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Discussion Starter #1
I loaded up some swc cast 158gr and went to the range this morning with the labradar.

158gr swc & #2400 4.25” barrel
12.0gr- 1190fps
12.5gr- 1161fps
13.0gr- 1151fps
13.5gr- 1161fps primers starting to flatten

My expectation was to see velocities start about 1200fps at 12.0gr like they did, and progressively move up well into the 1300s with charge weight increases but they appeared to stay the same.
Why? I haven’t loaded a lot of cast so maybe this is one of the nuances, meaning gas is escaping around the bullet or something of that nature?
 

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Just to check your thinking of bullet to gun fit; measure the diameter of the bullets, slug the barrel, for a revolver measure the cylinder throats. As a starting point, cast bullets should be the same diameter as the throats and larger than the groove diameter of the barrel.
 

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Just a questions, that comes to mind,... how many rounds did you load and shoot of each powder charge listed?
 

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Elk Whisperer (Super Moderator)
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I size cast bullets .002" over bore diameter. For a bore of .358 I size to .360 for a example.

RJ
 

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I shot 6 of each charge weight.
I didn’t really do any measuring of bullet fit. That’ll be my next step.

Thanks,... I do the same (6), seems to be adequate, for me.

edit;,.. I highly recommend slugging your bore, I find that lead has to be over sized, with a soft lube, to eliminate leading and result in best groupings possible, imo.
 

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More suspects than you'd think.

Could be based on bullet hardness/obturation. More pressure = more obturation = more resistance/friction = no significant change in speed.

Primers show presure is increasing with charge weight....so somthing else is going on.

BTW: you are at about as good as solid SWC's get so far as performance....1200fps is about where a hard lead SWC does as much as it can do.
 

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2400 is too slow for cast bullets, IMO. Try a faster powder (Unique is the standard). You don't have enough resistance to get a good burn with 2400.
 

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Elk Whisperer (Super Moderator)
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I've chronographed Dad's load of a 358156 (158 grain gas checked) and 2400 at 1325 fps out of a 6" GP161 ( blued gp100, full shroud) cast from wheel weights ( Dad's bullets were Linotype) He worked up this load for his 6" Security Six back in the early 70's and it's plenty snappy.

A shorter barrel on any revolver is a hindrance when trying to shoot "magnum" loads. There's just not enough "room" to get all the powder burnt but you still end up with the pressure (a theory of mine with no proof behind it)

Another factor is bullet lube (another theory with no proof) The harder the lube, the less "effect" it has. Rooster Zambini Red and Thompson Blue Angel are popular because they stay on the bullet during shipping, aren't "waxy" to the touch and produce less smoke and "dirt", but IMO, they are too "hard" to be effective. I've recovered a few bullets lubed with those from the clay bank behind my backstop shot by others and there's still lube in the groove. "Oh RJ, that's a good thing." Well, maybe not If you are cleaning lead from your barrel and I am not. I'll stick with Lyman ALOX as its what works for me and mine.

Last part of my rant: As I stated earlier ( but didn't really pontificate on) bullet fit/hardness is a very important factor. Obtruation can't occur if the bullet is too small or too hard. Too much antimony in bullet alloy will cause lead stripping as the bullet is too "brittle" or "crystalized" to properly obtruate. Too soft and the lead just smears as it runs down the barrel no matter if the bullet "fits" or not. Both "theories" have been proven in my revolvers and lessons learned early in my revolver bullet casting/shooting career.

Anyways . . . . .

RJ
 

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Congratulations! Your learning how to use a chronograph, pretty much every cartridge I've ever worked up loads for has behaved that way.
When the velocity stops going up and starts decreasing don't add more powder because higher pressure is the only thing you'll get more of at that point.
Try shooting 11.0,11.5 and 12.0 again, two cylinders of each and record the standard deviations, one will probably shine above the others.
You didn't mention if there gas checked or not, 1200fps is pretty fast for a plain base revolver bullet. You could get some pretty serious leading going any faster.
 

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When loading cast bullets with slow powders you will reach a point when adding more powder does not increase velocity . The 4 " barrel is using all the 2400 it can burn ... the rest of the powder is more or less wasted .
To get a higher velocity with your guns 4 " bbl . you will need to use a powder with a faster burning rate .
1200 fps is as good as it gets ... I would load 12,0 to 12.5 grs. 2400 with that 158 gr. bullet and call it a Good Load !
Gary
 

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In my experience with .44 Rem Mag, one of the first signs of over-pressure was a drop in velocity with increasing charge weight. Lead bullet/jacketed bullet—it made no difference.
Next, the powder that produces the highest velocity in an 8" barrel will produce the highest velocity in a 2" barrel. Magazine articles have covered this since the 1970s.
Finally, you could look at the standard deviation and run a Student T-test to determine if the difference in velocity is really any more that normal statistical deviation from the same data set.
 

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I am guessing your increasing charges with decreasing velocity had increasing muzzle noise and flash along with unburned powder grains in the barrel or on the bench ahead of the muzzle.

