300 RUM Barrel Length

[River Man]

Hello All,
 
This is my first post, so be gentle on me.
 
I have a 300 RUM with a Rem 700 action and a Krieger Light Varmint contour 35 inch barrel. 
It is set up as a tactical rifle with a McMillan A5 stock. (I am in my Tactical Toys phase right now.) 
The gun will be used for target shooting as well as long range hunting. 
 
 
I plan to primarily shoot either 240 SMKs or 210 Berger VLDs pending the
results of future accuracy tests.
 
 
I bought the extra long barrel because some wise person posted on long range hunting 
that you can cut a barrel shorter but you can't add length to an existing barrel. 
Currently the barrel is a bit long for carry. 
I want to cut it to either 28, 29, or 30 inches. 
Based on my data below, I am leaning toward the 30 inch barrel. 
 
 
I would appreciate some feedback from the wise people on this forum.
 
My test results are below.  
Factory velocity's are from Hodgdon's website. Hodgdon data is from 24 inch barrels.
 
190 gr sierra  35 inch barrel
            Grains  Velocity   Factory        Increase     Speed/inch
US869        104     3240       3035           205           18.63636
 
Retumbo      96       3200      3204            -4            -0.36364
 
H50BMG       105     3136      3085              51            4.636364
 
IMR 7828     86      3209      2985            224            20.36364
 
 
210 gr berger 35 inch barrel 
           Grains  Velocity   Factory        Increase     Speed/inch
US869       101      3126       2897           229          20.81818
 
Retumbo     92      3063       2977             86           7.818182
 
H50BMG     101      3061       2900            161          14.63636
 
IMR 7828    83       3013       2816           197          17.90909
 
 
240 gr Sierra 35 inch barrel 
           Grains   Velocity 1    Velocity 2    Velocity 3 
US869       97        2908             2928         2933         Good
 
US869      98         2964             2954          2974        Best
 
US869      99         2923             2997          3024        Max
 
US869     100         2981             Err 2         3017 
 
US869     101         2992             3042           3115 
 
 
 
Estimated velocity change per inch extrapolated from my data 
and corresponded to Lilja 50 BMG data
 
 bbl length         + fps        30 inch        29 inch     28 inch 
24-25                 31           x              x            x 
26                    29           x              x            x 
27                    27           x              x            x 
28                    25           x              x          135 fps 
29                    23           x            156 fps
30                    21        175fps 
31                    19 
32                    17 
33                    15 
34                    13 
35                    11 
 
          Total     231fps

 

[davewilson]

if it's shot out, i'd go back to 32" and shoot,experiment with every bullet/powder combo and practice a whole bunch. then you could set it back another 3" to 29 if the accuracy falls off you'd probably get another 500 rounds out of it. then when you rebarrel, you can make it a big 338 and have a real hammer! i think the barrel length question is more of a personal preference. myself i don't like the real long rigs so i just made a short gun with a long barrel. some hunt open terrain and a long barrel doesn't make much difference. others have to traverse more woods with thicker cover and a shorter barrel is a lot easier to carry around. to each his own, but it seems a waste of a good barrel to chop half a foot off of it.

by the way, welcome aboard! you're at the right place.

 

[River Man]

Thanks for having me, I am glad to be on this forum. There is a wealth of information in this forum.

The 338 is my next project. It is probably 2 to 3 years down the road. I am gaining experience with the 300 Rum. If I had known about long range hunting and had researched my caliber selection here on long range hunting, I probably would have started with a big 338. Oh well I am only a few hundred yards shy of a 300 SMKs in a 338 LM with the 240 SMKs in my 300 RUM.

There is another reason that I am cutting the barrel. I have on order an Advanced Armament Corporation 300-SD suppressor (silencer.) Remember this is also a tactical rifle. The suppressor is about 10 inches long. The suppressor is a fast attach model. I am going to have the muzzle threaded and a fast attach flash hider installed which will add 1 9/16 inch to the length of the barrel so the suppressor will add an effective 8 1/2 inches to the overall length of the barrel. If I don't cut the barrel, the barrel plus the suppressor will be 45 inches. A bit long.

Now some of you are asking why I am getting a suppresor. I have a few reasons.

1. Because I can.
2. Suppressors also act a muzzle brakes, albeit an expensive muzzle brake.
3. By nature, I am a quiet kind of guy.
4. I like to experiment with technology.
5. I don't want to damage any Elks or Deers hearing! No Not Really, I'll take it off for hunting.
6. And the most important reason, Suppressors are really cool! You can shoot a 300 RUM without hearing protection.

I hope Shawn Carlock and Kirby Allen respond to my thread. I would like their input on optimum barrel length.

Thanks,
Dennis

 

[Down Under Hunter]

Welcome to the forum. I asked this question a while back and most people thought the rum sweet spot was 28-30 " for barrel length. I was looking at rebarrelling a std factory 26 " on a sendero. I might be wrong, but this is what I was leaning to ?

Good luck !

