Checking headspace

[Tiny Tim]

If using a full length die, and firing a load that expands your brass enough, you may be able to partially full length size your case and it will grow in length due to the case body being squeezed. This will often times lengthen your case enough that the round will be difficult to chamber. You can now measure that length and adjust your die down until the shoulder is pushed back enough to chamber, then set back an additional. 001-.002".

 

[Clem Bronkoski]

Well Cajun I guess there was a miscommunication or misunderstanding in what was typed. And it does appear that a case will not be fully fire formed on the first firing and it may take another firing or two.

 

[Clem Bronkoski]

If using a full length die, and firing a load that expands your brass enough, you may be able to partially full length size your case and it will grow in length due to the case body being squeezed. This will often times lengthen your case enough that the round will be difficult to chamber. You can now measure that length and adjust your die down until the shoulder is pushed back enough to chamber, then set back an additional. 001-.002".

And that's where the headspace comparator comes into play. From what I understand you measure a fired case and see it if will chamber in your rifle. You have to have a base line so you can bump back .001"-.002".
The reason I'm getting critical on doing this is the fact that the 300WM is notorious for having virgin brass being really short. That is the reason Peterson is making a "long" version of their brass in the 300WM. The price is up there too. Not super expensive like some other brands but salty enough for a guy like me on SS. I need it to last as long as possible. So I don't want to overwork it and constantly pushing the shoulder back too far can result in case head separation.

 

[Tiny Tim]

And that's where the headspace comparator comes into play. From what I understand you measure a fired case and see it if will chamber in your rifle. You have to have a base line so you can bump back .001"-.002".
The reason I'm getting critical on doing this is the fact that the 300WM is notorious for having virgin brass being really short. That is the reason Peterson is making a "long" version of their brass in the 300WM. The price is up there too. Not super expensive like some other brands but salty enough for a guy like me on SS. I need it to last as long as possible. So I don't want to overwork it and constantly pushing the shoulder back too far can result in case head separation.

Precisely. My peterson Long brass grows about .006" to completely fill the chamber. But as I stated, partial full length sizing makes the case longer and will then force you to set back the shoulder to achieve your .001-.002" set back.

 

[quigley257]

A proper annealing after the first firing will help your brass conform to your chamber quicker and more precisely than a non annealed case. It will also keep the case spring-back to a minimum as the neck/shoulder is softer. I recently built a couple 6.5-06 Ackleys. I used 270 Win brass to load the initial rounds. Whenever I'm forming cases to have custom dies made, I load and fire the same five cases a minimum of five times. I anneal after the first firing and then only partially neck size for each subsequent loading to ensure that the brass is fully formed to that chamber before sending in three fired cases for measurement to have the dies made. I keep one of the fired cases as a reference and drill and tap the final one to make a custom OAL cartridge to use with my Hornady OAL comparator setup. This method has worked well for me.

 

[Bang4theBuck]

Guys (and gals) I'm learning a lot here about precision shooting, especially in regard to reloading. I've been doing this for over 60 years now and I guess you can teach an old dog new tricks.
Like I recently found out that you should not full length resize your brass nor just neck size but rather just bump the shoulder back about .002".
That is all well and good but here's my question: I found out that brass will bounce back a bit so if I have virgin brass should I take a couple and load them up and fire form them to my case more than once, like 2 or 3 times before measuring the headspace in order to get the correct bump then set my sizing die to that or is one firing sufficient?
My rifles are a 6.5CM and a 300WM. Now I realize that because of their design the actual headspace is different. The 6.5 headspaces off the shoulder and the 300 off the belt but for my purposes of bumping back the shoulder is what I'm concerned with for both cartridges.
Inquiring minds want to know

I think your question introduced a little confusion by suggesting to not full length size. When actually what I think youbmeant was to not use the full length sizer die as the instructions dictate, which would be to size the brass to the full extent that the die will allow. You definately want to full length size, and you definately can use the full length sizing die to do that, you just don't want to blindly size the brass to the max. What you want to do is measure the fired case with a headspace comparator, and then set the die up to be just short of touching the shell holder on a full stroke. Then lube and size the case and measure it. Chances are, the case will actually grow a few thou. As you actually pushed the case walls in causing it to grow, but haven't got to the part of the stroke that sets the shoulders back. So, screw the die down in about 1/8 turn increments measuring after each (don't forget to relube each time), and you will eventually start to see the brass shrink to a dimension that is less than the fired dimension.
As for the 300 WM headspacing off the belt, we reloaders don't really pay attention to that. The process is the same. We are trying to get a case resized to around .002" shorter than a fired case.

To be honest, loading and shooting a virgin case 2 to 3 times isn't a bad way to establish your chamber size. I don't do thay only because I like all of my cases to have the same number of firings on them and I use premium aftermarket brass. If you have some random once fired brass recovered from factory ammo, it works well for this. Especially the softer stuff like Hornady.

