Poor accuracy past 50yds

[chboats]

Poor accuracy past 50yds

I am shooting a 458x2 with a 340gr gas check boolit. The boolit is an Accuracy 46-335 AG. It is loaded with 33gr of 4759. At 50 yards 20 rounds will produce a 1.05 inch hole measured edge to edge. by my calculation it is a .59 in group at 50 yds. The problem is when I move the target out to 100yds the 5 shot groups open up to 3 to 4 inches. What can I do to improve the 100 yard accuracy? As I decrease the powder charge 50 yd accuracy suffers. I don't want to go to much heaver powder charge without published load data. I have been using 45-70 Win 1886 data from the lyman 4th edition Cast Bullet Handbook as a general guide line.

The rest of the information
gun - Mauser action
20" barrel 1-18 twist
Grove - .458
Bore .450
Throat .462
boolits sized .462
Alloy mixture Bhn 14-15
Lube FWFL

Help please

Carl

[jimb16]

You probably need to INCREASE the charge. It sounds like the bullet is slowing and you are loosing stability. Inspect the 100 yard holes carefully. You may find the bullets are starting to yaw or tumble.

[Oklahoma Rebel]

.04 over groove diameter is a lot, although I know you are supposed to size to the throat, but could that be doing anything?

[Larry Gibson]

I suggest you back off 6 gr of 4759 to 27 gr and use a 1 gr Dacron filler. Work back up in 1 gr increments.

Larry Gibson

[chboats]

Thanks for the replies
Haven't tried sizing to smaller than the throat. I will have to go to .460, don't have a .461 die.
When I started working up a load I started at 28gr of 4759. 50 yard groups were 1.5 to 2 inches. Each grain up the accuracy got better. Have always had good luck with 4769 in other calibers without fill but at this point will try almost anything
When the target was at 100yds the holes did not appear to be out of round but I did not inspect that close.

Back to the bench with some new things to try. With summer activities it will be a while before I get back to the range.

Thanks
Carl

[Oklahoma Rebel]

you know, I really liked imr4198 in my 45-70, and I think reloader 7 worked well too

[chboats]

Oklahoma
But I have a lot of 4759
Carl

[tsubaki]

Have you done a chronograph of these loads?
It might answer a couple of things.

[Whitespider]

Are the 100 yard groups elongated or stringing??
Vertically or horizontally??
*

[Ballistics in Scotland]

The shape of the 100 yard holes is worth checking, and considerably further if your range permits. I don't believe it is rifling twist or velocity. 20in. twist and heavier bullets were routinely used with long range black powder rifles in the 1400ft./sec. class, and the early .45-90 Winchesters had a 32in. twist, designed by people who knew for bullets up to about 340gr., although it was later modified to 20in. because people who kept using heavier and complaining.

A very general rule with exceptions is that when the group size is about proportional to range, it is the rifle, but when the bullets' paths go trumpet-shaped it is the bullets. I know it might pain you to use factory jacketed bullets, but trying a few might give some useful information. It seems possible that that .462in. bullet diameter could be causing finning at the rear. Relying on them leaping in a straight line from case-neck to rifling might do as well, at least if you cast them as hard as you can. I don't believe, for example, a military Lee-Enfield barrel was ever made too short for the original 215gr. round nosed bullet.

As Whitespider says, a definite orientation to the groups would shout "Rifle", and if it grows as the rifle heats up it would suggest bedding. If it starts from cold and stays the same, the barrel crown is a possibility.

[chboats]

To answer some of the questions.
I have tried jacketed, 350gr Hornady round nose over 46gr of RL7 would give me 1" groups at 100yds. I don't like to shoot that many of those because they are expensive and more recoil than I like (OK I'm a wimp)
The 100 yd groups did not string horizontal or vertical. I didn't measure the horizontal and vertical of the groups. They were bad enough that I didn't measure them at alll.
Finning is generally not a problem on gas check boolits

next time out I will pay a lot more attention to the target.

Carl

[Larry Gibson]

With the 18" twist stability should not be and issue what so ever with your 350 gr bullet.

That little amount of 4759 under the 350 gr cast bullet can give erratic ignition and thus poorer accuracy as the range increases. The use of the Dacron filler will increase the efficiency of ignition and of the burning rate. Improved internal ballistics should improve the external ballistics giving better accuracy. I still suggest trying as I mentioned in post #4.

Larry Gibson

[chboats]

The easiest thing to try is the use of filler and in another batch sized to .460.
Carl

[chboats]

To answer some of the questions.
I have tried jacketed, 350gr Hornady round nose over 46gr of RL7 would give me 1" groups at 100yds. I don't like to shoot that many of those because they are expensive and more recoil than I like (OK I'm a wimp)
The 100 yd groups did not string horizontal or vertical. I didn't measure the horizontal and vertical of the groups. They were bad enough that I didn't measure them at alll.
Finning is generally not a problem on gas check boolits

next time out I will pay a lot more attention to the target.

Carl

[robg]

I've the same problem some days .I think it's the nut behind the butt! Me��

[mnewcomb59]

We generally shoot low velocity, low BC bullets.

Running a 38 special rifle load through my ballistic calculator with a 2 mph crosswind, we see 1.2" wind drift at 100 yards.

125-rf @ 1320 fps. BC .13

Since I can't call 2 mph of wind, in the above example I would consider 2.4" at 100 yards to be the best precision I could hope for. I have decided through experience that 3 MOA is all I might get for 22 lr speeds and sub .2 BC bullets.

I would really like to see how these loads do at 100 yards indoor.

[Geezer in NH]

Oklahoma
But I have a lot of 4759
Carl

And that would be your problem.

Ask for help but stop and make excuses why I cannot change what obviously is not working for you.

[chboats]

Got to the range yesterday. Tried 2 loads with Dacron fill as Larry Gibson suggested. The difference was remarkable. Shot 3 five shot groups. 2 of the groups were 1.25 inches for 4 shots with the 5th opening the group to 2 inches. The third was 1.5 inches with one round opening it up to 2.5 inches.

[Larry Gibson]

You're welcome, got to love it when a plan comes together......

Larry Gibson

[Michael J. Spangler]

So this issue was probably due to inconsistent ignition?
The filler solvingthe issue?