Can you explain the difference between actual chrono numbers and ammo company numbers?

LocoGringo

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Today I finally got to chronograph ammo out of the 29" barreled bolt action 30-06 my grandfather gave me decades ago. I've had other priorities, so it's taken a while to get to testing. The ammo I used was Hornady 178 ELD-X and on the box it says 2750 fps from a 24" barrel. My chronograph gave me 2709 fps for 10 rounds with an extreme spread of 46 fps. I thought surely I'd get over 2800, but not LESS than 2750. I figured the idea behind my grandfather making the barrel so long would be to maximize the muzzle velocity out of the 30-06 and maybe approach 300 Win Mag velocities...not equal, but get more than a standard 30-06 barrel length of 24" or so. He's no longer alive, so I can't ask him (wish I had thought to ask him while he was alive, but I didn't know enough).

I understand ammo makers may fudge some numbers and possibly even exaggerate some, but this is puzzling. Is the barrel too long and causing drag?
 
Slower powders will be better in a longer barrel. Do you have a 24inch? To test them in. Or maybe know someone who does. ? The hornady may be optimized for the 24 inch barrel too.
 
This is the only 30-06 I have. I don't know anyone else with a 30-06, much less a 24" barrel. I haven't looked either. East Tennessee doesn't need anything so powerful to reach out there. You're lucky if you get a 150 yard shot on a deer.
 
Today I finally got to chronograph ammo out of the 29" barreled bolt action 30-06 my grandfather gave me decades ago. I've had other priorities, so it's taken a while to get to testing. The ammo I used was Hornady 178 ELD-X and on the box it says 2750 fps from a 24" barrel. My chronograph gave me 2709 fps for 10 rounds with an extreme spread of 46 fps. I thought surely I'd get over 2800, but not LESS than 2750. I figured the idea behind my grandfather making the barrel so long would be to maximize the muzzle velocity out of the 30-06 and maybe approach 300 Win Mag velocities...not equal, but get more than a standard 30-06 barrel length of 24" or so. He's no longer alive, so I can't ask him (wish I had thought to ask him while he was alive, but I didn't know enough).

I understand ammo makers may fudge some numbers and possibly even exaggerate some, but this is puzzling. Is the barrel too long and causing drag?
I've shot Hornady 117gr 25-06 through my fast twist 25-06 with a 26in barrel and got less than advertised velocity actually... about 100fps less. Wierd. So idk what to think about that.
 
Some guns shoot “fast,” and give higher velocities than others with a similar (or longer) barrel length that shoot “slow.” As for your particular gun, without checking it out and shooting it we can only guess what may be going on. (Here is another variable, is your chronograph good for accurate readings, too?)

And yes, velocity and energy figures do help sell cartridges, so ammo makers sometimes print velocities for their loads that can be called “optimistic,” to be kind.

Stay safe.
 
One word: variables. Atmospheric differences, powder and primer freshness vs. storage conditions and age, bore dimensions and finish for each specific barrel, and so on.

Or maybe two words: variables + cherry-picking.

On the rare occasions when I buy factory ammo and actually look at the velocities printed on the box, I see them as ballpark figures at best.

BTW, ever since I bought my Labradar chrono, I've been learning that the shot-to-shot variation for even relatively tightly-grouping handloads can be pretty surprising.
 
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I can't prove it, but I'm pretty sure Hornady uses Superformance or a near equivalent in the 178eldx 30-06
Precision Hunter ammo. I can almost exactly duplicate thier load with same charge wt, same velocity etc. in my 700 cdl sf and in my Howa.
I suspect a slower powder like 4350 in that 29" barrel might gain some velocity, but chamber dimension and bore conditions can also have a big affect.
My X-bolt 300wm almost always shows higher velocity than published with factory ammo.
 
