Riddle me this... the important OAL measurement of a cartridge is from the base to the widest circumference on the ogive, with the intent of yielding consistant jump or jam. However, a majority of seating dies make contact on the circumference of the ogive about a calibers length from the tip of the bullet. Sounds a little inconsistant...
Seating depth consistency
- Thread starter rimfiremac
- Start date
thunderstruck
Regular
- Location
- Northern B.C.
What is inconsistant is the bullet tips.The ogives are consistant. It dosen't matter where your seating die contacts the ogive . The seater circumference contact dosen't change therefore it consistantly contacts the same place on the bullets. The bullet comparator also measures the length consistantly besause the circumference of the ogives are realitavily consistant. Even though the seater and the comparators don't contact the same place on the bullet they are consistant realitive to each other. The actual OAL is not consistant because of the tips or meplates(+/-3-5 thou) of the bullets, but the OAL to the ogives are consistant giving you a consistant seating.
So to clarify, the bullet length variation is localized to the immediate meplat exclusively, not the upper region of the ogive in general?
I built myself an OAL guage, but then had a hard time understanding how to ensure consistency when seating, seeing how the contact point of the seating stem is very close to the tip of the bullet, thus may be in a region of variation anyways.
I built myself an OAL guage, but then had a hard time understanding how to ensure consistency when seating, seeing how the contact point of the seating stem is very close to the tip of the bullet, thus may be in a region of variation anyways.
thunderstruck
Regular
- Location
- Northern B.C.
Yes it is the meplate that is inconsistant. You can view bullet comparaters that attach to your calipers on "sinclair international" website to get a better idea how they work.
I use the Hornady bullet comparator, which measures the seating depth fairly close down to actual rifling diameter. Further, I understand your point, that the bullet seating die usually contacts the bullet much higher up. Obviously this is a theoretical concern. However, I think once you get away from the actual tip of the bullet, the bullet form is pretty quickly uniformed. As a point of reference, my el-cheapo Lee Dead Length Seating Die (for 223) maintains a consistancy of about +/- .0015", which I feel is pretty good.
Unless fitting your mag is desirable then OAL does'nt matter much.
Find the distance to your lands using a dummy bullet. Measure this round with your ccomparator.
Determine where you need to be in relation to the lands and measure all rounds with the same comparator.
If your seater is not introducing runout then its doing its job.
Find the distance to your lands using a dummy bullet. Measure this round with your ccomparator.
Determine where you need to be in relation to the lands and measure all rounds with the same comparator.
If your seater is not introducing runout then its doing its job.
Before I had my comparator I used the marker method of seating the bullet jammed, colouring the bullet with a sharpie, then seating slowly deeper until no more land marks were visible on the bullet. Re-marki g after every seating depth change of course. After I got my comparator I was worried that this system wasn't that accurate then I tried the dummy round method with the slightly sized neck (just enough to hold the bullet). Got my 10 thou jump measurement that I wanted and measured my new rounds against the old system. And what do you know, the measurements were within a couple thou of each other.
So in the meantime, if you don't have one do not be afraid to not act until you do, there are other methods but a comparator is ideal.
So in the meantime, if you don't have one do not be afraid to not act until you do, there are other methods but a comparator is ideal.
