case neck runout

[1stmar]

If you have a match chamber and throat, why wouldn't Fire formed cases straightened out (to some degree, not to perfection) case necks?

Bart- 257 collet sound about right for 22 cal?

[Greg Mercurio]

Hi Steve: Thanks for the reply. I'm going out on a limb here and suggest you start looking at neck wall thickness as the primary contributor rather than the neck being non-concentric to the case. If you have access to a pin mic you can see if the necks are thicker on one side than the other. I'm not an expert in the why's, but have spent my entire professional career identifying and minimizing variables. It's an interesting problem and better your shoulder than mine.

[Bart B.]

I don't think ammo should be bent with its bullet in something it's diameter. That'll bend the bullet in the neck loosening the necks grip on it. It's the case neck axis off alignment with the case body that causes 90% of bullet runout. The case neck needs to be held in place while the case body is bent behind it. The hole it's a tight fit in needs to be metal so it won't elongate from use.

If the case neck wall thickness spread is .002", a full length sizing die without an expanded ball will size it straight and parallel to the body axis. Bullet axis in them will be parallel to the case axis but half that off the chamber center. Moving a perfectly centered bullet hole in a case neck .001" off center thins one side that amount and thickens the point opposite that thinned part the same amount. That makes the case neck wall thickness vary .002" around it. Doesn't matter how thick it was to start with. Neck wall thickness spread of .002" is not catastrophic to accuracy, but most people think it is.

Necks on cases headspacing on their shoulder do nothing to center them in the chamber neck when the round's fired. They float free in the chamber neck with one to a few thousandths inch clearance around them. How well centered they are in the chamber neck is determined by how straight and centered they are on the case shoulder as well as how little they are bent after coming out of the sizing die's neck.

[Bart B.]

Steve,

What things about bullet runout, its cause, effects and correction don't you understand?

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1stmar,

Match chambers and throats, as well as chamber necks don't straighten out cases any better than standard SAAMI ones. Crooked necks are caused by case wall thickness variables and forces acting on the case neck after it comes out of the sizing die's neck. While in the sizing die, they're very straight, but can bend a tiny bit coming out of the die's neck due to the elasticity of the metal at different amounts around the neck's uneven thicknesses. Match chambers (smaller diameters) can enable longer case life but they do little for accuracy compared to standard SAAMI ones.

For 22 caliber centerfire cases, mic the loaded rounds neck diameter then get a puller collet the next size larger. Some will be able to use a .257" collet while others may need a .264" one.

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Greg,

Variables in ammo are there, but it's amazing to me that unless they're way out on the far end of the measurement numbers, they are not all that harmful to accuracy. Consider what happened back in 1991 when a few of us developed loads for Sierra's prototype Palma bullets; their 30 caliber 155-gr HPMK bullet. New cases with Fed 210M primers and bullets seated to 2.800 OAL was the standard for loads tested. Any powder could be used and we tried a lot of them but all charges were metered, not weighed. AA2520 produced the smallest spreads in charge weight, muzzle velocity and peak pressure; it shot the least accurate of all. IMR4895 produced average or larger spreads in those three areas but shot the most accurate. Bullet runout on the ammo made on two Dillon 1050's was .003" max with an occasional one at .004".

That ammo shot about 1/2 MOA (3 inches) at 600 yards in a couple dozen rifles from around the world with a variety of bore and groove diameters and profiles. A test of 20 production rounds taken at random shot into 2.7 inches at 600 yards. Compare that to the current 600-yard benchrest records with ammo that has virtually zero variables in its makup.

[Greg Mercurio]

Merry Christmas Bart. As always, your inputs are spot on. My best ever group was shot with ammo made on my 550B. No special anything. Just 10 rounds into one hole not much bigger than a penny.

But for those that seek to isolate and control every conceivable variable, I tip my hat. It's a noble quest, but may not pay dividends.

[Bart B.]

Greg, Seasonal Sensations to you, too.

If one thinks about all the variables of the ammo, rifle, shooter and environment, they may finally realize that the smallest groups are shot are the result of one of two situations:

One is when everything is perfect and all the variables' value is zero so the group will be zero MOA.

The other is when they all add up in different directions for some of the shots and the group is very large. But a few shots with smaller variables in all directions will be very close to the group center and the rest will be sprinkled around between the extremes with a spread of variables.

[stevesmith]

my rig is a savage le 110ba 338 lm..what i have managed to do so far is to isolate the problem cases and start over. pull the bullet dump the powder pop out the primer resize now using better dies that seemed to be my biggest problem..before i pulled bullets i took rounds from .010-.001 of runout to a 100 yard range to test..the measurements were tir... .001-.003 made no apparent difference all shot in a ragged hole...004-.010 followed suite the more runout the bullet had the farther off zero it shot..i marked the bullets this weekend with most significant runout at 12:00 , 3:00 , 6:00 , 9:00 ..not everytime but better than 3/4 would tend to be off in the direction of the most runout..IE: if i put it at 12:00 it would shoot high the most runout the highest off zero at 6:00 it would shoot low and the ones with the most runout was lowest from zero shooting in the direction of the runout most times..but after purchasing forster ultra fls die and micrometer seating die and detailed case prep to the best of my ability before even sizing the case ive been able to keep my runout down to .002 or less and that .002 seems to have no affect on 100 yard accuracy..all shoot in one ragged hole as many as 10 shots all in the same ragged hole, best i have ever shot with this gun actually.. and if i do my part it will do it every time. my next venture is goin to 500 yards and testing the same load . i was able to run 10 rounds through a chrono and was averaging 2810 fps with a 250g smk..if i can maintain that accuracy at 500 yards next is 1000.. ill have to work up a load for 300g pills to go out more than that.

[Bart B.]

Sierra's Infinity ballistics software lists their accurate load across several rifles with both the 250 and 300 HPMK's from the .338 Lap Mag as maximum ones:

250 HPMK, Viht N165, 92.4 gr., 2900 fps
300 HPMK, IMR-4350, 78.2 gr., 2650 fps

While other powders slower than those will give 100 fps more muzzle velocities, these loads produce the most uniform pressure curves which means their trajectories are most repeatable. Departure angle and muzzle velocity spreads are the lowest

[stevesmith]

BartB,
i have already ran a lot of rounds through the tube to get to where i am now. i have no doubt that there is another load out there that is as good and maybe better thn what i have right now. but for my shooting ability what i have now is as good as i can shoot anyway. i havent tried another powder or primer. i started with retumbo and loved its consistanct and accuracy. after i found a load that produced a good group i chsed the lands around a little tht didnt reveal a bunch of extra either way i went. it likes .050 better than anywhere closer or farther out. i can shoot 91g of retumbo under a 250g SMK or a hornady 250g match hpbt and shoot in a ragged hole at 100 yards..im goin new years day for my first time out to 600 yards. that might not be the load i need for that but want know until i do it. but from my research it should shoot just as good even out to a 1000... really think any farther will requie a 300g pill but that will be according to the wind and all of this is based on what i have learned with 550 rounds through the tube so far..within the next year there is a range being built as we speak goin to 1800 yards..and within 30 miles from my house..so when that happens i can really get down to some shooting then..i figure ill have to replace the barrel sometime about then..lol but it aint no fun if you dont shootem..without reloading there would be no way for me to shoot as much as i do..so i found a good load pretty quick and for the most part have been able to stick with it and keep producing the results i want to see thats the only reason i havent tried anything else i figure if it aint broke dont fix it..