Home Forums Reloading Big Game Rifles Bumping shoulders back

I’m quite aware of the difference between bumping the shoulders and partial sizing. However, since people seem to have a lot of difficulty achieving the proper bump I thought I’d offer the Skip’s shims suggestion. The shims make it a lot easier to achieve a perfect fit.
I also realize that partial sizing some less tapered cases (IE: .243 win. and probably some of the newer short magnums) has been declared impossible by many as the partial sizing tends to push brass forward into the shoulder. That being said, I have used shims successfully in partial sizing .243, .308 and .284 Win. brass - although there might have a bit of shoulder bump. If that’s the case, it demonstrates that the shims can be used for bumping as well as partial sizing.

IME, what you’re calling ‘partial’ is generally called neck sizing. Partial FL sizing is typically considered to be bumping the shoulder, but not all the way back to SAAMI dimensions, while FL sizing usually means restoring body dimensions and headspace to SAAMI spec while also sizing the neck.

That’s a diplomatic way of clearing the air.😊 However, with partial sizing the die does come in some contact with the case body but stops a couple of thou short of touching the shoulder hence, it’s neither pure neck sizing nor shoulder bumping. Case lube is required whereas, with pure neck sizing it isn’t - other than using a (preferably) dry lube such as graphite on the inside of the case necks. If I choose to shoulder bump, a shim about .002 thinner than my pre-determined partial sizing shim Will generally do the trick.

With all of that said, if you're using an off the shelf FL die you're most likely sizing the neck section of the brass more than necessary.

You’re probably correct there mathman. Nonetheless, I still get nicely accurate and dependable ammo with the partial sizing. Also, excellent case longevity - although I don’t load to “burn, blind & deafen” levels and I anneal after every 3rd firing, which I’m sure helps with longevity.

That's mitigating the effect of cold working the neck.

No, that's never been the meaning of partial sizing as I've ever understood it or seen it used. Perhaps that's what some guys call it, but that's incorrect and misleading IMO. Sizing the shoulder to fit your chamber IS full length sizing - neck, shoulder, and body all get sized full length. Anything more is just excessive sizing (i.e. bumping the shoulder back too much causing excess headspace) and poor die adjustment, most guys just don't realize it. Just because your die is capable of being run down to the shell holder doesn't mean that is correct "FL sizing".

Neck sizing is a different thing from partial sizing the neck with a FL die. Partial sizing still reduces body diameter to fit the chamber easily while leaving an unsized ring of the neck to center the cartridge. The neck is only partially sized, hence the term.

Regardless, bobber257's idea of "less fiddling" is actually a lot more fiddling than just measuring and adjusting the die correctly.

I get what you're saying but I've always heard people use the term "partial neck sizing" to refer to, well, only partially sizing the neck leaving some of it unsized.

Whereas "partial FL sizing" refers to what that the others are saying, setting the FL die to just bump the shoulder.

Four terms to describe four basic ways to size, "neck sizing", "partial neck sizing", "full length sizing", "partial FL sizing".

I agree about setting up the die correctly in the first place, but this is the first time I've seen someone describe FL sizing that way. Pragmatically, the purpose of partial FL sizing has always been to tailor the case dimensions with a specific chamber in a non-interference relationship. The reason some people FL size (meaning to SAAMI spec) has always been to use the ammunition in various chambers that may vary somewhere between SAAMI min and max specs.

Your description of "partial" sizing also leave me a little confused, since IME when the FL die sizes the entire neck and approaches the shoulder, it begins sizing the body enough to stretch it so that you have negative headspace. Doing it that way, you'd likely be approaching a fine line between partial neck sizing and negative headspace. Personally, I prefer to do my partial neck sizing with a neck die, and then size the body and bump the shoulder with purpose every few firings.

