[Matthew T.]

I saw some posts on another forum that mentioned using 7 mm Rem Mag cases for loading the .257 Weatherby Mag. Anyone over here tried this? Some of the dimensions are very similar, but the .257 WM cases have more powder capacity . . .

[GooseGestapo]

It can be done.
First start with once fired or new 7mmRemMag brass.
Polish if ofb (once fired)
Size first in a 7mm die, full length.
Size then, in a .257wm full length die.
Check and verify that it will chamber in your rifle. Load a sample round without powder or primer to verify neck clearance of case. If this is too tight, difficult chambering and insufficient neck clearance will cause excessive pressures. Too thick of necks can be remedied by neck turning the cases before loading. Check neck diameter. Max SAAMI is for .283" for unloaded cases per Nosler #4 page 208. A loaded max. should be .290".

First loading should be to starting pressures with a relatively quick burning powder. For the .257wm this will be something on the order of Varget or IMR4064. If you don't have these, a starting load of IMR4350 or H or IMR4831 should work.
Seat the bullet OUT to where it is impinging on the lead in the throat. This is very important to hold the back of the case against the bolt face so that the double radius will be formed to the shoulder and head space set correctly.
After first firing, check cases closely for overall length and any other defects.

A better starting point would probably be .300WinMag but would almost assuredly require neck turning. This would result in the radiused shoulder being in the proper place and improve headspacing on the first firing.

Let us know what you experience. I'm looking at a Vanguard in .257wm. I have a large quantity of WC-860 that should really shine, as well as a generous quantity of .257" bullets, and range pickup 7mm OFB.

I guess I better go get that gun and a set of dies. Both will run me about $350.00 USC.

[GooseGestapo]

Well, I got the gun and dies.
Went home and after going though the rifle and cleaning, tweaking the trigger as much as I could, and cleaning it well (has had apprarantly less than 40rds or so through it, maybe only 20rds, but was well copper fouled) I turned my attention to the brass/ammo situation.

I located an assortment of 7mmRemMag, 7mmWeatherbyMag, and some .300WinMag brass from range-scounging. I selected 29 pieces of Remington headstamp 7mmMag and a single piece of Winchester 7mmRemMag to form.

I started by full-length sizing in a Lee Full Length sizing die for 7mmRM. This turned out to be insightful as this greatly aided later forming/sizing in the .257WbyMag dies.

I then proceded to start them through the .257WbyMag dies. After running the case in the die with the die set to hard-contact the shell holder, I removed the first one and inspected and measure it.

The first "suprise" of several suprises. The cases miked out OK. The necks are .284" o.d. and case lenght ran 2.485" for the R-P's, and the Win case ran 2.505". Somewhat under the max. OAL of 2.535" for the .257WbyMag. Not really bad however. I then "quick and dirty" trimmed and chamfered the single case Winchester case with a Lee Trimmmer for the .257Roberts and weighed it and the other cases to check for uniformity. The Winchester was within the weight range of the Remingtons, with some of the Remington's running about 2.0gr heavier than the others, but still quite close compared to some .243's that I weighed earlier this year. I've elected to load them all together.

All the cases were good looking, and the second suprise was that they came from the .257WM die with the double radius shoulder/neck !!! Sizing effort was suprising low.

But, it couldn't be that easy !!

It wasn't. I tried to chamber them in the rifle and the bolt would go foward, but would not close. After burnishing a case well with 0000-steel wool, I tried running it in again. It was then apparant that the shoulder was not allowing the case to fully seat. Having several shell holders, I decided to grind down the shell holder to get it to go far enough into the dies to set it back sufficiently. It took approx 0.08" in order to size sufficiently to get the bolt to close. Hence, either the 7mm Lee dies didn't take the cases down enough in the shoulder (I'd never had a problem with them before), or the .257WM RCBS dies I got are a tad long. (I've not had this issue with RCBS before either).

Two last suprise's are that with the cases snug in the chamber, I don't need to long seat the bullets to get proper headspacing for the first shot. The other that I forgot that with the -LOOONG- freebored throat on the Weatherby chambers, A bullet can't be seated into the lead, at least not with the shorter reformed 7mag brass and 100gr bullets and touch the lands of the grooves. Necks with loaded bullets went .285" so are well within tolerance.

So, it worked out OK, just not exactly as I'd surmised based on SAAMI data. Between the particular rifle's chamber, and the tolerance stacking related to the dies, things were a little different.

As regards total powder capacity, I doubt that there's a meaningful difference. Variations in case length, internal capacity, and variations in chamber reamers essentially make it a "wash".

Tomorrow, I'll get to see how the ammo and the rifle shoots. I loaded a mix-match of 100gr bullets I had left over in odd quantities from load development over the years with my .257Roberts. Powder charge is a "light" load of 59.0gr of H4350, the fastest powder I had available and found listings for. Some data said 62.0gr is max, another 63.0 and a third said 66.0gr.

We'll see!

[Matthew T.]

You're downright inspirational. The high cost of Weatherby brass has been holding me back from a .257 Vanguard (on those rare occasions when the funds were available). And there is that issue of the cheek rest being on the wrong side.

[GooseGestapo]

Matt, mine IS a Vanguard, and yeah, the cost of brass "was" a biggie.

Actually, $1,000+ for a MkV, that I might get tired of in a season was really IT.

You a "Lefty" TOO !!!
I shoot from the "off" side of the rifle too due to a Left dominant eye, though I can shoot right handed if neccessary.

The "wrong" sided "hump" ain't a real problem. Just makes it easier to sell the rifle if/when you get tired of it.

[Matthew T.]

Yeah, I'm cross dominant. I fire a rifle left handed, but I never could figure out which side of the plate to bat from in softball as a kid.

[GooseGestapo]

After visit to range, a few anectodal observations.

Indeed, the cases formed from 7mmRemMag cases have less internal capacity than those formed from Weatherby (Norma) cases.

I had a single 7mmWM case in my collection. It was a very simple and easy reform by sizing it in the .257WM die. OAL came out at the published max of 2.545". I weighted it and it ran 207.7gr after trimming to match the other cases at 2.485". The other brass weighs 230gr +/- 3.5gr including all makes! Variation within makes is greater than difference between makes (Rem, Fed, Winchester, PMC). Internal capacity isn't as great as the weight would indicate. The Weatherby/Norma case held 82.8gr of H4350 whereas the R-P reformed case holds 80.2gr for a 3.14% difference in internal volumn.

At range, a load of 59.0gr of H4350 gave good accuracy with 5-shot groups running ~1.2-1.5" with 100gr Sierra FB and BT. Velocity is 3,350fps, or right about book. But, since these cases are approx 3% lower in capacity, this was probably a good "working" load rather than a low starting load. I intend to try 60.0 and 61.0 to see trend.

64.0gr of IMR4831 turned out to be at or over Maximum loading for this rifle. Velocities ran slightly upward of 3,500fps, significantly higher than I'd expected. Accuracy was poor, with groups running over 3". Some of the rounds gave increased bolt effort, and one "burnished" the case head. So, I intend to back this one off and retry for accuracy, and consider 62.0gr to be max, or 10% under published Maximum in most manuals with the Norma/Weatherby headstamped brass.

I also intend to try an expanded assortment of powders and heavier bullets. Perhaps I'll start another thread when I report back in the future.