Without having to get my chrony out every time I want to think through a velocity question is there a rule of thumb so to speak for inches of barrel less than what is shown in my reloading manuals?
For instance in my loading manual a certain bullet for a 30/06 goes 2800 FPS from their 24" test barrel. Realisticly what can I expect from my 22" barrel?

I know each gun is different thats why I have a chrony but just as a point of discussion do you shave off 50, 100, 150 FPS per inch of barrel thats shorter than the published data?
Thanks for the help.

Its different for every cartridge too. Large bore, low pressure cartiges change very little; a couple of ft/s down to a cirtain length then drop off more quickly. EX, .44 mag in a 16" carbine gets about 1700FPS, in a 24" rifle it goes about 1740FPS.

Smaller bore, higher pressure cartriges can drop dramatically. Your .30-06 should drop about between 30-50FPS/inch, depending on what powder/charge and weight of bullet.

My suggestion... get used to carring your chrony.

The "rule of thumb" is something like 25-50fps (25 for bores over 30 & 50 for bores under 30), but it's still a WAG (wild-ass-gusess). There are so many variables from one barrel/cartridge/chamber to another, just drag the chrono out & then you'll know for sure.

Without using the chrony, it's all a guess. Yours may go 2800 out of your 22 in. barrel. I have a pair of 7x57's I hunt with a lot, one is a 22 in. one is 24, they are within 15 fps with the same ammo. All else being equal (which it never is) you wil lose in the vicinity of 25-30 fps with a .30-06.

quote:

Originally posted by jstevens:
Without using the chrony, it's all a guess. Yours may go 2800 out of your 22 in. barrel. I have a pair of 7x57's I hunt with a lot, one is a 22 in. one is 24, they are within 15 fps with the same ammo. All else being equal (which it never is) you wil lose in the vicinity of 25-30 fps with a .30-06.

True! But there is a rule of thumb, and in my experience it is related to the expansion ratio of the caliber/chamber volume of the cartridge in question. For rounds in the 7X57mm to .30/'06 class, velocity loss from 24" down to 18" or so can be predicted rather closely on the basis of +-25 feet per second per inch. When one is discussing cartridges having a lot greater capacity for a given bore size, this figure jumps up to between 35 to 50 FPS per inch, depending on how "over-bore" the case is. The bigger the case in relation to bore volume, the worse velocity loss becomes. A good example is the .264 Win. Mag. With a 26" barrel, this rtound can get very close to 3200 FPS with a 140-grain bullet, but from a 22" tube, it is no better than the .270 Win., giving little more than 2900 with that same bullet. Yet it requires at least 15 grains more powder to do so......

Now, as jstevens says, some barrels are different!

Get the chrony....it's the best way.....as there's also the loss varies as the barrel gets shorter.....the loss going from 26 to 22 inches isn't as great as the loss of going from 20" to 16"

If one wants he can estimate 30'/sec per inch and hit a lot of things fairly close......but it's a "WAG" for sure.....there have even been some claims of a barrel shooting faster with a shorter barrel!

This happened to me when I shortened a 12 Ga barrel from 26 to 19 inches for shooting slugs.....it actually shot 100'/sec faster at 19" than at 26"!!!!!

quote:

Originally posted by Snellstrom:
Without having to get my chrony out every time I want to think through a velocity question is there a rule of thumb so to speak for inches of barrel less than what is shown in my reloading manuals?

Hey Snellstrom, Back a good number of years ago, I was very concerned about "what" the Velocity happened to be in a whole bunch of rifles. So, I did a small Test & Analysis on the ones I had at hand. From that I found I could better estimate Velocity reductions in the exact same rifle with the exact same barrel reduced in length by using a 1% Reduction per inch of barrel shortening.

For example, if I had a 26" barrel that had a velocity of 3000fps and I cut 1" off, it was pretty close to a 30fps loss. Meaning that exact same barrel(1" shorter) with the exact same Load was now running about 2970fps.

Cut it another inch and remove 29.7fps(or just round it to 30fps) and end up with 2940fps.

quote:

For instance in my loading manual a certain bullet for a 30/06 goes 2800 FPS from their 24" test barrel. Realisticly what can I expect from my 22" barrel?

The REAL problem here is your specific barrel might be slower, the same or faster than what the Test Barrel indicated. So, you either measure the specific Velocity from "your" barrel, or you really are just guessing.

However, this is where it really gets interesting and where the arguments really get going. Knowing the exact Velocity is of little benefit.

Since we need to actually shoot the specific rifle with it's specific load at the distances we intend to Hunt, that is what will be used to develop an accurate Drop Chart. And Velocity is immaterial.
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So then the argument goes, "But what about way out yonder? Doesn't Velocity matter so we have enough Retained Energy?"

Actually......, "guessing" by looking at the Velocities shown in the Manuals get you close enough that we can make that decision before we ever buy the Rifle/Cartridge or the Components which will be used in it.

Just use a Negative Fudge Factor when considering the info in the Manuals, and make the decision if the Cartridge is up to the task based on a slightly reduced Velocity.

