How do I increase velocity?

[CamTheBam]

Hi Guys,

Please bear with me, because I don't have a scooby doo about this stuff, and in many respects I don't even know the correct questions to ask...

Basically I want to increase the velocity of my home loads – without changing bullet weight or barrel length. For the sake of an example - 168gr SMK and a 24" barrel.

The obvious answer of course, is to use more powder? But I fear that eventually one of two things is going to happen: 1. problems with pressure; 2. not achieving a 'full burn'.

I note that in Sierra's reloading manual, the .308WIN 168gr MatchKing (#2200) has charge weights listed for both N140 and N150.

I know that N140 has a faster burn rate than N150.

The maximum charge for N140 is listed as 42.3gr (2600fps).
The maximum charge for N150 is listed as 44.3gr (2700fps).

I guess if you go higher than 42.3gr of N140 you start to run into pressure problems, but it appears as though its possible to go up to 44.3gr of N150 before encountering pressure problems AND there's an increase in the velocity produced.

Or to put it another way, the slower burning N150 produces a faster bullet velocity than N140, without producing any more pressure.

Is it all over and done with early doors with the N140, whereas the slower burning N150 has more 'dwell' time (assuming the barrel length supports it)?

If so, is it generally more efficient (higher bullet fps) to pick the slowest burn rate powder that still achieves a full burn in your barrel?

And obviously, I always work up to a charge weight rather than jumping right in.

Thanks again, it's always greatly appreciated!

Cam.

 

[StevenDzupin]

Hi Guys,

Please bear with me, because I don't have a scooby doo about this stuff, and in many respects I don't even know the correct questions to ask...

Basically I want to increase the velocity of my home loads – without changing bullet weight or barrel length. For the sake of an example - 168gr SMK and a 24" barrel.

The obvious answer of course, is to use more powder? But I fear that eventually one of two things is going to happen: 1. problems with pressure; 2. not achieving a 'full burn'.

I note that in Sierra's reloading manual, the .308WIN 168gr MatchKing (#2200) has charge weights listed for both N140 and N150.

I know that N140 has a faster burn rate than N150.

The maximum charge for N140 is listed as 42.3gr (2600fps).
The maximum charge for N150 is listed as 44.3gr (2700fps).

I guess if you go higher than 42.3gr of N140 you start to run into pressure problems, but it appears as though its possible to go up to 44.3gr of N150 before encountering pressure problems AND there's an increase in the velocity produced.

Or to put it another way, the slower burning N150 produces a faster bullet velocity than N140, without producing any more pressure.

Is it all over and done with early doors with the N140, whereas the slower burning N150 has more 'dwell' time (assuming the barrel length supports it)?

If so, is it generally more efficient (higher bullet fps) to pick the slowest burn rate powder that still achieves a full burn in your barrel?

And obviously, I always work up to a charge weight rather than jumping right in.

Thanks again, it's always greatly appreciated!

Cam.

Cam, you need precision first,accuracy second and velocity last.
That is to say ,good grouping,adjust sights to center that grouping on target ,and let the velocity fall as it may.

You can also pull the trigger harder LOL

 

[nicholst55]

In a nutshell, yes. All other things being equal, a slower burning powder will normally give you more velocity than a faster burning powder. Up to a point. Some powders are simply too slow to perform acceptably in a given cartridge. An example might be something like Retumbo or AA8700. While they may shine in a large magnum cartridge, they are less than ideal for the .308. You simply can't get enough of those powders into a .308 case to take advantage of their potential.

Besides going to a slower powder, your only two other choices are really using a larger case that holds more powder, and/or using a longer barrel. A longer barrel normally gives an increase in velocity, once again, up to a point. Larger cases mean more recoil and muzzle blast, and shorter barrel life.

Just remember, you can't miss them fast enough to kill them!

 

[DRNewcomb]

One thing that has not been mentioned is moly coating the bullets. This reduces friction in the barrel allowing for the use of the faster powder without excess pressure, in theory.

 

[hunter243sgk]

Also always work up slowly. I have gone past book max on some and got no where near book max with others. So just because a manual lists a powder max and velocity don't mean you wont get safely above them both. And those book velocity numbers are just references you may get more or less at or below max. All barrels are different. I have had pressure signs way before max. Be safe!

 

[gotcha]

Cam, you didn't mention what primers you're using. Often a simple primer swap can increase velocity by 50 fps. It's a fact that some primers burn hotter. ................ I can't cite a reference since I don't shoot a
308. Perhaps someone else could ?? If you tell us if you use SRP or LRP.

 

[dragman]

With the right powder, setup, and some patients you can get the 168's around 2800 up to maybe 2850 with a 24" barrel.

