Update: Velocity & Bullet vs. Cylinder Throat Size for .44 Magnum

[TheTinMan]

I have researched this topic, but want some clear guidance if possible.

Should a cast bullet pass be able to through the cylinder throats without much effort?

Could tighter throats yield increased velocity (and pressure)?

I recently tried to work up a load with some 240 grain cast bullets I bought around 15 years ago but only used in a 24-3 back then. Accuracy then was bad in a 1970s Marlin 1894 - I blamed that on Microgroove rifling at the time. Out of my Dan Wesson 744-VH8 the starting load produced velocity almost 200 fps higher than book (for an 8-1/2” barrel) and close to max for this powder/bullet combination.

The bullets measure .432” in diameter. They go through the 624 throats easily. They don’t quite fit in a 696-1 I haven’t shot yet. The Dan Wesson throats are significantly tighter and yes I know that I need to “slug” them. A .4295 jacketed bullet will not go through the throats.

The DW is nicely accurate with jacketed .429-.430” bullets and wasn’t bad with the lead bullets. My concern is the velocity as a proxy for pressure. The primers were not flattened with the starting load; however, by 2 steps up my ladder I think I saw the beginnings of flattening. Could these tighter throats be the cause of the unexpected velocity results?

One last data point: the primers did not look different when I shot through my newer Marlin 1894.

 

[trulyapostolic]

Cylinder throats should be .001-.0015 over intended bullet diameter.

 

[Yendor357]

Guns don’t read “The Rules”.

If it’s safe, and I get good velocities and groups, I quit asking questions.

 

[cowboy4evr]

You need to know the groove diameter of the barrel , then the cylinder throats should be 1-2 thousands larger . Then you size your cast bullet to a slightly snug fit through the cylinder . This is alll explained in Veral Smiths book , " Jacketed Performance with Cast bullets " . I hope this helps . Regards Paul

 

[mikld]

My cast loads in 3,44 Magnum revolvers; First slug barrels and throats, making sure throats are larger than groove diameter. I size all bullets to the largest cylinder throat per each revolver (my revolver's throats don't vary much if any). I have gotten excellent performance from 5, 44 Magnums, my favorite caliber for over 20 years...

 

[mtgianni]

Cylinder throats should be .001-.0015 over intended bullet diameter.

I have always sized my bullets to 0.001" minimum over throat diameter. I was taught that failure to do so was the start of leading and allowing the bullet nose to enter the barrel forcing cone at less than 100 % straight.
I have only been casting and sizing since the early 90's and surely don't know it all but that has worked for me.

 

[mtgianni]

I have researched this topic, but want some clear guidance if possible.

Should a cast bullet pass be able to through the cylinder throats without much effort?
[They should have resistance.]

Could tighter throats yield increased velocity (and pressure)?

[Yes, though not a significant amount. Velocity results from pressure and gas volume so not a bad thing]

I recently tried to work up a load with some 240 grain cast bullets I bought around 15 years ago but only used in a 24-3 back then. Accuracy then was bad in a 1970s Marlin 1894 - I blamed that on Microgroove rifling at the time. Out of my Dan Wesson 744-VH8 the starting load produced velocity almost 200 fps higher than book (for an 8-1/2” barrel) and close to max for this powder/bullet combination.

The bullets measure .432” in diameter. They go through the 624 throats easily. They don’t quite fit in a 696-1 I haven’t shot yet. The Dan Wesson throats are significantly tighter and yes I know that I need to “slug” them. A .4295 jacketed bullet will not go through the throats.

[Probably time to slug the 624]

The DW is nicely accurate with jacketed .429-.430” bullets and wasn’t bad with the lead bullets. My concern is the velocity as a proxy for pressure. The primers were not flattened with the starting load; however, by 2 steps up my ladder I think I saw the beginnings of flattening. Could these tighter throats be the cause of the unexpected velocity results?

One last data point: the primers did not look different when I shot through my newer Marlin 1894.

Answers are in parenthesis above.
Lastly I would be concerned somewhat with a higher than expected Chronograph reading. Recheck it, then fire a 22 lr across it as a standard check.

 

[rockquarry]

Some years ago (maybe fifteen) I called Lyman and spoke with the guy that does much of the pressure testing and ballistic work. I asked how much pressure difference there was in using slightly oversize cast bullets in a revolver. He said that generally the difference was minimal, as I suspected.

However, we weren't talking about extremes, just a few thousandths. And this didn't include other extremes like dead soft or very hard alloys either.

Based solely on my experience, I size bullets at chamber throat diameter or slightly greater. But don't take my word for it. Shoot some benchrested groups at 25 yards with bullets of slightly varying diameter, but never undersized unless you're familiar with bullet obturation and know how to control it by adjusting powder charge and alloy mix. Of course, if you're not a caster, this is pretty hard to do, and you need a sizer/ lubricator and different bullet sizing dies.

