Velocity vs claimed velocity

[Mr.Snerdly]

I tried the chronometer out yesterday. I am well below the reloading manual claimed velocity. However, I know most of the data is based on a 26" barrel. I was getting around 3025-3050 with a 53 grain bullet, 223 caliber. 25 grains of 335. I would rather be using CFE 223 or Varget but you take what you can get in today's situation. Does this sound reasonable?

I was looking on the internet and I ran across an article that claimed the 223 will actually LOSE velocity with a 26" barrel due to the gas pressure dropping to the point that the friction of a longer barrel nets a velocity decrease. I find this hard to believe but maybe it is so. What do you guys say?. I believe the Axis has a 22" barrel.

[Dave Hoback]

That is a real thing. Here is a video proving this. https://www.youtube.com/watch?v=lR_oshbhII8

Of course that was 9mm, but it follows the same logic. For 223 I don’t believe any velocity would be lost at 26”. Yes, your Axis should be 22”. You did not give us the velocities you were seeing. I do believe you will pick up a decent bit from 22” to 26” Normally, I’ve seen about 50FPS+ from 16”-18” and 18”-20”. Roughly 25FPS/inch. I believe you’d see that in on your chrono, which would give you another 100fps from your 22”.

Velocity doesn’t always adhere to what is written though. Your gun, your barrel, your chamber, etc, etc.. Your chamber might have higher tolerances causing less chamber pressures. This can account for lower velocities among other guesses. Ya know? So, what was your velocity?

[Mr.Snerdly]

That is a real thing. Here is a video proving this. https://www.youtube.com/watch?v=lR_oshbhII8

Of course that was 9mm, but it follows the same logic. For 223 I don’t believe any velocity would be lost at 26”. Yes, your Axis should be 22”. You did not give us the velocities you were seeing. I do believe you will pick up a decent bit from 22” to 26” Normally, I’ve seen about 50FPS+ from 16”-18” and 18”-20”. Roughly 25FPS/inch. I believe you’d see that in on your chrono, which would give you another 100fps from your 22”.

Velocity doesn’t always adhere to what is written though. Your gun, your barrel, your chamber, etc, etc.. Your chamber might have higher tolerances causing less chamber pressures. This can account for lower velocities among other guesses. Ya know? So, what was your velocity?
3025-3050 with 3050 being the highest. This was the first time I used it and due to unfamiliarity. I missed a few checks that would have given me probably a better picture of average velocities.

[Dave Hoback]

Ahh, I apologize.. I said that wrong. I meant to ask what was the velocity the manual claimed?

[Mr.Snerdly]

They don't list it for 25 grains but 24 is 3060 and 26 (max) is 3300. Hodgon online manual. I have a couple others I could check and see what they say.

[Dave Hoback]

Well, your velocity doesn’t seem bad to me from a 22” barrel. With a 26” barrel I believe it could vein that roughly 100fps. That’s based on just what I’ve seen over & over in 223 velocity, from 16”-18”, and 18”-20”. Roughly 25FPS per inch. So, a 26” might have you around 3150. And there just really is a whole host of other things that can have your velocity lower than published. I honestly wouldn’t worry about it. Reloading manuals are just guidelines for starting your loads. Work up your own loads & get to know your gun’s barrel & chamber inside & out.

[Mr.Snerdly]

Lee book says 3203 for 25.3 grains. Nosler book doesn't list a 53 grain bullet. They list a 50 and 52 grain bullet but the same velocity is listed for both so it is would be hard to get an accurate figure from their book. Other book is so old it doesn't list 335.

[charlie b]

Sounds like you are within the ballpark based on book and your measured loads. They will rarely match. For example:

Sierra data for the .308 is listed with the 12BVSS, the exact rifle I have. The only difference is they use Federal cases And I use Lapua. I also use the Fed 210M primers they use and use same oal.

155SMK 2.775oal
book 43.1gn 2700fps 44.8gn 2900fps
mine 43.7gn 2775fps 45.2gn 2875fps (Hodgdon lists 47.0gn as max so I felt safe going a bit over the Sierra data)

168SMK 2.80oal
Book 41.9gn 2600fps 43.5gn 2700fps
Mine 42.1gn 2750fps

They list data for the 175 and 180gn bullets together. I have fired the 175SMK over my Labradar.

175SMK 2.80 OAL
Book 39.9gn 2400fps 41.7gn 2500fps
Mine 41.0gn 2625fps avg

So, even with almost exact components and rifle the velocity difference can be quite a bit.

The biggest issue with book load data is the barrel length. You can kind of 'adjust' for it as Dave mentioned. Typically it is 25fps per inch of barrel length.

Using a chronograph you will also have a bit of statistics to deal with. Your measurements will have some variation. Until you fire at least 10 rounds you won't know what the average really is, and sometimes it will take more, especially if you have a wide spread of velocities.

