NATO brass not chambering

[F. Guffey]

http://www.saami.org/PubResources/CC_Drawings/Rifle/308 Winchester.pdf


Jersurf101,

“I think the problem is that I am not getting the shoulders set back far enough. I am using a Lee .308 win die on a Lee challenger kit. Is it possible I need a new sizing die? The sizing die I have cannot go any lower as it is touching the shell holder on the ram. The micrometer says that the shoulders on the LC read 1.72" while the Nosler and Winchester that were fired in the gun measure 1.715" if that helps. Is this a known problem with a Lee sizing die?”

1.715” and 1.720” ? I am the fan of standards, and transfers and verifying. That puts me in a class all by myself. To use a gage like the Hornady comparator there must be a way to zero/index the tool, I know, a comparator is used to compare, problem comparators are referred to as head space gages, the head space gage is a standard. Back to the comparator, the comparator compares before and again after. that would be before firing and again after firing, problem, most measure the case after firing and after sizing.

The measurements from the datum to the head of the case as in 1.715” and 1.720 are no where to be found listed in SAAMIs chart for the 308W. The maximum chamber length from the datum to the bolt face is 1.640”, the minimum is 1.630”, SAMMI list the case length from the datum to the case head as 1.634 with a min. of -.007”.

The difference between 1.720” and 1.640” would lead me to believe you are using the incorrect datum, I make datums, I collect datums and on occasion I purchase datums. when I use a datum the plaine is zero.

F. Guffey

 

[Unclenick]

I don't know why that didn't jump out at me before. He's not measuring at the datum, but where the neck meets the shoulder. His numbers are about right for that.

I hate to beat a dead horse, since the OP reported the problem solved in post #16, but getting the basics of the measuring right seems worthwhile, and maybe this will help someone else trying to make the same measurement.

Mr. Guffey is correct that the normal measuring point is an intersect with the shoulder of a bottleneck cartridge called the datum line. It's actually the intersection of the outside of the shoulder with a plane through it and perpendicular to the axis of the case. This intersection describes a ring around the shoulder at 0.400" diameter. Here's a drawing I did awhile back to explain this:

The reason for using that datum is to get around having to estimate exactly where the vertex of the slight radius of a corner is. The old way of measuring headspace was where the slopes of the side and shoulder would intersect, but it requires that estimation factor and is a less repeatable measurement for that reason. Same with the neck and shoulder junction.

If you don't have a tool for measuring this exactly, comparative measurements approximate to the datum line are good enough for adjusting dies. You just won't necessarily get a number you can compare to anyone else's number. That's because this will hit the shoulder a little bit off from the datum line, so the lengths won't be exactly right. But if the hole through the spacer is anywhere close to the datum line diameter, then using this method to see how much you are pushing a shoulder back works just fine.

Below is an improvised measurement using a spacer from Lowe's that claims to be for 3/8" bolts. The actual ID is 0.409", IIRC, and that's close enough to the .400" datum diameter for comparative measurements of shoulder setback. You can see from the number, 1.594", when it should be about 1.640" that the spacer sets a little lower on the shoulder than an actual datum diameter hole would. This is mostly because of the chamfer in the hole, and not the fact it is a little large. Since you zero on the length of the spacer, that chamfer subtracts from the absolute value measurement.

Nick

 

[F. Guffey]

"Guffey, in the reloading industry, the operation of reforming a fired cartridge case to approximately its original dimensions has been called full length sizing for decades. There is no dimensional specification".

Depends: Who measures? I do. There is field reject length, there is no go- gage length and, there is go-gage length, there is factory, new over the counter minimum length ammo, and I ask : Who Measures? I answered that question with "I do". There are minimum length/full length sized cases.

We all remember the old saying about the chamber being reamed to accommodate all factory ammo, factory ammo is shorter in length from the datum to the case head than the chamber from the datum to the bolt face and we never ask 'by how much?'

IT IS NOTHING FOR ME TO MEASURE THE LENGTH OF THE CHAMBER AND COMPARE THAT DIMENTION WITH THE LENGTH OF THE CASE FROM THE USUAL PLACES WHEN DETERMINING THE AMOUNT OF CASE TRAVEL I WILL HAVE WHEN THE CASE IS FIRED.

Then there is SAAMI, it is not east to size cases for a chamber I do not have, that is the reason I determine the length of the chamber first.

F. Guffey

 

[Bart B.]

Unclenick, great post with lots of good info.

One can buy one of those spacers, borrow a GO headspace gauge, put that spacer on the gauge neck, measure it with a caliper, record the caliper reading then zero the caliper. Return the GO gauge to its owner.

Using that recorded reading on the caliper to zero it means you can measure fired case headspace and get a good idea of your rifle's chamber headspace; just add .001" to the reading. Also use on bottleneck cases and see how their headspace changes from new, after firing and again after full length sizing. Also where the die needs to be set in the press to get a given amount of shoulder setback.

I used steel tubing cut and squared to exact 1 inch lengths to do that long before gauges such as the RCBS Precision Mic was available.

 

[F. Guffey]

Bart B., I make datums, I collect datums and on occasions, I purchase datauns, the answer to your question begs another question: WHY? The plane is the 'measure from' anyone can zero 'from'.

Not a problem but if all measurements are going to agree the datum, round hole circle must be 90 degree to the plaine, if the hole has a radius the plaine of the datum will be below the top of the datum.

The Wilson datum has a radius that is convexed, since the early 50s.

F. Guffey

 

[Bart B.]

Good stuff on how case dimensions change when fired and resized.

The Rifleman's Journal: Basics: Resizing - Case Dimension Changes

 

[F. Guffey]

That article was almost as boring as a conversation that starts with "Hatcher said,,,,". Choices: There is full length sizing and no choice. I am not a fan of name dropping, I do not have heroes, I am the fan of cutting down on all that case travel, I am the fan of how and why, when it comes to thinking I am a fan of the free thinker.

And as always I determine the length of the chamber fist. Then there is that part where reloaders must do it like the bench resters? That is like pretend, pretend you have a bench rest type rifle etc..

F. Guffey

 

[George4376]

Your cases have been fired in machine guns which are known to have generous headspace and chamber diameters,perhaps a small base sizing die would help.

 

[Bart B.]

George, what is the dimension for "generous" headspace in a machine gun, for example the M60 using 7.62 NATO ammo?

 

[Unclenick]

Bart,

Good point on marking the spacer. I've used headspace gauges to zero these things before, then just looked at the resulting +/- readings on cases afterward. But zeroing first on the spacer, then on the GO gauge will give you a difference from the go gauge that should be constant for all cases with that same datum diameter as long as the shoulder angles aren't much different. Or, you could measure the GO gauge, then zero, then remove both the spacer and the gauge and close the jaws. The resulting number, less the minus sign, could be recorded, then you'd just open the jaws to that number and hit zero every time you wanted to use that same spacer with that same cartridge. No more Go gauge needed, as you point out.

Flanged Oilite sleeve bearings are another item I've used. The hole diameters are more exact. The flange makes it a little easier to hold square to the caliper jaw.