Any formula to estimate velocity with longer barrel, given velocity from shorter one?

[Tallbald]

First, I have no chronograph and don't anticipate buying one. Just wouldn't use it enough honestly. But I shoot Trail Boss loaded .38 Special cast loads from my Ruger 77/357 carbine, which has an 18.5 inch barrel. IMR data says that the maximum load gives 806 FPS. Supposing they test from a 10 inch barrel (years ago I read this was the "norm"), can a person estimate how many FPS per each extra inch would give as I go to the carbine length barrel? I just want to stay under about 1000 FPS.
Please don't ragtoo hard me for a novice question such as this. I just know that in the past I've seen discussions about for example, velocities from a 4 inch barrel versus a 6 inch barrel and wondered if it was a straight-line progression up to the time the powder is completely burned. And that made me wonder if the same could be done with the carbine length tube. Thanks. Yours truly in my neophyte ignorance, Don

[kenyerian]

What would the velocity of your ammunition if using a shorter barrel?Exact velocities cannot be calculated as there are generally variables associated with individual chambers and / or barrels that will affect velocity, but on average, velocity gains or losses will be approximately 25 – 35 fps per inch of barrel difference. This is an approximation, and will not hold true for every load or every gun. To truly measure performance, the load should be tested over a chronograph." http://www.hornady.com/support/faqs/ballistics-data

[kenyerian]

each specific product page. Why does velocity differ from what’s listed on the ammo box?In order to comply with industry standards, Hornady publishes data for ammunition derived from testing utilizing SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specification test barrels. SAAMI specifies minimum and maximum chamber sizes, and also specifies certain barrel lengths for certain cartridges i.e. most rifle test barrels are 24 inches in length. Unfortunately, due to variables associated with
individual firearm chambers and / or barrels, there may be variations in velocity from what is published by Hornady (either faster OR slower).http://www.hornady.com/support/faqs/ballistics-data

[tazman]

There is a web site called ballistics by the inch (http://www.ballisticsbytheinch.com) that has tested a lot of calibers in different length barrels. I am not certain how accurate this will be as each gun is different but it will at least give you an idea.

[kenyerian]

http://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/ Another view on velocity.

[scottfire1957]

From everything I've read, no. Each and every firearm, even of the same make and model, is different. There are general guidlines and "rules of thumb."

http://castboolits.gunloads.com/showthread.php?156283-caliber-barrel-length-chart

http://castboolits.gunloads.com/archive/index.php/t-199959.html

http://castboolits.gunloads.com/archive/index.php/t-84695.html

There have been umpteen magazine articles in ALL the shooting mags, numerous books and online articles.

Edit: there is more info using the search function, I posted only 3 because I'm lazy.

[Tallbald]

Thank you all so much. I'm going to read all the links shared with me here. I do have a friend across the state who's offered to loan me his chronograph but I have a personal wish never to borrow tools. I always worry they will be damaged accidentally. I'm going to check around local range friends. Might be I can arrange to accompany them on an outing wherein they will be using one and might let me try my loads. Don.

[Yodogsandman]

See below, screwed up when I added the link.

[Yodogsandman]

Just so you know, Midway has chronographs on sale for $69. Lots easier and more accurate.

http://ads.midwayusa.com/product/626107/caldwell-ballistic-precision-chronograph?cm_vc=ProductFinding

[khmer6]

I've looked into it many times. Honestly there's no rule of thumb. Look at some calibers like 40sw. Keep growing the barrel and veolicty barely bumps. Compare a 44mag and a 10mm with the same barrel length and it might surprise you. Longer barrels are usually more beneficial for cases that are a bit larger and using slower powders.

[Lloyd Smale]

that would be my suggestion
Just so you know, Midway has chronographs on sale for $69. Lots easier and more accurate.

http://ads.midwayusa.com/product/626107/caldwell-ballistic-precision-chronograph?cm_vc=ProductFinding

[jonp]

Just so you know, Midway has chronographs on sale for $69. Lots easier and more accurate.

http://ads.midwayusa.com/product/626107/caldwell-ballistic-precision-chronograph?cm_vc=ProductFinding
Thanks for the heads up. It figures that one is on sale 2weeks after i bought my first one but only one week after i shot my first one. Im getting it as a back up


HIJACK WARNING: i dont have an iphone and most chronys seem to use one for remote recording. Has anyone tried one of the free programs like blueshot or chrono connect for a galaxy?

[khmer6]

I think I saw a Caldwell app in the play store.

[Tallbald]

I didn't realize chronographs had become so inexpensive... DOn.

[MBTcustom]

I didn't realize chronographs had become so inexpensive... DOn.

They are very inexpensive and accurate. There's no way you can estimate velocity especially with cast bullets, and over ten shots you will not have one velocity, you will have a range of speeds that you can average. Swings in speed of up to 75FPS are common when dialing in a load. Fact is, if you care about speed for any reason, there's no excuse to not measure it when the tools to do so are so inexpensive (seriously, you're going to spend half the cost of the chronograph on a cheap tripod from WalMart to hold the thing in place!)

[Yodogsandman]

I like yard sale tripods for a buck!