conditionzero
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Learning how to find jam is a great skill to develop as you begin to learn about advanced reloading techniques. Especially as they relate to barrel harmonics.
To get started you will need a few things materials and tools.
A. Bullet / Projectile
B. Unprimed Case
C. Calipers
D. Ogive / Bullet comparator device
E. Bullet Seating Die
F-G. Some way to record the data
Procedure Overview
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Step 1 - Make the initial bullet seating.
Step 2 - Gently chamber the round.
Step 3 - Thrust the bolt forward and lock it down.
I have experimented with this step and you don't need so much force that you have a running start. But also gently cam'ing over the bolt has not generally been enough to get the bullet seated deep enough. Essentially just throw the bolt forward as if you were doing a fast follow up shot with a bit of authority. You should then be able to lock the bolt down with relative ease.
Before thrusting, you can see the bolt is back a bit.
After, it is seated completely. At this point the bullet has jammed in to the rifling of my barrel.
Step 4 - Quickly lift the bolt and eject the round.
Step 5 - Measure Ogive.
This is your first measurement. For this specific chamber and this specific bullet. You cannot transfer this data to a projectile of different shape etc.
For my chamber, and the Berger VLD Target 140gr 6.5mm, jam length at the ogive is 2.2760"
Step 6 - Subtract twenty thousandths from the measurement in Step 5, adjust your die, and reseat.
Step 7 - Validate your seating depth and test the ease of chambering and ejection of the round.
---
And that is it! You now have two very important measurements for your chamber and bullet. Jam & maximum OOAL (Ogive Over All Length, Jam - 0.002" (twenty thousandths). It is important to note that your OOAL is almost certainly too long to magazine feed. That is a choice you will have to make on your own, if you want to start load development here or at your maximum available length of your magazine.
Once you determine your powder charge and have consistent combustion, you can start to tune barrel harmonics by adjusting the seating depth. Armed with this data, you know exactly how far you can go before you hit the lands of your barrel with this bullet. Repeat this process as many times as necessary for new bullet testing.
To get started you will need a few things materials and tools.
A. Bullet / Projectile
B. Unprimed Case
C. Calipers
D. Ogive / Bullet comparator device
E. Bullet Seating Die
F-G. Some way to record the data
Procedure Overview
- Seat the bullet in the case JUST enough so that it will not fall out on its own.
- Gently insert the round in to the rifles chamber.
- Thrust your bolt forward and lock it down.
- Quickly lift the bolt and eject the round.
- Measure jam ogive.
- Subtract 0.002" (twenty thousandths) from the measurement, adjust die, reseat.
- Test ease of action operation and ejection.
---
Step 1 - Make the initial bullet seating.
Step 2 - Gently chamber the round.
Step 3 - Thrust the bolt forward and lock it down.
I have experimented with this step and you don't need so much force that you have a running start. But also gently cam'ing over the bolt has not generally been enough to get the bullet seated deep enough. Essentially just throw the bolt forward as if you were doing a fast follow up shot with a bit of authority. You should then be able to lock the bolt down with relative ease.
Before thrusting, you can see the bolt is back a bit.
After, it is seated completely. At this point the bullet has jammed in to the rifling of my barrel.
Step 4 - Quickly lift the bolt and eject the round.
Step 5 - Measure Ogive.
This is your first measurement. For this specific chamber and this specific bullet. You cannot transfer this data to a projectile of different shape etc.
For my chamber, and the Berger VLD Target 140gr 6.5mm, jam length at the ogive is 2.2760"
Step 6 - Subtract twenty thousandths from the measurement in Step 5, adjust your die, and reseat.
Step 7 - Validate your seating depth and test the ease of chambering and ejection of the round.
---
And that is it! You now have two very important measurements for your chamber and bullet. Jam & maximum OOAL (Ogive Over All Length, Jam - 0.002" (twenty thousandths). It is important to note that your OOAL is almost certainly too long to magazine feed. That is a choice you will have to make on your own, if you want to start load development here or at your maximum available length of your magazine.
Once you determine your powder charge and have consistent combustion, you can start to tune barrel harmonics by adjusting the seating depth. Armed with this data, you know exactly how far you can go before you hit the lands of your barrel with this bullet. Repeat this process as many times as necessary for new bullet testing.
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