How much headspace is too much?

[McCrazy]

I'm having a heck of a time getting a quantifiable answer on this so any help would be appreciated.

Most people recommend bumping the shoulder back about .002" or .003" after firing in order to prolong the life of the brass and prevent casehead separation. That is fine and not what my question is.

I have a new .300 Norma Magnum barrel chambered by Short Action Customs. The brass I am using is Peterson. Using my shoulder bump gauge, the unfired Peterson brass measured between 2.022 and 2.032 with the vast majority being around 2.026 prior to firing. After firing, they are all at 2.042 +/- .001

From here I can obviously bump the shoulders back .002 after each firing.

My questions are:

1. Will this initial .016 to .020 headspace difference significantly decrease the life of my brass and lead to casehead separation sooner than later?

2. What is a normal amount of headspace stretch for virgin brass to have to stretch within a match chamber?

FWIW, this is not my first precision rifle and I have been reloading for about 10 years. This is just the first brass/chamber combination I have had that has given me concerns. I have read multiple threads on multiple forums about headspace but they all address excessively bumping the shoulder back after firing instead of the shoulder excessively moving during initial firing.

 

[Sheldon N]

16 to 22 thou headspace is a lot, IMO. If you are dealing with 100 pieces of brass or less I would fireform them all with a bullet jammed hard into the lands and a moderate charge. Will prolong brass life, and doing load development after 100 rounds is good because the barrel will have broken in and velocity should be stable. Of course, if you run hot loads the primer pockets may give out long before there is any case head separation.

 

[Juggerxxx]

I'm having a heck of a time getting a quantifiable answer on this so any help would be appreciated.

Most people recommend bumping the shoulder back about .002" or .003" after firing in order to prolong the life of the brass and prevent casehead separation. That is fine and not what my question is.

I have a new .300 Norma Magnum barrel chambered by Short Action Customs. The brass I am using is Peterson. Using my shoulder bump gauge, the unfired Peterson brass measured between 2.022 and 2.032 with the vast majority being around 2.026 prior to firing. After firing, they are all at 2.042 +/- .001

From here I can obviously bump the shoulders back .002 after each firing.

My questions are:

1. Will this initial .016 to .020 headspace difference significantly decrease the life of my brass and lead to casehead separation sooner than later?

2. What is a normal amount of headspace stretch for virgin brass to have to stretch within a match chamber?

FWIW, this is not my first precision rifle and I have been reloading for about 10 years. This is just the first brass/chamber combination I have had that has given me concerns. I have read multiple threads on multiple forums about headspace but they all address excessively bumping the shoulder back after firing instead of the shoulder excessively moving during initial firing.

I know you said you have been around the reloading block but we all make mistakes. Are you sure you are making the measurement correctly and consistently? That is a massive delta that I have never seen even when sampling random range brass from god knows how many different rifles.

 

[McCrazy]

I know you said you have been around the reloading block but we all make mistakes. Are you sure you are making the measurement correctly and consistently? That is a massive delta that I have never seen even when sampling random range brass from god knows how many different rifles.

Yes, I'm sure I have been measuring them correctly. I had about 20 pieces of fired brass and 30 pieces of unfired on my reloading bench. I measured all of them at the same time at least once and the measurements were consistent.

I have 50 pieces of the Peterson brass and at this point they are all fire formed. Time will tell if the primer pockets or the case heads wear out first.

I just remembered that I have Norma brand brass as well. I'll check it later and see what the shoulders measure. At least that will help me decide if the error is more related to the chamber or the brass.

 

[GrandpaDeadLegs]

You can never get enough headspace, but you gotta make sure the runout stays in the chamber...

Sorry, serious dudes, back to it

 

[lash]

That initial difference should not be too detrimental to the brass in the long run. Case head separation comes from Doing this over a period of time as stressors accumulate at the case head and you lose material in that area.

 

[918v]

Lube the cases for the first firing and fireform them using a casefull of trailboss

 

[Codiekfx400]

Lube the cases for the first firing and fireform them using a casefull of trailboss

I would not recommend this without a little more knowledge of HOW TO. Could possibly lead to severe injury or death if done wrong.

