Can I safely extrapolate 1 caliber to another

[dsandfort]

I carefully measured the capacity of case A and Case B which is a different caliber. Case A holds almost exactly 3 grains more than case B. Can I safely reduce the safe load I'm using in Case A by 3 grains and use it in case B? I'm thinking of going 3.5 grains less for a 0.5 grain safety factor. Bullets weights are 32 and 27 respectively.

The reason I ask is there is no published data for case B (a 17 TAC) using the powders I have at hand.

Thanks in advance.

Del

[Grendel]

Gonna need a lot more info then that

[futuretrades]

If you don't get the info you need here, I suggest calling the Woodchuck Den, and order Todd Kindlers 5th addition Sensational Seventeen manual. Phone# is 330-897-0614. Todd is a great guy, and has done extensive work with the 17 and 20 caliber rifles. Over the years, he has developed a lot of the 17 and 20 calibers in use today.
I can give you load info on the 20 Tac, but not the 17. Also you did not mention the powders you have available.

[dsandfort]

I realize I should be more specific....sorry.

Using Benchmark as the filler, a 204 case holds, on average, 31.5 grains. A 17 TAC case holds 28.5 grains. The 17 TAC has 90.5% of the 204 ruger capacity. Currently shooting 27.3 grains of Benchmark with 32 grain Sierras. So the specific question is....if one reduces the charge from 27.3 to 24.7 (90.5% of 27.3), is this a safe way to find a load for a new powder? I'm also looking at this for H322.

Todd Kindler says shoot the Benchmark but can't give me a starting point. I do have all his books but he has not tried many powders in the 17 TAC.

On a more general side....it seems to me that if you pay attention to proportions and put a reduced charge in a smaller case, the pressure should remain the same. But I sure don't know that as fact. For example, if a case holds 20% less, will a 20% reduced charge of the same powder be safe? I now there are other variables but if the bullet is the same weight, it seems this should work. I would think there is a practical limit to this and I'd stay in the same class of cartridge, 223 family for example. Another example might be using 17 Rem load data and paying attention to proportions, use it for the 17 TAC.

What do you think?

[jo191145]

The change in bore size will be a variable to pressure.

Personally because I bite at math I would compare any load data you have with the 17 Tac with a similar burn rate and extrapolate from that with a good safety factor added.


I did a quick search on the 17 tac load data and BM seems to be a pretty fast burn rate compared to what others are using. My suggestion would be start with a powder more suitable before experimenting with unknowns.
The faster the burn rate for a particular application the faster bad things happen.

[futuretrades]

I would think for a comparison in case capacities, a better comparison would be to stay within the parent cartridge, i.e the 223 family. As far as I know the 17tac is basically a 223 case necked down to 17 cal and the shoulder set at a 30 degree angle. Where as the 204R's parent case is the 222 mag which is around 100 thousands in. longer than the 223 case. To me, and only in my little pea brain, it just makes more sense to look at the 223 load tables and extrapolate from there. With this thinking in mind, I agree with jo191145, The faster a powder burns, the faster things can go to sh#t! I might consider H335 or H4895, a little slower burning powders than benchmark, for a starting point. And then try Benchmark, using a safety margin of maybe 20% or just a tad more. Stay safe, and by all means, be careful!

[jo191145]

Fwiw here's what I looked at
http://saubier.tempwebpage.com/forum/sh ... hp?t=21089

Looked to me like Varget and slower is what's working.
While comparing similar case capacity is useful we cannot forget the smaller bore will have a large effect on pressure, especially with the faster burning powders.
As case capacity remains the same but bore sizes decrease burn rates must be slower. Just think of a garden hose. The smaller the jet the greater the pressure but also the less volume is allowed through.

308 Winchester middle of the road burn rate= Varget
243 Winchester middle of the road is more like, 4350 with lighter bullets than the 308. Same cartridge, smaller bore.