Bullet ogeeve length and seating depth.

[Alycidon]

Yesterday I was loading a batch of Sierra 39gr BKs into 20BR cases, dont those bullet weights vary !!.

 

My Wilson seater is set up for the 50gr Berger to have the ogeeve 2 thou off the rifling. Seated the first BK and its 20thou to long, measured with the tool suplied with the rifle that measures to teh ogeeve. I have to adjust the die to seat the bullet deeeper into the case to maintain the same length as the big Berger. This is the opposite of what I was expecting, but the Berger is a very long hollow point, the BK has a much blunter angle. I was expecting a shorter bullet to be seated further out.

 

I need to recheck the previous batch of 50s just to make sure they are OK but the 0 line on the die is for the 50 Berger, I am now at 20 longer, I also want to try the 39s in the rifle to make sure they are not engaging the rifling while I am working up a load from scratch.

 

Just seems odd, I was using the base piece of the seating die as well. I think it is the difference in the ogeeve that is causing the issue. Anybody any thoughts?.

 

A

[MJR]

I've experienced similar things happening when loading 87gn Hornady bthp. Loaded a dummy round and seated it 15thou off the lands then started loading proper rounds and found the ogive measurement to vary up to 5thou. I put it down to the bullet shape varying in front of the ogive - the part which the bullet seater stem contacts when it seats the bullet and that led to varying seating depths. Previously loaded some Nosler 80gn and had no such problems.

[varmartin]

To find out if it is the bullets that are varying in length, measure them before you load them using the same comparator.

 

I had a similar experience with varying ogive lengths , and realised I was running to much neck tension and engraving the bullets rather than seating them in the case...

[Laurie]

Different makes / models of bullet vary depending on the front end shape. The only way you can use seating depth measurements for one bullet on others is where they share the ogive / tip shape. eg many Sierra bullets in a calibre have identical front end designs - the original older model 155gn Palma MK, 175gn MK, 190gn MK, 200gn MK, and 180gn Game King all have 7-calibre radius tangent ogives, so should hit the leade at the same spot subject to manufacturing discrepancies (.308" Cal bullets). Other Sierras thirties are different and will need to be catered for individually. Bergers on the other hand seem to be mostly one-off designs, so you need to get an individual COAL for each.

 

Then there is the issue noted above that there may be variations within a box. Bergers are very good in this respect, some other makes not so good. It only makes sense to start batching bullets by base to ogive measurements for BR or extreme long-range shooting in a precision rifle - life's too short to spend too much time on this. If the bullet and load are well suited to the barrel, I think you'd be hard put to see any effects on .204 groups at normal ranges. The 39gn BK is a typical Sierra tangent ogive design, that is very tolerant about bullet jump.

 

The other thing to wtach out for in all this is that the sharp run in to the lands of a new barrel are quickly eroded down, so getting a lot of measurements on a brand new barrel based on touching the lands might see jump change noticeably after only a couple of hundred rounds - that and ongoing throat erosion are two more reasons for choosing non-fussy bullets.