SAAMI Headspace tolerance questions

[copperking81]

I've seen where some manufactures advertise a guaranteed headspace tolerance, against the SAAMI minimum i.e. within .002 of SAAMI min as opposed to within the SAAMI min / max range.

How and where on the gun is that actually achieved?

As an example, if you took two rifles of the same model and manufacturer, one within the bottom .002 and the other within the min/max range, what would you have to do to the later to tighten within the same tolerance? Are the actions themselves any different or is it all work done in the chamber?

 

[riflewoman]

It is done primarily by being careful in the chambering process. With modern machines it isn’t hard to do.

 

[BoydAllen]

Assuming that both rifles are within spec., and that you are a well informed reloader, the only time that this would matter would be the first time that a case is fired. After that the clearance will be determined by the person loading the ammunition for that rifle. Headspace is measured with gauges. GO, NOGO, and FIELD. Scotch tape is about .002 thick. If your rifle's bolt closes on a GO Gauge and does not close on a NOGO gauge, it is within spec. Beyond that you can add tape to the back of a GO gauge to get an idea of where you are within that tolerance.

 

[copperking81]

Assuming that both rifles are within spec., and that you are a well informed reloader, the only time that this would matter would be the first time that a case is fired. After that the clearance will be determined by the person loading the ammunition for that rifle. Headspace is measured with gauges. GO, NOGO, and FIELD. Scotch tape is about .002 thick. If your rifle's bolt closes on a GO Gauge and does not close on a NOGO gauge, it is within spec. Beyond that you can add tape to the back of a GO gauge to get an idea of where you are within that tolerance.

Are Go / No Go gauges machined to the SAAMI min / max lengths? So for .308 Win as an example, SAAMI's min/max difference is .010. Would that be the difference between the Go / No Go gauges?

What if you only full length size? It seems to me that to keep cartridges close to the min, if you had a chamber on the longer end of the SAAMI range, would only work if you neck size. Or am I thinking about this wrong???

 

[Richard Coody]

Are Go / No Go gauges machined to the SAAMI min / max lengths? So for .308 Win as an example, SAAMI's min/max difference is .010. Would that be the difference between the Go / No Go gauges?

What if you only full length size? It seems to me that to keep cartridges close to the min, if you had a chamber on the longer end of the SAAMI range, would only work if you neck size. Or am I thinking about this wrong???

you never use saami specs for fired brass. your fired brass tells you what the dimensions of your chamber are.

saami is only for manufacturers where mass produced ammunition will fit in all rifles chambered in that cartridge.

using a saami cartridge gauge or sizing fired brass to saami specs will cut brass life and can cause dangerous consequences.

read about how to set the headspace on a sizing die.

 

[copperking81]

you never use saami specs for fired brass. your fired brass tells you what the dimensions of your chamber are.

saami is only for manufacturers where mass produced ammunition will fit in all rifles chambered in that cartridge.

using a saami cartridge gauge or sizing fired brass to saami specs will cut brass life and can cause dangerous consequences.

read about how to set the headspace on a sizing die.

Thanks for sharing. That's one of the better videos I've run across. Most videos on setting up seating dies I've seen say to take the die down to the bottom of the ram then back if off 1/4 turn and they leave it at that.

That said, I've played a lot with my FL sizing dies and it doesn't seem to matter what adjustments I make, they never move more than .002-1 inches of brass. Anymore, I just set the die up 1/4 turn back from the top of the ram, check a few, and go with it. Maybe because I FL resize every time?

So when manufactures say that they keep it to the bottom or close to the min of the SAAMI range... does that really add any value? Or is it just a marketing ploy. That's really what I'm trying to understand.

 

[Texas10]

One could reason that if a particular off the shelf cartridge were chambered, and was found to be a snug fit to the chamber (stiff bolt drop), that little if any potential velocity would be reduced by the energy needed to expand the brass to chamber size (fire forming). So in that instance, the marketing geniuses would be correct, that a minimum size chamber would possibly be better. Enough to measure in terms of velocity....maybe.

What really matters, IMOP, is the dimension of your brass (base to datum) after sizing, and again after fired as this determines how well you've set up your die. One to two thousandths is optimal in my book for long brass life, along with proper annealing.

 

[Dusty Stevens]

Thanks for sharing. That's one of the better videos I've run across. Most videos on setting up seating dies I've seen say to take the die down to the bottom of the ram then back if off 1/4 turn and they leave it at that.

That said, I've played a lot with my FL sizing dies and it doesn't seem to matter what adjustments I make, they never move more than .002-1 inches of brass. Anymore, I just set the die up 1/4 turn back from the top of the ram, check a few, and go with it. Maybe because I FL resize every time?

So when manufactures say that they keep it to the bottom or close to the min of the SAAMI range... does that really add any value? Or is it just a marketing ploy. That's really what I'm trying to understand.

You really need a comparator to measure brass that has been fired in your chamber then set your dies. A fully formed case should bump .002 when your die is higher than 1/4 turn up

 

[BoydAllen]

Are Go / No Go gauges machined to the SAAMI min / max lengths? So for .308 Win as an example, SAAMI's min/max difference is .010. Would that be the difference between the Go / No Go gauges?

What if you only full length size? It seems to me that to keep cartridges close to the min, if you had a chamber on the longer end of the SAAMI range, would only work if you neck size. Or am I thinking about this wrong???

It seems that you are in an early stage of knowledge acquisition as far as the details of reloading are concerned. When loading for a particular rifle, a FL die is not set by a headspace gauge or to any standard but to the desired clearance for use in that particular chamber. This varies by action type with semiautomatics requiring more clearance for safe reliable functioning. For target applications with bolt actions I typically set my die to reduce the shoulder to head dimension .001 shorter than a case that is as large as can be produced by firing in that chamber. If you measure new cases from a number of calibers you may be surprised to find that their head to shoulder datum dimensions are considerably under SAAMI minimum for a chamber. After a case is fired the first time, it will come close to a maximum but will usually require more than one firing to achieve that dimension, head to shoulder datum. A number of companies have produced tools to facilitate measurement of this dimension. The readings that they produce are not important in their absolute values but only in how a case measures before and after sizing. Full length sizing does not imply returning a case to a universal standard. It means that the entire case is slightly reduced in diameter and when properly done the die is set to create a specific clearance at the shoulder if the head is fully in contact with the bolt face.

 

[MislMan]

Please remember SAAMI specs are provided as industry standards for manufacurers of firearms chambers and ammo/brass. They are intended for one-time use of the ammo and not for reloading. Once you have fired a cartridge you the reloader must take into account your specific chamber and brass dimensions to ensure safe reloads and longevity of your brass. As noted in the responses above.

 

[copperking81]

Thanks guys, really appreciate all the responses. I know detailed and well explained responses take time to write and I really do appreciate it. It helps a lot.

I read and learn a lot from old threads on subjects discussed at length so hopefully others down the road with similar questions will find and benefit from the dictated responses here