A couple of weeks ago I had Bill Leeper re-throat my .416T about .110 deeper to accomodate the 400gr Swift A-frames (they are fat!). As usual he did a great job, dismantling, reaming and putting her all back together with nary a scratch.

I had to go to the range to re-sight the scope, and anticipating that the deeper throat might result in less velocity, I took my chrony with me to see.

I only had 15 rounds, which were loaded for hunting, with 73gr of RL 15, CCI 250 primer and 400gr Hornady RN's.

The load averaged a little over 2460 the last time I tried it, prior to the "deep throat" operation. Yesterday I got an average for 6 shots of 2399 fps, so about 60 fps less.

The only variable that changed (besides the throat) was temperature. It was 1 deg C (34 deg F) yesterday, versus 15 deg C (59 deg F) last time. I think that would have to account for at least some of the velocity drop.

I realize the throat change would be hard to quantify, in terms of effect on pressure. Any opinions on how much difference the temperature might have made?

Regards, Canuck

ps: BW, I am still pretty darn happy with 2400 fps, especially at almost freezing temperatures!! The two factors we didn't discuss last time were the length of your throat and the temp at which your data was collected.

[This message has been edited by Canuck (edited 10-30-2001).]

Canuck - I have seen data from reliable sources that claim there is an approximate 2 fps change in velocity for every 1 degree F change in temperature for double base powders. I assume, because I don't know for sure, that Reloader 15 is a double base powder.

Your 14 degree C temperature change equals a 25 degree F change. Therefore, you could expect as much as a 50 fps loss in velocity. A 50 fps loss of velocity sounds reasonable. I have found Reloader 22 and 25 to give this much temperature variation.
Changing the length of the throat puts more variables into the equation. This probably reduced pressure also. These two changes could easily influence your velocities.

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Thanks Guy. Now that you mention it, I think I have heard that same "rule of thumb" somewhere before. I will definately start paying more attention to temp at my range sessions to see if I can corroborate that.

Canuck

Hi guys.
My advice to you when you are testing this loads is; BE VERY CAREFUL when it comes to using "hot loads" when the temperatures are raising!!
I saw that you Canuck, had some loads that developed 2460 f/s. with an 400grs. bullet. That's pretty hot i think. The 416 Taylor is a cartridge that uses high pressures as is, don't push it to far in cold weather.
I'm not out to offend anybody, just saving faces.

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Shoot well, and hit hard.

Arild.

Canuck,

My rifle also has a lot of freebore. Maybe too much, as I have a hard time with accuracy. This rifle is not a "M.O.A." shooter.

I'm thinking of sending it off to John Ricks to have the barrel removed, inspected, and reinstalled. Perhaps setting it back a thread or two, and even rechambering in the Taylor (or Howell) once again.

When it comes to temperatures...

Well, it just about always the same temp here in Sitka, Ak. We may get a 30F degree temperature swing between Summer and Winter on a bad year. But mostly is somewhere between the high 30's and low 60's Fahrenheit, and raining, all year long.

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Brian
The 416 Taylor WebPage!

BW

If you set your barrel back a thread or two, there will be a gap between the barrel channel of the stock and the barrel, making it unsightly.

Instead of that, have you considered rechambering to 416 rem mag?

Brian,

You know what my recomendation is I'm still looking forward to getting my 458 and 500 from John. I'm also thinking that if I get a lathe on of these days, I'll have to borrow my 416 Howell reamer back to make one for myself.

I know John has built a few 416 howells, or has a few in the works. I'll be curious to here how they perform.