Partial Neck Sizing

[amlevin]

First let me state that I am working with a Factory Barrel and Chamber, no custom anything.

The chamber has lots of freebore. So much in fact that if I load long enough to contact the rifling, there is barely enough bullet in the case to keep it straight.

I've run the idea of partial neck sizing as a means of at least keeping the bullet centered in the freebore prior to firing. I have been neck sizing my brass for some time using a Lee Collet Die and get great results but lately started using a Forster Shoulder Bump/Neck Size bushing die.

What benefits would I possibly realize by leaving a small "centering collar" at the shoulder/neck junction? In theory it at least should "aim" the bullet at the center of the throat.

Anyone with experience using this method with factory chambers? Results?

FWIW, the caliber is .308 and the rifle is a Remington 5R Milspec.

 

[ReedG]

You can partial neck size with the Lee Collet Die by getting a washer of the thickness you want and hole large enough to loosely fit over your case. Place the case in the shellholder, put the washer down over it, and resize. Whatever thickness of washer you use will leave that portion of the bottom of the neck unsized. I do that with all my .223 factory guns with good results. Of course, you have to adjust the die to properly work with the washer in place.

 

[MGYSGT]

I only size about 1/2 of the neck length and it seems to work well. I do that on my .223 and 30 BR.

 

[lpreddick]

i've tried partial necksizing using a bushing sizer for the same reason and discovered the following...if you seat a flatbase bullet BELOW the sized neck the pressure ring at the base of the bullet will drop below the last bit of sized neck and often you can push the bullet deeper by hand...not enough grip on the bullet remains since the majority of this grip on a flatbase is at this pressure ring. boat tail bullets are not as likely to do this since most don't seem to have this little bulge where the bearing surface goes to the boat tail. keeping the base of the flat base bullet in the sized neck works as long as seating into the lands doesn't push the bullet pass the end of the sized neck. try seating one below the sized neck and see if you can push it deeper...scary if it happens in your gun. p.s. a flat base bullet's pressure ring usu measures .0005 in greater than bullet bearing surface dia. once had some berger 25 cal 110 mef bullets whose ring was .001 greater and they actually fell into the case if seated thru the neck.

 

[amlevin]

I only size about 1/2 of the neck length and it seems to work well. I do that on my .223 and 30 BR.

Can you quantify any increases in accuracy? Group size with cases partial vs full neck sizing?

 

[MGYSGT]

I only size about 1/2 of the neck length and it seems to work well. I do that on my .223 and 30 BR.

Can you quantify any increases in accuracy? Group size with cases partial vs full neck sizing?

For me, it shoots better. I am not talking about a lot. Mabey from a group just touching to a group hugging. Might be a mind problem, but the groups, are more consistant. Just seems, that by only doing 1/2 the neck, the cartirdge self aligns to my chamber. It made sense to me, so I tried it, and I was happy at the results. I realize that all chambers are imperfect to some point, but then so are dies. So by giving a little movement to the bushing in my die, I think I remove some of the tension introduced by the die or chamber. Of course, I have been wrong before, just ask my wife.

 

[lpreddick]

the unsized portion of the neck does't actually touch the neck portion of the chamber since after firing the neck expands to the full diameter of the chamber, THEN "springs" down about .001 in. i once thought it stayed the same as the chamber and partially sized for the reason. if bullet runout in a partially sized neck is excessive, then accuracy could suffer, esp if this runout is corrected by total neck sizing. mine are the same and i can't see much difference on paper.

 

[mikecr]

Full length neck sizing isn't going to help with runout(actually adds to it), it leaves chambered necks even looser, and it puts your donuts back into play.
Partial neck sizing, like all other partial sizing, reduces runout over full sizing.

amlevin, don't forget to mind your head spacing, as this will influence your results here.

 

[Tozguy]

First let me state that I am working with a Factory Barrel and Chamber, no custom anything.

The chamber has lots of freebore. So much in fact that if I load long enough to contact the rifling, there is barely enough bullet in the case to keep it straight.

I've run the idea of partial neck sizing as a means of at least keeping the bullet centered in the freebore prior to firing. I have been neck sizing my brass for some time using a Lee Collet Die and get great results but lately started using a Forster Shoulder Bump/Neck Size bushing die.

What benefits would I possibly realize by leaving a small "centering collar" at the shoulder/neck junction? In theory it at least should "aim" the bullet at the center of the throat.

Anyone with experience using this method with factory chambers? Results?

FWIW, the caliber is .308 and the rifle is a Remington 5R Milspec.

If you are neck sizing then the unsized body of the case should already be 'centering' the round in the chamber to some extent. Partial neck sizing shouldn't make much difference in that situation. I partially neck size all my loads for target work but can't prove what difference it makes. It seems like the unsized portion of the neck seals the pressure really well and makes the necks easier to clean on the outside.

 

[243winxb]

Partial Neck Sizing with a Full Length Bushing Die in Rem 40X

Using FL sizing bushing die in 243win. Testing shows better accuracy when sizing only 1/2 of the neck. Size 3/4 or more and accuracy is not as good. Unsized part of neck turned brass, will expand to the factory chamber, no spring back after about 3-4 firings. Now have 17 & 18 loadings on the 2 lots of Win. brass. No annealing. Now the strange part is, on firing, the sized part of the neck is not expanding as much as the unsized part, looks strange. Measuring the loaded rounds neck diameter over the sized area now shows a variation in wall thickness. Did not before. Maybe brass needs to be turned again?? The pressure ring has not been a problem for me, when bullet is seated below the sized area. Using .002" neck tension. Could be why?? Bullet jump is very long, time for a new barrel. Need bigger social security checks. ;D

 

[lpreddick]

turning necks again? you bet. i had a 22br with a .251 neck. turned 6br brass just enough to measure .248 after necking down to .22cal and loading. shot great. then pressure problems with primer pockets really loose. measured loaded neck again and they measured .2495-.250. turned them a little and back shooting like before. got a new 22 br and same problem noted early. i'm measuring loaded necks now when i trim since if the brass "grows..flows" in length, then seems logical that it's thickness also increases.