Typical amount of case stretch after firing?

[E.Maker]

New here, and have a question as to what other's are seeing.

I am shooting a DT SRS-A1 in 6.5 Creedmoor. Shooting factory Norma Match 130 gr. ammo.

In checking the size of the brass after firing, on my Wilson case gauge, I find that the brass has grown 0.021".

I full size resize it, bumping the shoulder back 0.002". The cartridge is then 0.019" over the max headspace according to the gauge. Fits in the chamber perfectly, without any significant camming pressure afterwards.

Is this length of case stretch typical? My impression was that it seemed a bit much.

Ephram M.

 

[Shankin]

Depends on the rifle, brass and load.

With Hornady brass, my 6.5 Creed with 143’s and 46.1gr of Reloder 26, the brass would stretch an avg of .010”.

With Starline brass, 130 Berger hybrids, and 42.5 of H4350, I’m seeing an avg of .001”-.002”.

 

[Bradu]

New here, and have a question as to what other's are seeing.

I am shooting a DT SRS-A1 in 6.5 Creedmoor. Shooting factory Norma Match 130 gr. ammo.

In checking the size of the brass after firing, on my Wilson case gauge, I find that the brass has grown 0.021".

I full size resize it, bumping the shoulder back 0.002". The cartridge is then 0.019" over the max headspace according to the gauge. Fits in the chamber perfectly, without any significant camming pressure afterwards.

Is this length of case stretch typical? My impression was that it seemed a bit much.

Ephram M.

I would probably check the rifle with a go, no go gauge. Factory barrel or aftermarket?

 

[E.Maker]

It is a factory DT barrel.

Anyone know if Desert Tech barrels run slightly large chambers?

Ephram M.

 

[Steel head]

No
That a lot of stretch.

I set my chamber to within .002 of a go gauge.

Most no go gauges are .0035 to .006.

Chances are your will close on a field gauge and that’s definitely not a good thing.

 

[Juggerxxx]

I too have an SRS A1 but my 6.5CM barrel is not factory. I only see .003-.004 increase on the shoulder with all my loads. 140gr ELD with 42.2gr H4350 and 147gr ELD with 47gr of RL26. That’s with annealed (every other reload) Hornady brass.
If your measurements are correct, that sounds more like gas gun chamber slop and even worse. I would question your Wilson gauge. Do you have any factory ammo to check with the Wilson or even virgin brass?

 

[Sheldon N]

In checking the size of the brass after firing, on my Wilson case gauge, I find that the brass has grown 0.021".

Do you have access to a comparator like the Hornady/Sinclair style that clamp onto calipers and just measure the datum line on the brass shoulder? If so, what does the virgin brass vs fired brass measure? Even a piece of 9mm brass deprimed and flipped over the case should give a rough reading (just use one with a un-dented mouth).

I would probably trust that more than a general case gauge, too many potential interference points that could be affecting your measurements... stuff like neck/shouder radius, case mouth diameter, etc etc.

 

[AIAW]

New here, and have a question as to what other's are seeing.

I am shooting a DT SRS-A1 in 6.5 Creedmoor. Shooting factory Norma Match 130 gr. ammo.

In checking the size of the brass after firing, on my Wilson case gauge, I find that the brass has grown 0.021".

I full size resize it, bumping the shoulder back 0.002". The cartridge is then 0.019" over the max headspace according to the gauge. Fits in the chamber perfectly, without any significant camming pressure afterwards.

Is this length of case stretch typical? My impression was that it seemed a bit much.

Ephram M.

Just a thought - remove and re-install the barrel paying attention to the seating, then redo your measurements to take that piece of the puzzle out of the equation. Easy enough to perform on that rifle.

 

[E.Maker]

I too have an SRS A1 but my 6.5CM barrel is not factory. I only see .003-.004 increase on the shoulder with all my loads. 140gr ELD with 42.2gr H4350 and 147gr ELD with 47gr of RL26. That’s with annealed (every other reload) Hornady brass.
If your measurements are correct, that sounds more like gas gun chamber slop and even worse. I would question your Wilson gauge. Do you have any factory ammo to check with the Wilson or even virgin brass?

Thanks, yes, the Wilson gauge is calibrated. Factory ammo gauges perfectly.

Just a thought - remove and re-install the barrel paying attention to the seating, then redo your measurements to take that piece of the puzzle out of the equation. Easy enough to perform on that rifle.

Great thought. Thank you. I'll give that a go and let you all know.

Ephram M.

 

[Steel head]

Just a thought - remove and re-install the barrel paying attention to the seating, then redo your measurements to take that piece of the puzzle out of the equation. Easy enough to perform on that rifle.

Certainly a good idea.

 

[Sheldon N]

Thanks, yes, the Wilson gauge is calibrated. Factory ammo gauges perfectly.

It's not an issue with the gauge being "calibrated". The issue is that your fired brass might be contacting the inside of the gauge somewhere else besides the shoulder. I personally doubt that you've got 21 thou of headspace on the chamber vs factory brass. That would be a major screw up.

