Erratic Velocity

slimjim · Posted: Thu Mar 22, 2018 4:32 am Post subject: Re: Erratic Velocity

Aloysius wrote:

I point my barrel high, tap slightly my rifle so that all powder is seated near the primer and shoot.

Aloys, I'm not sure the deer would stand still for me while I do that.

Vince · Posted: Thu Mar 22, 2018 4:33 am Post subject: Re: Erratic Velocity

Interesting and all pertinent points Aloys. The only other thing I would consider is even only a slight crimp with a LEE FCD just to hold that boollitt long enough for the primer to do its job with the powder. Might also help with a little bit of consistency with the bullet grip in the case.

slimjim · Posted: Thu Mar 22, 2018 4:42 am Post subject: Re: Erratic Velocity

Elvis wrote:

what kinda plurry graph is that????

Elvis, my apologies. I should have explained better. Each line is a range session (I worked up my powder charge slowly over a couple of range session). The straight line with just two points had more shots but I failed to arm the chrono so missed the readings. So yes, each dot was a shot. To define performance boundaries especially with a new powder without factory load data, I shoot a powder vs velocity ladder with one charge weight per shot (0.5 grain increments in this example). I track velocity, point of impact, and pressure signs. 75% of the time, I find the accuracy node when 3 sequential shots group under and inch. The graph below is more typical of the powder vs velocity ladders I shoot. The accuracy node was 60.0 grains.

slimjim · Posted: Thu Mar 22, 2018 4:47 am Post subject: Re: Erratic Velocity

Vince wrote:

The only other thing I would consider is even only a slight crimp with a LEE FCD just to hold that boollitt long enough for the primer to do its job with the powder.

I use a Lee FCD die on all my rounds. My bullets don't leave home without it (a crimp).

slimjim · Posted: Thu Mar 22, 2018 4:51 am Post subject: Re: Erratic Velocity

Aloysius wrote:

I would not recommend the use of magnum primers in your example.

Aloys, I will try standard primers. I had some loads in my 6.8mm with heavy bullets that were more consistent and less temperature sensitive with standard primers.

slimjim · Posted: Thu Mar 22, 2018 4:54 am Post subject: Re: Erratic Velocity

Elvis wrote:

if Im reading it right your 56.5grn 3 shots have VS of 25fps or less???? and you pushing a 145grn pill at just under 3000fps...THAT ALONE would be an awesome load WITHOUT any more tweeking and says to me project worth time to continue

Elvis, 56.5 was what I was going to test next. I'll load 6 rounds for the next range session with this powder charge, 3 with magnum and 3 with standard primers.

Thanks all for the discussion.

English Mike · Posted: Thu Mar 22, 2018 1:38 pm Post subject: Re: Erratic Velocity

slimjim wrote:

Aloysius wrote:

I point my barrel high, tap slightly my rifle so that all powder is seated near the primer and shoot.

Aloys, I'm not sure the deer would stand still for me while I do that.

might be an idea to try it on your next range trip though, as it'd eliminate one variable, or demonstrate that is is indeed an issue.

Elvis · Posted: Thu Mar 22, 2018 2:13 pm Post subject: Re: Erratic Velocity

ok but graph still doesnt make sense.... dots should ALL be on a line and there should be same number on each line or figures will be skewiff.

as a side note Ive just ordered a box of hornady 180grn round nose interlocts for the .308........ wont want to put them over a chrony...but wouldnt want to be on recieving end either....sub hundy bush loads.

Azar · Member Joined: Jan 04, 2010 Posts: 275 Location: Utah

Slim,

Allow me to encourage you to spend some of your hard earned money and well deserved free-time with the purchase of a Pressure Trace II.

You know you want it! The fact that the rest of us will be able to benefit from your findings is simply icing on the cake. Very Happy

I recently tested IMR 4955 in a 6.5x55 and found a similar behavior for that combo, with larger than typical velocity swings from shot-to-shot. I picked the most promising powder charge and tried 3-4 different primers with it to see if I could tame the swings a bit.

Federal 210, Winchester WLR, Federal 215 (Magnum), and maybe CCI 200 (can't remember if that one was tried or not...)

I'm not in front of my notes on it at the moment, but the Federal 215 didn't fare as well as some of the others. The Winchester WLR gave the best results. So I'd say pick your best charge and see what other primers will give you.

slimjim · Posted: Thu Mar 22, 2018 8:00 pm Post subject: Re: Erratic Velocity

Elvis wrote:

ok but graph still doesnt make sense.... dots should ALL be on a line and there should be same number on each line or figures will be skewiff.

Elvis, the first range session was 4 shots from 55.5 to 57.0gr in Rem brass. No pressure sign but no indication that accuracy was going to be achievable. So I retried with Winchester brass but missed a shot because failed to arm the chrony. Velocity was more stable so loaded up 4 more rounds in Win brass in 0.3gr increments to approach suspected maximum charge. I keep a single line for each session because temp/environmentals can cause a shift up or down. Once I get a load developed, I plot velocities vertically to show how the acts over a years worth of range sessions. I've found some powders with 350 fps variation - very temperature sensitive.

The reason the graph doesn't make sense is because that is how erratic the velocities have been. It should have been three basically straight lines running parallel to each other (like the 7977 powder). I agree the graph of Superformance velocities doesn't make sense and thought it would make a good topic for our forum.

slimjim · Posted: Thu Mar 22, 2018 8:11 pm Post subject: Re: Erratic Velocity

Azar, the pressure trace equipment is some great gear. I have found primers (and swipes on semi-autos) aren't always reliable. I also look at velocities (jumps or drops from the linear progressions of velocity vs powder charge are a sign you have reached the limit) and measure case head expansion. I'll try and include that data in the next range session, too.

Elvis · Posted: Thu Mar 22, 2018 8:51 pm Post subject: Re: Erratic Velocity

ok that makes sense now...the line furtherest to right is your last four rounds in winchester brass going up in .3grn incriments....
SO to my tired old eyes if your last one went down because its too much powder you have found maximum usable powder at that seating depth...which I asume is seated to mag length if your poohseventy is anything like mine and close to lands is a pipe dream so projectile wont be able to go any further out without interupting smooth feeding.have I got it so far???

Elvis · Posted: Thu Mar 22, 2018 8:54 pm Post subject: Re: Erratic Velocity

sooooo chuck the last one off your line and take another gander Mate...... the other three dots arent far off a straight line...deviation would/could/should be in vacinity of 25fps so your wiggly line will in truth be about one square thick which would cover all your dots....... using edge of two sheets of paper on computer screen I can get 7 of the 10 into band that wide..... 25-30 fps VS isnt to be sneazed at I wouldve thought????

slimjim · Posted: Thu Mar 22, 2018 11:59 pm Post subject: Re: Erratic Velocity

Elvis wrote:

25-30 fps VS isnt to be sneazed at I wouldve thought????

The next test with multiple shots at 56.5 grains with two different primers will tell the story.

I've probably done 100+ of these powder charge vs velocity plots and this is thee most erratic powder/cartridge combo of any I have done.

I'm not holding out hope.

Elvis · Posted: Fri Mar 23, 2018 12:37 am Post subject: Re: Erratic Velocity

look forward to seeing results.