Sounds like you've never done it that way. That method has been around a long time, I certainly didn't invent it. When the die is backed off 1/8" or so to leave part of the neck unsized, the shoulder isn't pushed forward to any perceptible amount. Pretty easy to measure if you don't believe me. With most cases the shoulder doesn't move forward until the die is pretty close to bumping (maybe half turn of the die, give or take). Obviously it's not a techique to use in semi-autos but it works well in bolt actions.

I’ve done it that way with a FL die before, but I call it partial neck sizing, and these days I prefer to do it with a neck die. I see what you mean about minimally sizing the body, but don’t see much benefit in it. IMO if the body needs to be compressed, I want to bump the shoulder as well.

IMO partial neck sizing indicates using a neck sizing die to partially size the neck. Partial FL sizing is doing the same thing with a FL die. Partial sizing with a FL die holds the neck centered as it's sized, while a neck die does not.

Seems to me the definitions some of you guys are going by are pretty arbitrary. Is bumping the shoulders for a tight chamber still "partial" sizing? What about when it's tighter than SAAMI specs, is that still partial sizing if it's set to match the chamber? Or, if we have to set the brass back to SAAMI spec to consider it FL sized, how many of you actually measure that, vs just screwing the die down to the shellholder? I think this whole discussion is based on a common flawed perception of what FL sizing really is and how to do it correctly.
There is nothing "partial" about FL sizing cases to correctly fit your chamber, whether that's one rifle or several, or whether that happens to be at standard specs or a few thousandths on either side. The arbitrary distinction of calling a correct die adjustment "partial" and screwed to the shell holder "full length" is a bit absurd in my opinion.

Quote: “Regardless, bobber257’s idea of “less fiddling” is a lot more fiddling than just measuring and adjusting the die properly”.

Well, if Yondering (in his infinite wisdom) thinks that quickly and easily using the shim method for various tasks is more fiddling than re-adjusting your die for each task (IE: shoulder bumping, full length sizing to origional specs, or partial sizing (partial neck, partial body or whatever semantics you choose) then, so be it. The system has worked for me for years and will continue to work. (with minimal fiddling😁)

I can see where you’re coming from, but the definitions being used are due to common convention. A SAAMI adopted case starts off at SAAMI dimensions. Sizing it only partially back to its original spec, but more than the neck (differentiating it from neck sizing), is typically called PFLR. This includes your example of sizing down further than SAAMI as well, IMO, since FL sizing implies SAAMI spec, which means that it can be used safely in any SAAMI chamber. Don’t make the mistake of thinking you’re the only guy on planet Earth who measures things. I’m sure not everyone does, but SAAMI means SAAMI.

Commonly used arbitrary definitions are no more absurd than your arbitrary definitions. Being common practice means that most people understand each other when using the prevailing terminology.

In any case (pun be intended), you know what they say about opinions...

What you're saying would be correct if the common definition of full length sizing meant bumping shoulders back to SAAMI spec, but it's not. That would require measuring shoulders at a specific diameter and comparing to specs for that cartridge, which most people don't do and is definitely not the "common convention". Instead, the common interpretation of full length sizing is just screwing the die down to the shell holder, which in most cases is NOT bringing cases back to spec but something less, often .010" or even .020" below spec. I'm sure most people think that brings their brass back to correct spec, but it does not in most cases. Of course most people using that method don't measure it, and don't realize the dies are setting shoulders back a lot more than needed. Factory ammo and new brass is usually sized somewhat below spec as well.

Bumping case shoulders back to fit a chamber in most rifles is very close to SAAMI spec, usually within a few thousandths; it's usually closer in my experience than what you get with the die down the shell holder. That is where our interpretations differ. What you're insisting is "partial sizing" is actually correct adjustment for full length sizing (whether that is adjusted for SAAMI spec or to fit a specific chamber, very similar either way), rather than excessive sizing. Obviously there are exceptions that go either direction; I've had some setups where setting the die to cam over on the shell holder was correct, and others where a loose chamber needed the die backed off more than spec, but those are exceptions.