Thoughts on freebore

[BassinDmax]

I'm running an X-Caliber 20" barrel on an AR platform and I'm curious if I may have a shorter then spec freebore. It was cut with PT&G reamer and the drawing shows a freebore of .0899", but I wonder, is it? I'm running my start loads at .020" off jam.What I'm finding is a lot of bullet stuffed in the case. I'm using the Hornady L-n-L Bullet comparator tool with the Short Action Custom inserts to take all my measurements. I'm getting a base to ogive of 1.590" and COAL 2.243" with the Hornady 103 ELD-X, Berger 105 Target is 1.592" and 2.191", Sierra 107 SMK is 1.586" and 2.243" and Berger 108 Target is 1.590" and 2.215". Just seems like I should be able to get more bullet out of the case, but I only have .020" to play with before concern of jamming into the lands. I'm considering having the throat cut a little deeper, I could definitely add more length and still be under mag length. What has your all experience been with seating depth in the 6ARC? Are my findings abnormal or is this normal for seating depth?

[grayfox]

I have 3 barrels.  These are my measurements to the lands with my hornady comparator.  The Faxon has the most room, and the Monster and Uintah that I have are close equals, not far behind.  Your seating of the 103 Eldx is lots shorter than I need to go as you can see.  I do not have any 105 Bergers or 107 smk(well I have the smk but haven't seated them yet).

Hope the formatting comes out ok on this...

…   ,,,,,,,,,,Faxon-20 Uintah-22,,,, Monster-20
90 TGK: ,,,,,,2.338 ,,,,2.300 ,,,,,,,,….
95 Sst: ,,,,,,,2.203 ,,,,,2.202 ,,,,,2.202
103 Eldx: ,,,,,2.301 ,,,,2.313 ,,,,,2.320
105 Bthp
(Hdy Black):  ,2.277 ,,,,2.277 ,,,,2.274
Nos 95BT: ,,,,,2.222 ,,,,,2.210 ,,,,2.211
90 Eldx   ,,,,,,,,,,,,,,,,,,,,,,2.220 ,,,,,…
100 SGK: ,,,,,,2.140 ,,,,,,2.150 …
100 Hdy-sp  …  ,,,,,,,,,,,,,2.180 …
95 SMK …         ,,,,,,,,,,,,2.318 …
88 Berger …         ,,,,,,,,,2.333 …
95 Berger-
classic … ,,,,,,,,,,,,,,,,,,,,,,,2.186 …

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edit to add: similar to Dino I'm trying to seat most of them about 50-60 thou off the lands.

[Dino11]

My Odin barrel is like yours, it has a slightly short chamber. But it is my most accurate barrel.

My finding are these long skinny bullets like to jump a little more than the traditional methods used in the past. Now I have never shot the 103 ELDX, but I have loaded Berger 109's and 115's and a ton of the Nosler 105's. But I have not yet loaded the 103's and 109's for the Odin barrel yet. Your chamber may be a little on the short side looking at your numbers, but that may not be a bad thing. As stated my shortest chamber is my most accurate barrel. Play around with your seating depth, my findings are these bullets like to jump. I have loaded rounds that the overall length was as short as 2.185 with some of the lighter weight stuff. I have about 3500 of the 100 gn SPBT I got from American Reloading that I use for foulers and let my son shoot because he only likes to ring steel, and I'm not going to let him waste my good stuff doing that.

[BassinDmax]

I have 3 barrels.  These are my measurements to the lands with my hornady comparator.  The Faxon has the most room, and the Monster and Uintah that I have are close equals, not far behind.  Your seating of the 103 Eldx is lots shorter than I need to go as you can see.  I do not have any 105 Bergers or 107 smk(well I have the smk but haven't seated them yet).

Hope the formatting comes out ok on this...

…   ,,,,,,,,,,Faxon-20 Uintah-22,,,, Monster-20
90 TGK: ,,,,,,2.338 ,,,,2.300 ,,,,,,,,….
95 Sst: ,,,,,,,2.203 ,,,,,2.202 ,,,,,2.202
103 Eldx: ,,,,,2.301 ,,,,2.313 ,,,,,2.320
105 Bthp
(Hdy Black):  ,2.277 ,,,,2.277 ,,,,2.274
Nos 95BT: ,,,,,2.222 ,,,,,2.210 ,,,,2.211
90 Eldx   ,,,,,,,,,,,,,,,,,,,,,,2.220 ,,,,,…
100 SGK: ,,,,,,2.140 ,,,,,,2.150 …
100 Hdy-sp  …  ,,,,,,,,,,,,,2.180 …
95 SMK …         ,,,,,,,,,,,,2.318 …
88 Berger …         ,,,,,,,,,2.333 …
95 Berger-
classic … ,,,,,,,,,,,,,,,,,,,,,,,2.186 …

---

edit to add:  similar to Dino I'm trying to seat most of them about 50-60 thou off the lands.

