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Barrel Length Question

 
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  #1  
Old 09-07-2004, 09:16 AM
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Barrel Length Question

I have a question on barrel length. Right now I have a 375 H&H that I am using and it has a 24inch barrel. Now I am also having one built that is going to have a 28inch barrel. My question is should I be able to get 200fps faster than the 24inch barrel with the 28inch pipe using the same loads? Someone told me that you can expect to gain 40 to 65 fps per inch you add to a barrel. Is that a good guess or not?
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Old 09-07-2004, 10:11 AM
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Re: Barrel Length Question

I have a 26" barrel on mine and getting 2819fps on a 270 Accubond. I haven't tried for a fast load just dumped powder and shoot.

I take those "nn" fps faster per inch of barrel as a note but not anything to count on, it is what it is.
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  #3  
Old 09-07-2004, 10:33 AM
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Re: Barrel Length Question

Dan Lilja published on his website the results of a study he did a while back.

Based on his results I would expect something closer to 20 fps per inch of added barrel length.
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  #4  
Old 09-07-2004, 01:26 PM
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Re: Barrel Length Question

Dakor,

Len Backus is pretty close to on track in his comments in my opinion.

Lilja's tests were with very large high volume cases in the .308" or .338" calibers.

In your case, you are dealing with a relatively low pressure round at least in factory loaded form.

More importantly, the 375 H&H has a relatively small case capacity to bore volume ratio so you are able to use faster powders in the larger bores with much less worry of pressures.

This is because as the bullet travels down the bore, the ever changing chamber volume, the entire volume behind teh bullet, increases very quickly so that the faster powders have plenty of room to expand rapidly.

This is why these style of rounds are so efficent in shorter barreled rifles.

It is also the reason that they do not gain a great deal with longer barrels and also why they do not make a muzzle brake work efficently.

By the time the bullet reaches the bore, the pressure in the bore has dropped considerably so teh acceleration of the bullet is relatively low at this point at the end of the barrel.

Especially compared to a round like the 375 RUM or 378 Wby.

75 to 80 grains of powder simply runs out of expansion in this size of a bore to continue to add significant velocity in barrels from 24 to 28".

YOu will probably be looking at a true gain of more like 15 fps for the 375 H&H going from 24 to 28".

In my mind, if you are going with a 28" pipe, cut the barrel to the 375 RUM chamber, especially if you want that 200 fps gain over the 375 H&H.

Otherwise you will be reducing the fine handling characteristics of the 24" H&H rifle with no real improvement in performance.

The RUM with its +100 gr capacity will run much faster in the 28" barrel as will the 378 Wby but the RUM recoils quite smartly and the 378 can be rediculous as far as recoil goes.

As a rule of thumb, rounds with large bore(375 and up) to case capacity ratios will gain 10-14 fps per inch of barrel past 22".

Medium bores(30-338) with medium ase volume such as the 300 Win and 338 Win will average in the 15-18 fps range with barrels over 24".

Small bores(6mm-7mm) with medium case capacity rounds such as the 243 Win to 7mm Rem Mag will gain about the same 15-18 fps per inch over 22".

Medium bores(30-338) with large case volumes such as the RUM cases will gain 18-20 fps per inch over 24".

These bores with huge case volumes like the big Wby case and similiar cases will average around 20-23 fps per inch over 26".

The idea that you will get 50 to 65 fps for each inch of barrel is kind of a myth in our sport. If you had to average all the rounds I would say your looking at around 18 fps per inch of added barrel length over 24".

Good Shooting!!!

Kirby Allen(50)
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  #5  
Old 09-07-2004, 06:55 PM
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Re: Barrel Length Question

Thanks for the input. So you guys dont think I could gain 150 to 200 FPS over a REM 700 with a 24inch barrel with a Lilja 28 inch pipe? Well when the barrel comes in it might be time to make the 375 Ackley [img]images/icons/frown.gif[/img] Which I really did not want to do. As for the 375 Ultra no thanks!!! I like my shoulder and I hate Muzzle breaks. [img]images/icons/grin.gif[/img]
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Old 09-07-2004, 07:33 PM
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Re: Barrel Length Question

Dakor,

Do not get me wrong, you may full well get 200 fps more velocity with the Lilja barrel, it will not be simply because of barrel length though.

You will get more velocity from the tight match grade bore and mirror smooth bore finish as well as gained velocity with a quality chamber job.

Remember, if your comparing a factory REm barrel to the Lilja, its like comparing a 350 chevy V-8 that billy bob rebuilt in his garage, to a NASCAR V-8 of roughly the same size that produces twice the power.

Its all in the componants used as far as gains and losses, that and quality machining is just as important.

I've got a stainless Rem 700 26" take off barrel in 375 RUM if you want it, $100 + shipping or fitting cost. Its only had about 75 rounds throw the bore. I know this because it used to be the barrel on my 257 STW Rem action that I baught new.

Good Shooting!!

Kirby Allen(50)
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Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
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  #7  
Old 09-07-2004, 08:36 PM
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Re: Barrel Length Question

Fiftydriver is it a heavy barrel or standard? How bad does that baby kick? [img]images/icons/shocked.gif[/img] I can feel the pain already. [img]images/icons/shocked.gif[/img] I can handle the 375 H&H in a 9lbs gun pretty easy off hand. On the bench she bites a little bit but that is because the pads on a HS stock suck. Once the SIMMS pad is put on, It will be like shooting a 300 Win Mag.
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