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Measuring for Bushing Size. Help!!

 
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  #1  
Old 05-16-2009, 11:57 AM
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Measuring for Bushing Size. Help!!

Ok I haven't posted here for a while because usually I can find all the info I need via search.

I need help determining the sizes of bushings to buy for my 7mm Rem Mag. I have taken two different measurement methods many times.

1) I measured the diameter of the case neck after reloading with a Lee Collet Die.

It measured: .309; .308 1/2; and .308 fairly consistently.

2) Using an RCBS Case Master I measured the neck thickness, times by 2 - then added the bullet diameter (.284).

Case neck thickness: .014
X by 2: .028
Add .284: .312

Using 2 different methods I got 2 totally different measurements!! Now I understand that I need to subtract .001 to .002 from the latter and approx .002 from the first method because of brass spring back.

What am I doing wrong??

I checked to see if I was measuring my neck thickness incorrectly (Nosler Custom Brass) because the RCBS Case Master seems a little fickle sometimes. Keep getting .014...

I MAY be putting too much pressure on my downstroke using the Lee Collet die which would make the necks too tight (possibly??).

ANY SUGGESTIONS??? Getting rather frustrated here.... Don't want to buy the wrong bushings.

Thanks for the help.

Jim
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Old 05-16-2009, 12:15 PM
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Re: Measuring for Bushing Size. Help!!

I've used thickness measurements just as you did for years, based many reamers on them, and have never seen a discrepancy.
I think your 'Case Master' is wrong.
Get a Sinclair..

I would tend to believe your outside loaded neck measurements. No way to get it wrong.
And for smallest cases measuring .308, I'd go .306 bushing.

Never used collet dies.
What bushing die are you going to?
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Old 05-16-2009, 12:37 PM
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Re: Measuring for Bushing Size. Help!!

Well the easiest way to do it is to measure the outside neck diameter of a loaded round and subtract the bullet grip you want.

When you said

"I measured the diameter of the case neck after reloading with a Lee Collet Die."

did you mean to say after RESIZING with a Lee Collet Die? I think Mike thought you meant after seating a bullet but then the Lee Collet would be confusing.

Anyway, seat a bullet, measure the outside neck diameter with a caliper and subtract the bullet grip, usually .003". For instance if the OD of the neck was .312" then

.312"-.003"=.309"

get a .309" bushing and you can also get a .310" bushing to give a little lighter grip if you want.
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Old 05-16-2009, 02:07 PM
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Re: Measuring for Bushing Size. Help!!

Thanks for the quick replies! Just to clarify - I neck sized with a Lee collet die then seated with a RCBS competition seater. The ammunition is fully loaded when I measure the case neck.

I am leaning towards the Redding S Bushing Die... Any other suggestions?

I did measure the case neck thickness again with the RCBS Case Master and applied pressure to the "case neck pin sleeve" which tilted my brass up a bit straighter as I measured. That's one of the problems with the RCBS is if you have heavier brass (larger caliber) the case neck pin sleeve is not heavy enough to keep the inside of the neck held tightly against the case neck pin. The brass is horizontal and tilts slightly down towards the butt of the brass.

Anyway, doing this I got a measurement of .011 neck thickness. That gives me .306!! Ugh... I think I will adjust my collet die, load a few more rounds, and stick to the measurement I get with a loaded case.

Any suggestions??

Last edited by drenge; 05-16-2009 at 02:10 PM.
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Old 05-16-2009, 02:17 PM
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Re: Measuring for Bushing Size. Help!!

"I am leaning towards the Redding S Bushing Die... Any other suggestions? "

Yes. Stick with the Lee Collet.

Don't get caught up in the idea that a more expensive and fancy die will be superior, it won't. Unless you turn your necks to a consistant thickness ANY bushing die will give you neck tension that varies with the neck thickness and you have already measured that difference. All that's really important to us is the inside diameter of the necks and the Collet die insures that.
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Old 05-16-2009, 02:30 PM
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Re: Measuring for Bushing Size. Help!!

Thanks boomtube. I bought a neck turner for that reason. I'm trying to lower my ES (standard deviation) so I'm not stringing vertical at distance. I've played around a lot with powder load and seating depth. Still can't get ES under 25. Thought a bushing die would maybe help a little. But I've read the many opinions that suggest it's "90% powder and depth and 10% everything else".

I'm starting to get into the "everything else" part... My runout is very low with the Lee Collet. So I figured maybe it's my neck tension. I don't know... It's frustrating because I'm under .4 " at 100 yards. It's the distance that is killing me. Hopefully my chrony is accurate enough. In any case when I should past 500 yards I'm high and low because of my ES (I assume).
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Old 05-16-2009, 02:45 PM
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Re: Measuring for Bushing Size. Help!!

Along with BoomTube's response there was a good discussion about Collet die adjustments here: Lee Collet Die Adjustment - Benchrest Central Forums

Good luck
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