Today I finally got to chronograph ammo out of the 29" barreled bolt action 30-06 my grandfather gave me decades ago. I've had other priorities, so it's taken a while to get to testing. The ammo I used was Hornady 178 ELD-X and on the box it says 2750 fps from a 24" barrel. My chronograph gave me 2709 fps for 10 rounds with an extreme spread of 46 fps. I thought surely I'd get over 2800, but not LESS than 2750. I figured the idea behind my grandfather making the barrel so long would be to maximize the muzzle velocity out of the 30-06 and maybe approach 300 Win Mag velocities...not equal, but get more than a standard 30-06 barrel length of 24" or so. He's no longer alive, so I can't ask him (wish I had thought to ask him while he was alive, but I didn't know enough).

I understand ammo makers may fudge some numbers and possibly even exaggerate some, but this is puzzling. Is the barrel too long and causing drag?

Don't see any mention of: ambient temperature, feet above sea level, wind conditions, age of the barrel, number of rounds through the barrel, manufacturer of the barrel used or the chrono used, distance between the barrel and the chrono during testing, sample size, etc.

Theory vs Practice. In theory there is no difference...
 
Today I finally got to chronograph ammo out of the 29" barreled bolt action 30-06 my grandfather gave me decades ago. I've had other priorities, so it's taken a while to get to testing. The ammo I used was Hornady 178 ELD-X and on the box it says 2750 fps from a 24" barrel. My chronograph gave me 2709 fps for 10 rounds with an extreme spread of 46 fps. I thought surely I'd get over 2800, but not LESS than 2750. I figured the idea behind my grandfather making the barrel so long would be to maximize the muzzle velocity out of the 30-06 and maybe approach 300 Win Mag velocities...not equal, but get more than a standard 30-06 barrel length of 24" or so. He's no longer alive, so I can't ask him (wish I had thought to ask him while he was alive, but I didn't know enough).

I understand ammo makers may fudge some numbers and possibly even exaggerate some, but this is puzzling. Is the barrel too long and causing drag?
After all the propellant has burned, the expansion of the gas is going to be the only propulsive force. Since pressure drops as volume increases, and volume increases as the bullet travels down the bore, there will be a point where friction of the bullet in the barrel will exceed the pressure force behind the bullet and the bullet will begin to decelerate. Where exactly this occurs depends on the type of propellant. The faster the burn rate, the sooner the propellant is all consumed, so longer barrels offer less velocity gain, in this case. It could be you have a barrel that is "too long".

EDIT: A 150gr bullet in a .308 Winchester case using 44 grains of WC846 will have complete burn by the time the bullet is about 9 inches from the case mouth.

Oh the other hand, here are the average muzzle velocities of sixteen brand new rifles firing ten rounds on the same day, all shooting the same lot of ammunition:

2882.2
2913.7
2923.8
2910.4
2898.3
2897.0
2937.7
2925.9
2935.7
2946.5
2937.7
2926.2
2891.1
2891.1
2894.0
2900.6

You can see there is a 64 fps variation.

You have a velocity from the box that was rounded to the nearest (higher) 25 fps, from a different lot (which could be +/- 50 fps from nominal), and shot from a different gun. Swings of 100 to 150 fps would not be impossible.
 
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The Speer manual has a table of their .357 ammo chronographed in different make, model, and barrel length revolvers. The differences are great, even in supposedly duplicate guns. They had one Python that was over 200 fps slower than two others.
 
Just like test results in manuals
Different day, time, temp, humidity barrel, altitude, cosmic interference, etc etc. You results are not that much different.
 
No two barrels are the same. Even with identical barrel lengths you will see big differences in velocity with ammo from the same box. Somewhere around 25-50 fps difference is the norm, but much greater differences are possible.

My 22" Winchester 30-06 is consistently 90 fps faster than my 22" Remington 30-06. I have a friend with a 22" Remington that is 130 fps slower than my Winchester.

My 20" Tikka in 308 is the fastest 308 I own. It shoots the same ammo faster than my other 308's with 22" barrels.

