Headspace, case lenght, & RCBS Precision Mic

posigian · February 21, 2001, 07:11 PM

I’m new to reloading, trying to teach myself with the help of books, videos, & lots of reading over the last 3 years, and I am now ready to get started.

I am starting with 30.06 and I have tons of brass that I have saved over the years. I need HELP understanding “Head Space” and “Case Length”. I purchased an RCBS Precision Mic and I am trying to learn how to properly use it.

When you measure the case with the headspace gauge, how far down (below ANSI spec) can I push the shoulder before its considered too much? Example: I had some that read .005 below 0 (-.005). Is the shoulder on this pushed down to far for me to use it?

The instructions state that you should measure 5 cases (once fired in my gun and will be used in mine only) before running them through the sizing die. From that you can get an average of where the shoulder should be for your rifle. However, prior measurements of my brass show most cases -.001 to -.003. That is below ANSI Specs and I am not sure how to bring it up or if I even need to?

Further more, how close to the maximum case length do I need to be? If the length falls short, how short is too short? Max length on a 30.06 is 2.494. If that is max what is the minimum length allowed before it becomes dangerous? After sizing them in the die should I trim all of the brass so that it is the same length?

I am sorry for the length on this message and do appreciate all of the help I can get. Being new to this I have a lot of “fears” and I am going real slow so that I can pay attention to detail. In fact I might be worry about too much!

Monkeyleg · February 21, 2001, 07:36 PM

My 700 has a chamber that's very close to ANSI specs and the shoulder on fired brass is only .003 to .005 above spec. I'll push the shoulder to .000 or -.003. I'm not a pro at this, but I suspect that the case Mic could be off a little. Five thousandths is not a huge number.

Dick

RiverRider · February 22, 2001, 09:22 PM

I played around with an RCBS Precision Mic for a while, and came to the conclusion that it's good for relative measurement only. There are other, simpler ways of dealing with those things that need to be measured closely.

I got rid of it and have never looked back.

Doctari · February 23, 2001, 12:34 AM

howdy posigian,

I don't know that ansi specs matter a whole lot for what you are doing. If you are reloading these cases to shoot in your gun only, then set the die so it moves the shoulder back .002-.003 less then your once fired brass. Now the brass should chamber in your gun and undergo minimal "stretching" when fired again, prolonging your brass life. You are interested in sizing this brass to your chamber not sizing it to ansi specs.

Note this brass may not chamber in other guns. If you want it to chamber in other guns the full length resize it.

Most reloading manuals list the maximum case length and recommend trimming brass .01 shorter than max length. Trim them all to a uniform length (ex: 30-06 max 2.494, trim to 2.484). Not critical but will help consistency of bullet seating and accuracy.

If you havent already get one or better yet 5 reloading manuals and read the instructions most all have in front. The manual should supercede advice you get from yahoos like me on the net. But if what we say jives with the manual then so much the better.

Mike

posigian · February 23, 2001, 10:23 AM

Doctari Wrote:

Most reloading manuals list the maximum case length and recommend trimming brass .01 shorter than max length. Trim them all to a uniform length (ex: 30-06 max 2.494, trim to 2.484). Not critical but will help consistency of bullet seating and accuracy.

--------------------------------------------

Ok, but what if the brass is shorter than 2.484. Is there a minimum trim lenght or a point at which you cant use the brass because its to short?

Thanks to all,

Doctari · February 25, 2001, 12:29 AM

Hmm, lots of brass shorter than the trim to length. I don't normally run into this as brass tends to lengthen with firings.

Is this brass measured too short before or after resizing? Resize first then measure and trim. If it is still too short after resizing I would discard it. Reason: if you have mic'ed your fired cases and set the resizing die to bump your shoulder back only a few thousandths, and cartridges are coming up short that means your neck is short. Short necks may not hold bullets as well. Is it dangerous? I dont know for certain, but in general things out of tolerances aren't usually good.

Anyone else have any thoughts? You have a whole pile of too short 06 brass? Was all this brass in question shot out of the same rifle?

If it comes from various rifles, then I would full length resize it and fire it throught the rifle you want to reload for. Full length resizing just means you will get less reloading life out of the brass in the long run. After firing it through your rifle one time the brass should all be roughly the same headspace though not necessarily the same case length. Then you can resize and push the shoulder back the distance you want so it will just chamber in your rifle. Finally, you can measure the overall length and trim the neck back if needed.

