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Old October 19, 2009, 08:38 PM   #1
flintlock.50
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Can't achieve published velocity data

I reload .30-06. I'm using Nosler cases, Hornady 150 gr SST in front of 59.0 grains IMR 4350. I weight every charge. My first batch chronographed at 2886 fps (10-shot average). My second was 2857 fps, my third 2866 fps. This is out of a Remington Model 700 with a 22 inch barrel. My Speer number 10 manual lists a MV of 2955 fps. The test rifle was a Mod 700 with 22 inch barrel. Nosler used a 24 inch barrel and achieved 3000 fps. Both manuals list this load as maximum.

From what I've read about velocity vs. barrel length the 2 inch barrel length should not be significant. (See the Art of the Rifle forum.)

I'm puzzled as to why my first batch was so much faster than the later batches. Is this kind of variation common? I may have switched to a different can of powder, but I can't recall for sure. I also swear that I used the same brand primer for each, though I'm certain none were magnum primers.

Comments? Thoughts? Thanks!
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Old October 19, 2009, 08:48 PM   #2
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Some deviation is normal. Every case or other component is minutely different from each other. Air temperature plays a role as well.

I figure 50 fps loss per inch for a shorter barrel as a rule of thumb.
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Old October 19, 2009, 09:02 PM   #3
Christchild
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Your 1st group was faster, possibly because the barrel was cleaner, then fouled a little more with successive firings...possibly.

About the velocities and wanting to acheive Manuals Listed Velocities, there are a trainload of variables. There have been several threads I've read about what You're experiencing, and I've learned alot about the Bullet Company's or Powder Company's Manuals listed velocities, how THEY obtain them and the many variables that contribute to velocity.

The main thing I'd like to mention, is that the highest listed velocities may be fast, and lots of things accompany high velocity (flat trajectory, high ft./lb.s of energy), but trying to attain those top velocities can be a bit dangerous, and in most cases, I've seen accuracy suffer as velocity/pressure near maximum.

You're shooting 30/06, so 3000 FPS is very fast. 2800 FPS is quite fast. 2600 and 2700 FPS is very useful in hunting, and plenty fast.

Each barrel will be different, and alot of those differences will effect velocity, whether being higher or lower than the next barrel. I've read ALOT of good things about an extra 2" of barrel length, more so when using the "slower" powders, such as IMR and AA 4350, IMR 4831, AA 3100 and slower powders. Alot of factory ammo uses ball/spherical powders, even behind heavy bullets, as they many-times load by pressure using faster powders, so I believe THAT aspect would render extra barrel length semi-useless. I ReBarreled my Browning .270 Win. from 22" to 26" for that One Reason, getting extra velocity from my powder.

But to answer Your question, the best I can with my knowledge, the velocities in the manuals are not always attainable.

Always watch for signs of high pressure!!!!!!!!!!!!!!!!!!!!!!!!!

And the thought of NOT KNOWING if You switched powders.......You HAVE TO KNOW!!! Double Check Everything at all times! You can kill Yourself and Your rifle (or pistol, for that matter) doing that!

Last edited by Christchild; October 19, 2009 at 09:08 PM.
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Old October 19, 2009, 09:36 PM   #4
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You should see around 20-30 fps per inch of barrel length. QuickLOAD predicts 3016 fps for 24" and 2953 fps for the 22" shooting the SST over 59 grains of IMR4350. That is with the default military brass with 68.2 grains of water capacity. It is so close to the manual results, I suspect their 700 has a tight chamber. If I put the same load in my Springfield '03, the cases will expand to 69.8 grains of water capacity. That drops the 24" velocity to a predicted 2980 fps, and would drop 22" barrel velocity to 2916 fps. And this is still in Lake City military brass. Most commercial brass is at least slightly bigger, then gets still bigger when pressure expands it to fill your chamber, and that's the volume that determines peak pressure in cases at over about 30,000 psi.

