A concentricity gauge story

[AlNyhus]

Yesterday, I test fired five rounds in a new barrel chambered in 30BR to begin the break in and more importantly, to get the f.l. bushing die set up for shoulder bump. The cases came out looking great and per my normal routine with a new chamber, I rolled them across the Sinclair concentricity gauge....they barely wiggled the needle off the black '0' mark. Another great chamber by 'Humble' Henry Rivers. Thank you, 'Humble'! This was the first chamber done with my JGS 30BR Robinett V2 reamer.

The die body was set up for .002 shoulder bump (no bushing in it). Run out was checked again and once more, the needle barely wiggled off the mark...same as right out of the chamber. Next, I plopped my bushing in and sized the case. Now there's .004 runout.

Took the die out of the press, double checked everything and repeated the process with another case. Same results.
Had another bushing of the same size and substituted that. Bingo...now we're looking at less than .001. With a bullet seated, there was right at .001 runout. I pin gauge all my bushings for size but this is the first time I've had a bushing that's shown that kind of run out.

I don't get slaved to the concentricity gauge. Once everything checks out, it gets set aside unless I change something. Like all good tools though, when you need one...nothing else will do.

For what it's worth. -Al

 

[BoydAllen]

Yep, there are significant differences in the runout different bushings produce. One thing that most of us will never have a way to check directly is how square the hole is to the faces of the bushing but we can certainly test the effect the bushing has on brass. Question, have have you looked at carbide bushings this way? If so, what were the results?

 

[rwj]

Did you chamber the case having .004” runout?

 

[Eagle Six]

Neck runout was .003 with the bushing included with my die. I replaced it with another brand and the runout went to less than .001. Same brass, same prep.

 

[AlNyhus]

Boyd, I've got a few 6mm carbide bushings...they've all checked out fine. The common line of thinking is that carbide bushings must be better. But a good pal has one that's as wonky as this steel bushing. Like Ronald Reagan said: "Trust, but verify." -Al

 

[AlNyhus]

Did you chamber the case having .004” runout?

Yes.

 

[Eagle Six]

The .003 bushing is Titanium Nitride (Redding), the .001 is polished stainless (SAC). I have three of the SAC bushing .287, .288, and .289 and they all have .001 or less runout.

 

[STS]

I have a small box with 5 or 6 bushings that have earned their way into 'the box of shame'. Bushings that do exactly what Al just experienced. It's actually not difficult at all to diagnose a bushing that the hole is not straight in. Mark the bushing at 0, 90, 180 and 270 degrees. Measure the bushing wall thickness with a ball mic at those positions on each end of the bushing. Compare measurements end to end, and side to side, and if the hole isn't on the centerline of the bushing it is obvious. Wilson bushings have a .0005 taper so you have to take that into consideration when evaluating. It's not at all difficult to do.

 

[Eagle Six]

I've used my mediocre OD and ID mic's to compare sides, ends, and every witch way and the SAC bushings appear to be within .0002 and the Redding is within .0012 at various points. All of witch seem to be far within the clearance of bushing in die seat. I do not have a means to measure the square of the bushing ends. Yet I get .003 with the Redding and .001 or less with the SAC. That makes me happy.

Keep in mind I'm a Redneck Machinist (hammer, file and hand drill) and I was trained by my grandfather turkey farmer who instructed me that a hammer is for putting wood screws in and a screw driver is for taking them out, and I have pretty much followed that mentality as I cobble things together!!

I try for the best loading precision I can, but primarily rely on the target for results!

 

[Chris Edmondson]

Question about case neck runout for you guys:

Considering the silly sketch below where the top piece is perfect, the next piece shows the neck in the same horizontal plane as the body but it's vertically offset, the third piece shows the neck at a different angle than the body, and the last piece shows both defects.

Which one is believed to be the most common affliction? I don't know the answer, just asking .

 

[ShtrRdy]

@AlNyhus - did you try flipping the bushing over to see if the result is different?

 

[BoydAllen]

Question about case neck runout for you guys:

Considering the silly sketch below where the top piece is perfect, the next piece shows the neck in the same horizontal plane as the body but it's vertically offset, the third piece shows the neck at a different angle than the body, and the last piece shows both defects.

Which one is believed to be the most common affliction? I don't know the answer, just asking .

View attachment 1521376

I am pretty sure that the angled neck is the most common. The way that you can tell is by measuring runout in several places on the neck and on the seated bullets. Bullets tend to follow the necks they are inserted in and extend any angle with the result that runout increases the further out from the shoulder you measure.