[CFJunkie]

Both Dave and Charlie b are right that barrel length and the chamber and bore differences between barrels are factors in velocity at the muzzle, but there are two other conditions that might create some differences as well.

You didn't mention what Chrono you are using.
Lab Radar and the units the mount on the barrel measure right at the muzzle but my Oehler 35P and most other chronos measure whereever they are set up (and they need to be set up where the shock wave from the muzzle blast won't impact the readings.)
Use your ballistic calculator to see how much 12 to 16 feet makes in velocity compared to muzzle velocity. Your numbers will be slower with a chrono that is mounted away from the muzzle.

Have you taken temperature into account?
I believe that H335 changes more than 1 fps per change of 1 degree F, maybe as much as 1.25 fps.
You need to know what the temperature was the published velocity was measured and the temperature of your shooting condition to see how much difference that would make.
That might be the largest contributor to the difference in measured velocity, especially if the published velocity was measured in the middle of summer. A temperature difference of 60 degrees could drop the velocity by 60 to 100 fps if you are shooting a temperature sensitive powder (if the published velocity reading was measured at 90 degrees in the middle of summer and your measurement was at 30 degrees in the middle of winter)

To illustrate that you need to consider your powder before you go off the deep end in making comparisons of velocities,
Varget has a 0.032 fps change per degree F
H4895 has a 0.064 fps change per degree F.
IMR 4166 Enduron has a 0.16 fps change per degree F.
N140 has a 0.8 fps change per degree F.
IMR 4895 has a 1.24 fps change per degree F.
The first two are 'extreme powders' and N140 and IMR4895 are not.

[pdshooter2]

i have a 26 and a 27 inch 223 ar...THEY DO NOT LOOOOOOSE VELOCITY.
YOU DEVELOP A LOAD FOR A GUN......shoot it elsewhere ..well gee wiz it aint the same.
having loaded thousand and thousands of 55 and 62 mil equivilent loads, there are lots of powders
that will get it done all between 23 at 26 or so

[pdshooter2]

I tried the chronometer out yesterday. I am well below the reloading manual claimed velocity. However, I know most of the data is based on a 26" barrel. I was getting around 3025-3050 with a 53 grain bullet, 223 caliber. 25 grains of 335. I would rather be using CFE 223 or Varget but you take what you can get in today's situation. Does this sound reasonable?

I was looking on the internet and I ran across an article that claimed the 223 will actually LOSE velocity with a 26" barrel due to the gas pressure dropping to the point that the friction of a longer barrel nets a velocity decrease. I find this hard to believe but maybe it is so. What do you guys say?. I believe the Axis has a 22" barrel.

were you using the same
primer
bullet
case
lot of powder
the same chamber and bbl
atleast that many variables

[Dave Hoback]

Thank you CFJunkie. I had said many things affect velocity, Charlie expounded on what I said with some very good insight. And you expounded even MORE.. And in excellent detail. Great post my friend!:redface-new:

pdshooter2, thank you for adding to and clarification on. I didn’t think any velocity was lost up to, at least, 26”; and thought in fact, it would still show some improvement with even a longer barrel. Just that all of my 223 work over the last 17years has been with AR15’s. Also only up to 20”. You just backed up my initial thoughts. Good stuff to know.

[Mr.Snerdly]

were you using the same
primer
bullet
case
lot of powder
the same chamber and bbl
atleast that many variables


Same case brand but I know even the same brand can vary with different lots and I did have different primers. I knew it would be different than the book but was just wondering if I was getting about what I should expect and also how much APPROXIMATELY the shorter barrel would cut the velocity. I am glad to hear that a 26" barrel doesn't LOSE velocity. I thought it sounded crazy when I read it. I tell you, you can't believe everything you read on the internet.

[Dave Hoback]

Wait...., WHAT?:confused: You can’t?? So are you telling me I’m NOT getting that $20 Million from Prince Velnicov from Ukrain?? He told me because of what’s going on, he needed to get his 1.2 billion in Gold out of the country, but could only do it if it went through an American to back him up. Yeah, so his bank just needed my bank info and he told me he CHOSE me. Said I could keep 20 million Somalians!

Pretty sweet deal I think. But are you saying that’s not believable? I mean, c’mon man! Uhh, he’s a Prince with over a BILLION! Seriously, why would he lie? LOL!
:rolleyes:

[charlie b]

Losing velocity.

The only cases I can come up with are 'mouse fart' loads. If enough of a charge is not in there the bullet can slow down and sometimes even jam in the barrel (slows down to zero). So, a 15" barrel might be short enough for the bullet to exit while a 26" might allow the bullet to jam. A very unusual case.

[CFJunkie]

I tried to see it I could determine if QuickLOAD would show a velocity loss using 53 grain Sierra SMK #100 bullets and 25 grains of H335 with different barrel lengths.
All other factors - seating depth, trim length, temperature 70 deg F. - were unchanged.

