Home Forums Reloading Big Game Rifles Got IMR 4166 today, first impressions on loading

Got 8 lbs of IMR's new "Enduron" powder 4166 in today for use in my 308. I normally prefer IMR 8208 XBR for the 155's that I shoot but couldn't find any in stock as I'm running out and I love to tinker with new things. Have a workup loaded with 155 Scenars ready for the range on Wednesday. I'll update the post with some basic firing info after that but wanted to put up a pic to show the granule size for those curious as IMR touts in their press release that it is short grained to flow smoothly through powder measures. My opinion is that is misleading or at least not what I was hoping for but I'll let you be the judge.

New label:




Below is a pic of the new powder next to some other extruded offerings I have on hand. You can see that 4166 has pretty thick granules, the only one in the group that has longer grains is old school IMR 4831 which is like trying to run toothpicks through my Redding powder measure. I'm putting this out there for those who may be wanting to use 4166 in a progressive. You can see also that XBR has by far the smallest kernels in this group.



Looking at load data by Hodgdon my guess is that 4166 falls right between H4895 and Varget in burn rate but we'll have to wait and see when it is added to the burn rate chart. Only thing pertinent I can say at this point is that this powder is pretty bulky and gives good loading density. I loaded 20 rounds up for an OCW test from 43.8 to 45.8 grains in Lapua 308 brass with the 155 Scenar(Hodgdon data indicates min of 43.0/ max of 46.2c for the 155 SMK) and I started compressing powder at 44.6 while using a 5" drop tube and loading to a COAL of 2.835". At my highest weight of 45.8 the base-ogive length was 0.003" longer than the start load and had lots of crunch when seating. By comparison, I don't have any compression at all even at max of 45.3 with XBR (still have a tiny bit of shake space even) and don't start crunching until 46.0 with Varget. So take away from this what you will, hope it helps others make a decision.

I'll be back later in the week with a limited range report, my rifle got scrubbed clean tonight so I'll be able to have a look at how clean burning 4166 is. Barrel doesn't pick up copper much at all as is so not sure I'll be able to say whether or not their "copper killer" claim is true, but if I find anything unusual I'll report back here about it.