question for you balistic junkies

[chet]

I just converted my ruger 10/22 to a 17mach2.
It is extremely accurate! I used a fluted 920 20" barrel.
I almost always end up wanting a longer barrel on everything, so i ordered the longest one they had (18" or 20" were my choices)
advertised velocity of this round is 2100fps.... I was hoping for a little more due to the extra two inches of barrel...... however..... it is less. average velocity is 2003fps.

here is my theory: longer barels create more velocity, due to pressure. but at some point the extra length causes extra drag and that drag offsets the gain of pressure????????
also im at 5000 feet...... any thoughts?
I really doubt ive got too much drag as I've seen 17hmr's in 24" tubes before.........


im not dissapointed at all.... the project turned out very nice and it is still very impressive!

so what do you think?
barrel too long?
typical advertising tactics?
elevation issues?
semi automatic action stealing some energy?
all of the above?

I guess what it boils down to is i need to shoot the 18" barrel in the same situation and see if it is faste/slower/same??? I can always cut my 20"er

 

[FOTIS]

There was a test conducted a while back.

It was found that most 22 LR's burned all powder by the first 16" of barrel length. So in theory anything over this length velocity falls due to barrel drag on the bullet.

BTW shotguns bun their powder during the first 16" too, so a longer barrel helps the swing and nothing else.

 

[chet]

ok, so do you think this 20" tube is actually slowing down this 17 grain bullet?
if i cut, should i try 19" or go right to 18"?
decesions decisions............

 

[Ol` Joe]

Advertised velocity is not an exact velocity, usually it is a estimation under perfect conditions. Check the different manufactures and I believe you`ll find they all claim the same number. I doubt you will find it worth adding or subtracting from your present barrel lenght. You MAY gain a few fps, but how much is the extra going to aid your accuracy or improve killing power?