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Old thread but I'm new here. Let me throw some corn starch into the mix. I load for five M1 rifles (among others). USGI spec ammo is 0.006" longer then the shortest chamber and is 0.006" shorter then the longest chamber.

So a M1 will force size any long rounds. When I reload I never set the shoulder back. I set the sizing die, standard RCBS, so that the case is sized to want is referred to as "partial resizing." I place a dime between the shell holder and the sizing die. The shoulder is fire formed to the chamber (less spring back) but the body of the case is sized to within 0.0001" of where it would be if full length sized. You get basically zero headspace. Your cases last longer the they do if you set the shoulder back.

Some one asked about weather or not cases require trimming to length. If you have any headspace your cases will grow. If you let the case grow too long in length without trimming back to length the end of the brass can grow enough that the case extends beyond the lead and can be pinched between the bullet and the bore of the barrel. This will ruin a day and gun in quick order.
 

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Yea I know old! But only read the first few post's and the OP did a great job. Something I read down a few post's was by a 63 yr old guy that didn't know about the hear, or what was called the head. I see a lot of people asking question's about rifles and especially cartridges that don't know what things are called they are talking about. Seem's what most do is assume what they are talking about, normally correctly and just move along. I think that a dis service to them. Problem being they aear ignorant, and they are, and another person with the same problem get's lost till he/she figure's out what is being talked about. I recall one guy talking about his new reloads saying, "the bullet won't load". He was talking about his case's but refereed to them as bullet's. Amazing how many people actually do refer to ammunition as bullet's. With the first guy calling loaded ammo, bullet's, I have to think he never read directions in a manual! Another guy mentioned reading the manual and he was right on. I've got several different manuals and haven't read them in years but as I recall they all say pretty much the same thing about reloading but in different ways! Buying several different manuals would have to be confusing to someone new and I always recommend buying a manual for the brand bullet someone will use and stay with it till they are good to go, takes a while sometimes. But learn one way and once's you have it you can learn to experiment! I can use any manual I have for anyone's bullet by simply starting low and working up watching for pressure sign's as I go, just like using the manufacturer's manual. Lot of people don't understand that even some of the long time loader's. I think it's necessary to reach this point by learning what things are properly called.
 

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learning what things are properly called.

Pet peeve of mine. Like "what's your favorite caliber" when cartridge is meant.
 

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I see "headspace" was brilliantly explained in the 2nd post back in 2010 - yet, here we are!!!

Gotta LUV TFF forum
 

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Headspace is the distance from the head of the cartridge to the face of the bolt. If there is not enough room, the gun won't function. The bolt won't close, or (in the case of a revolver) the cylinder won't turn all the way. This is "too little headspace".

When the cartridge is fired, before the bullet starts to move (remember the law of inertia - whatever is at rest tends to stay at rest, and the more mass it has, the harder it is to put into motion) the lighter brass case first expands out until it hits the chamber wall, and then it is slammed backwards until it hits the bolt (or, in the case of a revolver, the recoil shield). Once it has done that, the case can't move anymore, and the only thing that can move is the bullet, so it, finally, starts to move forward. If the distance between the head and the boltface (or recoil shield) is too great (this is referred to as excessive headspace) the case has farther to go before it stops, which allows it to build up more speed and more pressure before it hits, which can cause damage to the gun. Also, if the headspace is excessive, the firing pin may not be long enough to pop the primer, and you have misfires.

Cartridges "headspace" in different areas, depending on the design of the cartridge.

Rimmed cartridges headspace on the rim. That's why you can use both 38 and 357 in a 357 revolver. The 38's being shorter does not matter, since the rim is in the same spot on both rounds.

Belted magnums headspace on the belt. They work the same as a rimmed round, in that if the case is a little too short, it doesn't matter, since the belt is always in the same place.

Bottlenecked rimless rounds headspace on the shoulder. Like with the belted cases, it doesn't matter too much if the overall length is a little short, as long as the shoulder has not been blown forward or pushed back.

The last group is the straightwalled rimless cartridges. They headspace on the mouth. 45 ACP, 9mm, 40 S&W, etc. If you look in the chamber of most modern pistol rounds, you will see a little "step" in there. This gives the case mouth somewhere to sit. Without it, since the case is rimless, the entire cartridge could fall through the chamber. Because they headspace on the mouth, overall length of the cartridge is critical. Too long and the bolt won't close (too little headspace) and too short and the cartridge goes too far forward into the chamber (excessive headspace).

Some of the older revolvers don't have this step in them. The cylinder is bored straight through. There is no need for the step, since they headspace on the rim. Most modern revolvers have this step, though, but it is more of a safety issue than for headspace. The step will not allow you to chamber a 357 in a 38 special. Without the step, one might fit, with disastrous results.

Thank you, clear, concise and thorough. Well done.
 
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