I'm working on some loads for my 308, and I've read lots of tid bits about seating the bullet to "jump" or "touch" the lands. I'm wondering if someone could post how to determine the easiest way to find out what the COAL would be if the bullet was just touching the lands? So for example: If the COAL is 2.875 touching the lands, and I want to jump, would I set the COAL to 2.855? Any advice on this will help clear my confusion.
How to seat bullet to "touch" the lands
- Thread starter datatools
- Start date
I'm pretty happy with the OAL of my loads so I haven't tried his but... I've heard that coating the jacketed bullet of a dud cartridge with a black sharpie and then carefully chambering it will reveal how deeply your bullets are engaging the lands. Measuring the amount of sharpie that has been wiped off by chambering the round is a pretty ghetto way of measuring this but it should work...
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- inside a huge cloud of MOSQUITOS
I partially size a neck of a prepped case just enough to hold the bullet but allow it to be pushed in by the rifling. I chamber, then I extract the dummy and measure it with my Sinclair comparator tool. Takes a bit of fiddling around but seems to work well.
Good thinking. I have heard of this but they used a VERY thin layer of spray paint over the bullet.
In my Savage 6BR I find 0.010" jammed into the lands gives the best accuracy. Here is the method I use:
Split Case Method
1. Take a neck sized only fired case, and use a Dremel to cut a single narrow slot in the neck and shoulder.
2. Select a bullet from the box you plan to load and fit it in the split case. Pick a bullet with a consistent flat tip, or file it a touch to square it up. Adjust case by squeezing the neck to increase tension as required. It does not need a lot of tension and just enough hold the bullet.
3. Carefully chamber it, and remove it slowly. If the ejector is pushing the case sideways, use your finger to keep the bullet from dragging on the side of the chamber or receiver.
4. Measure the overall length of the cartridge to the tip of the bullet, and record it.
5. Repeat step 4 until you get consistent numbers within .001". When you think you are close, then just pull the bullet a slight touch out from the self seated position and confirm it consistently returns to that same spot, and record the final length of the cartridge, and record in you loading book. Mark this bullet so you don't mix it up with the rest.
6. This length represents what overall length you need for that specific bullet to touch the lands. In my opinion just touching the lands is a poor position to seat too. I go either 0.010" longer to jam the bullet, or increments of 0.010" shorter to create a jump to the lands. Calculate your desired OAL to give the jam or jump you want, and record that number.
7. Use this marked bullet to load a live round long in the case, and by seating it deeper and deeper by trial and measure match the OAL you have calculated in step 6.
8. At this point methods may differ. Some save this load and use it to set up your die for the next loading session. I have a micrometer style seating die, so I just record the seating position in my loading book and use the test round at the range.
9. This test load, or recorded seating depth in theory is good for that specific batch of bullets, if it were not for throat burning. Especially when new the throat burns so is a moving target. So, especially with a new barrel you may want to repeat this exercise more often, or if you bought a large batch of the same bullets.
This is great info, exactly what I was looking for. Thanks a bunch Ron
. I want to confirm the procedure with an example: When I pull the dummy round out and record the length (after numerous confirmations), lets say it is 2.875. Now I need to try a few groups at various lengths to see what works best. So I would start at a COAL of 2.865 and 2.885. If it groups tighter with the lower length, keep testing in that direction until it opens up again and so forth. Is this correct? Is it safe to assume that the COAL makes a minor difference in accuracy, and the bullet/powder combination makes the most difference?
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- Halifax, NS
Im pretty sure that powders and primers make th largest difference, but even with the right powder, some bullets such as the VLDs will not work unless they are properly seated into or out of the lands.
This is why when I start reloading, the first step is to take into consideration the general seating preference (as found on the interwebs from people who have results) and go from there.
From what I understand, Berger VLDs need to be seated into the lands, and the SMKs like a jump. Before starting a ladder or OCW test, I might quickly check to see how a load performs at 95% maximal charge, seated -0.010, 0.000, 0.010, and maybe even 0.020 for the VLDs.
This is why when I start reloading, the first step is to take into consideration the general seating preference (as found on the interwebs from people who have results) and go from there.
