Precision mic

Kentucky

Well-Known Member
Joined
Dec 19, 2014
Messages
101
Hey folks, another head scratcher for me. I have used a comparator for my sizing for along time and never blew myself up. I was recently introduced to head spacing using the RCBS Precision Mic. I could t wait to use it on some already sized 22-250 bras. To my surprise I had .010 - .012 variances. I set up and sized more brass, measuring each one and low and behold, I cannot keep my size consistent. One will be +.005 and the very next one may be -.005. I am hoeing RCBS ram with Hornady dies. My Buddy was doing the same and decided to buy precision shell holders. His are now precise consistently. Can anyone explain to me why the shell holders would make such a dramatic difference?
 
Are you saying a shell holder is making the difference? If so, the only thing I can think of is if your friend has adjusted the die with a little "cam over" in the stroke.

The other thing that comes to mind not related to a shell holder is the brass may be work hardened and in need of annealing.
 
I think you are talking about the Redding competition shell holders. These are useful in setting the shoulder bump. There are five in a pack, each is .002" higher than the other. Start with the small one, work up until the brass fits the chamber snuggly. The Precision Mic measures the amount of bump, if you also buy the dial indicator.
 
When sizing, do you keep your ram at the bottom of the stroke for a couple seconds? Makes a difference. If sizing too fast, your brass could be springing back, giving inconsistent readings.
 
When sizing, do you keep your ram at the bottom of the stroke for a couple seconds? Makes a difference. If sizing too fast, your brass could be springing back, giving inconsistent readings.
I have not done that, it's worth a try. Thank you
 
I think you are talking about the Redding competition shell holders. These are useful in setting the shoulder bump. There are five in a pack, each is .002" higher than the other. Start with the small one, work up until the brass fits the chamber snuggly. The Precision Mic measures the amount of bump, if you also buy the dial indicator.
Yes that is the set I am talking about. I'm trying to wrap my head around why these shell holders are so precise on length and my Hornady ( and his ) are so erratic. Going from a .010 variance to a consistent.002. I guess I will just have to accept the facts and stop trying to figure it out. Thanks for your time and help
 
Any given shell holder should give you consistency (depending on brass springback/softness). Might the "bad" shell holder have a burr or some crud on it somewhere? Is your technique at the bottom of the stroke consistent?
 
Consistency....

Same amount of lube, same stroke, same timing ect. It matters a lot for consistency of results. Annealing will help A LOT too
 
I use my RCBS precision mic to measure and set headspace to .001-.002 back. The RPMic at zero is at min SAMMI spec. I am not using the Redding shell holders as what I am doing works for me. I have found that As part of the process, I have my headspace where I want it. Then I use a Hornady concentricity tool to get them at concentric. IMHO it sounds like a consistency issue. Once I get a case sized, all the following are the same.
 
[QUOTE="Pete Callamaras, post: 1629844, member:

Then I use a Hornady concentricity tool to get them at concentric. [/QUOTE]
 
Warning! This thread is more than 6 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.
Top