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Cinco Peso

Interpolation of Velocities is it OK

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looking at a specific powder to reload, the min charge will provide x velocity, and the max is y velocity. If I interpolate, a powder charge within the min and max, will the result be in the ball park, knowing that pressure is not constant?

 

CP

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Cinco Peso....... How Ya doin' Pard and Merry Christmas !!!!!!!!!

 

What the heck are you asking ???????

I hope you're not mixing powders... That is a Major NoNo !

But if you're asking can you load a volume of a specific powder somewhere between the Min & Max, the answer is Yes!!

Thats why they sell chronographs, so you can tell what the velocity of your load is.

I just load to something that is within the min & max and is accurate and comfortable to shoot. 

I havn't used my Chrono in years..........

 

We met at your office over a year ago & I misplaced your # ...... Have you started shooting yet?

We need to meet up at the TinHorns.... I plan to be at the TSRA match on the 29th.

 

If you have a question about CAS and I cant answer it, I can introduce you to someone that can!

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28 minutes ago, Silver Sam, SASS #34718L said:

Cinco Peso....... How Ya doin' Pard and Merry Christmas !!!!!!!!!

 

What the heck are you asking ???????

I hope you're not mixing powders... That is a Major NoNo !

But if you're asking can you load a volume of a specific powder somewhere between the Min & Max, the answer is Yes!!

Thats why they sell chronographs, so you can tell what the velocity of your load is.

I just load to something that is within the min & max and is accurate and comfortable to shoot. 

I havn't used my Chrono in years..........

 

We met at your office over a year ago & I misplaced your # ...... Have you started shooting yet?

We need to meet up at the TinHorns.... I plan to be at the TSRA match on the 29th.

 

If you have a question about CAS and I cant answer it, I can introduce you to someone that can!

 

No,  not mixing powders, just trying to estimate velocities for different  powder weights, within the min and max recommended from the manufacturers  loading data.

 

I am glad to hear from you, and look forward in seeing you at the next Ten Horns shoot!

 

CP

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18 minutes ago, Sedalia Dave said:

No velocity does not increase linearly with powder charge.  You need a chronograph.

Thank you sir, clears up my question

 

CP

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There are some apps that will get you somewhat close for estimation. If you want to be accurate then you'll have to use the chrono

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2 hours ago, Sedalia Dave said:

No velocity does not increase linearly with powder charge.  You need a chronograph.

^  this.

 

Heck, sometimes even the manuals listed charges, both min and max, will not give you the

same velocities they list.

Sometimes, YOUR velocity can be less  and sometimes it could be more using the powder

charges listed.

As mentioned, each load in YOUR firearms should be chronographed if you are seeking

data for yeownself.

 

..........Widder

 

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Certainly chrono  is the way, but you can get a good idea by interpolating published data. Distance between min power factor and max load pretty small so even if real result is not linear it may not be far off. 

image.jpeg

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Widder nailed it. Manufacturer spec's are like the MPH sticker on a new car window. If you really want to know you have to get a chrono.

 

If I didn't have a chrono I'd start right in the middle or slightly higher of the Cowboy load data (for SASS) because it gives you wiggle room on both sides. Too low is the worse thing IMO because if you are using Cowboy data it's max is not a max load for that caliber anyway but the lows are lower. So if anything you are probably going to end up lower than too hot. Then you add that most of us are shooting 357 guns that gives you even more head room to boot. 

 

Don't get me wrong I'm not saying we should be shooting hot loads for SASS or that you don't need to worry about pushing the max. I'm not saying that at all......and want to make that clear. 

 

What I am saying is that if you shoot the middle of a cowboy load (or slightly higher) you'll have a great load for this sport IMO and it will be very safe and functional. Many people shoot loads so light they are counterproductive, more hassle and not as safe. I was told that by a lot of great shooter's for years to shoot stronger loads before I finally listened...….but I'm glad I finally did. 

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If you are looking to get a load for cowboy shooting it should be good enough if you're not pushing either the minimum Power Factor of 60 or the maximum velocity of 1000 feet per second for the pistol or 1400 feet per second for the rifle.  Now that we can post loads, you can probably post the caliber/powder/bullet combination and somebody has probably checked the speed and will let you know.   Your particular guns will vary, but so long as you are not near the limits, you'll be fine.

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The velocity for a given charge in the same case with the same weight and style bullet will change if you change the seating depth of the bullet, reducing or increasing the case volume.

The data will get you close but a chronograph is needed to check the results.

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Thanks for posting the graph Black Mike,  I plotted one using  Unique in the 45acp and it was a linear trend.  Can't find it now. 

 

Things will probably go non- linear at the Minimum and maximum loads.

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16 hours ago, Cinco Peso said:

looking at a specific powder to reload, the min charge will provide x velocity, and the max is y velocity. If I interpolate, a powder charge within the min and max, will the result be in the ball park, knowing that pressure is not constant?

 

CP

Others gave good answers, but I was thinking that if the loads max rated velocity is still below 1000 fps, there are more important things about which to be concerned. How the gun handles when you shoot it would be my priority. FWIW I am doing fine with the minimum charge of Trailboss but am shooting pretty light guns rated for 38 Colt but shooting 38 Special. In that lighter, smaller Model P Jr type gun the load has pretty good snap to it, which is what suits me.

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15 hours ago, Sedalia Dave said:

No velocity does not increase linearly with powder charge.  You need a chronograph.

 

  This has not been my experience at all. In most every cartridge I've handloaded including .38 Special, .357, 38-40, .44 Special, 44-40 and 45 Colt, velocities, as powder charges increase, are predictable, for the most part until one begins to get close to the maximum charge. This of assuming one uses the same bullet, primer, crimp, etc.

 

  Data developed by Hodgdon  et al and their reported velocities, are rarely close to those obtained in "normal" firearms because they use universal receivers minimally cut chambers. I've found velocities out of my firearms (handguns) to generally be significantly lower than those published by powder manufacturers.

 

 All that said, I highly recommend the purchase of a chronograph.

Edited by Cholla Hill Tirador
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Owning a chronograph, while not absolutely necessary is a great idea.  They aren't all that expensive.  I believe Oehler has started producing the Model 35P again.  It uses "Skyscreens" which the bullet passes over.  There are three screens and it will give you two readings to compare the velocities so you can tell if you have a valid reading.  (Sometimes lighting conditions will cause a glint off the bullet.)

 

Understand, that not only your readings may vary from the published velocities because of the reasons listed above, but they may even vary from two supposedly identical guns.  Yes, the interpolated data between the loads listed in the handbooks will be pretty much linear within the limited range of maximum and minimum loads listed.  But it is better to chronograph your loads to find out what you are actually getting from your guns.  I would, however, stay at least a bit ABOVE the minimum loads, and be sure to roll crimp and get good tension on the bullet by the case mouth, to insure proper, stable ignition of smokeless powder!

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