Bullet Seating

Lhedrick1 · Dec 30, 2018

What is a typical variation when measuring CBTO of a particular rifle?

I took several unprimed brass with different 7mm 160 grain Nosler Partitions. I seated the bullets slightly into the brass so they wouldnt fall out, loaded them into the rifle and bolted it shut. I then measured the CBTO with Hornady Comparator. The length to Ogive when chambered into the rifle varied from 3.785 to 3.750 based on 3 different bullets, 3 different brass (same 160 grain Nosler Partition bullets and Hornady Custom brass) mixed and matched appx. 10 times.

Is this normal?

Zeke · Dec 30, 2018

LAST EDITED ON Dec-30-18 AT 06:45PM (MST)[p]I have not measured the CBTO with a Partition so I don't know about those but 35 hundredths is quite a spread and might be influenced by many factors.

Is you brass sized? If so, your neck tension might be varying and forcing one bullet in deeper compared to the others.

Use brass fired in that rifle and make sure it will chamber. Punch the primer without sizing it. Slightly dent the case mouth just enough to keep the bullet in the case and chamber it and carefully remove and measure. Do this a dozen times to determine the actual touching the lands seating depth and then go on to seat your ammo somewhat shorter than that, usually around 10 to 50 thousandths off the lands. Your groups will tell you what the gun likes.

I hope that's what your asking and what you're trying to do. Give more info if I'm barking up the wrong tree.

Zeke

#livelikezac

Lhedrick1 · Dec 30, 2018

Thanks for the input.

Here's what I did. I took once fired factory Hornady brass (fired from this gun) and resized/removed primer.

I then trimmed the brass to length, was shooting for 10 thou shorter than factory length but ended up closer to 15 thou.

I then seated a bullet just slightly into case with the seating die. Put it into the rifle and bolted it shut. Most often it bolted shut hard. Also, I cannot simply slide a bullet into the casing as I've seen people do on Youtube. I have to use the seating die to get the bullet started into the casing. The videos I've seen the bullet will often fall to the bottom of the casing, that's how loose they fit. You are likely spot on. I shouldn't have sized them first. If I don't size them, the bullets should fall right into the neck correct?

On anothet note, for the VLD, Berger recommends reloading .010,.050,.090 and .0130 off the lands to find which of the four the rifle likes best and to dial it in more concise from there. Is that a practical approach for other bullets as well?

Zeke · Dec 31, 2018

Yes, under most circumstances the bullet should slide easily into the neck. That's why I said ?dent the mouth? a bit to hold the biller slightly.

The way you're doing it now produces a ?jammed? depth rather than a ?touching? depth. I don't use touching for hunting rounds. I usually end up 10 thousandths off of a gun like em close.

Yes, Berger says something like you've said and I've done it and shot two 3-shot groups with several depths at 300 yards to see which one is more accurate and then go I n or out slightly (like 5 thousandths) from there. I've just not seen the best groups with any rifle when the bullet is seated deeper than 50 thousandths. BUT every rifle is different so I cannot speak about yours.

There also might not be a ton of difference in groups between one seating depth to another in YOUR gun.

Zeke
#livelikezac

Zeke · Dec 31, 2018

By the way, some Weatherby?s have a really deep free-bore which means all this seating depth stuff goes out the window. Seat them as long as you can and still have them function and fit the magazine and do deeper from there to check accuracy since you might not be able to ?find? the lands.

Zeke
#livelikezac

Lhedrick1 · Jan 1, 2019

Thanks, that gives me a great starting point!

RELH · Jan 2, 2019

Your problem may be in the bullets. Nosler Partitions have a soft lead spritzer nose. That soft lead nose could be damage just enough to push the pointed nose back and give you a false measurement.
Be sure to select 3 bullets that measure identical from base to nose with a mike or caliper.

RELH

Lhedrick1 · Jan 2, 2019

I'm measuring using the Hornady Comparator which measures from the ogive, not the tip. However the very first one I tested bend the tip slightly. That was the only this happened to however several went into the chamber hard.

