Chamber specs

davchr

New Member
Joined
Dec 23, 2020
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2
Location
Tucson, AZ
Having done some varmint hunting with .223's and a .243 I am looking to buy a 7mm Rem Mag long range rifle for deer and elk in Arizona.

So, I ordered a new Remington 700 long range. Before taking possession I measured the throat depth (actually the ogive distance from the case head to the bullet ogive). It appeared to be WAY too long as the bullet cannelure was about .210" beyond the end of the case neck. (Hornady 162 gr SST bullet) I rejected the gun and ordered a Browning X-Bolt Long Range. Measured the throat depth on this gun. This time the bullet cannelure was "only" .142" beyond the case neck. I rejected that gun as well. The C.O.L. was 3.400".

I looked up the SAAMI specs for the 7mm Rem Mag chamber. They have a reference dimension of 2.7256" from the bolt face to the end of the throat. The Browning measurement gave me 2.767" from the head of the cartridge case to the ogive of the bullet or about .041" over what I think SAAMI says. If the chamber was in spec the bullet cannelure would be ~.100" beyond the end of the case neck.

I have several questions:
1. Is there something wrong with my assumption that the cannelure should be near the end of the case neck when the bullet ogive is at the lands? Not > .100" off? (I am a retired mechanical engineer, and have spent a LOT of time in machine shops making parts, molds, and prototypes so I am pretty sure my measurements are close.)
2. Should I be rejecting these rifles? Or is that all that can be expected from production rifles?

Any insight here would be appreciated.

thanks,
Dave Christensen
 

cajun

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Joined
Dec 11, 2007
Messages
504
It is not uncommon in factory rifles where you are limited by magazine length to be a WAYS from the lands. What you have found is not uncommon. FWIW you dont have to be close to the lands to get an accurate load. It’s nice to have that option but most bullets can be tuned for a jump.
 
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Send it 284

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Oct 15, 2020
Messages
369
Location
Conus
Having done some varmint hunting with .223's and a .243 I am looking to buy a 7mm Rem Mag long range rifle for deer and elk in Arizona.

So, I ordered a new Remington 700 long range. Before taking possession I measured the throat depth (actually the ogive distance from the case head to the bullet ogive). It appeared to be WAY too long as the bullet cannelure was about .210" beyond the end of the case neck. (Hornady 162 gr SST bullet) I rejected the gun and ordered a Browning X-Bolt Long Range. Measured the throat depth on this gun. This time the bullet cannelure was "only" .142" beyond the case neck. I rejected that gun as well. The C.O.L. was 3.400".

I looked up the SAAMI specs for the 7mm Rem Mag chamber. They have a reference dimension of 2.7256" from the bolt face to the end of the throat. The Browning measurement gave me 2.767" from the head of the cartridge case to the ogive of the bullet or about .041" over what I think SAAMI says. If the chamber was in spec the bullet cannelure would be ~.100" beyond the end of the case neck.

I have several questions:
1. Is there something wrong with my assumption that the cannelure should be near the end of the case neck when the bullet ogive is at the lands? Not > .100" off? (I am a retired mechanical engineer, and have spent a LOT of time in machine shops making parts, molds, and prototypes so I am pretty sure my measurements are close.)
2. Should I be rejecting these rifles? Or is that all that can be expected from production rifles?

Any insight here would be appreciated.

thanks,
Dave Christensen
The cannelure has nothing to do with proper seating depth.
What you need to do is see where the boat tail /bearing surface junction ends up in your case neck.
You want it at or below the case neck shoulder junction.
Pretty much anyone who shoots a custom for long range has the throat modified to seat high bc bullets further out of the case.
My 7mms throat is .340 longer than saami for 195's
 
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QuietTexan

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Joined
Nov 16, 2020
Messages
297
Location
Texas
Just ignore the cannelure. The SST is the only bullet I've loaded for that even has one, its vestigial.

