Have you tried IMR Enduron powders yet (IMR 4166, 4451, 4955, 7977, and/or 8133)? We’ve been impressed with what we’ve seen. IMR’s line of Enduron extruded powders offer excellent temp stability, reduced copper fouling, and good load density for many popular cartridges (such as .223 Rem, 6mmBR, .308 Win, .30-06, 300 WSM to name a few). Some of our Forum members have reported excellent results with IMR 4166 in the 6mmBR, Dasher, 6.5×47 Lapua and .308 Win. One member wrote: “in my 6.5×47… 4166 gives speeds and accuracy pretty much exactly the same as Varget.” And other shooters have observed reduced copper fouling with Enduron series powders, so IMR’s Enduron anti-fouling chemistry does seem to work.
IMR now offers five (5) Enduron powders: IMR 4166, IMR 4451, IMR 4955, IMR 7977, and IMR 8133. Shooters looking for good alternatives to hard-to-find extruded powders should definitely check out the Enduron line-up. Precision shooters will find an Enduron option well-suited to most popular precision cartridge types. For example, IMR 4166 is a good replacement for Hodgdon Varget (commonly used in the .223 Rem, 6mmBR and .308 Win), while IMR 4955 is a fine substitute for H4831 (favored by F-Open shooters for the .284 Win and 7mm WSM cartridges).
The Enduron Line-Up of Five Powders
IMR now offers five Enduron powders that cover a broad range of burn rates. They are suitable for a wide variety of cartridges, from small varmint cartridges all the way up to the .338 Lapua Magnum.
IMR 4166 possesses the fastest burn rate in the Enduron lineup. It is the perfect burn speed for cartridges such as .308 Win, 7.62mm NATO, 22-250 Rem and 257 Roberts. A versatile, match-grade propellant, IMR 4166 is comparable to Hodgdon® Varget.
IMR 4451 is a mid-range burn speed powder, ideally suited for cartridges such as .270 Winchester, .30-06 and 300 Winchester Short Magnum. This powder is comparable to Hodgdon H4350.
IMR 4955 is a medium burn speed powder, falling in between IMR 4451 and IMR 7977 in burn speed. It provides top performance in big game cartridges such as 25-06, 280 Remington and 300 Winchester Magnum. This powder is comparable to Hodgdon H4831.
IMR 7977 is a slower burn rate in the Enduron family. Loading density is perfect for magnums. This is a true magnum propellant yielding outstanding performance in .300 Winchester Magnum, 7mm Remington Magnum and .338 Lapua Magnum. IMR 7977 is comparable to Hodgdon H1000.
IMR 8133 IMR Enduron 8133 is the slowest burn rate in the Enduron family. Loading density is perfect for the very large magnums, including the 6.5mm and 7mm magnums. This is a true magnum propellant yielding outstanding performance in 6.5-300 Weatherby, .264 Win Mag, 28 Nosler and .300 Rem Ultra Mag, among other cartridges.
IMR Enduron Technology powders are sold in one-pound (1 lb) and eight-pound (8-lb) containers through quality retailers including Graf & Sons, Midsouth, and Powder Valley. Check frequently for current availability as these will sell out quickly after arrival. Also check your local sporting goods dealers for recent powder shipments.
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Have you tried IMR Enduron powders yet (IMR 4166, 4451, 4955, and 7977)? We’ve been impressed with what we’ve seen. IMR’s line of Enduron extruded powders offer excellent temp stability, reduced copper fouling, and good load density for many popular cartridges (such as .223 Rem, 6mmBR, .308 Win, .30-06, 300 WSM to name a few). Some of our Forum members have reported excellent results with IMR 4166 in the 6mmBR, Dasher, 6.5×47 Lapua and .308 Win. One member wrote: “in my 6.5×47… 4166 gives speeds and accuracy pretty much exactly the same as Varget.” And other shooters have observed reduced copper fouling with Enduron series powders, so IMR’s Enduron anti-fouling chemistry does seem to work.
Varmint hunters, big game hunters, match shooters and military snipers all seek powders that are insensitive to temperature changes. These powders all have it. This translates to point of impact and group size remaining the same, no matter what temperature conditions prevail. Another huge benefit is an additive that prevents copper fouling from building during dozens of rounds being fired. Here the advantage is top accuracy for longer periods of time, and less cleaning time.
