H4198: good numbers-bad accuracy?

[DanM]

I have tried H4198 in a few military medium case carts like 7.5 Swiss, .303 British, and 8x56r, all with similar results. Velocity was always high, 2000fps was easy to get, and SD was very low, single digit numbers with dacron fill, but accuracy was never good. Usually 3-4" at 50yds. I had my lowest ever recorded SD, 6fps, with this powder in the M95, but accuracy was poor with hose 19bhn boolits. Most of my rifle boolits are in the 23-26bhn range. I like the numbers I get with this powder, but I can't seem to get any decent groups with it. I wonder why, is it just too fast or what?

[Larry Gibson]

Your problem is two fold but one is directly related to the other. First of all H4198 is too fast a powder to approach 2000 fps with. Bad things are probably happening internally in the barrel during accelleration. ES and SD with a regular chronograph will not sho this. Second when the bullet exits at 2000 fps you are pushing 144,000+ RPM. This is above the upper limit of the RPM threshold. As you excede the upper RPM limit for your alloy/accelleration rate the accuracy deteriorates. Some say there is no such thing as the RPM threshold but you just found out there is.

You can bump up the RPM threshold some by switching to a slower burning powder such as 4895 (with a dacron filler) or the slow powders like H4831, RL19, etc. Changing from a bullet with a bore riding nose to a Lovern design or a custom design is also a good thing for high velocity loads. With the right combinations and an accurate rifle you should get the same 3-5" groups at 100 yards up through 2300 fps if your rifles are as issued. If sporterized you might maintain a consistent 2 moa with a scope sight in the 2200 fps range.

BTW; what bullet are you usning?

Larry Gibson

[felix]

Not either too fast or too slow, but just cannot burn at the correct rate for the boolit in that gun. Fit, shape, weight must change, or the powder/primer changed, assuming no changes to the gun itself. The powder selected must be such that it can be off in volume/weight by a quarter grain in variance (half-grain in spread) and produce the numbers and accuracy desired using the primer selected. ... felix

[scrapcan]

Felix,

How do you determine which powder will fit the goal of half grain spread? Is this just a shoot and see situation or is there rules of thumb to help get you in the ball park? I have read this several times in various places ( some benchrest literature alludes to this process also), but have not heard the entire treatise on methodology to choose the proper powder.

Sorry just trying to gather more info in anothers thread.

[DanM]

I am using the Lee 309-200gr RN and Lee 309-180gr RN for 7.5x55, and the Lee312-180RN and the Lyman 314299 both beagled for .303. BTW, I do see good results with IMR4350 with COW fill with all these boolits.

[Larry Gibson]

I don't use COW. Dacron is the only filler I use as it works and is very convenient. 4350 powder should work, testin will tell. My recent tests with 311291 cast hard like your bullets and shot at 2400+ fps in 3 different rifles showed no difference in accuracy with powders slower than 4895.

The bullets you are using are in the "heavy for caliber" range and most probably
would benifit from the slower powder. All of them are also nose bore riders so fit of the nose in the bore will be critical in it's effect on how high a velocity they will shoot with accuracy as felix mentions.

Larry Gibson

[felix]

Don't know, Jeremy, unless you have an intimate knowledge of your gun. There are many surprises, such as powder going bananas (ape ****) with another half grain to compensate for a vertical dispersion at the target. This usually works, and is what BR folks normally do. But, they know the gun and bullet and the throat wear, like 200 rounds ago a half-grain made just the right amount of gain, and now, a quarter inch out of the group. Throat? Possibly. So, to get rid of the verticals, change the barrel, or find another primer, or another powder. For a barrel late in life, changing barrels (shorten and re-chamber maybe) is the only option that makes sense. The opposite makes sense for us folks. We would change powders to a faster speed as SEEN by the gun. BA's Mr. Gun, if you will, will determine what the speed is. Usually, I don't go to these efforts unless I have the powders on the shelf to play the game. Mostly, it is just easier to select a different boolit. That would be out of the question for BR work. ... felix

[26Charlie]

I'm supporting Felix on this - I think - as soon as I figure out what he said - (Felix you've been getting somewhat obscure lately). I think you'll get great results from the H4198 and the bullets you are shooting, if you step the velocity down to the 1550-1650 fps. range. You won't need no steenking filler neither, compadre. Seriously, these faster powders don't need it and it is a time consuming step.

[felix]

Sorry, about the obscurity. I was trying to relate to the BR question too much, where verticals come into play most often. Large round groups typically mean there is a vibe problem. Two groups when there is supposed to be one means a holding/recoil/bedding problem. Naturally, this assumes the shooter is confident of his sight picture, which includes all the weather conditions. I tend to load all the guns at max pressure for continuous use for that gun. I guesstimate loads that produce velocity increments of 300 fps, while keeping the pressure up, to get the vibe harmonic required, when reducing loads. Now, I have notice that all different powder lots of the same "brand" are to be treated as unique powders in terms of speed. This is almost not true with the V-V powders, however, but most especially true with the surplus military powders. N120, a V-V powder, is perhaps my favorite in the circa 4198 arena. For example, if you can get the gun to shoot with 21 grains and the same eyeball accuracy with 23 grains of that powder (in the 30 cals), that is the powder to use. Load for real at 22 grains. ... felix

[Larry Gibson]

Agree with felix that 4198 is a pretty good powder. But disagree that it is good for that velocity level with those weight of bullets. Sometimes it works ok but most often it does not. That seems obvious with the groups reported.

Using a slower burning powder changes the time pressure curve (accelleration rate) and also lowers the peak pressure given the same velocity level. Lowering the powder charge lowers velocity, which lowers pressure, which lowers velocity, which lowers accelleration and which lowers RPM. Increased accuracy would most likely be the result.

Switching to a milder primer most often results in a lowering of pressure, velocity and RPM and at this level can give the false impression of "better accuarcy". Meaning; accuracy may be better because the pressure/velocity/RPM is lower. But raise the pressure/velocity/RPM with the milder primer by adding more powder back up to original velocity level and accuracy deteriorates again.

All of this with the slower powder adds up to less damage to the bullet during accelleration which means there is less imbalance to the bullet for the RPM to adversly affect during flight. This basically means accuracy is better at high velocity with medium and slow burning powders.

Larry Gibson

[DanM]

4350 does work for me in these calibers. My standard load is 34gr in the .30cal carts with COW fill. I like COW with 4350 because it does bump the pressure up over dacron. I can use 2-4gr less powder with COW fill for the same velocity with dacron. I also get a cleaner burn with less residue in the barrel. I got a bator .22 mold recently, maybe I will put the H4198 aside, and save it for the small case stuff....

[Echo]

An old-time shooter told me that 4198 was 'Silk stockings - smooth,slick, snappy'. I think I understand...