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Headspace and accuracy

rain164845

Has anyone ever tested at what point excess headspace due to pushing the shoulder back affects accuracy? I ask because I have determined that I was pushing my shoulders back .007 vs my usual .0015.
I had been having some unexplained flyers.
Any input?
Thanks!
 
My experience is that it can very from caliber to caliber, brass brand to brass brand, how many cycles on the brass, etc.. That said, and again in my experience, 0.007 is excessive that could havoc flyers (especially on older or non-annealed brass). Plus risks of "case head separation" and/or case fracture goes up when sizing that much.
Donovan
 
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Ideally for a bolt rifle about .001 to .002" shoulder push back from a fire case in the rilfe you're loading for.

Oversizing can create head separation. I have no idea about accuracy since I would never push the shoulder back that far (i.e. .007") but my guess is that it isn't helpful.
 
While FF 6 BR to Dasher, with bullets seated hard against the lands, I have done groups in the 0.25 MOA at 100 yards, to my surprise :confused:
 
rain164845 said:
Has anyone ever tested at what point excess headspace due to pushing the shoulder back affects accuracy? I ask because I have determined that I was pushing my shoulders back .007 vs my usual .0015.
I had been having some unexplained flyers.
Any input?
Thanks!
Click to expand...


I guess the real question to you is this... If you know that you have shoulders shoved .006+ from your norm , WHATELSE has been altered to the case besides that??
Assuming your die is a very nice fit to your chamber you would be lucky that it might only change a few other dimensions such as case diameter at the body shoulder junction etc in relative numbers to what your excessive shoulder bump was ( that would be luck )

However if your die is not a close match.. You may think all you have done is moved a shoulder back too far but in reality you more than likely have excessively reduced other dimensions like body diameter at various points. Or even caused them to grow by way of not being supported.

Without measuring ALL the areas of the brass before firing, after firing and finally after sizing do you start to see what is taking place... And so this opens another question for you to ponder , is it excessive headspace that diminished accuracy or was it that the case is now tight in the back as well as tight at the body shoulder jct. but with lots of headspace and that has put the rig out of tune.

Measure stuff... Good luck
 
How many folks have commented that their dasher Fire form loads are extremely accurate..... moving that shoulder a lot more than .007

I have heard just as many shooters comment that their Shehane Fire form loads are the most accurate.

However though it is on brass, I doubt it negatively effects accuracy, assuming a jammed buLet.
CW
 
@Mulligan -
I agree on the expansion of new brass when fire-forming. But the fire-forming new brass verses sizing cycled brass are two separate aspects, that do not trait the same (expansion verses contraction) - IME.
Donovan
 
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It's your rifle and you eyes...I am not sure firing 10 rounds in a rifle .007" under headspace is a good idea...testing or not. There's a reason the no-go gauge is .004". Case head separations are never good and often dangerous, but, since you aint doin' it at my range....do as you wish.
Personally, I would size the cases right and try it that way...if the flyers went away I'd be happy. If not then you know it wasn't the excess headspace anyways.......better to be safe 100 times than dead or injured once!!!!
 
I would think varying degrees of headspace would change the amount of bullet jump from case to case, unless you were hard jamming.
 
Sure you do and will. So will ten thousands of others every day. It is called factory ammo and a lot more of it is fired than hand loaded ammo.
Just because you hand load and pursue perfection in head space does not mean that ammo will not function as intended by its designers when produced in factories by the millions of rounds.
If you obsess over the details of your ammo so much that you are worried about .0005 head space you are no longer living in a world where ordinary ammo works at the worst case longest possible chamber with the shortest ammo permitted by the drawings. So you don't shoot a SAAMI standardized round? The length of firing pins still permit them to set off a primer that is .007 from the bolt face.

msinc said:
It's your rifle and you eyes...I am not sure firing 10 rounds in a rifle .007" under headspace is a good idea...testing or not. There's a reason the no-go gauge is .004". Case head separations are never good and often dangerous, but, since you aint doin' it at my range....do as you wish.
Personally, I would size the cases right and try it that way...if the flyers went away I'd be happy. If not then you know it wasn't the excess headspace anyways.......better to be safe 100 times than dead or injured once!!!!
Click to expand...
 
I sized 59 Winchester 220 Swift cases in the last few days, all had been fired in my rifle 2-3 times. Fired case dimension 1.806 from base to shoulder using Hornady tools. Tried to set die to get 1.804 and did achieve that + - .001 on most cases. Had four that measured 1.801- 1.802. Had 4 iirc that came out of the die at 1.809 even after three attempts and some added dwell time. Finally had to use a shim under base of case to get them to 1.8045 or close. It will drive you crazy sometimes. I sort the short ones for foulers but I don't think they would be a problem for 200 yard coyote killing. I use RCBS fl die and a T7 press. Just an observation. Barlow
 
Barlow said:
I sized 59 Winchester 220 Swift cases in the last few days, all had been fired in my rifle 2-3 times. Fired case dimension 1.806 from base to shoulder using Hornady tools. Tried to set die to get 1.804 and did achieve that + - .001 on most cases. Had four that measured 1.801- 1.802. Had 4 iirc that came out of the die at 1.809 even after three attempts and some added dwell time. Finally had to use a shim under base of case to get them to 1.8045 or close. It will drive you crazy sometimes. I sort the short ones for foulers but I don't think they would be a problem for 200 yard coyote killing. I use RCBS fl die and a T7 press. Just an observation. Barlow
Click to expand...
Yep, if you are not measuring each time and adjusting dies or annealing, shoulder bump lengths can be a crap shoot.
CW
 
My hunch is there's about ten more likely causes, ahead of what are essentially fully-resized cases, which would be causing true "flyers". But you didn't provide detail or pics of the groups and the apparent outliers. What constitutes a "flyer" for you?
-
 
If the bolt closes on the chambered round without any force I am as lost as to why one would want to 'bump' the shoulder any amount at all.
If your desire is to work the brass (needlessly) bumping will do it. If your goal is to find out what they meant by excessive head space well .007 is on the right track. I think in doing so a 'flyer' will be the least of your problems.
Some engineer figured out the dimensions for a go and no/go gauge. The difference is not .007
This whole post can be a lure to fguffy.
 
You do not shoot go and no go gages. You shoot ammo in a chamber.

M-61 said:
If the bolt closes on the chambered round without any force I am as lost as to why one would want to 'bump' the shoulder any amount at all.
If your desire is to work the brass (needlessly) bumping will do it. If your goal is to find out what they meant by excessive head space well .007 is on the right track. I think in doing so a 'flyer' will be the least of your problems.
Some engineer figured out the dimensions for a go and no/go gauge. The difference is not .007
This whole post can be a lure to fguffy.
Click to expand...
 
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