On top of that, lot-to-lot powder burning rates can vary 10% pretty easily. So getting up to 200 fps difference from manual velocity is still within fairly common experience, gun to gun, and component to component. 100 fps difference from primers alone can happen with some powders. And we haven't even touched on the fact some chronographs have less than spectacular accuracy (my dad has an early Chrony that reads about 200 fps faster than either my Oehler 35P or my CED Millennium). Longer chamber freebore also reduces pressure and velocity for a given charge. That means difference in COL will matter, too.

So, all in all, the readings you are getting are within the norm. If you have a means of calibrating your chronograph, you can work loads for velocity IF THE SAME POWDER AND PRIMER AND CASE AND BULLET are all used as in the manual. No substitutions; no kidding. As long as you stay within those limits, then, for a given powder you will find, even with changes in burn rate, that more pressure equals more velocity and vice-versa. This equation depends on the powder to have the same energy content per kilogram from lot to lot, which it generally does, unless the maker has changed. What changes burn rate is the exact deterrent surface penetration and its effect and sometimes the exact size of perforations in stick powders. But the fundamental energy content just depends on the measured amounts of combustible materials, which they usually get pretty close. As a result, if you have all those other ducks in a row and if you trust the accuracy of the manual velocity measurements (Sierra's are all real fired and measured quantities; some of the others use calculations after firing just one value (maximum, I hope) to avoid extra range work), and you can validate your chronograph, you can add or subtract powder from the published charges to match velocity from your gun, and know you are getting essentially the same peak pressure they did. But the chronograph is key. Watching for pressure signs to allow for differences in your copy of the gun is also minimum prudence.

I would take to asking others to let you fire a few over their chronographs on days when you also have yours out just to get a comparison. See if yours has an average difference from the others and adjust your readout values accordingly?

Your different results for the groups of ten are normal. Averaging all three you listed gives 2870 fps. 30 samples is considered a minimum by the statisticians I know for getting reasonable confidence that the average value is a fairly accurate average. If you follow the common benchrest and sniper practice of cleaning every 10 rounds at the range (during which the barrel temperature has time to cool), errors due to difference in fouling and barrel heat should tend to equalize out among the three 10 shot strings.
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Old October 20, 2009, 10:27 AM   #5
flintlock.50
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The statement about "not knowing if I switched powders" was about finishing one can of IMR 4350 and starting on a new can of IMR 4350. I DEFINITELY did NOT mix up powders. But thanks for the warning anyway. I never get bothered about safety reminders for shooting or reloading.
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Old October 20, 2009, 11:01 AM   #6
flintlock.50
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Thanks for the feedback; definitely a lot of information and variables to consider. One variable that I did not record was the primer brand. I used standard primers, but the higher velocity loads may have been with a different brand than what I used for the slower loads.

I have not seen any signs of high pressure.

I should clarify one point. Each group of 10 was shot on different days after different reloading sessions. I had started with 55 grains and worked up to 59 grains. When 59 grains looked promising I loaded some more to chronograph and shoot for group size. So while the barrel did get hot and dirty between rounds, each group started out with a clean, cool barrel.

I think I'll leave this load alone. The 150 gr Hornady SSTs have proved to be devastating, at least on antelope, out to 402 yards. So I don't really need to increase the velocity. I also ran the ballistics for 165 gr Nosler Accubonds that chronographed at 2790 fps and the two bullets are within an inch of each other at 500 yards!

I've shot 3-shot groups of 3/4 inch with the Hornadys. The Accubonds also shoot well. But then the biggest factor in shooting tight groups is ME.
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Old October 20, 2009, 12:01 PM   #7
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Ambient temperature can make a big big difference as well, depending on the powder. I'm not familiar with 4350's sensitivity.
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Old October 20, 2009, 12:30 PM   #8
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I think this is an example of where chronos do more harm than good. The velocity differentials you're seeing are insignificant, and well within the velocity deviations you'd observe with factory ammunition.
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