pls help as I clearly dont undersand headspace

[bullspotter]

As stated in a book headspace is the fit of a cartrige in a chamber measured as the distance from breech face to the part of the chamber witch stops the cases forward movement.

Questions...

1. Is the shoulder of the case what stops if from going forward?

2. Book says to back off size die in small amounts untill you feel a slight crush apon chambering the case. What is causing the crush feel? Is it the length of the case fitting tighter against the shoulder of the case. or diamiter of the case being tigher as its not been made a smaller diamiter buy full length sizing.

3.Im loading 270 win and 300 ultra mag shells. Have been for several years, I have always full length resized all brass. I dont recall any markings on the 300 brass or primers, and dont have any spent cases to look at now. But my 270 is getting slightly flattend primmers. Not real bad, but you cans see their slightly flattend, their is not any black sepage and no holes or odd looking dents or holes in the primer. I have been told this is somewhat normal because their is a slight amount of headspace to allow the shell some slight movemet when fired?

4. I have seen go-no go gauges. Dont know anythig about them, Are they like fake sheels you put in your gun to check headspace issues with the chamber itself?

5.I have read of others using a case gauge to check their cases for proper headspace. What exactly dose this measure?


I have not had any issues with either of these, both shoot really well, both guns are not shot much, just hunting mostly with a few trips to the range to check zero every now and then. I also trim the overall brass length to spec after sizing. Very little most of the time.

[JohnKSa]

Headspace is a measure of how much a chambered round (of proper dimensions) can move back and forth with the gun in battery.

Obviously the breechface is what stops the cartridge when it moves to the back of the chamber, what stops the cartridge when it moves to the front of the chamber varies based on caliber.

Some calibers headspace on the case shoulder (bottlenecked cartridges), some on the case mouth (most autopistol cartridges), some on the case rim (most revolver cartridges and rimmed rifle cartridges).

Go/No-Go gauges look a little bit like dummy cartridges. A Go gauge should chamber in a gun that has a chamber of proper dimensions and a No-Go gauge should not chamber.

A case gauge is a piece of metal with a chamber sized/shaped hole in it. It's used to check a the size of a loaded round--usually to make sure it's not too long or too fat to chamber properly.

Has your 270 always flattened primers or is that a new development?

[bullspotter]

Im not real sure if it has always flattend primes or not. I always reload 100 at a time for it and it takes several years to shoot them up, I just did 100 new rounds, shot 4 of them for a zero check, and still had about 10 shells from the last reload set. and found 5 from who knows when..... they all did flatten the primes slightly. all about the same. all with the same powder charge, bullets and seating depth. so pry for the last 10-12 years yeah its been doing it. Zero was the same on all, they all grouped together . im seating about .040 off the rifling. Not for sure as i havent checked that, but i have never adjusted the seater. Its close to a max load, Maybe i need to pipe them down some, or seat the bullet to .050. I dont have any problems with the bolt being hard to open after discharge or anything.

[Smaug]

Originally Posted by JohnKSa

Some calibers headspace on the case shoulder (bottlenecked cartridges), some on the case mouth (most autopistol cartridges), some on the case rim (most revolver cartridges and rimmed rifle cartridges).

To add to what John said, I believe most magnum cartridges headspace on the belt.

[snuffy]

Reading primers for pressure signs is like reading tea leaves to predict the future. If you're really serious about finding out exactly what your headspace is, you need to get a RCBS precision mic. They're sold for most popular cartridges, and your are on that list.

[kraigwy]

Symptoms of excess headspace can be seen on the cartridge case. The first thing that happens is stretch, which is a bright zone around the case about a half inch frome the base. As it gets worse the stritching gest worse, beginning to crack. The next step is actuarl seperation.

Excess headspace allows the bolt to have play,. When the case goes off the bolt can move back and slam against the locking lugs.

On hard recievers this can cause it to shatter. Not that common or serious on modern actions but it does add gradual stretching of the action but wont normally cause the bolt or action to shatter.

The biggest problem with excessive headspace is with autos that seat on the shoulder. The shoulder dosnt provide a good stopping place like rimmed cases and belted magnums, because the force of the action slams the cartridge further in and that overdrive further adds to the problem.