22-inch barrel shows 3146 fps
24-inch barrel shows 3209 fps - 63 fps faster
26-inch barrel shows 3264 fps - 55 fps faster
28-inch barrel shows 3314 fps - 50 fps faster

For each 2 inches of barrel added the amount of increase is slightly smaller for each addition two inches, so the bullets are not accelerating as quickly as the barrels lengthen.
(I think you would find that friction would cause that for 16 to 20 inch barrels as well.)
But the muzzle velocity is still increasing for each additional 2 inches.

If someone claimed that the bullet would be losing acceleration as the barrel lengthens, they would be right.
But to claim that the bullets are losing velocity is clearly not correct.
The velocity continues increasing over the 6 inches of added barrel length so there is no loss in velocity.
The claim that pressure drops as the bullet goes down the barrel is correct (at least after the first few inches) - but the conclusion that the muzzle velocity will be lower is not correct at these barrel lengths. Acceleration continues as long as there is enough pressure in the barrel to press on the base of the bullet.

Further corroberation:
For my .308 rifle, adding a 30 caliber, 8.5 inch compensator (no rifling and plenty of holes to vent pressure and reduce noise) added 16 fps in measured velocity.
For my 6.5mm CM rifle using the same 30 caliber compensator (even more pressure loss for the .264 bullet) there was still 13 fps added velocity measured.
Granted there was no added friction in the compensator tube (no rifling), but the pressure drop was considerable.

[CFJunkie]

One more thing that the data shows is that the change of 25 fps per inch of barrel length is only rough estimate around a specific barrel length.

It is right on for a .223 bullet at 28 inches but off by 6.5 fps at 24 inches. for this bullet and powder load.

I suspect that estimated change may not be consistent for all bullet types in the same caliber since friction will be different depending upon the amount of bullet body touching the rifling.
I'm not even sure that factor would be accurate for all calibers.
There are probably a couple of other factors that might also complicate the estimated change per inch as well.

[CFJunkie]

Rather than have you all have to wonder what it would be if you were shooting at 40 degrees with a barrel as short as 18-inchs, I reran the numbers and calculated the speed factor for the last two inches of barrel.
Powder - H335
Charge - 25.0
Bullet - 53 gr Sierra SMK # 1400
The Diff is the difference between the previous barrel length. It is almost identical for either temperature. At most 1 fps.

Length Vel 40deg 70 deg Diff Per in
--- 18 ---- 2939 ---- 2996
--- 20 ---- 3020 ---- 3076 -- 80 -- 40.25
--- 22 ---- 3091 ---- 3146 -- 70 -- 35.25
--- 24 ---- 3154 ---- 3209 -- 63 -- 31.5
--- 26 ---- 3210 ---- 3264 -- 55 -- 27.75
--- 28 ---- 3260 ---- 3314 -- 50 -- 25

Now you know the importance of knowing the barrel length and the temperature that the manual you are using actually measured with.
Admittedly, H335 is a temperature sensitive powder.
It does make an enormous difference.

You also now know why I use QuickLOAD when I develop my loads and load them for temperatures forecast at the day and time I will be shooting.
Over the last 10 years, I am rarely off by 2 degrees F when I actually pull the trigger on each load.
It also shows that the factor of velocity per inch is not linear - really couldn't be since the pressure behind the bullet has to drop as the volume between the bullet and the base of the cartridge increases as the bullet moves down the barrel.
While there is friction between the bullet body and the barrel rifling, that remains constant and is relatively small compared to the pressure that the burning gas exerts on the bullet itself on a centerfire caliber.

Charlie b,
Those light 'mousefart' loads you mentioned probably burn out very quickly and the much smaller initial pressure eventually can't overcome the friction as the volume expands as the bullet proceeds down the barrel.
That example provides a really good reason for considering staying above the minimum loads recommended for a powder-bullet combination, although in my experience, there is very little chance that a minimum load will become a squib.

[charlie b]

Yes, they do. :) Most of the powder is consumed by the time the bullet enters the bore. They are called mouse farts due to the reduced noise. The reduced noise is because the pressure is getting near zero when the bullet leaves the barrel. Which is why there is a risk of a bullet remaining in the barrel.

[GrenGuy]

Yes, they do. :) Most of the powder is consumed by the time the bullet enters the bore. They are called mouse farts due to the reduced noise. The reduced noise is because the pressure is getting near zero when the bullet leaves the barrel. Which is why there is a risk of a bullet remaining in the barrel.

This thread is drifting away from Mr Snerdly’s original question, but since He seems to appreciate all good information, I hope He won’t mind. I’m guessing the reason for these light loads is for Military or Law Enforcement use. Reduce the muzzle velocity to subsonic, and eliminate the crack, and suppress to minimize the noise. Other than that, I don’t get the purpose of “mouse fa#*” loads.