Headspacing question

[Roz762]

Hi folks. New member here with a quick question about headspacing:

I'm starting a .308 build soon based on a cheap Stevens 200 action. I received my Shilen select match barrel last week and I'm read to start assembling the rifle. I had the chamber reamed to a dummy cartridge that I loaded up and sent to Shilen. This rifle will be shooting lapua brass and Scenar 155gr hpbt bullets loaded to SAAMI OAL specs.

My question is regarding headspacing TO MY SPECIFIC LOAD. I plan on using match headspace gauges to accomplish this. I've invested a fair amount of cash in this thing and I want it fine tuned. Besides, lapua brass ain't exactly cheap, so minimal case wear is a bonus as well. Let me be clear that this rifle will never fire factory ammo or any ammo that I have not loaded personally hand-loaded, for that matter.

I have not measured my resized brass yet, so I'll use some hypothetical numbers out for examples. Lets say I get my Hornady Comparator out and find the measurement of my case to be 1.632".

What size headspace gauges should I use? From what I've read, as long as I keep tight specs on my cartridges, .002-.003" of headspace tolerance is acceptable. So with that being said, should I use 1.632" and 1.634" headspace gauges for go and no go, respectively?

Thanks in advance.

Josh

[CharlieNC]

You can use your dummy cartridge to measure headspace. Check the length using your comparator; then insert a spent primer and bolt it in and measure; the difference is the headspace. I read about this technique in the forum here a couple of years ago and it has worked well for me so far. I usually set at .003" which shoots well and ejects fine as long as I full length size occasionally to maintain the headspace.

[kslefty]

When you say that your hypothetical brass measures x.xxx is this new brass that you have resized or once fired from another gun? I would think that .002" on new brass would be hard to ever get fired brass back this "tight". Have no experience with match chambers but I always set my rifles with a piece of resized once fired brass which still allows any new brass to easily fit.

[Roz762]

This is new brass that has been resized.

[stangfish]

I may have overlooked this in the previous or OP post but there are a couple of aproaches to take with regards to headspacing for brass. Since you have mentioned using match* gauges then lets USE the match gauges. I would not worry about the brass deminsions and feel like you sized your brass prematurely. I have no idea your experience in reloading or accuracy reloading and case preperationnor do I know if you used a full length die or a neck sizer. I feel at this time we should concentrate on setting the headspace per the gauges.

With the 308 the headspace is determined by a established standard length from the base to a datum at .400 diameter on the neck. Saami specs are 1.630 +.010. I think most gauges are tighter and hold .004 between go and no go. Does a match chamber gauge use something different?.

Time to set your headspace with the gauges. Since we have set the chamber to spec, did you use a ful length sizer die? If so we need to check to see if we oversized or undersized our brass. Put an empty case in the chamber and close the bolt. It should be easy. Now put a shim on the end of the case, roughly .004 in thickness. Some use celophane tape, It is important to know what thickness you are dealing with. If it is tight or will not close and you are the man.

If it is loose or rattles around you have oversized your brass and may want to tighten your headspace a little and try to fire form your brass back to your correct chamber specs. Having more that .004 stretch it is possible you will see IHS after about three firings.

[Roz762]

Sorry, let me clarify. When the brass was resized in a FL die, it was well within saami specs (don't have the exact numbers with me, they're written down in my notebook at home). The barrel/chamber is made to that dummy cartridge. Match headspace gauges are available from 1.630 to 1.640 in .001 increments.

What I'm trying to determine is the proper headspace gauges to buy. To further explain:

If my hypothetical case is 1.632 and I want a .002 tolerance, do I buy 1.632 and 1.634 gauges? Or should there be any allowance or extra offset, if you will. So should I allow for an extra .001 meaning I need to buy 1.633 and 1.635 (still .002 of tolerance). I know it sounds like a dumb question, but I've not been able to find a good answer on this and I'm trying to learn more on the subject for future builds.

It sounds to me like based on your descriptions that the "go" gauge needs to simply measure the same as your brass, correct?

[stangfish]

I size my brass to fit my chamber. The most economical and sensible way that I know of. You may be more advanced reloader riflesmith guru than me.

