454 in 460 accuracy question


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Vurtle
September 12, 2011, 12:20 AM
I recently acquired a 460 20" Katahdin Encore barrel. I know it's a rifle, but I figured the handgunners would have the better advice in this scenario.

I tried two Unique loads with 454 brass and got two completely different impact points on the target.

If I load 10 gr Unique with 300 gr bullet, the bullet impacts 10" above bullseye at 50 yards.
14 gr Unique with 300 impacts close to bullseye at 50. Similar results at 75 yards. I would kind of expect the lighter load to impact just a hair lower than the heavier load. And the groups are horrible. I would like to stick with unique, but I will try something else if I have to.

I had to adjust my peep sight all the way to the right and bottom just too get these results. And my sights are nowhere close to matching my bore sight. Is this common to see the impact change that much at 50 yards between these loads? Is it because the 454 in the 460? I don't currently have any 460 brass right now to try.

I also had a lot of lead fouling happening at the breech side of the rifling. Bullet is a cast performance 300 gr gas check. i ran some XTPs through the barrel with out fouling, but same accuracy issues.

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daorhgih
September 12, 2011, 12:50 AM
2 weeks ago at a garage sale I bought an "old shot-gun barrel" and "a pistol that needs another handle" from a woman's husband stash of stuff (he being deceased.) The shot-gun barrel is a Katahdin ProHunter "S&W .460." I called T/C and verified that this serial number IS INDEED a pistol. I'm waiting on dies for loading for it. The gun that needed a handle is a T/C Encore in .22-250, 8", and the lonely barrel is .45C-.410, 15" and appears to have a screw-in choke system. Probably NOT for the .45C !! Total outlay was $One Benjamin. She said she'd sold a lot of his other stuff. I wish I had been THERE, THEN !! DAO.

Vurtle
September 12, 2011, 01:43 AM
2 weeks ago at a garage sale I bought an "old shot-gun barrel" and "a pistol that needs another handle" from a woman's husband stash of stuff (he being deceased.) The shot-gun barrel is a Katahdin ProHunter "S&W .460." I called T/C and verified that this serial number IS INDEED a pistol. I'm waiting on dies for loading for it. The gun that needed a handle is a T/C Encore in .22-250, 8", and the lonely barrel is .45C-.410, 15" and appears to have a screw-in choke system. Probably NOT for the .45C !! Total outlay was $One Benjamin. She said she'd sold a lot of his other stuff. I wish I had been THERE, THEN !! DAO.
Nice! I hope you have better luck on your first loads. I'll keep trying different loads and see what happens. I've read several times people having accuracy problems with the katahdin. Usually sights not matching barrel or 460 brass not being accurate and 454 brass being accurate

NavyLCDR
September 12, 2011, 01:20 PM
I tried two Unique loads with 454 brass and got two completely different impact points on the target.

If I load 10 gr Unique with 300 gr bullet, the bullet impacts 10" above bullseye at 50 yards.
14 gr Unique with 300 impacts close to bullseye at 50. Similar results at 75 yards. I would kind of expect the lighter load to impact just a hair lower than the heavier load. And the groups are horrible. I would like to stick with unique, but I will try something else if I have to.

I'm assuming you mean .454 Casull? Where did you get your loading data? This page shows 12.5gr as the starting load:

http://www.reloadammo.com/454casull.htm

What is happening is you are getting dismal velocity with the 10 gr load. The bullet stays in the barrel for a longer period of time and is more affected by the rise of the barrel during recoil thus causing your point of impact to rise.

This effect would be exaggerated by the length of the barrel of a rifle v. the shorter barrel of a pistol.

buck460XVR
September 12, 2011, 07:08 PM
My oldest bought an Encore with a 20'' Katahdin barrel because I was already reloading for my .460 X-Frame. After a year of no success finding any .460mag loads that shot worth a damn outta it, he sold it and bought a Marlin lever in .44.(again, cause I already load for .44, he's like that;)). The Marlin was easy, it likes the same loads as my 629s and 77/44. Only loads he ever got to shoot decent outta the Encore were .45LC cowboy loads. After he sold the gun I started thinkin' maybe I was loading the ammo too hot, as I was basically using the same revolver load recipes that shot well in my X-Frame, and the wimpy Colt loads shot well. I dunno. I wish you luck.

Vurtle
September 12, 2011, 09:32 PM
My data came from Freedom Arms with 10 gr Unique as the starting load for 300.
Velocity out of my barrel at starting load should approximately be 1400 fps.
http://www.freedomarms.com/loadingdata.pdf

NavyLCDR
September 13, 2011, 11:00 AM
Your point of impact rising with lower charges (and heavier bullets) is still caused by the slower bullet spending more time in the barrel.

Accuracy may also be due to shooting .454 Casull in a .460 chamber. The .460 cartridge is longer, so when shooting the .454 Casull there is a larger gap between the bullet and the lands of the barrel. More gap generally reduces accuracy. Benchrest shooters measure the gap and adjust their overall length so the gap is reduced to 1 or 2 thousandth's of an inch.

