is on this site!

Ethan

 

[BenPerfected]

I was posting while you wrote your last question. The effect of FL or body sizing on brass life is directly related to the match between the die's dimensions and that of the chamber. The greater the difference, the more the case will be lengthened during from sizing, as the brass from the body's reduction in diameter is forced into the case neck, lengthening the case. With a die that is closely matched to the chamber, such as is commonly use for competition (speaking of bolt actions here) and properly controlled shoulder bump (I use .001) cases may be used for a great number of firings, and as I said above, the usual place that they fail will be that their necks will crack, unless cases are annealed, but this may not happen for a great number of firings if the chamber is such that necks are not worked excessively by firing and sizing. In order to get a fix on what your particular body or FL die is doing, I suggest that you measure your cases after they are fired, and then again after they are sized, checking the diameters just above the extractor groove, where you can see the end of the chamber by looking at the surface finish, and also at the shoulder, and neck. It is also good to measure necks of loaded rounds, over the part of the seated bullet shank that is largest in diameter. You can use a dial caliper for this, and I would measure several cases.

Hi Boyd,
I have attached a picture my cases and the head space tools I just got for my 6 Dasher. (Wilson Case Gage & a Harrell's Head space gauge). I just got started with a Carstensen neck/body die and sized a few cases. The picture is of a (1) fired Dasher case (after hydro-forming) and a unfired but body size case, both fit perfectly in the Wilson Case Gauge. Not sure this is clear, but isn't this saying that there is very little to no change in the re-sized case compared a fired case? Should I just stay the course with decapping, body sizing and neck sizing all in one step?
Ben

 

[BoydAllen]

What I was referring to was the amount that a fired case's body diameter is reduced by FL or body sizing. Your gauges do not measure that. As to your continuing your current sizing procedure, assuming that you sent in fired brass when you ordered the die, yes I would keep using the Carstensen die, with appropriate attention to shoulder bump when setting it. If you want to see an extreme example of body diameter reduction, measure a case fired in a factory chamber, and then size it with a one piece RCBS FL die and remeasure. Measurements should be taken above the extractor groove, where chamber contact ends, and at the shoulder. Then you can do the same thing with your Carstensen die, using fired brass from the same barrel that it was ordered for. You should see quite a difference. You might also want to note case lengths, before and after sizing for both tests.

Boyd (my first name

 

[BenPerfected]

What I was referring to was the amount that a fired case's body diameter is reduced by FL or body sizing. Your gauges do not measure that. As to your continuing your current sizing procedure, assuming that you sent in fired brass when you ordered the die, yes I would keep using the Carstensen die, with appropriate attention to shoulder bump when setting it. If you want to see an extreme example of body diameter reduction, measure a case fired in a factory chamber, and then size it with a one piece RCBS FL die and remeasure. Measurements should be taken above the extractor groove, where chamber contact ends, and at the shoulder. Then you can do the same thing with your Carstensen die, using fired brass from the same barrel that it was ordered for. You should see quite a difference. You might also want to note case lengths, before and after sizing for both tests.

Boyd (my first name

Sorry Boyd, it was corrected. Thanks for your response and help.