Good luck and feel.free to reach out via PM if you have more questions.

 

[Huntaddict]

Guys (and gals) I'm learning a lot here about precision shooting, especially in regard to reloading. I've been doing this for over 60 years now and I guess you can teach an old dog new tricks.
Like I recently found out that you should not full length resize your brass nor just neck size but rather just bump the shoulder back about .002".
That is all well and good but here's my question: I found out that brass will bounce back a bit so if I have virgin brass should I take a couple and load them up and fire form them to my case more than once, like 2 or 3 times before measuring the headspace in order to get the correct bump then set my sizing die to that or is one firing sufficient?
My rifles are a 6.5CM and a 300WM. Now I realize that because of their design the actual headspace is different. The 6.5 headspaces off the shoulder and the 300 off the belt but for my purposes of bumping back the shoulder is what I'm concerned with for both cartridges.
Inquiring minds want to know

Going to bring something else to think about into the discussion. It sounds like we are dealing with factory chambers...at least that I what I am gathering. Factory chambers can be less consistent to SAAMI than custom chambers. That being the case, this can be a moving target for sure.
Perhaps try this:

• Measure each brand new case and record OAL, OAL to shoulder, and OAL to neck and if you want to get very specific add in case body length, neck diameter, headspace, and neck thickness
• Fire round with case capacity about 90% full of powder to make sure it expands as much as possible
• Remeasure everything - now you should know the dimensions of your chamber.

Once you have that - try to re-chamber that same spent case. You are NOT trying to ram the case back in the chamber. You are going slow to get a feel for how it chambers. If there is any appreciable tension or resistance, you have for the most part, fire formed that case. Now you can record all your measurements and size accordingly to the specific area or areas that are causing the resistance. Go slow when you resize not to overdue it.

Re-chamber to ensure it is now smooth.. IME, my heavy magnums that are running big bullets with lots of powder do this on their own - I run my cases at a node that is >90% full if I can.

 

[Eric H]

For those hating to keep adjusting your die for the perfect "bump". Just a suggestion, the competition case holders work for me. Adjusts height in .002, .004, .006, .008 and .010 https://a.co/d/1UKqAGz

 

[bluedog69]

A video is worth 1000 pictures.

 

[Clem Bronkoski]

saw that dog

 

[Doom2]

Ultimately there are just a few goals with resizing brass and it's best to look at what those are. As @Huntaddict mentioned most commercial are on the generous side. So the goals of resizing are:

1) Easily fit in chamber
2) Minimum clearances in headspace/datum dimension between resized and fire formed case.
3) Limit case growth
4) Maximize case life

To Eric Cortina's point on galling ties in with 1) and 2). Personally I've never seen lug galling but I guess he has. As an F Class shooter he wants easy chambering to minimizing upsets during reloading in a string.

2) is where consistency and accuracy comes into play. Minimizing case expansion results in lower deviations in velocity.

3) is where things can get a little dicey especially with commercial chambers. By far the biggest contributor to case growth comes from expansion of the case body. Unfortunately without using custom dies and/or chambers the reloader has little control over the body resizing. When full length sizing the body is the first thing sized and as it it squeezed the fire formed shoulder is pushed up. As the case moves further into the die the shoulder is reformed from the old shoulder and part of the body and the the new neck is formed from the old neck and part of the old shoulder resulting in a longer case length. The degree to which this happens is almost entirely dependent in the difference in fire formed and resized body diameters.

4) Related to resizing minimizing 3) limits the effect of case sizing on case life.

Ultimately whether the case has fully expanded to fill the chamber or not if the shoulder is set back only 0.002" between the fired and resized dimension then it minimizes the shoulders effect on case length growth.

 

[Clem Bronkoski]

Doom I reload for numerous cartridges. For most of the rifles that I only hunt with I full length resize all the time. I only shoot these rifles occasionally to verify zero and, hopefully, to help fill the freezer and shots are normally within 100 yards so I'm not too concerned about splitting hair accuracy or case life.
The rifles I shoot for target and steel at extended ranges I do care about accuracy and case life. Especially in my 300WM. Because it headspaces on the belt, once fire formed to my chamber, I only want to bump the shoulder back enough to feed smoothly so as not to continue to stretch the case and weaken the area in front of the belt and get a case head separation.

 

[MOA or bust]

OP, your question was how many times to shoot the brass before you start "bumping" back the shoulder. See post number 7.
To summarize the various comments, I think the recommendation is shoot the brass and only neck size (don't full length size) until the case elongates enough that it is "snug" to chamber, or won't chamber at all. Then try gradually resizing the brass with your FL die until you get the desired .001" to .002" BUMP that is desirable for precision shooting.