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6.5 prc COAL and cbto question 156gr Berger

Mustbenice1214

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Nov 23, 2020
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Hello everyone. First time reloaded here. Just want to make sure I’m doing everything safely. A little background:
Using an XM length action from defiance. Loading 156 burgers with either h1000 or n565, and 215s (all I have)

I’m getting a cbto and coal length at the lands well beyond the recommended COAL length in reloading guides of 2.995. So I’m going to have a huge jump. The factory ammo is also a huge jump.
Question is: is this based on a short action for reloading manuals? I assume there’s a lot of people going beyond the COAL in the book. Making sure I’m researching this correctly. But it seems like I should be loading past that and more so based on my lands measurements, since I have an XM action. Or do I load to “max coal”?
Again this is my first load development so I’m triple checking everything!
 
Recommended COAL of 2.995” is based on a short action and mag. Take advantage of that XM extra length and throw some more powder in
 
The COAL from the reloading manual is going to be based on CIP or SAAMI cartridge length min and max specifications.

Do you need it to load out of a mag?
Since this is your first work up, you may try starting at book length, trying some different powder charges, and then working COAL out to max mag length or to just under what your touch measurement was. To keep it simple, I'd stay out of the lands until you've got some confidence in your loading process.
 
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Hello everyone. First time reloaded here. Just want to make sure I’m doing everything safely. A little background:
Using an XM length action from defiance. Loading 156 burgers with either h1000 or n565, and 215s (all I have)

I’m getting a cbto and coal length at the lands well beyond the recommended COAL length in reloading guides of 2.995. So I’m going to have a huge jump. The factory ammo is also a huge jump.
Question is: is this based on a short action for reloading manuals?
Yes, that's based on a short action.

I assume there’s a lot of people going beyond the COAL in the book. Making sure I’m researching this correctly. But it seems like I should be loading past that and more so based on my lands measurements, since I have an XM action. Or do I load to “max coal”?
Again this is my first load development so I’m triple checking everything!

I load my Berger 153.5's to a COAL of 3.056" (that's a .029" jump for my particular chamber) and of course, that means they don't fit in a mag and need hand feeding. Though my mag can easily handle COAL's to 2.995, I've also loaded these 153.5's to a COAL of 2.969 for a .117" jump and they performed quite well, even though it's a long jump.

Keep in my that the amount of jump really isn't as big an issue many shooters make it out to be. When you find a good accuracy node for a particular powder charge, then SEATING DEPTH is what's really important to get really good groups, much much more than jump. If you haven't read them yet, there's a 4 part series of articles regarding jump you should read to better understand, here:


 
Hello everyone. First time reloaded here. Just want to make sure I’m doing everything safely. A little background:
Using an XM length action from defiance. Loading 156 burgers with either h1000 or n565, and 215s (all I have)

I’m getting a cbto and coal length at the lands well beyond the recommended COAL length in reloading guides of 2.995. So I’m going to have a huge jump. The factory ammo is also a huge jump.
Question is: is this based on a short action for reloading manuals? I assume there’s a lot of people going beyond the COAL in the book. Making sure I’m researching this correctly. But it seems like I should be loading past that and more so based on my lands measurements, since I have an XM action. Or do I load to “max coal”?
Again this is my first load development so I’m triple checking everything!
2.95” OAL is to fit in SA AICS magazines w/o front plate. XM action allows for 3.150” OAL, from memory, so utilize that extra room.

I’d jump 0.040” as a starting point.

Longer OAL will drop pressure (and velocity) vs shorter OAL.
 
Yes, that's based on a short action.



I load my Berger 153.5's to a COAL of 3.056" (that's a .029" jump for my particular chamber) and of course, that means they don't fit in a mag and need hand feeding. Though my mag can easily handle COAL's to 2.995, I've also loaded these 153.5's to a COAL of 2.969 for a .117" jump and they performed quite well, even though it's a long jump.

Keep in my that the amount of jump really isn't as big an issue many shooters make it out to be. When you find a good accuracy node for a particular powder charge, then SEATING DEPTH is what's really important to get really good groups, much much more than jump. If you haven't read them yet, there's a 4 part series of articles regarding jump you should read to better understand, here:


I did read those. I with they did that data on more bullets, but at least for those it looks like .05-.06 is the sweet spot.
 
2.95” OAL is to fit in SA AICS magazines w/o front plate. XM action allows for 3.150” OAL, from memory, so utilize that extra room.

I’d jump 0.040” as a starting point.

