Author Topic: Bullet runout (Read 1227 times)

Selmer · « **on:** February 10, 2003, 04:14:12 AM »

I've been reading about the effects of bullet runout on accuracy, I checked mine by doing the simple rolling on a flat surface test and they come out pretty well, but I'd like someone to explain this to me. The theory goes that if the bullet enters the barrel canted or off-center, it will leave the barrel canted or off-center. Isn't this what 22" of barrel are supposed to correct? How can a bullet that's being forced down a tube slightly smaller than the diameter of the come out at a canted angle unless the crown of the barrel isn't even or marred? I don't hold degrees in physics or barrel harmonics, so I'm asking those of you might or might understand this better than I to explain it to the rest of us, thanks.
Selmer

TexasMac · « **Reply #1 on:** February 10, 2003, 06:51:53 AM »

Selmer, the throat will certainly force the bullet to conform to the insides dimensions of the bore but does not insure the bullet mass will be concentric around its spin axis. The bullet is forced into the bore so fast it does not have time to completely center itself while being reformed. If the bullet is canted (has some runout) to a significant degree prior to being forced into the bore the resulting mass of the bullet will not be uniform around its spin axis as it exits the muzzle and progresses down range, resulting is some instability. This may not be a good analogy but consider what would happen if you shaved a good portion of the nose off one side of the bullet prior to chambering it. The results are similar to the effects caused by bullet runout. Hope this helps.
Wayne

Selmer · « **Reply #2 on:** February 10, 2003, 08:02:42 AM »

Okay, that makes a little more sense, thanks. How much runout is unacceptable? I had never been concerned with it before until I started reading about it, I have a load for my .243 with 55 gr. NBT that I have seated out as far as I can and there is very little of the shank of the bullet being gripped by the neck. I checked some of my loads and the wobble was very distinct, so I seated them a little farther in and it went away for the most part. Before I adjusted my seater die in I had been shooting this load for five years and got sub-MOA accuracy at 100 yds. with it. I wonder if I shouldn't have messed with it, but maybe ignorance really is bliss... I checked my other loads, .308 and .30-06 with 150 and 165 gr. BT's respectively, and I couldn't detect a wobble, these are out of RCBS and Redding dies, the .243 is a set of old Hornady dies.
Selmer
Selmer

TexasMac · « **Reply #3 on:** February 10, 2003, 08:31:09 AM »

Selmer, the amount of runout you can tolerate depends on the type of shooting you do and the amount of accuracy you expect. For the average hunter or casual shooter who reloads runout is normally not something to be concerned about. Benchrest shooters spend a great amount of time and BTUs insuring there loads have close to zero runout and use special jigs and gauges to measue it. I cannot give you an absolute number. I never worry about runout in my hunting rifle loads but I do check runout and do everything I can to minimize it in my long range black powder cartridge rounds used for silhouettes out to 500 meters. One wants to make sure those very heavy very long soft lead bullets are not unduly reformed out of alignment.

Maybe others reading this can provide some rule of thumb guidelines. I recommend you share with us the type of shooting you do and your accuracy expectations.
Wayne

Selmer · « **Reply #4 on:** February 10, 2003, 09:26:23 AM »

I'm a regular reloading joe that shoots for fun and to fill his freezer. The most demanding shooting I do is varminting and that 55gr. load with the poor runout has connected on p-dogs for me out to 500 yds, which is plenty far for me! The rest of my hunting is done with .308 and .30-06 and my .308 shoot 1/2 moa with NBT's so I'm not complaining or blaming runout on anything, I was just curious as to how it affected accuracy, I'm a curious person who always likes to learn as much as I can about my hobbies and professions.
Selmer

rpseven · « **Reply #5 on:** February 11, 2003, 05:27:07 PM »

So if I understand this right what you are saying is that it is possible to seat the bullet in the case canted? I have heard of this before and it has posed a question in my mind. If you put the bullet in the case and run it up into the die don't the die keep the bullet from canting. I haven't gave it much thought up until a few weeks ago when I heard about this but it seems to me that the dimensions in the die are so close to specs that it would have to push the bullet into the case straight. This is just my thought, I have been reloading for about 5 years and I learn more every time that I do it. But what your saying it does make sense. Maybe this is why my accuracy is not has good as I wish it could be. One of the reasons anyway. And now that I found out about this the bullets that I made the other day I did make sure that they were sitting in the case straight. Thanks for the info. :shock:

KN · « **Reply #6 on:** February 11, 2003, 05:48:37 PM »

Not all dies will do that good a job of keeping your bullet in line with the case. Thats one reason I like Hornady dies. They use a floating bushing that supports the bullet as it enters the die. Seems to work really well. Any one who has crushed a case neck from having the bullet fall to the side at the last second knows what I'm talking about. Boat tail bullets are more forgiving to this problem than a flat base bullet for obvious reasons. If you look at large pistol rounds you will almost always see where the bullet bulges the case a little more on one side than the other. This is caused by missalignment. Not near as critical in big bore rounds but you see what I mean. KN

rpseven · « **Reply #7 on:** February 11, 2003, 05:59:43 PM »

Thanks for the info. I am really going have to keep my eye on this. Cause I would say that if that bullet is being canted its going to play heck with the accuracy. :roll:

TexasMac · « **Reply #8 on:** February 11, 2003, 06:53:31 PM »

As I mentioned earlier, unless you are striving for sub MOA accuracy I wouldn't worry too much about bullet canting with any pistol or hunting rifles with seating dies from any of the reloading equipment suppliers. It's those benchrest guys that take this to the extreme, and rightly so as their sport is demanding as is BPCR silhouette shooting.

By the way, one simple way to minimize canting with standard dies is not to lock the seating die in the press. This allows it to "float" in the threads of the press, which will allow the bullet to self align as it is forced into the case. Just put a reference mark on the die and top of the press with a felt tip marker and insure it doesn't rotate from bullet to bullet. This is also a good technique when resizing brass.
Wayne

KN · « **Reply #9 on:** February 11, 2003, 07:02:41 PM »

TexasMAC, Theres some thing about that that bothers me. I can't quite figure out just why so I'll not knock it till I try it. KN

TexasMac · « **Reply #10 on:** February 11, 2003, 07:34:49 PM »

KN, I had to laugh when I saw your response because I had the same feeling when a very experienced reloader mentioned this some time ago. It just did not feel right but I could not put my finger on it. But I've been using this technique for some time now and it really works for me. I grant you the Hornady system is a better approach since it grabs the bullet and holds it in alignment as the die is lowered before it is forced into the case. But if you don't have the Hornady dies this is the next best thing. As you well know, except for the nose, there is nothing holding the bullet in alignment in most other "standard" dies. This extra movement allows the nose to move some and self align. In fact I gone so far as allowing the seating stem to float also. Think about it for a while. It'll grow on you.
Wayne

KN · « **Reply #11 on:** February 11, 2003, 08:31:47 PM »

Thats another thing about the Hornady I like, the seating stem does float. KN