 

[AlNyhus]

@AlNyhus - did you try flipping the bushing over to see if the result is different?

No, I haven't.

 

[Timon]

I had this issue with my Redding S die, with Redding bushings. I switched to Short Action Custom bushings and my run out was one thousandth or less. Just well made bushings. I then went to a Whidden die, but stayed with the SAC bushings and again, next to no run out. Currently, I’m using a SAC FL sizing die, with their bushings. This setup is the best I’ve ever used.

 

[D Coots]

Yesterday, I test fired five rounds in a new barrel chambered in 30BR to begin the break in and more importantly, to get the f.l. bushing die set up for shoulder bump. The cases came out looking great and per my normal routine with a new chamber, I rolled them across the Sinclair concentricity gauge....they barely wiggled the needle off the black '0' mark. Another great chamber by 'Humble' Henry Rivers. Thank you, 'Humble'! This was the first chamber done with my JGS 30BR Robinett V2 reamer.

The die body was set up for .002 shoulder bump (no bushing in it). Run out was checked again and once more, the needle barely wiggled off the mark...same as right out of the chamber. Next, I plopped my bushing in and sized the case. Now there's .004 runout.

Took the die out of the press, double checked everything and repeated the process with another case. Same results.
Had another bushing of the same size and substituted that. Bingo...now we're looking at less than .001. With a bullet seated, there was right at .001 runout. I pin gauge all my bushings for size but this is the first time I've had a bushing that's shown that kind of run out.

I don't get slaved to the concentricity gauge. Once everything checks out, it gets set aside unless I change something. Like all good tools though, when you need one...nothing else will do.

For what it's worth. -Al

Al

Did you try shooting a group with each bushing?

 

[Eagle Six]

@AlNyhus - did you try flipping the bushing over to see if the result is different?

I have and it made little difference.

 

[JEFFPPC]

Well this thread made me drag out my Sinclair Concenricity Gauge, your fault Al. Just fired my first rounds out of my first ever 6bra barrel done by Attrum. Annealed them then sized them with a bushing in my Harrells die, neck stays in .001. I guess I will put the tool away again for a few more years, lol. I shot my first 4 groups, 3 shots, today. 30.8, 30.9, 30.0, 30.1. First 3 all cloverleafs but not quite touching. Every tenth getting closer, showed me it wants to shoot round. I like round. 30.1 sucked them to a tight cloverleaf at .153. I hope to shoot 30.2 thru 30.6 tomorrow, looking good at this point.I started out .015 in. After I settle on charges I will revisit seating but may not need to as all groups show round.....That makes me smile. Looks like Andy Murtaugh did me a good job.

 

[Old Navy]

Yesterday, I test fired five rounds in a new barrel chambered in 30BR to begin the break in and more importantly, to get the f.l. bushing die set up for shoulder bump. The cases came out looking great and per my normal routine with a new chamber, I rolled them across the Sinclair concentricity gauge....they barely wiggled the needle off the black '0' mark. Another great chamber by 'Humble' Henry Rivers. Thank you, 'Humble'! This was the first chamber done with my JGS 30BR Robinett V2 reamer.

The die body was set up for .002 shoulder bump (no bushing in it). Run out was checked again and once more, the needle barely wiggled off the mark...same as right out of the chamber. Next, I plopped my bushing in and sized the case. Now there's .004 runout.

Took the die out of the press, double checked everything and repeated the process with another case. Same results.
Had another bushing of the same size and substituted that. Bingo...now we're looking at less than .001. With a bullet seated, there was right at .001 runout. I pin gauge all my bushings for size but this is the first time I've had a bushing that's shown that kind of run out.

I don't get slaved to the concentricity gauge. Once everything checks out, it gets set aside unless I change something. Like all good tools though, when you need one...nothing else will do.

For what it's worth. -Al

Thanks very much for posting that. I have had problems with runout in the past. How would you check for that. Veniers maybe? Was the bad bushing a name brand?

 

[AlNyhus]

Al

Did you try shooting a group with each bushing?

No I haven't. Since this is a new barrel on a new build, I didn't want anything to skew initial results. At some point I'll A-B-A it and see how it acts 'on target'. Assuming this barrel likes the usual 30BR tune up routine, it will be interesting to see if the neck tension and seating depth minimizes the  presumed effects of excessive runout.

 

[D Coots]

Thanks Al.