103 Grn 6mm Flatbase

[jackieschmidt]

I have been making a 103 6mm Boat Tail for a while, and it shoots pretty decent.

I recently acquired a set of Rorshach 6mm dies, primarily to make 68 grn Flat Base bullets on .825 jackets.

So I got to thinking. (That can be dangerous). Take my 1.140 SierraJackets and set the FB core seating die up to seat the 72 grn cores to make a Flat Base Core. The size came out just right out of the die to match my 15 ogive long range bullet die.

I had to make a flatbase punch, I always keep a couple of Diesel engine head bolts around for material for these kind of projects. Having made the punch, I set the point up die up and it makes a pretty darned nice bullet.

the next step was to throat out a 6mm 1-8 twist. My standard reamer is a .060 throat. in order to keep the flat base above the neck shoulder junction, I ended up with about a .180 throat.

here is what the seated bullet looks like just on the lands.

I figure N150 powder will be just right.

Don’t ask me why I am doing this. I guess because I can.

 

[bozo699]

Looks great Jackie!… what distance you plan on shooting them?
Wayne

 

[jackieschmidt]

Looks great Jackie!… what distance you plan on shooting them?
Wayne

Primarily at 200 and 300 yards.

I know it is giving up BC numbers to the boat tail but I’m hoping it will be less finicky in the tuning department.

 

[bozo699]

Primarily at 200 and 300 yards.

I know it is giving up BC numbers to the boat tail but I’m hoping it will be less finicky in the tuning department.

Jackie,
I don’t compete at close range like you do so I don’t have much knowledge on the subject but playing with my .222 , br’s or the ppc they all loved flat based bullets at 100 and 200 I never shot them out to 300 much but I bet they will work great for ya I bet your onto something there especially out to 300 in windy conditions, please let us know how they perform for ya
Always love and learn from your posts
Wayne

 

[rogina]

Primarily at 200 and 300 yards.

I know it is giving up BC numbers to the boat tail but I’m hoping it will be less finicky in the tuning department.

I did the same thing with my 6mm dies. Made a 98.5 grain bullet that shot great at 1000 yards. There is more pressure with those bullets compared to the vlds. I shot those bullets in a Bartlein 1 in 9.5 twist in 6X47 lap.

 

[DaveTooley]

Jackie
We made 6.5 FB bullets. 140 gr. The original lot of jackets worked great. The next lot we started losing bullets. We never did get it sorted out. I have some 25 dies and we made 79-110 gr FB. They worked great. It will be interesting to see how things go on the 6's. I had Randy Robinett make me some 95 gr FB. I need to find them. Working on a barrel for the Tacdriver match.

 

[RGRobinett]

Left to RT: 121 Gr. FB; 95 Gr. FB; 104 Gr. BT - all 11 caliber tangent ogive 6mm. The 121 are great, but try giving one away! No, don't ask, the remaining 121FB are for personal use - pic just to illustrate that if you can visualize it, for a given jacket length/die, there are MANY "fill" options . . . and most will shoot quite well. RG

 

[urbanrifleman]

You will need a 7 twist with that bearing surface. I would think.

 

[jackieschmidt]

You will need a 7 twist with that bearing surface. I would think.

We are heading to the range this morning, so I guess we will see.

 

[RGRobinett]

Regarding gyroscopic stability, except that it increases mass, the bearing surface has little function: OAL is THE BIG factor . . . and the lack of BT - drag is a stabilizing force.

Those 1.3xx inch long 121 Gr. FB, via 1:8" twist, are more stable than the classic 1:14" twist/68 Gr. FB (>0.845" LONG) point-blank model for precision.

As compared to a FB sibling (and artificially retaining the SAME OAL), adding a BT to a 6mm bullet, will increase the twist rate requirement by 1.0". The only down-side to going FB is the increased potential
for bullet failures and, possibly, the need for more free-bore . . . can't wait to read about Jackie's adventure! RG

 

[gunsandgunsmithing]

I have been making a 103 6mm Boat Tail for a while, and it shoots pretty decent.

I recently acquired a set of Rorshach 6mm dies, primarily to make 68 grn Flat Base bullets on .825 jackets.

So I got to thinking. (That can be dangerous). Take my 1.140 SierraJackets and set the FB core seating die up to seat the 72 grn cores to make a Flat Base Core. The size came out just right out of the die to match my 15 ogive long range bullet die.

I had to make a flatbase punch, I always keep a couple of Diesel engine head bolts around for material for these kind of projects. Having made the punch, I set the point up die up and it makes a pretty darned nice bullet.

the next step was to throat out a 6mm 1-8 twist. My standard reamer is a .060 throat. in order to keep the flat base above the neck shoulder junction, I ended up with about a .180 throat.

here is what the seated bullet looks like just on the lands.

I figure N150 powder will be just right.

Don’t ask me why I am doing this. I guess because I can.View attachment 1329743View attachment 1329744

Looks good Jackie and I bet they'll shoot, too!
Keep us posted on this.

