Headspace and presure

M

mswart

Guest
How do I fix the headspace problem when I'm reloading? I have tried neck sizeing only and full length sizing and I still have the signs of problems. Had a case break a quarter of an inch down and four others show cracking in the same place. On my other rifle I have problems on some cases while closing the bolt and when fired the same. I have them trimmed to the specs they require but still go in hard when I turn the bolt. Some don't feel anything. ???? I have been playing with the bullet depth but I didn't think to that exent. I have tried to just chamber a empty case after I have resized it and the bolt was hard to close. Any ideas what I'm doing wrong? Thanks.
 
Headspace is determined by the "type" of cartridge in ues. What caliber are you talking about?

A rimmed case headspace is determined by the thickness of the cartridge case rim.
On a rimless case the case headspaces on the shoulder of the case.
With a belted case the case is stopped by the top rim of the belt.

More often than not when a headspace problem is suspected when firing reloaded ammo, the dies turn out to be the culprit rather than an over or under sized chamber in the rifle. Are you noticing a bright ring around the case just above the head after firing? Try a different set of dies and if the stretching and separation problem continues it's possible your barrel may have a significantly over sized chamber which will probably require a new barrel to completely rectify the problem.

Ford42
 
If the rifle has headspace, the first time a case is fired, the brass stretches and a weak spot is formed... when you reload it, it is very important not to push the shoulder back as the same process on firing will take place. Hot loads also contribute to case separations.

If the rifle's headspace is correct, you may still have a problem with undersized cases and excessive head clearance. Headspace is fixed by the gunsmith when the barrel is fitted. Head clearance has to do with the cartridge and a re-loader can adjust this.
 
First of all, you need some measuring tools so that you can see what is actually happening. Working strictly by feel is not a good idea. Dial calipers, a 1" micrometer that reads to .0001 and some caliper attachments to measure shoulder bump, and bullet seating depth off the ogive are a minimum. Until you have these tools, you are guessing.
 
When a case is fired, it emmediatly expands to seal the chamber walls. As a bottle neck case expands, the shoulder expands toward the shoulder in the chamber, and as it makes contact, pushes the case body back against the positive stop of the bolt face. Keep in mind, all of this happens in a nano second.

What can go wrong?? If the distance between the face of the case and the bolt is too much, the case wall will grip the chamber before the the case can seat against the bolt face. What can result is a separated case, much what you are seeing.

Are you noticing your primers backed out a little after firing. That is something that sort of goes hand in hand with to much head to bolt face clearance.

These types of things are often difficult to diagnose without actually seeing your set-up, and knowing first hand your general knowledge of what is really going on here.......jackie
 
As Boyd says you need some tools to measure fired and unfired (or fired and sized) cases.

If the ammunition is being fired in a strong bolt action and the cases are rimless, the problem is likely due to over-sizing the cases. Most FL die instructions call for the die to be screwed down onto the shellholder when the press ram is at the top which will allow the sized cases to fit into most any rifle chambered for that cartridge. What is needed is sizing that pushes the shoulder back 0.002-3" which can only be done buy measuring fired cases, then sizing them to move the shoulder back that distance. It requires a little time and fiddling, maybe ten or fifteen minutes, to get the die set where it's supposed to be. First screw the FL die down onto the shellholder, and back it off ~1/2 turn. Measure the case head to shoulder dimension of a fired case with the proper tool (Hornady, Sinclair, and likely others make caliper attachments for this purpose), then size it. The case head to shoulder measurement will likely be greater than it originally was. If so adjust the die down about 1/8 turn and resize the case. Measure again. Keep this up until the head to shoulder dimension is 0.002-3" less than the original fired dimension. Measure another fired case, and size it without adjusting the die then measure this case. If that die setting gives the same shoulder bump, lock the lockring in that position. Your cases should now all be properly sized.

If your rifle is another style action or firing a rimmed cartridge the FL die can be adjusted in a similar fashion, but you may need to size the cases another thousandth shorter to assure proper feeding and chambering. If the rifle is a military rifle firing a rimmed cartridge (.303 in an SMLE or 7.62x54R in a Moisin Nagant) you'll notice that case shoulders are blown well forward of where they were on the unfired rounds. That means neck sizing only or a custom sizing die, and likely shorter case life.

If you're having case failures with neck sizing there is likely a problem with an oversized chamber. Neck splits are common on cases fired in factory chambers multiple times, but body splits and head separations aren't if cases are neck sized unless the chamber is WAY oversized.

Some more information or maybe pictures of case failures would be helpful.
 
thanks mr. elliot

hey, thanks on the info. i received my sinclair bump gages yesterday and now i can see my faults ! i must say there is more to reloading than de-priming, priming, adding powder and a bullet then shooting. I wish I had taken the time years ago and educated myself on this, it would have saven me alot of time and frustration !!! There is still alot I would like to learn. Is there any good books out there ? what is the process of annealing and what do you benefit from it ?
 
jackie schmidt said:
When a case is fired, it emmediatly expands to seal the chamber walls. As a bottle neck case expands, the shoulder expands toward the shoulder in the chamber, and as it makes contact, pushes the case body back against the positive stop of the bolt face. Keep in mind, all of this happens in a nano second.
Click to expand...

