7/300WSM Case Capacity and Forming

[300magman]

I am just curious what the typical case capacity is for the 7/300WSM wildcat.

I have been thinking about a 7mm SAUM, but if the 7/300 falls about halfway between the SAUM and the straight 7mm WSM I just might give it a try....assuming case forming isn't too much of a challenge.

Can I just bump the necks down in one step, run a 7mm expander ball through them, and then neck turn to fit my chamber?

 

[J E Custom]

I am just curious what the typical case capacity is for the 7/300WSM wildcat.

I have been thinking about a 7mm SAUM, but if the 7/300 falls about halfway between the SAUM and the straight 7mm WSM I just might give it a try....assuming case forming isn't too much of a challenge.

Can I just bump the necks down in one step, run a 7mm expander ball through them, and then neck turn to fit my chamber?

The 7/300wsm has less case capacity than eather the 7mmSAUM or the 7mm WSM.

IMO. There really isn't any reason to go with a 7/300 and deal with the problems of having a
wildcat that does not exceed a factory round.

The 7 SAUM or the 7WSM will push heavy bullets faster and can be loaded down to mild loads
as low as the 7/300 can.

You can buy ammo for ether the SAUM or the WSM but not for the 7/300 and that can be a big
advantage in my opinion.

J E CUSTOM

 

[300magman]

I didn't really want to use the straight 7mm WSM because the extremely short neck makes it next to impossible to seat long VLD type bullets out far enough to not contact the neck/shoulder junction, even in "WSM" length actions. (And I don't want to use a long action)
Also the straight WSM has a huge case capacity (81.5g if memory serves) which seems to be beyond what is necessary to get big VLDs up to the speeds I want to reach.

As for the SAUM, I was sure that it was the smallest of the group...I have never formed a 7/300 so I can't say from experience what its case capacity is, but all the research I have done had lead me to believe that it was still larger than the SAUM (@ approx 73gr)
I was hoping the 7/300 was in the middle of the two, and I wasn't really concerned about it not being a factory round, because from everything that I hear, neither is the 7mmSAUM anymore....though maybe new ammo will continue to be made for a time, even if new rifles aren't.

 

[nheninge]

The advantages of the 7/300 are not case capacity. I chose this round for what I am able to do with the neck compared to the 7wsm. Just cause u can cram more powder in a load does not make it more accurate. Availability of Norma 300WSM brass also helped to make my decision. My 7/300 will outshoot every 7wsm I have seen. However, someone with good rifleman skills could likely outperform my 7/300 with a .308. Hold/technique is everything.

I perform case capacity tests with an "empirically derived" combination of DSS and H2O to minimize H2O tension. Plain water capacity tests are hard to duplicate since the meniscus of plain water (and therefore weight) varies between users and between tests.

My sweet load uses 66.2 H1000 behind a Berger 180g at 2950fps with fed215m primers and near perfect brass. I can get more powder in this case, but groups open up pretty quick. Just because a wildcat doesn't "exceed a factory round " doesn't really tell the whole story. A keen handloader will maximize advantages that will outperform any factory loads available. Good handloads in a factory chambering will also perform well, but the amount of work is the same. Crappy factory ammo in a custom gun will still give crappy results.

 

[backwoods83]

With the reamer blueprints I looked at a 7/300wsm is virtually a 7mm wsm they are the same length all you are doing is necking down a 300 wsm to 7mm. 300wsm blueprint shows 80.4grns capacity, 7mm wsm shows 80.3grns, 7/300 shows 80.1, the only advantages is good 270/300wsm brass verses winchester brand 7mm wsm brass, to work the brass less I'd get 270wsm norma brass and neck it up, your only expanding .007". But yet these with vlds will not fit in a remington sa.