Looks like you're getting roughly 40 to 50 thou more length out of the 103 ELD-X's, if you're seeing most of your success 50-60 thou off then I'm really going to have a lot of bullet stuffed in the case. I've just started load development with LeverEvolution looking for charge weights that performed consistent in the 2,650 - 2,700 range. Now going to do seating test next starting at .020 off to .050 off in .003 increments. I'll see how they perform before I make any drastic decisions. Thanks for the feedback.

[BassinDmax]

My Odin barrel is like yours, it has a slightly short chamber. But it is my most accurate barrel.

My finding are these long skinny bullets like to jump a little more than the traditional methods used in the past. Now I have never shot the 103 ELDX, but I have loaded Berger 109's and 115's and a ton of the Nosler 105's. But I have not yet loaded the 103's and 109's for the Odin barrel yet. Your chamber may be a little on the short side looking at your numbers, but that may not be a bad thing. As stated my shortest chamber is my most accurate barrel. Play around with your seating depth, my findings are these bullets like to jump. I have loaded rounds that the overall length was as short as 2.185 with some of the lighter weight stuff. I have about 3500 of the 100 gn SPBT I got from American Reloading that I use for foulers and let my son shoot because he only likes to ring steel, and I'm not going to let him waste my good stuff doing that.

Seating depth testing is next, I'll be starting .020 off to .050 off in .003 increments, definitely see how she performs before getting too far down the rabbit hole! My loads will be on the short side, but glad to see you've seen success running on the lower side. I hear ya on the good stuff, I picked up a few hundred of the Sierra 90 grain FMJ's for foulers when Sierra was closing them out.

[Dino11]

Jump your seating depth in .005 increments, then when you find your groups getting smaller go back and load some around that ladder.

It will save you a lot of time and ammo.

[grayfox]

I was going to say 0.003 as a delta is tough to do in my experience. My depth changes are at 0.010 diff's...many bullets (I use OAL however so if you cbto you might to better) have 0.003-0.004 differences in length. sierra's can have up to 0.005 and these are all + or - type reads, so even at 0.005 for my tools, is tough to do. If you can do it, great. I'm not a match shooter so if I use 0.010 (as the nominal) I get results that I can see and use.
The nosler's I've used have been usually the tightest bullet lengths, more like 002-003.

[BassinDmax]

Jump your seating depth in .005 increments, then when you find your groups getting smaller go back and load some around that ladder.

It will save you a lot of time and ammo.

Good idea, in our current times bullets, powder and especially primers have been tough to come by

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I was going to say 0.003 as a delta is tough to do in my experience.  My depth changes are at 0.010 diff's...many bullets (I use OAL however so if you cbto you might to better) have 0.003-0.004 differences in length. sierra's can have up to 0.005 and these are all + or - type reads, so even at 0.005 for my tools, is tough to do.  If you can do it, great.  I'm not a match shooter so if I use 0.010 (as the nominal) I get results that I can see and use.
The nosler's I've used have been usually the tightest bullet lengths, more like 002-003.

I am using CBTO, I'm trying for 2-3 tighter groups in a row and then I'll use the middle of them, this allows for some variation and limits the impact to the group.

[Dino11]

I use CBTO, it is a little more accurate. Usually within .001 to .002. That is why I told him to go at least .005. You will always get some variance. I just measured the chamber on my Faxon Match barrel I just got and with a Nosler 105 RDF it measured 1.642, it is the tightest one I have now. Going to have to get it to the range and get it broke in and work up a load for this one now. It is amazing the variance you get from one manufacturer to another on a SAMMI spec chamber. Were not talking a little bit but sometimes .020 to .040, that's a lot of difference.

[grayfox]

Yeah, probably relates to how tightly they control reamer sharpness and cutting depth/time, cutting oil lube etc.
Real sharp vs 50-60 barrels later.