Question for gunsmiths

[bomberodevil]

I recently bought a CA Mesa in 6.5 CM, and I have shot about 100 rounds through for break-in. I'm now starting to do load development for hunting rounds. For a ladder test, I planned to seat the bullets (Nosler Ballistic Tip, 140 grain), at .020 off the lands, and to play with seating depth after powder and charge weight selection.

I measured the headspace with a Hornady OAL gauge and I checked it several times. I even painted the bullet with a magic marker to make sure I was in the land grooves. I found out that my overall COAL length with the ogive touching the lands was averaging 2.776, while the SAAMI cartridge length is 2.825. That means my max cartridge length, at least with this particular bullet, is .049" shorter than what SAAMI has for the cartridge standard. Does that sound right?

I have no intention of shooting one-shot lengthy target loads, but I do want to get the maximum accuracy and performance out of my hunting loads. Thanks for your help in advance!

 

[elkaholic]

Im not a gunsmith but I can answer the question. A Nosler ballistic tip is a tangent ogive bullet, not a secant like the higher b c Bergers, etc This makes the bullet hit the lands farther forward on the bullet because the nose is as pointed. Essentially moves the bullet back into the case more.

 

[Mram10us]

What he said.
To add, CA would have used a saami reamer. If your ammo fits fine without the bolt needing extra force, then it is most likely correctly headspaced. I can't imagine a way that a saami spec reamer could give you a short throat.

 

[bomberodevil]

Im not a gunsmith but I can answer the question. A Nosler ballistic tip is a tangent ogive bullet, not a secant like the higher b c Bergers, etc This makes the bullet hit the lands farther forward on the bullet because the nose is as pointed. Essentially moves the bullet back into the case more.

That makes sense. I'm not an expert reloader, just an average Joe. What's weird is I spoke to technical service at both Christensen Arms and Nosler today, and neither one could answer the question. CA said to send it back and they will check it. I'd rather not lose it for weeks (months?) if there's nothing wrong with it. Thank you!

 

[bomberodevil]

What he said.
To add, CA would have used a saami reamer. If your ammo fits fine without the bolt needing extra force, then it is most likely correctly headspaced. I can't imagine a way that a saami spec reamer could give you a short throat.

The loads I used for the break-in loads were hand-loaded ELDM 147's cause they were on sale. I seated them at 2.577, what I figured were about .020" off the lands.

Like I said, I'm fairly inexperienced at really fine-tuning handloads for max performance, so two types of ogives on bullets doesn't seem fair! Thank you!

 

[elkaholic]

correct free bore for a given bullet can vary by .200" or more in the same cartridge. No such thing as one size fits all!

 

[bomberodevil]

Here's a good article discussing the different types of ogives in bullets. Every day is a learning opportunity!

https://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/

 

[Edd]

The SAAMI spec for COAL is 2.700" - 2.825". Your COAL is less than the maximum but it is within the SAAMI standard.

 

[RevJim]

For what its worth, my CA Mesa 6.5CM is like yours. The 120 TTSX and the 110 HH both "touch" the rifling at 2.75" I myself never use hunting loads that are into the Lands. So I have the Barnes set at 2.70 and the Hammers at 2.735 to start. I hope to get to the range soon to try them out. Since the Mesa is a Mod 700 "clone" I was hoping that I had a long enough throat for a C.O.A.L of 2.79 or so, but hey, this is my first factory Creedmoor. It doesn't bother me.

 

[bomberodevil]

For what its worth, my CA Mesa 6.5CM is like yours. The 120 TTSX and the 110 HH both "touch" the rifling at 2.75" I myself never use hunting loads that are into the Lands. So I have the Barnes set at 2.70 and the Hammers at 2.735 to start. I hope to get to the range soon to try them out. Since the Mesa is a Mod 700 "clone" I was hoping that I had a long enough throat for a C.O.A.L of 2.79 or so, but hey, this is my first factory Creedmoor. It doesn't bother me.

That makes a lot of sense, on top of the other replies. Over the next year, I'll likely develop a couple of more loads, maybe play around with a hybrid bullet for hunting. The only rifles I've reloaded for in the past were older 30.06, .308 and.270. All those are working guns that have shot hunting loads. I'll dial in the Nosler BT hunting load and then play around with longer distance loads and bullet seating. Thank you!

 

[Edd]

For what its worth, my CA Mesa 6.5CM is like yours. The 120 TTSX and the 110 HH both "touch" the rifling at 2.75" I myself never use hunting loads that are into the Lands. So I have the Barnes set at 2.70 and the Hammers at 2.735 to start. I hope to get to the range soon to try them out. Since the Mesa is a Mod 700 "clone" I was hoping that I had a long enough throat for a C.O.A.L of 2.79 or so, but hey, this is my first factory Creedmoor. It doesn't bother me.

If 110gr Hammer Hunters contact at 2.750", you don't have a SAAMI chamber. Your freebore is about .085" short.

 

[freddiej]

I recently bought a CA Mesa in 6.5 CM, and I have shot about 100 rounds through for break-in. I'm now starting to do load development for hunting rounds. For a ladder test, I planned to seat the bullets (Nosler Ballistic Tip, 140 grain), at .020 off the lands, and to play with seating depth after powder and charge weight selection.

I measured the headspace with a Hornady OAL gauge and I checked it several times. I even painted the bullet with a magic marker to make sure I was in the land grooves. I found out that my overall COAL length with the ogive touching the lands was averaging 2.776, while the SAAMI cartridge length is 2.825. That means my max cartridge length, at least with this particular bullet, is .049" shorter than what SAAMI has for the cartridge standard. Does that sound right?

I have no intention of shooting one-shot lengthy target loads, but I do want to get the maximum accuracy and performance out of my hunting loads. Thanks for your help in advance!

Bomber, of the people that responded I will agree with them. As they are correct. I am a gunsmith, I have been for the last 13 years. the more blunt your tip is the farther forward on the slug the lands and grooves will touch your slug, hence making your personal over all length shorter than SAAMI spec. VLD's will be longer and will come very close oif not over SAAMI COAL of 2.825"..
For you 2.776" COAL is your absolute top length with that Nosler slug. Drop 0.010" to 0.020" from 2.776" and start load development. have a great one Y'all.

 

[RYEWSKY25284]

For what its worth, my CA Mesa 6.5CM is like yours. The 120 TTSX and the 110 HH both "touch" the rifling at 2.75" I myself never use hunting loads that are into the Lands. So I have the Barnes set at 2.70 and the Hammers at 2.735 to start. I hope to get to the range soon to try them out. Since the Mesa is a Mod 700 "clone" I was hoping that I had a long enough throat for a C.O.A.L of 2.79 or so, but hey, this is my first factory Creedmoor. It doesn't bother me.

What kind of velocity are you getting on the 120gr TTXS?
Thank You.

 

[RevJim]

Sorry to be slow in getting back to you. I "hope" to get to the range tomorrow in fact. If I can get there early enough I can set up my chrono and check everything as I work up my loads. I will report back my findings.