Setting Bump on Belted Cases

[EasyShooter]

How do you set up your sizing die when setting up for bump on a belted case? Normally headspace is set up off the shoulder that you are measuring for bump. On belted cases headspace is set off the belt.

 

[L.Sherm]

Just like any other case, I just ignore the belt.

 

[BoydAllen]

You ignore the belt, and do it just like it was any other rimless case. If you want to see something interesting, measure a new case, datum to head and compare it to a fired case. Let us know what you find. On once fired brass, always try setting the die to produce the same datum to shoulder dimension as the fired case (measured with primer removed or seated deep in the pocket.) Because it usually takes more than one firing to bring a case out to its maximum shoulder to head dimension, you typically don't need to bump shoulders back on once fired brass.

 

[mikecr]

You'll heaspace off the belt initially, but eventually the shoulders will overtake this. You'll have to bump shoulders to manage it at that point (~3rd fire forming).

 

[RegionRat]

Now would be a good time to play with learning to inspect your brass.

Grab the SAAMI spec off their web site for reference and learn to measure the brass. The shoulder datum length is just a starting point but an important one. I would also advise you to measure several other points on the brass including the diameter just above the belt, as well as the body-shoulder junction.

Grab samples of virgin brass and then study your fired brass before and after sizing. Keep good notes as the brass accumulates cycles.

As noted above, it takes more than one cycle to fill out the brass. To learn faster, it makes sense to take a few cases and get several cycles on them at first. This helps avoid bulk loading problems and establishes a better sizing setting up front. YMMV

 

[EasyShooter]

You ignore the belt, and do it just like it was any other rimless case. If you want to see something interesting, measure a new case, datum to head and compare it to a fired case. Let us know what you find. On once fired brass, always try setting the die to produce the same datum to shoulder dimension as the fired case (measured with primer removed or seated deep in the pocket.) Because it usually takes more than one firing to bring a case out to its maximum shoulder to head dimension, you typically don't need to bump shoulders back on once fired brass.

I am thinking the datum point is the back side of the belt. For 30-378 datum point to head;
New Brass is 0.248"
Once fired brass that bolt will close tight on is 0.250"
Once fired brass that bolt wont close on is 0.251"

I'm just measuring with calipers and not getting very consistent readings on different spots of the case. Would need to make a tool to hold the brass with my chamber reamer to get better readings.

 

[BoydAllen]

I was referring to the shoulder to head dimensions. Do you have an attachment for your caliper to do that with? If not, that is what you need. For setting up the die, literally ignore the belt. What I was trying to get to discover is that belted cases are made VERY short at the shoulder because there is so much variation in chambers in that dimension. For a .300 Wby. I measured a .021 difference, and the same for a Remington 7 Mag. Years ago guys that I know would get split case failures from belted magnums, which they thought were caused by "magnum pressures" Back then no one had a tool to measure shoulder to head, and they were undoubtedly screwing their dies down to the shell holder, a big mistake. Getting back to the attachment, you cannot measure shoulder to head accurately with bare calipers. It can't be done.

 

[EasyShooter]

I was referring to the shoulder to head dimensions. Do you have an attachment for your caliper to do that with? If not, that is what you need. For setting up the die, literally ignore the belt. What I was trying to get to discover is that belted cases are made VERY short at the shoulder because there is so much variation in chambers in that dimension. For a .300 Wby. I measured a .021 difference, and the same for a Remington 7 Mag. Years ago guys that I know would get split case failures from belted magnums, which they thought were caused by "magnum pressures" Back then no one had a tool to measure shoulder to head, and they were undoubtedly screwing their dies down to the shell holder, a big mistake. Getting back to the attachment, you cannot measure shoulder to head accurately with bare calipers. It can't be done.

I have made a tool for that measurement for most my guns but not this one. I use a chamber reamer to cut just past the shoulder in a barrel stub. I then turn that stub down to fit into my comparator. Here is a pic of the tool for 308 win brass.

 

[M-61]

On belted cases headspace is set off the belt.

For the first (or maybe second shot only)
After that the belt is to be ignored

 

[AckleymanII]

I have made a tool for that measurement for most my guns but not this one. I use a chamber reamer to cut just past the shoulder in a barrel stub. I then turn that stub down to fit into my comparator. Here is a pic of the tool for 308 win brass.

That is just too easy!

 

[BoydAllen]

Setting up a sizing die really has nothing to do with SAAMI spec. It is about getting the relation of the die to the shell holder set up so that the case fits in the chamber but is not sized so much (pushing back the shoulder) so as to cause excessive stretching from subsequent firings and sizings, leading to incipient separations and if the same faulty setting continues to be used full separations. Integral to this process is the measuring of fired cases, datum to head, as well as sized cases for the same dimension. You do not want to reference a drawing for this, because there is allowable tolerance for chamber headspace. You reference fired brass. What ever you do, do not follow any manufacturer's directions that do not mention this measuring and instruct to turn the die in until it touches the shell holder, lower the ram and turn is some fraction of turn lower than that.

 

[M-61]

The belt did have a 'real' purpose when first designed. You might think of it as an additional rim for straight cartridges (no shoulder)
But it became a sort of sales gimmick. It certainly worked in that regard. It causes no harm and I guess it 'looks' good. But like everything else, tastes change over time.

 

[jds holler]

Who among us didn't at sometime think that the belted case was necessary to prevent the incredibly powerful magnum cartridge from exploding the rifle??

And if you saw that your buddy's new rifle shot a belted cartridge, you just knew that it was the fastest, flattest, farthest shooting rifle in camp. jd