Author Topic: Headspace Question (Read 644 times)

Patriot_1776 · « **on:** November 27, 2004, 12:13:20 PM »

I wanted to have some advice on whether I should be concerned about this or not. What's happening is my cases (300 WBY) are causing the bolt to close a little tight. I found out it was a headspace thing because of several reasons. First, I full-length resized, AFTER neck-resizing only. Second, I used Innovative Technology's collet die for belted mags. And after all that, they still where tight in closing. Third, there is a shiny ring around the top of the shoulder. I did all that to help pinpoint the trouble area, of which it certainly did. I know that belted cases headspace on the belt, not the shoulder. So to get to the point, should I have to worry about pressures or anything hazardous? Can the shoulder be set back in any way, or are the cases pretty much at the end of the rope? How can headspace be watched to prevent anything like this from occuring? Any answers and advice will be greatly appreciated.

Patriot

Lone Star · « **Reply #1 on:** November 27, 2004, 12:33:20 PM »

Reloaded belted cases should NOT headspace on the belt. They should be sized to headspace on the shoulder, just like any other bottlenecked cartridge. One of the best ways to have problems with poor accuracy and short case life is to headspace belted brass on the belt....

Reed1911 · « **Reply #2 on:** November 27, 2004, 12:41:32 PM »

I assume you have don this, but it never hurts to ask. What is the brass length, is it over 2.820"? The ring above the shoulder could be a number of things. You also need to measure the belt thickness, both front to rear and circumfrence. Directly ahead of the belt should measure .512", the belt should measure .530", and the belt length is ?. Sorry I don't have the dimensional data on the belt, but I'd check it against a new case, or one that chambers freely.
The next qeuestions I'd ask are, how many times have these been re-loaded and are you using max loads?

Catfish · « **Reply #3 on:** November 27, 2004, 12:42:41 PM »

Belted mag. do head space on the belt. Lone Stare is right about getting them to short though. Sounds to me like you need to bump the shoulders back, but do it just a few .001 at a time till the bolt closes easily and stop there before you get them to short.

Patriot_1776 · « **Reply #4 on:** November 27, 2004, 01:25:08 PM »

Reed1911 Wrote:

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I assume you have don this, but it never hurts to ask. What is the brass length, is it over 2.820"? The ring above the shoulder could be a number of things. You also need to measure the belt thickness, both front to rear and circumfrence. Directly ahead of the belt should measure .512", the belt should measure .530", and the belt length is ?. Sorry I don't have the dimensional data on the belt, but I'd check it against a new case, or one that chambers freely.
The next qeuestions I'd ask are, how many times have these been re-loaded and are you using max loads?

The case length is 2.818". I forgot to mention one of the other steps, I did trim the cases to safeguard against excess length. Belt length, front to back is .195". Dia. AHEAD of belt measures .512". Dia. OF belt is .534". Belt thickness, according to said measurements would be .022". Belt circumference is 1.677". These cases have been reloaded about 2-3 times using at least a starting-medium load; never put any max loads through them.

Catfish Wrote:

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Sounds to me like you need to bump the shoulders back, but do it just a few .001 at a time till the bolt closes easily and stop there

Thanks for the insight; one question: How do I set the shoulder back? Forgive me, but I'm quite unfamiliar with those processes because I've never really had a headspace issue. Thanks again guys. :wink: Patriot

sgtt · « **Reply #5 on:** November 27, 2004, 07:35:11 PM »

Have you tried a no-go gauge? Or measured the shoulder datum? I to headspace all my mag and rimmed cart. off the shoulder.

calvon · « **Reply #6 on:** November 28, 2004, 09:34:30 AM »

First, what is headspace? It can be defined as the lengthwise free play of a cartridge in a closed chamber.

For a rimmed cartridge the lengthwise play is controlled by the thickness of the cartridge rim vs the distance from the face of the closed bolt to the chamber end of the barrel. It headspaces on the rim.

For a rimless cartridge the free play is measured from the bolt face to to the shoulder area in the chamber. If a loaded round has any freedom to move back and forth in the closed gun, you have headspace. It headspaces on the shoulder. A little headspace is ok but too much results in 'head separation' meaning that the brass breaks in two in the gun.

For a belted case, the free play is measured from the bolt face to the forward edge of the belt recess in the barrel. It headspaces on the belt.

Having said all that, a belted cartridge only headspaces on the belt the first time it is fired or after being full length resized. If it is neck sized only and then reloaded it will headspace on the shoulder and not on the belt. This is the correct way to resize belted brass.

In all cases the 'correct' headspace is that which (a) the brass is held snugly enough to prevent fore and aft movement, and (b) you can still load it reliably into the gun.

Go to:

http://www.google.com/

and type "headspace in firearms" into the search box for everything you ever wanted to know about headspace.

Patriot_1776 · « **Reply #7 on:** November 28, 2004, 10:00:48 AM »

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In all cases the 'correct' headspace is that which (a) the brass is held snugly enough to prevent fore and aft movement, and (b) you can still load it reliably into the gun.

