7mm Rem Mag COL

M

math teacher

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Why is the listed maximum overall length of the Rem 7mm Mag 3.29 inches when the other cartridges based on the same case, such as the .264 and the .338 all call for a maximum length of 3.34 inches? Likewise cartridges based on the 30-06 case call for a maximum of 3.34 except strangely the 25-06 which calls for a maximum of only 3.25 inches.
 
Blame the parents

This is not uncommon.

Shoulders are moved, necks are trimmed, etc.

The parent cartridge is only a base for its offspring.

30-06 to 6mm; 30-30 to 7x30 Waters, etc.
 
In this case however the .264 and the .338 have the same exact case except for bullet diameter. Both of those have the same overall maximum length. Yet the 7mm which falls in between is for some reason shorter which makes no sense to me.
 
This is just a guess, perhaps it was set this way based on what bullets the designers expected to be used and they set the chamber dimensions accordingly. For example the 25-06 was factory loaded with 87 grain bullets, to seat this bullet with at least one diameter's length in the neck would result in a short OAL. To prevent a big jump to the start of the rifling in the barrel, they set the chamber dimensions based on the 87 grain bullet. Then they used the same OAL for the 120 grain bullets. Similar for the 7mm Magnum, although I forget what range of bullet weights it was released with.

You can measure to the start of the rifling in your gun and adjust the OAL to say .020" off the riffling, as long as the rounds will feed OK through the magazine. There are several gauges that will measure to the start of the rifling, I use the RCBS precision mic for this. In general it's OK to go longer, going shorter than listed in the reloading manuals will likely result in higher pressure.
 
There are easy ways to determine the actual maximum overall length for a particular bullet. In this case it is usually more than the length of the magazine. The .264 came out first. Since Remington copied Winchester's case, you would think they would use the same COL. Remington came out with the 175 grain load with the introduction of the 7mm, so they certainly knew it would be used with long bullets. I am hoping someone will be able to reply, "Remington said they did it that way because ......." I have wondered about this for several years, and this is the best place I know of to ask other than perhaps Remington themselves. They did not answer the last inquiry I made to them.
 
Well for starters you have Springfield Armory for the 30-06, and Remington for the 25-06.
Same with Winchester for the 264, 338 and Remington for the 7mm Mag.

Everybody wants to do something a little different just so it's not a direct copy of someone else.

Corporate law and all...
 
There is another possible reason:

The 7mmRM is very close to, and considered by some to be, overbore.

Keeping the cartridge a bit shorter means a bit less powder, so a bit less overbore.

I think we would have to travel in time and ask the designer to know for sure.

7mmRM is one of my favorites either way.
 
The 264 max OAL is 3.340" and same for 338mag and real world difference is .050" for 7mag.

I think Rem just wanted to be different OAL vs what Win used. Win never did neck 264/338mag case to 30 cal.
 
SAAMI

When Remington applied for standardization, they already had a bunch of data on throats and seating from the wildcat community, so they developed the throat length/OAL relationship that gave the best accuracy and performance. Over the years, I've just loaded my 7mm Mags to max OAL and haven't worried about it. When they shoot less than MOA, it's mahvelous.
 
Does it have anything to do with preventing the inadvertent chambering of one caliber in another rifle with a similar case but different caliber?
 
Boy my 7mm rem mag was a long long time ago. Didn't get the accuracy I wanted with 160gr bullet's but 139's shot great. Finally loaded up a dummy round and took it to a gunsmith and had him bore out the throat to accept it. Base of the bullet ended up right at the bottom on the neck and did not enter the body at all. Result's were I uped the charge of N205 two grs up. Accuracy stayed just around 5/8th inch all the time.
 
Thanks everyone for your feedback. std7mag, I have formed 7mm mag cases from 338 and 264 cases. They all use the same case. cdoc42, you explanation sounds as good as any.I have a query into Remington. If I get a reply, I will post it. Those who said they did it just to be different may also be right.
 
Right after 338mag came out, Fred Huntington (RCBS) neck down 338 mag for the 30-338mag and Remington chambered the 40x for the 30-338mag.

The 30-338mag was used by Army Marksmanship Unit (AMU) and was also used to win Wimbledon and Leech Cup both 1000yd matches.