 

[Alex Wheeler]

I think @GlennK tested some 108ish flat bases at 1k. They did pressure up quite a bit sooner if I remember right. But even at 1k, accuracy still trumps speed or bc. Cool project.

 

[GlennK]

They were a 105.7 gr fb. They tuned into the same window as the boat tail, but the dillon wind beat then up a bit. They did shoot small without conditions.

 

[jackieschmidt]

Well, we had a great day at the range. Sunny, fairly low humidity, 80 degrees and jus enough wind to keep yo on your toes.

I started out with the same load that I shot when the bullet was a boat tail, 30.8 grns of N150 just off the lands. This is a standard .269 neck 6BR with a .180 freebore, (as best I can tell). Today I was shooting 100 yards.

It did not shoot that well. Shooting ragged mid “threes”. I tried a few tuner adjustments With no improvement.

I sensed the load was to hot. So I set up my Ohler 35 Chronograph and wow, the thing was zinging out at 2950. Too hot. I figure the added shank length, or bearing surface, accounted for this.

So I dropped the load untill the Chrono hit 2850, an it really started acting like a Benchrest Rifle. 5 shot spreads were averaging just under 10 fps spread. The final was a flat 30 grns of N150, about .010 off the lands,

I found a good tuner setting and then shot these four groups.

I am very pleased. Tomorrow I will set up at 200 and see how she does.

Here are four 5-shot groups I shot. This just might be one of my ideas that work.are four 5 shot groups I shots.

 

[bozo699]

Well done Jackie!….hope she holds in there for your 200 yard test
Wayne

 

[jackieschmidt]

Bad day at the range.

I had all day to work with this combo at 200 yards yesterday, and while it was a beautiful day, the wind was atrocious. 15/20 mph all day. That is not fun at Tomball.

I am not doing something right. I had four powders, N150, Reloader 15, Accurate 2495, and H4895. I used my standard 5 flag set.

When shooting the straight away south wind, I could keep the groups at least inside the moth ball at around 7/8 inch. But any turn at all, something I could barely read, resulted in around 1 3/4 inches of deflection.And not just straight across. Sometimes across and down, sometimes across and up.

I had my Ohler 35 Chronograph set up, so With each powder I could keep track of the velocities.

All four loaded within a grain of each other to achieve the 2850 to 2900 fps.

But not combo of charges and tuner setting made this thing remotely competitive.

Either this is the most wind sensitive bullet ever created, or I was just having a bad day. Since I had my 6PPC LV with me. I got disgusted and set it up, loaded my favorite load of 30.4 grns of 133 with my 68 grn flatbase, and shot a nice round .500 group right smack in the middle of the moth ball.

As good as this 103 FB shot at 100, I was really expecting great things. Granted, Saturday was a MUCH better day at 100 yards, but I always feel that as an experienced Benchrest Shooter, I can read conditions better than what was showing up on the target, especially when I am not on the clock.

The wind is doing strange things to this bullet. The bullet holes are nice and round in the target, So I doubt it is a stability issue.
Any thoughts?

 

[boltfluter]

Personally I could never shoot anything remotely good in those kind of conditions. I would try again in a somewhat normal wind. Good luck!

 

[Mulligan]

Bad day at the range.

I had all day to work with this combo at 200 yards yesterday, and while it was a beautiful day, the wind was atrocious. 15/20 mph all day. That is not fun at Tomball.

I am not doing something right. I had four powders, N150, Reloader 15, Accurate 2495, and H4895. I used my standard 5 flag set.

When shooting the straight away south wind, I could keep the groups at least inside the moth ball at around 7/8 inch. But any turn at all, something I could barely read, resulted in around 1 3/4 inches of deflection.And not just straight across. Sometimes across and down, sometimes across and up.

I had my Ohler 35 Chronograph set up, so With each powder I could keep track of the velocities.

All four loaded within a grain of each other to achieve the 2850 to 2900 fps.

But not combo of charges and tuner setting made this thing remotely competitive.

Either this is the most wind sensitive bullet ever created, or I was just having a bad day. Since I had my 6PPC LV with me. I got disgusted and set it up, loaded my favorite load of 30.4 grns of 133 with my 68 grn flatbase, and shot a nice round .500 group right smack in the middle of the moth ball.

As good as this 103 FB shot at 100, I was really expecting great things. Granted, Saturday was a MUCH better day at 100 yards, but I always feel that as an experienced Benchrest Shooter, I can read conditions better than what was showing up on the target, especially when I am not on the clock.

The wind is doing strange things to this bullet. The bullet holes are nice and round in the target, So I doubt it is a stability issue.
Any thoughts?

Jackie,
Thanks for the update.
I am watching to see how this sorts out.
At the risk of exposing my ignorance on this, twist rate jumps out at me. The powders you tried, are proven performers, no doubt about that.
CW