From what I understand, Berger VLDs need to be seated into the lands, and the SMKs like a jump. Before starting a ladder or OCW test, I might quickly check to see how a load performs at 95% maximal charge, seated -0.010, 0.000, 0.010, and maybe even 0.020 for the VLDs.
I just tried loading a dummy round as per Ron's suggestion, and this worked great. But the results surprised me. With a SMK 168, the COAL when I remove the round was consistently 2.922. This seems huge, since I've been loading my rounds to a COAL of 2.80 before trying this test. With the VLD 155, inserted into the rifle with the dummy round, I cant even eject the round after chambering because it remains too long. I can visually see that the VLD has a smoother transition (more steamlined). So, is it safe to assume that with everything I've read about the SMK's (they like the jump), that I should chamber some round with a COAL of 2.902 and try this? My reloading manual says the max length is 2.80, whats the real scope on this?
This is great info, exactly what I was looking for. Thanks a bunch Ron
Yes that is basically correct. Remember though that touch the lands COAL is valid only for that one particular bullet (not bullet type but individual bullet)'. If you don't have a micrometer style seater die, you may want to load that bullet that represents touch the lands. Then use it only to set up your die, and by using the thread pitch on the seater figure out how much you have to adjust it down or up to get a jump or jam that you want.
I find seating depth makes small differences. Seems bullet is more critical followed by powder.
It is a common problem with the low drag style of bullet that they are long when touching the lands. It is because they have such a gradual slope to the nose. I don't think there are any hard and fast rules about what works best with low drag bullets -- jump or jam. I believe Berger recommends jump, but I find jam gives me a touch better accuracy. You pretty much have to try it and see what works for you.
Loading manuals mainly use COAL to ensure it meets standard cartridge specifications for dimensions and it will fit in a magazine. It is not an accuracy setting. If the length results in a bullet sitting significantly back into the case using up powder space, the load should also consider that pressure will be increased due to the lower case volume.
Here is another method recommend
To establish the 'zero' or 'just touching' point:
-Remove firing pin. assy from bolt.
-Full length size a case that's been fired in your chamber. If you are using a bushing die, use a bushing that's .003-.004 under loaded round measures. You want a good amount of neck tension for this process.
-Seat the bullet 'way long.
-Polish the bullet with some 0000 steel wool.
-Make sure the chamber/barrel are clean and dry. Lube the locking lugs.
-Chamber your dummy round. It will close hard, as the long seated bullet meets the rifling.
-Open the bolt and remove the round. If the bullet stays in the bore, just tap it out with a cleaning rod or wooden dowel.
-Examine the bullet and you'll see the marks from the rifling. If the bullet stayed in the bore, just resize the case, reseat it and repolish with 0000.
-Seat the bullet deeper by .010 and repeat. You'll see the marks starting to fade as you move the bullet further into the neck each time you change the seating depth. When the marks start to get noticably lighter, change the seating depth change to .005, as you're getting closer to 'zero'.
-When the marks just disappear, you're at the 'zero' or 'just touching' point for that bullet.
Record the seating stem length or base-to-ogive dimension and record that. Repeat for each bullet you're going to use.
Once you've done it a time or two, it will take you about 5 minutes to find your 'zero' with any new bullet.
Depending on neck tension but what most people call JAM is really .010 or more into the lands. I figure with .004 neck tension a person can pull a bullet from the lands that is at least .012 in.
To establish the 'zero' or 'just touching' point:
-Remove firing pin. assy from bolt.
-Full length size a case that's been fired in your chamber. If you are using a bushing die, use a bushing that's .003-.004 under loaded round measures. You want a good amount of neck tension for this process.
-Seat the bullet 'way long.
-Polish the bullet with some 0000 steel wool.
-Make sure the chamber/barrel are clean and dry. Lube the locking lugs.
-Chamber your dummy round. It will close hard, as the long seated bullet meets the rifling.
-Open the bolt and remove the round. If the bullet stays in the bore, just tap it out with a cleaning rod or wooden dowel.
-Examine the bullet and you'll see the marks from the rifling. If the bullet stayed in the bore, just resize the case, reseat it and repolish with 0000.
