Fireformed neck -0.005” under reamer???

[Plowboy85]

Hey guys seeking some opinions here. I have a freshly built 30 Nosler that was chambered with a new JGS 0.343" neck reamer, I am confident it is the reamer used incase it is thought. I measured my reamer to confirm and it is indeed 0.343". I have 3 pieces of virgin ADG brass that has been 2x fireformed, brass was neck sized 0.002" under to allow second fireform. 1x and 2x fired brass on all 3 pieces is 0.338" at multiple areas on the necks. So my question is does that seem right for that amount of spring back?? If I missed a variable please let me know…brass was being fireform so I can send off for Whidden dies. I have been reloading for 15ish years but never had the reamer or plug gauges to compare to my brass. I have always taken fireform neck OD at face value and set up too size 0.002" under but now I'm thinking i have been incorrect.

 

[Coyote Shadow Tracker]

Hey guys seeking some opinions here. I have a freshly built 30 Nosler that was chambered with a new JGS 0.343" neck reamer, I am confident it is the reamer used incase it is thought. I measured my reamer to confirm and it is indeed 0.343". I have 3 pieces of virgin ADG brass that has been 2x fireformed, brass was neck sized 0.002" under to allow second fireform. 1x and 2x fired brass on all 3 pieces is 0.338" at multiple areas on the necks. So my question is does that seem right for that amount of spring back?? If I missed a variable please let me know…brass was being fireform so I can send off for Whidden dies. I have been reloading for 15ish years but never had the reamer or plug gauges to compare to my brass. I have always taken fireform neck OD at face value and set up too size 0.002" under but now I'm thinking i have been incorrect.

I'll try to help you out, but I may not be sure what you are looking for. If you Reamer is 0.343 and you bullet is 0.308 then you have 0.035 space. If your fire formed cases measure 0.338 then you have 0.005 left in your chamber which is enough space.
Looks like you currently have .015 neck wall thickness on your brass. Is that correct?
Don't know what you mean by 0.002 unless you mean shoulder.

The way I measure is by the bullet diameter + the neck wall thickness (X2) to determine my neck reamer for spring back.
Usually SAAMI Reamers will have at least 0.006. I have our custom reamers down to 0.003 to 0.004 and that is dependent by the neck wall thickness by turning necks.
You can call me if you want. PM me for my Phone.

Thanks
Len

 

[Plowboy85]

I'll try to help you out, but I may not be sure what you are looking for. If you Reamer is 0.343 and you bullet is 0.308 then you have 0.035 space. If your fire formed cases measure 0.338 then you have 0.005 left in your chamber which is enough space.
Looks like you currently have .015 neck wall thickness on your brass. Is that correct?

The way I measure is by the bullet diameter + the neck wall thickness (X2) to determine my neck reamer for spring back.
Usually SAAMI Reamers will have at least 0.006. I have our custom reamers down to 0.003 to 0.004 and that is dependent by the neck wall thickness by turning necks.
You can call me if you want. PM me for my Phone.

Thanks
Len

I may indeed take you up on the call. I'll try to clarify first, the 3 pcs were measured fireformed and without a bullet seated. However, my loaded rounds are also 0.338" and the average neck wall on 3 other pcs of brass is 0.0152"-0.0155". Like you I typically spec for 0.004"-0.005" chamber clearance over a loaded round. My question which is largely driven by my curiosity, does it seem normal for my 0.338" loaded round to go boom, expand to the chamber ID of 0.343" then spring back to 0.338"? I have measured with my Starett and Mitioyo (however you spell it).

 

[Coyote Shadow Tracker]

I may indeed take you up on the call. I'll try to clarify first, the 3 pcs were measured fireformed and without a bullet seated. However, my loaded rounds are also 0.338" and the average neck wall on 3 other pcs of brass is 0.0152"-0.0155". Like you I typically spec for 0.004"-0.005" chamber clearance over a loaded round. My question which is largely driven by my curiosity, does it seem normal for my 0.338" loaded round to go boom, expand to the chamber ID of 0.343" then spring back to 0.338"? I have measured with my Starett and Mitioyo (however you spell it).

Good question & food for thought. Brass does spring back after firing and remember that you need to divide by 2 so your 0.004 or 0.005 is actually 0.002 or 0.0025 in reality (Maybe????) I'm past bed time. we can talk tomorrow and sure some other member will chime in.
Len

 

[Mikecr]

No the necks would only spring back from chamber neck ~1 thou for that cal.
I'm thinking that you don't have as much clearance as expected from that reamer.
It seems like the chamber neck is .340

I wonder if you expanded a neck to .341 OD, if it would chamber.

 

[Plowboy85]

No the necks would only spring back from chamber neck ~1 thou for that cal.
I'm thinking that you don't have as much clearance as expected from that reamer.
It seems like the chamber neck is .340

I wonder if you expanded a neck to .341 OD, if it would chamber.

That has always been my understanding as well. I will see if I have a larger expander and try that Mike.

 

[Plowboy85]

@Mikecr so I checked and all of my expanders are for setting neck tension or turning therefore, all are 0.3075" or smaller. It is worth mentioning I observed no sign of pressure on the 6 fireforms although they were at book minimum with some 190 VLDs I had laying around. A loose bullet will slide through a fired case with minimal friction, a fired case certainly will not hold a bullet. Now that my OCD is winding up I may pull the barrel and gauge it.

