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I have been reloading pistol ammo for ipsc competition for years now, but recently got the long range bug and want to load some good quality rifle ammo. What is the prefered method for measuring headspace? For example, how do I know when the ogive of a particular bullet is just touching the lands? I will be loading .308 to be shot out of a model 10 fp-sr. Thanks Doug
Might want to edit the title of your thread. Headspace refers to the fit of the cartridge in the chamber.
What you want to know is how to check the engagement of the bullet in the lead/rifling. Yes, that is a very tricky question since the geometry of the bullet tip impacts the measurement.
What many of us do is follow the recommendation of the bullet maker (berger has a reloading manual for example) and start at the recommended cartridge overall length. The bullet tips tend to be a bit inconsistent, but you do a bit of averaging and that gives you a seating depth that is reasonably consistent. Hopefully your seating die does not make contact with the bullet tip, or else you will have a bunch of problems ?
You try out that basic dimension to see how it works, and if you are not satisfied you load up groups of 3 to ever increasing length provided it still fits in your magazine and has enough neck engagement to be robust in handling. Steps of 0.020" are fine enough. Then go and fire off your 3 round groups and somewhere in there will be a batch that may be substantially better than the others. You might even need to try some loaded shorter than the recommended length, but if you do that watch carefully for pressure signs since you are reducing case capacity and pressure will go up.
David Tubb claims that he loads his match loads longer than the point it will engage the rifling and the bullet basically gets pushed back into the neck by the rifling so that the bullet is guaranteed to be jammed every time. I don't like the sounds of that, but then I'm not a match champion either, so apparently it works for him.. Not sure I would want to take loads like that into the field anyway because 95% of the time I don't get to fire a shot...
Thanks for the heads up Westcliffe. I just changed the topic. Good info.
Bugger, I forget that you can change the title of your post but not the title of the thread. Might want to ask a moderator to fix it...
Here is a link to the David Tubb story http://www.6mmbr.com/6XC.html
quote from story
I use moly-coated bullets exclusively, so the loads listed need to be reduced 1-1/2 grains if an uncoated bullet is substituted. All of my long range loads are seated long and are pushed back into the case upon the closing of the T2K bolt. Likewise, all of my long range loads are full-length resized each and every time (approximately .003 inches shoulder set back). I use the Superior Shooting Systems Custom 6XC die set (see below). I used the .268 bushing in the sizing die with the expander plug (for long range only; I use a smaller bushing for across the course rounds).
PRIMERS: I have been using Russian primers exclusively. They use a different sinoxide (close to the European type) compound mix which (in my testing) consistently delivers better extreme spreads over Federal 210's. Be sure they are seated firmly into the case--if not they can be hard to ignite.
The old timer/owner of a local gun shop told me how he measures this. He would close the bolt and insert a rod (unknown material- wood, metal, plastic) until it touches the bolt face. He would then mark the rod where it exits the barrel. Then he would insert a round that was loaded long David Tubb style and push it into the lands and then re-insert the rod until it touches the point of the bullet and mark the rod. The distance between the marks is the length of cartridge touching the lands. I dont know why you couldn't just measure the cartridge after it has been pushed into the rifleing, maybe it would be pulled back out of the neck when removed. Does anybody else do this?
Berger has a chapter in their reloading manual where they discuss the difficulty with this issue. Part of the problem is that the dimension from the bolt to the throat can be different on 2 identical looking rifles standing in the rack. The bullets may be from a different batch and have some variance. The seater die may make contact at a different point on the ogive, even if you and your buddy buy the same brand of die.
That was the reason why Berger recommended the "coarse" step test for seating depth, since it need not take long and one only has to find the "window" of seating depth that works best for you.
Something I've done is seat a bullet in a ctg fired in my rifle. I can usually start it in the case by hand. Then I very carefully chamber it & remove it. You do have to be careful because a bump can alter the depth the bullet is in the case. When you take the ctg out of the chamber, the lands will have pushed the bullet into the case to the depth that it touches the lands.
Hornady makes a device to measure this. That being said, I've been using Franks method. It's not an exact science though. Best thing is to perform the operation 5 times and take the average of these measurements.