A third major accomplishment with this technology is ideal load density. Experienced reloaders know that a case-filling load often delivers the most uniform velocities and best accuracy. We see this in popular match cartridges such as the 6PPC, 6mmBR, 6BRA, 6.5 Creedmoor and .308 Win. These new Enduron powders offer excellent “full case” load density for the most commonly used cartridges with popular bullets.
These three powders, IMR 4166, IMR 4451 and IMR 7977, are environmentally friendly by not having any ingredients harmful to the environment. Add to that, the three of them cover the most popular cartridges from .204 Ruger up to the mighty 500 Nitro Express, and the handloader “has it all”.
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Well folks, it’s July 6th already — the means we’re moving into “peak heat” summer conditions. It’s vitally important to keep your ammo at “normal” temps during the hot summer months. Even if you use “temp-insensitive” powders, studies suggest that pressures can still rise dramatically when the entire cartridge gets hot, possibly because of primer heating. It’s smart to keep your loaded ammo in an insulated storage unit, possibly with a Blue Ice Cool Pak if you expect it to get quite hot. Don’t leave your ammo in the car or truck — temps can exceed 140° in a vehicle parked in the sun.
To learn more about how ambient temperature (and primer choice) affect pressures (and hence velocities) you should read the article Pressure Factors: How Temperature, Powder, and Primer Affect Pressure by Denton Bramwell. In that article, the author uses a pressure trace instrument to analyze how temperature affects ammo performance. Bramwell’s tests yielded some fascinating results.
For example, barrel temperature was a key factor: “Both barrel temperature and powder temperature are important variables, and they are not the same variable. If you fail to take barrel temperature into account while doing pressure testing, your test results will be very significantly affected. The effect of barrel temperature is around 204 PSI per F° for the Varget load. If you’re not controlling barrel temperature, you about as well might not bother controlling powder temperature, either. In the cases investigated, barrel temperature is a much stronger variable than powder temperature.”
Powder Heat Sensitivity Comparison Test
Our friend Cal Zant of the Precision Rifle Blog recently published a fascinating comparison test of four powders: Hodgdon H4350, Hodgdon Varget, IMR 4451, and IMR 4166. The first two are Hodgdon Extreme powders, while the latter two are part of IMR’s Enduron line of propellants.
The testers measured the velocity of the powders over a wide temperature range, from 25° F to 140° F. Hodgdon H4350 proved to be the most temp stable of the four powders tested.
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Hey guys, you’ll probably want to download this Powder Burn Rate Table issued by Hodgdon/IMR. This table shows the latest IMR powders including the Enduron series (IMR 4166, 4451, 4955, 7977), high-lighted in green below. This 163-entry comparison table provides useful information for all hand-loaders. When doing load development, and testing one powder versus another, it’s generally wise to choose propellants that share the same relative burn rate, as least for starters. This invaluable burn rate chart ranks powders from eight major powder-makers: Accurate, Alliant, Hodgdon, IMR, Norma, Ramshot (Western), Vihtavuori, Winchester.
NOTE: Hodgdon powders are blue, IMR standard powders are yellow, IMR Enduron powders are green, and Winchester Powders are Red. DOWNLOAD Chart HERE.
A couple seasons back, PrecisionRifleBlog.com (PRB) published a significant field test of powder temperature stability. The test was designed to quantify the temperature stability of Hodgdon H4350 and Varget powders compared to IMR’s Enduron line of powders, specifically IMR 4166 and 4451. The results were very interesting, to say the least…
Hodgdon Extreme Series powders have attracted quite a fan base, with over 90% of the top shooters in the Precision Rifle Series choosing to run one of those powders. IMR offers a modern line of powders “with Enduron Technology” — which is also marketed to have “extreme temperature stability”. Sounds familiar! These new powders should compete directly with the Hodgdon Extreme Series, which gives shooters more temp-stable powder options to consider.
The top shooters in the PRS and veteran long-range shooters in other disciplines have learned to value a temperature-stable powder. That’s because a change in temperature can affect the trajectory or “flight path” of the bullet in two well-known ways:
1. Assuming all other environmental conditions remain the same, an increase in air temperature will cause a flatter trajectory due to a lower air density (easier for the bullet to cut through the air).