 

[blackco]

Just my 2-cents worth...I am in the process of an almost identical build, mine is for hunting only though and will be shooting bullets 200-220grs, and after some discussion with my smith decided a 26" was best. Heavier bullets are somewhat slower therefore in the barrel longer, thus more time for the powder to burn. What I would get wouldn't outweigh the drawbacks of a longer barrel.
This is my first build so my inexperience may be glaring but that was my decision.

 

[jwp475]

Just my 2-cents worth...I am in the process of an almost identical build, mine is for hunting only though and will be shooting bullets 200-220grs, and after some discussion with my smith decided a 26" was best. Heavier bullets are somewhat slower therefore in the barrel longer, thus more time for the powder to burn. What I would get wouldn't outweigh the drawbacks of a longer barrel.
This is my first build so my inexperience may be glaring but that was my decision.

Contrary to popular belief the powder is burnt completely in the first 3 to 4 inches and a longer barrel gives more velocity,with all bullet wieghts.....

 

[davewilson]

could you tell me where your source was that said the powder burns completely in the first( i assume you're talking about bullet travel) 3 or 4 inches? you're right, this would be contrary to popular belief.

 

[Varmint Hunter]

"Contrary to popular belief the powder is burnt completely in the first 3 to 4 inches and a longer barrel gives more velocity,with all bullet wieghts....."

If that were true than bullet drag in the barrel would cause longer barrels to give LESS velocity after the first 3 to 4 inches. Interesting theory though????

 

[dirtball]

"Contrary to popular belief the powder is burnt completely in the first 3 to 4 inches and a longer barrel gives more velocity,with all bullet wieghts....."

If that were true than bullet drag in the barrel would cause longer barrels to give LESS velocity after the first 3 to 4 inches. Interesting theory though????

With slower powders you extend the burn time, BUT 80 to 90% of the powder is burned within the first 6+/- inches of the barrel. This results in peak pressure developing at that time. The pressure beguines to decrease after that, but even at 35" or more there is still enough pressure to continue the acceleration of the bullet. This decreasing pressure is why the amount of increased velocity that is achieved per inch of barrel length drops of so much after 29" or 30". This also varies greatly depending on case volume vs. bullet diameter. That is why they have 50 foot barrels on 16" guns on battleships, and why Kirby's AM's are so much in demand.
Dave

 

[jwp475]

could you tell me where your source was that said the powder burns completely in the first( i assume you're talking about bullet travel) 3 or 4 inches? you're right, this would be contrary to popular belief.

John Barnsness has writen several articles about this... I have aslo asked a few people that work in balistics labs and they concurred.........

 

[River Man]

I too have long wondered how far down the barrel the powder burned.

I have shot AR-15 carbines with 16 inch barrels without flash suppressors well after dark. The flash is blinding. There is an oblong bright white and yellow fireball that is about 6 inches in diameter and about 10 inches long. This is from a 223 cartridge that holds about 25 grains of powder.

Why would you get such a large fireball if the powder burned in the first few inches of the barrel? Could it be super hot gasses glow? I don't have an answer. I always assumed it was powder still burning.

 

[Agunner012]

Interesting about the powder being burnt in the first few inches. I can't for the life of me remember where I read this but: Some of the big magnums don't burn all the powder in short barrels 26" and under. If you hang a white sheet several feet in front of a big magnum and shoot through it the un-burnt powder will collect on the sheet. If you increase the length of the barrel and do the same test you will see less un-burnt powder or none all at. The less un-burnt powder the more efficient use of that powder.

HTH

AG

 

[River Man]

One thing I noticed during my testing was that some powders produced a higher velocity with the longer barrel than did others.

Per Hodgdon, a 24 inch barreled 300 RUM with 190 gr SMK loaded with 104gr of US869 should achieve 3035 fps. I got 3240 fps out of a 35 inch barrel which is a 205 fps increase.

Also per Hodgdon, a 24 inch barreled 300 RUM with 190 gr SMK loaded with 96 grains of Retumbo should achieve 3204 fps. I got 3200 out of a 35 inch barrel which is a loss of 4 fps.

Clearly, 35 inches is not too long for US869 but is ineffective for Retumbo. This demonstrates what people have said earlier that the powder burn rate will affect maximum effective length of barrel.

The Retumbo is a faster burning powder than US869. But not by a whole lot. Retumbo is #99 on Hodgdons burn rate list. US869 is #104 on the list. I suspect that the 35 inch barrel is approaching the maximum effective limit for US869 in a 300 RUM.

 

[jwp475]

H869 is too slow in the RUm with any barrel lenght when compared to Retumbo with a bullet as light as the 190 grain. Move up to ,say a 240 grain SMK and then h869 will give faster velocities than will Retumbo.....JonA got up to 3000 fps with H869 and the 240 SMKs about 200 fps faster than Retumbo ( if my memeory is carrect) Case capacity for the bore size and bullet is the determining factor for powder burn rate not barrel lenght..
I talked to Tye at Barnes yesterday about when all of the powder is burned and he said that he ands theier ballistics engineer have talked about this recently (they have read JBs article also) and they are not sure that the powder is completly burned in the first 3 or 4 inches...Tye is going to conduct a few experiments to see if he can get a better idea if this is true or not......