I've replaced the SSTs with Nosler Partitions for up close, and ELD-Xs for out further. If I could get AccuBonds in .264 right now I'd use those instead of the Hornady bullets, Nosler has never let me down.
 
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Jud96

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Joined
Jun 30, 2013
Messages
3,022
Location
Michigan
As others said, ignore the cannelure. Another thing, not all bullets are going to touch the lands at the exact same CBTO. Every bullet will touch the lands at a different length. Getting rifles and measuring the throat length on them is wasting everyone’s time including your own. Factory rifles are what they are and if you want a special chamber design or dimension then you’ll have to rebarrel the rifle with a reamer of your choice.

I’m not trying to be harsh, but I would select a rifle based on its features and it’s reputation. I can tell you that factory Remington 700s in 7mm Rem Mag really like Hornady 162gr ELDs and some, including @Creedmoor shooter have really good luck with the heavier 180gr ELDs. The chamber design is just about perfect with the 162s and a little short with the 180s but neither bullet is held back much. I would focus on a lot more than getting hung up on chamber specs for your first long range hunting rifle. Again, I’m not trying to come off the wrong way, I’m just trying to offer some advice to help you make a good decision.
 

FEENIX

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Joined
Dec 20, 2008
Messages
16,427
Location
Great Falls, MT
Having done some varmint hunting with .223's and a .243 I am looking to buy a 7mm Rem Mag long range rifle for deer and elk in Arizona.

So, I ordered a new Remington 700 long range. Before taking possession I measured the throat depth (actually the ogive distance from the case head to the bullet ogive). It appeared to be WAY too long as the bullet cannelure was about .210" beyond the end of the case neck. (Hornady 162 gr SST bullet) I rejected the gun and ordered a Browning X-Bolt Long Range. Measured the throat depth on this gun. This time the bullet cannelure was "only" .142" beyond the case neck. I rejected that gun as well. The C.O.L. was 3.400".

I looked up the SAAMI specs for the 7mm Rem Mag chamber. They have a reference dimension of 2.7256" from the bolt face to the end of the throat. The Browning measurement gave me 2.767" from the head of the cartridge case to the ogive of the bullet or about .041" over what I think SAAMI says. If the chamber was in spec the bullet cannelure would be ~.100" beyond the end of the case neck.

I have several questions:
1. Is there something wrong with my assumption that the cannelure should be near the end of the case neck when the bullet ogive is at the lands? Not > .100" off? (I am a retired mechanical engineer, and have spent a LOT of time in machine shops making parts, molds, and prototypes so I am pretty sure my measurements are close.)
2. Should I be rejecting these rifles? Or is that all that can be expected from production rifles?

Any insight here would be appreciated.

thanks,
Dave Christensen
Dave,

Welcome to LRH and enjoy it! Don't complicate it unnecessarily; when you are actually ready to load, the CBTO of the actual bullet you will use is what matters. Finding the sweet spot of the seating depth is half the fun.

Ed
 

Creedmoor shooter

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Oct 21, 2013
Messages
2,724
Location
Monroe, Newhampshire
As everyone has said, ignor the cannelure. Ive owned a browning x bolt 7mm mag and currently own a remington 700 long range. Surprisingly both were throated nearly identical. They're throated pretty much perfect with the 162s as @Jud96 said. 180s aren't horrible but it is a wee bit short. Just load them to wherever you desire and go have fun.
 

nksmfamjp

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Joined
Jan 5, 2004
Messages
1,150
1) answered

2) When touching the lands, the neck and bullet should be fully engaged on the bearing surface. Also, the OAL should be close to mag length.
 

Hecouldgoalltheway

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Aug 30, 2020
Messages
895
Location
Tennessee
I knew you were an engineer before I got through the first paragraph. You probably smoke a pipe and carry a slide rule in your back pocket. 😆

You guys are the kings of overthinking things. I'm a Weatherby guy, and as someone already mentioned, those measurements would send you into shock. The jumps are wild, but you won't find one that won't shoot better than my own ability.
 

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