Headspace on Tikka T3 308 win

[shredder4286]

Howdy and hello 'der fellow ammo makers.

I recently bought a new Tikka T3 and started handloading for it. I was wanting to try "partial" resizing and monitor the headspace on the brass, so I bought the Hornady headspace gauge kit that mounts on your calipers.

However, I'm confused about the measurements I've been getting. I measured two different kinds of cases before and after firing to see what I could figure out.

Lot "1": Winchester case, Full length resized (hornady die), 168 gn hornady AMAX, 35.0 Varget.

Headspace before firing: 1.622" After: 1.620/1.621"


Lot "2": Hornady Superformance 165 gn SST FACTORY ammo

Headspace before: 1.622" after: 1.622"


I thought that factory and/or full length sized cases were sized somewhere in the middle of SAAMI specs so they could be chambered in a wide variety of actions, manufacturers, etc.

With that, I thought that once you fired a case in a chamber, the headspace would grow longer. Obviously that didn't happen here.

Anyone care to tackle this one?

 

[243winxb]

Takes at least 3 firings of neck sized reloads, at near maximum pressure, to fully expand the brass to your chamber. Brass has spring back after firing. When the bolt starts closing hard, you have found the correct head to datum measurement. Or just start FL sizing with .010" between the shell holder & FL die. Adjust if FL sized empy brass will not chamber.

 

[Brian Pfleuger]

The case will not be perfectly sized to the chamber after a single firing, most of the time.

If you run those case through a FL die, so the body is sized but the shoulder does not contact the die, you will find that the headspace gets longer and they will no longer chamber. Keep moving the die down until you're "bumping" the shoulder only 0.001 at a time and keep trying to chamber the case. Eventually, it will chamber with only the slightly indication of contact and the next step it will chamber with no resistance at all, that's where you want to be, 0.001 short of the chamber.

 

[shredder4286]

The case will not be perfectly sized to the chamber after a single firing, most of the time.

Takes at least 3 firings of neck sized reloads, at near maximum pressure, to fully expand the brass to your chamber

So, just neck size and keep firing until brass extends the headspace length to the point that it's tight in the chamber- then start sizing the case back down with the FL die? Am I in the ballpark?

 

[Brian Pfleuger]

Depends on what you want...

Best accuracy would be if the FL die sized the body 0.001 from chamber size and the shoulder was set back 0.001 from chamber size.

Most FL dies are closer to SAAMI minimum and chambers are close to SAAMI max, which means there's a lot more than 0.001 body sizing.

Still, you're probably better off to set the shoulder back by 0.001 every time. I've tried it both ways in a couple of my guns (all just normal, factory, off the shelf guns) and can detect no difference in accuracy between FL sizing every time and neck sizing only until they get tight. My guns shoot 1/2-3/4MOA no matter what.

So, I don't bother with FL dies until things get tight. If I were competing with a top-dollar gun, I'm sure it'd be different.

 

[shredder4286]

can detect no difference in accuracy between FL sizing every time and neck sizing only until they get tight.

Really? it's interesting how some people have SUCH STRONG opinions toward only neck sizing, or partial sizing with a FL die. For some I suppose it's the way their daddy showed them, friends etc. Thanks for the info.

 

[Brian Pfleuger]

Really? it's interesting how some people have SUCH STRONG opinions toward only neck sizing, or partial sizing with a FL die. For some I suppose it's the way their daddy showed them, friends etc. Thanks for the info.

Yeah, truth is it's all a matter of %s. Let's say FL sizing every time makes a difference of 1/10MOA average group. If you're shooting 0.2MOA, that's 50% worse groups by not doing it. If you're shooting 0.5", it's only 20% worse and you're not likely to ever know it unless you shoot a lot of bullets and carefully measure.

Those numbers are just examples but that's the general idea.

What I actually do is use Lee collet neck dies and Redding body dies. No lube at all for the neck dies. Super easy.

 

[Metal god]

The thing I don't get is

Headspace before firing: 1.622" After: 1.620/1.621"

How'd the case get smaller after firing ? I can see it not expanding to full chamber size but why did the case shrink ? The only thing I cam think of is the datum line on the shoulder changed after firing .

