THE HEADSPACE

I'm trying to determinate the headspace with rcbs mic and i'm finding some difficulties.

1.- I choose some cases getting from NORMA DIAMOND LINE HPBT 168 grains after shooting with my sako trg22 .308 rifle and I measure the level (or the value) with the headspace nut.The result that I obtain is -0,002.Because of the "dimension A" is 1,6300 / 1,6400, I think then that the obtain result means that my headspace is 1,6280. But this data is lower than the ANSI measure. How it is possible?

2.- I choose some cartridges of NORMA DIAMOND LINE HPBT 168 grains and I measure its headspace , I obtain the level (or the value) -0,002. Is that possible? From the two previous facts I can deduce that my headspace is exctly the same as the ammunition measure before I shoot. I can not understand this.

FINDING
THE BEST BULLET SEATING DEPTH
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I insert the freebore tool in the chamber and the value that I obtain is 0,32. But, What kind of unity is this? I suposse to understand that it is 0,32 + 1,6300 connecting to "dimension A" or not? If I measure with a caliper is 2,18 inch. Do you think that it is right? The OAL that I obtain is 2,850 inch, do you think is also correct or not?

thanks a lot

You`re lucky, your ammo fits your rifle. The factories go for a headspace that will fit in all chambers and it is normal for them to be at the lowest end of tolerance. The fact you are .002" under is likely a matter of how you measure or any slop in the tools you are useing.

There is some tolerance in the headspace figures. The amount I`m not sure of but I think most are on the order of -.004"/+.006" (inches) If your cases fall with in this, you are OK. The headspace we as reloaders worry about is the figure we get on our resized cases. The idea is to match the chamber size as best we can. The only time I`d worry about factory ammo fit in my rifle is if I had a chamber I was suspect of.

BTW,
measure a fired case or two after you`ve resized them. I`ll bet the lenght changes a bit unless your die is adjusted exactly to match your chamber....

Madrid,

You can use the tool to set headspace without knowing or using the raw reference: 1.6200 - 1.6300. Knowing these numbers has some value, but let's consider the tool without them first.

Keep in mind what it is you're measuring. Factory-loaded ammunition is made as short as it can be by standards so that it will fit in the shortest standard chamber. Ammo makers don't want you unable to chamber a factory-loaded round.

OTOH, rifle makers want to make the chamber as long as possible within standard so that they can fit the longest standard factory loaded round. The rifle maker does not want you to fail to chamber the longest factory round. So, within standards, the chambers tend to be long and factory ammunition tends to be short. The difference is observed "headspace."

Handloaders tend to reduce the headspace because it's more accurate and minimizes case stretch.

So, you can measure a cartridge (or three) against the reference line on the nut before chambering, then fire them, and measure again. (You can do this even without knowing whether the reference mark is max or min length.) If they are the same, and I gather that's what happened, you basically had 0 headspace for that cartridge. I've had rifles that did that. I simply adjusted the die to move the shoulder back a bit - .002 or .003.

This will work for practical purposes, but if you have a real desire to know what the exact measurement is in thousandths, then you'll need the raw reference numbers. I've never felt the need to go that far, so I can't tell you whether the reference mark on the nut is max or min length. The instructions should tell you that, if you're interested. Was this clear?

Jaywalker