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Head space?????

Have been reloading sometime now an just getting into the long range. I was wanting to know if someone could explain head space,in simple terms) and how to get it correct. What equipment is needed? Thank you for your info and patients
 
well, headspace is somewhat tricky but very important issue. Here's my take on it, i'm no expert so please someone else chime in.

you say you're reloading, are you full length resizing or neck sizing? Anyways, back to headspace. headspace on a cartridge is taken off a reference line, or datum line. This "line" falls somewhere on the case's shoulder. The datum line on a 308 family case is .400". So where ever the shoulder of the case opens to .400", that is the headspace, as measured from the case head to that point on the shoulder. In the chamber of your rifle, you would measure from the bolt face to the spot which the cartridges' shoulder would hit, at .4". There are 2 measurements of headspace, one taken off the cartridge, and one a gunsmith would take, inside your chamber. When a gunsmith chambers a rifle, he has to make sure he leaves enough room for a round to be chambered in the gun.

How to measure headspace: I use a stone point headspace comparartor. It attaches to there bullet comperator, and is used the same way. Once you put the right bushing in the bullet compararator, you can then measure your cartridges headspace. You can find them at midway, sinclair, etc. fairly cheap tool, easy to use. I asked if you neck size or f/l resize. If you neck size w/out "bumping" the shoulders, pretty soon one day your going to try to chamber a loaded round and the bolt won't close. Or maybe you'll find that bolt is getting harder and harder to close. basically what's happening is after every time you fire that case, the headspace is getting a tad longer. Take some measurements on new brass, and then fire it & reload a couple times. you'll see that cartridge is getting "longer", but not oal, just from headspace. another words trimming wouldn't solve the problem, because trimming does not set the shoulder back. Basically, you don't want to let your headspace get so long that it interferes or causes problem with you bolt & chamber dimensions. If your full length resizing, normally not so much an issues. If your neck sizing only, than itcan become a problem.

Sorry, didn't mean for this post to get so long. There's alot more to it than what i posted, I hope it helps. take the time to learn about it. If not checked, excessive headspace can lead to excessive pressures and stuck bolts.

just my .02
 
If you take into account the three types of cartridge cases most of us work with straight, tapered and bottle-neck account for the five case head configurations rimmed, semi-rimmed, rimless, rimless belted and rebated understanding and controlling a cartridge head space starts here. Your specific chamber is a factor to. Head space is a measurement taken from the breech-face to a specific place in the firearms chamber that will stop the forward movement of the cartridge case. Various parts of a specific cartridge type and case head configuration will be used for the purpose to establish a cartridges head space measurement. On a rimmed case head space is controlled by the case rim. On a bottleneck case head space is controlled by the case shoulder or datum point or datum line. some refer to this as the base to datum length. A rimless belted case head space is controlled by the belt and depending on your specific issues potentially the case shoulder. A rimless straight or tapered case type head space is controlled by the case mouth. As I'm sure you know understanding cartridge head space is critical to correct die adjustment. The specific chamber your working with needs to be factored into your head space measurements as-well as the specific cartridge type and head configurations. I'm sure others here can help you with understanding head space and correctly measuring to your specific needs. Wish you the best Lane
 
The headspace of new, unfired factory brass is all over the place. The same is true of factory loaded ammo in many instances. The quality control is simply not that good of late.

It is not uncommon for some brass to be substantially shorter than a "go" gauge in my experience.

I have seen a freshly chambered rifle that, when test fired with factory ammo, had primers backed out way more than was acceptable. The headspace was checked and was just over "go". When the factory ammo was measured and compared to the "go" gauge it was obvious that the ammo was at fault. The 'smith was then left with the problem of what to advise the customer as no one knows what the next batch of ammo he purchased might be.

Others with whom I have spoken have encountered factory ammo that is sufficiently long that it was necessary for them to change their "no go" gauge from about +0.006" to as much as +0.010" in order for the factory ammo to chamber!

The point here is to adjust your dies to fit your chamber with your cases.
 
I have a 20 BR and a reading full length resizing die. I can not screw my die down any further to get it to bump back the shoulder. I am loading on a dillon 550 and grinding my shell plate is not an option. Can I have my die machined down some?
 
PAshooter20BR said:
I have a 20 BR and a reading full length resizing die. I can not screw my die down any further to get it to bump back the shoulder. I am loading on a dillon 550 and grinding my shell plate is not an option. Can I have my die machined down some?

Sure, have whoever chambered the rifle for you do this if he is convenient, otherwise most any machinist should be able to do that for you. The sizing die is hardened and so an appropriate cutting tool should be used and the resulting sharp edge at the bottom of the die should be relieved slightly so that your cases are not shaved by it.
 

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