 

[E.Maker]

It's not an issue with the gauge being "calibrated". The issue is that your fired brass might be contacting the inside of the gauge somewhere else besides the shoulder. I personally doubt that you've got 21 thou of headspace on the chamber vs factory brass. That would be a major screw up.

Thanks. Factory ammo gauges perfectly. If the gauge was off, I am thinking that the factory ammo would gauge off as well.

I'll reset the barrel and see if that changes anything. I had thought that the DT SRS-A1 system does not need to be headspaced, or maintains its headspace when the barrel is changed. But perhaps there is some movement regardless.

If that does not correct the problem, perhaps I'll give DT a call.

Sounds like the 0.021" is definitely way too much.

Ephram M.

 

[Steel head]

Thanks. Factory ammo gauges perfectly. If the gauge was off, I am thinking that the factory ammo would gauge off as well.

I'll reset the barrel and see if that changes anything. I had thought that the DT SRS-A1 system does not need to be headspaced, or maintains its headspace when the barrel is changed. But perhaps there is some movement regardless.

If that does not correct the problem, perhaps I'll give DT a call.

Sounds like the 0.021" is definitely way too much.

Ephram M.

To me half that amount is too much.

 

[spife7980]

Thanks. Factory ammo gauges perfectly. If the gauge was off, I am thinking that the factory ammo would gauge off as well.

Not necessarily and, as Sheldon described, with the wilson gauge you have no idea of telling.

The wilson is a elementary pass/fail. It doesnt tell you how much of what and/or where the issue is. You might not have .021 of stretch, it might only be .004 but some other dimension such as the base diameter could be causing the case to bottom out before its actually get fully into the gauge leaving all of that extra handing out the end. With that sort of tool you dont know, you are missing all of the other data necessary to accurately judge.

 

[Sheldon N]

Thanks. Factory ammo gauges perfectly. If the gauge was off, I am thinking that the factory ammo would gauge off as well.

Not really an issue with either the gauge being off or the factory ammo being off. More of a potential issue of the shape of the brass coming out of the chamber not matching the shape of the case gauge giving you false readings. Here's a picture to explain the potential scenario.

 

[E.Maker]

Not really an issue with either the gauge being off or the factory ammo being off. More of a potential issue of the shape of the brass coming out of the chamber not matching the shape of the case gauge giving you false readings. Here's a picture to explain the potential scenario.

View attachment 7055652

Very interesting. Had not thought of that. How can I check to see if that is the issue? I'll definitely research this to see if there are ways I can measure from the base of the brass to the datum point.

Put a .003' shim under the sizing die and then measure the cases. Since you have a method of measuring the shoulder bump you should adjust the sizing die to give .001 to .002' shoulder bump . It sounds like you are adjusting the die to bear against the shellholder like is taught in the mass market reloading books.

The die shims are available from the BR oriented vendors listed on this site.

I am adjusting the die based upon the measurement of the fired case, then moving the die down to bump the shoulder 0.002".

Not necessarily and, as Sheldon described, with the wilson gauge you have no idea of telling.

The wilson is a elementary pass/fail. It doesnt tell you how much of what and/or where the issue is. You might not have .021 of stretch, it might only be .004 but some other dimension such as the base diameter could be causing the case to bottom out before its actually get fully into the gauge leaving all of that extra handing out the end. With that sort of tool you dont know, you are missing all of the other data necessary to accurately judge.

Thanks! The Wilson gauge now has a micrometer top that can measure how far the base is from the max and min headspace. I'll definitely check to see if the case is perhaps hanging up on someplace other than the shoulder. That drawing from Sheldon N. is enlightening. I'll see if I can't find a secondary way to measure.

Ephram M.

 

[Snuby642]

I spent a lot of time and money chasing bullshit with case gauge.
As soon as I listened to the hide heard and got a comparator things got better fast.

@spife7980
Has helped me a lot as well as many others here.
You measuring overall case length?
Or measuring headspace?

In iether case nothing moved twenty thousands on you. Nothing.
Check your decimal points .

Factory ammo has been running around 0.007 thousands under go gauge in several calibers for me.

That sir is not close to perfection you are after imho.

 

[spife7980]

Thanks! The Wilson gauge now has a micrometer top that can measure how far the base is from the max and min headspace. I'll definitely check to see if the case is perhaps hanging up on someplace other than the shoulder. That drawing from Sheldon N. is enlightening. I'll see if I can't find a secondary way to measure.

We like the hornady and sinclair comparators around these parts.

But the empty 9mm case will do in a pinch as well. Replace the silver and red part in that image with the 9mm case and you will have a makeshift .380 datum and you will have a way to compare the shoulder lengths from new>fired>sized with no other potential interference.

 

[E.Maker]

We like the hornady and sinclair comparators around these parts.

