[blacksamwell]

I just slugged the chamber and barrel for my pt709 and I'm getting .358 on my micrometer. I know it isn't unheard of to see 9mm bore diameters that large but was wondering if this is similar to other 709 owner's findings.

Anyone else measured the bore in their 709? What diameter did you find?

Thanks in advance!

 

[TXEric]

Welcome to the forum!
I haven't done mine, but it would be interesting to see the results from other 709 owners.

 

[Ranch Dog]

I haven't done any work with the 709, but as an "over the top" cast bullet shooter, I have made chamber casts of my 738B, PT111 Pro, and PT138 Pro and rendered the dimensions to very detailed drawings. You will see that my bore measurements are the same leading me to believe that any 9mm or 380 Auto is barreled from the same stock.

I have done this work with all the Taurus semi autos except the 40 S&W and the 25 ACP, 32 ACP, and 45 ACP are over bore as well. Some manufacturers use this, over boring, to help reduce pressure at the shot but it is only speculation as to what is on Taurus' mind. I see a lot of comments about factory ammo not producing the velocity specs, even with like length barrels used in the figures and this is why, the barrels are dumping the pressure behind the shot.

Here are the cast bullet sizes that I recommend for the various barrels

• 25 ACP - .256"
• 32 ACP - .314"
• 380 Auto - .358
• 9mm Luger - .358
• 45 ACP - .457"

This is what the barrel of a 25PLY looks like with a Speer .251 Gold Dot pressed into it. It could be any of the barrels I've checked but it is easier to get the bullet in and out of a 25 caliber barrel.

If you want to tighten up the performance of your Taurus semi auto, both accuracy and velocity, shoot a properly sized cast bullet.

As a note, the barrel stock that Taurus uses on the 357 Mag, 41 Mag, 44 Mag, and 45 Colt is appropriate for the caliber and matches the stock used in the Rossi rifles. Of course, they have the cylinder gap to relieve pressure in the revolver applications.

 

[andreew]

I hope this is not a dumb question, but what about jacketed/plated bullets? Do we need to worry about bullet diameters, since Taurus barrels are overbore?

 

[Ranch Dog]

I hope this is not a dumb question, but what about jacketed/plated bullets? Do we need to worry about bullet diameters, since Taurus barrels are overbore?

Not a dumb question. Nothing you can do about it but understand that you will not achieve the velocities advertised for factory ammo or published data and the resulting terminal ballistics. Only way to tell for sure what velocity your handgun is achieving is with a chronograph. Messing with different diameter jacketed bullets is a little tough as there just aren't any choices unless you are a guy with the Corbin equipment rolling your own. Then you would need to worry about the initial start pressures created by the over bore bullet as copper is not as forgiving as lead.

 

[andreew]

Not a dumb question. Nothing you can do about it but understand that you will not achieve the velocities advertised for factory ammo or published data and the resulting terminal ballistics. Only way to tell for sure what velocity your handgun is achieving is with a chronograph. Messing with different diameter jacketed bullets is a little tough as there just aren't any choices unless you are a guy with the Corbin equipment rolling your own. Then you would need to worry about the initial start pressures created by the over bore bullet as copper is not as forgiving as lead.

Thanks! I understand that lead bullets should be slightly oversized by 0.001" to ensure a good gas seal, and that lead is soft enough to be swaged down to the bore diameter upon firing.

What is the ideal plated/jacketed bullet diameter for a .358" bore? I am thinking that the plate/jacket is a little harder, so it cannot be swaged down as easily.

 

[william]

Excellent! Thanks Ranch Dog for time spent with the drawings and the information.

 

[blacksamwell]

Thanks everyone. Ranch Dog, that information surpasses my expectations and is greatly appreciated.

I'm loading lead bullets for the various 9mm pistols I own and have access to. I'm still working out the particular challenges associated with using cast bullets in 9mm and taking measurements of the bores of my guns was the first step in really dialing things in. Since this was my first attempt it helps to know that others are finding the same results and that I'm not just messing up the measurement process somehow.

 

[Ranch Dog]

What is the ideal plated/jacketed bullet diameter for a .358" bore? I am thinking that the plate/jacket is a little harder, so it cannot be swaged down as easily.

I would only use the standard. 355" bullet. Initial start pressure might change significantly with anything larger.

Blacksamwell, I will add some info tomorrow, I'm heading to work right now.



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[Ranch Dog]

I'm still working out the particular challenges associated with using cast bullets in 9mm and taking measurements of the bores of my guns was the first step in really dialing things in. Since this was my first attempt it helps to know that others are finding the same results and that I'm not just messing up the measurement process somehow.

I've spent quite a bit of time with the 9mm Luger and in that have tried a lot of different things. First and foremost, the 9mm Luger is a high pressure cartridge and needs to function as such as the design of the pistols have taken that into consideration with their choice of slide mass and recoil spring(s). As such, it is my experience that the bullet needs to have a gas check. It is very tough to successfully launch a cast bullet at the operating pressure of this cartridge and have the alloy survive without the check. Acknowledging that, Hornady, the sole commercial supplier of gas checks no longer markets a 35 caliber pistol check so the 35 caliber rifle check must me used. The use of the larger check requires special attention to the gas check shank to ensure there is room for the copper to flow around the shank with the slightly larger check.

You have identified the dimension but using a .359" (.001" larger) or even a .358" bullet is not going to work. In that the 9mm Luger has a tapered case, either of these sizes will cause enough case swell that the cartridge will not dependably chamber. The bullet I designed, the TLC356-135-RF, has a .357" body. As a note, the "356" in its designation reflects the diameter of the bore rider nose. I have since changed the designation to reflect the body diameter that I use on all my other designs. So, because of case requirements, the bullet's greater diameter does properly fit the bore, however, this is where the 9mm's pressure is put to use. With appropriate alloys, pressure is used to obturate the bullet to the bore. I have been using a 95/5, wheel weight/tin, alloy mix with a bit of #8 shot added to the pot water quenching the bullets at the drop. The bullets measure between 19 and 21 BHN and have been providing great results.

 

[blacksamwell]

Thanks Ranch Dog. My 9mm loading began when I started competing in IDPA and USPSA competitions. One goal I was looking to achieve was the lowest possible recoil while still meeting the power factor requirements of competition. One well accepted approach to that is using the heaviest bullet you can with fast powder. I'm loading commercial cast 147 grain bullets and only pushing them to about 900 fps. The bullets I'm using are 19 BHN per the manufacturer. I believe I'm in the right neighborhood as far as bullet hardness goes and with the low velocities I'm pushing should be alright without a gas check as long as the bullet fits the barrel correctly. If I'm still getting leading after verifying the bullet fits the barrel I'll look into gas checks.

Since the 709 isn't my competition gun I'll likely look at 124 grain bullets and can work up a faster load that will obdurate to the barrel better.

I know from my measurements that there's enough room for a .359 bullet plus the case neck thickness at the mouth of the case. But I also know that the case walls are tapered and the deeper the bullet is seated the more case wall I must account for. In order for the .359 bullet to work I know that I first must find a way to get that fat bullet seated in the case without squeezing it down in the process and that I then have to test and measure to ensure the loaded case will chamber in the 709. Ultimately this may all just be academic since the 709 doesn't see much volume of shooting. I'm not sure it would be worth all of the work to create the perfect bullet and load for it. A couple strokes with a chore boy wrapped brush takes care of the leading I'm getting.

Still though, I greatly appreciate the information you've kindly provided.