Ruger PC Carbine Tungsten weight and caliber conversions

[Crosshair]

Well I got my Ruger PC carbine and stripped it down, wanting to check out the Tungsten weight that some have theorized will have multiple versions for converting calibers.

The holes have the following dimensions, they are different sizes on the top vs the bottom:

10 holes

0.105" wide (0.0525" radius)
0.280" deep

Volume per hole, 0.00242 Cubic inches

0.0242 Cubic inches

14 holes

0.095" Wide (0.0475" radius)
0.225" deep

Volume per hole, 0.00159 Cubic inches

0.02226 Cubic inches

Total 0.04646 Cubic Inches worth of holes in the bolt weight

Total weight that could be added to the bolt weight, assuming 11.13 ounces per cubic inch = 0.52 ounces.

To me, that does not seem like a lot of weight that can be added, considering that weight weighs a good pound or so already. (I find that I do not have a scale that can weight the bolt components accurately. Oops.)

The Tungsten weight is clearly cast, these holes might be there for casting/manufacturing reasons. Or perhaps it is for reducing the mass of the weight, no way to know for sure without asking Ruger.

The 9mm Luger, 40 S&W, and 45 Auto all produce around 350-500 ft⋅lbf of energy. A 40 S&W and 45 Auto may not need a different bolt weight, given that this gun is rated for +P.

A 45 Auto cartridge will TECHNICALLY fit the action of the Ruger. I can see how someone could rig it up to feed 45 Auto. In practice, with proper clearance for the ejector and other working bits, the action probably will not fit a 45 auto. This is just fine. As much as people talk about "one lower with multiple uppers", pretty much nobody actually does this unless you have a SBR or FA lower or live in a place where the term "pre-ban lower" is a coherent statement. Everyone just buys another lower receiver. Why bother increasing length, weight, and cost to make the action long enough to take 45 Auto when most don't care about that feature?

Given the modest cost of these carbines, $500, if someone wants multiple calibers it will be easy to just buy a 40 S&W version when it comes out and not bother with swapping parts. You would want a complete bolt along with a barrel if you were going to convert. You do not want to be swapping bolt heads all the time on this thing. It is actually relatively easy to do with just a flathead screwdriver, but the parts you are working with are not very large. Any caliber swaps will be done indoors at home.

Hope people will find this information useful and I await your thoughts.

 

[ewlyon]

Is there no additional room around the block that could be used for a larger weight?

 

[JohnKSa]

The 9mm Luger, 40 S&W, and 45 Auto all produce around 350-500 ft⋅lbf of energy. A 40 S&W and 45 Auto may not need a different bolt weight, given that this gun is rated for +P.

The critical factor in this case is momentum which translates directly to bolt momentum/velocity. My back of the envelope calculations suggest that maintaining the same bolt velocity/momentum would require increasing the overall bolt weight by roughly the amounts below.

40S&W--20% additional bolt weight.
45ACP--30% additional bolt weight.
10mm--45% additional bolt weight.

Note that this increase would be a change to the OVERALL bolt weight, not just a change to the weight of the internal tungsten weight.

 

[Crosshair]

Is there no additional room around the block that could be used for a larger weight?

Nope. The room that is there is for the weight to move back and forth slightly.

The critical factor in this case is momentum which translates directly to bolt momentum/velocity. My back of the envelope calculations suggest that maintaining the same bolt velocity/momentum would require increasing the overall bolt weight by roughly the amounts below.

40S&W--20% additional bolt weight.
45ACP--30% additional bolt weight.
10mm--45% additional bolt weight.

Note that this increase would be a change to the OVERALL bolt weight, not just a change to the weight of the internal tungsten weight.

I kinda thought that I was messing something up, but figured that someone would correct me. Thank you.

 

[RecoilRob]

Hey.....I've got the original PC-9 and was wondering if the new version has a similar toggle lock to hold the bolt closed so it won't move when you strike the butt on the ground? The toggle moves up when you pull the trigger to allow the bolt to move, and it's nice to not have to worry that it might eject a live round or...even worse, chamber one when you had been carrying with mag in but chamber empty. Could be a nasty surprise if it ended up with a live round when you thought it should be empty....though proper safety discipline should prevent catastrophe...some people don't exercise such things very well all the time. Thanks!

 

[Sistema1927]

I know nothing about the PC-9, but the new PCC uses the same system to hold the bolt open as exists on the 10/22.

 

[chicharrones]

I know nothing about the PC-9, but the new PCC uses the same system to hold the bolt open as exists on the 10/22.

Recoil Rob is referring to a device that keeps the bolt closed on a blowback gun if the gun is dropped from height on its butt.

Since a blowback doesn't have a locking bolt, there is sometimes a safety feature added to prevent the bolt from cycling from only inertia.

 

[Sistema1927]

Recoil Rob is referring to a device that keeps the bolt closed on a blowback gun if the gun is dropped from height on its butt.

Since a blowback doesn't have a locking bolt, there is sometimes a safety feature added to prevent the bolt from cycling from only inertia.

He said that he was wondering about the new version. I answered his question.

 

[chicharrones]

He said that he was wondering about the new version. I answered his question.

What holds the bolt closed on the new version besides the recoil spring? I don't know since I have neither gun.

 

[Sistema1927]

What holds the bolt closed on the new version besides the recoil spring? I don't know since I have neither gun.

Now you have gone from bolt open to bolt closed. The PCC is a blow back, and recoil spring and bolt weight are what keep it closed. The 10/22 style latch holds the bolt open. I believe that the PC9 was also a blow back.

