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Normal Topic Gaining back fps in 7mm08 (Read 1029 times)
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Gaining back fps in 7mm08
Apr 3rd, 2020 at 7:07pm
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My current hand load is as follows:

41.5grains 2206H,
140grain Nosler Ballistic Tip.
Fps 2620 out of a Tikka 18 inch Barrel.

My question is,

If i chop the barrel back to 16inchs, i know i will loose further fps. So, i guess i can add .5gr of powder and slowly bring ti back up to get the fps i lost back. There is room in the case so is this an option?

I know there will be a reloading guru out there somewhere that will give me the best idea.
  
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Re: Gaining back fps in 7mm08
Reply #1 - Apr 3rd, 2020 at 7:34pm
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CFE223 powder works for me. 2800 with 18", 140 Berger. So you should be able to get circa 2700 when you chop.
  

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Re: Gaining back fps in 7mm08
Reply #2 - Apr 4th, 2020 at 11:31am
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Ran your current setup thru Quickload. Keep in mind Quickload is just one tool and not always spot on. Chronograph results need to be used sometimes to tune Quickload, other times it is pretty close.

Assumed COAL of 2.8"
Max Pressure for cartridge case = 60191 psi

Your current set up, 18" 41.5 2206H, 140 Nos BalTip -
psi = 59636 (v high), 2694 fps

Barrel cut to 16", 41.5 2206H, 140 Nos BalTip -
psi = 59636 (unchanged, v high), 2615 fps

Barrel cut to 16", 42.0 2206H, 140 Nos BalTip -
psi = 61795 (over max rating for case), 2646 fps

As I said Quickload is just a tool and not always correct. You need real world data - chronograph, pressure signs? etc. to make your assessment. Quickload has predicted a much higher velocity with your load/barrel length than you have actually got so pressure should be down on QL's prediction. Around 80 fps loss after chop looks about right though. Also lifting your charge (if safe) by 0.5 gr may only claw back ~ 35 fps
As always what works safely in one rifle may not be so in another, even if the same maker.
  
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Re: Gaining back fps in 7mm08
Reply #3 - Apr 4th, 2020 at 11:52pm
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I'm running a similar rig using 2206H and 120 Sierra Game Kings  and 140 Nosler BTs out of my T3 Hunter full length 24inch barrel.

140s get 43.5 gr 2690 f/s
120s get 43 gr 2750 f/s

- Very accurate loads all group 3/4 inch @ 100M as long as I do everything right. Cool
  

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Re: Gaining back fps in 7mm08
Reply #4 - Apr 7th, 2020 at 6:45am
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6.5x55bjai wrote on Apr 4th, 2020 at 11:31am:
Ran your current setup thru Quickload. Keep in mind Quickload is just one tool and not always spot on. Chronograph results need to be used sometimes to tune Quickload, other times it is pretty close.

Assumed COAL of 2.8"
Max Pressure for cartridge case = 60191 psi

Your current set up, 18" 41.5 2206H, 140 Nos BalTip -
psi = 59636 (v high), 2694 fps

Barrel cut to 16", 41.5 2206H, 140 Nos BalTip -
psi = 59636 (unchanged, v high), 2615 fps

Barrel cut to 16", 42.0 2206H, 140 Nos BalTip -
psi = 61795 (over max rating for case), 2646 fps

As I said Quickload is just a tool and not always correct. You need real world data - chronograph, pressure signs? etc. to make your assessment. Quickload has predicted a much higher velocity with your load/barrel length than you have actually got so pressure should be down on QL's prediction. Around 80 fps loss after chop looks about right though. Also lifting your charge (if safe) by 0.5 gr may only claw back ~ 35 fps
As always what works safely in one rifle may not be so in another, even if the same maker.


Really interesting data. I guess does it matter if i loose 80fps. I think the projectiles ideal velocity is about 2900fps, so being down at 2500fps is a fair bit slower.

I original had 2800fps out of a full length 24inch barrel.

It going to be a bush gun with the occasional shot to 350 yards max 400 yards. The current set up sacks deer so i dont think 80fps loss would change that much.
  
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Re: Gaining back fps in 7mm08
Reply #5 - Apr 7th, 2020 at 2:41pm
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Years ago, Handloader magazine did a test with a couple of calibres, I recall one of them was 7mm Rem mag, where they started with 30 inch barrel blanks & shortened them 1 inch at a time, chronographing at each shortening. The point that came out of it was there wasn't as much velocity lost per inch of barrel as convention wisdom at the time had it, something like 20-25 pfs per inch, even with the large overbore Rem mag, so if you got 2800 with a 24 inch barrel, you could expect to lose 160-200 fps going down to 16" if I'm doing my sums right. The other thing to think of is loosing that extra 2 inches really worth it, that's for you to decide?
  
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Re: Gaining back fps in 7mm08
Reply #6 - Apr 7th, 2020 at 10:25pm
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There’s a few videos on YouTube that show that experiment of velocity loss as the inches get cut back.

Back to the OP’s question... have you thought about a lighter projectile going from a 140 gr to a 120 gr?

CFE223 is also a good powder to try
  

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Re: Gaining back fps in 7mm08
Reply #7 - Apr 8th, 2020 at 7:19am
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The purpose is one purely for cosmetics and practicality of it being a small short rifle for bush hunting.

The current load, projectile is brilliant and I wouldnt really want to change it. I guess my concern was just that loosing the extra couple inches i would loose how good the round is and was going down to 2500fps now to slow.

I did some ballistic app investigation yesterday and it appears id loose about 80flbs at 400 yards, so probably not as big a loss as i originally thought.

I really just wondered if i increased the powder to say 43grains instead of the 41.5grains would i gain the loss in fps back. Appears the pressure is probably already maxed out.
  
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Re: Gaining back fps in 7mm08
Reply #8 - May 4th, 2020 at 10:09pm
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If you want the velocity, you've got to carry the steel mate.
  
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