 

[lancetkenyon]

If you are looking to get custom dies made, you could have them make a bushing die FL set. That would allow you to fine tune your neck tension once you start actual load development, and also eliminate any worry about incorrect neck size.

Did you anneal your necks to soften them up for fire forming? That might be one last step you want to take and fire form a final time after.

 

[Plowboy85]

If you are looking to get custom dies made, you could have them make a bushing die FL set. That would allow you to fine tune your neck tension once you start actual load development, and also eliminate any worry about incorrect neck size.

Did you anneal your necks to soften them up for fire forming? That might be one last step you want to take and fire form a final time after.

The brass is headed to Whidden for FL bushing dies today actually, I use bushings and/or mandrels to set desired neck diameter.

The necks have not been annealed by me, it is my understanding that ADG anneals after sizing.

I'll see if I can get time to anneal a piece then fireform….thanks for the suggestion.

 

[Coyote Shadow Tracker]

I'll try to help you out, but I may not be sure what you are looking for. If you Reamer is 0.343 and you bullet is 0.308 then you have 0.035 space. If your fire formed cases measure 0.338 then you have 0.005 left in your chamber which is enough space.
Looks like you currently have .015 neck wall thickness on your brass. Is that correct?
Don't know what you mean by 0.002 unless you mean shoulder.

The way I measure is by the bullet diameter + the neck wall thickness (X2) to determine my neck reamer for spring back.
Usually SAAMI Reamers will have at least 0.006. I have our custom reamers down to 0.003 to 0.004 and that is dependent by the neck wall thickness by turning necks.
You can call me if you want. PM me for my Phone.

Thanks
Len

Plowboy and everyone else I am off on my calculations have a lot going on mentally and should have just went to bed without an answer.

First do you have the "Print"" for the JGS Reamer used and it shows the neck od cut at 0.343 or did you just measure the cutting flukes on the reamer? You could be off by measuring the cutters. Did you or your GS design the Reamer or just ask JGS of r a 30 Nosler Reamer?
Moat SAAMI speck Reamers for cartridges with a .308 bullet is 0.340 or 0.3397 neck. I have seen reamers showing 0.342 most likely having cartridges with heavy walls
If you have fired cases that measure 0.338 you might have a SAAMI Speck Reamer 0.340 then you are getting 0.002 spring back. Usually brass will spring back 0.001 X 2 sides =0.002 spring back which is enough for your case to eject from the chamber.
Re-measure you neck wall thickness with a Ball Micrometer and then a loaded case neck after you run through you sizing die. Measure your loaded case neck size.
The main thing is having the actual your Reamer Print for that chamber.

 

[Plowboy85]

Plowboy and everyone else I am off on my calculations have a lot going on mentally and should have just went to bed without an answer.

First do you have the "Print"" for the JGS Reamer used and it shows the neck od cut at 0.343 or did you just measure the cutting flukes on the reamer? You could be off by measuring the cutters. Did you or your GS design the Reamer or just ask JGS of r a 30 Nosler Reamer?
Moat SAAMI speck Reamers for cartridges with a .308 bullet is 0.340 or 0.3397 neck. I have seen reamers showing 0.342 most likely having cartridges with heavy walls
If you have fired cases that measure 0.338 you might have a SAAMI Speck Reamer 0.340 then you are getting 0.002 spring back. Usually brass will spring back 0.001 X 2 sides =0.002 spring back which is enough for your case to eject from the chamber.
Re-measure you neck wall thickness with a Ball Micrometer and then a loaded case neck after you run through you sizing die. Measure your loaded case neck size.
The main thing is having the actual your Reamer Print for that chamber.

Don't worry about being off buddy, we all have those times. My reamer was specified based off of some changes I wanted from SAMMI, the JGS SAMMI reamer was 0.346". After I measured my necks on my lot of ADG brass I specified the dimensions and throat ID I wanted. The 0.0152" necks were indeed measured with my ball micrometers and not calipers. The 0.338" loaded neck diameter was verified with 2 sets of calipers after sized as you suggested. As far as measuring the flutes on the reamer, it was also 0.343" but a little more crude value, I set a slight bit of tension on my calipers and rotated the reamer….I could consistently measure 0.343" just before the cutting edge broke over. I would by no means consider this a useful measurement but for a supporting value it was sufficient.

Here is my reamer print as well as the SAMMI which is labeled "3830".

Also the 0.002" you were unsure of last night was the amount of neck sizing I performed to allow enough grip for fireforming the brass. My process has always been to remove the ejector and form the initial few pieces of brass with jammed loads, I will do this for my custom dies and maintain a spare piece of brass for chamber reference if ever needed.

 

[Varmint Hunter]

Something just doesn't sound right. Assuming that the necks expanded to .343" upon firing, it seems rather unlikely to have .005" of neck contraction.

Just sayin'

 

[Plowboy85]

Something just doesn't sound right. Assuming that the necks expanded to .343" upon firing, it seems rather unlikely to have .005" of neck contraction.

Just sayin'

I have the same head scratching going on.

 

[milo-2]

I have the same head scratching going on.

Does fired brass necks have a carbon ring on them from sealing off? Or is it down on the shoulder?