Head clearance affecting accuracy?

T

tensnxs

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Does anyone know how does the amount of head clearance affect accuracy?

I just found out the once fired brass out my newly built long range rifle is 0.006" longer than when it was new. My other rifles of the same caliber have fired brass less than 0.003" longer than when new (same new Lapua brass). This makes sizing for all 3 rifles difficult.

This is a prone comp rifle for long range matches so reliability is a concern. I use brand new Lapua brass and full length size fired brass with a shoulder bump of 0.002". Granted I only shot it once and have not shot the fired formed brass for accuracy yet.

I noticed fliers in 8 out of 10 groups (5-shot ea) and most of them ain't me. The fliers are mostly vertically stringing from 2 different primers. So this seemingly long head clearance is raising the question in my mind.

thanks in advance for your input.
 
What are you calling "head clearance"?

Try this, after fire forming the brass in the new rifle, then trim it to the trim-to length. Then see if it grows after that and how much compared to the other rifles you mentioned.
 
Need better details

I'm going to assume that you mean headspace clearance. How are you measuring this??

1. Headspace will effect accuracy, sometimes a lot, sometimes little.

2. Again, how are you measuring this? Is this headspace or overall length?

3. Shoot the brass with the correct bump and see how it performs...what is the chambering?

4. If yours shooting unformed brass and different primers, I would suspect you would get fliers, just as you said, I believe you answered your own question there or I don't understand what the question is.....why would you think it's the headspace or length?

Hovis
 
Tensnxs

If you are truly measuring your brass growth correctly, then the simple answer is your new Rifle has about .003 more "headspace" than the others.

I am assuming that by head clearance, you are talking about the amount of clerance between the bolt face and the chambered round. If your brass is growing a measured .006 from the head's face to the shoulder, then you do have .006 head "clearance". (notice I avoided the term "headspace").

Of course, this is of no consequence if you keep that brass, (after firing), with that Rifle, and set your dies accordingly. But since you want to be able to load rounds that will work in all of your Rifles, then you do have a problem. You could compromise, set the die where one Rifle has .004, and the others .001. But .004 is getting pretty loose. Too loose.

If it were my Rifle,I would simply unscrew the barrel and just face the appropriate amount off of the barrel shoulder, so it produced the exact same length cases as your other Rifles. Is this an option for you??. In the long run, that might be the best course..........jackie
 
If you're talking headspace, .006" headspace could be too much depending upon how each chamber fits on a go gage. The bolt should just close on a go gage. If it won't close on a go gage on the original rifle, then your headspace is too short. .006" is the difference between a go gage and a no go gage. If the bolt on the new chamber will close on a no go gage, then headspace is unnacceptable and the shoulder should be set back.

However, there shouldn't be a problem with accuracy after fireforming as long as you fit your brass to your chamber. It would be no different than some of the cartridges such as the 6 Dasher that have their shoulder moved forward during fireforming to create more case capacity. The simple solution would be to have the shoulder set back just enough to allow the bolt to just close on a go gage. Another way to go would be to get a set of the die shims that Sinclair's sells that used to be made by Skip Otto and use the appropriate sized shim to get the .002" shoulder bump with each of your rifles. You would need to have ammo dedicated to each rifle going that route.
 
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i do mean 'headspace clearance'. this rifle doesn't close on 1.636" 'no go' guage (there are other no-go guages that are 1.634 and 1.635 which this rifle closes on & partially on). headspace on this chamber is 1.6345

Since everyone seems to want a chamber at the minimum. I want to know if anyone know if .006" headspace clearance affects accuracy compare to fire formed brass and how?
 
That amount of headspace will definently overwork and wear out the brass quickly. As far as accuracy...it will probably effect it in a poor way but by how much...only the target will tell. Either get shims, another die or rechamber.

Hovis
 
not if you size for the rifle...as in not full length, but just enough to close the bolt. all should be fine.

mike in co
 
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