Questions about neck tension, gas leakage and load selection.

[TQB]

Hi,


I'm back and still trying to learn a little more every time I reload.

Today's question is about neck tension.
My .308 Win loads with 39gn of N140 with a Scenar 185gn bullet are somewhat nice. But there is gas leakage to the neck, shoulder and body of the case. Average speed is around 2300 fps.
I’m aiming to get 0.0015'' of neck tension. If I try 0.0025'' of neck tension, could it solve the gas leakage problem? Will it affect speed, ES and SD a lot? Is it expectable to change the accuracy?

I will try to test of course, but range access is limited due to the pandemic.


In the photo there is a small load test near the load that looked more promising (39gn). All groups are 5 shot groups.
I will test the 38.8gn and 39.2gn again.


Thank You,

Tiago

 

[Straightshooter1]

Hi,


I'm back and still trying to learn a little more every time I reload.

Today's question is about neck tension.
My .308 Win loads with 39gn of N140 with a Scenar 185gn bullet are somewhat nice. But there is gas leakage to the neck, shoulder and body of the case. Average speed is around 2300 fps.
I’m aiming to get 0.0015'' of neck tension. If I try 0.0025'' of neck tension, could it solve the gas leakage problem? Will it affect speed, ES and SD a lot? Is it expectable to change the accuracy?

I will try to test of course, but range access is limited due to the pandemic.


In the photo there is a small load test near the load that looked more promising (39gn). All groups are 5 shot groups.
I will test the 38.8gn and 39.2gn again.


Thank You,

Tiago

What brass are you using? How many firings do they have?

As you are probably aware, whether gas leaks is dependent on how well the neck and shoulder seals the chamber. Softer necks seal off better than harder necks. This is just one of thing issues that annealing helps with. Neck thickness is also a factor that goes along with this as it takes more pressure to push thick necks against the chamber wall than thin necks. So, it's not just about neck tension. Also, if you have a light pressure load, it too can also contribute to not getting a good seal.

So, you need to look at these things and see which is involved . . . like maybe all of them???

 

[338 dude]

Sooty necks and cases are sometimes a sign of low pressure check the reloading manual of course if you were not somewhere near the top you may try going up a few tenths of a grain in powder

 

[LCazador]

What 338 dude says. You found a low node and have low pressure and you can only eliminate the soot on your cases by increasing the powder charge. I'd test carefully and see if there's a higher node for that powder. How full is the case? Two thousands neck tension is a good default tension for testing with a seating depth of ten thousands off. Do you know how to find your measurement to the lands?

 

[TQB]

What brass are you using? How many firings do they have?

As you are probably aware, whether gas leaks is dependent on how well the neck and shoulder seals the chamber. Softer necks seal off better than harder necks. This is just one of thing issues that annealing helps with. Neck thickness is also a factor that goes along with this as it takes more pressure to push thick necks against the chamber wall than thin necks. So, it's not just about neck tension. Also, if you have a light pressure load, it too can also contribute to not getting a good seal.

So, you need to look at these things and see which is involved . . . like maybe all of them???

The brass is Lapua, 4 times fired brass. I haven't annealed yet, burt I have bought a salt bath annealing kit.

 

[TQB]

What 338 dude says. You found a low node and have low pressure and you can only eliminate the soot on your cases by increasing the powder charge. I'd test carefully and see if there's a higher node for that powder. How full is the case? Two thousands neck tension is a good default tension for testing with a seating depth of ten thousands off. Do you know how to find your measurement to the lands?

I used a hornady comparator and after touching the lands, I backed out 0.020''.
The charge is on the low end. Maximum pressure at this load is 42396 psi (SAMI - 62000 psi; CIP - 60000psi) and load table is from 37.7 to 41.5 gn. The case has some space in it.

I will try to find another node on the higher end of the load window.

Thank You,
Tiago

 

[243winxb]

Maximum looks like 41.5 grs? If you cant drop a bullet into a fired case, the pressure is to low & brass is not expanding to seal.

 

[Straightshooter1]

The brass is Lapua, 4 times fired brass. I haven't annealed yet, burt I have bought a salt bath annealing kit.

As you're probably more aware now, a light-load/low-pressure load can lead to blowby as you've described. And with 4 firings, the neck and shoulder has certainly hardened some to contribute (though I wouldn't think much).

Since you're going to anneal using salt bath, you might find the following article of some interest:

Salt Bath Annealing - Does It Work? | Learn More | AMP

View the latest articles from AMP Annealing. Get tips and tricks from our R&D. Here we upload articles to provide your the best possible information on innovations in the annealing process.

www.ampannealing.com

And if you have some time to read the other articles along with that one, there's a lot you can learn from them that just may help you with you're reloading.

 

[TQB]

Continuing with my testing I re-tested the 38.8 and 39.2 grain loads. I did not change any other variables and experienced some blowy as well.

The results are in the picture below.

Regarding annealing, I am still not convinced by the AMP claims about salt bath annealing. I would like an independent view on the subject, with proper metallurgic testing as well. But I must confess I ordered a flame annealing machine as well. For educational purposes….



From what I could see from this test and the latter, I would assume the proper load should be 39.2 grains, right?

I will test 39.4 grains next time to see if I’m in the middle of the node or on one of the extremities.



Thank You,

Tiago