COL testloads with chronograph

[BJung]

I am aware of using a chronograph to confirm MV variations between powder charges for a ladder test but what about COL. Can this same method apply or do I need to just make 4-5 test loads with varying COL? I want to save time and components. I'm testing Barnes TTSX bullets and not only are they rare like other bullets but there are less bullets per box and they are more expensive.

 

[lordpaxman]

I’m not exactly sure what you’re asking, but changing COL will vary MV. The chrono will measure those changes, but bear in mind with small sample sizes the confidence of those numbers is low, and you may not see V differences you’re expecting.
If you change COL, you may need to adjust the charge slightly to stay in the V node. Barnes does have info on their website:
https://www.barnesbullets.com/load-data/
Good luck.

 

[JFrank]

I don't believe so, the changes in mv will be so small they will be lost in the white noise of chronographs. Conventional methods of establishing seating depths is probably the better way to approach the test.

Buy more bullets before you start because as soon as you get a tune you'll be out.

 

[Charlie98]

Minute changes may not necessarily affect velocity to a large degree, sometimes not even more than the SD of the initial loading, but it can change pressures... sometimes drastically. Much of it depends on the exact bullet/cartridge/powder combo you are loading, and how close you are to max, among other things.

The real answer is... if you are splitting hairs enough with your handloads where you are adjusting COL, it's going to cost you some components to put them over a chrono and put them on paper... there is no shortcut.

 

[Hugger-4641]

I did a 3rd Col test on my 30-06, .003 increments, from 0.010 off lands to 0.040. That's 40rds, so from a box of 50 Tssx, you'd have 10 left. You better buy another box.

 

[Charlie98]

I did a 3rd Col test on my 30-06, .003 increments, from 0.010 off lands to 0.040. That's 40rds, so from a box of 50 Tssx, you'd have 10 left. You better buy another box.

Question: Did you see anything significant in your load refinement?

 

[Lennyjoe]

I think you’ll see more evidence of COL variation in your grouping on target more than MV.

 

[rfwobbly]

This question does not have a yes or no answer. Some thoughts....

► While changing OAL will change the chamber pressure, it can also change the feed characteristics. When you pick an OAL, and then fire (for instance) 50 rounds in the course of "working up your load", then you have not only discovered the best load for your criteria, but you have also (at the same time) proved that it feeds well. Never under estimate the value of "feeding well".

► Sometimes competitive shooting may require a minimum velocity, and you may wish to add 2-4 additional PF as a safety factor. You might find that 3.7gr falls precisely on the requirement, while 3.8gr raises the velocity too much. In those cases, shortening the OAL by (for instance) 0.005" might give the required margin that you seek.

Shortening the OAL will raise the velocity, but it is not preferable over adding more powder. However, it is a viable tool and may sometimes be needed.
.

 

[Hugger-4641]

Question: Did you see anything significant in your load refinement?

Yes, I found 3 accurate nodes , one of them really narrow. If IRCC, 3.260 and 3.236 were good +/- .003, and 3.221 was narrow. No significant MV differences, but the sd was wide, about 40fps , so I wouldn't have noticed unless it was extreme. 40fps is fine for the reload equipment I have and I'm just working up hunting loads anyway.

 

[bluejay75]

It will also vary by powder. Some powders you cannot compress too much. Some powders will be over pressure slightly compressed. 3031, Varget and 4064 show pretty big velocity gains at the start of compression.

 

[Charlie98]

Yes, I found 3 accurate nodes

Interesting.

I've got a .308 Savage bolt gun I'm fixing to work up, I've not yet fooled with changes in bullet seating depth.

 

[Hugger-4641]

Interesting.

I've got a .308 Savage bolt gun I'm fixing to work up, I've not yet fooled with changes in bullet seating depth.

When I say accurate, let me clarify, the paper targets below are a couple of the "inaccurate" groups, which were still 1 1/2 to 2 1/2 Moa , the 12" reactive target is one of the "accurate" nodes that I am loading to now.