New brass headspace variance

[6Creed73]

So, I just got my whidden go/no go gauge and the first thing I'll say is it's a great little tool. Not sure why I waited this long to get one, it's much better than relying soley on a comparator.

Anyway, I decided to spot check some new brass and was quite surprised by the variation in headspace. In the video, the loaded round is fire formed brass that I neck sized only with no shoulder bump. It reads exactly .000 on the Whidden gauge (saami spec). The second one is a new piece of Alpha brass and it reads almost .004 under. The last one is a new piece of Federal brass and it reads exactly .005 over and in the "No-Go" section. That's about .009 difference between the two pieces of NEW brass.

It's funny because someone on this forum recently asked about prepping new brass and I commented that I didn't see a reason to FL size new brass. This has me rethinking that. I'm most definitely going to size this Federal brass.

 

[Straightshooter1]

RCBS has the same kind of tool, which I've been using for a long time. I sure makes it quick and easy to take some measurement; just pop a case in and give it a spin to get the reading, then a quick revers spin to pop the case out and pop in another. I'm always using it for my quality control checks as this RCBS tool does the job well.

As usual, Whidden tools are well built.

 

[txtaxman]

The Whidden Case Gauge is a nice tool, and it gives you an actual measurement rather than a comparison.
How do the readings from your comparator relate to your Whidden Case Gauge?

 

[6Creed73]

The Whidden Case Gauge is a nice tool, and it gives you an actual measurement rather than a comparison.
How do the readings from your comparator relate to your Whidden Case Gauge?

They compare in the sense that I can see there is a difference between brass pieces with both, but I like that the Whidden gauge is actually measuring based on the saami spec dimensions. With the Whidden I know exactly how far out of saami spec brass is, and where my chamber falls on the saami scale.

The comparator is simply getting a measurment from somewhere on the shoulder. I have 3 different comparators and all three of them give different measurements for the same piece of brass.

 

[Straightshooter1]

The Whidden Case Gauge is a nice tool, and it gives you an actual measurement rather than a comparison.
How do the readings from your comparator relate to your Whidden Case Gauge?

I use my RCBS gauge measurement as it relates to my go-gauge, which it indicates at -0- and the no-go gauge indicates just above the 4 mark (there's an actual .004 between the two gauges). Case measurement are then +/- that measurement. But when bumping shoulders, I simply look for the difference between the fired cases and the sized (like getting .0015 - .002" bump that I'm looking for).

 

[6Creed73]

I use my RCBS gauge measurement as it relates to my go-gauge, which it indicates at -0- and the no-go gauge indicates just above the 4 mark (there's an actual .004 between the two gauges). Case measurement are then +/- that measurement. But when bumping shoulders, I simply look for the difference between the fired cases and the sized (like getting .0015 - .002" bump that I'm looking for).

View attachment 1432647
View attachment 1432646

Yeah, that's basically why I got the Whidden. I wanted it as a better way to check that my dies are set properly. I can simply bump the shoulder, pop the case in the Whidden and see if it reads .000 and then proceed with sizing the rest. To me, it's just a tad bit easier than the comparator.

 

[Ned Ludd]

Unless the virgin brass *might* be too long to chamber like the Fed brass mentioned by the OP above, the more important question is how consistent the BTS dimension is straight out of the box. As long as the virgin brass isn't too long straight out of the box, it will expand to fit the chamber upon firing. In my hands, the BTS measurements for virgin brass are pretty consistent...typically anywhere from .004" to .006" (or more) shorter than fire-formed, but fairly consistent.

On the other hand, neck diameter can be all over the map in virgin brass. For that reason, I generally size virgin brass first with a bushing die set so that it doesn't touch the shoulder, then open up the necks with a mandrel. I use a bushing that is approximately .001" smaller than I would use if the bushing die were to be the only neck sizing step. That allows the mandrel to do work when opening up all the necks, resulting in more consistent neck tension. Because of the direction of springback once the necks have been sized down to a diameter smaller than the subsequent mandrel step will leave them, a mandrel that is .0015" under bullet diameter will typically yield very close to .002" neck tension/interference fit. Thus, the desired final neck tension can usually be readily achieved by simply by using a larger/smaller mandrel relative to the .0015" under bullet diameter/.002 neck tension "standard" relationship.

 

[D-4297]

^^^^^^^^ What he said , and a light chamfer , deburr of the necks doesn't hurt anything , before sticking them in your Dies , but it sure can save some grief , scratches in the Die or the cases if you don't .

 

[6Creed73]

Unless the virgin brass *might* be too long to chamber like the Fed brass mentioned by the OP above, the more important question is how consistent the BTS dimension is straight out of the box. As long as the virgin brass isn't too long straight out of the box, it will expand to fit the chamber upon firing. In my hands, the BTS measurements for virgin brass are pretty consistent...typically anywhere from .004" to .006" (or more) shorter than fire-formed, but fairly consistent.

