Powder Weights vs Velocity

[Fergus]

The reloading tables give minimum and maximum powder weights for a given projectile weight, COL, barrel etc...

Is the velocity increase linear [straight line] between those two points?

Can a person expect to see about the same incremental increase in velocity? [even though a person may be starting at a different velocity than the test barrel]

Just curious.

Dave

[Solvability]

No it is not linear but there is almost no way to know what it will be - QuickLoad can help but an estimate and a chrono are the way.

[b1gcountry]

Not only that, but I have never been close to the advertised fps with the published starting load.

[Hi-Power Jack]

My experience is that for some powders, it is linear for a short while,

i.e. if I go from 3.0 to 3.6 grains of some powders, it will go up

in a linear manner - but not for long.

After a while, it can drop off or increase rapidly.

Best to use a Chrono.

[superdude]

Some powders behavior linearly, others not so much. It might depends on several factors, such as the range a powder is used for a given cartridge, but there is some speculation in that comment.

Below is an example of 231 in a 9mm that shows just how linear they can be = very! But I have also documented some non-linear behavior as well with other powders.

http://38super.net/Pages/Primers.html#Anchor-35882

[Fergus]

Okay - was hoping it might be linear for the range the manufacturer recommends but I guess the take away here is use caution and a chrono [which I have]

I mostly load for 40 but I was doing some load development - trying some new powders other than the usual titegroup and the thought/question popped into my head.

I too am typically below the velocities they quote in the table. But I believe that's probably because I tend to run anywhere from 0.1 - 0.3mm longer than they say in the table and the barrel is a bit shorter.

Thanks for the reply's - much appreciated.

Dave

[RDA]

What powder are you curious about?

[jmorris]

No it is not linear. At zero to something your bullet will get stuck in the barrel. At some point it will seem pretty close to linear, after that you are on the other side of the curve and at some point the bullet could remain in the barrel as something gives out before the bullet gets moving (aka a kaboom thread).

[RDA]

No it is not linear. At zero to something your bullet will get stuck in the barrel. At some point it will seem pretty close to linear, after that you are on the other side of the curve and at some point the bullet could remain in the barrel as something gives out before the bullet gets moving (aka a kaboom thread).

True, but he was asking for the area between the min/max of published information, that is a bit different than zero to kaboom.

[jmorris]

Still not linear or it would be identical from start to finish. The "seems pretty close" is close, in the sweet spot, but still not linear.

Lots of variables and safe(er) to assume little, when it comes to reloading.

Edited October 5, 2014 by jmorris

[Fergus]

RDA - you are correct in that I was thinking that the manufactured powder would be linear between the min and max values that they state in their table. Also that in constructing the table they would consider pressure generated for a typical barrel. I use a chrony, and I would think that the manufacturer uses something a little more elegant for generating the information they provide.

My thought was that while I may not generate the min / max velocity in the tables if the trend is linear and I knew the min velocity for my gun then I could reapply the slope and generate what I could expect for a max velocity. Then decide if it is in the range I want or not.

I was looking at a few powders: N340, N320 and Longshot with the goal of being within or very close to SAAMI for a desired power factor.

Regards

[ttolliver]

Even though we know they're not linear, I do treat them that way just to pick a starting point for a range of chrono loads.

For instance, say a given powder has published powder charges of 3.1 to 4.6 and the PF I want if calculated linearly from their velocity data would be 3.8. What I'll do for my first chrono trip is take some rounds loaded to 3.4, 3.6, 3.8, 4.0, and 4.2. If their data was from a longer barrel than I'm shooting I might drop the 3.4 and extend the range up to 4.4 in anticipation of slightly less velocity off the bat. As most people say, I don't tend to get published velocities either.

So on a typical first round like that I'd probably get the velocity I want around 4.0 but occasionally it's at 4.2. Say in this case it falls around 4.2. For the next trip I'll go back with rounds loaded to 4.1, 4.2, and 4.3 to check each of the 3 for any advantage in accuracy and get a second chrono reading. Most of the time 2 of the 3 will be equally accurate and I pick the one closer to my target PF.

[RDA]

I don't have any specific data on N320, but here is an example of AA#2 using Montana Gold 124 JHP with CCI500 at 1.120 (out of a Glock 19), ten rounds at each load:

3.6 grains - 900 avg fps - 111.6 PF

3.7 grains - 915 avg fps - 113.4 PF

3.8 grains - 924 avg fps - 114.6 PF

3.9 grains - 949 avg fps - 117.5 PF

4.0 grains - 971 avg fps - 120.4 PF

4.1 grains - 992 avg fps - 123.0 PF

4.2 grains - 1,012 avg fps - 125.5 PF

4.3 grains - 1,027 avg fps - 127.3 PF

4.4 grains - 1,038 avg fps - 128.7 PF

4.5 grains - 1,052 avg fps - 130.4 PF

4.6 grains - 1,064 avg fps - 131.9 PF

This range is basically larger than Western Powders' recommended range (i.e., a little above and below their recommended min and max).

So, my sample isn't perfectly liner, but it isn't too far from it and the difference is minor enough to be attributable to the variance in my loading accuracy or my chrono's accuracy.

[jmorris]

That is a good example of a non linear curve that is close. Could you post one from 1.8 to 6.8 of the same load?