Vurtle
September 13, 2011, 10:01 PM
Made another trip to the range today. Loaded 10 gr, 12 gr, and 14 gr of Unique with neck sized only brass that had been fired in the chamber already. This first range trip had significant blow-by with the 10 gr loads and minor blow-by with the 14 gr load. No blow-by with the neck sized only brass this time. Groups were slightly better. The 10 gr load was the only load that hit in the same location as the bore sight. The 12 gr was about 6" lower and the 14 gr was 12" lower than the bore sight.
I installed the correct height front sight that now matches my bore sight (which should have been correct from the factory and wasn't). Which means, my barrel is not rising before the bullet exits, but the hotter loads are hitting lower than where my barrel point of aim is. The factory front sight was .420 in height and the sight I put on it is a .580 height. I guess if I want to shot the max loads, I have to use the factory sight which bugs me because the bore is pointed higher than the sights and I have a hard time imagining the bullet coming out at a downward angle.

On a side note, I loaded 35 gr (volume) triple seven and they shot good groups at about the same position as the 10 gr Unique load. They were just really dirty but the smoke is cool. I guess my next step is to buy some 460 dies and brass and see what happens.

NavyLCDR
September 13, 2011, 11:05 PM
Gravity has no effect on a beam of light. Sights should be adjusted to take into account the drop of the bullet over distance due to gravity pulling the bullet down so that, for a given bullet weight and powder charge, the point of impact will equal the point of aim at a desired distance. Gun manufacturers will test fire their guns to determine the approximately correct sight height.

The reason your bullet with 10grains of powder is hitting at a point of impact even with the bore sight is because when you pull the trigger, the barrel begins to rise before the bullet exits the barrel. Thus, at the point where the bullet exits the barrel, your point of aim has already risen to a point above the point of aim when the sear released. Gravity then pulls the bullet back down, creating it's ballistic curve, and every lines up just right so the amount of drop in the bullet equals the amount of rise of the barrel.

Once again, with the higher powder charges and increased velocity, the bullet spends less time in the barrel, the barrel does not rise as much before the bullet exits, so the final point of aim when the bullet exits is closer to the original point of aim when the sear released. Gravity, a constant force, affects the bullet exactly the same, thereby pulling the higher velocity bullets lower because they started out at a lower point of aim when they left the barrel.

http://www.chuckhawks.com/bullet_trajectory.htm

Notice this from the article:
Bullets are affected by gravity whether in flight or not, and, when they leave the barrel, they no longer have any physical support, such as the brass, the box, your pocket, the magazine, the chamber, or the barrel, so they begin to fall. In addition, they are traveling through air, so air resistance progressively slows their flight. On most occasions the barrel is slanted upward slightly to compensate for this immediate drop; thus, for all but extreme shots, since the barrel is aimed slightly upward, the bullet does, indeed, rise slightly after it leaves the barrel, but it bullet never rises above the axis of the barrel.

http://www.loadammo.com/Topics/October01.htm
http://www.hornady.com/ballistics-resource/external

Notice all these articles show the same thing - the bullet trajectory cannot possibly follow the same path as the beam of light from a bore sight.

When your sights (or scope) are adjusted properly, they will cause the barrel to actually be pointed at an upwards angle, above the desired point of impact.

Vurtle
September 14, 2011, 12:21 AM
I appreciate the explanation NavyLCDR. It makes sense and it is hard to argue with what sounds logical. I just can't imagine 12" of difference when there is only 250 fps difference. I am new to reloading handgun cartridges and it appears they are drastically different in small changes when compared to when I experiment with rifle loads. And at that, only 50 yards zero vs 200 yards zero. So 1/4th the length and 6 times the difference in bullet placement changes (maybe 2" at 200, light load vs heavy load). So total difference looks like 24 times. Yes the bullet is traveling roughly twice the speed as the handgun cartridge though.

BCRider
September 15, 2011, 01:14 PM
Vurtle, your barrel will always rise from the moment the bullet starts to move in the chamber. That's just the physics of the situation. Action and re-action.

If your bore sighting happens to be extactly in line with the sights then that is because it's sighted in to the distance where the trajectory arc has allowed the bullet to fall to the same height as it started out in the chamber.

And as mentioned a slower bullet will spend more time in the barrel so it leaves when the muzzle is higher in this recoil rise travel. That's why your higher powder loads are impacting lower. They are faster so they leave the barrel sooner in the recoil rise cycle.

Folks, like myself, that shoot a mix .357Mag and the slower .38Spl from the same gun are used to seeing this. The faster magnum rounds impact the target at some distance lower. For me if I'm playing "Revolver Roulette" with five .38Spl and one .357Mag and shooting at around 12'ish yards my five .38's will all be in about a 1.5 to 2 inch round group and the lone .357 will hit about 4 inches lower than the .38 group's center.

If shooting from a rifle at greater range then at some point the slower rounds will arc over to meet the trajectory of the faster rounds and they'll all impact at the same point. But for closer in the slower will leave with a higher initial angle to the trajectory due to this time in barrel.

Heavier and lighter bullets will also play a part in this too. But to keep things simple it's easier to just consider same weight bullets with varying powder loads. Or to look at same powder loads with varying weight bullets. Otherwise it all gets mixed up.

Looking for a moment at same powder loads and varying weight bullets a heavier bullet will accelerate more slowly so it again spends more time in the barrel and exits later in the recoil rise cycle. So a heavier bullet will tend to impact higher when shooting at shorter distances. And again if shooting out to medium and long range the slower bullet will start out at a higher angle but arc over sooner and at some point will cross the trajectory of the lighter and faster bullet option. But that's the external ballistics as opposed to the internal ballistics.

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