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All handloading data posted on Full-Bore UK from 23/2/2021 must reference the published pressure tested data it was sourced from, posts without such verification will be removed.
Any existing data without such a reference should be treated as suspect and not used.
Use reloading information posted here at your own risk. This forum (http://www.full-bore.co.uk) is not responsible for any property damage or personal injury as a consequence of using reloading data posted here, the information is individual members findings and observations only. Always verify the load data and be absolutely sure your firearm can handle the load, especially older ones. If in doubt start low and work your way up.
Forgive me if this has been asked before but I'm trying to get my head around the neck sizing dies with interchangeable bushings.
If I measure a fired case from my F/TR rifle I get a diameter of 0.342", if I then measure a loaded round (neck sized by a Forster die without interchangeable bushings) I get a diameter of 0.336" giving a chamber clearance of 0.006" (if you assume a fired case is a 100% chamber fit which of course it isn't).
Now I've read that the desired chamber clearance is between 0.002" & 0.003" but if I stump up the cash for a bushing die with a bush diameter of 0.339' rather than the 0.336" I'm currently getting am I going to see any difference in performance at all?
Stuck wrote:If I measure a fired case from my F/TR rifle I get a diameter of 0.342", if I then measure a loaded round (neck sized by a Forster die without interchangeable bushings) I get a diameter of 0.336" giving a chamber clearance of 0.006" (if you assume a fired case is a 100% chamber fit which of course it isn't).
Now I've read that the desired chamber clearance is between 0.002" & 0.003" but if I stump up the cash for a bushing die with a bush diameter of 0.339' rather than the 0.336" I'm currently getting am I going to see any difference in performance at all?
If you used a 0.339 bushing with the same brass your bullets would fall out of your cases (so yes, you would probably see a performance difference!).
You can't control neck clearance with bushings, you can only control neck 'tension', or rather, the interference fit between the bullet and case. Neck clearance will always be the difference between the chamber neck ID and: size of bullet plus 2 x case neck wall thickness (assuming the bullets aren't loose, as above).
The figure of 0.001 to 0.002 you have probably read about is how much under the size of a loaded round your bushing should be. So if your loaded round measures 0.336 you should choose a bushing of 0.335 or 0.334. Anything more than 0.336 and the bullet will be loose in the case.
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Last edited by rox on Mon Sep 22, 2014 6:40 pm, edited 1 time in total.
I can see that you could vary neck tension with different bushings but assuming the neck tensions are the same for all rounds loaded with the same die (or bushing) why bother?
I can see that you could vary neck tension with different bushings but assuming the neck tensions are the same for all rounds loaded with the same die (or bushing) why bother?
<cynical>It helps manufacturers to sell expensive dies and generate an ongoing revenue stream by selling bushings. And then selling more 'upmarket' bushings with hi-tec cryogenic coatings (that will get you more points).</cynical>
Bushings let you achieve a specific neck tension regardless of brass neck wall thickness (by changing the bushings to achieve a particular neck ID for a given neck wall thickness). Apparently necks sized about 0.001 under bullet size give good accuracy (older advice was to size 0.002 under - see 'cynical' section!). This assumes that you don't chuck your ammo around or fire it from a magazine etc.
On the other hand there can be drawbacks to bushing dies.
Neck wall thickness is rarely even around the circumference. When you size from the outside with a bushing you push inconsistencies to the inside - the part that interferes with the bullet. For this reason bushing dies are often best combined with turned necks (that have an even neck wall thickness).
Bushings usually can't size all the way down to the neck/shoulder junction.
Bushing dies don't necessarily result in the best bullet runout.
Here's a couple of alternatives:
Size with a one-piece FL die (without expander ball) then expand the necks with a floating mandrel (such as Sinclair carbide or 21 Century TiN).
Use the Lee collet neck die.
Both the above result in very concentric necks and a very consistent and round neck ID (regardless of neck wall thickness or neck wall uniformity). I personally favour the first of the two if not neck-turning, and my various bushing dies go unused these days.
Couldn't work out the benefits & sounds like you've saved me a quid or two.
Don't get me wrong - they have their place, they're a useful tool and they are doubtless used by many top shooters (not that this necessarily means anything). But if you start with good quality brass and especially if you don't want the faff of neck turning (which in turn depends on having a suitable chamber) you can do just as well by other means.
If you have a rifle with a custom chamber with a non-standard neck-diameter (i.e. slightly smaller), then a standard die won't touch the brass on your neck-turned cases so, a 'bushing' die is the answer.
If you ain't neck-turning, a std. quality sizing die will do the job fine.
