Actual FPS much less that "book" indicates. Any explanation for a newbie?

[philcox]

I have developed a load that is shooting sub-moa and no pressure signs:

• Projectile: Barnes 168g TTSX
• Powder: Ramshot Hunter
• Charge: 78.5g
• Primer: Winchester Magnum
• Brass: Nosler
• Avg velocity: 2995 with a low SD and ES (sub 20)

Rifle: Stock TIkka 300WM (1:11) with 24" Barrel. I do have a Muzzle Break on it.

My question is about velocity. The Barnes site says that using the Powder and a Charge of 77.9, should push about 3221. I am getting 2995, that 200 seems to be quite the difference. Any input as to why that might be? I am chrono with magnetospeed at about 1400' elevation.

Insight is appreciated.

 

[tim tarras]

If your barrel length is shorter than their test gun it will make a difference. Temp and elevation will also factor into this.

 

[lennywd87]

There are a lot of variables to the reloading game. The most obvious would be the load data being based on a gun with a 26” barrel and your gun barrel being a 20”-22”. That would give a 200-300fps difference, around 50fps lost per inch conservatively.

You’re gun is different in many ways to the gun used for load testing and that’s why we always start on the bottom end of the data and work up to “my guns” max. Every single gun is different and the book is only a reference of safe “guidelines”.

A direct comparison of the gun used in the book you are loading from and the one you have would be needed but even then it’s not likely to ever be a spot on match.


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[philcox]

There are a lot of variables to the reloading game. The most obvious would be the load data being based on a gun with a 26” barrel and your gun barrel being a 20”-22”. That would give a 200-300fps difference, around 50fps lost per inch conservatively.

You’re gun is different in many ways to the gun used for load testing and that’s why we always start on the bottom end of the data and work up to “my guns” max. Every single gun is different and the book is only a reference of safe “guidelines”.

A direct comparison of the gun used in the book you are loading from and the one you have would be needed but even then it’s not likely to ever be a spot on match.


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Good insight. I didn't think of Barrel Length. New at this whole thing

 

[Vandy321]

It's a tikka...come to find out, a ton of tikka barrels are 200fps slower than they "should be" according to the box/data.

A search on here will reveal many threads. I had, and asked, the same question

Is tikka bbl extra slow?

No chrono available, ballistic trueing only today (is that the right word?) Based on environmentals (80 deg, 13% humidity, 5-15mph wind, I forget the maybe 23.4 or so on the pressure, 5300ft elev) Based on verified drop, my 7RM is shooting factory federal berger hybrid 168s at over 200fps less...

www.rokslide.com

Are Tikka barrels slow?

In the next couple of weeks, I'm going to put together a short action magnum Tikka. I'm trying to keep it on a reasonably tight budget to keep money open for other projects. One way or the other, it will be a short magnum (25 PRC, 7 WSM, or 300 WSM). I'll use HCA mags and I already have a...

www.rokslide.com

 

[philcox]

It's a tikka...come to find out, a ton of tikka barrels are 200fps slower than they "should be" according to the box/data.

A search on here will reveal many threads. I had, and asked, the same question

Is tikka bbl extra slow?

No chrono available, ballistic trueing only today (is that the right word?) Based on environmentals (80 deg, 13% humidity, 5-15mph wind, I forget the maybe 23.4 or so on the pressure, 5300ft elev) Based on verified drop, my 7RM is shooting factory federal berger hybrid 168s at over 200fps less...

www.rokslide.com

Are Tikka barrels slow?

In the next couple of weeks, I'm going to put together a short action magnum Tikka. I'm trying to keep it on a reasonably tight budget to keep money open for other projects. One way or the other, it will be a short magnum (25 PRC, 7 WSM, or 300 WSM). I'll use HCA mags and I already have a...

www.rokslide.com

Ah, good to know. So I am not crazy after all. Thx for pointers. Will be looking at swapping for a Proof at some point in the near futre.

 

[lennywd87]

If it’s a new barrel it may be tighter and will be slower until it’s broke in and could speed up that extra 50-150 FPS. A lot of variables but I love my tikkas!


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[35WhelenAI]

One question, are factory loads clocking 200 fps less than advertised?

My knowledge is load data is done with chambers cut to min SAAMI specs which also means min spec freebore/throat. The folks developing the data, (Nosler, Barnes, etc) get higher velocity, which looks good in the load manual, and also they know a min spec chamber is not common on most mass produced sporting rifles so it hedges their data on the safe side of pressure (liability) when the data is used by guys like us. A chamber or throat cut on the higher side of spec does have advantages in that it is more likely to not have issues with chambering/extraction.

Barnes uses a 24" bbl for their testing, same length as yours. Bbl length is worth around 25-50 fps/inch, so you shouldn't be at a disadvantage there as you have the same length bbl.

In the same vein, I've seen 100-200 fps difference in velocity from different lots of powder, so it's safe to assume we don't get to reload with the same lot they tested with which could be years apart.

Many variables for sure, as you are already over the book max load by about a half grain and under published velocity.