 

[ebb]

Have a gunsmith open the bolt face, and rechamber the barrel to 300WSM. If the velocity is not enough a near max loads you picked the wrong chambering. Running at 100 percent or more in a case reduces the life of every thing, ( maybe even your own life ) when choosing choose some thing that gives the velocity you need at about 80 percent of max case capacity then there is room to experiment.

 

[Joe R]

Hi Cam,
The way must of us F-TR competitors push the boundaries of the 308 is by increasing case capacity. This is done by moving the bullet as far out of the cases as is possible while still getting decent neck tension. This is where the amount of freebore of a given chamber plays a big role. Most factory rifles have around .090 freebore. Must F-TR shooters running heavy bullets have a freebore of .180+. Extending the freebore on a barrel is quite easy and most gunsmiths have a unithroater that can do that in about 10 minutes.

Another thing you need to consider is that the max loads published in the manuals are very conservative, and rightly so. The publishers don't want the liability. To give you an example, the Sierra manual says that with a 200 grain bullet the max load for Varget is 38.0 grains. Most of us TR shooters are using somewhere around 44.0 grains. I've gone as high as 45.2 grains and I never found the usual signs of overpressure, however, recoil spoke volumes.

It also seems to me you're trying to understand how powder burn rates and bullet size are interconnected to achieve higher velocity. Please correct me if I'm wrong.

A way that has helped me understand that concept is as follows: First take a volleyball hold in one hand and slap it with the other as hard as you can. The result will that the volleyball will go flying. Second repeat the same procedure as before but use a bowling ball instead of a volleyball. The result will be painful. The point is that the selection of the powder to complement a given (weight) bullet is very important. As Erik Cortina once taught me, the Holy Trinity of precision handloading are:

1. Powder (selection and measurement).
2. Seating depth.
3. Neck tension.

I hope I haven't confused you.

Kindest regards,

Joe

 

[CharlieNC]

For this exercise Quick Load is your friend, coupled with Optimum Barrel Time. You can specify various parameters and QL will search the powder base for exact matches for that parameter. For example, specify the barrel time (which matches an upper node) and it will automatically provide a list of 50+ powders that match, and list them typically in the order with highest velocity first. Or specify pressure, velocity, etc to match. In a few minutes a few prime powder candidates can be identified to evaluate within a narrower charge range than if you started with limited info. Much faster and less costly than buying multiple powders to evaluate.

 

[geraldgee]

You might consider trying Alliant's PP 2000 MR. It shoots really well in my 308 and increased velocity a good bit. Start low and work you way up to a safe, acceptable load.

Good luck

 

[snowpro440]

Fast is fine but accuracy is final ... why the need for speed ? If it shoots good go with it .

 

[CharlieNC]

Fast is fine but accuracy is final ... why the need for speed ? If it shoots good go with it .

Depends on the course of fire. In a tactical/PRS match the targets are "large", the wind and its angle vary target to target, no sighters, and the time for shooting is limited. In this case getting relief from the effects of the wind is more important than improving from 1moa to. 5 moa groups.

 

[SheepDog]

Cam,
As long as you are selecting a load for your own use and not for competition then forget about the velocity. You won't get the velocity listed in the book most of the time any way. Select your powder based on the three powders that list the highest velocities in the manual and then work from the starting load to where you get the best group sizes consistently. An added 200 fps will only gain you about 40-50 yards in a 6 inch point blank range so it just isn't worth anything. The 308 gets it's optimal velocity/energy with 150 to 155 grain bullets. Using the slightly lighter bullets will give you higher velocities but if you get better accuracy with a heavier bullet that is what you should use. No target or game animal is going to know the difference between getting hit with a 150 grain bullet or a 180 grain bullet as long as they are placed in the kill zone.

I applaud you for not exceeding the maximum listed loads - that is the safest way to do things. Until you gain the ability to recognize the signs of excessive pressure staying within the book maximum loads will keep you from injury - personal or to your gun.

 

[Ned Ludd]

There are a number of ways to increase velocity by fairly small increments. Increasing the pressure cell volume (i.e. effective combustion volume) is one. This can be achieved by seating the bullet farther out, and/or switching to a brand of brass that has larger internal volume. The effect of either of these approaches in modest. Using a longer barrel is another approach, but you stated you want to stick with the 24" pipe.

Finding the right combination of powder and primer is another approach. As mentioned above, Quickload is a very useful tool for making estimates/predictions in this regard.