-Seat the bullet deeper by .010 and repeat. You'll see the marks starting to fade as you move the bullet further into the neck each time you change the seating depth. When the marks start to get noticably lighter, change the seating depth change to .005, as you're getting closer to 'zero'.
-When the marks just disappear, you're at the 'zero' or 'just touching' point for that bullet.
Record the seating stem length or base-to-ogive dimension and record that. Repeat for each bullet you're going to use.
Once you've done it a time or two, it will take you about 5 minutes to find your 'zero' with any new bullet.
Depending on neck tension but what most people call JAM is really .010 or more into the lands. I figure with .004 neck tension a person can pull a bullet from the lands that is at least .012 in.
- Location
- Somewhere on the Hudson Bay Coast
Step 1 - Seat a plain base bullet nose first into an empty cartridge case and chamber it in your rifle. Add steady slow pressure to the bolt handle to allow the bullet to slide gently back into the case as it engages the lands.
Step 2 - Take a bullet of your choice, and with firm steady pressure between your fingers push it nose first into the muzzle of your rifle, then with pressure on the bullet, turn it to scribe a line at the front edge of the bearing surface.
Step 3 - Use a micrometer to measure the length of the dummy cartridge from its head to the base of the bullet. If you adjust your seater stem to bring the scribed line on your bullet of choice to this length, the front edge of the bearing surface will meet the lands.
Step 4 - This technique provides a means by which you can easily calculate and adjust the seating depth to accommodate either a jump to, or a jam into the lands.
Step 2 - Take a bullet of your choice, and with firm steady pressure between your fingers push it nose first into the muzzle of your rifle, then with pressure on the bullet, turn it to scribe a line at the front edge of the bearing surface.
Step 3 - Use a micrometer to measure the length of the dummy cartridge from its head to the base of the bullet. If you adjust your seater stem to bring the scribed line on your bullet of choice to this length, the front edge of the bearing surface will meet the lands.
Step 4 - This technique provides a means by which you can easily calculate and adjust the seating depth to accommodate either a jump to, or a jam into the lands.
Seating Depth
Measureing COAL from the tip of a bullet will give you variations in length , bullet tips can be slightly deformed and inconsistant , just take a few bullets and measure their oal, you will find it will vary , The most accurate way is to measure off the bullet ogive as mentioned a couple of times in this post useing the Sinclair or Hornady comparator and a caliper, this tool measures off the bullet ogive at the point where the bullet contacts the rifleing and will give you consistant resuls , measureing chamber lenght with a Sinclair or Hornady chamber lenght tool and useing the comparator body will give you the best results, I use a Redding comp seating die to seat my bullets , with its Micrometer head it allows me to seat them right where i want them.
Measureing COAL from the tip of a bullet will give you variations in length , bullet tips can be slightly deformed and inconsistant , just take a few bullets and measure their oal, you will find it will vary , The most accurate way is to measure off the bullet ogive as mentioned a couple of times in this post useing the Sinclair or Hornady comparator and a caliper, this tool measures off the bullet ogive at the point where the bullet contacts the rifleing and will give you consistant resuls , measureing chamber lenght with a Sinclair or Hornady chamber lenght tool and useing the comparator body will give you the best results, I use a Redding comp seating die to seat my bullets , with its Micrometer head it allows me to seat them right where i want them.
This is true. But if, you only use one specific bullet to measure to the lands, and use that same specific bullet to set up your die, then the base to ogive dimension will be right and consistent. This method eliminates the variation in ogive to bullet tip dimension.
The problem with any system where a case grips a bullet AT ALL is that your seating depth measurement will be influenced by the tension on the case neck.
If you are careful, you can simply use a fire cased with the neck pinched slightly out or round with a bullet seated long and then closed into the chamber.
Try this several times to make sure you get a consistent measurement, and if your case is too loose, you may have to poke a a bullet out of the rifling, but I have extensively tested this against the Sinclair tool ad it is bang on.
If you are careful, you can simply use a fire cased with the neck pinched slightly out or round with a bullet seated long and then closed into the chamber.
Try this several times to make sure you get a consistent measurement, and if your case is too loose, you may have to poke a a bullet out of the rifling, but I have extensively tested this against the Sinclair tool ad it is bang on.
