Neck Bushing Sizing

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Sep 17, 2022
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All,

I am new to reloading and am starting out with 7mm-08. Like a "noob" I did not realize a full length bushing die needed a separately purchased neck bushing. I plan to start out with new starline brass and either acccubond 140's, ELD-X 150s or ELD-X 162s. Measurements are below for this brass and bullet combo. I've also included dimensions from some once fired Hornady and Nosler brass I have as well as the neck measurements for new factory 140 Accubonds and 150 ELD-X ammunition.

I've got RCBS matchmaster dies, and on their guidance measuring the neck wall thickness and bullet diameter then subtracting .001" I land with a bushing size of .317" for new Starline Brass. Should I assume that I will need a separate bushing for once fired brass?

.001" does not seem like enough "interference" for good neck tension from what I've read. I would have thought subtracting .003" would be more appropriate to result in .001" of springback leaving .002" of interference for neck tension. Further it SAAMI specs show a neck diameter of 0.315", which the bushing my math shows is over by .002" using RCBS guidance and dead on if I use the .003" bump.

Looking at Short action customs neck bushings for 7mm-08 they list a range of .304" to .312" this seems more in line with what I would have expected to need.

Any help clearing things up would be appreciated as I am clearly confused; or perhaps over thinking everything.

BulletAccubond 140ELD-X 150ELD-X 162
OD=0.2840.2840.2845
New Starline Brass Total Diameter0.31750.31750.318
Bushing Diameter (.001 bump)0.31650.31650.317
Once Fired Hornady Total Diameter0.30950.30950.31
Bushing Diameter (.001 bump)0.30650.30650.307
Once Fired Nosler Total Diameter0.31450.31450.315
Bushing Diameter (.001 bump)0.31350.31350.314
Factory 150 ELD-X Neck OD:0.31
Bushing Diameter (.002 bump)0.308
Factory 140 Accubond Neck OD:0.3115
Bushing Diameter (.002 bump) 0.3095
SAC 7mm-08 Bushing Range0.3040.312
 
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So which dimension should I subtract .003 from? The new starline brass combo, the SAAMI spec, or something else?

3 thou less than the loaded neck diameter of whatever brass you're sizing with that bushing. 1 bushing size is not ideal for all brass if they vary significantly in neck thickness.

If you dont want to buy more than one neck bushing size, get 2 or 3 thou tighter than the brass with the smallest loaded neck diameter. The downside to that is you're over working the brass with the thicker necks. That is in effect what a standard, non-bushing, FL sizing die does. They spec them so they will size the thinnest of brass necks down small enough to have sufficient neck tension and then the expander ball opens the neck back up on it's way out. The whole point of bushing dies is to: a- avoid sizing the piss out of the neck just to open it back up with an expander ball every time you resize brass and b- allow people to adjust how much neck tension they have by swapping bushings.
 

TaperPin

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I agree with Wind Gypsy‘s description. It seems the first bushing is not the one I’ll end up sticking with for one reason or another - that’s just part of using them.
 
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JollyRogers
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Sep 17, 2022
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That explanation makes sense. I don't mind buying multiple bushings; trying to pick 1 or 2 to get started with. It seems starline brass has pretty thick wall thickness when new which is what's really driving my concerns as it seems the final dimensions will be larger than SAAMI based on a .003 bump. I'm leaning towards picking up a 0.312" bushing to start with which may over work the brass initially but hopefully will be about right after the first firing.
 
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I don't understand your table, are you measuring fired brass before resizing or only fired brass after sizing and seating a bullet? The useful measurement is neck diameter after firing, before sizing so you get a picture of the chamber neck diameter. There is usually some springback so measured neck diameter isn't exact chamber diameter but it gives you some of the info. I would not expect neck thickness to change materially with firings.

I looked at SAAMI specs and min chamber neck of 0.317 doesn't play well with the dimensions you're showing for Starline brass. If starline is in fact making 7mm-08 brass with a 0.0165" thick necks, they are effing up pretty bad on that cartridge. I'd not use that brass in a SAAMI chamber without turning the necks. Without turning the necks, it doesn't matter how much you size it down, when you seat a bullet it's going to be too thick.
 
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JollyRogers
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I don't understand your table, are you measuring fired brass before resizing or only fired brass after sizing and seating a bullet? The useful measurement is neck diameter after firing, before sizing so you get a picture of the chamber neck diameter. There is usually some springback so measured neck diameter isn't exact chamber diameter but it gives you some of the info. I would not expect neck thickness to change materially with firings.

I looked at SAAMI specs and min chamber neck of 0.317 doesn't play well with the dimensions you're showing for Starline brass. If starline is in fact making 7mm-08 brass with a 0.0165" thick necks, they are effing up pretty bad on that cartridge. I'd not use that brass in a SAAMI chamber without turning the necks. Without turning the necks, it doesn't matter how much you size it down, when you seat a bullet it's going to be too thick.
In my chart for the hornady and Nosler once fired brass I am measuring the fired brass before resizing.

I added two measurements of new factory hornady and nosler ammunition just for reference at the end of the chart.

That was my concern regarding wall thickness being so high was that regardless of the resizing efforts, once a bullet is seated I'd still be over the SAAMI spec.
 
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In my chart for the hornady and Nosler once fired brass I am measuring the fired brass before resizing.