On the other hand, neck diameter can be all over the map in virgin brass. For that reason, I generally size virgin brass first with a bushing die set so that it doesn't touch the shoulder, then open up the necks with a mandrel. I use a bushing that is approximately .001" smaller than I would use if the bushing die were to be the only neck sizing step. That allows the mandrel to do work when opening up all the necks, resulting in more consistent neck tension. Because of the direction of springback once the necks have been sized down to a diameter smaller than the subsequent mandrel step will leave them, a mandrel that is .0015" under bullet diameter will typically yield very close to .002" neck tension/interference fit. Thus, the desired final neck tension can usually be readily achieved by simply by using a larger/smaller mandrel relative to the .0015" under bullet diameter/.002 neck tension "standard" relationship.

I do pretty much the same thing. Typically, I only touch the neck of virgin brass so I can get the neck tension that I want. I almost always buy Alpha when I get new brass and I've had great luck with it. Like you said, .004 is about what I'd expect from new brass. I was a little surprised by this Federal brass being .005 over. I'm just going to full length size with a .005 bump and call it a day.

 

[Coyotefurharvester]

So you never mentioned trying the new Fed in the rifle?

 

[6Creed73]

So you never mentioned trying the new Fed in the rifle?

I did try it. It chambered but with a bit more force than I care for. No big deal, I bumped the shoulder back on all the Federal brass. This is my first time buying new Federal, I usually get Alpha and it's always sized correctly. I got a deal on the Federal or I wouldn't even have bought it.

 

[barefooter56]

Unless the virgin brass *might* be too long to chamber like the Fed brass mentioned by the OP above, the more important question is how consistent the BTS dimension is straight out of the box. As long as the virgin brass isn't too long straight out of the box, it will expand to fit the chamber upon firing. In my hands, the BTS measurements for virgin brass are pretty consistent...typically anywhere from .004" to .006" (or more) shorter than fire-formed, but fairly consistent.

On the other hand, neck diameter can be all over the map in virgin brass. For that reason, I generally size virgin brass first with a bushing die set so that it doesn't touch the shoulder, then open up the necks with a mandrel. I use a bushing that is approximately .001" smaller than I would use if the bushing die were to be the only neck sizing step. That allows the mandrel to do work when opening up all the necks, resulting in more consistent neck tension. Because of the direction of springback once the necks have been sized down to a diameter smaller than the subsequent mandrel step will leave them, a mandrel that is .0015" under bullet diameter will typically yield very close to .002" neck tension/interference fit. Thus, the desired final neck tension can usually be readily achieved by simply by using a larger/smaller mandrel relative to the .0015" under bullet diameter/.002 neck tension "standard" relationship.

Ned is spot on. The chamber in YOUR RIFLE is the last form die a NEW piece of brass goes through!

 

[Chris Edmondson]

They compare in the sense that I can see there is a difference between brass pieces with both, but I like that the Whidden gauge is actually measuring based on the saami spec dimensions. With the Whidden I know exactly how far out of saami spec brass is, and where my chamber falls on the saami scale.

The comparator is simply getting a measurment from somewhere on the shoulder. I have 3 different comparators and all three of them give different measurements for the same piece of brass.

What I found with both Hornady and Sinclair headspace comparator inserts is the beveled edge allows the shoulder to rest at a point inside the insert's bore, rather than resting on the .400 datum line.. I ended up facing a Hornady insert on my lathe, deep enough to reveal a crisp 90 degree edge without a bevel, once that was done, all my out-of-spec brass samples measured in-spec. The underlying problem with the bevel is it makes it impossible to accurately set zero on the calipers. When zero is set, the assumption is the shoulder will rest on the face of the gage, the bevel ensures that will not be the case.

Since this isn't a machinist forum, here's a brief description of the facing operation:

Facing on the lathe uses a facing tool to cut a flat surface perpendicular to the work piece's rotational axis. A facing tool is mounted into a tool holder that rests on the carriage of the lathe. The tool will then feed perpendicularly across the part's rotational axis as it spins in the jaws of the chuck. A user will have the option to hand feed the machine while facing, or use the power feed option. For a smoother surface, using the power feed option is optimal due to a constant feed rate. Facing will take the work piece down to its finished length very accurately.

Here's a picture showing a stock insert on the left, the faced one on the right:

 

[6Creed73]

What I found with both Hornady and Sinclair headspace comparator inserts is the beveled edge allows the shoulder to rest at a point inside the insert's bore, rather than resting on the .400 datum line.. I ended up facing a Hornady insert on my lathe, deep enough to reveal a crisp 90 degree edge without a bevel, once that was done, all my out-of-spec brass samples measured in-spec. The underlying problem with the bevel is it makes it impossible to accurately set zero on the calipers. When zero is set, the assumption is the shoulder will rest on the face of the gage, the bevel ensures that will not be the case.

Since this isn't a machinist forum, here's a brief description of the facing operation:



Here's a picture showing a stock insert on the left, the faced one on the right:

View attachment 1433113

That's awesome! You are absolutely right about the Hornady...and the Whidden I have is the same way. My favorite, and the one I typically use, is the SAC (Short Action Customs) gauge. As you can see in the pic, the insert is shaped where the brass sits in it more like it would sit in the chamber. Of the three, the SAC comparator gives me the shortest measurement, but I think it's the most accurate to an actual headspace measurement. At the end of the day, a comparator is good to do just that...compare. Can't rely on it to tell you what the actual headspace measurement is as far as saami goes.