any idea t what is causing my COL to vary +/- 10 thousands" ?

[Skelt11]

3 hours ago, lgh said:

Skelt -  Unless you have really, really precise and accurate calipers, it is probably not possible to measure accurately to 1/10,000. The calipers might read to that level but that does not mean it is accurate to that level. So in your example, the comparison is more appropriately 1.142 to 1.143.

That’s a very good point. That’s the read out on the Mitutoyo digital calibers I use. I’ve realized I was chasing my tail trying to get so close after read this thread and others. I went the range yesterday and ran 110 round through a CZ. 100% reliable, SD of 16 and 16.2 between three strings of five rounds, and a high extreme spread of 44. 

[Skelt11]

38 minutes ago, Ssanders224 said:

Has it been established what projectiles the OP is using?  Small variances in ogive can absolutely affect OAL to this degree. 

 

Also, make sure you are not measuring high primers.  I've seen guys not consistently seating primers below flush, and then drive themselves crazy because they cannot figure out why some rounds are measuring long. 

I’m not the OP but I’m using PD 124gr JHP. 

[Skelt11]

20 hours ago, ddc said:

 

The stated OAL in a load recipe is not meant to imply that it is the only OAL you should consider.

 

If the recipe comes from a commercial source such as a powder company then it is the OAL that they used that created a cartridge that they considered to be appropriate for that powder and also was safe as far as pressure considerations are concerned.

 

It should be considered a reasonable starting point for your own load development. If the charge weight you think you will use is at the upper end of the load range I would suggest starting a little lower and checking for any adverse pressure indications as you work it up.

 

There are so many variables to consider as far as varying OAL, choosing bullets, selecting a powder, stc... there is no way to put it all in a single chapter in a book let alone into a single email.

 

I would suggest you start with a known recipe from a commercial source and stick to it as closely as possible. As your experience grows you can start to consider variations on that.

 

Alternatively if you are working with a mentor then I would follow their suggestions.

 

Thanks for the info ddc. I have a question about lowering the oal when loading on the upper end of the receipe’s charge weight. Why you do that in that situation? If there is more powder and less space inside the cartridge, wouldn’t that increase pressure?

[ddc]

1 hour ago, Skelt11 said:

Thanks for the info ddc. I have a question about lowering the oal when loading on the upper end of the receipe’s charge weight. Why you do that in that situation? If there is more powder and less space inside the cartridge, wouldn’t that increase pressure?

 

My understanding is that if everything else remains the same then reducing OAL will increase pressure. Sometimes dramatically. Where did you read that?

[Skelt11]

1 hour ago, ddc said:

 

My understanding is that if everything else remains the same then reducing OAL will increase pressure. Sometimes dramatically. Where did you read that?

I read some info on another forum that talked about that specific topic. I’ve attched the graph in the thread from a Ramshot reloading manual that shows how shorter oal increases pressure. 

[ddc]

Yes, I agree with your chart 100%

 

What I was asking about was when you said "I have a question about lowering the oal when loading on the upper end of the receipe’s charge weight. Why you do that in that situation?"

 

I thought you had may have read or someone had told you that there are situations when you are on the upper end of the charge weight that you could reduce OAL. That could  be dangerous and I wanted you to know that.

 

Maybe I misunderstood what you were asking.

 

[ddc]

Also: We are getting away from Dillon specific concerns.

 

I'd suggest moving this sort of more general reloading question over to the reloading forum.

 

There are people over there who can give you chapter and verse on this sort of issue.

[Steelheader]

All I can contribute to this discussion is my limited experience with the Dillon 550B that I just bought from a friend.  I purchased the Hit Factor Shellplate Bearing Kit.  It took my variances down to .001s.  You have to make micro adjustments to the shellplate bolt to get it set just perfect.  I set mine to where there is no vertical movement by rocking the shellplate while adjusting the bolt until there is no play whatsoever.  This is what has worked for me.  YMMV.