Two of my elk rifles are chambered for the 30-338mag and I use 7mag case neck to 30.
 
math teacher, are the OAl numbers you initially listed the size of the empty cases or COLs with a bullet seated?

I ask because the 7mm Rem Mag, .264 Win Mag and .338 Win Mag empty cases, resized and trimmed, should all be 2.500." The measurement from the base to the beginning of the shoulder in all 3 are the same: 2.0401" (altho that number is 2.0400 for the .338 in one book) The shoulder angle is 25 degrees for all 3. They differ (in caliber, so the mouth diameter differs) in case measurement from the base to the beginning of the neck:

7mm RM = 2.2288"
.264 RM = 2.2459"
.338 WM = 2.1698

That may prevent them from being chambered in the other rifles.

I say that because the same issues appear with the .270 and 25-06. I cannot chamber a resized, trimmed empty case of either caliber into the other rifle.

Both cases measure 1.9480" base to shoulder; shoulder angle is the same: 17 degrees, 30 min. The OAL of the .270 case measures 2.540" and the 25-06 is 2.494" but once again, the base to the beginning of the neck differs:

.270 Win= 2.1557"
.25-06 = 2.1858"

So even though the 25-06 is shorter than the .270 (OAL), the base to shoulder is longer and that may be why it will not chamber in the .270.

As well the .270 simply will not chamber in the .25-06 -but maybe because the OAL is longer-?

Is this what you had in mind?
 
The lengths I quoted were for the overall length of the loaded cartridge. I promised I would get back if I heard from Remington. They replied, "Our firearms and ammunition are manufactured to SAAMI specifications." That does not answer the question as to why the Rem 7mm mag is held to a shorter overall length than the .264 (smaller diameter bullet) and the.338 (larger diameter bullet.) All use the same basic case.
 
The lengths I quoted were for the overall length of the loaded cartridge. I promised I would get back if I heard from Remington. They replied, "Our firearms and ammunition are manufactured to SAAMI specifications." That does not answer the question as to why the Rem 7mm mag is held to a shorter overall length than the .264 (smaller diameter bullet) and the.338 (larger diameter bullet.) All use the same basic case.
Click to expand...

Sadly, I am not surprised. The Remington that designed the great 7mmRM is no more.

In short: They don't know.
 
math teacher, if you're talking about the length of the finished cartridge, that's a horse of a different color. The Lyman 50th edition handbook shows the various measurements of all the cases, including the overall length of the finished cartridge (C.O.L.) and these agree with your observation:

7mm Rem Mag = 3.290"
.264Win Mag= 3.340"
.338 Win Mag =3.340"

But this does not state which bullet is used in each case.

For bullets used in the Lyman book, the COL differ:

7mm Rem Mag: 3.290" for 120-140-150-154-160 and 168 grains
3.235" for 130gr SP
3.260" for 175gr

.264 Win Mag: 3.340"for the picture measurement, but 3.250" for 129gr and 3.220 fo 140gr

.338 Win Mag: 3.340" for 180-200-225 grains
3.410" for 210 Barns and 300 jacketed HPBT
3.300" for 250gr jacketed RN

A quick look at the Hodgdon manual for 7mm RM does not show a picture of the finished cartridge when case measurements are given. But the COLs listed for the various bullets range from 3.150" to 3.290." But note the ONLY bullets they list as 3.290" COL are for 160-162-175 grains.

These are seated bullet COL measurements they used to develop the load data in their books. You can use these as a guide when you reload the specific bullets in the manuals, but one way to maximize accuracy when reloading your own is to seat the bullet you are using a distance from the lands that may be 0.01" to 0.02" which will generally make that bullet in your rifle a longer than the measurements you see in the manuals. The COLs they offer should easily fit in anyone's rifle but accuracy is another story.

Does this answer your question?
 
cdoc42,

Your explination explains why the COL for particular loads vary, something that years of handloading has taught me. As you listed:

7mm Rem Mag = 3.290"
.264Win Mag= 3.340"
.338 Win Mag =3.340"

My question is, since the 7mm Rem Mag falls between the .264 and the .338, and they all use the same basic case, why is the SMMI spec for the 7mm COL shorter than the other two? It must have been Remington's doing. but why? It makes no sense to me.

As disseminator said, probably no one at Remington knows why. The people who did know are all dead or retired.
 
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