Didn't want to hijack big_bwana's thread so I figured I start another.

There was mention that different powders affected regulation even if the muzzle velocity was the same. I would guess that this is due to the change in the total mass traveling down the barrels.

Has anyone put this to the test or has anyone seen this proven out while regulating?

I'd be curious to know what type of impact different powders may have. I guess I'd always worked under the supposition that if you changed powder but kept the same MV that the point of impact would be the same for all intents and purposes.
Eric

Graeme Wrights "Shooting the British Double". The pressure curve of the powder is also important to regulation
Jim

If you are shooting a modern day double then most likely you can use the powder that gives you the best results. Trying to reproduce the regulation load is the goal.
With vintage cordite proofed rifles as the Ross Seyfried pointed out you need to be concerned with pressure curve. I have been using RL-15/Norma 203B plus filler, with great success for over 15 years. It performs and the felt recoil is reduced. I like that.

Unless you have the rifle re-regulated, you have to deal with the way it was set up. It is all about barrel harmonics and trying to find the regulated sweet spot. It is totally, what your rifle likes. Most likely some experimentation on your part.

Reproducing the regulated MV is a great place to start.

I agree with what Rusty said above, but there are other things involved that most people would never consider factors that affect regulation. Bullet type, whether it is cast lead, jacketed, or solid bullet type affects the recoil, the barrel time, and the rotation of the gun barrels. Harmonics has a lot to do with it but so does barrel time. It may be that just because you wind up with the same velocity at the chronograph that the actual barrel time and recoil of different bullets might be different. The recoil impulse created by different powders may be very different but still produce the same velocity. Velocity and pressure are related but they are not directly corrilated.

The only double of mine that gave me fits trying to work up a load was my 375FL. I started with RL 15 and tried 5 or 6 different bullets and could never get the barrels to converge closer than 4". After at least 250 rounds tried RL 17 and it came right in. Now it shoots 1.5" 100 yard groups consistently and often 4 shot 1" groups. RL15 has worked in my 6 other and previous doubles but not this one.

Absolutely, different powders make for different regulation dynamics. It is vitally important to duplicate the muzzle flip that was in effect when the rifle was regulated. Just duplicating the bullet velocity won't work. Mostly.
Barrel flip and jump are also important in tank gunnery but at least we only have one barrel.

quote:

Originally posted by dpcd:
Absolutely, different powders make for different regulation dynamics. It is vitally important to duplicate the muzzle flip that was in effect when the rifle was regulated. Just duplicating the bullet velocity won't work. Mostly.
Barrel flip and jump are also important in tank gunnery but at least we only have one barrel.

I agree! Every double rifle is it's own master and a combination of velocity, and muzzle flip, along with the way the shooter holds the rifle is the recipe for success!

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Different powders most definitely will affect regulation. It's not enough to just achieve the regulation velocity, you have to get the barrel time of the bullet to match the regulation load as well. Doubles are greatly affected by the recoil arc. Since the barrels are on opposite sides of the centerline, the recoil arc differs from the left and right barrel. You have to time the bullet leaving the muzzle as the recoil arc "swings" the muzzle into the correct position for its respective barrel. Leave the barrel too quickly and the POI will cross. Leave the barrel too late and they spread.

Different powders have different pressure curves which produce different acceleration rates. Think of it this way: In drag racing, two cars may cross the 1/4 mile finish line with exactly the same speed (muzzle velocity) but one reaches the finish line first with a lower time. Time wins the race, not MPH at the finish line. The two cars are accelerating at different rates. Different powders will give you variation in this acceleration rate of the bullet.

Yes, and also, powder weight contributes to recoil so it's like shooting a heavier bullet when you go to a heavier powder charge; as Todd said, although both bullets are going at the same velocity, how they got there is as, or more, important.

quote:

Originally posted by Todd Williams:
Different powders most definitely will affect regulation. It's not enough to just achieve the regulation velocity, you have to get the barrel time of the bullet to match the regulation load as well. Doubles are greatly affected by the recoil arc. Since the barrels are on opposite sides of the centerline, the recoil arc differs from the left and right barrel. You have to time the bullet leaving the muzzle as the recoil arc "swings" the muzzle into the correct position for its respective barrel. Leave the barrel too quickly and the POI will cross. Leave the barrel too late and they spread.

Different powders have different pressure curves which produce different acceleration rates. Think of it this way: In drag racing, two cars may cross the 1/4 mile finish line with exactly the same speed (muzzle velocity) but one reaches the finish line first with a lower time. Time wins the race, not MPH at the finish line. The two cars are accelerating at different rates. Different powders will give you variation in this acceleration rate of the bullet.

Very well described!

Seven or eight years ago I spent some very focused effort working up accurate loads using both RL15 and H4831 for my 450/400. What attracted me to the 4831 was interest in an accurate load that did not require filler. Other than different powders, I used the same Rigby cases, Fed215 primers and Woodleigh 400 grain softs for all loads. I used polyfill in the RL15 loads.

I got to equally accurate (regulated) loads with both powders, and velocities with both powdwers were about the same in the 2150-2200FPS arena. One thing that was very clear was that the 4831 loads produced significantly more felt recoil in either a bench mode or when using a standing rest. I've stuck with the RL15 load ever since...

Good hunting

When I started with my first Chapuis, it was regulated with Norma Oryx factory 286 grain loads. I chronographed them, then tried a number of different powders at the same velocity with Hornady 286 grain bullets. I worked up the loads over a chronograph at fifty yards. Then checked for crossing and spreading at 100 and a few at 150. I found that the only powder that gave me a regulated load with that rifle was 65 grains of IMR 4831 (thanks to 450 No. 2). It did so with Hornady, Privi, and Woodleigh soft bullets. Woodleigh solids took a slightly lighter charge, but regulated. Case and primer did not make any difference. Nor did primer brand. In that gun, faster powders crossed at the 'regulated' velocity, sometimes out at 100 yards, but still crossed.
One rifle, one persons results. Well spent evenings that summer and fall.
Bfly

H4831/65.0 also works for 286 Norma Plastic Pt. and Norma Oryx in my FN-Browning CCS25.

Every new double should come with a target and tell you the load, brand etc.

On an old English gun that information is long gone, so you have to discover the "regulation". I start with Woodleigh softs and solids as they are of the same dimension as the old Kynoch bullets that most English doubles were regulated with..You can get the starting loads out of such books as "Shooting the English double rifle". Its always been my practice to start with 4831 as it seems to meld with the Woodleigh bullet and the old cordite stuff and there is a formula in the books for that and will give you a starting charge to work up with. Once that is done and its pretty easy but requires a good amount of shooting as you will have to load up 4 shots in each one gr. advancement, they shoot them to get the best powder amount. I shoot for at least a 3" 4 shot group at 50 or 75 yards. prefer a 2" group if possible..When done I usually then go to RL-15 another formula is available, and work up a load for it with about 3 or 4 grs. of Dacron or Kynoch filler and get myself an alternative load one way or the other depending on which final load shoots the best...

Never accept the old adage of "minute of Grapefruit" most doubles are capable of at least a 3 inch group and many will do much better..and I always figured that I want a accurate double more so than and accurate PG rifle, because I may have to shoot something ugly and mean coming my way in its 2 inch eye!

Unfortunately, the only new double I know of that will provide you load data is Searcy. European doubles all provide you the factory load they used; no hand load data.
Anyway, I had the same issue that Emory had with my 450-400 Krieghoff; 4831 kicked like hell (and the K is a heavy rifle), and would not regulate with 4831 at all. But it will, very nicely, with RL15, and 4350. And that is after I added a scope, which did not change the factory regulation print at all.