Increased powder charge decreased velocities

[Silver Jack Hammer]

Twice I have gotten reduced velocities by increasing the powder charge of 2400.
I went to the range with primed and belled brass and bolted my Rockchucker on my tailgate, weighted and loaded charges with RCBS dies then fired the rounds and measured the velocities with a Chrony. A tight crimp was used as I am a student of Elmer Keith.

March 2000 S&W Model 29 6 1/2"
Laser Cast 240gr .430" CCI 300 Remington .44 special brass, 2400 powder.
14 gr: 1082, 1047, 998, 865, 893 (977 average)
14.5gr: 921, 926, 961, 945, 906 (931 fps average)
15 gr: 955, 968, 967, 963, 956 (962 fps average)
16 gr: 1194, 1232, 1230, 1232, 1243 (1226 fps average)
16.5gr: 1092, 1172, 1122, 1041, 1073 (1100 fps average)
17 gr: 1171, 1183, 1101, 1224, 1144 (1164 fps average)
17.5gr: 1214, 1230, 1200, 1165, 1163 (1194 fps average)

June 2011 Ruger SBH 3-screw 7 1/2"
RCBS 44-250-K 100% Linotype sized .430" Alox lube, WLP white box standard or magnum primer, Winchester brass seated over the driving band a COL of 1.573" as this SBH will not chamber the RCBS Keith bullet in magnum brass, 2400 powder.
15 gr: 1160, 1183, 1226, 1270, 1267, 1234 (1223 fps average)
15.5gr: 1250 fps
16 gr: 1248 fps, 1243 fps
16.5gr: 1208 fps
17 gr: 1224 fps

[Bwana]

I also have run into this over the years. My experience also showed, like yours, that the initial peak in velocities is about all you're going to get. In some cases it is possible to get higher velocities with larger charges; but, you always wonder about the wisdom of it. So I don't go there as a regular load.
I have also experienced the "below 32 degrees" pressure spikes with Blue Dot. The first time it happened I thought I had accidently over charged the cases. Went home and pulled the rest of the rounds and found everything as it was supposed to be. Loaded new rounds with the same load and went back out and got the same thing. This was a load that was just fine at 90 degrees. Reloading is science and art and a bit of voodoo on the side.

[geargnasher]

I'd be more interested in discovering and eliminating the 10% ES than I would be about the actual velocity numbers. There isn't enough data in the recent session to conclude the trend you indicate.

I've used as much as 21 grains in a M29 with a 229-grain Ideal 429421 Keith Hollow point cast of 16:1, but the best accuracy with that combo was around 19.5 or so. Velocities are in the 1380 fps arena with 19.5 grains, and the way I load them I'm getting a very small ES, I don't remember exactly at the moment but I think it was less than 20 last time I checked it. I'm thinking you have a little less case capacity than I did, so you're right to be cautious about powder charge, but if you're getting results so erratic I'd either switch to a faster powder, softer boolit, or work up the charge more with what you have, provided you're not seeing excessive pressure signs.

Gear

[felix]

The cylinder gap is like an exhaust valve. Opening the valve too early for the kind of gas and spark and you don't have to guess for what happens. Lots of flash and thunder, right? If the pressure is too high for the moving boolit, the escape hatch is used. ... felix

[44man]

Powder weight also adds to boolit weight. You are pushing more. Will it all burn in 6"? No idea.
BP does the same, more powder reduces velocity. Once it can't all burn, you just push more weight.
Don't you just love a 2" .500 S&W?

[Silver Jack Hammer]

Bwana, great post, thanks for the insight. I worked up some Blue Dot loads and had not heard of the below 32 degrees pressure spikes.

Geargnasher, what do mean by the 10% ES? And you are dead on right about the lack of data. The numbers caused me to decide to not go down that trail any further. 1150 fps is the velocity I am seeking, nothing more.

Unique is giving me satisfactory results right now.

[303Guy]

It looks to me that you have found the point in the powder charge/pressure curve that matches the strength of your particular alloy. It would be interesting to know how the accuracy was influenced at that transition.

[rintinglen]

Gear hit the nail on the head--your data is insufficient to draw conclusions from. The standard deviations are for the most part so large, that any conclusions drawn from them have a confidence limit of "none." Ten round round samples are better, but when you have an 860ish low and a 1050 ish high in a five shot string, it is pointless to pursue.

[ColColt]

I have a 6 inch M29-3 and 20 gr of 2400 gave me a little sticky extraction so, I backed off to 19 gr. All loads using CCI 300 primers, 243 gr boolit from the Lyman 429421 mold with 50-50 lead/Linotype and Starline cases. I'm not privy to a chrony so I don't know the velocity figures.