Neither one of these should be confused with guns that fire from an open bolt, such as the M2 submachinegun. Could that be what you are thinking of?

 

[chicharrones]

Now you have gone from bolt open to bolt closed. The PCC is a blow back, and recoil spring and bolt weight are what keep it closed. The 10/22 style latch holds the bolt open. I believe that the PC9 was also a blow back.

Neither one of these should be confused with guns that fire from an open bolt, such as the M2 submachinegun. Could that be what you are thinking of?

To tell you the truth, I didn't know of this feature on blowback carbines until I got my CX4.

In the CX4 there is a hook shaped metal casting (or forging) below the bolt that is spring loaded to stay out of the way of the bolt in most cases.

If the gun is dropped, that metal casting overrides it's small springs and engages a hole in the bottom of the bolt. This prevents unintentional cycling of the bolt. Which is a safety device for keeping a chamber empty while a loaded magazine is in the gun.

 

[Sistema1927]

If the gun is dropped, that metal casting overrides it's small springs and engages a hole in the bottom of the bolt. This prevents unintentional cycling of the bolt. Which is a safety device for keeping a chamber empty while a loaded magazine is in the gun.

Does that keep the bolt open or closed?

With the PCC, I can't envision any fall or jolt hard enough to open and cycle a closed bolt without doing serious damage to the gun, such as fall off of the Empire State Building.

 

[chicharrones]

Does that keep the bolt open or closed?

With the PCC, I can't envision any fall or jolt hard enough to open and cycle a closed bolt without doing serious damage to the gun, such as fall off of the Empire State Building.

Closed, but it only activates if the gun is dropped on its butt or if someone were to buttstroke the gun onto something. Otherwise, the device stays inactive and lets the bolt travel when cycled by hand or when fired.

From what Recoil Rob mentioned, his PC9 has a similar feature except he mentioned a toggle lock.

 

[someguy2800]

There must be a reason why they decided to design that feature into the CX4 and the older Ruger but I too have a hard time seeing hitting a blowback 9mm hard enough on the butt to cycle the action without some crazy 10 foot fall onto concrete or something.

 

[RecoilRob]

It was pretty common for things like Sten guns to fire if you jumped into a ditch (or the like) and jarred the butt. The heavy weight of the bolt WILL move rearward with a bit of a bump on the stock. The PC-9 has a toggle in the top of the receiver that is spring loaded to push one end down to hold the bolt when the trigger isn't being pressed. When you pull the trigger it pushes up on the toggle which frees the bolt to move. Granted you have to hit the butt with some force to move the bolt against the spring...but it will move and it's a nice safety feature IMHO so long as it's transparent when operating the carbine.

 

[Crosshair]

Hey.....I've got the original PC-9 and was wondering if the new version has a similar toggle lock to hold the bolt closed so it won't move when you strike the butt on the ground? The toggle moves up when you pull the trigger to allow the bolt to move, and it's nice to not have to worry that it might eject a live round or...even worse, chamber one when you had been carrying with mag in but chamber empty. Could be a nasty surprise if it ended up with a live round when you thought it should be empty....though proper safety discipline should prevent catastrophe...some people don't exercise such things very well all the time. Thanks!

No it does not.

Personally, it always struck me as an unnecessary feature. You would have to literally throw the gun onto concrete butt first, or be in the process of beating someone to death with it, to get the bolt to move enough for that to be a problem. If it fell far enough for that to be a concern, or you just bludgeoned someone to death with it, you would be checking it over anyway to make sure it was still in functioning condition.

It was pretty common for things like Sten guns to fire if you jumped into a ditch (or the like) and jarred the butt. The heavy weight of the bolt WILL move rearward with a bit of a bump on the stock. The PC-9 has a toggle in the top of the receiver that is spring loaded to push one end down to hold the bolt when the trigger isn't being pressed. When you pull the trigger it pushes up on the toggle which frees the bolt to move. Granted you have to hit the butt with some force to move the bolt against the spring...but it will move and it's a nice safety feature IMHO so long as it's transparent when operating the carbine.

The only open-bolt guns that do that are ones that are in disrepair or were poorly designed/built to begin with. Given that the Sten was designed to be made of mostly non-strategic materials with mostly non-strategic tooling, components like the bolt and sear suffering premature wear, or being out of spec in the first place, is a real possibility.

It is a good idea to check over older open-bolt guns to make sure the bolt is held securely by the sear. Easily done by bopping the bolt with the charging handle when the gun is empty. Checking the condition of the sear engagement and return springs is far more reliable though.

 

[RecoilRob]

Perhaps the original...being a 'Police Carbine' was thought to possibly encounter some rough handling? Don't know, but the real problem with Sten and Grease Guns was when someone had the bolt down and full mag inserted then jumped and broke their fall with the butt. The open bolt guns using advanced ignition tended to have fairly gentle springs on the bolt unlike the semi-versions which have a LOT more pressure on them. If the new Ruger did away with the bolt lock...maybe in retrospect they agree that it was superfluous for the job at hand.

 

[someguy2800]

I've seen the stories about the open bolt guns. In fact I was talking to a ww2 vet once that said someone in his unit traded a pistol of some sort for a sten from a pomey soldier. He said the guy took a fall with it and the bolt dropped and emptied the whole magazine. He said after they checked everyone for holes his Sargent stomped over and grabbed it by the barrel and heaved it into the woods then turned back and bellored at them "no more stens!" and they carried on there bussiness.