 

[603Country]

I suppose that these days, I would think that what Brian does (Lee Collet and Redding Body Die) would probably be the best way to go, but the truth is that I don't do that for any rifle I have. I use the Lee Collet only for the 223. The 260 works extremely well with standard Hornady FL dies and I just bump the shoulder back as I size the neck (Partial FL resizing, by another name). The 220 gets neck sized with Redding NK dies (non-bushing). I neck size (RCBS) for the 270 and use the FL die to bump the shoulder back a bit when it's needed. So...if somebody ask how I do it, I guess I don't have a 'one way' approach. Of course, if I was shooting long range in competition, I'd go for the Redding bushing dies and a new scope and even a new rifle. But, I'm just a hunter that punches paper when the whim strikes - though I am quite picky about accuracy.

 

[shredder4286]

How'd the case get smaller after firing ?

that's what I'm sayin!!!!!

I don't have a 'one way' approach

Well, aren't you special?! Just kidding

Sounds like you've maybe found that different cartridge/rifle combos work better when the cases are sized a certain way. I'm a hunter who likes to punch paper on a whim as well, but lately I've been finding less time than I'd like to be able to keep the neighbors from afternoon napping.

 

[F. Guffey]

http://saami.org/PubResources/CC_Drawings/Rifle/308 Winchester.pdf

Headspace before firing: 1.622" After: 1.620/1.621"

Headspace before: 1.622" after: 1.622"

I thought that factory and/or full length sized cases were sized somewhere in the middle of SAAMI specs so they could be chambered in a wide variety of actions, manufacturers, etc.

You have no choice but to agree with the WWW of reloading, they paint with a broad brush then there is the risk when trying to pin one of them down they go straight to BENCHREST, like "I got a cousin that knows this guy that is a bench rester and he says etc.." and me? I have no way of knowing how to contact the cousin.

You purchased the Hornady head space gage that is a comparator, it is not a head space gage. I make head space gages and comparators, the round hole/datum/ measured from for the 308 W family of chambers is .400", that goes for everyone except me, because? I make comparators, I decide 'measured from' and 'measured to', I choose the diameter of the datum/round hole/measured from. For that reloaders do not have a standard.

I added a link to SAAMI for the 308 W, problem? Not for me but this should be post #11 and no one has mentioned your numbers for before and after do not match up with SAAMI's before and again after specifications.

Does not agree? Not a problem for me, I make gages to check Sinclair/Hornady gages.

http://www.tikka.fi/pdf/manuals/TikkaT3_RH.pdf

A technique that is not acceptable to the WWW reloader is measure the length of the case from the shoulder/round hole/datum before firing, meaning measure new over the counter factory ammo before firing. I measure new ammo with other reloaders in the area, we do not walk around telling scary stories about how bad things can be, because? We have been impressed with the ability of manufacturers to produce ammo that fits the description of 'minimum length' reloaders believe minimum length/full length size back to minimum length is something that is floating somewhere out there along with all the chambers the ammo may or may not fit.

It is possible to measure the length of the chamber in your rifle before firing it, if you knew the length of the chamber from the shoulder to the bolt face you would know the length of the case after firing and you would know there are some problems with your measurements before firing and after firing.

F. Guffey

 

[Brian Pfleuger]

How'd the case get smaller after firing ?

Hodgdon's listed starting load with that combination is 42.0gr.

You're WAY under at 35.0gr.

The case is shorter because you're making enough pressure to expand the body but not enough to stretch the case head backwards once the body is stuck to the chamber walls.

If you picture in your mind a cylinder that gets fatter, you can see that it has to also get shorter, unless you make the sides thinner. Under normal pressure conditions, you've got enough pressure to stretch (thin) the walls, which is what ultimately leads to head separation.

If you want to form the cases to your gun without stretching them, use either ordinary starting loads or IMR Trail Boss max loads with the bullet jammed in the rifling. The bullet hitting the rifling ensures that the head is pressed back against the breach and the shoulder will expand forward instead of the head stretching backwards. Trail Boss is a ton of fun. Your .308 will sound like a .22.

 

[F. Guffey]

Quote:
Originally Posted by shredder4286
How'd the case get smaller after firing ?

