Slower powders for .308 Win

[Lefty Trigger]

Why is VV N550 a top recommended powder for the .308 but none of the other "slow" powders are? N550 is right there on my burn chart with RL19 and H100V but none of these powders or any all the way up to CFE223 are even an option. Curious about why this is??

 

[Ned Ludd]

Why is VV N550 a top recommended powder for the .308 but none of the other "slow" powders are? N550 is right there on my burn chart with RL19 and H100V but none of these powders or any all the way up to CFE223 are even an option. Curious about why this is??

Much depends on your intended use and the desired bullet weight. As an example, F-TR shooters generally tend to prefer single-base powders for .308 Win, which are usually less sensitive to temperature-induced velocity excursions. Uniform velocity is critical during the long (20+) shot strings that we fire in each match. N550 is a double-base powder, and although double-base powders are known for the ability to generate outstanding velocity, they also tend to be noticeably more sensitive to temperature as a general trend.

In terms of single-base powders, there is a well-known/appreciated "gap" in the burn rate chart between the region around Varget and the region around H4350. In terms of powders in the H4350 range and slower, there are certainly some shooters that have managed to get them to work. Others have found it difficult to get enough of these powders in the case to reach the desired velocity range (i.e. insufficient burn rate/bulk density).

FWIW - there have been F-TR shooters that have had outstanding success using VV's single-base N150 powder with 200+ gr bullets in .308 Win, most notably, this year's F-TR National Champion, Jade Delcambre. N150 is listed on the burn rate charts only slightly above H4350, i.e. near the bottom of the burn rate "gap", yet it clearly can work extremely well.

The bottom line is that although powders that are optimal for a given cartridge/bullet weight (such as a .308 Win and 200 gr bullets) typically fall within a given region in burn rate charts, you can usually develop decent loads with several different powders having burn rates throughout that given region. I've seen plenty of F-TR shooters load 200s over H4895, which has a burn rate faster than Varget, with excellent results. In other words, burn rate is only a coarse and incomplete description of a given powder's inherent properties. Other factors such as energy content and kernel size are also critical; you really want to be able to load sufficient powder into a given cartridge to achieve the desired velocity range without having to grossly compress the load. As you go further down on the burn rate chart below H4350, the powders are typically suitable for much larger cartridges and tend to have much larger kernels, meaning that it might be difficult, if not impossible, to get enough of those powders in a .308 Win case to reach the velocities you can easily hit with faster-burning powders having much smaller kernels.

As to why there seems to be a "gap" in the burn rate chart for single-base powders between approximately Varget and H4350, you'd have to ask an expert from a powder manufacturer. It might be an actual production issue, it might only be a marketing issue. I've often wondered about that myself.

 

[Lefty Trigger]

I found that Bergers load data book has useful information giving you the "case fill percent". Where I'm at only having access to 300 yards on a regular basis velocity is NOT king, accuracy is. I have been finding that some slower loads are extremely accurate albeit too slow for 1000 yard shooters to maintain energy out to the target. Our club matches are won on group size only and 3 shots precisely placed will win every time. I finally got this down with my 6mm BR and now I'm back fooling around with another .308 (not sure why) trying to get small groups. Starting to think it's harder to tune the short range than it is the long...

 

[Twicepop]

My last 308 thrived on plain ole' IMR 4064, it did well with IMR 4895 also, both medium burn rate powders.

 

[NZ_Fclass]

The main reason for N550 in .308 - bulk density. You can get a fairly dense load without too much compression. never found it much use under 208g pills - and then not as good as Varget/4350 for me. The Aussies were keen on it for a while - even for TR with 144g. Lovely powder in 7-08 with 162's though.