The significance of barrel length and velocities...the:ratio?

C

CommonSense

New member
Hello. I am new to the forum however am quite familiar with The Firing Line. It has helped me reach conclusions on what is the popular opinion on many subjects I had been interested in. It is now time I participate.
I have a question that needs assistance. On the theory that barrel length has to do with the overall projectile's velocity, I am curious where I can attain such information in the world wide web. If you may have prior knowledge, I am all ears. My question is:
What is the optimal length barrel for a .17HMR rifle to have in order to maximize full use/ efficiency of the charge? (To reach peak velocities from .17HMR cartridge)
 
Per that data, anything over 16" is wasted steel. However, since a longer barrel reduces the db of muzzle blast, and in this case doesn't harm anything, a longer barrel might be considered helpful to the ears.
 
I can't find the list but velocity change per inch of barrel depends on the velocity. For example I had no hesitation on cutting my 1885 Browning from 28" to 22" and didn't even calculate because I knew as a low velocity cartridge it wouldn't be significant ! However with a high velocity 223 a 6" change would be very significant !
Different powders are a factor also.
 
Well "Peetza" and Art Eatman, you both taught me something I did not know today! Thank you for the information by Bullberry. I am however still curious on the subject and gathering more information. I wonder how would the (inside) diameter of the barrel along with length influence the velocity? Also, what are the various barrel lengths/ diameters of the popular Marlins, savages, rugers, and anschultz? I'm sure I'm being a little lazy at this point, and could manage to find this information even as computer illiterate as I may be. Hmmm... I wonder how many of the above manufacturers actually persued closer tolerances to achieve higher velocities... Assuming accuracy is not compromised. Thinking aloud here...
 
One problem with the test from Bullberry is no mention of who's ammo they used and all factory brands weren't tested so it's pretty limited.
 
CommonSense said:
Well "Peetza" and Art Eatman, you both taught me something I did not know today! Thank you for the information by Bullberry. I am however still curious on the subject and gathering more information. I wonder how would the (inside) diameter of the barrel along with length influence the velocity? Also, what are the various barrel lengths/ diameters of the popular Marlins, savages, rugers, and anschultz? I'm sure I'm being a little lazy at this point, and could manage to find this information even as computer illiterate as I may be. Hmmm... I wonder how many of the above manufacturers actually persued closer tolerances to achieve higher velocities... Assuming accuracy is not compromised. Thinking aloud here...
Click to expand...

The inside diameter of a barrel, the "deep" part of the rifling, is the diameter of the bullet, or .001-.002 smaller than the bullet if you're talking about lead bullets. More precisely, the lead bullets are .001-.002 larger than the bore, not so much that the bore is smaller than the bullets, the lead ".308" bullets would be .309-.310.

The affect of different diameter bores could get complex but all you really need to know is that the sizes are standardized and all the same, within manufacturing tolerances, for any modern gun. For instance, the groove diameter of .308 Winchester is... .308. You can't always count on the size being correctly indicated by the name though, as many cartridges are *not* what their name suggest. .22-260, 5.56 NATO, .223 Remington and many other cartridges, actually use bullets (and barrels) that are .224 inches.

The internal ballistics of a fired round are incredibly complex. Everything from barrel material, temperature, bullet construction, barrel fouling, rifling twist rate and more can and does affect velocity.

You mention "pursuing tighter tolerances", in what regard? The tolerances in today's barrels are generally incredibly small, often within .0005-.0003 inches of standard and varying no more than .0003 to .0001 from end to end. Naturally, the more precision you want, the more money you pay.

And, yes, the affect of this precision on accuracy is well understood and has been for decades, that's why the best competition shooters demand the best barrels.
 
Last edited:
"...optimal length barrel for a .17HMR rifle to have in order to maximize full use/
efficiency of the charge? (To reach peak velocities from .17HMR cartridge)"
Click to expand...

http://bullberry.com/HMRdata.html

Per that data, anything over 16" is wasted steel.
Click to expand...
I have a hard time believing the final observation from the article -- other than using stock
commercial loading with fast powders. But maybe with the reeeeeeeaally low weight projos in
a .17 that might be the case.

I'll ask Mr QuickLoad tonight....
 
Well as soon as QuickLoad pulled up ".17 Hornady Mag Rimfire," I saw the light.
FOE Fast powder and that's it -- no reloading -- and 16" is probably as good at it gets
.
.
.
.
.
.
.
BUT if I COULD reload it -- heavy bullet/optimal powder, this is what it would look
like accelerating down a 24" barrel: :D

23s6842.jpg
 
"anything over 16" is wasted steel"

That is a common belief, based on a fallacy. The correct statement (at least for .22 LR) is that all the powder is burned in the first 16" of the barrel. But that does not take into account that the hot gas generated by the burning powder continues to expand and increase velocity well beyond 16". If pressure was not being generated, a barrel over 16" would not need a suppressor; there would be no noise.

Jim
 
Turn on long barrel friction. ;)
Click to expand...
Peetza nailed it. Barrel friction at that small a diameter is a killer.

QuickLoad nosed over (and was at best flat) from 16" on -- no matter how I switched things out. :mad:

Old Dogs.... :rolleyes:
 
Exellent info guys, I was referring to a more precise "stock" barrel when I said "...persue tighter tolerances". As in do the manufactuerers persue tighter tolerances for their stock barrels like the aftermarket seems to do. Bullberry metioned that they have incredible tolerances in their custom barrels... so, whould r&d push the firarm manufacturers to produce more precision barrels? maybe you all might know if one such company does this...not referring to a $1,000 plus rimfire, I mean are the Rugers, the Marlins the more blue collar favoring companies doing this? Does one of these companies consistantly get a higher muzzle velocity over the other competitiors? Thats where I was going with that comment Peetza. Lastly, you all are droppig knowledge bombs left and right on a subject i was struggling to find out more about for a bit! I actually started to give up, thinking I was digging for unavailable information...obviously not the case. Outstanding input guys.
 
Does one of these companies consistantly get a higher muzzle velocity over the other competitors?
Click to expand...
Tighter barrels give you (slightly) higher velocities -- but at the expense of higher pressures.
Custom barrelmakers therefore don't pursue smaller/tighter diameters so much are tighter/more
consistent tolerances.
 
The 17HMR has SAAMI spec chamber and they include Bore/Groove dia.

Here is article from Bullberry

The Bullberry 17 HMR is a proven cartridge. Our test gun in the photo is a "3rd generation chamber". This 11" pistol using the new Hornady 17cal, 17 grain bullet finally satisfies our "World Famous Accuracy Guarantee."

Initially we had our reamer made to Hornady specifications, but were not happy with the results. The chambers were – by Bullberry standards – far oversized. A subsequent batch of about 8 barrels were chambered .002" smaller in diameter. Now, with a new reamer, our chambers are nearly .004" smaller in diameter than the original. This is giving us the accuracy we were looking for. And we're not having a ruptured case problem as was predicted by Hornady, by shrinking the dimensions to just accept the ammo.

Velocity tests were conducted on this barrel, as well as on a test barrel. Below is the chart based on this barrel. All velocity tests were conducted using a 5 shot group. Special Note: The average velocity of this 11 inch barrel is only 132 fps slower than the 22" carbine barrel shown in the next table.


How oversized was the Hornady spec reamer vs SAAMI spec vs the last reamer Bullberry used.
 
You must log in or register to reply here.
Back
Top