Hello, first time poster here. I'm just curious how often you all use your OAL gauges when reloading. I'm working with a 7-08 Tikka and it loves the 140 accubonds over 46.8 gr of Big Game. When I put together the load last year, I ran the OAL gauge for one bullet in the box, used the comparator to get my measurement to the lands, and then used that number to calculate jump for the rest of the batch of 50 bullets. Is this number still good when I buy a new box of accubonds? What about if I change bullets? Is anyone running an OAL gauge for every bullet in a batch? Also, I understand that the ogive occurs at different places along each bullet, but I would think the measurement from the base of the cartridge to the lands would remain the same. So I'm confused why I got a different measurement when I ran the OAL guage on some Speers and ended up with a different number than the accubonds when I hit it with a comparator. I'm so confused. Please help!
OAL Gauge - how often
- Thread starter Needbacon
- Start date
Help Support Long Range Hunting Forum
dok7mm
Well-Known Member
There is a difference in oal length and the base of bullet to the ogive measurement in a box of bullets. Picking one bullet to set up your seating die can be counter productive to accuracy. The Accubond is a fine hunting bullet, but I've always sorted every batch of Nosler bullets by base to ogive. It's not uncommon in a box of 50 to have 8-10 thousandth difference. That could really mess up your seating depth consistency and therefore your accuracy. Easy to sort with your bullet comparator and calipers.
You were using OAL in your post, but I think you were referring to CBTO ( cartridge base to ogive on a loaded round) measured with your bullet comparator on your calipers.
Forget OAL except to assure your rounds will fit your magazine. CBTO is the important part of consistent accuracy.
Won't take long to measure and separate 50 bullets with your comparator to bullet base length. OR you can measure say just 10 bullets to get an idea of difference. Then, say the difference is .007", you would seat your bullets .010" longer than your target depth. Measure base to ogive of each loaded round. I set mine in a cartridge tray depending on whether each round is 1-2-3' or 7-8-9" short of your target cbto, adjust your die as you go to get same cbto on all rounds. Micrometer seaters are really handy here.
To your other questions,
different lots of bullets will have different base to ogive measurements, even high quality bullets like Berger's will have some outliers, Nosler and Hornady will have more. Changing to different brands, styles and weights of bullets require different seating depth workups along with powder charge workup.
If you only shoot 100 yds or so you can shoot 'em and get away with it. If you want to stretch it out, consistent CBTO and proper seating depth on your loads make a world of difference.
You were using OAL in your post, but I think you were referring to CBTO ( cartridge base to ogive on a loaded round) measured with your bullet comparator on your calipers.
Forget OAL except to assure your rounds will fit your magazine. CBTO is the important part of consistent accuracy.
Won't take long to measure and separate 50 bullets with your comparator to bullet base length. OR you can measure say just 10 bullets to get an idea of difference. Then, say the difference is .007", you would seat your bullets .010" longer than your target depth. Measure base to ogive of each loaded round. I set mine in a cartridge tray depending on whether each round is 1-2-3' or 7-8-9" short of your target cbto, adjust your die as you go to get same cbto on all rounds. Micrometer seaters are really handy here.
To your other questions,
different lots of bullets will have different base to ogive measurements, even high quality bullets like Berger's will have some outliers, Nosler and Hornady will have more. Changing to different brands, styles and weights of bullets require different seating depth workups along with powder charge workup.
If you only shoot 100 yds or so you can shoot 'em and get away with it. If you want to stretch it out, consistent CBTO and proper seating depth on your loads make a world of difference.
Well said and good explanation!
Gotcha. So I think I'm doing all that correctly, I just didn't have the vocabulary to ask my question accurately. My OAL guage put my lands at 2.371 when I checked last year. I started seating all my bullets at 2.291 CBTO because I found that was what grouped best. I make sure all my bullets are seated at this CBTO before I fire them and it works great. Then I bought some Speer 145s, decided to try them at 2.361 CBTO to start and find my powder node. Well, when I cycled them they had marks from the lands on them. So I ran the OAL gauge again and it put my lands closer to 2.338 using the Speer bullet. I guess what I'm asking is, I wouldn't think my lands would move, so is that maybe due to fouling? Or would my CBTO length to the lands change with a different bullet type? I'm just kinda confused on why I would get a different measurement to the lands and I need to make sure I don't do something I'll regret here...
