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Neck vs FL Resizing

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britrifles View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: July 14 2020 at 5:38am
There’s been some interesting debate on several other forums of late regarding resizing cases for reloading.  And, the debate has been intense.  

It has been a widely accepted practice to only FL size cases for autoloading rifles, and that’s what I do for my M1 and AR.  The reason is to ensure reliable bolt locking and extraction.  Failure to fully lock the bolt can cause a slam fire in the M1.  I adjust the die to give a cartridge case headspace that falls within min and max using a case headspace gage.  All very simple, has never given me a problem in thousands of rounds each in of these rifles.  And brass life has been very good, I eventually get neck cracks in the .30-06, but never had a case head crack.  I’m sure I’ve loaded my RP .30-06 cases 50 or more times, Win brass cracks at the neck after about 30 reloads.

Bolt rifles, I will neck size.  I use a Lee Collet die for .303, .30-06 and .308.  Two reasons:  significant time saver (no need to lube case and then clean lube off) and seems to lengthen life of the case.  This seems particularly true for the .303. But does it really?  What about reliable bolt locking and extraction?  I continue neck sizing until I feel light resistance to fully locking the bolt. “Light” is a relative word, so say a few pounds pressure with the thumb on top of the bolt handle.  Once I feel this resistance on say 10 out of 40 cases, the next resizing cycle will be using a FL die.  Because the .303 has a very long chamber from breech to shoulder compared to commercial sizing dies, I use a case length comparator to measure the distance to the shoulder on a few of the cases that I feel resistance to bolt fully locking.  I then adjust the FL die to push the shoulder back .003 to .005 inches and check the case in the rifle to be sure the bolt locks with no resistance.

Before I had the case length comparator, I used the rifle chamber as a go/no go gage on the resized case.  But, before I had the comparator, I‘m sure I pushed the shoulder back much farther than necessary, and certainly enough that the sized case would no longer headspace on the .303 chamber shoulder

How case head cracking figures into this I believe is fairly complicated and I don’t really know.  My experience tells me the .303 case head cracks show up after FL sizing the second or third time.  At this point, I have 30 or more neck sizing cycles on the brass, perhaps more than 50.   From others experience, I should not complain and just carry on what I’m doing. 

With a new batch of PPU, I’m monitoring my reload cycles.  I’ve neck sized the brass 8 times now for my 0L Mk 1/2, a new rifle to me, and I’m just beginning to feel slight resistance of bolt lock up in the last few degrees of bolt rotation. I will likely FL size after 10 neck size cycles, setting up the die as explained above, and continue back with neck sizing after that.  I’m thinking of running a new lot of PPU and only FL size with the same method to bump back the shoulder each reload cycle to see what affect this has on case life. 

Benchrest and F-Class shooters will say that FL sizing is more accurate, it offers better alignment of the bullet to the throat.  I doubt a LE rifle is accurate enough to see this difference, so I’m mostly interested in prolonging case life and ensuring reliable lockup and extraction.  I’ve not noted better accuracy with FL sized cases vs neck sized in my rifles. 

I’ve rarely encountered any moderate to heavy resistance to bolt lift by neck sizing, however, I do feel some resistance if I neck size for too many cycles after I first feel resistance to bolt lock up.  Even some resistance in locking and unlocking the bolt is not helpful during rapid fire stages of match shooting, so I’m usually careful not to go into a match with brass that is approaching my threshold for FL sizing. 

I know several forum members who use a FL die to bump back the shoulder, Shamu does, maybe a few others.  Zed and Goosic, not sure what you do.  I would like to hear from our members who shoot a lot and what resizing dies (type and manufacturer) you are using and how many reloads cycles do you get? Do you anneal?  Issues with neck cracking and case head cracking?  

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