According to that sentence, I should have nothing to worry about then. I feel a small to moderate amount of resistance, but not severe, and still chamber the round. It does chamber snug, I'm sure of that. I myself prefer only neck-sizing; but I full-length resize only when I really have to. I went through all the other sizing methods according to a process of elimination; trying to pinpoint where the problem lie, if there was one.

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Have you tried a no-go gauge?

Where can I find one?

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Or measured the shoulder datum?

How do you measure that with a double-radius shoulder? Like I said, these are all facets I never knew much about or dealt with before. I'm an intermediate when it comes to reloading. I'm still trying to gather as much info there is to reloading, especially when it comes to match-type ammunition for rifles. To be sure, this info will be remembered for as long as I reload. Thanks fellows for all the help.

Patriot

Catfish · « **Reply #8 on:** November 28, 2004, 02:48:28 PM »

Just take your sizeing die and screw it down 1/4 a turn and try chambering the case. If it`s still thight turn the die down another 1/4 turn. If that should do it or at least you should see improvement. If you don`t at least see some improvement you eather had your sizeinf die way to lose or you have another problem.

Lone Star · « **Reply #9 on:** November 28, 2004, 03:13:35 PM »

A 1/4 turn of the die is too much! That's 0.016" per each 1/4 turn, meaning you can go from okay headspace to excess headspace in one try. A 1/16" of a turn is a far safer way to go, that's just 0.004" each try. Modern ammunition should hold excess headspace to 0.004-0.006" (Sierra).

Reed1911 · « **Reply #10 on:** November 28, 2004, 03:58:18 PM »

Lone star, when discussing a belted case screwing the die down by a full turn is acceptable. Remember it will headspace off the belt if the shoulder is pushed back further. The only result will be very short brass life if this is a continued operation.

Patriot_1776 · « **Reply #11 on:** November 28, 2004, 06:17:46 PM »

That is one interesting pointer I found out with belts. You can either headspace on the belt, or the shoulder. Of course, I now know headspacing on the shoulder is the best way to go for accuracy and for case life. As for my resizing die (I assume you all mean the full-length) I have it set so the belt is just about all the way in. I can't remember exactly where I have it set, but the next time I have to use it, or just want practice and find the right headspace niche, I'll bear it in mind where to set and what to watch for. This might be a dumb question, but would it be a good rule of thumb to start off by having the bottom of the die touch the shellholder, or at least clear it by a few .001", with the press in the fully "DOWN" position, or could that be too much? FYI, the brand of dies are RCBS. Patriot

Lone Star · « **Reply #12 on:** November 29, 2004, 01:13:26 AM »

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when discussing a belted case screwing the die down by a full turn is acceptable.

You're right, it is acceptable if you are not that interested in accuracy or case life, or even safety. If you are gong to the trouble of fitting the cartridge to the chamber, why do it sloppy and set yourself up for trouble? Belted cases should be sized to headspace off the shoulder, this is clearly mentioned in reloading manuals (although not in many die instructions). It is the "excesss" headspace ( over 0.006") caused by oversizing the case which is the cause of case head separations. Case head separations are not an appectable result of safe reloading, in my opinion anyway.

Reed1911 · « **Reply #13 on:** November 29, 2004, 02:56:33 PM »

LoneStar,

You are correct, I didn't mean to imply otherwise, except for the safety portion. It appeared that you seemed concerned that the case would seperate if the shoulder was pushed back too far. In any cartridge case that headspaces solely off the shoulder this is an absolute safety concern, however with a belted case, if the shoulder is pushed back too far to headspace off it, it will then headspace as intended off the belt. So it will not cause a seperation, unless this is done multiple times. [/i]

Lone Star · « **Reply #14 on:** November 29, 2004, 03:03:25 PM »

Right, it would have to be done repeatedly of course. One of the complaints about belted cases has always been their short case life, with incipient head separations the cause. This is due to repeatedly pushing the shoulder back; however, if you set your die 0.013" too deep and continue to reload you will eventually have a crack or incipient separation. A few reloaders do not understand the potential "danger" of a case separating in the chamber and the subsequent gas venting, so they will keep doing it wrong - just like those who follow die makers' instructions. It's more of a safety issue for the rifle than the shooter, but why take a chance when you can do it right the first time?

John Y Cannuck · « **Reply #15 on:** November 29, 2004, 03:13:05 PM »

Considering the cartridge you are using. As long as the bolt closes without any force, just light resistance, I think I'd leave it alone, until I found out how it was shooting.
Then if I did want to shorten things up...
Many reloading dies today are designed to be seated right down on the shell holder. If your dies are like that, the only way to get the length shorter, is to mill off the die, or the shell holder a few thousandths, and reset your adjustments. (I do the shell holder myself, it's cheaper if something messes up) Also, some brands of shell holders are thicker. You may be able to get a thinner one.