I think Zeke resolved this from me, he said to not resize the brass first which I will try when I can get back over to the reloading stuff this weekend.

roadrunner · Jan 3, 2019

Also will depend on the rifle. Some are designed to have a little "free float" prior to meeting up with the lands.

I tried this (except colored the bullet with a black Sharpie and allowed the casing neck to rub off the marker as the bullet seated against the lands) with a Win model 70 and did not work.

Lhedrick1 · Jan 3, 2019

My Dad used to do this back when he was reloading a lot, prior to all the measuring tools that was the the only way to find the lands I guess. There are some good videos on Youtube where people will "smoke" the bullet with a lighter or candle so they can see the grooves in the soot.

ELKOHOLIC · Jan 11, 2019

Don't size the case. Dent the case slightly and then color the bullet with black marker. It will scrape the marker off and you will be able to see this point. Then you just push the bullet back into the case until you hit the mark and measure. It's always been really accurate for me.

Lhedrick1 · Jan 11, 2019

The 270 Weatherbys a lost cause. I'm limited to a 130 grain bullet due to the slow twist so Ill never get to the lands.

However on my Husky 7mm with 160 Nosler AB's, today I did some experimenting.This bullet touches the lands at an OAL of 3.350 - 3.360.

I'm going to try 4 loads of H4831SC with tomorrow starting at a COAL of 2.335. Think that''s a good starting point?

kalielkslayer · May 25, 2019

I size the case, seat the bucket long, soot the bullet with a wooden match.

Then slowly try to seat the bullet.

When I feel pressure, I adjust the die slightly and repeat.

I like this method since once I seat without hitting the lands, my die is set.

Someone tell me if there is a more accurate method, always looking to learn.

deadibob · May 27, 2019

LAST EDITED ON May-27-19 AT 10:11PM (MST)[p]I also color the bullet with marker but sooting them would probably be better. If you are jamming the bullet into the lands that is probably what is giving you the variation in length as the bullet can pull out of the case when you extract it, if the barrel gets a bite on the bullet.

HiMtnHntr · May 27, 2019

It's really easy to do what you are trying to do with an overall length gauge and a modified case.

muliehntr1017 · May 28, 2019

>It's really easy to do what
>you are trying to do
>with an overall length gauge
>and a modified case.

^agreed. Also a higher quality bullet comparator, like a bob green. After a little getting use to, I now get the same measurements time after time.

buckhorn · Jun 1, 2019

LAST EDITED ON Jun-01-19 AT 07:45AM (MST)[p] I also use the overall length gauge a.k.a. the stony point gauge. You can buy your caliber of casing to fit that gauge at the sporting goods reloading supply section also. Use the comparator on your calipers to get your CBTO.Pretty sure this is a common method for Reloader?s nowadays.
The Berger VLD Bullets seem to be tougher than some others to find the ogive because I think it's the extra sharp taper of the bullet.
Using the above mentioned over all length gauges and Berger VLD Bullets the method I have found to be the most accurate is this:
Set the butt of the gun on the table with the Muzzle pointing straight up.
With the modified casing on the gauge and the bullet set extra deep in the casing push up into the chamber until the casing seats. Then push the bullet up to the lands. When it touches tighten the gauge and lower everything out. If the bullet doesn't stick in there I will know I didn't push it too tight. Take the measurement with the calipers and comparator and write it down. If the bullet does stick in there I know I'm into the lands but maybe too far. If I tap the side of the gun with a rubber mallet and the bullet falls out easily then I call it good. If the bullet won't fall out with a few taps then it is in too far. I back the gauge out a couple thousands until I can get the bullet to drop out with an easy tap.
I do that procedure with about 6 bullets from the same box and write each one down and take that average number and use that as my CBTO.
I would say with the burgers all you need to do is load a group at .040 off and another group at .030 and so on in .010 increments closer and you'll find a sweet spot in there somewhere