Headspace is the distance from the case head to the datum line on the shoulder of the brass. Case length (overall length) is the distance from the case head to the end of the neck. After firing a case in your guns chamber you essentially have a fireformed case which gives you close to your chambers headspace measurement. Then you can measure that brass' headspace. Comparing that measurement to ANSI specs may tell you if your chamber is a little long or short, but doesn't necessarily mean a whole lot unless it is way out of spec. Brass does have a little spring to it and doesn't remain at the exact headspace length of the chamber but shrinks back slightly from the chamber walls when it cools.

Mike

Is this helpful? Or do I suck at explaining these things?

posigian · February 25, 2001, 12:45 AM

Ok, so I need to learn how to neck size only then? All of the brass I have has been fired in my gun only! So just move the shoulder back .002-.003 and I will be good to go?

Thanks everybody!

Doctari · February 25, 2001, 09:23 PM

You can buy neck sizing only dies. You can partial case size with a full length die by setting it correctly. Advantage of neck sizing is you don't have to lube cases, because the side wall is not touched by the die. Which is better? I dunno..... I have some neck sizing dies for my varmint calibers. Bigger hunting calibers I tend to partial length resize. Maybe because I am too cheap to buy new dies?

If you think you ever might want to shoot the ammo in another gun partial length resizing gives you a better chance to chamber it.

Shoot safely,

Mike

Bogie · February 26, 2001, 03:32 PM

This assumes you can have a bolt action rifle, and that you can remove the firing pin to allow you to "feel" the bolt close on the fired/sized case.

A fired case is going to cause the bolt to close stiffly. No case will let the bolt just drop. Try it a couple of times.

Now, take your press, and screw your FL die into it. Unscrew it a turn or two, lube up a case, and run it through the die. Put it in the rifle. Does the bolt still close hard? Tighten the sizing die about an eighth of a turn, and try chambering the case again. Keep doing this until the bolt drops easily. Back up an eighth of a turn, and now, just "edging" the die further in, repeat the size/try routine until you just barely feel the case when you close the bolt.

February 21, 2001, 07:11 PM	#1
posigian Senior Member Join Date: May 31, 2000 Location: Great Lakes State Posts: 115	I’m new to reloading, trying to teach myself with the help of books, videos, & lots of reading over the last 3 years, and I am now ready to get started. I am starting with 30.06 and I have tons of brass that I have saved over the years. I need HELP understanding “Head Space” and “Case Length”. I purchased an RCBS Precision Mic and I am trying to learn how to properly use it. When you measure the case with the headspace gauge, how far down (below ANSI spec) can I push the shoulder before its considered too much? Example: I had some that read .005 below 0 (-.005). Is the shoulder on this pushed down to far for me to use it? The instructions state that you should measure 5 cases (once fired in my gun and will be used in mine only) before running them through the sizing die. From that you can get an average of where the shoulder should be for your rifle. However, prior measurements of my brass show most cases -.001 to -.003. That is below ANSI Specs and I am not sure how to bring it up or if I even need to? Further more, how close to the maximum case length do I need to be? If the length falls short, how short is too short? Max length on a 30.06 is 2.494. If that is max what is the minimum length allowed before it becomes dangerous? After sizing them in the die should I trim all of the brass so that it is the same length? I am sorry for the length on this message and do appreciate all of the help I can get. Being new to this I have a lot of “fears” and I am going real slow so that I can pay attention to detail. In fact I might be worry about too much! __________________ Posigian I AM THE NRA

February 23, 2001, 10:23 AM	#5
posigian Senior Member Join Date: May 31, 2000 Location: Great Lakes State Posts: 115	Doctari Wrote: Most reloading manuals list the maximum case length and recommend trimming brass .01 shorter than max length. Trim them all to a uniform length (ex: 30-06 max 2.494, trim to 2.484). Not critical but will help consistency of bullet seating and accuracy. -------------------------------------------- Ok, but what if the brass is shorter than 2.484. Is there a minimum trim lenght or a point at which you cant use the brass because its to short? Thanks to all, __________________ Posigian I AM THE NRA

February 25, 2001, 12:45 AM	#7
posigian Senior Member Join Date: May 31, 2000 Location: Great Lakes State Posts: 115	Ok, so I need to learn how to neck size only then? All of the brass I have has been fired in my gun only! So just move the shoulder back .002-.003 and I will be good to go? Thanks everybody! __________________ Posigian I AM THE NRA

February 26, 2001, 03:32 PM	#9
Bogie Senior Member Join Date: June 5, 2000 Location: Job hunting on the road... Posts: 3,827	How to Full Length Size for Minimum Headspace This assumes you can have a bolt action rifle, and that you can remove the firing pin to allow you to "feel" the bolt close on the fired/sized case. A fired case is going to cause the bolt to close stiffly. No case will let the bolt just drop. Try it a couple of times. Now, take your press, and screw your FL die into it. Unscrew it a turn or two, lube up a case, and run it through the die. Put it in the rifle. Does the bolt still close hard? Tighten the sizing die about an eighth of a turn, and try chambering the case again. Keep doing this until the bolt drops easily. Back up an eighth of a turn, and now, just "edging" the die further in, repeat the size/try routine until you just barely feel the case when you close the bolt.

