Estimating pressures in a wildcat

[briannmilewis]

This relates to the 223 Short project.

When asked what receiver to buy for the 223 Short barrel, Larry replied by saying it depends on how much pressure will be developed in the round.

Can I reference the 221 FB for pressures for starting purposes, or is there a better way short of loading up and finding someone with a pressure barrel (or whatever they use)?

[Reed1911]

I think what he meant was, what is the max pressure you will be loading to. Since you are designing a new caliber, you'll need to set a pressure limit on it. The ONLY way to measure pressure is via a strain gauge properly calibrated and used or a proper copper crusher properly calibrated and used. Head measurement, primer flow, backthrust, etc. are all ways to indicate OVER PRESSURE but you will likely be in proof load territory of 70KPSI or more. In short, you can't do it without the equipment.

[briannmilewis]

I think what he meant was, what is the max pressure you will be loading to. Since you are designing a new caliber, you'll need to set a pressure limit on it. The ONLY way to measure pressure is via a strain gauge properly calibrated and used or a proper copper crusher properly calibrated and used. Head measurement, primer flow, backthrust, etc. are all ways to indicate OVER PRESSURE but you will likely be in proof load territory of 70KPSI or more. In short, you can't do it without the equipment.

If it is a given that I do not have access to the tools mentioned above, it looks like the 218 Bee has close to or the same case capacity as the 223 Short - 1.0cc.

Does that mean I can use 218 Bee load data to start with, and avoid hiding behind a tree with a string attached to the trigger?

I will ask Hodgdon for their opinion before we load anything.

Looking at Lee Reloading, the maximum Bee pressures are 40,000 CUP.

The maximum 221 FB pressures are 52,000 CUP.

The regular SB2 receiver can handle 61,000 PSI for 243 Winchester, 60,000 PSI for the 30-06.

The 357 Mag receiver has to withstand 44,000 CUP, the 44 Mag receiver has to withstand 40,000 CUP.

My take away from this is to use a SB2 receiver.

Any other opinions please?

[Reed1911]

(this is a bit of a general answer so I can address anyone else too) If your cartridge has the same or slightly higher capacity (i.e. internal volume with the bullet seated) and is in the same caliber, then yes you can use the same data.

In your case, since the .218 Bee and your .223 Short have roughly the same capacity and are both .22CF caliber, you would be safe in using the same data.

On the receiver chosen, you will be fine using it. What does need to be said though, is that it is more a backthrust question rather than straight pressure. What needs to be considered is the pressure as well as the surface area of the head that will be thrusting against the breechface/boltface. Since you are going to be working with such a small case, you will have no problems at all. This is not always the case when moving the other way.

I know you likely already know this Brian, but I wanted to expand on it for anyone else reading it. In short you are well in the safe point as far as your chosen starting point.

[briannmilewis]

Hey Ron:

Very well put and I do not know it all, as I have just been messing around in centerfire stuff since late 2008, let alone having any wildcat experience.

I am lucky that Jed and Larry are on board to help find our way in this, and your additional expertise is always welcome.

Your explanation put it in very clear and straight forward terms, even a caveman could understand it!

It will be an interesting time testing the round when we are ready to go.

Brian

[Catfish]

If your cutting down the case size your eveidently are not after velocity, so there is no reason to over load. As Reed posted look for rounds in the same caliber with the same case capacity. I bought a .25 cal on the .221 fireball case years ago. I did some looking around and found the the .221 case held 1 gr H2O more than a .256 Win mag case so I used that data. I could have gone alittle higher as once the case was blown out to .25 cal. the capacity would have been more, but I had a .257 AI. so why push it.

[briannmilewis]

On the receiver chosen, you will be fine using it. What does need to be said though, is that it is more a backthrust question rather than straight pressure.

Ron: Does this mean I could use a 20g or 12g shotgun receiver for the project?

[Reed1911]

No, well, possibly.

So long as it is a multi-use shotgun frame like a T/C then yes. A lot of shotgun frames are either Aluminium or soft steel and are not rated to take the abuse that a rifle or pistol shell would put on them. A shotgun shell by design, only has a very brief period of pressure with little to no rearward thrust by comparison to a rifle or pistol shell. So for most shotgun frames, no. For a few you can use them since they are actually built for rifle useage and just happen to also have shotgun shooting capability.

[briannmilewis]

Ron: OK, we will stick with the H&R SB2 receiver. Thx for your help again.