The real key as to whether any of these approaches is practical in terms of what you will get in return is how much extra velocity can you actually generate while remaining at safe operating pressure. If accuracy/precision are equal, I'll take an extra 25-30 fps any day of the week. As an example, 25-30 fps is a reasonable expectation for velocity increase at the "sweet spot" when switching from Varget to H4895 for a variety of .223 and .308 load. However, you only need to plug the numbers into a ballistic calculator to see how much that small increase in velocity affects wind deflection to see that it is not a huge difference, even at 1000 yd. As I mentioned, I'll take it, all else being equal, but it's not a huge increase in performance. Obviously, increasing velocity by 75-100 fps (or more) will provide greater gains in wind resistance. You can make very good estimates of how much effect a given velocity increase will have using any ballistic calculator. If the gains are extremely small and high pressure is an issue, I would suggest it may not be worth it in the long run.

Another option to increase performance would simply be to use a higher BC bullet. There are also limits to this approach in terms of what bullets your rifle's chamber and barrel twist rate will allow you to load optimally. However, you mentioned the 168 gr SMK in your post. There are far better choices from a ballistics standpoint, while remaining in the same weight class. For example, the Berger 168 Hybrid has a significantly higher BC ((0.264 vs 0.218 G7 BC), while retaining dimensional properties that would allow you to load it to reasonably similar specifications as the 168 SMK ("reasonably similar" as compared to going up in weight class to 175 or 185 gr bullets). Maybe all you really need is a more efficient bullet.

It's also worth noting that reloading manual "MAX" values are often extremely conservative. Much of that is because they typically specify loads that can be accommodated within magazine length. Single-feeding, such as in F-Class competition, allows for longer freebore, which reduces pressure at a given velocity as described above. With bullets seated much longer than is usually found in mag length loads, typical charge weights can exceed reloading manual MAX charge weight values by a considerable amount, while still allowing safe operating pressure.

If your needs will allow you to single feed, you can figure out pretty easily about where you are with regard to your potential COAL, and the reloading book COAL values. If you have the room and can single feed, you can usually load to greater velocity than predicted by the reloading manual MAX values, without generating unsafe pressures. Again, Quickload is a very useful program for making these kinds of pressure/velocity predictions without having to load and shoot a huge number of rounds. There are certainly caveats to the "predictions" it generates, but I have found it generally gives pretty reasonable estimates, especially after you have calibrated it to your specific setup, lot of powder, lot of primers, etc.

 

[Joe R]

For this exercise Quick Load is your friend, coupled with Optimum Barrel Time. You can specify various parameters and QL will search the powder base for exact matches for that parameter. For example, specify the barrel time (which matches an upper node) and it will automatically provide a list of 50+ powders that match, and list them typically in the order with highest velocity first. Or specify pressure, velocity, etc to match. In a few minutes a few prime powder candidates can be identified to evaluate within a narrower charge range than if you started with limited info. Much faster and less costly than buying multiple powders to evaluate.

Amen brother,
However, reality is that Cam probably doesn't have it and as a beginner it would probably overwhelm him. Common problems have common solutions.

Joe

 

[Liven The Dream]

Can,
.308 for years 4064 powder was the powder to use... Yes some Barrels like 4895.
As send above speed is not the answer.
A one hole group at 200 years is the dream come true.
I will add 168 Gr. Bullets are limited to 600 and a little more. As we long range shooters say !"friends don't let friends shoot 168's at 1000 yards.
Speed Kills !
Best of Luck,
Don

 

[Ned Ludd]

That is relatively specific to the 168 gr SMK and is caused by dynamic instability due to the boattail angle. Other 168 gr bullets such as the Berger 168 Hybrid do not suffer from that issue and are absolutely fine to shoot at 1000 yd. Of course, they will still be subject to any ballistic deficiency associated with having a significantly lower BC than longer, heavier bullets like the 185 Juggernaut or 200 Hybrid. But they don't exhibit the dynamic instability associated with the 168 SMK. As another example, people have fired 155 gr bullets in 1000 yd matches for a very long time. The 155s also don't exhibit the instability observed in the 168 SMKs because their boatail angle is much more optimal. Even though relatively light by today's F-Class standards and certainly lighter than a 168 gr bullet, they fly just fine out to 1000 yd in competition. It's not the weight that's the problem, it's that specific bullet.

 

[CamTheBam]

Wow!

Thanks for all the replies guys.

Plenty there for me to think about...

 

[Brians356]

CamTheBam,

Thinking outside the box here, with no preconceived notions of what application you are trying to load for, or how important velocity should be:

You want to increase velocity. Fair enough. Assuming you are asking about 308 Win and 168-gr bullet, from a 24-in barrel, some questions:

1. What is the maximum velocity you have achieved to date?

2. What powder/primer combo was used in #1 above?

3. What is your desired velocity?
-