Gotcha. So I think I'm doing all that correctly, I just didn't have the vocabulary to ask my question accurately. My OAL guage put my lands at 2.371 when I checked last year. I started seating all my bullets at 2.291 CBTO because I found that was what grouped best. I make sure all my bullets are seated at this CBTO before I fire them and it works great. Then I bought some Speer 145s, decided to try them at 2.361 CBTO to start and find my powder node. Well, when I cycled them they had marks from the lands on them. So I ran the OAL gauge again and it put my lands closer to 2.338. I guess what I'm asking is, I wouldn't think my lands would move, so is that maybe due to fouling? Or would my CBTO length to the lands change with a different bullet type? I'm just kinda confused on why I would get a different measurement to the lands and I need to make sure I don't do something I'll here...
General RE LEE
Well-Known Member
Everytime you change bullets, you have to get a new CBTO measurement. The dimensions change for different bullets.
Gotcha. So do you do that every single bullet, every lot of bullets even if they're the same exact thing (like just opening a new box of 140 accubonds in my case), or just when you switch to different bullet type, say an accubond to a partition or something.
Your CBTO dimension will change with every different bullet because the shape of the ojive is different. It should not change from bullet to bullet of the same lot or box of bullets or at least not enough to alter your results. This is a big rabbit hole and there is no end in sight. You can literally measure every single bullet you seat and then adjust it to be the exact same as every other bullet you seat. That is not necessary to good accuracy you are looking for a node that is wider than .001 seating depth. I only check CBTO on every lot of bullets that I use. I set up my seating die for my distance from lands that I desire and load the rest from that setting I have no accuracy problems.
The above is assuming you have a good seating die with the proper seating stem that is designed for the bullet shape you are seating.
The above is assuming you have a good seating die with the proper seating stem that is designed for the bullet shape you are seating.
dok7mm
Well-Known Member
What you say is very true when using consistent bullets or shooting relatively short distances, say 200 yds or less.
Because the OP stated he had been using Noslers (great bullets I've used for many years), but my experience has been that their lots have a fairly wide base to ogive length variance and I've sorted thousands.
If you have a fairly wide seating depth and seat in the middle, you may see nice groups to extended ranges. Likewise if you have a narrow seating depth sweet spot and a wider variance in your bullets, groups may be scattered at longer distances.
Just my opinion, but I'm three layers down the rabbit hole.
We are absolutely on the same page. I too have measured and weighed thousands. I just didn't feel the OP was as far down the rabbit hole as we are. Noslers are not Bergers for sure.
dok7mm
Well-Known Member
This was 1000 .264, 120 gr Noslers I sorted during the "big freeze" by .001" increments. There were 900 bullets that had a total 9 groups -
Shortest was -.004"
Mean was .000"
Longest was +.004"
The nine groups showed a variance of
.009" from shortest to longest. Another 109 bullets were even shorter or longer and
went into the fouler box. The winner was a tie, 2 bullets measured
+.011" longer than the mean .000".
When I go to load rounds, I usually start with shortest group and adjust micrometer seater as I work my way thru the the entire lot.
If I set up my seater on one bullet that happened to be a -.004" and the bullet that ended up in my hunting chamber was a +.011"=
.015" total variance, I can guarantee my "bucket buck" will step out at 600 yards.
So back on topic. We check our BTO with a bullet comparator and calipers, right? But the comparator isn't a true .284, so it's not really measuring the ogive. So is it possible to get say two bullets that measure the exact same BTO, but the actual ogive (the point along the bullet that will engage the lands when fired) occurs at different spots? Like even though the BTO is the same, the actual jump is different?
