Base to Ogive 77 TMK?

[TimberHunter]

Can someone measure base of bullet to ogive on a 77 TMK?


I know where I hit land in a 223 with a 77 and I’m trying to anticipate where I would with a 80 and 88 ELDM. In case anyone is curious, I found that the ELDM 80 had a base to ogive of .608 while the 88 is .680


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[Axlrod]

I get .610 with the Forster datum tool and .658 with 88gr Horn.

 

[TimberHunter]

Thank you!


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[wind gypsy]

Are you trying to figure how much bullet will be in the case? Or what the COAL will be?

BTO measurements with something like hornady comparator isn’t going to tell you exactly where lands will touch because it varies quite a bit with different ogive shapes and land angles.

 

[wind gypsy]

With hornady comparator-

I get 0.630” bto on 77 tmk
I get 0.617 bto with 80 ELDm

Measuring loaded cartridge base to ogive at jam for my 223 Wylde I get the following measurements:
77tmk- 1.994”
80 eldm- 1.950”

Because the 77 tmk has a much steeper angled ogive than the 80 eldm, it has a longer base to ogive length at jam.

 

[TimberHunter]

Are you trying to figure how much bullet will be in the case? Or what the COAL will be?

BTO measurements with something like hornady comparator isn’t going to tell you exactly where lands will touch because it varies quite a bit with different ogive shapes and land angles.

I hit the lands with the 77 with at approx 2.370 OAL. I’ve been loading them at 2.280 because of factory mag. Was seeing if the juice was worth the squeeze of going to the 80 ELDM with a longer mag. I don’t think it is since the 80 would still be sitting way deep in the case taking up a lot of case volume.

With a heavily compressed N150 load, I’m getting 2740 fps with the 77 out of a 16” barrel. May try N540 and longer mags to get that little extra FPS to help reduce wind drift. Trying to make the 223 my go to rifle but my 6.5/140/147 is hard to deny when it comes to longer across canyon shots


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[HuntHarder]

With hornady comparator-

I get 0.630” bto on 77 tmk
I get 0.617 bto with 80 ELDm

Measuring loaded cartridge base to ogive at jam for my 223 Wylde I get the following measurements:
77tmk- 1.994”
80 eldm- 1.950”

Because the 77 tmk has a much steeper angled ogive than the 80 eldm, it has a longer base to ogive length at jam.

I also use the Hornady comparator set and I get .641 BTO on a 77tmk. Just shows the accuracy of their machining @ Hornady. No big deal, just know that you can not go between comparator sets and expect repeatability. My buddy here in Az had me load him ammo a couple years ago. Luckily, he had a round or 2 left because when he ran out, he was going to duplicate my load at his house. Our CBTO #'s were off considerably, with both of us using the Hornady set.

 

[wind gypsy]

I hit the lands with the 77 with at approx 2.370 OAL. I’ve been loading them at 2.280 because of factory mag. Was seeing if the juice was worth the squeeze of going to the 80 ELDM with a longer mag. I don’t think it is since the 80 would still be sitting way deep in the case taking up a lot of case volume.

With a heavily compressed N150 load, I’m getting 2740 fps with the 77 out of a 16” barrel. May try N540 and longer mags to get that little extra FPS to help reduce wind drift. Trying to make the 223 my go to rifle but my 6.5/140/147 is hard to deny when it comes to longer across canyon shots

75 ELDm is the answer for maximizing a saami 223 chamber with longer COAL on paper, more so than the 80. It has a very short bearing surface and aggressive profile. It’s just more finicky than a TMK.

 

[wind gypsy]

I also use the Hornady comparator set and I get .641 BTO on a 77tmk. Just shows the accuracy of their machining @ Hornady. No big deal, just know that you can not go between comparator sets and expect repeatability. My buddy here in Az had me load him ammo a couple years ago. Luckily, he had a round or 2 left because when he ran out, he was going to duplicate my load at his house. Our CBTO #'s were off considerably, with both of us using the Hornady set.

Multiple factors at play. There is lot to lot bullet differences, comparator variance, and measuring techniques that can impact results.

 

[longrangelead]

I also use the Hornady comparator set and I get .641 BTO on a 77tmk. Just shows the accuracy of their machining @ Hornady. No big deal, just know that you can not go between comparator sets and expect repeatability. My buddy here in Az had me load him ammo a couple years ago. Luckily, he had a round or 2 left because when he ran out, he was going to duplicate my load at his house. Our CBTO #'s were off considerably, with both of us using the Hornady set.

Because of this, I started sharpying bullets and locking a mic. .001" under bullet diameter, give it a twist with LIGHT pressure and you get a mark at the functional end of bearing surface/beginning of ogive.

 

[TimberHunter]

75 ELDm is the answer for maximizing a saami 223 chamber with longer COAL on paper, more so than the 80. It has a very short bearing surface and aggressive profile. It’s just more finicky than a TMK.

Thanks I’ll give it a try. I’ve read the 75 is a killer of a bullet on animals as well


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