2. The same increase in temperature also causes the nitrocellulose-based powder inside the cartridge to burn at a higher rate, producing approximately four times the Point of Impact (POI) shift than just air temperature alone. (SEE: Temperature Effects On Zero on KestrelMeters.com.)
“The initial heat condition of your powder will affect the burn rate,” Bryan Litz explained at a recent Applied Ballistics Seminar. That means swings in ambient outside temperature can affect your internal ballistics, which will directly affect your muzzle velocity, which will change your bullet’s trajectory. Some powders are more affected by changes in temperature than others. So if your goal is first-shot hits and you may shoot in a variety of conditions — you should care about temperature stable powders.
The folks at PrecisionRifleBlog.com meticulously loaded 6.5×47 Lapua ammo with each powder using some of the best equipment available. This included the top-of-the-line Prometheus Gen II Powder Scale, which is capable of loading to the nearest kernel of powder. This ensured the powder charges were identical for each round of ammo. PRB’s testers explain the full set of equipment and steps in their loading process in the Full Test Report.
Once they had a couple dozen rounds loaded with each powder, they went and shot them with each powder at 25° F, 65° F, and 140° F. The muzzle velocity of each shot was recorded using BOTH a LabRadar Doppler Radar and a MagnetoSpeed Chronograph. That provided two sets of velocity numbers. When placed and configured optimally, the LabRadar can measure muzzle velocity with +/- 0.1% accuracy, according to the manufacturer.
Here are the results from the PRB Powder Temp Stability Tests:
You can see Hodgdon H4350 had the least variance in muzzle velocity, with just 25 fps over the 115° swing in temperature! That is very, very low. Hodgdon Varget was the second least temperature sensitive powder in this test, with 46 fps of variance in muzzle velocity between temperatures of 25° F and 140° F. IMR 4166 performed very similar to Varget, and proved to be fairly insensitive to large swings in temperature. IMR 4451 had the largest swing in muzzle velocity of the powders tested, but keep in mind just 68 fps over 115° F swing is still a good performance.
Most powders aren’t specially formulated to be temperature stable. So they would likely show much larger swings than what these four top-performing powders showed. However, Alliant’s relatively new Reloder 16 is an extremely temp-stable powder, with a burn rate that is a close match to H4350. Many F-Open competitors are now using Reloder 16 with considerable success.
PRB’s test team also noticed other interesting trends in the data. For example, variation in velocity does NOT appear to be linear across the full range of temperatures. By that, they mean the change per degree from 20° to 65° might be smaller or larger than the change per degree from 65° to 140°.
PrecisionRifleBlog.com (PRB) recently published results from a field test PRB conducted to quantify the temperature stability of the popular Hodgdon H4350 and Varget powders and compare those to IMR’s new Enduron line of powders, specifically IMR 4166 and 4451.
Hodgdon Extreme Series powders have attracted quite a fan base, with over 90% of the top shooters in the Precision Rifle Series choosing to run one of those powders. IMR recently released a new line of powders “with Enduron Technology” — which is also marketed to have “extreme temperature stability”. Sounds familiar! These new powders should compete directly with the Hodgdon Extreme Series, which gives shooters more temp-stable powder options to consider.
The top shooters in the PRS and veteran long-range shooters in other disciplines have learned to value a temperature-stable powder. That’s because a change in temperature can affect the trajectory or “flight path” of the bullet in two well-known ways:
1. Assuming all other environmental conditions remain the same, an increase in air temperature will cause a flatter trajectory due to a lower air density (easier for the bullet to cut through the air).
2. The same increase in temperature also causes the nitrocellulose-based powder inside the cartridge to burn at a higher rate, producing approximately four times the Point of Impact (POI) shift than just air temperature alone. (SEE: Temperature Effects On Zero on KestrelMeters.com.)
“The initial heat condition of your powder will affect the burn rate,” Bryan Litz explained at a recent Applied Ballistics Seminar. That means swings in ambient outside temperature can affect your internal ballistics, which will directly affect your muzzle velocity, which will change your bullet’s trajectory. Some powders are more affected by changes in temperature than others. So if your goal is first-shot hits and you may shoot in a variety of conditions — you should care about temperature stable powders.
