Help w/ 105vld dummy round

[gemmellsc]

How much of the bullet should be seated below the neck/shoulder junction? I took the following measurements:

- 1.24" oal for the 105vld bullet
- 1.06" from the tip of the bullet down to the start of the boat tail taper
- My cases are measuring 1.5555"
- My neck length is .32"
- Base to neck/shoulder is 1.2355"
- If I seat the bullet so that the start of the boat tail taper is +.07 up from the neck/shoulder junction,doughnut area) I'm coming up with a "calculated" cartridge oal of 2.3655". Does this sound correct?

I'm supposed to have a .06" freebore according to McGowen's reamer drawing, so I purchases a uni-throater from PTG to bring my freebore up to between .09-.104 as recommended for the 105s.

Here's my problem... I loaded a round to the 2.3655" oal, and it is not touching the lands yet??? I loaded a round long, and it got pushed back to 2.441". This would mean that start of the boat tail taper is .1455" above the neck/shoulder junction not .07" as recommended.

Do you think the .06" freebore dimension is possibly listed wrong on the drawing, or am I getting normal readings for the 105vld?

If I'm doing this right then it would seem that I'm already seated .0755" out further than I need to be. My barrel is set up for about .001" headspace on factory Lapua brass. I could see how excessive headspace would be an issue, but I'm on the minimal side of things. Sorry for the long email, but I've wanted to give you all the details.

Any help would be greatly appreciated,
Bill

 

[TonyR]

I just took some measurements on some Berger 105 VLDs I have and everything seems to be pretty much the same as you are seeing. The Lot number is 1067. Here are a couple of things to consider. I bought 500 of these bullets from the same lot number and sorted all of them by bearing surface using two Sinclair comparators on my calipers. There was a .012 inch difference between the shortest and longest bearing surfaces which really surprised me. The 2.441 inch OAL number is interesting because it is the OAL shown in QuickDesign for the 6mm BR Norma cartridge, but you might want to look closely at the bullet to see if there are rifling marks on it because, it is not hard to jam the bullet in pretty far into the rifling if you have a lot of neck tension. Some people recommend using whatever seating depth gives square marks on the bullet when you chamber a dummy round as you did.
I found all of this very frustrating when I started reloading so I bought a tool from Sinclair that lets you find a dummy round that just touches the lands in your gun. Here is the link for this tool: http://www.sinclairintl.com/cgi-bin/category.cgi?category=RESDTSD&item=59-4000&type=store. It is very helpful.
For what its worth, I haven't found that having the boattail/shank junction right at the neck/shoulder junction matters all that much as long as you stay away from any donuts. I have done load development for the 95VLD, 105VLD, 108BT, and 115VLD in the same rifle which was originally chambered for the 107 Sierra MatchKing and I was able to find very accurate loads for all of them even though the boattail junction of the 95VLD was way out into the neck while the others were much closer to the neck/shoulder junction.

 

[gemmellsc]

Just for some more information... I performed the same process with a Berger 108gr BT using the same brass, etc... I seated the bullet long, and it was set back to a cartridge oal of 2.3545". Tony, I have the Sinclair seating tool and I'm breaking it out of the box now. I'll report back with some finding on both bullets here in a bit.

Tks,
Bill

 

[gemmellsc]

Using the Sinclair tool:

For the 105vld
- Sinclair measurement between collars was 1.196"
- Bullet used measured 1.239"
- Calculated cartridge oal = 2.435"

For the 108gr BT
- Sinclair measurement between collars was 1.1135"
- Bullet used measured 1.24"
- Calculated cartridge oal = 2.3535"

It looks like the readings are pretty much in line with what I came up with earlier. I'm confused... I have posted a link to their reamer drawing below. Unless I'm doing this wrong the freebore measurement I'm coming up with is .06". Can someone check my measurements and see if I'm doing something wrong?

McGowen reamer drawing

Thanks for the help,
Bill

 

[TonyR]

Bill, I just looked up some old test data from last year where I tested the 105, 108 and 115 on the same day. The bearing surface measurements were 105 =.281 inches, 108 = .355, and 115 = .381. Most of the difference in bearing surface is in the front of the body, so, for any base to ogive cartridge length, the OAL you are measuring will be shorter if the bearing surface is longer. Since I jump the 108 and jam the 115, I use the identical bullet seater setting for both. It sounds like the 108 may seat about where you want relative to the neck/shoulder junction. I have shoot some of my best vertical at 300 yards and under with the 108. I have shoot both the 105 and 115 at 1000 and they performed very well.
Now to the reamer drawing. The base to ogive length for my gun is 2.763 with the comparator minus 1.104 for the comparator which is 1.659 inches net,approximately since there is a little radius at the mouth of the comparator.) As I read the McGowen drawing, the throat begins to taper from .2435,roughly the bullet diameter) at 1.64375 at an angle of 1.5 degrees so the bullet will engage the rifling at a distance greater that 1.64375. The inside diameter of my comparator is .242 so that means that the bullet should begin to touch the rifling about .038 inches into the throat or at a base to ogive length of 1.64375 plus .038 = 1.682 inches compared to my 1.659 or about .023 longer. These last calculations are full of possibility for error, but it sounds to me like the McGowen reamer is very similar to what was used on my gun. I bought the gun used and I have no idea what reamer was used but I do know it was set up for the 107 SMK. I just measured the bearing surface on one of those at .358 inches, almost the same as the Berger 108. I am interested in hearing more about this as you move along.
Tony

 

[gemmellsc]

Thanks for all the help. I'm going to contact McGowen today to see if their reamer drawing is up to date, and to get their opinion on the matter. I don't know a good way to actually measure the freebore, but I guess I'm about where I need to be with the 108gr, and a little bit up in the neck with the 105gr. It seems like their are a lot of variables that can play in to how much freebore you need. I would think that land/groove dimensions and the throat angle would also have an impact on when/where the ogive makes contact. I still have a lot to learn!!! :crazy: I'll post what McGowen tells me later in the day.

Thanks a bunch for the input,
Bill

 

[gemmellsc]

I think I found my problem... I called McGowen who sent me to PTG for the reamer information. I didn't talk to Dave directly, but I was told that the reamer McGowen uses for their 6mmBR Norma has a freebore of .113". That would make a whole lot more sense than the .06" Freebore they originally told me. I don't have a way to measure this, but based off of the numbers I'm getting would you guys agree with this number?

 

[gemmellsc]

Tony,

I talked to Dave Kiff at PTG, and he confirmed that the reamer McGowen ordered has a .113" freebore not the .06" they told me on the phone. I'm really glad I took some measurements before I started cutting away with the uni-throater!!! Anyway, it looks like the mystery has been solved. Thanks for all your input!

Take Care,
Bill