CBTO Help

[Hschweers]

Alright, I’m in the process of loading my first ever batch. I used the hornady COAL gauge and their bullet comparator system to find my lands at 2.371” CBTO (6.5 PRC). I’m loading Nosler Custom Competition 140gr over H1000 with RCBS matchmaster dies. On to seating, I made a dummy round at 2.351” CBTO, checked function in my rifle, and all was well. Die is set, seated my first 5 live rounds at 2.351” +/- .0005”. On my 6th round I did nothing different, loaded over the same charge as rounds 4 and 5, and am getting 2.363” CBTO. Rounds 7, 8, and 9 were 2.351” CBTO.

Did I just get one weird/bad bullet? The COAL of round 6 was also about 0.020” longer than the rest. I’m not compressed (53.5gr - near book minimum and can hear powder shaking if I shake it). I just cranked my die down a little bit, seated it to proper CBTO, and am good, but I want to know why this happens and how often it happens. Thanks!

 

[Chuckybmd]

I don’t have the answer, but would be interested if someone has one.

Personally, if it was me, I would run it through again assuming that I hadn’t ran the case all the way through the bullet seating die seeing that it came out too long.

Reading your description, it sounds that you are very precise in your reloading, so honestly, I can’t tell you.

 

[Hschweers]

Update: it’s happened a lot. 80%ish of the time the die is dead on with my initial setting, but I’ve had 4 now in 21 rounds that come out ~0.010” long. Wonder if it’s a die issue (they're brand new, as is everything else I’m using), a bullet issue, or a brass issue (also brand new. Lapua, but didn’t do any sizing so I’m going off factory neck tension etc)

 

[BjornF16]

I always at least size the neck on virgin brass.

What % is your powder fill?

 

[TxLite]

Do some qc checks on your bullets. Check 10 or so and see how they end up.

I’ve seen this quite a bit with my Hornady and Lee dies. In my experience it’s just been bullet variation where the die contacts the bullet. Small variations will translate to differing seating depths, thus cbto variation.

 

[bmart2622]

How is your press mounted? I was getting inconsistent seating depths once, I had my press mounted to the top of a wooden bench, when I would seat bullets the top would flex. I got a solid mount from Inline Fabrications and it took care of it

 

[SDHNTR]

It’s either bullets, the seater die, or the press. In that order. .001-.003” variance is to be expected. Rule out one by one. That said, with most bullets, I doubt even .010” is enough for most shooters to notice on paper.

 

[Chad717]

This isn’t uncommon, anealing your brass will help with consistency, I have noticed seating a bullet firmly when you bottom out the press handle versus lightly can make a difference alone. When I’m shooting rounds that are for long range hunting that need to be dead nuts I check every round and adjust accordingly.

 

[Chad717]

If you’re shooting past about 500 yards you will definitely see a difference at .003+ variation

 

[Hschweers]

Appreciate all the feedback.

@BjornF16 i wanted to neck size, but I went with the FL matchmaster set so don’t currently own a neck sizing die. I measured a handful of cases and they were pretty consistent .003” +/- .0005” under bullet diameter. I don’t know my fill %… how do I calculate that? This is literally the first batch I’ve ever loaded. Ran 53.0-58.0gr at .5gr increments - 3 rounds at each powder charge.

@TxLite spot checked 10. Bullet variance was 0.002” OAL and 0.0035” base to ogive… pretty consistent.

@bmart2622 I thought about the press mounting potentially causing it. I don’t have a lot of room in my current house, so I’m bolted to a 2x6 which is clamped to a desk. Allows me to remove if I need the desk for other things. There is a small bit of wiggle to the desk top at the top of the stroke.

@SDHNTR I’m sure I can’t notice 0.010” difference, but I want to try to keep everything as consistent as possible and only play with one variable at a time (right now charge weight) until I get more comfortable with reloading and what impacts each variable have

It’s not a big deal. Very easy to adjust the die a little when you have one of these odd lengths, I was just curious what people have seen that cause this. Thanks again!

 

[dct73]

When seating, always make sure you are doing the same amount of speed and pressure on the press handle. Inconsistent press operation will cause varying seating depths. Just one more thing to check.

 

[Harvey_NW]

Swap to a VLD style seating stem that has room for the noses and makes contact further down, you might be bottoming some of the noses out in the stem. I'd say .003" variation is realistic, .010-.020" something seems wrong. I also rotate the case 180 and run the ram through again when seating just because I feel like it helps with consistency.

If you’re shooting past about 500 yards you will definitely see a difference at .003+ variation

Test that with a significant sample size and post results, you'll be surprised.

 

[longrange13]

Alright, I’m in the process of loading my first ever batch. I used the hornady COAL gauge and their bullet comparator system to find my lands at 2.371” CBTO (6.5 PRC). I’m loading Nosler Custom Competition 140gr over H1000 with RCBS matchmaster dies. On to seating, I made a dummy round at 2.351” CBTO, checked function in my rifle, and all was well. Die is set, seated my first 5 live rounds at 2.351” +/- .0005”. On my 6th round I did nothing different, loaded over the same charge as rounds 4 and 5, and am getting 2.363” CBTO. Rounds 7, 8, and 9 were 2.351” CBTO.

Did I just get one weird/bad bullet? The COAL of round 6 was also about 0.020” longer than the rest. I’m not compressed (53.5gr - near book minimum and can hear powder shaking if I shake it). I just cranked my die down a little bit, seated it to proper CBTO, and am good, but I want to know why this happens and how often it happens. Thanks!

I want to point out an issue I’ve had in the past. My first set of calipers were a 15$ pair of Frankfort arsenal digital calipers. I always seemed to find variance in my seating depths and when I’d adjust my competition dies they never seemed to move accurately. Loads always shot good so I just wrote it off and “is what it is”. Well down the road I upgraded all my equipment and picked up a set of mittatoyo calipers. They are about $130 on Amazon. After doing this I found that my bullets were actually seating extremely consistently and my dies were also adjusting extremely consistently. It was just error in a cheap set of calipers. For peace of mind that is some of the best money I’ve ever spent on relegating gear. With the new calipers the only load I’ve struggled with inconsistent seating is from an extremely compressed 338 edge +p load with n570, which makes sense.

 

[sdupontjr]

Not a PRC but similar situation. In my press, my 308 using 155 scenars did this. What I found was every now and then, 1 or 2 bullet tips would actually bottom out on the seating and seating depth would be affected. Once I stumbled on this, i drilled out a small hole so that the seating die would hit further on the shoulder of the bullet rather than an occasionally the tip. Now every now and then I get a .001" change in CBTO. I actually am having a custom seating stem made for these bullets just to rule out any issues. This may or may not help with your issue.