RCBS Concentricity Gauge

[Matt]

For the bit of testing I do the RCBS is fine. I’ve found it’s important to have very clean cases and case necks ( inside and out) to get smooth readings. The only “sorting” I do is case neck thickness and that’s steel on steel. The necks need to be very clean to get accurate readings. The other concentric issues I’ve found can be determined with a case or two and are based on the chamber at firing or what your sizing and seating dies are doing. It’s nice that they have a hook to check head separation too.

 

[CWLONGSHOT]

RCBS called back!!

Apparently there is two sets of "V blocks with this tool. I only remember one and dont remember the cap on the post... So the nice lady found my email. Said WOW! Hahahaha. And that she would send a set if lg & sm V blocks and a "cap".
But that they was very short handed so might be two weeks for delivery.

Im still waiting on the shims to clock my meter rods in the uniflows.

CW

 

[fiver]

2?
hmm.
i better go see if i still have the box.
i do like the ball bearing idea though, that would sure help make rolling the case easier.

 

[nanuk]

Depends. The main use of a concentricity gauge is to determine exactly what part of the process (including the FIRING process!!) is causing concentricity issues. If it's the sizing process such as off-center flash holes and a Lee collet sizing die, then pull out or grind off the decapping pin and try again to see if it's the press alignment causing the problem. If you meant post-sizing a loaded cartridge with the collet die....um, no.

Could one just use some washers to lift the collet high enough to just be above the flash hole, so the collet "Floats"??

 

[nanuk]

Okay, here's another question: Using Sinclair's gauge, for instance, to determine runout, would Lee's collet neck sizer die correct it? With the decapping pin removed, of course.

I've used the LEE Collet sizer to size necks where the flat based bullet entered crooked and bulged one side of the neck so much, it wouldn't even come close to entering the chamber

once I squeezed everything concentric (or as much as I could tell) they chambered fine

ima use that technique to load some .312 revolver bullets in my 30-30. they simply won't seat correctly no matter what I have done. As soon as there is ANY neck tension, they go cockeyed.

these are only for plinking in the yard for pest control, but I'd love to have a concentricity gauge to test the runout, AND ima pull some bullets to see how much damage is being done

 

[fiver]

might be easier if you put a lot less neck tension on those cases.
could try using your 308 die to NS the 30-30 cases.
i use a 30 cal. NS die to get 309 case ID with my 30-30's,,, it's enough to hold my 310 bullets.
anyway it works out because 30-30 cases are much thinner than 308 cases are.

the bonus with the 308 die versus a neck size die is you can usually buy larger expander balls [310,311] like for a 303 brit or 7.62X39 to open the neck a bit further.

 

[nanuk]

Fiver, if you are talking to me, I opened the mouth, and the .312's just dropped in with no room to spare
I sized the brass with a LEE Collet sizer til the .312's would just about fit, and they would seat cocked
I used a Lyman M 31cal expander, and it didn't help

I am sure it is my technique. When I get some time, I'm going to work on this issue.

Good idea on the 308Win sizer, gonna try that. I use the 308Win LEE FCD if I need to with the 30-30.

 

[fiver]

i don't know about M-dies or the like.

it might be your seating technique too.
i like to spin and seat in small steps, either the case gets spun or i lower the die and seat in 4-5 steps.
the first step is to just bump the bullet in the case like a millimeter, and then i work it down from there.