Todays Load Conundrums with My M41B

[Wildalaska]

Started load development for my 6.5x55 M41B sniper rifle...a few issues..

What I am trying to do is duplicate, as close as possible, military trajectory (so I can use the scope camming feature)...I chronoed military loads and the 139 grainers are running about 2550 fps +/-....My ideal load is gonna be in that velocity, I hope..

I am using Sierra 140 Match Kings, Lapua Brass, Fed 210M primers and Reloader 22..All cartrides are OAL 3.150 +/- .002..I ran 50 rounds starting at 39.7 grains and finsihing at 46 grains...

Some intersting things....

The best group of the day (all 3 shotsd) came at 42 grains for av velcotiy of 2419...this group measures about .425...42.2 grains average velocity was 2413, group size .480..going to 42.8 grains gave a velocity of 2488 and a group of .430...

But when I hit 43.2 grains my velocity had jumped to 2525...there was a flyer however that was running 2550....two shots were touching however they were 2506 and 2515...

In the 44s I was averaging about my target velocity groups were opening up,,,this could have been me however..

Question therefore...should I keep working the 44 grainers and try to get may target velcoity..or maybe try some strings of 43.4, 43.5 which is cose to my target velocity and maybe vary seating depth?

WildlookingforthemoreexperiencedguysAlaska

 

[Jaywalker]

WA,

I'm not sure I understand the issue yet. My Speer 13th indicates an average velocity increase of 55 fps/grain, and your data shows a jump of 88 fps/grain between 42 grains and 43.2. The fact that it went up in steps doesn't strike me as out of the question, but standard deviation could indicate how likely a loading variation would be. (It wouldn't be particularly effective if you're resetting after only three-shot groups, but maybe a SD that you leave running for three or four three-shot groups would be valuable data.)

Were they shot on the same day? Same lot of bullets? Powder?

I think I'd want to shoot the same charge again and verify the observation. Other issues could relate to sunny vs cloudy day chronograph errors (theoretical errors to me, as I don't own a chronograph, but I'm researching a purchase).

I'm trying the same research you are right now in 6.5X55 (Ruger M77 MkII), but I'm varying the seating depth, rather than the powder charge, and am seeing significant group size changes. I'm doing it with five-shot groups, though, since I'm not sure I'd understand what a three-shot group was trying to tell me. (Two in and one out - would that have been "four in and one out," or "two together and three separate and together?"

Tell us more.

Jaywalker

 

[Wildalaska]

Everyhting was shot the same day, same lot of powder, bullets etc..

Reason I shot 3 shot groups was becasue of the large number of powder steps I had...now that I have a narrower range I will increase to 5 shot

I guess any questions are premamture since I really need to do more investigation...Im gonna do five shot groups with the narrower charge range (42- 44.5 or so) in increments of .5 and keep my seating depth the same...then I guess I cvan ask question..

Wonder if the fact that the cases are now once fired will make a diff...I am neck sizing only


WildenthusiaticaboutmynewtoyAlaska

 

[Jaywalker]

I think neck-sizing only will be beneficial. The problem with full-length sizing is the neck expander plug and the unsupported case pulling the neck out of line.

Most folks will agree that varying the powder charge .5 g is the way to go. (FWIW, the Lyman - or Speer, I forget - agree with the charge variation part of my argument, saying one or two grains are the smallest increment to worry about.) I think that's really too small an amount to worry about and am testing the seating depth variation as the agent of change.

Jaywalker