Neck sizing or full length problems. Advice needed

[tisme]

Hi
I'm new to comps and this weekend did my first F T/R comp. First two rounds were ok getting 5th in the second match. In these rounds I used ammo that had been full sized before reloading. The next two rounds were no where near as good, scores were 20 points down! The only difference was the ammo was neck sized, not FL, in the last two rounds.

Tested the remaining ammo this morning and the first ammo groups very well (FL), the second, neck sized ammo won't. Both lots of ammo are Lapua cases, 46.8 gr varget, 155.5 bergers.

What have I done wrong?

 

[brian427cobra]

FL every time, set up your die to bump the shoulder .001-.0015, your ammo will chamber and will be accurate.

 

[tisme]

Thanks for that. Does neck sizing increase the capacity so change the load and POI?

 

[Erik Cortina]

Thanks for that. Does neck sizing increase the capacity so change the load and POI?

It depends. The capacity is the same because you are shooting it in the same chamber. How are you setting up your FL sizing die? How much are you bumping the shoulders back?

I always advise to F/L size every time. It will allow your ammo to chamber/extract easily and stay consistent.

 

[BradY]

Its a shame alot of FL dies arent sold with comparators like the whidden dies. That way you can set them up properly. The old instruction of screw down to touch the shell holder and screw back out 1/4 of a turn or what ever it is, just doesnt cut it if you want the most out of it.

 

[tisme]

Thanks for the advice really appreciated
I think your both right I only have RCBS dies and the instructions say screw in down until ............... I have no idea how far I bump the shoulder back.

What dies should I get

 

[BradY]

You can get by with the dies you have, but you will need something like this to measure it.
http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/hornady-lock-n-load-headspace-kit-prod55256.aspx

Just make sure your caliber is compatible with it. Start with your dies out where they normally are and measure a fired case and zero your calipers. Then size your case and measure again. You want the cases coming out about a thou smaller. When the die is set to give this each time, lock the ring off on the die and your set.

 

[Erik Cortina]

If you can remove firing pin easily you can do it without a gauge. That's how I do it because I prefer direct measurements.

 

[Bart B.]

Make a set of these labels (on sticky back label paper) to put on your die's lock rings so you can adjust the die height in the press accurately.

http://s860.photobucket.com/user/jepp2/media/DieAdjustment-1.jpg.html

I've suggested to some reloading die companies to stamp their die's lock rings with one side with the .002" marks and the other with .004" ones. That was years ago.

Note that the type and amount of case lube used will have an effect on how much case headspace spread is after full length sizing a batch of cases. It's normal to have a few thousandths spread which is caused by how much spring the press frame has as well as how long the case stays up into the die before it's pulled back out. Using the right height Redding competition shell holder in the press' ram that the die stops against keeps that spread down. I've not noticed any accuracy problems with cases with a .002" spread in headspace as long as head clearance on loaded rounds is no more than .003".

 

[mikecr]

FL sized cases are not the same H20 capacity, and so initial confinement/load density is different.
You would need to work up a load with neck only & bump sized cases, just as you might have with FL sized.
You also need to know exactly how much you're bumping shoulders.

How crooked are your cases?
Have you measured loaded runout?

 

[Cigarcop]

If you can remove firing pin easily you can do it without a gauge. That's how I do it because I prefer direct measurements.

+1 No other way in my opinion

 

[tisme]

Big thanks to you all for the help. I'll get some gauges and have a go with the firing pin removed (if I can work out how to do it this way) to see what way I like best. I'll also try and do some testing on just neck sized cases but I'm very low on Varget, just enough for the comps and I doubt if we will see any more this year.

 

[Bart B.]

Best wishes in your accuracy venture with neck only sized cases.

It's my opinion that best accuracy comes from full length sized cases properly done with dies whose neck diameter's a couple thousandths smaller than that of a loaded round's neck. Full length bushing dies, for example, are the best available over the counter ones. Or just hone out the neck of your existing full length sizing die with Flex Hone:

http://www.brushresearch.com/brush-types.php?c1=4

One-piece sizing dies have their necks perfectly and consistantly aligned with their body section resulting in straightest necks on cases. Neck only sizing dies don't do that.

 

[Shynloco]

Best wishes in your accuracy venture with neck only sized cases.