[Bwana]

Gear hit the nail on the head--your data is insufficient to draw conclusions from. The standard deviations are for the most part so large, that any conclusions drawn from them have a confidence limit of "none." Ten round round samples are better, but when you have an 860ish low and a 1050 ish high in a five shot string, it is pointless to pursue.

What are you talking about? That string you cite is the starting, "low", powder charge of a series. It is not uncommon at all to get that kind of spread from a load that is not burning efficiently because of lower than necessary pressure.
As the charges increased the spread decreases as it normally does. I run three rounds for each increase in charge and if in doubt I will later run five rounds to confirm a specific load. I am able to do this with confidence having run multiple thousands of rounds over my chronographs over the last thirty plus years.

[prs]

Elmer Keith techniques will not lead you astray too often, but using a tight crimp can be a Huckelberry no matter who you are with lead pills. Your variability may very well be related to inconsistent boolit retention in the cases. I like the comments offered by other posters too and Felix thought of a very logical factor to consider.

prs

[Larry Gibson]

How are the charges being measured/ Weighed or thrown?

Also, That RCBS 44-250-K should chamber if sized correctly for the throats. The oal of the cartridge should not be too long for the cylinder. I find with my Colt Anaconda .44 that hard alloyed bullets must be sized to .429 to chamber when seated and crimped in the crimp groove. Perhaps the throats in the SBH require a .459 sized bullet when they are cast of linotype.

Larry Gibson

[Char-Gar]

I would want that test and results to be repeated with the same results about 3 or 4 times before I drew any conclusions and started looking for explanations.

[Bass Ackward]

Twice I have gotten reduced velocities by increasing the powder charge of 2400.


March 2000 S&W Model 29 6 1/2"
Laser Cast 240gr .430" CCI 300 Remington .44 special brass, 2400 powder.

June 2011 Ruger SBH 3-screw 7 1/2"
RCBS 44-250-K 100% Linotype sized .430" Alox lube, WLP white box standard or magnum primer, Winchester brass seated over the driving band a COL of 1.573" as this SBH will not chamber the RCBS Keith bullet in magnum brass, 2400 powder.




I think that looking for statistical certainty is foolhardy. We reload on the principle that adding more is supposed to create more. More means faster if everything is the same / correct. That is how it is supposed to work.

Something is not right. And I focus on 44 Special brass in one gun and deep seating in another. Sizing can be the false factor.

Seems to me with that hard of a bullet that isn't sealing, that the extra gas is simply lost. The more you add, the faster it escapes. You probably aren't seeing the dreaded gas cutting because the slug is harder and there is soooooooo much escaping that it isn't hot enough to cut. (Focusing a cutting torch)

But I don't read anything about accuracy either. Sounds like some slugging is in order for proper diagnosis.

[Silver Jack Hammer]

I appreciate the posts. I have not slugged the bore nor had the cylinder throats measured. Sure need to. That Ruger has tight cylinders and requires full length resizing in the RCBS dies, it won't accept neck resized handloads. A Sierra jacketed bullet slips through the cylinder throats so I know it does not suffer from the undersized cylinder throats some Rugers have.

Still I have observed 2400 counter indicating velocities with powder charges. It's like turning on the hose in the swimming pool and observing the water level drop. Maybe the Crony is off, but I have not observed this phenomenon with Blue Dot, Unique, Bullseye, 296, or Herco, Red Dot. I have two 5"x7" 3 ring binders full of data from the Chrony; different guns, powders, loads, bullets. 2 more 8 1/2"x11" binders full of accuracy data.

Alan Jones recently wrote an excellent article in Shooting Times denoting our inappropriate conclusions based in insufficient data. His article referred to accuracy. I do have limited hard data showing decreased velocities with increased powder charges of 2400 in the 900 - 1200 fps range with 2 guns, 2 bullets, 2 brass and erratic velocities. After confirming the crimp my next guess would be stepping up to a hotter primer, but wouldn't the WLP in standard or magnum white box be enough primer for 2400? Right now I'm abandoning 2400 for anything other than middle of the road velocities and short range work.

[Bass Ackward]

Well Jack, you don't mind if I call you Jack do you? (love that move line) (actually it was Dick)

I have shot a can or two of 2400. Even shot a chronograph or two. One by accident. I never have heard of any problems like you are seeing with anything other than Trailboss. I would slug and end the pain. :grin:

[Larry Gibson]

How were you measuring the charges when loading at the range?

