Chamber specs

[davchr]

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

 

[Frog4aday]

Longer throat = less peak pressure = lower liability of someone blowing the gun up. Weatherby is famous for this (long leade) & their rifles shoot fine (accurate). Pick the rifle you want and give it a go. It just might surprise you.

 

[cajun]

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.

 

[Send it 284]

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

 

[QuietTexan]

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.

 

[L.Sherm]

You want it at or below the case neck shoulder junction.

Sure you didn't me at or above case neck shoulder junction.

 

[Jud96]

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.

 

[L.Sherm]

If you want more freebore a competent smith can throat to a dummy round

 

[FEENIX]

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

 

[Send it 284]

Sure you didn't me at or above case neck shoulder junction?

Well you don't want your bullet half way up the neck so I'd stick with at or below the junction

 

[L.Sherm]

I prefer at or about .010 above so I don't have to worry about donuts.

 

[Creedmoor shooter]

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]

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.

 

[Deleted member 115360]

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.