It's my opinion that best accuracy comes from full length sized cases properly done with dies whose neck diameter's a couple thousandths smaller than that of a loaded round's neck. Full length bushing dies, for example, are the best available over the counter ones. Or just hone out the neck of your existing full length sizing die with Flex Hone:

http://www.brushresearch.com/brush-types.php?c1=4

One-piece sizing dies have their necks perfectly and consistantly aligned with their body section resulting in straightest necks on cases. Neck only sizing dies don't do that.

After years of chasing consistency in my loads and accuracy down range, plus trying all sorts of things to improve it, what Bart suggests is the way to go...Full Length Bushing dies where you can set the neck tension of a couple thousands smaller than the loaded neck size. Also follow Eric's advice to hep you find the sweet spot when you resize. The brass also needs to be monitored in terms of hardness which means annealing something like every 3- 5 firings, but that's another issue that you will have to decide upon or set up a regimented schedule that makes your brass perform at it's best.

Alex

 

[Erik Cortina]

Here's how you do it.

1. Remove firing pin from bolt. If you don't know how just ask.
2. Back your F/L die so it only neck sizes. Chamber a neck sized piece of brass. You should feel resistance when closing the bolt.
3. Adjust the die down a little at a time and keep trying to chamber the brass. Brass will get tighter right before it fits properly because squeezing the sides of the brass will make the brass grow longer.
4. Adjust your die to where the bolt will close on a piece of brass with very little resistance (bolt should close on its own about 80% of the way).
5. Lock your die and you are good to go.
6. F/L size always. If you want consistent ammo you must be consistent in your reloading steps.

Good luck.

 

[Bart B.]

Adjust your die to where the bolt will close on a piece of brass with very little resistance (bolt should close on its own about 80% of the way).

When I tried this method, accuracy was never as good as when the bolt closed freely on the case. But only with about .001" to .002" of head clearance of the chambered round.

I don't think the bolt will close and lock up in exactly the same place for every shot when it binds a bit closing on a chambered round. Especially if the bolt face isn't squared up with the chamber axis. Besides, .308 Win cases center perfectly up front when they're fired anyway. Even with a lot of slop (case head clearance to the bolt face) when the firing pin finally detonates the primer. When the bolt closed with a bit of extra force needed, shot strung out more horizontally than when the bolt closed easily; at least in my tests and that of others I've talked about this issue.

Isn't a binding bolt closing on a chambered round one of the red flags short range benchresters got with their neck only sized cases after 4 or 5 cycles between the chamber and sizing die? 'Twas a signal the case shoulder had finally ended up far enough forward that the bolt no longer closed easily and that case had to be minimally full length sized.

 

[Erik Cortina]

Bart B., you are talking about something totally different.
Size a piece of brass like I told you, and you will realize that the "resistance" is extremely minimal.

How do 308 cases self align when fired? Would that not be true for all cases besides .308's?

 

[Bart B.]

Eric, I don't think I'm referring to anything different. Be more specific about that and I may well agree with you.

.308 Win cases (cartridges) don't self align; at least in my opinion. They only move in the chamber by the external forces put on them by parts in the bolt. Excluding the bolt binding a bit on a case that's got more headspace than the chamber does, .308 Win cases/rounds are no different than any other bottleneck case that headspaces on their shoulder. I think you already know what external forces there are on such a case after the bolt's closed on it and when it's fired. They're what centers the front of the case in the chamber and positions the back end of the case against the chamber wall. And every case/round is done so very repeatably as long as the bolt doesn't bind up on the bolt when closed on them.

 

[Erik Cortina]

I have always had great accuracy with the method I describe. Coincidentally, Tony Boyer describes the same method in his book. All I use is custom actions, so maybe the fact that they are "straighter" than a factory action is the reason I don't have problems.

 

[Bart B.]

I agree that custom aftermarket actions are "straighter" than factory actions. I've got a 4-lug Paramount action on one of my Palma rifles and it's as straight as can be. But it's always shot most accurate with a thousandth or two head clearance on full length sized cases. Sub half MOA for 20 consecutive shots at 800 yards with such ammo is good enough for me.

The smallest series of 10-shot groups at 600 yards I know of were all made with a wood stocked pre-'64 Win 70 with cases so sized. Standard SAAMI minimum chamber, too. All 12 or so of them were under 1.5 inches down to the smallest at about 0.7 inch. Then a 40-shot group with that same ammo went into 1.92 inches. All shots in each group were fired about 20 to 25 seconds apart.

There are some strange things that make one rifle and ammo system shoot well but in another it doesn't.