View attachment 7055660

But the empty 9mm case will do in a pinch as well. Replace the silver and red part in that image with the 9mm case and you will have a makeshift .380 datum and you will have a way to compare the shoulder lengths from new>fired>sized with no other potential interference.

View attachment 7055661

Looks like great advice. I'll pick up the Hornady set and remeasure. Thank you!

Ephram M.

 

[spife7980]

Looks like great advice. I'll pick up the Hornady set and remeasure. Thank you!

Ephram M.

You may get the same number you already have now with the gauge!
Its just nice to be able to know definitively that your measurement is what it shows and not due to some unseen interference. The gauges are worth the price for the confidence it instills in my measurements.

Also, take note that the numbers provided by the gauges arent absolute numbers, they very well might not match up to the saami spec charts or your neighbors measurements with their tool.
They are relative measurements, they apply to your set up only.
They have a chamfer on the inside edge so that the metal doesnt bite into the case and that leads to a bit of variance.
But they will allow you to directly relate your virgin, fired and sized cases to one another. Hence they are called "comparators" and not "gauges"


Edit: this post walks you though how the numbers youll get arent absolute but shows you how to justify them to absolute if you feel so inclined.

You are being redirected...

 

[Bradu]

Thanks. Factory ammo gauges perfectly. If the gauge was off, I am thinking that the factory ammo would gauge off as well.

I'll reset the barrel and see if that changes anything. I had thought that the DT SRS-A1 system does not need to be headspaced, or maintains its headspace when the barrel is changed. But perhaps there is some movement regardless.

If that does not correct the problem, perhaps I'll give DT a call.

Sounds like the 0.021" is definitely way too much.

Ephram M.

The desert tech barrels are supposed to headspace correctly when you close the bolt before tightening the cross bolts. It should be within spec but anything is possible.

 

[E.Maker]

You may get the same number you already have now with the gauge!
Its just nice to be able to know definitively that your measurement is what it shows and not due to some unseen interference. The gauges are worth the price for the confidence it instills in my measurements.

Also, take note that the numbers provided by the gauges arent absolute numbers, they very well might not match up to the saami spec charts or your neighbors measurements with their tool.
They are relative measurements, they apply to your set up only.
They have a chamfer on the inside edge so that the metal doesnt bite into the case and that leads to a bit of variance.
But they will allow you to directly relate your virgin, fired and sized cases to one another. Hence they are called "comparators" and not "gauges"


Edit: this post walks you though how the numbers youll get arent absolute but shows you how to justify them to absolute if you feel so inclined.

You are being redirected...

Again, great advice. Thank you. I'll let you all know how it turns out.

Ephram M.

 

[Juggerxxx]

Very interesting. Had not thought of that. How can I check to see if that is the issue? I'll definitely research this to see if there are ways I can measure from the base of the brass to the datum point.



I am adjusting the die based upon the measurement of the fired case, then moving the die down to bump the shoulder 0.002".



Thanks! The Wilson gauge now has a micrometer top that can measure how far the base is from the max and min headspace. I'll definitely check to see if the case is perhaps hanging up on someplace other than the shoulder. That drawing from Sheldon N. is enlightening. I'll see if I can't find a secondary way to measure.

Ephram M.

I was wondering if there was confusion as to what exactly you were measuring and how. Definitely get a headspace gauge.

As others have mentioned; make sure to close the bolt before torquing down the barrel. I also lightly twist the barrel clockwise every time before torquing.

 

[Rhed]

I check sizing, case length, seating, with a Redding instant indicator.

 

[E.Maker]

I was wondering if there was confusion as to what exactly you were measuring and how. Definitely get a headspace gauge.

As others have mentioned; make sure to close the bolt before torquing down the barrel. I also lightly twist the barrel clockwise every time before torquing.

Thanks. Here is how I am measuring the headspace.
- I use a L.E. Wilson Case Gage with the Case Gage Depth Micrometer on a fired case.
- I believe this will tell me how much headspace above maximum (or below minimum) SAAMI spec of the fired case

As I understand it, headspace on the 6.5 Creedmoor, a bottleneck cartridge, is the distance from the face of the bolt to the datum line on the shoulder of the cartridge (at 0.400” diameter). The Wilson case gauge uses this datum line.

Pointed out was that the Wilson gauge may not be letting the cartridge fully sit against the datum point, so actually I may be getting a false, overly long reading. Perhaps this is where the Hornady comparator will be superior, as it looks like there would be no interference on the body or shoulder of the case.

Does that sound right? Or I am misunderstanding something?

Thanks for all the advice,

Ephram M.

 

[Snuby642]

You got it.

To be honest took me a while because I expected complete accuracy with every tool.

 

[Dunraven]

I find that case length actually increases after full length sizing/bumping shoulder .002(based on overall case length), so I make sure I trim to length AFTER that stage. Is this typical?

 

[Shankin]

Yup. Trimming gets done after sizing for that very reason. Your good to go.