From what I have always seen that after firing, with the exception of when the brass is highly polished, the case has grown to fit the chamber. If it grows or even needs to grow more than .004 it is a bad thing. What you are talking about is foriegn to me but I may be the DA. Use since the size of your case right now is important to you just headspace to your brass. Take a piece of .003 shim stock or whatever you want to hold your chamber to and cut it out to fit the head using some grease to hold it in polace and try to close the bolt,

It is much easier to bump the shoulder each time you resize or use a neck sizer and body die when you need to but you can do it however you want.

[stangfish]

If you are looking for accuracy look at the freebore and throat and see if it is matched to your bullet. Someone chime in if I am talking out my Honk Honk

[sharpshooter]

Get the gauge that matches your ammo. If it is 1.632" get the same gauge. When you tighten the nut, the threads will tension up and stretch, giving you another .002" clearance.

[stangfish]

...if you have a case headspace gauge you can compare a fired round to a sized one and know if you are where you want to be.

You will need to know more than hypothetical length to order your gauge.

[mnbogboy2]

Sharpshooter & Stangfish have nailed it in their last two posts....Your "new" full length sized case most likely will be short of your end result...Also I believe Shilen most likely would chamber sammi and take in consideration for your freebore but not undersized your chamber to match an unfired case....I may be wrong if Laupa makes brass larger than a sammi FL die, but all the brass I have measured is undersized of a sammi chamber or a FL die otherwise it wouldn't fit in all chambers....If your chamber does end up small you may need custom dies as well as custom "match" go/no-go gauges....It normally takes three firings for brass to normalize its chamber fit even if it is FL sized each time....
My opinion would to headspace "tight" with a standard sammi go gauge.....Compare your once, twice and three fired cases after FL sizing with your die...Keep particular notice of chamber fit with loaded rounds....If the FL cases begin to tighten after two or three firings your headspace is too tight for your die....You can modify a shell holder at this point to loosen you up a tad or reset the headspace.....

My $.02,
Randy

[stangfish]

I want to add to what Randy is telling you. When setting up a FL die read the instructions. You usually bottom the die out on the shell holder then back of a turn or so. Size the die and then check the case headspace, turn the die in 10* increments until you bump the shoulder back .001 -002. much more than that and you have "oversized" your brass.

Each full rotation of the die is about .0715 linier movement. 10* is about .0019 linier movement. If you do it that way you wont oversize any brass. Remember when tightening your die jam nut you loose 1 or 2 thousandths.

[bsekf]

You can use your dummy cartridge to measure headspace. Check the length using your comparator; then insert a spent primer and bolt it in and measure; the difference is the headspace. I read about this technique in the forum here a couple of years ago and it has worked well for me so far. I usually set at .003" which shoots well and ejects fine as long as I full length size occasionally to maintain the headspace.

Please explaine the spent primer. I don't understand why you need a primer in the case to measure headspace.

[stangfish]

Please explaine the spent primer. I don't understand why you need a primer in the case to measure headspace.

How many bears have you had?.......Well thats not enough. At least 4 more to grasp the concept.

[bsekf]

Thanks for the reply, I guess I haven't had enough "bears". I don't keep many "bears" on my reloading bench. Still don't understand the concept. I seat my primers flush or below and do not see where they would figure into the headspace measurement. We are talking face of the bolt to the datum line?

[stangfish]

LOL Beers! I was thinking about big browns in a beautiful vallley on the Kenai Pennisula.

Primers not required

[BillPa]

Still don't understand the concept. I seat my primers flush or below and do not see where they would figure into the headspace measurement. We are talking face of the bolt to the datum line?

Its a depth gauge of sorts to determine cartridge head clearance. You seat a primer about 1/2 the way, chamber the case then lock the action to battery which will seat the primer deeper into the pocket when the shoulder, rim, belt and etc bottoms in the chamber. The amount the primer protrudes above the case head is the cast head clearance. If the primer protrudes .002" the case has .002" head clearance.

Bill

[CharlieNC]

Yes. What Bill said. Use an empty sized case, no bullet; measure the length using either a standard caliper or one with a headspace comparator. Then insert a spent (previously fired) primer half way and bolt it in; remeasure; the difference in lengths represents how much the primer protrudes which is the head space. I have measured factory Savage this way at .003", which is typically what I set my barrels to as well for normal use. This is an actual measurement, not just a reference go/no go type gauge comparison.

[bsekf]

OK, now I understand. Thank you.