Let your groups tell you what works best. With cast rifle bullets, the softest alloy that won't lead the bore at the desired velocity is usually the most accurate. I don't see why it would be any different for handgun cartridges.

As you've guessed, this takes a good bit of experimental work and load development. It's worth the effort to some, but it may be more than others want to put into such a project.

Flat primers may or may not mean something. Don't depend on this as an indication of pressure unless you're fired your gun a lot using the same primers with a variety of powders and charges , examining primer condition along the way. Even then, flattening may not be a reliable indicator.

 

[TheTinMan]

Thanks guys!

I am still stumped by the higher than expected velocities through the Dan Wesson revolver. Thought maybe oversized bullets were the cause but it appears no.

When I started handloading for handguns, I went with lead bullets for cost savings. Jacketed bullets are easier to load with for semiautos. Probably revolvers as well based on my searches and what you all have laid out here. If I only a couple hundred of these Penn bullets I would’ve given up on them already.

You need to know the groove diameter of the barrel , then the cylinder throats should be 1-2 thousands larger . Then you size your cast bullet to a slightly snug fit through the cylinder . This is alll explained in Veral Smiths book , " Jacketed Performance with Cast bullets " . I hope this helps . Regards Paul

This is short and to the point.

 

[rockquarry]

Thanks guys!

I am still stumped by the higher than expected velocities through the Dan Wesson revolver. Thought maybe oversized bullets were the cause but it appears no.

When I started handloading for handguns, I went with lead bullets for cost savings. Jacketed bullets are easier to load with for semiautos. Probably revolvers as well based on my searches and what you all have laid out here. If I only a couple hundred of these Penn bullets I would’ve given up on them already.



This is short and to the point.

As for velocities, you may have a "fast" barrel. How do other loads chronograph in it? Are the velocities higher than anticipated? What about your cylinder/barrel gap? This can make a significant difference in velocities.

 

[stansdds]

Some guns produce faster velocities than others, even when comparing the same barrel length, same manufacturer, and same model.

 

[mtgianni]

Since it is a DW, what do you have the cylinder gap set at?

 

[TheTinMan]

Since it is a DW, what do you have the cylinder gap set at?

0.006”. I used the gap gauge that came with the revolver.

 

[M29since14]

In my older S&W .44s, I try to use bullets 0.0005”-0.001” larger than the exit bores of the chambers. As a practical matter, that is about 0.4325”. My guns might benefit from slightly larger bullets, but with some brass I run out of clearance in the chambers, so 0.4325” is about the largest I can use.

I’ve never seen a barrel on an S&W .44 that was not smaller in diameter than that, so I quit slugging them a long time ago. (Admittedly, I haven’t got much experience with the newer S&W .44s.)

It’s hard to generalize about velocity and primer appearance regarding pressure. I have a 7mm magnum rifle that is extremely “fast.” It is consistently 200 FPS or more faster than it should be, with no indication of unusual or unacceptable pressure. When I ask people about this who are far more knowledgeable than I, invariably the response is (roughly), “Every gun is different. If nothing else seems wrong, don’t worry too much about that.” It’s a bit of black art to try to link up primer appearance and velocity with pressure in any given individual gun, IMHO.

 

[gwpercle]

The cylinder throats should be just slightly larger than the bullet diameter.

The bullet diameter should be .001" - .002" over bore diameter .

The forcing cone should be slightly larger than bore diameter .

Everything must work hand in hand with no constrictions along the way . Tight spots are not good ... they will size the bullet down and cast lead bullets , once squeezed down , stay small and are not that accurate amnd tend to leave lead in the barrel .

Gary

 

[TheTinMan]

Dan Wesson 744-VH8

Cylinder throats 0.4285”
Barrel 0.4275 or 0.428”

Throat measurements very consistent. I only slugged a barrel once before years ago. I did it twice and got 0.4275” once and 0.428” the second time. I think the second time was more accurate. I used both my RCBS digitial calipers and my Starrett micrometer for measuring and got consistent readings with both tools.

 

[TheTinMan]

Well this is embarrassing! I learned today on the Dan Wesson forum that you have to clean the barrel and shroud frequently if you have a ported barrel. Plus you really shouldn’t shoot lead bullets through the ported barrel at all.

The nut at the end of the barrel came off easily enough, but it was covered with wet, black gunk. It took a while and a lot of Kroil to get the shroud off the barrel.

This is the muzzle end of the barrel shroud!

I need to find a non-ported 8” barrel!

 

[stansdds]

The downside to the DW tensioned barrel system. It's fantastic until you use a ported barrel, then all that gsr gets trapped between the barrel and shroud.