The folks at PrecisionRifleBlog.com meticulously loaded 6.5×47 Lapua ammo with each powder using some of the best equipment available. This included the top-of-the-line Prometheus Gen II Powder Scale, which is capable of loading to the nearest kernel of powder. This ensured the powder charges were identical for each round of ammo. PRB’s testers explain the full set of equipment and steps in their loading process in the Full Test Report.
Once they had a couple dozen rounds loaded with each powder, they went and shot them with each powder at 25° F, 65° F, and 140° F. The muzzle velocity of each shot was recorded using both a LabRadar Doppler Radar and a MagnetoSpeed Chronograph. The LabRadar is a new type of device that allows you to measure muzzle velocity within at least +/- 0.1% of the reading.
Here are the results from the PRB Powder Temp Stability Tests:
You can see Hodgdon H4350 had the least variance in muzzle velocity, with just 25 fps over the 115° swing in temperature! That is very, very low. Hodgdon Varget was the second least temperature sensitive powder in this test, with 46 fps of variance in muzzle velocity between temperatures of 25° F and 140° F. IMR 4166 performed very similar to Varget, and proved to be fairly insensitive to large swings in temperature. IMR 4451 had the largest swing in muzzle velocity of the powders tested, but keep in mind just 68 fps over 115° F swing is still a good performance.
Most powders aren’t specially formulated to be temperature stable. So they would likely show much larger swings than what these four top-performing powders showed.
PRB’s test team also noticed other interesting trends in the data. For example, variation in velocity does NOT appear to be linear across the full range of temperatures. By that, they mean the change per degree from 20° to 65° might be smaller or larger than the change per degree from 65° to 140°.
Many Forum members have been looking for a good substitute for Hodgdon H4350 powder, which remains hard-to-find in many parts of the country. One of the best alternatives is IMR 4451, part of IMR’s new Enduron line of powders. Last year, top F-Class shooter Rick Jensen did a comparison between H4350 and IMR 4451, shooting the two powder in a wide range of temperatures. His data suggests that both powders show good temp stability.
Powder Comparison Test: H4350 vs. IMR 4451
Rick Jensen, Captain of the U.S. F-Open Rifle Team, has tested some of the new IMR 4451 powder. Rick and other team members were looking for a good powder that could replace Hodgdon 4350 which is difficult to obtain currently. The makers of IMR 4451 claim that it is not sensitive to temperature and that it delivers competitive accuracy. So far, Rick’s tests, done with a .284 Winchester and 180gr Berger Hybrids, appear to confirm those claims. Rick posts:
“I did a little informal powder comparison of H4350 versus the new IMR 4451. Rifle used was a Kelbly Panda with a 30″, 1:8.75″ twist 5R Bartlein barrel [chambered in .284 Win]. All charge weights were 50.0 grains using CCI BR2 primers. I was very impressed with this new powder and I believe it to be equal to H4350 as far as temperature sensitivity.
I did not test for accuracy but I will tell you my groups were pretty much equal between the two and all were in the .2-.3 MOA range. I will defiantly be shooting more of this powder in the weeks to come, assuming the supply chain will allow. It looks very encouraging to finally have a alternative to H4350 that we might actually be able to buy.”
Chronograph Results with Temps from 23° F to 101°
Here are chronograph results of a comparison test between IMR 4451 and H4350. Rick’s rifle was cleaned and allowed to cool between each test. Five fouling shots were fired before each test. Important: Note that for both Test #1 and Test #2, the powder order is reversed in the mid-temp fields (IMR 4451 first, then H4350). For the low and high temp entries, H4350 is listed first.
Here are the IMR 4451 fired cases, displayed Left to right, coldest to the hottest (in terms of case temp when fired). All charge weights were the same: 50.0 grains.
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Well folks, it’s July 1st already — the means we’re moving into “peak heat” summer conditions. It’s vitally important to keep your ammo at “normal” temps during the hot summer months. Even if you use “temp-insensitive” powders, studies suggest that pressures can still rise dramatically when the entire cartridge gets hot, possibly because of primer heating. It’s smart to keep your loaded ammo in an insulated storage unit, possibly with a Blue Ice Cool Pak if you expect it to get quite hot. Don’t leave your ammo in the car or truck — temps can exceed 140° in a vehicle parked in the sun.
