How Much Do Your Bushings Size the Neck?

[brshtr]

I decided to measure how much my bushings were actually sizing my necks and got some unexpected results.

The cases are Lapua 6mmBR Norma cases that I shoot in a 6BR with a .272 neck. The fired cases come out of the rifle with a .271 outside diameter.

I sized them with Redding titanium nitride bushings in .266 and .267. I expected them to come out of the die a tad larger than the bushing diameters after accounting for springback.

With both bushings the cases came out of the die at .265.

I sized at least a half dozen cases with each bushing. Same results for all.

These cases have been fired about 7 times and recently were annealed. I am measuring with a Mitutoyo caliper whose accuracy I have verified.

So then I got the same brand of bushings in .268 and .269. Each one sizes .001 less than the diameter of the bushing.

Is it typical in your experience for bushings to size smaller like that?

Dave Rabin

 

[tashabay716]

I have had the same experience. My Redding .267 bushing sizes the neck .2665 and the .266 sizes .265 and the .265 bushing sizes .2644. All 6 of my Neil Jones bushings size right on the money except for the .265 bushing and it sizes .2658-almost .266. I have sent it back to Neil for a re-do on the .265. The Reddings are the most inconsistent and may be because of the titanium coating on the bushings. I have ordered another Redding .266 and .265 just to test consistency.

 

[LHSmith]

You know I never actually measured the neck OD after sizing.......to me it's a meaningless number. What matters is the loaded round OD and how much side to side clearance there is to the chamber neck. Then I use various size bushings to find an optimum tune. I know some claim the size marked on Redding bushings are not true, but when I change bushing size, groups either improve or get larger ......and this is repeatable if loading in like conditions. Re-measure the neck OD on sized cases after sitting a few weeks and note some change.
FWIW- I avoid Ti N coated bushings.

 

[artbosco]

My bushings size the neck so that when I'm finished sizing, the combination of bullet, brass, powder, primer, seating depth and neck tension have bullets going through the same hole.

How much it sizes doesn't really matter, only the results matter.

What you need to be concerned with is that the OD of your loaded round gives you at least .002" total clearance in the neck chamber for safety, and that you've started with at least .001" less than the Outside Diameter measurement, with a bushing. Apply in increasing .001" increments until you've achieved your goal, in combination with seating depth, and the bullet, brass, powder, and primer components.

Trying to measure a soft substance like brass with a handheld device is an exercise in futility since it doesn't take much force, or lack there of, to arrive at a reading of + or - .001", regardless of tool manufacturer.

If you don't think your bushings were constructed precisely as advertised through their markings, send them back.

 

[KMart]

I wish I had read this thread befor I hit the "buy" button a couple of hours ago
Live and learn. It gets expensive sometimes.

 

[jimcasey01]

Freshly annealed brass, my brass finishes at the stated bushing diameter. I assume that the bushing is sizing .001 smaller, then the brass is springing back.

 

[tenring]

Only the results really matter. For the sake of consistency, I note the stamped bushing size on each reload. When I find the right tune, I have no trouble repeating it. BTW, using a bushing .002" or .003" less than loaded diameter at the pressure ring does not always guarantee good results. My 30 BR loaded neck measures .328 but the best bushing for it is a .322. Some barrels like a hard fit.