I do like Frank's idea. It seemed to be a straight forward way to measure this. I also like that Brian takes the average of 5 measurements. I am still waiting on my model 10 FP-SR, B&C Tactical Medalist, and Vortex PST 4-16x50 FFP. When I recieve all these goodies I can start working up a load. I am sure I will have more questions then. Thanks for all the info guys. Doug
This is the way I used to do it too. Then I bought this:Quote:
Originally Posted by Frank V
http://www.midwayusa.com/product/570...ge-bolt-action
Yep!Quote:
Originally Posted by Texas Solo
BTW it is good to see a Brother here on the Forum. Welcome to another brotherhood my brother from another...local.
Something else I did was to measure the seating depth the way I described then size a case & seat a bullet to that depth & mark it maximum. That tells me I can't seat the bullet out any farther than that.
You need to check to make sure the rounds will work through your magazine too. Sometimes the magazine is the limiting factor.
I am a huge fan of dummy rounds for seating & case trimming. It makes setup so much faster. Once I have determined the best seating depth, I make a dummy round for that seating depth.
Bingo! I have one of these for every different bullet I use. It's most important especially when measuring OAL from the ogive with a comparator. I get .022" difference between Berger VLD's and Sierra MK's.Quote:
Originally Posted by Frank V
dummy rounds are an excellant thing to have for each bullet. even old cases will work for those.Quote:
Originally Posted by Texas Solo
no need for measuring devices either to get the legnth. just close the bolt to seat the bullet.
then use a match to smoke the bullet or a marking pen and seat deeper till the rifeling is barly visable when the bolt is closed.
then measure with calipers
Well, it depends on how accurate/consistent you want to be. Measuring to the tip of bullet with calipers gets you close, but bullets do vary in length, even in the same lot #. Using a chamber gauge and bullet comparator is absolute accuracy.Quote:
Originally Posted by yobuck
Using the method you describe is a common starting point, we've all used it at one time or another. But you need to be careful that the bullet doesn't sightly pull out of the case during the extraction process.
Yeah, there's no "need" for measuring devices, but their nice to have :)
When pushing the bullet in the first time or two yes the bullet can get moved. In subsequent checks though with the bullet seated deeper each time it isn't going to move, especially when it gets to where it's just touching the lands.Quote:
Using the method you describe is a common starting point, we've all used it at one time or another. But you need to be careful that the bullet doesn't sightly pull out of the case during the extraction process.
in more than 60 years ive never had one get stuck. i of coarse use an unprimed uncharged case for determining legnth.
as for legnth differences in bullets were using the same bullet untill the proper legnth is obtained. the die seats off the ogive anyway
so minor legnth differences dont matter. but of coarse theres a tool for that also for those who like tools.
its called a megplate trimmer.
I've tried most of the different techniques and they all seem to have their pluses and minuses--but you get used to them. The one caliber that stumps me is my 111 6.5 284--I'm guessing the throat is so long and gradually-tapered that even the slightest pressure seats the bullet into the lands to varying degrees. Otherwise, all the rest of my calibers are easy to figure out.
i use the hornady chamber guage and comparitor i also sort my heads another thing i do is to recheck after awhile my chamber for errosion since my 308 like them .005 off the lands i want to make sure it stays that way i'm saying like every 500-600 rounds i check.
Didnt read all the posts but frank V had It right, the most accurate way Is to take a case thats been fired In your gun, size the neck and ream the inside out to have just enuff tension so the lands will seat it when you close the bolt, with just enuff that you can still manage to get it back out of the case by hand. Always do twice. You should get the exact same reading, or within half a thou. Invest In a good pair of calibers. Digital are junk. Starett makes nice analoge ones for around 150.00 Seems like alot but If your worried about exact seating depths then It shouldnt be an issue. I usually have one case for each lot and brand. If you use a lee collet die like I use for some of my .308 loads you can size it exactly right just for this purpose. Overall Length doesnt do alot really. The objive guage, ones like sinclair sell are the way to go. In my opion this Is the most accurate and also cheapest way to this. Super simple and no tools to buy other than the objive gauge, bout 30 dollars and most have several calibers on the same gauge. I can seat bullets with accuracy less than the thickness of a human hair. Other methods just dont offer that.
Take a sized case and cut two slits in either side of the neck... Then you can squeeze the two halves together with your fingers to increase or decrease the neck tension for seating... You want it to be hard but not hard enough not to be able to move it with your fingers.Quote:
Originally Posted by Frank V
Close the bolt on the overly long seated bullet, then guy the round out with your hand so the ejector does not slant the bullet as you remove it.
Measure the length from the ogive... repeat five times. You will see a value that repeats.