To learn more about how ambient temperature (and primer choice) affect pressures (and hence velocities) you should read the article Pressure Factors: How Temperature, Powder, and Primer Affect Pressure by Denton Bramwell. In that article, the author uses a pressure trace instrument to analyze how temperature affects ammo performance. Bramwell’s tests yielded some fascinating results.
For example, barrel temperature was a key factor: “Both barrel temperature and powder temperature are important variables, and they are not the same variable. If you fail to take barrel temperature into account while doing pressure testing, your test results will be very significantly affected. The effect of barrel temperature is around 204 PSI per F° for the Varget load. If you’re not controlling barrel temperature, you about as well might not bother controlling powder temperature, either. In the cases investigated, barrel temperature is a much stronger variable than powder temperature.”
Powder Heat Sensitivity Comparison Test
Our friend Cal Zant of the Precision Rifle Blog recently published a fascinating comparison test of four powders: Hodgdon H4350, Hodgdon Varget, IMR 4451, and IMR 4166. The first two are Hodgdon Extreme powders, while the latter two are part of IMR’s new Enduron line of propellants.
The testers measured the velocity of the powders over a wide temperature range, from 25° F to 140° F. Hodgdon H4350 proved to be the most temp stable of the four powders tested.
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IMR® Legendary Powders now offers four (4) Enduron powders: IMR 4166, IMR 4451, IMR 4955, and IMR 7977. Shooters looking for readily-available alternatives to hard-to-find extruded powders should definitely check out the Enduron line-up. Precision shooters will find an Enduron option well-suited to most of the popular precision cartridge types. For example, IMR 4166 is a good replacement for Hodgdon Varget (commonly used in the .223 Rem, 6mmBR and .308 Win), while IMR 4955 is a fine substitute for H4831 (favored by F-Open shooters for the .284 Win and 7mm WSM cartridges).
Modern Powder Technology for Enhanced Performance
The technology in IMR’s Enduron line of powders provides four very important qualities that enhance both in-gun and downrange performance.
Copper fouling reduction – these powders contain an additive that drastically reduces copper fouling in the gun barrel. Copper fouling should be minimal, allowing shooters to spend more time shooting and less time cleaning a rifle to retain accuracy.
Temperature change stability – the Enduron line is insensitive to temperature changes. Whether a rifle is sighted in during the heat of summer, hunted in a November snowstorm or hunting multiple locations with drastic temperature swings, point of impact with ammunition loaded with Enduron technology will be very consistent.
Optimal load density - Enduron powders provide optimal load density, assisting in maintaining low standard deviations in velocity and pressure, a key feature for top accuracy.
Environmentally friendly - Enduron technology is environmentally friendly, crafted using raw materials that are not harmful to the environment.
The Enduron Line-Up of Four Powders
IMR now offers four Enduron powders that cover a broad range of burn rates. They are suitable for a wide variety of cartridges, from small varmint cartridges all the way up to the .338 Lapua Magnum.
IMR 4166 possesses the fastest burn rate in the Enduron lineup. It is the perfect burn speed for cartridges such as .308 Win, 7.62mm NATO, 22-250 Rem and 257 Roberts. A versatile, match-grade propellant, IMR 4166 is comparable to Hodgdon® Varget.
IMR 4451 is a mid-range burn speed powder, ideally suited for cartridges such as .270 Winchester, .30-06 and 300 Winchester Short Magnum. This powder is comparable to Hodgdon H4350.
IMR 4955 is a medium burn speed powder, falling in between IMR 4451 and IMR 7977 in burn speed. It provides top performance in big game cartridges such as 25-06, 280 Remington and 300 Winchester Magnum. This powder is comparable to Hodgdon H4831.
IMR 7977 has the slowest burn rate among the Enduron Technology powders. Its loading density is perfect for magnum cartridges and contributes to superb uniformity, yielding outstanding performance in 300 Winchester Magnum, 7MM Remington Magnum and .338 Lapua Magnum. IMR 7977 is comparable to Hodgdon H1000.