Hodgdon's listed starting load with that combination is 42.0gr.

You're WAY under at 35.0gr.

We do have the 'firing pin strikes the primer' and then everything runs to the front of the chamber, somewhere in their someone should mention protruding primers.

F. Guffey

 

[Metal god]

I missed the OP saying his load was 35gr of what ?? I agree with Guffey and if his is way under pressure there should be some pimers backing out .

 

[pbcaster45]

My Tikka T3 in .308 Winchester requires cases with a headspace of 1.616 – 1.617 or I run into problems closing the bolt. Sounds bad but Lake City ammo fired in my Tikka requires minimum sizing to work in my M1A! The headspace on my M1A is 1.631 (Stoney Point 1.619).

 

[shredder4286]

no one has mentioned your numbers for before and after do not match up with SAAMI's before and again after specifications.

I make comparators, I decide 'measured from' and 'measured to', I choose the diameter of the datum/round hole/measured from. For that reloaders do not have a standard

.

If I understand you correctly, you're saying that because hornady's gauges are comparators, they may not necessarily measure from the same reference point as other headspace gauges, so my measurements of 1.622 may not be actual headspace.

Hodgdon's listed starting load with that combination is 42.0gr.

You're WAY under at 35.0gr.

Hornady load manual puts Varget charges for 165-168 gr bullets starting at 34 and goes up to 42.

(Briand Pfleuger)

If you want to form the cases to your gun without stretching them, use either ordinary starting loads or IMR Trail Boss max loads with the bullet jammed in the rifling

(243winxb)

Takes at least 3 firings of neck sized reloads, at near maximum pressure, to fully expand the brass to your chamber.

I know high pressures can be attained by both min and max charges, but those 2 sentences still conflict with each other in my mind.

Just trying to walk away from this with enough of an understanding to know how to continue with my loads.

 

[603Country]

Shredder, that statement that it takes at least 3 neck sized max load firings for the case to fully match the chamber didn't sound quite right the first time I read it, but I do believe he's correct. If I shoot max loads and neck size, sooner or later the fireformed cases are going to get a bit tougher to chamber. That they are getting tougher to chamber tells me that the cases have gotten fully the size of the chamber and that the shoulder needs to be set back a bit.

 

[Brian Pfleuger]

Just trying to walk away from this with enough of an understanding to know how to continue with my loads.

It may take more than one firing, it depends on the brass and the pressure.

Trail Boss burns lighting fast, it's 100% burned before the bullet moves an inch or so. With the bullet jammed in the rifling, you're not leaking any gases past it. Max pressure is reached very, very quickly and the brass should seal and blow the shoulder forward pretty well.

In any case, once they're fired and the shoulder is blown forward, there is a small enough difference between the case and the chamber so that sizing the body will push the shoulder "up" and you can match the actual headspace of your barrel.

It really doesn't matter if a gauge is an absolute measurement or if it matches other gauges. It matters that it takes a measurement that is representative of your gun.

 

[shredder4286]

Things are starting to come together here. Sounds like there are several different ways to get your brass to form to the chamber.

So let me see if I understand this process:

Once you reload the same lot of cases several times by neck sizing, and they become hard to chamber(as a general rule), you're at the point where the brass has "fire formed" to your chamber.

Then, at this point, you can begin to knock the shoulder back .001/.002 with your FL length die to keep the "custom fit" to your chamber without having to size all the way back down (raise ram, screw die in until it touches shell holder, etc).

Am I in the ballpark?

 

[Brian Pfleuger]

Except that you don't have to wait several firings. The case doesn't necessarily "crush fit" the chamber after a single firing but it's only going to be a couple thou short. When you size the body it gets narrower. That brass has to go somewhere, it can't go down since that's where the ram and shell holder are so it goes up. You increase the case headspace. Think of a stress ball. You squeeze it in your fist and it pops out the top and bottom of your hand. Same idea.

If you measure a case before sizing and then run it into a FL die without going the full length, so the shoulder doesn't hit the shoulder of the die, and then measure it again you'll find that the headspace has increased probably several thousandths. If you tried to chamber that case you'd find that it wouldn't fit. Now you can start adjusting the die 0.001 at a time until you can chamber the case without effort.