In 50 years of loading I've had only two casehead separations, and one was in a 375. So, I'm a tad cautious. Also, I admit to being irrationally committed to maximum accuracy. That is, if I can use the word irrational in combination with reloading.

Question: Will the firing pin push the loaded case forward to headspace on the belt, or should the bullet be seated to the lands for fire forming? Has anyone tested this using a gauge? I've found conflicting opinions on the net. (Big surprise!) Yes, I know that rounds loaded to touching will not fit most 375 H & H magazines.

Thanks

Most likely the headspace is just fine. The belt functions much like a rim on a rimmed cartridge as far as positive headspace. The problem is some have generous chambers.

Fire form and then resize off of the shoulder like a rimless case is a popular option. Myself I split the difference as my pre 64 Win 70 has a generous chamber. I don't fully resize off of the shoulder but do back the Die off .010" from the Shell Holder.

Most likely your, and most factory, magnums have way more extra space between the case head and bolt face than you think; the difference between brass and chamber tolerances is about .017; I always forget.
Both the rifle and brass are within tolerances, just they are generous between min brass and max chambers. Anyway, yes, the firing pin pushes the case forward. If you are truly trying for a fitted case; then you have to either jam the bullet into the rifling and fire with a starting load, or make a new shoulder and headspace on the shoulder. Do not rely on the belt. And don't FL resize.

Thanks, esp. dpcd. I suspected that a jamb fit would be needed. Now I'm hoping that my RCBS FL die will partially resize. I've read that some FL dies will not.

quote:

Originally posted by Brice:
Thanks, esp. dpcd. I suspected that a jamb fit would be needed. Now I'm hoping that my RCBS FL die will partially resize. I've read that some FL dies will not.

My RCBS .375 H&H FL die will not partially size due to it being somewhat narrower at the shoulder than my chamber -- and my .375 is a Sako which usually will have fairly tight chambers. I'm not sure if RCBS's specs are too tight or if SAAMI chamber specs are too loose, but you are correct that partial or neck sizing with RCBS FL dies is not always possible.

I much prefer a "false shoulder" to jamming the bullet into the lands for assuring tight headspace. If you can find an expander button for a .40 or .41 handgun it should expand necks enough for your .375 die to create a false shoulder for initial firing. In effect, I use a false shoulder when making .280 Rem cases from .30-06 and they are just as accurate on the first firing as when reloaded after fireforming.

I cannot foresee a problem, but, I fireform my H&H brass in my 375 Weatherby chamber with Clays and a twist of TP, shoot and retrieve.
I have never had a case head separation doing this, and my brass has lasted several firings.

Cheers.

Then you have a good tight fit between brass and chamber; if you do not hold the case back against the bolt face, you will get stretching for sure. if there is any appreciable "extra" space. I have used both methods for wildcats. bullet jamming and second shoulder; both work; there is no reason not to do either one except creating a second shoulder is more work. Hence, why I rarely use it. Now, it does use bullets, but you can practice with it.

quote:

Originally posted by Brice:
In 50 years of loading I've had only two casehead separations, and one was in a 375. So, I'm a tad cautious. Also, I admit to being irrationally committed to maximum accuracy. That is, if I can use the word irrational in combination with reloading.

Question: Will the firing pin push the loaded case forward to headspace on the belt, or should the bullet be seated to the lands for fire forming? Has anyone tested this using a gauge? I've found conflicting opinions on the net. (Big surprise!) Yes, I know that rounds loaded to touching will not fit most 375 H & H magazines.

Thanks

To answer your question, Yes the firing pin will push the case forward. Then when the round fires the case will move back against the bolt and stretch the case.
If you have any problem with your RCBS die not PFL sizing send it and 5 fired cases to RCBS and they will fit the die to your chamber.

quote:

Originally posted by dpcd:
Then you have a good tight fit between brass and chamber; if you do not hold the case back against the bolt face, you will get stretching for sure. if there is any appreciable "extra" space. I have used both methods for wildcats. bullet jamming and second shoulder; both work; there is no reason not to do either one except creating a second shoulder is more work. Hence, why I rarely use it. Now, it does use bullets, but you can practice with it.

I am not sure if you're answering my post or not, dpcd.
Chamber design, such as the coned breech face on some rifles, causes belted mags to bulge at the web and stretch more than other designs. By fireforming with light pressure, even if the chamber is sloppy, no stretching occurs at the web. I do this for all my AI cases, belted cases and my comp rifles. I start with 99.9% fireformed cases and develop loads from there. It may seem unnecessary by most, but it works for me, and my brass lasts a long time.

Cheers.

Depending on how much fooling around you want to do...
A 3/8 wooden dowel cut into small sections with a cardboard washer glued on. Just punch the cardboard washers with a case. Pistol powder, and the dowel inserted, the cardboard will center and push the case back to the boltface.

quote:

Chamber design, such as the coned breech face on some rifles, causes belted mags to bulge at the web and stretch more than other designs.

I'm amazed how this myth continues to be propagated. The only thing about "chamber design" which causes belted cases to bulge in front of the belt is sloppy, oversized chambers. ALL case designs, whether rimmed, rimless, rebate, belted, or semi-rimmed bulge at the pressure ring -- the point just in front of the head where the brass becomes thin enough that it cannot resist the pressure and expands until it is restrained by the chamber wall.

The larger the diameter of the chamber wall at this point the greater the amount of the "bulge", again, regardless of case design. The reason that belted cases are perceived as being more subject to bulging is that manufactures take advantage of the belt for headspacing and choose to make belted magnum chambers much larger in diameter than they should be.

The "bulge" on a belted case is no different from the bulge on a rimless case, it's just got a belt in front of it.

By the way, the higher the pressure the further aft the bulge will occur and the more prominent it will be. For whatever senseless reason, both manufacturers and reloaders think that they can load belted cases to higher pressures than rimless cases. High pressures are one more reason that people notice the pressure ring ("bulge") more on belted cases than on rimless cases.