February 21, 2001, 07:36 PM	#2
Monkeyleg Senior Member Join Date: January 25, 2000 Posts: 4,625	My 700 has a chamber that's very close to ANSI specs and the shoulder on fired brass is only .003 to .005 above spec. I'll push the shoulder to .000 or -.003. I'm not a pro at this, but I suspect that the case Mic could be off a little. Five thousandths is not a huge number. Dick

February 22, 2001, 09:22 PM	#3
RiverRider Senior Member Join Date: November 30, 2000 Posts: 341	I played around with an RCBS Precision Mic for a while, and came to the conclusion that it's good for relative measurement only. There are other, simpler ways of dealing with those things that need to be measured closely. I got rid of it and have never looked back.

February 23, 2001, 12:34 AM	#4
Doctari Member Join Date: March 27, 1999 Location: Lansing, MI Posts: 86	howdy posigian, I don't know that ansi specs matter a whole lot for what you are doing. If you are reloading these cases to shoot in your gun only, then set the die so it moves the shoulder back .002-.003 less then your once fired brass. Now the brass should chamber in your gun and undergo minimal "stretching" when fired again, prolonging your brass life. You are interested in sizing this brass to your chamber not sizing it to ansi specs. Note this brass may not chamber in other guns. If you want it to chamber in other guns the full length resize it. Most reloading manuals list the maximum case length and recommend trimming brass .01 shorter than max length. Trim them all to a uniform length (ex: 30-06 max 2.494, trim to 2.484). Not critical but will help consistency of bullet seating and accuracy. If you havent already get one or better yet 5 reloading manuals and read the instructions most all have in front. The manual should supercede advice you get from yahoos like me on the net. But if what we say jives with the manual then so much the better. Mike

February 25, 2001, 12:29 AM	#6
Doctari Member Join Date: March 27, 1999 Location: Lansing, MI Posts: 86	Hmm, lots of brass shorter than the trim to length. I don't normally run into this as brass tends to lengthen with firings. Is this brass measured too short before or after resizing? Resize first then measure and trim. If it is still too short after resizing I would discard it. Reason: if you have mic'ed your fired cases and set the resizing die to bump your shoulder back only a few thousandths, and cartridges are coming up short that means your neck is short. Short necks may not hold bullets as well. Is it dangerous? I dont know for certain, but in general things out of tolerances aren't usually good. Anyone else have any thoughts? You have a whole pile of too short 06 brass? Was all this brass in question shot out of the same rifle? If it comes from various rifles, then I would full length resize it and fire it throught the rifle you want to reload for. Full length resizing just means you will get less reloading life out of the brass in the long run. After firing it through your rifle one time the brass should all be roughly the same headspace though not necessarily the same case length. Then you can resize and push the shoulder back the distance you want so it will just chamber in your rifle. Finally, you can measure the overall length and trim the neck back if needed. Headspace is the distance from the case head to the datum line on the shoulder of the brass. Case length (overall length) is the distance from the case head to the end of the neck. After firing a case in your guns chamber you essentially have a fireformed case which gives you close to your chambers headspace measurement. Then you can measure that brass' headspace. Comparing that measurement to ANSI specs may tell you if your chamber is a little long or short, but doesn't necessarily mean a whole lot unless it is way out of spec. Brass does have a little spring to it and doesn't remain at the exact headspace length of the chamber but shrinks back slightly from the chamber walls when it cools. Mike Is this helpful? Or do I suck at explaining these things?

February 25, 2001, 09:23 PM	#8
Doctari Member Join Date: March 27, 1999 Location: Lansing, MI Posts: 86	You can buy neck sizing only dies. You can partial case size with a full length die by setting it correctly. Advantage of neck sizing is you don't have to lube cases, because the side wall is not touched by the die. Which is better? I dunno..... I have some neck sizing dies for my varmint calibers. Bigger hunting calibers I tend to partial length resize. Maybe because I am too cheap to buy new dies? If you think you ever might want to shoot the ammo in another gun partial length resizing gives you a better chance to chamber it. Shoot safely, Mike