That is mostly due to tolerances in the rifles chamber and barrel. Guns with loose tolerances tend to shoot slower than those with tight tolerances. Most ammo manufacturers use test guns with very tight tolerances to test their ammo. Same with the load data you see in load manuals. Very few production rifles will be built to the same tolerances, and that is why few factory rifles will shoot factory loads, or handloads to speeds that actually match their published data.

Your grandpa's 29" barrel is faster than a 22" or 24" gun, but it won't come close to a 300 WM. From a 24" barrel it would have been somewhere around 2650-2675 fps.

There is a point of diminishing returns, which varies depending on the powder, projectile and barrel combination.

This too. Manufacturers have settled on 22"-24" as the standard for 30-06 and 30-06 based cartridges. There is no guarantee that any 24" barrel will be faster than another rifle with a 22" barrel. If you go longer, you have to go a lot longer just to see small gains. A 29" or 30" barrel might be 50 fps faster than a 22" barrel. For most people 22" or 24" is the best length. You choose which based on how you want the rifle to look and balance, not for speed.
 
How can you determine if your chrono is accurate?
Good question...how CAN one determine if the chronograph is correct? 30-06 wasn't the only ammo or cartridge tested that day. My brother and I shot 3 different factory loadings through his 6.5 Creedmoor, my 30-06, .22 LR (2 different lots of Lapua Pistol OSP), a .223 69-grain handload and a .308 hunting load. A lot of testing occurred. If the chronograph was wrong on the 30-06, would it be wrong on all of the others? I did put a brand new battery in it.
 
Different barrels of the same length will cause people to pull their hair out when the same ammo shoots differently in each of them. (Since I started replying to this thread others have already mentioned that).

Many ammo manufacturers don't list velocities from their own tests. That sort of data is for internal use. Instead they list the obligatory SAAMI ideal. 2750 fps from a 24" barrel is the listed velocity for 180 grain projectiles according to SAAMI standards for 30-06. It may be that Hornady's ELD-X in 30-06 is not a very stout load in practice. Ammo makers may come close to SAAMI numbers +/- a bit. Some fall disappointingly short.

Federal also loads Hornady's ELD-X 178gr in 30-06, and their listed velocity is also 2750. Odds are they too are simply giving a nod to SAAMI's listed load with a projectile of that weight range. It doesn't mean it actually hits that mark in every gun, and possibly not in any gun. Ammo makers like Cor-bon and Buffalo Bore do use their own velocity numbers for their more exotic loads.

Manufacturers couldn't possibly list velocities for all the barrels out there for a given cartridge, but neither does SAAMI. SAAMI's pressures and velocities are based on a specific chamber and internal barrel dimensions with very little +/- wiggle room. In practice, barrel manufacturers give themselves more wiggle room for the guns we actually shoot.

So we all have to establish a baseline for our firearms with factory loads, the same as with our handloads. 2700 fps with that nicely designed high BC Hornady bullet is nothing to sneeze at. I would choose a more commonly used reference load so you have more input to help you get an idea of where your rifle falls in the average. Then you can compare more exotic loads to that reference.

That's very cool you have a rifle that your grandfather put together, but we have a mystery barrel to figure out. That's a whole 'nother thing. Slugging the bore would be helpful in figuring out what you're working with. Having a smith examine it might be a good idea.

How tight is the bore? How deep and sharp are the groves? What does the chamber throat look like, and the barrel look like in general as far as wear. Is there pitting from long storage? Are you setting up your chronograph at least 10 feet from the muzzle? If you're using an optical chronograph, the error rate increases as you move the muzzle closer from 10 feet. That applies to the de facto standard Oehler 35 as well as the less costly chronos most of us can afford. Chronographs can be 30 fps, and more different than each other for the same shot fired through both at once.

Like the old song by Chicago, "Does anybody Really know what time it is?" We could write our own song, "Does anybody really know how fast it is?" We really don't know that precisely.
 
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