For example let's say the Cartridge in the Manual said it would send the Bullet in question at 3000fps from a 26" barrel.

Then toss in a Negative Fudge Factor of 5% or -150fps which says your "guesstimate" for your real-life 26" barrel would start at 2850fps. And lets also say it was in reality a 22" barrel(4" shorter or another reduction of 4%) which gets it close to 2736fps and you can feel free to round it to either 2725fps or 2750fps.

Now you look in the Ballistic Tables and see if it has the Energy Retention you want at X00yds. If it has enough, load it up, go sight it in, shoot it at the distance you intend to use it and create your own Drop Chart.

If the Rifle you happen to buy has the exact same Velocity or slightly higher, then the Retained Energy will be even more. And since we already know it had enough Retained Energy when we calculated it on the Slow side, there will still be plenty.

And thus, whatever the actual Velocity happens to be doesn't amount to a hill of beans.

Hot Core and everyone thanks a bunch, you all confirmed my suspicions.
I should probably apologize to Hot Core you put a lot of effort into answering my question and I appreciate it but you shouldn't have worked that hard to answer my piddly question.
I should probably explain myself and my question.
Years ago before I had a chrony I worked up a load that my finicky Lightweight 30/06 likes real well. My gun has a 22" barrel on it and the load is 56 grains of IMR-4350 in WW cases and CCI primers shooting a 180 Sierra SPBT ( boat tail) This load prints well in my gun right at 1" sometimes under sometimes a little over but a good shooter nonetheless. I've shot this load in this gun for just about 20 years and shot it from the bench at 100, 200, 300 yards and by reverse engineering I've concluded that I am right at 2800 FPS, however the manuals I have show it at roughly that speed with a 24" barrel so I always wondered about it.
I've thought about setting up the chrony and seeing what it says but never have with this load......seems like there is no reason to because the load works and shoots accurately and shoots predictably where it is supposed too at all ranges within reason ( 425 yards longest shot taken = one shot kill on bull elk). I may never run it over a chrony cuz' it's not like I'm developing a new load ( then again I just might!) but if I did run it by a chrony I'm almost afraid I'd find out something bad with this load that I didn't know before and have to start changing things. ( afraid I'd find erratic velocities or something else that will make it start shooting bad!)
Anyway thanks again and I'm sure I'll get plenty of comments about my short barreled '06 not going 2800 with 180's but I'll just keep hunting with it, it has done well on Elk, Deer, Antelope, Bighorn Sheep and Mountain Goats so far and I've never felt under gunned.
Thanks all.

quote:

Originally posted by Snellstrom:
...by reverse engineering I've concluded that I am right at 2800 FPS, however the manuals I have show it at roughly that speed with a 24" barrel so I always wondered about it.
I've thought about setting up the chrony and seeing what it says but never have with this load......seems like there is no reason to because the load works and shoots accurately and shoots predictably where it is supposed too at all ranges within reason ( 425 yards longest shot taken = one shot kill on bull elk). I may never run it over a chrony cuz' it's not like I'm developing a new load ( then again I just might!) but if I did run it by a chrony I'm almost afraid I'd find out something bad with this load that I didn't know before and have to start changing things. ( afraid I'd find erratic velocities or something else that will make it start shooting bad!)

Hey Snellstrom, That is the "Second Biggest Problem" with using a chronograph - rethinking a perfectly good Load that works well. Of course the Biggest Problem is they can be totally mis-leading for the Beginners, who really don't watch for Pressure Indicators.

quote:

... I'm sure I'll get plenty of comments about my short barreled '06 not going 2800 with 180's but I'll just keep hunting with it, it has done well on Elk, Deer, Antelope, Bighorn Sheep and Mountain Goats so far and I've never felt under gunned.
Thanks all.

Velocity in itself is a fine thing. The problem begins when folks think it is the only thing that matters.

I like a SAFE MAX load as well as anyone, but I let the Pressure Indicators tell me when I'm there not some arbitrary, randomly picked Velocity that my rifle might or might not be capable of attaining.

Good hunting and clean 1-shot kills.

Thanks Hot Core I really have no intention of changing the load but the sarcasm I used with the following quote is not far from the truth.

"I'm almost afraid I'd find out something bad with this load that I didn't know before and have to start changing things. ( afraid I'd find erratic velocities or something else that will make it start shooting bad!) "

You know ignorance is bliss in this instance especially. I "developed" this load for my gun with only 3 criteria in mind it had to be accurate and it had to be safe and it had to be utterly reliable no feeding or extraction issues to fiddle with in the field. It met all of these things for me and velocity was nowhere in the equation. I did at one time "up" this load by .5 grain increments and accuracy started to unravel so I stayed right where it is and for all these years it has worked fantastic and still does. Realistically I won't change it but if I did chrony it and found that it was a very erratic FPS load it would nag at me, if the velocity was not what I expected it wouldn't bother me in the least.
When I've worked up loads in the past and the present I still use the same criteria as always:
Accurate
Safe
Reliable

Thanks again.