January 04, 2011
By Layne Simpson
A lot of new bullets and powders have been introduced since the powerhouse 7mm STW round was wildcatted by our own Layne Simpson back in 1988. Here's a special 20th birthday update.
By Layne Simpson
Shortly before Kenny Jarrett finished building the very first rifle for my new 7mm wildcat in 1987, I decided to dedicate the cartridge to readers of Shooting Times. I figured it would be ideal for hunting in the west, so I named it the 7mm Shooting Times Westerner.
My first article on the new cartridge was published in these pages in 1988. To simply say that it took off like a scalded dog among hunters across the country would be an understatement.
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Early on, top management at Remington had no interest in the 7mm STW. The 8mm Magnum, upon which it was based, was proving itself to be a dead duck at the time. However, the folks at Remington were quite puzzled when orders for thousands upon thousands of rounds of unprimed 8mm Magnum brass began to pour in from distributors across the country.
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Slow-Burning Powder Bulk-Densities Percent Water 100.0 US 869 98.1 Magnum 98.1 AA 8700 96.7 VV N170 92.9 H4831SC 91.5 H1000 90.5 Reloder 22 90.5 Reloder 25 90.5 Retumbo 90.0 H4831 89.6 H50BMG 89.6 VV 20N29 89.0 IMR-7828 88.7 NOTE: This chart compares the approximate bulk densities of various powders with that of water and has absolutely nothing to do with burn rates.
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As Remington's investigation revealed, all those cases were being sold to handloaders who owned rifles in 7mm STW. Soon after Remington realized that 7mm STW rifles and factory ammo would sell, the wheels of progress began to pick up more speed. In a ceremony held during the 1997 NRA annual meetings, I was presented with the very first production Model 700 built in 7mm STW along with the first box of 140-grain Core-Lokt ammunition to come off the production line.
A lot of water has passed under the bridge since I unveiled the 7mm STW in the May 1988 issue of Shooting Times. In that report, I included 28 loads with bullets weighing up to 175 grains along with all then-available powders I considered to be suitable for the cartridge. More specifically, they were H4831, IMR-7828, H5010, H870, and AA 8700.
Shortly after the Remington announcement about factory 7mm STW ammo in 1997, I put together an update containing loads with four additional powders: Reloder 22, H50BMG, VihtaVuori N170, and Norma MRP. At that point, a couple of powders included in my 1988 report were being phased out. One was H5010, a surplus powder developed by DuPont during World War II for the .50 BMG. It was being replaced at Hodgdon by newly manufactured H50BMG, another stick powder designed for the big .50-caliber cartridge.
Sometime later, H870, which was also military surplus but spherical in shape, was discontinued when the supply was exhausted. Lucky for those who preferred it in the 7mm STW, its burn rate is quite similar to those of H50BMG and Accurate 8700. Since my last update on the 7mm STW, five additional powders suitable for use in the cartridge have been introduced. They are Magnum from Western Powders, Retumbo and US 869 from Hodgdon, VitaVuori 20N29, and Reloder 25 from Alliant Powders. Let's take a closer look at each of them.
New Propellants
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7mm STW Optimum Powder/ Bullet-Weight Combos Powder Bullet Weight (grs.) H4831 100-120 Norma MRP 100-150 Reloder 22 100-150 IMR-7828 100-160 VV N170 100-150 H1000 120-160 Reloder 25 150-175 Magnum 150-160 Retumbo 120-160 AA 8700 160-175 H50BMG 150-175 US 869 150-175 VV 20N29 175
Layne introduced the 7mm Shooting Times Westerner as a wildcat in the May 1988 issue of Shooting Times. Since then, several new top-performing powders and bullets have been introduced.
As is sometimes the case with a spherical powder, US 869 also produced brighter muzzle flash than the other propellants.
Like Hodgdon's US 869, Magnum from Western Powders is an extremely dense spherical powder, but its burn rate in the 7mm STW is quicker and more closely compares to that of Retumbo, which is considerably less dense. Its burn rate is also similar to those of H1000, Reloder 25, and VV N170. As top velocities go, Magnum propellant is best suited for bullets weighing 150 grains and up, and while it has not delivered the highest velocities with any bullet weight for me, accuracy seldom leaves anything to be desired. Proof of this is in the fact that a maximum charge behind the Swift 150-grain Scirocco produced groups that averaged 0.52 inch at 100 yards from a Remington Model 700 APR.