 

[J E Custom]

With the reamer blueprints I looked at a 7/300wsm is virtually a 7mm wsm they are the same length all you are doing is necking down a 300 wsm to 7mm. 300wsm blueprint shows 80.4grns capacity, 7mm wsm shows 80.3grns, 7/300 shows 80.1, the only advantages is good 270/300wsm brass verses winchester brand 7mm wsm brass, to work the brass less I'd get 270wsm norma brass and neck it up, your only expanding .007". But yet these with vlds will not fit in a remington sa.

Just to clear it up.

The 7mm WSM is different than all of the other WSMs and uses it's own head space gauge.

The 300 WSM has a body length of 1.802 and the 7mm WSMs body is 1.856 (.054 longer)

The neck is shorter (.244 compared to .298 of the 300) but is not two short.

It is .020 shorter than one caliber .284. And The tried and true 300 Win Mag has a neck length
.044 shorter than the caliber (.308 ) so it has a shorter neck based on the bullet dia than the
7 WSM.

All of the WSMs are the same OAL so you can make any caliber from any of the WSM brass if
you want to go to the trouble of resizing and fireforming.

In fact , Norma makes brass for the 270 and the 300 WSM an I had thought about buying some
300 WSM Norma brass and turning the necks and sizing it to 7mm WSM then fireforming it but
the Winchester brass with careful sorting and case prep has worked very well, and the accuracy
at 100 yards with 5 shots in a sporter weight custom rifle was .174 (best) and .212 (Worst)
with a 140 Accubond @ 3307 ft/sec.

I know that the accuracy could probably be improved with a different bullet/powder combination
but For hunting It shoots as well as I can under those conditions.

If I wanted to size down I would go to the 7/08 or the 6.5x47 lapua, Both are capable 1000 yard
shooters.

Again, just an opinion.

J E CUSTOM

 

[Mikecr]

This what I come up with [PICs]
from 7WSM to 7/300WSM you gain .038"neck
From 7WSM to 7SAUM you gain .068"neck

The 7SAUM is ~6-7gr less capacity

 

[J E Custom]

I see how You came up with the capacity and understand. But I never count the neck because It
is being used by the bullet and only adds unusable space.

I normally subtract one caliber of neck as an average and it works out very close to what you can
actually get in a case.

A longer body will contribute more to case capacity than neck length, and that's what I was
referring to when I said that the 7WSM would hold more powder than the 7/300 wsm because
of the .054 Thousandths longer body.

I find it very hard to get much more than 72 Grains of powder in the 7 WSM and would suspect
that the 7/300 would be around 68 grains If one caliber of bullet engagement is used. and if less
is used then it kind of defeats the purpose of a longer neck except for reaching the lands.

Again ; I have nothing against the 7/300, I just don't see the need when a 7 WSM is available
with no fuss, other than to have something different.

Just an opinion.

J E CUSTOM

 

[Mikecr]

Personally, I wouldn't worry about the shorter neck either.
If getting a barrel chambered, I'd pay the $100 to get and hold a reamer that puts the throat the way it should be for desired bullets seated with bearing clear of the neck/shoulder junction.
This reamer can also be used to make custom dies, and a headspace tool(gizzy).

 

[300magman]

While we are messing around with basically identical cartrides anyway, I might as well toss this out there.

Has anyone heard of a 7mm SAUM Improved? The 30* shoulder seems fairly conservative, I wonder how much more case capacity you would get by pushing the body forward just enough to make a 35* shoulder.

I don't think that I will do such a thing, but I'd be surprised if someone else hasn't tried a 35-40 degree shoulder.....just looking at some load data, it seems (on paper anyway) that the sweet spot for some of the popular powders is a few grains less than the WSM and a few grains more than the SAUM to get nearly 100% density with no compression.

 

[Mikecr]

Using 'Cartridge Designer' within RCBS.Load:

 

[300magman]

Well, that works.

Thanks

 

[300magman]

Mikecr, would you be kind enough to punch those numbers for the 40* shoulder in one more time, except with the case length to shoulder changed from 1.726 to the longer length of 1.739

 

[Mikecr]

You can only make small capacity gains with this cartridge, as it's already a pretty good design in base form. But I like it like this(brass should last forever)