 

[918v]

There is no risk of death at all. Wtf are you talking about??

 

[Codiekfx400]

Just thought you left out some of the how to.

 

[Supersubes]

I just had a conversation with peterson about this. Apparently they’re addressing itnin their next run, which I think is going on now. FWIW, Lapua brand .338 brass is dang short too.

My 300 norma cases are doing fine thus far, given a choice though, I’d certainly prefer not to have excessive expansion on the first firing.

 

[918v]

Just thought you left out some of the how to.

Take a case and prime it. Then pour in the trailboss until you reach a powder level just short of where the bottom of your bullet sits, then seat the cheapest bullet you can on top well short of the lands. Lube the case sparingly and proceed to shoot

 

[Codiekfx400]

Just googled this method and your spot on with your recommendation. I had never heard of it before and should have done my research before posting that bone head post. Good info please forgive and forget what I said carry on.

 

[MrSmith]

When a new or resized case is chambered the ejector pushes the round forward until the shoulder/chamber or the casehead/extractor stops forward movement. Any resizing gap due to a "bump" dimension is at the rear of the case between the casehead and boltface. When fired, gas pressure obturates the brass and seals it to the chamber walls. The stretch can't go forward if the shoulder is in contact with the chamber. The case body is sealed to the chamber walls so that portion of the case is relatively fixed. The stretch goes toward the boltface gap and is concentrated in the very short section of the case at the rear of the supporting chamber wall and forward of the case web. In your situation, depending on how tight or loose your specific extractor is there could be gap on both ends of the case.

When loading new cases I use an extra step. As you note, some new brass can be quite short. I have found some .338 Lapua at .007" which your example far exceeds. That is a lot of stretch to force into the short unsupported portion of case just forward of the web. Initial stretch should go forward where it is distributed over a longer portion of the case. If not, the case, just forward of the web, will be strained, slightly thinned and a permanent weak zone created. My new cases get slightly squeezed with a set of padded pliers so that the upper body, just below the shoulder, is slightly out of round. On the first firing the bolt will force the case into the chamber with enough drag to overpower the ejector spring so that the casehead is in firm contact with the boltface. When fired the case becomes formed to that chamber. I only do this on the first firing of a new case.

918v and I have danced around this a little bit before. I had not thought about his Trailboss method of fireforming but I think it would likely be better than what I do with squeezing the case. Probably more evenly distribute the "stretch" along the case. As to dangerous, not unless the Trailboss is compressed, or so I'm told. I have never compressed it. One of the desired results of loading subsonics is that the bullet actually comes out of the barrel and on lighter loads of Trailboss a stuck bullet can occur. My assumption would be that a stuck bullet would generate the max pressure for a specific load combination. I start at 70% of uncompressed case volume for subsonic load development. I would probably go a bit lighter for fireforming, but I have no experience using this technique .. yet. And I will be checking to verify the bullet does come out.

Thank you,
MrSmith

 

[918v]

A casefull of trailboss makes maybe 30000 PSI. You can accomplish the same thing with other powders but trailboss is stupid proof as long as you don’t compress it too much.

Bring some kids with you and let them shoot your big gun. They will have a blast and the recoil won’t hurt them. And you’ll have your fireformed cases. Win, win.

 

[MtnCreek]

I oversized some LC once fired being careless with a dillon die. Expanded the necks with an 8mm mandrel and neck sized enough for a tight fit on the 'shoulder'. Seemed to work well.

 

[McCrazy]

As an added data point, I just measured 10 of my virgin Norma brand .300 Norma Magnum brass. They all measured 2.040 at the shoulder +/- .001 which would made them about perfect in my SAC chamber which is producing 2.042 fired brass.

It definitely looks like Peterson needs to refine the measurements in their .300 NM brass a bit. We will see if casehead failures are a problem later on.

Thanks everyone for your helpful and on topic replies.