Basicly, though excessive headspace may not destroy your rifle, it does accelerate wear in both the action and the cases, accuracy is effected.
Notice when people are putting together target rifles, they call for tight chambers. Consistancy is accuracy. No one, or no semi auto action, can close the bolt the same way everytime, therefore with excessive headspace you dont drive the case in the same way, it dosnt set in the chamber the same way. Proper, somewhat tight headspace and propertly sized cases, kind of forces the cartridge to only go in one way, and set in the chamber the same way. Consistancy.

I'm a firm believer in proper head space. I preach the use of a case gage, like Wilson, RCBS Mic gage, or one you made yourself. I would never load a round for a semi auto without using such gage to set up the sizing die.
Good accurate actions are pricy, I dont want to accelerate wear with excessive headspace. Cases arnt getting any cheaper either. The more you have to size them, the less reloads you are gonna get. And I kind of like my ammo/gun combo to be as accurate as possible. I need all the help I can get.

[LHB1]

Theoretically, belted magnum cases headspace on the front of belt for the first firing but after being reloaded, I suspect they subsequently headspace on the shoulder like non-belted bottlenecked rifle cartridges.

[Gun 4 Fun]

All the others have given you good advice. but I would like to address some of your questions a little more directly.
1-a case gauge for bottle neck rounds like the two you mentioned measures the length of the case from the bottom of the rim to a datum point [usually the center of the shoulder] located on the shoulder. Manufacturers all have a minimum and maximum length to work within for a given caliber, and it only varies by a couple thousands. The gauge measures the length of your loaded rounds to make sure that they fall within those specs.
2- a go gauge is usually made to the average length allowed by industry standards [saami], or centered between shortest and longest length if you prefer, for a given cartridges overall length, and should be able to chamber in any factory rifle. A no-go gauge should not be able to chamber in a properly chambered rifle, due to the fact that it is made longer than industry standard maximum length.
3- flattening of primers is normal to a point. There should still be a radius at the juncture of the base of the primer and the sides of the primer. Not all primers are of the same hardness, and therefore can look quite different when used in loads that are otherwise identical. If you fire a load that is at min. specs in a chamber that is at max. specs, you can get primers that look really flattened, when the load is totally safe. Like someone already said, the looks of the primer are a poor way of judging weather or not your loads are too hot.
4-When the "book" says that you should feel a slight crush, what they are refering to is a load that is set up for proper functioning, but is still within specs. The shoulder of your case has not been set back to far during resizing,causing excess headspace. The crush is simply that the case is a snug fit between the face of the bolt and the shoulder in the chamber.
5-"Is the shoulder of the case what stops it from going forward?" Usually, however some people prefer to make the bullet just make contact with the rifling, and use that to set overall length. It's usually done by target shooters looking to make sure every bullet is positioned the same when it starts into the rifling. You have to be careful with this approach, because seating a bullet in this fashion causes pressure to rise rapidly. In a hunting load, you're much better off with loads that feed and chamber properly every time.
I went into a little detail, because when I was new to reloading, I didn't have any one to show me anything and I didn't always know what the manuals were talking about. Hope this helps.

[JohnKSa]

-"Is the shoulder of the case what stops it from going forward?" Usually, however some people prefer to make the bullet just make contact with the rifling, and use that to set overall length.

Bullet seating depth will affect OAL, but it shouldn't affect headspace unless some games are being played. Headspacing a round using the bullet's contact with the rifling is not advisable.

[bullspotter]

I will be getting some tools and such so i can determine my headspace. Im not sure i really have a problem thats serious. But its something i will be looking into checking, Im 100% sure my bullet is not touching the riflings to take up any extra head space, as i loaded a dummy round today and didnt seat it as deep as my loaded ammo, smoked it and set it back till their were no marks on it, OAL was longer then my loaded rounds. So im safe their, I will be doing some measuring, testing ext, then start all over with some new loads, working my way up, seeing what primes are doing ext. Maybe i can sqeeze a little better groups out of it, not that theirs anything wrong with them now, but hay its winter time right!! Thanks to all of you for your help!!!!!!

[Gun 4 Fun]

JohnKSa- You are wise my friend and correct. I wasn't as clear as I should have been. I meant to say some people use a round so loaded, to set the cartidge back against the bolt face, which temporarily sets headspace, so as to form the case to the chamber, resulting in a case with proper headspace, and then adjust the die so as not to set back the shoulder.