OK I need some mathematicians.

[gt40]

I am trying to make a decision on what length I should have my barrel. The barrel blank I have could be a maximum finished length of 30 inches.

What length barrel is needed for a 6mm Norma BR shooting 105 grain bullets using Varget or other similar burning powders.

I would imagine that the optimum burn would be right to the end of the barrel. ( The 6mm br doesn't hold very much powder) If this is true and the gas pressure drops off lets say at 26 inches in a 30" barrel and the barrel has a 1 in 8" twist doesn't the bullet start to slow down do to friction inside the barrel?

If the barrel was only 26" wouldn't you get more velocity than a 31" barrel?

I'll tell you why I am asking after I get some answers.

gt40

 

[Charles E]

You don't need a mathematician; you couldn't possibly furnish data for all the needed variables. You need empirical testing. And fortunately or you, Jackie Schmidt did just that for a piece on the 6mm BR, published by 6mmbr.com. Go look up the thread.

Best for you to look it up. As I remember, velocity did increase all the way to a 30-inch barrel, but after a certain point, only by about 5 fps per inch.

 

[Lynn]

gt40

There are lots of 28-30 inch barrels out there winning matches each weekend.Let your gunsmith cut the barrel were he wants it and all will be fine.

From 30 to 32 inches you will gain 7.5 fps per inch of barrel length.

If you look for posts by Larry Bartholome who actually shoots longrange regularly you will get a wealth of knowledge from his posts.
Lynn

 

[.25shooter]

length of barrel

After 28 inch your gain in velocity is negligible for all practical purpose. Then it becomes a matter of personal taste. I would however look up what Jackie Smith observed and wrote about the matter. Then you can make an informed desition for your self.

 

[R. G. Robinett]

My most recent guinea pig . . .

Whacked 6 inches off a .243 capacity 6MM wild-cat (30" to 24") and lost a whopping 75 FPS, or, 12.5 FPS per inch of barrel (108 Gr. bullet and RL-22) : What he got in return: no more bullet failures, improved precision: consistently and repeatably < than 1.5" of vertical at 600 Yd. Anecdotal , but consistent with what pals have experienced with several other barrels of late.

Prior to shortening, this barrel consistently destroyed my FB 108 Gr. bullets, but NEVER the BT version. Following the bobbing, there have been ZERO failures with the 108 Gr. FB bullets . . . oddly, with the shortened barrel, the BTs are now out performing (grouping) the FBs . . . prior to the whacking, the FB bullets - those which DID NOT vaporize - out grouped the BTs! No doubt a "tuning window" thing . . . It's a strange world out there.
Good shootin'!
RG

 

[mike in co]

Whacked 6 inches off a .243 capacity 6MM wild-cat 30" to 24") and lost a whopping 75 FPS, or, 12.5 FPS per inch of barrel (108 Gr. bullet and RL-22) : What he got in return: no more bullet failures, improved precision: consistently and repeatably < than 1.5" of vertical at 600 Yd. Anecdotal , but consistent with what pals have experienced with several other barrels of late.

Prior to shortening, this barrel consistently destroyed my FB 108 Gr. bullets, but NEVER the BT version. Following the bobbing, there have been ZERO failures with the 108 Gr. FB bullets . . . oddly, with the shortened barrel, the BTs are now out performing (grouping) the FBs . . . prior to the whacking, the FB bullets - those which DID NOT vaporize - out grouped the BTs! No doubt a "tuning window" thing . . . It's a strange world out there.
Good shootin'!
RG

ok off track a little....
with this info(above),
if building a 1000yd 300 win mag br rifle......11 twist......what length and bullet weights would you chose( yes i know i limited your answers)
mike in co

 

[Lynn]

Mike In Co

Mike
With an 11 twist use the 208-220 grain bullets and a 30 inch barrel.Those extra 2 inches will cost you about $30 up front and will give you 40-50 fps in velocity.If you can buy 50 fps for $30 any other way for 1500 rounds I haven't heard about it yet.
When your barrel gets 500 rounds down it cut an inch off and have it re-crowned.When you get a 1,000 rounds down it do it again.If it shoots better after that first 1,000 rounds order yourself up a 28 inch barrel on the next one.
My standard 30-06 with a 30 inch barrel will push a 190 Sierra to 3,000 fps with 61 grains of RE22 in a Lapua case.That ain't bad when you consider the pet load for the 300 Win Mag was always 2930-2950 with the same bullet.In my case the gun shot best at 2825 fps so the extra barrel wasn't a plus.
In your example I think you'll find the 210's like 3075 fps and the extra barrel is a must.
Lynn
Edit:Mike my 3075 fps velocity ws for a 300 Weatherby.Just wanted to clarify that.

 

[Tony Shankle]

Mike,

I shoot an 11 twist and it likes the 208 & 210 best. 76.5 gr H1000 (full case) gives me 2850 for my accuracy load. It is 28".

I see this "what barrel length" thing discussed a lot but seldom is it mentioned that it depends on what powder and bullet. IMHO you should pick a desired powder/burn rate and bullet weight to get to the length or vice versa. 4350 might do the same thing in a 26" while you would need 30 or more for Retumbo.

 

[gt40]

Quote: "I'll tell you why I am asking after I get some answers".

I have been asking many gunsmiths about what length the barrel should be and got a lot of different answers including one that said 24 to 26" would be fine and he was very convincing.

Everyone else suggested 28" to 30" which is the consensus here also. I do not want the rifle to be very heavy and will probably get the 2 1/2 pound stock and have the barrel cut at 28 inches to keep the weight down to I hope under 12 pounds. I am hoping that the balance will be ok with out adding lead to the butt of the stock.

What do you guys think about what I wish to do?

Thanks for all the input you fellas have put here.

gt40

 

[Lynn]

Gt40
I believe Roger Amos "The Expiper" is shooting a lightweight lightgun because he doesn't like to pack all the extra weight around.Try looking for posts by him on www.6mmbr.com in the competition forum as he describes his rifle very well.
He just re-set the NBRSA 600 Yard Score Record with that gun a month ago.
Lynn