Neck Clearance/Turning

[HTSmith]

My neck turning journey began a bit ago when I was getting some larger than normal groups from one of my 6BR's with a .271" neck diameter. A very experienced reloader and former competitive bench rest shooter came over to my bench and found that bullets would not fit back into my fired brass. He said this was likely a problem as I was not getting a clean bullet release. I came back home and set to measuring the diameter of my remaining loaded rounds with a micrometer. I got a maximum neck diameter of .270"--too close (maybe).

I'll skip the long story in between, but I went to the range yesterday with some turned neck rounds that measured .268" and my unturned rounds measuring a max of .270. My first three fouler shots with the unturned rounds went into a bughole despite the normal velocity variation due to the clean bore. The next 5 shots were the turned rounds. The group was good for me (0.3" at 100yds) but the velocity was lower and ES was higher (20 fps) than what I expect from this rifle and load.

Then I fire my old loads with the thick necks (.270"). I got a little better group and the ES was 10 fps. No pressure signs whatsoever.

So I figure I changed the tune of the load by turning the necks because the bullets seated easier in the turned necks. With this little bit of data I certainly don't conclude that unturned is more accurate than turned, but...

What I am asking is if a close neck fit is necessarily a problem or said another way if a bullet won't fit into a fired case is that a problem. What says ye?

(Load info is Lapua brass, CCI450, 30.1 Gr Varget, Berger 105VLDH .025" off)

 

[geo.ulrich]

bullet should drop in a fired case

 

[Alex Wheeler]

George is correct. And notice he said drop. If it takes any force to go through you can still be too tight.

 

[HTSmith]

Thanks much! I just tried to put a bullet back into my turned, fired cases and it took a little force to get them in. This was with .003 clearance (assuming the chamber measures what its marked). How much clearance, in your experience, does it take to get a drop in fit?

The cases have been fired 5 times and have not been annealed if that matters.

 

[geo.ulrich]

Thanks much! I just tried to put a bullet back into my turned, fired cases and it took a little force to get them in. This was with .003 clearance (assuming the chamber measures what its marked). How much clearance, in your experience, does it take to get a drop in fit?

The cases have been fired 5 times and have not been annealed if that matters.

check the case mouth see if it is hitting end of chamber. a fired case will look rolled in at mouth if its hitting an easy fix just trim case length. .003 seems good for clearance you could skim a couple thinner on neck and see if it helps

 

[Chuckhunter]

My competition rounds have .003 thou. neck clearance and the bullets slip right in, no drag. My rule of thumb is better to have a little more clearance than not enough. Especially in a hunting rifle. Let us know how you make out. Mr. ulrich's suggestion is a good one and very easy to check.

 

[geo.ulrich]

Please call me George, when people say Mr. Ulrich I start looking around for my father

 

[Chuckhunter]

Please call me George, when people say Mr. Ulrich I start looking around for my father

You got it George.

 

[BoydAllen]

Questions for the OP: If you are using a bushing die, did you change the bushing for sizing the cases with turned necks? Did you size them again after expanding and turning? As you mentioned, differences in bullet pull, which we can infer from differences in seating force, affect tune. This sort of test mistake happens all the time. The main place I see it is when fellows test primers, keeping every thing constant except the primer. What they should really be concerned with is the best accuracy that they can tune to with a primer.

 

[HTSmith]

OK now I gotta tell some bad stuff, at least for this audience. I size necks with a Lee Collet die. So after I turned the necks, it was back in the die (w/.241 mandrel) for two good cranks of the handle (turn case 180 between cranks). I'm pretty sure the necks were "looser" than the unturned necks because I could feel it when seating the bullets. So I'm pretty sure I changed the "tune" and that could account for the bigger group and higher velocity spread. I've got a bushing sizing die, but the Lee die has given me slightly better accuracy with my no-turn necks. Thanks for all the help. Every day I find out I still have a lot to learn.

 

[gman47564]

any time you change a variable you will have to tweak the powder charge or seating depth to counteract the change you made...I suspect turning the necks gave you a little less neck tension so I would counter that with a tenth more powder and see if that brought it back to life.. my .02 cents worth...

 

[mikecr]

3thou is plenty of clearance, and so is 1thou. You've only changed tension with thinner necks.

 

[geo.ulrich]

.001 you are running in the danger zone slightly different dia. bullet then what .0005 clearance a little carbon then .0002 clearance. I tried fitted necks when it was the rage 30 plus yrs. ago. rifle will shoot better with clearance and more consistant bullet must drop in after firing....same with running brass at chamber length I used to run around .005 clearance to end get a bit lazy and don't trim everytime, start to crimp bullet you get pressure and a crappy shooting rifle. bullet release is where you want to be...

 

[Boatschool02]

Without knowing:
1. Actual dimensions of the reamer (JGS openly states they get +.0005 to work with)
2. Lathe runout
3. Die/sized round runout
4. Quality of neck turning (I recently found out mine wasn't as good as I thought)
5. Quality of loaded round measurement

... these conversations are like discussing cleaning methods with people who don't own a borescope.
In my limited experience, with prepared brass, 0.0030-0.0035 is usually plenty to achieve "drop-in" if everything else is in place. That being said, measure it any way you like: it either drops in or it doesn't.

FWIW, this is on my list of beginner mistakes I used to make while seeking to "min spec" anything that could be measured. Now days, I'll take consistent & sufficient clearance all day long. (Same goes for shoulder set back.)

 

[HTSmith]

I hear you and what you say makes sense, but it makes my head hurt. My chamber is marked ".271" and it was done by very reputable gunsmith that specializes in shortrange bench. My rounds measure .270 at the biggest point using a Starrett micrometer. They chamber with no resistance and shoot pretty doggone good--BUT a bullet will not fit into the neck of the fired brass.

This is the 5th firing on this brass and when I loaded new brass the first time the necks measured .268--so they have grown .002. At this rate of brass growth I'm going to have to turn the necks and it looks like I'm going to have to develop a new load for the turned necks.

Anyhow I think a reamer with say a 273 or 274 neck may be in my future

Thanks for all the advice.

 

[HTSmith]

check the case mouth see if it is hitting end of chamber. a fired case will look rolled in at mouth if its hitting an easy fix just trim case length. .003 seems good for clearance you could skim a couple thinner on neck and see if it helps

I measured length on about 10 of them and none were as long as the chamber print indicates but there was a lot of variation so I'm going to trim them all. Thanks for the advise.

 

[HTSmith]

Just another update. Based on Boatschool's post (that I can't find anymore), I measured the diameter of some custom 103 Gr bullets that I got just last week (my first customs). They are "fatter" than the lot of Bergers I've been shooting for sure. Dang there's lots of pieces to this puzzle.

 

[Ccrider]

Yea, but you got the right answers. Thinner neck requires a smaller bushing or more powder to stay in the same tune. More clearance is better than less. Don’t be afraid to play with the bushing size once you get the load tuned. Can make a big difference.