tested some loads today, a couple where giving me spreads of nearly 100fps, what is the main cause of this??

preference of load to primers, neck tension, %fill of case to name a few. Can you tell us a bit more about the loads?

In detail please - sometimes extreme spread give excellent groups but that's not the entire story. Like what kraky asked there are countless reasons - it starts with the entire reloading process - fill us in.

I have been experimenting with getting rid of runout or at least reducing it to .003 of less I loaded up 12 rounds or 4 3 shot groups, I used a standard RCBS FL die to size 6 of them the other 6 I used a redding type S bushing FL die to size, I still got nearly 100fps regardless of what the die I used was. to be fair I only bought 2 type S bushing sizes a .250 and a .246 I tried loading some dummy rounds with the .250 bushing and its just not quite enough tension but the .246 bushing I think is causing me more problems than good as I get much better concentricity with the .250 bushing. I have noticed that after measureing sized brass the bushing setup adds a bit more runout to the case neck but this comes back into line after bullet seating. I am wondering if this is normal?? I got 249 and 248 bushings on the way, these should be me what I need tension wise

The .246 is more than likely overworking the neck. What measurement do you get on the neck after seating a bullet. You will find that the bushing that is .002 smaller than a loaded neck will work just fine for tension.

chrony is to close and your readin muzzle blzst?

The largest effect on spreads I have ever found is based on the powder used in that particular firearm. (considering you have a descent loading process which, you probably do)

Some rifles just don't do well with certain powders when it comes to velocity spreads. My most accurate rifles I own will still get huge spreads with certain powders yet, with the same bullets and different powders the spreads get very low.

I like to stay within about 20 fps on my target loads if I can get there. I prefer less than 50 on hunting loads. Some loads are just darn accurate despite big spreads but, this will bite you at longer distances.

Funny thing I see alot is loads that give single digit spreads but, only so so accuracy.

Another thing for us to chase with this wonderful hobby. Sort of like run-out

My loading standards for my paper punchers are:
-Brass weights within a grain or so of each other
-trim length the same
-Less than .002 run-out(.001 prefered)
-Spreads of around 25 or less (prefer 10-20)

I'm sure I could get real anal about it but, that gets me to below .5moa with several rifles and well below that with others and I'm just not confident enough in my abilities to shoot less than .25moa.

Have a Good One

Reloader

If your loading proceedures are good, charge wweights correct, then it is likely neck tension. How old is the brass?

CC

It really does matter what the exact load is, and the particulars. It would seem that the .248 bushing is going to be an asset. Also the powder charge and primer relationship, how clean a burn. Is the powder appropriate for the bullet weight and cartridge being loaded. Of course the brass could be a culprit if the flashholes aren't uniform and the depth isn't uniform, or the firing pin is not hitting just so. Yup, it's endless chasing the demons which haunt or rifles.