Larry Gibson

[Silver Jack Hammer]

Measuring charges with Ohaus 505 single beam scale.

[BWelch47]

Thirty years ago I obtained similiar results using my SW Model 29-2 4" revolver. I
used 2400, Lyamn 429421 cast from ww, RCBS 1010 Scale, CCI 300 primers, sized .429 with a Lee hand resizer, using a chronograph at a local rifle range. Using my wife's Ruger Super Blackhawk, I obtained higher velocity results. I obtained maximum velocity with my 29-2 with 21,5 grains 2400 with decreasing velocity as I increased the load (max load according to Lyman was 23.0 grains). My wife's Super Blackhawk maximum velocity with 22.0 grains of 2400. I discovered from my experiments that each gun has its own zone of maximum effectiveness.:cbpour::redneck:
,

[303Guy]

... that the extra gas is simply lost. The more you add, the faster it escapes. You probably aren't seeing the dreaded gas cutting because the slug is harder and there is soooooooo much escaping that it isn't hot enough to cut. There's another possible explanation. Gas cutting on harder boolits is real and alive and well and hard to detect as it leaves no leading in the bore. I eventually found one such boolit and the rifling grooves impressed into the boolit were the highest ponts of the boolit! The rest had been cut away. Yet that boolit had not slipped in the rifling.

(The other possibilty remains boolit upset in the forcing cone due to increased pressure. Gas escape through the cylinder gap could be another possibilty but I would think that would be in conjunction with another factor - slugging up of the boolit).

[prs]

Regarding the rifling lands imprints being the highest landmarks left -- WOW, amazing! At least to me.

Regarding a revolver that will not accept "neck" sized cartridges or cartidges sized only where boolits are seated; are we talking about cases fired in that same cylinder?

Any how, DO check the throats and bores for size.

prs

[Larry Gibson]

June 2011 Ruger SBH 3-screw 7 1/2"
RCBS 44-250-K 100% Linotype sized .430" Alox lube, WLP white box standard or magnum primer, Winchester brass seated over the driving band a COL of 1.573" as this SBH will not chamber the RCBS Keith bullet in magnum brass, 2400 powder.
15 gr: 1160, 1183, 1226, 1270, 1267, 1234 (1223 fps average)
15.5gr: 1250 fps
16 gr: 1248 fps, 1243 fps
16.5gr: 1208 fps
17 gr: 1224 fps

Were all of those 6 shot averages or was the 16 gr load just 2 shots and the 15.5, the 16.5 and 17 gr loads just 1 shot?

Larry Gibson

[fredj338]

IME, you'll see this w/ every caliber, every powder/bulelt combo @ some point. You hit a flat spot vel wise & adding more powder doesn't significantly increase vel. To me, that means stop there as you are only increasing pressures.

[leftiye]

Ah don' think so. pressure and velocity both keep rising until the burning rate curve (and pressure) go vertical. Thas one trigger pull before you lose them body parts. Don't forget to be careful when you try to test this! If pressures get too high, you may want to give up the quest fer that flat spot, or decreasing velocities and pressures.

Onliest time I ever saw this happen was in a .38 super with Herco. I increased powder charges .1 grain at a time and measured cases, etc. After reaching max. book load, the pressures slowly dropped off. I attributed this to the powder being relatively slow, and the peak pressures not being reached in the short barrel. (I didn't load any a them at that charge either)

[fredj338]

Ah don' think so. pressure and velocity both keep rising until the burning rate curve (and pressure) go vertical. Thas one trigger pull before you lose them body parts. Don't forget to be careful when you try to test this! If pressures get too high, you may want to give up the quest fer that flat spot, or decreasing velocities and pressures.
)

Yes & no. I have seen vel flatten out, then a spike as you increase. It's why I said it's a good indication you are reaching max & should NOT add more powder trying to get higher vel. That spike may happen. Often I see this in fast & uberfasst powders like Clays, TG, RedDot, etc. With slower powders, you usually do not see this, the pressure curves seem more linear. I'ld love to have pressure equip. to prove this, for now it is just an observatrion based on chronograph & case head measurements.

[Mal Paso]

20 to 22 gr of 2400 is Book Load depending on the book for Magnums. 22gr being Ruger/Colt only. Special stops at 13-14gr.

Curious!

I don't load less than 18gr in the Magnum Case because I have had erratic burns. Some batches of powder more erratic than others. Batch #760 was the worst out of 6 batches since I got a chronograph.

14gr is nice in the Special case