Question about trimming a 30-06 neck to be similar to 308

How will the bearing surface effect my velocity?

  • It will decrease

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eldest584

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Hello guys,
I was wondering if anyone has trimmed 30-06 cases to have a similar neck length to match a neck length of a .308.

So from what I can determine, a 308 neck length should be around .294", while a 30-06 neck length is around .375".

So, is there anyone out there who trims 30-06 necks to be around .294"? Aka about .081" short of published trim length?


My idea was reducing bearing surface to squeeze out some more velocity. But I have no idea if that will even make a difference. Just curious if anyone else has messed around with that or if I'm just stupid.

I figured with headspace being based off the shoulder it can't cause safety issues...right? I have the shoulders bumped about .002-.003"


I'll monitor this thread for a few days before I go out and test my theory. Think I'll load a batch of 178grn eld-x rounds with the published trim length and then my .080" shorter than published trim length. I'll try to keep seating depth +- .001" of each other and charge weight +- .02grns of each other to see of the reduced bearing surface makes much of a difference.

20200227_021702.jpg
 

eldest584

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I guess it all ready depends on what I want my B.T.O/C.O.L. to be... I guess what I would need to do in order to get an accurate test is keep the same BTO and COL for the normal trimmed and short trimmed cases. Which as I write this seems obvious, but it is late and I am doing this as I go.

I am going to load up a couple dummy rounds to see what they look like
 
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eldest584

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Have the dummy rounds loaded up, decided to do the hornady reccomended COL for the 178 eldxs of 3.220, I have a BTO of 2.5545"

Visually I just feel having less bearing surface like that is better... but I know nothing, and obviously whoever designed the case dimensions the way they did, did so for a reason. Time to load up some actual rounds and go from there. Now my concern is that my 30-06 test rifle is a 1903a3 with a barrel manufactured in 1943 :LOL:. So depending on what kind of ES/SD the rifle is even capable of getting might change things a little. I wouldn't be surprised if the barrel causes some "unnatural" ES/SD changes. as compared to having a newer barrel. Again I don't really know from experience. I read somewhere once that burned out barrels can cause some pretty significant velocity swings. But I don't know if that is just reduced velocity while keeping a similar ES, or if they just go all wonky and ES increases.

20200227_031716.jpg
 
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eldest584

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Many want a neck that is at least 1.5 bullet diameter, why are you trying to shorten yours?
It was honestly by mistake, I had my case trimmer set up (trims off the shoulders) for my 308 cases. Tossed a 30-06 case in there and trimmed it like .085" shorter than I meant to. Which got me thinking 🤷‍♂️
 

eldest584

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Many want a neck that is at least 1.5 bullet diameter, why are you trying to shorten yours?
I was curious and decided to compare some cartridges, 6 creed has a neck length of .259-.269, and 6.5 creed has a neck length of .275-.285" depending where you trim between 1.910-1.920.

assuming I trim to the 1.910 for both, those are 1.06x and 1.04x neck length to bullet diameters.
 

eldest584

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And looking at 300PRC which I guess is all the rage has a neck length of .3076 according to published hornady specs
 

eldest584

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1 caliber of baring surface contacting the neck is what I always read/was taught
That is what I have heard as well. Going to trim up a box of short necked brass and then a box of normal brass and go out and chrono the loads. I'll try to group some but the rifle is like a 2moa rifle at best so we will see.
 

918v

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The idea is to support the bullet shank until it contacts the rifling. If you cut the neck short you will fail to support some bullet depending on their weight and bearing surface. Dumm idea.
 

Ryridesmotox

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That is what I have heard as well. Going to trim up a box of short necked brass and then a box of normal brass and go out and chrono the loads. I'll try to group some but the rifle is like a 2moa rifle at best so we will see.
I kinda mean that more like... when you seat the bullet to get near the lands, you need that. You're going to be seating bullets really short.

My expectation of accuracy would be really low
 
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eldest584

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The idea is to support the bullet shank until it contacts the rifling. If you cut the neck short you will fail to support some bullet depending on their weight and bearing surface. Dumm idea.
It all makes sense now, with a sober and well rested brain. Regardless I'm going to test it out just for the fun of it 😂

Also, my 6.5 RPR had about .100" jump to the lands and it shot pretty well before I sold it
 

spife7980

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Also, my 6.5 RPR had about .100" jump to the lands and it shot pretty well before I sold it
The bullets relation ship relative to the lands is a dimension independent of the length of the neck.

With less neck you may need to use more interference fit or treat the neck some how to make up for the loss in bullet grip. I’d just keep for a sighted/barrel warmer/toss that one piece and not fuck up the rest if them just to match it like an idiot
 
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supercorndogs

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Short cases will burn out the throat prematurely.
I can only reply to this anecdotally, but I trimmed some 22-250 brass too short once and burned up the barrel in 700 rounds. I can't say if it was the rate of fire, short brass, or long heavy bullets, but it didn't last long. I might measure that brass and see what length it has reached before messing with it in my new barrel.
 
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