I added two measurements of new factory hornady and nosler ammunition just for reference at the end of the chart.

That was my concern regarding wall thickness being so high was that regardless of the resizing efforts, once a bullet is seated I'd still be over the SAAMI spec.

It doesn't make sense to me that you'd have differences in fired diameter based on the bullet used or that once fired Nosler after shooting a 162 eldx would measure 0.315" but once fired Hornady after firing a 150 ELDx would measure 0.3095". That's over 7 thou of spring back on the hornady case. The neck had to expand to seal off the chamber, and SAAMI min chamber neck is 0.317", to have it spring back to 0.3095 sounds really unusual.

Have you chambered a piece of loaded Starline brass? Because if it's 0.318" neck I wouldn't be surprised if it doesn't even chamber or at least not without resistance.
 
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JollyRogers
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It doesn't make sense to me that you'd have differences in fired diameter based on the bullet used or that once fired Nosler after shooting a 162 eldx would measure 0.315" but once fired Hornady after firing a 150 ELDx would measure 0.3095". That's over 7 thou of spring back on the hornady case. The neck had to expand to seal off the chamber, and SAAMI min chamber neck is 0.317", to have it spring back to 0.3095 sounds really unusual.

Have you chambered a piece of loaded Starline brass? Because if it's 0.318" neck I wouldn't be surprised if it doesn't even chamber or at least not without resistance.
The fired brass measurements are just 2x wall thickness+bullet diameter. I didn’t measure actual fired neck diameter. I will measure that this evening and expect those dimensions to be very close.

I will also try chambering this afternoon. Signs are pointing towards needing to contact starline
 

eoperator

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The fired brass measurements are just 2x wall thickness+bullet diameter. I didn’t measure actual fired neck diameter. I will measure that this evening and expect those dimensions to be very close.

I will also try chambering this afternoon. Signs are pointing towards needing to contact starline
You need to seat a bullet in your new (or sized) brass and measure the outside neck dimension with bullet seated, order a bushing -.003 (or more).
 

wapitibob

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My 7 with Nosler brass is .314 loaded, I use a .309 sac bushing, for a .310 finished dia. I would go with a .310 redding bushing (they're cheap) to get started and do all my other work on the load way before I stated going down the neck tension hole.
 

Scotto

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Good info here already.
My 280AI Nosler brass measures ~.3105"-.311" loaded and I use a .309" Redding bushing.
 
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Harvey_NW

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You need to seat a bullet in your new (or sized) brass and measure the outside neck dimension with bullet seated, order a bushing -.003 (or more).
This. I prefer .003" interference so I deduct .004" from my loaded round OD measurement (to account for est .001" springback) and use that for my bushing size. I also polish my expander ball down .003" below bullet diameter, to help mitigate any variance in the neck thickness.

You can't accurately measure wall thickness with calipers, pretty sure you need a ball mic on a clean case, and you would need to measure in multiple places and take an average. That might be part of the table measurement confusion.

Also, the SAC bushings are tapered and size the least amount of the neck by design compared to other bushings. If you go SAC I would deduct an extra thou from your calculated bushing size, possibly more. I had a loaded round OD of .284 and a .281 SAC bushing only sized once fired brass enough to put some resistance on a bullet, but I could pull it by hand.
 

SDHNTR

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Figure out what you need with a cheaper Redding bushing. Then buy an SAC bushing .001 smaller. That’s what I’ve done with the last several new rounds I’ve started loading. Much cheaper than experimenting with SAC bushings.
 

Mulyhuntr

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Measure the necks, multiply by two, add bullet diameter, subtract .002-.003". I'd be surprised if you didn't land around a .310" bushing. Most necks I've measured on 6.5cm and 7mag brass are .014-.015". No way a .317" would be right.
 
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.002 under the size of a loaded round is what you need
Bushings sometimes do weird things if they have to move the brass a lot
 
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Measure the necks, multiply by two, add bullet diameter, subtract .002-.003". I'd be surprised if you didn't land around a .310" bushing. Most necks I've measured on 6.5cm and 7mag brass are .014-.015". No way a .317" would be right.

There’s a way. This is a 7 SAUM with ADG brass. Factory Norma 6 creedmoor match ammo necks measure over 0.275", that's at least 0.016"+ on a 6mm. Just because it shouldn't doesn't mean it couldn't.


648A0F3E-0EC9-4B9B-AD5C-1160E36066AB.jpeg
 

Mulyhuntr

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There’s a way. This is a 7 SAUM with ADG brass. Factory Norma 6 creedmoor match ammo necks measure over 0.275", that's at least 0.016"+ on a 6mm. Just because it shouldn't doesn't mean it couldn't.


View attachment 679967
.318" loaded rounds means .017" necks. I'd be VERY surprised. Every Starline caliber I've measured has been .014-.015", except 223.
 
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JollyRogers
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.318" loaded rounds means .017" necks. I'd be VERY surprised. Every Starline caliber I've measured has been .014-.015", except 223.
so I’m measuring an average of 0.01675” neck wall thickness across a random pull of 12 cases from 100 pieces of new starline brass. Granted I’m using calipers and not a ball mic so that could be causing in accurate readings. My largest wall thickness was 0.017” and thinnest was 0.0155 most measured at 0.0165.
 
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