When loaded in the 7mm STW, the burn rate of Hodgdon's Retumbo falls somewhere between H1000 on the slightly faster side and H50BMG and US 869 on the slower side. A stick powder, its claim to fame in this cartridge has to be its ability to deliver maximum or near-maximum velocities with all bullets ranging from 120 to 160 grains in weight. Retumbo burns cleanly and with minimal muzzle flash, and since it is a member of Hodgdon's Extreme family of powders, it delivers relatively low velocity differences from one temperature extreme to another.
The slowest burning powder readily available to handloaders, VihtaVuori 20N29, is recommended by the manufacturer for loading bullets weighing from 647 to 850 grains in the .50 BMG and those weighing 180 grains and up in the .30-378 Weatherby Magnum and .300 Lapua. I had high expectations for this stick powder behind the 160- and 175-grain bullets, but due to its extremely low density and slow burn rate, I was unable to squeeze enough into the 7mm STW case to increase velocities beyond what are possible when burning other propellants behind 160-grain bullets. It is a good choice for 175-grain bullets, although a heavily compressed charge is required to push that weight beyond 3,000 fps.
Soon after Alliant Reloder 25 was introduced, I tried it in the 7mm STW and experienced unexplained pressure spikes. Starting low in powder-charge weight and carefully working up, I found that chamber pressure had a tendency to sneak up on me. A particular charge weight would show absolutely no sign of excessive pressures, and then a 1-grain increase would suddenly blow a primer. And it wasn't just happening to me; I received letters from several Shooting Times readers who were experiencing the same problem. That powder worked fine in other cartridges, but I had given up on using it in the 7mm STW.
I am happy to say the problem does not exist with a current production lot I am using. Between the two, I still prefer Reloder 22 for bullet weights up to 140 grains, but when used with heavier bullets, Reloder 25 has a slight edge in velocity.
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New Bullets, New Powders 7mm STX Load Data
BULLET POWDER (type) POWDER (grs.) VELOCITY (fps) Barnes 120-gr. TSX Magnum 87.0 3468 Nosler 120-gr. Ballistic Tip Retumbo 89.0 3448 Sierra 130-gr. MatchKing Reloder 22 80.0 3563 Hornady 139-gr. InterBondMagnum 86.0 3338 Barnes 140-gr. MRX Retumbo 85.0 3303 Barnes 140-gr. TSX Magnum 84.0 3266 Nosler 140-gr. AccuBond Retumbo 88.0 3454 Remington 140-gr. C-L Ultra US 869 92.0 3277 Remington 140-gr. C-L Ultra Reloder 25 85.0 3327 Nosler 150-gr. E-Tip Reloder 25 80.0 3324 Nosler 150-gr. E-Tip Magnum 81.0 3214 Swift 150-gr. Scirocco Retumbo 81.0 3028 Swift 150-gr. Scirocco US 869 91.0 3151 Swift 150-gr. Scirocco Reloder 25 82.0 3362 Hornady 154-gr. InterBond Magnum 81.0 3164 Nosler 160-gr. AccuBond Retumbo 80.0 3071 Remington 160-gr. C-L Ultra US 869 90.0 3120 Remington 160-gr. C-L Ultra VV 20N29 93.0 3063 Hornady 162-gr. SST InterLock Reloder 25 80.0 3154 Hornady 162-gr. A-Max Match Reloder 25 80.0 3122 Nosler 175-gr. Partition Retumbo 77.0 2877 Sierra 175-gr. SBT GameKing US 869 88.0 2972 Swift 175-gr. A-Frame Reloder 25 79.0 3097 Swift 175-gr. A-Frame VV 20N29 93.0 3045 Notes: Velocity is the average of five rounds measured 12 feet from the guns' muzzles. Barrel lengths were 26 inches. Remington cases and Federal 215GM primers were used in all loads. All powder charges are maximum and should be reduced by 10% for starting loads.
