fire forming 375h&h cases

[rp85]

good afternoon;

need to fire form 375h&h case to 375 Weatherby. is there any risk stretching 375h&h case above belt using 16gr red dot (1460fps) or 32.5gr 5744 (1952 fps) using 285 grain cast bullets. thanks for any input.

rp

[lar45]

I would think that if you seated the bullets to engage the rifling, then the case would be held back against the bolt face so no stretching could occur.

[oger]

The belt will hold the headspace.

[skeettx]

Great loads for fire forming and general use
Let us know how they turn out
You using a WBY or some other rifle?
Thank
Mike

[TurnipEaterDown]

Belt recesses are often cut generously deep -- one reason why accuracy & case life is generally bettered by having a bottleneck belted case headspace against the shoulder (same goes for many rimmed cases & chambered guns), so it would be an advantage to either seat the bullet out to rifling to fireform, or neck up to 416, and then back down to get a false shoulder to HS on w/ bolt resistance to closure.

[M-Tecs]

Belt recesses are often cut generously deep -- one reason why accuracy & case life is generally bettered by having a bottleneck belted case headspace against the shoulder (same goes for many rimmed cases & chambered guns), so it would be an advantage to either seat the bullet out to rifling to fireform, or neck up to 416, and then back down to get a false shoulder to HS on w/ bolt resistance to closure.

That is spot on.

Also the shoulders on belted brass tend to be short and the reamers long in the shoulder area make it less than ideal. For all of the belted reamers I own I have headspace gauges made to measure the shoulder datum not the belt.

For my 375 H&H's I used a RCBS Precision Mic. For the 375 WBY I would use the Hornady Case Comparator and set shoulder bump to .002" for normal shooting. For dangerous game I would double that.

[stubshaft]

16.0 Red Dot should do you just fine, it's what I generally use too.

[Bigslug]

I would think that if you seated the bullets to engage the rifling, then the case would be held back against the bolt face so no stretching could occur.

DING! DING! We have a winner!

The belt WILL regulate your headspace within the range of that headspace, but it still has that tiny bit of tolerance that allows the round to fit the chamber. The firing pin impact will shove the round to the forward limit of that tolerance and the case head will slam backward by that much when it pressurizes. If the case walls are seized against the chamber at the same time, this is how your stretching occurs. Seating into the lands will take up that tolerance and help ensure that the case is getting blown forward at the shoulder and not stretching backwards at the web.

(A pretty common practice for any of the Ackley Improved rounds)