The Enduron Technology powders are available in one-pound (1 lb) and eight-pound (8-lb) containers from quality reloading retailers. Learn more about Enduron powders at www.enduronimr.com. For info on other IMR powders, visit www.imrpowder.com.
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In 2015, IMR® Powder introduced a new line of powders with Enduron® Technology. These powders are designed to address several performance gaps as powder technology has advanced. Here are key features of the Enduron line of propellants:
Enduron powders contain an additive that drastically reduces copper fouling in the gun barrel. Copper fouling should be minimal, allowing shooters to spend more time shooting and less time cleaning a rifle to retain accuracy.
The new Enduron line is insensitive to temperature changes. Whether a rifle is sighted in during the heat of summer, hunted in a November snowstorm or hunting multiple locations with drastic temperature swings, point of impact with ammunition loaded with Enduron technology will be very consistent.
Enduron powders provide optimal load density, assisting in maintaining low standard deviations in velocity and pressure, a key feature for top accuracy.
Enduron technology is environmentally friendly, crafted using raw materials that are not harmful to the environment.
New IMR 4955 for Larger Cartridges
For 2016, IMR has introduced IMR 4955, a new Enduron extruded powder that is a top performer with popular cartridges such as 270 Winchester, 25-06 Remington, 280 Remington, 300 Winchester Magnum and many more. This new powder falls directly between the new IMR 4451 and IMR 7977 in burn speed, providing excellent performance for most big-game cartridges. Like all Enduron Technology powders, IMR 4955 is temperature insensitive, as shown below.
Adding this propellant to the Enduron line filled in an important place on reloading benches. IMR 4955, plus the original three Enduron powders, provide excellent loading solutions for cartridges from 223 Remington to the massive 500 Nitro Express Magnum. Further, in these days of powder shortages, these new Enduron powders can fill a gap by providing comparable performance to select Hodgdon® powders. Specifically, IMR 4955 is a great choice for cartridges that work well with Hodgdon H4831.
IMR Enduron 4955 is available in one-pound (1 lb.) and eight-pound (8 lb.) containers from quality reloading retailers.
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Hey guys, you’ll probably want to download this new Powder Burn Rate Chart issued by Hodgdon/IMR. This new table shows the latest IMR powders including the Enduron series (IMR 4166, 4451, 4955, 7977), shown in green below. This chart provides useful information for all hand-loaders. When doing load development, and testing one powder versus another, it’s generally wise to choose propellants that share the same relative burn rate, as least for starters. NOTE: Hodgdon powders are shown in blue, while IMR standard powders are shown in yellow. DOWNLOAD Chart HERE.
The 2015 Hodgdon Annual Manual (the 12th Annual Edition) has been released. The 2015 Hodgdon Manual now contains over 5000 loads — more load data than you’ll find in any other annual reloading resource. The 2015 Manual has updates for numerous rifle and pistol cartridges. Featured in the 2015 Manual are the new IMR Enduron™ powders such as IMR 4166, IMR 4451, and IMR 7977. Enduron powders feature a built-in copper fouling reducer, along with small kernels for easy metering and good load density. IMR also claims that Enduron powders are not sensitive to ambient temperature changes. It appears IMR 4166 may be a viable alternative to Hodgdon’s popular, but hard to find, Varget powder.
Along with comprehensive load data, the 8 1/2″ by 11″ magazine-style Hodgdon Annual Manual offers authoritative articles by top gun industry writers. You can purchase the 2015 Manual at news-stands (and gunshops) for $8.99. In a few weeks, you should also be able to purchase the manual from Hodgdon’s online store. For more info, visit Hodgdon.com or call 913-362-9455.
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To learn more about how ambient temperature (and primer choice) affect pressures (and hence velocities) you should read the article 
“I did a little informal powder comparison of H4350 versus the new IMR 4451. Rifle used was a Kelbly Panda with a 30″, 1:8.75″ twist 5R Bartlein barrel [chambered in .284 Win]. All charge weights were 50.0 grains using CCI BR2 primers. I was very impressed with this new powder and I believe it to be equal to H4350 as far as temperature sensitivity.
The 2015 
