IMR 4064 and 50 gr BlitzKings in my Swift.

[Wyoredman]

I have posted earlier in this forum about how my Winchester .220 Swift really liked 55gr blitzkings and IMR 4064 at 38.5 gr. This load was averaging around 3750 fps for me and very accurate.

Lately I have been experimenting with the lighter 50 gr BK's and 4064 using win brass, WLR primers and a COAL of 2.680".

After referencing the Sierra V manual, they show a max (and best hunting load) for the 50gr BK's of 39.9 gr. So I started my work up with this combo at 38 grs and in 0.5 gr steps, built 10 rounds each stopping at 40 grs.

I shot each 10 rounds in 2-5shot groups over my chrony. I was very surprised to see that unlike the 55 gr BK's, as velocity increased, group size decreased.

For example at 38 grs, my velocity was 3823 fps and the two groups averaged 1.23". The 39 gr load was clocked at 3902 fps and the two groups averaged 0.98". The 39.5 gr load clocked in at 3976 fps and the group average dropped to 0.89". Finally the book max load of 39.9 gr (actually loaded 40 grs) was flying down range at 4045fps but grouped a 2 group average of 0.63"!

Also of note, the 40 gr load in my gun didn't show any signs of pressure. The bolt was easy to open and the primers and case heads looked fine. My 10 shots averaged 45 fps faster than the Sierra manual predicted of 4000fps.

Has anyone else found that near max loads can be accurate with these lighter bullets in their Swift. I wasn't expecting this outcome, but I am not dissapointed in any way!

[Unclenick]

Nothing very unusual in that. A lot of benchrest shooters have reported accuracy to be best at near maximum loads for as long as I've been reading about handloading. Though I'll also point out you may well have missed another barrel timing sweet spot by not starting at 10% below maximum pressure. Western Powder's FAQ cites that, in addition to safety, as a reason for not starting in the middle of a published load range, but going all the way to the bottom. On the safety side it's because a lot of loads are still measured in copper crushers and, as SAAMI's example of sending the same lot of reference ammunition to 9 different test facilities shows, below, those instruments can be off by around 25% sometimes.

Due to dimensions in your individual chamber, your top load may well be above SAAMI MAP. As long as the accuracy is tight, it's not likely to be outside its own individual limits. I would suggest, however, that 0.5 grains is a little large and you might miss some accuracy sweet spots. Try about .3 grains as you go up any further.

[Wyoredman]

Thanks for the insight, Unclenick. I do agree that starting load work up at 10% below max should be the norm. Let me give you a bit of my reasoning for starting at 38 grs., though.

I had already done a complete load work-up from min to max listed in the Sierra manual for the 55 gr BK. I new that 38.5 gives me the best accuracy with the 55 gr bullet and I had a measured velovity with that charge.

In switching to the 50 gr BK, being 5 grs lighter, I figured that 38 would be a good starting point.

I wasn't planning on going up any further, as 4050fps seems pretty much at the limits of safe velocity (pressure) in my mind. It's pretty fast!

Anyway, that is the explination of my thinking with this "experiment". I think I will mess around with some different loads between 39 and 40 grs 4064. Maybe do these in .3 gr steps? See if the barrel sweet spot is in there some place.

BTW, I have also read on this forum and in other places that small variations in powder charge, like .3 grs, often don't make much differance at all in accuracy and velocity? In other words, if a group of 100 rounds is loaded with charges ranging from 39.8 to 40.1 grs, the rifle and shooter will not tell the differance in POI and velocity measurements? Is this true?

[Unclenick]

With 4064, in particular, it often is the case that's is not too sensitive to small load variations. The reason for 0.3 grains is partly that it's the smallest measure you can make on a scale with ±0.1 grain accuracy that you can be sure is actually different from the previous load. The other is that it comes from Dan Newberry's OCW approach of using about 0.7% to fire his round robins where he identifies a sweet spot by finding a load range where the point of impact doesn't change for three loads (a 0.6 grain span). That makes the midpoint easier to identify. But there's nothing to say you couldn't have a wider one. At the extremes, I've seen an accuracy load that was completely opened up when I went .5 grains either side of it (this was in .308), and at the other, a different load that stayed right in there for a span of 2.5 grains. (That was using Brigadier 3032, so naturally the plant burnt down and you can't get it anymore.)

Gotcha on the load workup. Since both were BK's you weren't likely to run into construction differences that raised pressure as can happen when switching the bullet type or make. Still, you might have a low load somewhere down there that shoots well for you.

[Wyoredman]

Thank you, Sir. You make it easy for me to achieve that personal goal of learning something new every day!

[603Country]

Wyo, I think we've already noted that our favorite loads for 55 gr bullets is that 38.5 gr of IMR4064. That is interesting. Now if you just had a magic load for the 60 gr Partition in my 220......

[Ralph Allen]

Looked up my old data for my 220 Swift on 60 gr Vmax and 63 Sierra and I was useing 38.0 gr of H4350. Still have a box loaded of each on the shelf.
Ralph