Imr4166 308win test results


Well-Known Member
Jan 8, 2011
I couldn't find alot of info or reviews on this powder so I finally got to test some. The results are similar to what I expected, contrary to the Hodgdon website this powder is slower than Imr4064 or Varget. In Lapua brass under 168 Berger hybrids I stopped at 46.2grns .010" off jam, yes this is 3.1 grains over there listed max for 168 Sierras. It showed slight primer flattening throughout the entire work up as does my PP2000MR go to load. This brass has 5-6 firings on it and is still like new. I intend to go a little higher maybe load some at 46.5 and 46.8, I think 46.8 is all thats going to fit in Lapua brass. My rifle also has a short throat so my base to ogive is less than 2.180". I was using CCI BR2s with this powder, the interesting thing is that 45, 45.3, 45.6, and 45.9 all shot .3" or less at 100 yards. I did not get any velocity readings this go around but it shoots within a 1/4" of the same point of impact as my PP2000MR load that runs 2877fps average. So for those who were looking for some information on this powder, I think it is a very good alternative to Imr4064 or Varget, it is cleaner burning than Varget and Imr4064 so if it lives up to the other claim of temperature insensitivity it will be a great powder. If I had a longer throat I would try it with 175smk and 185 Juggernauts, I will try it with 185 hybrids as I can get those up out of the case far enough because I think this is going to be a top performer with 175 and heavier bullets as it seems to be a little on the slow side for 168s. As far as pressure goes I do not read primers unless they are so flat they fill the entire pocket, I judge pressure from case head expansion and bolt lift, the bolt lift was like shooting factory ammo and the case head measured the same before and after firing. At any rate give it a try just don't jump right in at the charge weights I listed, work up your own for the obvious safety reasons. As for looks this powder looks like a darker version of Imr4064 that has the IMR ssc grain structure and meters much better than Imr4064.
Good info. Thnx Backwood83, my shooting buddy will like to know this. He's got a .308Win and he and I go out when we can. Right now, I'm wearing him out at all ranges with my 6.5-284Norma. Lol, he needs all the help he can get.
I read the articles in Hodgdon's Reloading annual manual/magazine on the three new IMR Enduron powders. The articles didn't do them justice but I think the reloaders will wring the most out of them. JohnnyK.
I hope it helps some, however I have been shooting a 6.5x284 since 2008 and there is no amount of help thats going to get him even close to the same league with a 308. A 300wm shooting 230 hybrids at 2850fps still takes 1200+ yrds to catch my 6.5x284 load. I love the 308 because its cheap to load and easy to find components but it sadly gets raped by the baby 6br. He should probably switch calibers if he intends to compete with a 6.5x284. When I can find Imr7977 I intend to try it in the 6.5 since I currently use H1000 and Retumbo.
I have been using it in my TRG22 308 26" for a couple of months. I settled on (don't laugh) 41.66grs under a 175 SMK in a FC case. It does 2625 FPS with an ES of 10. Been using BR-2 primers, 210's and 200's. My lot of 200's makes 20 FPS less velocity. Accuracy wise, I can put three through the same hole at 100 yards, but then satan interferes and I get a flier or two. But it always shoots .5" or less.

To compare it with 4064, I get similar velocities with 41.75grs of 4064. The difference is 4166 is a double base powder and 4064 is single base. 4166 is much cleaner and does not leave 10% of the carbon that 4064 does.
I've been using this powder for a couple months as well. My best load so far is 41 grains behind a 175 Nosler custom competition with BR-2 primer. Out of a 24 inch barrel I am getting 2553 fps. I am consistently getting 5 shots under a 1/2" at 100 yards. The powder burns clean and does help reduce copper fouling.
Good info. I've got a couple pounds I'm hoping to do some testing with this summer as well. All indications point to these new Enduron powders as being winners.
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