[superdude]

RDA, that looks linear to me. It certainly will pass any statistical test! At 0.1 grain intervals, minor deviations could be due to measurement error = scale sensitivity (and consistency) and user judgement if using a beam scale.

[RDA]

That is a good example of a non linear curve that is close. Could you post one from 1.8 to 6.8 of the same load?

I don't believe 1.8 and 6.8 are anywhere near the published min and max, respectively.

[jmorris]

I agree but still interested in the rest of the curve, if QL can provide it, just to see the "full picture".

Not trying to be a stickler but the chart above is still not linear. Linear is a direct line from point A to B, from that chart you can already see an up and down inside of a single grain difference in powder charge, vs velocity. Does look really close to linear from 3.9-4.2 (half a grain) though.

Edited October 6, 2014 by jmorris

[jmorris]

I guess the next natural question would be is an increase in pressure equal an increase in velocity in a linear fashion too. The answer to that is also no, regardless of propellant.

Edited October 6, 2014 by jmorris

[RDA]

I don't have QL, I have considered it but haven't convinced myself to spend the money on it.

I said it wasn't perfectly linear, but it isn't terribly far from it in the fairly large range I tested.

Had my loads only been 3.6, 4.1 and 4.6 as follows:

3.6 grains - 900 avg fps - 111.6 PF

4.1 grains - 992 avg fps - 123.0 PF

4.6 grains - 1,064 avg fps - 131.9 PF

And I extrapolate the 0.1 grain intervals, I could calculate the following:

3.6 grains - 900 avg fps (actual measurement) - 111.6 PF

3.7 grains - 918 avg fps (compared to 915, a difference of 0.32%) - 113.8 PF

3.8 grains - 937 avg fps (compared to 924, a difference of 1.39%) - 116.2 PF

3.9 grains - 955 avg fps (compared to 949, a difference of 0.63%) - 118.4 PF

4.0 grains - 974 avg fps (compared to 971, a difference of 0.30%) - 120.8 PF

4.1 grains - 992 avg fps - 123.0 PF (actual measurement) - 123.0 PF

4.2 grains - 1,006 avg fps (compared to 1,012, a difference of 0.60%) - 124.7 PF

4.3 grains - 1,021 avg fps (compared to 1,027, a difference of 0.59%) - 126.6 PF

4.4 grains - 1,035 avg fps (compared to 1,038, a difference of 0.29%) - 128.3 PF

4.5 grains - 1,050 avg fps (compared to 1,052, a difference of 0.19%) - 130.2 PF

4.6 grains - 1,064 avg fps - 131.9 PF (actual measurement) - 131.9 PF

Those differences of 1% or less are nearly insignificant and far better than the abilities of my equipment/scales.

This is just an example, but a little math between known, safe loads can be helpful if you are looking for a particular power factor or speed.

Disclaimer: Don't rely on math alone, or a post on the Internet, or one piece of software, or one day at the range or even one published load. Be smart, be safe.

[jmorris]

Those differences of 1% or less are nearly insignificant and far better than the abilities of my equipment/scales.

This is just an example, but a little math between known, safe loads can be helpful if you are looking for a particular power factor or speed.

Yeah, within the one grain powder charge difference going by tenths of a grain SD is likely high enough to cause overlap in data and agree with your disclaimer.

[Fergus]

I worked up some chrono loads for the N320. That said with a shorter barrel and a little longer COL I ended up almost 1 grain outside the max. I was kind of hoping to be a little closer to the max.

A linear line was the best fit through the data points - yes I did try a few other fitting options.

Edited October 6, 2014 by Fergus

[superdude]

That looks linear! Nice work.

The Sierra manual for 40 S&W shows 5.2 as maximum for their 180 JHP producing 1000fps. In fact, their start load is 4.1 @ 850 fps.

[Fergus]

That looks linear! Nice work.

The Sierra manual for 40 S&W shows 5.2 as maximum for their 180 JHP producing 1000fps. In fact, their start load is 4.1 @ 850 fps.

Well now, never thought to cross-reference against sierra or the like. I usually just go onto the website for a given powder and see what the recommendations are. Not sure why say a flat point, round point or HP etc. would make any differences to the gun and powder with the exception of plated vs jacketed but I'll leave that for another time.

I'm carrying on with working on a 165gr projectile load. Initial test feels quite nice but I've got to do some more work as I've only roughed in a powder weight at this time.

[RDA]

Just for fun, and to attempt to illustrate my comments above as well as John's (hopefully he'll chime in on it), I took my actual data for 3.6 grains to 4.6 grains and the linearity of those loads and added hypothetical loads from 2.5 grains (I made the assumption that anything less wouldn't leave the barrel) to 3.6 grains and hypothetical loads again from 4.7 grains to 5.5 grains (assume anything more is a kaboom) to show the potential non-linearity of the entire curve compared to a portion of the range that can be appear to pretty linear.

The left half of the picture is the linearity of the actual loads from 3.6 to 4.6 and then right half of the picture combines that actual data with hypothetical data to show what the entire range may look like:

If I get ambitious some time, I may try to complete with actual data.

Dislaimer: DON'T TRY ANY OF THESE LOADS, THEY ARE HYPOTHETICAL AND FOR DISCUSSION PURPOSES.

[jwhittin]

data and graphs and technical discussions... this is the place for me! must be some engineers in the bunch.