Can any one verify this? RFB 32 inch barrel ballistics

[shooker8]

Looks like out of a 32" barrel:
A .308 175 grain = 2,901 fps.
A .300 Win Mag 190 grain = 3,150 fps.

A 180 grain bullet bullet in a 24" .308 would be about 2,600.
Same bullet in a 24" 30-06 would be about 2,800.
Same bullet in a 24" .300 Win Mag about 2,950.


Here is the link
http://www.ktog.org/cgi-bin/yabb2/Ya...num=1179515537

[harold63]

Don't understand what you want verified. The numbers look like the tables that I keep in my notes. I'll say that last year, we chronographed some Speer 150gr BT hand loads out of a cheap WM 770 300WM that averaged 3223fps, and it has a 26" barrel. Don't know if that means anything to you.

[knight0334]

It'll depend on the loading too. You can only lengthen a barrel so far to the point which there isn't enough pressure behind the bullet to keep the drag on the insides from slowing it down.

The fortunate thing is - most centerfire rifle cartridges are overbore in 24" and shorter barrels, not allowing enough barrel to effectively make use of the powder charges.

[Tomcat088]

As others have said, this is a VERY subjective question. It would depend on LOTS of things that can change SIGNIFICANTLY, from variables that some people would consider "small". I have quite a few loads that aren't at max (or all that close), that will push a 190 grain bullet 3,150 fps with only a 26" barrel. As others have said, there's some other loads that the bullet would actually slow down some before it exited a 32" barrel. Hope this helps you understand how vague of a question this is.

There is a lot that goes into the equation, and one of those things is powders. Different powders will have different "optimum burn lengths". It is usually expressed in inches (barrel length), and is the length that it takes for the powder to burn completely and build up some pressure, but not have the bullet slow down before it exits the barrel. Some powders have an optimum burn length of 20", and in pistol powders, even less. Others will have an optimum burn length of 26" or more, just like some of the powders used in the .50 BMG. The "pressure curve" of these powders will also have an effect, and it's also related to the projectile weight. The pressure curve is related to the burn rate, and it depends on if the powder builds up most of it's pretty at initial ignition, or if it slowly and steadly builds up pressure as the bullet travels down the barrel. There are different reasons to use different powders. Let's say that I was using a slow burning powder with a long steady pressure curve; if I was using a 22" barrel and a light/mid weight bullet like (155 grains), the bullet may exit the barrel before the powder builds up enough pressure to push the bullet very fast. I might use the same powder and 22" barrel with say a 180-190 grain bullet, and get as much or more velocity. This can happen because the projectile is heavier and takes more force to push down the barrel. Since it takes more force, it may stay in the barrel longer, and allow the powder to build up more pressure. There's just a LOT that can change with different powders, in different barrel lengths.

As if things weren't difficult enough with just powders and barrel lengths, there's quite a lot of other variables that can have pretty drastic effects. Some of the things that can also effect how the pressure effects the bullet is related to the bullet design. You have to consider the bearing surface of the bullets. This is somewhat related to bullet weight, but also just as much to bullet design. The thing that I'm talking about is "bearing surface", which many times is related to ogive. The length of bearing surface will effect how much drag the bullet experiences while it's going down the barrel. Drag isn't necessarily a bad thing, but something to consider. If bullets have the same weight, but different length of bearing surface; the bullet with the longer bearing surface will experience more drag. This does NOT necessarily mean that the bullet will be slower exiting the barrel, but it WILL take more force to push the bullet down the barrel than it would one of equal weight with a shorter bearing surface. Sometimes the bullet with more drag, will allow a slower burning powder to build up more pressure than it would with a bullet with a shorter bearing surface. This means that the bullet with the longer bearing surface could actually be moving at a higher velocity. How bullets "seal" with the rifling and bore is also related to their design and bearing surface. Boat tail bullets "vent" more gas around the tail of the bullet before it seals with the rifling than a flat base bullet does. So initially, the flat base bullet may build up more pressure than a flat base bullet of the same weight. The seal of the bullet can also be effected by the bearing surface, since on a bullet with a longer bearing surface, it will get to the rifling faster than a bullet with a shorter bearing surface. In case you aren't familiar with "bearing surface", here's a graphic to help you understand what it is.



There's still a lot of other variables to consider, but that I won't really get into. Different primers will tend to ignite different amounts of powder. Some primers burn hotter, or for a longer duration of time than others. This can GREATLY effect how much powder initially gets ignited, and impact the burn rate and internal pressure curve INSIDE of the brass of the cartridge. The rifling of the barrel and twist rate will all effect the friction of the bullet traveling down the barrel. Number of lands, how wide they are, and how deeply they cut into the bullet will have effects. They will effect how much friction is on the bullet, and the pressure curve. Chamber dimensions and how much the brass is allowed to expand will also effect the pressure curve and internal pressures of the cartridge. Even the neck tension or crimp on a bullet will effect the internal pressure of the cartridge and pressure curve in the barrel. Keep in mind that there is tension that holds the bullet in the brass, this holds the bullet in place for a period of time while the powder burns inside of the brass before it engages the rifling. Bullets with more neck tension will stay attached to the brass longer than the exact same bullet that had less neck tensions. How far the bullet is seated into the brass will effect how much pressure builds up inside of the brass. How far from the rifling the bullet is seated will effect the time it takes for the bullet to engage the rifling and seal.

As you can see, there are TONS of variables that effect the velocity of bullets. There's a lot of others that I didn't even go into because it's already probably a lot more information than you were interested in anyway. Still, there could be some others who are curious and would like to know a bit more about the factors that have an impact. It's not as easy as saying, "this bullet weight vs. that bullet weight from a barrel that is XX length". You really have to start considering everything about the whole equation, and try to decide what you think is a "fair" comparison. It all gets subjective then because you have to start looking at operating pressures, bullet weights, chamber dimensions, bullet design, powders, etc, etc. Since you're not comparing apples to apples, it can get pretty murky and opinionated. Either way, I still don't know many people that want to carry around a 32" barrel. Most people don't quite understand how long that is, or how much it can get in the way in field conditions. I have a 26" barrel on my custom tactical rifle, and most people think it's pretty long once they see it. It's very possible to push a 190 grain bullet to 3,150 fps WITHOUT a 32" barrel.

[harold63]

Mr. Tomcat088, that is a great explaination. I got carpel tunnel just reading it.lol It is now printed and in my notes, as well.

[shooker8]

Thanks for the information Tomcat rep going your way!

[aubie515]

There is nothing to verify since the RFB is only offered in the 18" barrel. The 24" and 32" barrels have been discussed from KT, but KT cannot even produce enough RFBs in 18", so why would they offer in other length barrels?

[Asmodeus6]

It's very possible to push a 190 grain bullet to 3,150 fps WITHOUT a 32" barrel.

It is a bullpup. Making it's OAL quite small compared to other more traditional rifles with similar length barrels.

So the 32" barrel is actually much more like your 26" gun.


But as Aubie mentioned. Good luck getting one. Excellent post as usual Tom. You're a wealth of information. I learn something every time you weigh in on a subject.