I don't believe this description to be accurate.

Shoulders don't move forward except in the case of rimmed cartridges or setups with so incredibly much extra space that the extractor holds the case from moving forward. Nor will a bullet hold it back.

In a normal setup the firing pin drives the case forward and buries it into the shoulder. In a dry chamber situation there it stays during the firing cycle. For the casehead to contact the boltface either the cartridge brass must stretch at the rear or the chamber must be greased. "popped primers" or primers protruding above the surface of the casehead are the result of dry chamber and the case NOT stretching back. Only the primer pops out and contacts the boltface.

PO Ackley proved all this to be true 60yrs ago.
 
I don't know what, if any, loading manuals you have on hand, but one or two of them will give the basics. A lot of good information was published in HANDLOADER magazine back in the 70's on adjusting sizing dies, but they're mostly not available anymore except maybe in CD. PRECISION SHOOTING published a Reloading Guide which went into a lot of information from beginning to advanced methods, but I don't know if it's still available. You can call PS at 860-645-8776 to see if they have any copies of their Reloading Guide available. If they do order one. It has no loading data, but it's full of good information.
 
If you have rifles with absolute zero headspace, do you guys think it will create more pressure than guns with .002-.003 headspace? The reason I ask this is because my local 'smith does this with all rifles and many of my hunting rifles reach max safe pressure levels with corresponding lower velocities with powder charges under the "normal" max loads listed in the manuals, sometimes by quite a bit. I know tight chambers can cause this, but I have seen it in over twenty rifles.
 
sambubba1 said:
If you have rifles with absolute zero headspace, do you guys think it will create more pressure than guns with .002-.003 headspace? The reason I ask this is because my local 'smith does this with all rifles and many of my hunting rifles reach max safe pressure levels with corresponding lower velocities with powder charges under the "normal" max loads listed in the manuals, sometimes by quite a bit. I know tight chambers can cause this, but I have seen it in over twenty rifles.
Click to expand...


Zero headspace will not cause excessive pressure. And in order for headspace to decrease pressure, it would have to be enough headspace to increase case capacity/powder volume.

Slight headspace or with reloads that have a slight head clearance or gap, may have primers that look quite flattened due to the cartridge being driven forward by the firing pin strike and as pressure builds the primer backs up and if the pressure is sufficient it will then be flattened when the case either stretches or slides back to contact the bolt face.

It is not uncommon for loading manuals to show higher velocities than individuals may obtain with the same loading data. Much of the loading data is obtained in aftermarket barrels and some is even obtained by calculations, not testing...
 
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I guess maybe the harder extraction and bolt lift is due to this instead of excess pressure. I am talking about loads well under "book" maximum or from other reliable sources from the shooting community.
 
OK, let's be clear here......you say your local gunsmith "chambers to absolute zero headspace."

Well so do I and here's how it works. Just yesterday I had a friend over and demonstrated what I think is "perfect fireforming headspace" which is well BELOW "zero." This particular chamber is cut 18 thou under the 'GO' gage.The result is that you must palm the bolt closed for the first shot....HARD.... you actually must hold the rifle firmly and LEVER the bolt closed against a firm resistance to get it to close on a virgin piece of brass.

VERY TIGHTLY JAMMED

Now you pull the trigger. ka-POOM..... and the bolt FALLS open and the case FALLS out. It goes back in with just the slightest resistance, you can JUUUST feel it......

And now, using a fitted Full Lenght Sizing die I can maintain this feel for many-many firings.

And I can run pressures up until the brass fails and never get a sticky bolt. Bolt lift and extraction are smooth and effortless.

My "maximum load" BTW doesn't come from any source but my own rifle. I run pressures up until the brass FAILS from pressure, then back down a couple grains and stay down. IMO each rifle establishes it's own personal "MAX" capability.


opinionsby




al



I must add a safety caveat.....

I do this on MY OWN rifles, having designed MY OWN reamers/gages and making my own brass with full understanding of all the parameters involved. Please DO NOT take this as license to arbitrarily short-chamber a rifle 10-20thou under and fire away. Going under like this there's always the chance you'll crimp onto your necks unless you KNOW the relationship between brass and true chamber length.

Any gunsmith who chambers to "zero headspace" is doing so with full understanding of the critical dimensions.
 
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Another way to adjust your brass for the headspace of a particular rifle is to use an expander to open the neck to an oversize condition (say a .338 plug in a .308 cartridge) and then re-size the neck to the proper size. You need to set your die to where the bolt will close on the case with minimal force. This will set the shoulder forward when you fire-form the round.

This process will require annealing the case neck, but will insure that the brass is appropriately sized for the chamber. Be careful not to push the shoulder back on subsequent re-sizing.

Frequently, belted magnums are re-sized in this manner so that they register on the shoulder.
 
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