Longer OAL will drop pressure (and velocity) vs shorter OAL.
I think it is 3.150 which is why I was surprised to see the max in the book so low. I’ll start with .04 off and work up from there
 
I did read those. I with they did that data on more bullets, but at least for those it looks like .05-.06 is the sweet spot.
To reemphasize . . . it's not the jump that's the "sweet spot" as it's the seating depths for a particular chamber and powder combination. Measuring your freebore to deciding on a particular jump for a starting point is ok. From there, you should focus on seating depths. Once you find a seating depth for a particular powder - bullet combination, stick too it for a long time until accuracy degrades even though your jump increases with throat erosion over time, then adjust seating depth to bring back the accuracy (not the jump).
 
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To reemphasize . . . it's not the jump that's the "sweet spot" as it's the seating depths for a particular chamber and powder combination. Measuring your freebore to deciding on a particular jump for a starting point is ok. From there, you should focus on seating depths. Once you find a seating depth for a particular powder - bullet combination, stick too it for a long time until accuracy degrades even though your jump increases with throat erosion over time, then adjust seating depth to bring back the accuracy (not the jump).
They are essentially the same thing no? If you seat the bullet deeper then you are in turn increasing the jump. Or am I understanding this wrong.
Or are you saying use the OAL as a starting point then just worry about what seating depth on my die is from then on, not comparing it to the "jump". (Even though it's technically the same thing)
Not trying to be argumentative, just trying to make sure I understand everything correctly. I don't have anyone to really teach me so I've learned by watching a bunch of videos.
 
They are essentially the same thing no? If you seat the bullet deeper then you are in turn increasing the jump. Or am I understanding this wrong.
No, it's not the same thing. Certainly, when you change your jump measurement, your seating depth changes the same amount. But your jump is constantly changing as your throat erodes, while your seating depth remains the same (unless you chase the lands at some point).

When you change your seating depth for a particular load, that directly changes volume of the interior of the case for the powder and the pressure curve of the load as well and the time it takes for the bullet to clear your muzzle. Keeping that pressure curve and the bullet dwell time through the barrel the same is important for keeping your load as accurate as you've developed. When you're .010 or more off the lands, the pressure curve is almost not effected at all whether you're .020 or .100 off the lands. Only when you're into the lands will you get significant change in the pressure curve. The goal is to keep that pressure curve constant as possible as well as the time it takes the bullet to exit the muzzle to keep in the harmonic node for your consistent accuracy. These two factors are way, way more important than the distance of the jump.

In these threads, people most often mention how much jump they are using. But someone's jump really has no meaning since everyone's chamber is a difference configuration and size. When I say my jump is .117", that cartridge in someone else gun might be .030" of jump or .150" of jump depending on the amount of freebore their particular gun's chamber has. It's better to know the COAL, where one can then calculate how much jump (or better yet, the seating depth) that represents in a particular chamber.

Or are you saying use the OAL as a starting point then just worry about what seating depth on my die is from then on, not comparing it to the "jump". (Even though it's technically the same thing)
Not trying to be argumentative, just trying to make sure I understand everything correctly. I don't have anyone to really teach me so I've learned by watching a bunch of videos.
Once you've located where you lands is, you decide on a starting point somewhere off the lands, .010, .020, .030" off . . . whatever. From there you focus on the powder charge that works best, then the seating depth to fine tune your load (ignoring jump all the while as it's constantly changing over time anyway). CAOL is only an issue when you're trying to fit a cartridge into your mag. So, one might try to get the maximum COAL that'll fit into their mag, as a starting point (still ignoring jump, unless the jump then happens to be into the lands or is just too close to it).

When you find a "seating depth" that is working well, you can keep your seating die set there, unless there's a significant change in bullet dimensions, and do just fine even though the jump changes over time.

One other thing I do to keep my seating depth very consistent, it sort my bullets from the base to the contact point of my seating stem. It's like measuring the bullets BTO, only using a different comparator (for my 6.5 a 17 caliber Sinclair comparator is very close to the right diameter) that touches the ogive at a much higher place. That makes for very consistent seating depth. In addition, because there can significant differences from lot of lot of bullets, I'll adjust my seating die so that the actual seating depth (the distance from the base of the bullet to the rim of the case mouth) is the same. I want the base of the bullet to be in the same distance so there's no change in the cases volume do the variance in bullet dimensions. I continue to ignore bullet jump, and only make changes in seating depth when I see significant changes in accuracy.
 
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