Chev. William
 

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Noylj has a good answer. Revolvers often don't show flattened primers until other pressure signs have already appeared. Since you have flattened primers it is more likely your velocity drop is due to pressure from your lot of powder being high enough to stretch the gun metal some, increasing the volume the powder is burning in or possibly opening the barrel/cylinder gap a little under pressure. Either will drop velocity. What you want to do next is step down from your 12-grain load and find out where your velocity peak actually is.

You'll have noted your charge is smaller than Alliant allows for your bullet weight in the Gold Dot. But your bullet's lube grooves will make it longer and that can raise pressure.

ON THE OTHER HAND, what Chevwilliam said bears watching for. If you see a lot of unburned grains, the problem is likely to be that your primer is unseating the bullet before the powder burn gets well underway. The flattened primer can occassionally occur with low pressure loads if the primer backs out into a large enough gap between the case and recoil shield to start to swell before there is enough pressure to push the case back and re-seat the primer. This is called mushrooming. You can determine whether this is happening by carefully decapping the spent primers and looking for fattening of the primer at the bottom. CAUTION: high pressure can also mushroom primers and is the more likely cause. However, if you have and increasing number of unburned grains and some swelling of the primer, the unburned powder nods toward a low pressure event. In this case, you want to try a milder primer, if you have one on hand.
 

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Elk Whisperer (Super Moderator)
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I just looked at Alliant data for 158 grain jacketed and it's WAY over what I'm running with a 357156 to get 1300 with 2400.

If your revolver is a S&W I would cease and desist as you will likely stretch the top strap.

As I am at work so don't have access to my notes, I will look that of mine (Dad's) load up and report back.

RJ
 

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ShooterPaul,

Yes. The Alliant data for +P 38 Special stops at 9-grains and 952 fps for a lighter 146-grain bullet from a longer 6" barrel.

I loaded up some swc cast 158gr and went to the range this morning with the labradar.

158gr swc & #2400 4.25” barrel
12.0gr- 1190fps
12.5gr- 1161fps
13.0gr- 1151fps
13.5gr- 1161fps primers starting to flatten

My expectation was to see velocities start about 1200fps at 12.0gr like they did, and progressively move up well into the 1300s with charge weight increases but they appeared to stay the same.
Why? I haven’t loaded a lot of cast so maybe this is one of the nuances, meaning gas is escaping around the bullet or something of that nature?
I did a little more looking and am wondering who it was that got that 1200 fps? The Maximum loads on Alliant's site are higher, but with the 158-grain Gold Dot. But even with a whopping 10" barrel, their 14.8-grain load only gets to 1265 fps. From a 4¼" barrel, it will be rather lower and that charge is a good bit heavier than yours. I also looked at the Ballistics By The Inch site where they tested a discontinued 158-grain LSWC load from Magtech, and where the barrel was cut to 4", the velocity isn't quite as high as yours. So, your lot of 2400 or your primers or something is hot in your load and you are about where you should be from the data I can see, and maybe a little warm. QuickLOAD predicts 12 grains would give you 1145 fps, but it doesn't have your exact bullet. If I seat it shorter, velocity and pressure climb quickly and significantly.

I would need your actual bullet length and seated bullet COL to get any closer.
 

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Elk Whisperer (Super Moderator)
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Yeah, I saw the ten inch barrel too.

Another thing is no two revolvers shoot the same load the same. I have three .357's, a KGP161, the aforementioned GP161 and a Blackhawk, all with 6" barrels. The KGP161 (stainless) will shoot (hot) loads the other two won't (high pressure signs, split cases sooner etc) The Blackhawk is the "wimp" of the three, which is ok because that's not why I got it. Actually I'm not really sure why I got it.🙄

Oh, there's the fact Rugers have longer cylinders so the bullet can be seated out further.

Anyways, there's that theory, for what it's worth.

RJ
 

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Yeah, and it's not going to be a 10" revolver barrel. It will be the unvented 10" single-shot-type velocity and pressure test barrel that SAAMI has as the alternate 357 test barrel. So it will be a minimum chamber gun in a universal receiver with the length from the beginning of the freebore to the muzzle being 8.6", but without a vent. The Ballistics By The Inch experiment shows that will produce about 80-90 fps more speed than a vented 10" revolver barrel.
 

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Discussion Starter #20
Thanks for the help guys. That was kind of my biggest concern was no increasing velocity indicating high pressure.
I didn’t really notice any unburnt powder on the upper charge weights but I really only looked for it on the first set as its typically been something I’ve seen at lower pressures, higher air space.

slugged the bore and throats (King Cobra Target)
Bore- .354 kinda tight?
Cylinder throats at .359
Bullets at .358 (Missouri bullets coated)

primers are WSPM

bullet length .720
COL: 1.607

The data I was using was Sierra 158 jacketed showing 1470fps with 14.0 grains in a 5.6” barrel and Lyman 160 cast showing 1344fps with 15.5 grains in a 4” barrel.
 
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