243 ai dirty case problem

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Edouard M.

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Hi!

I’m not using this forum really often, but I thought that I would give it a try on that topic.

So basically, I’m currently developping a load recipe for my .243AI.
I’m using varget powder, as it is super weather stable. And I have a good amount on hands. I’m using Berger 69gr high bc FB bullets. The rifle like them!

I started using 40 grains of varget and working my way up. The most accurate load was with 42 grains. I was quite impressed with the .719" 3 shot group at 200y. I’ve continued to work my way up but the groups started to open slowly. Stopped at 43gr.

Everything is great with that load but one thing. The case gets partly covered with fouling. Well over the shoulder. I understand that it’s usually a light load symptom, or bad combinaison of slow powder and light bullet. But is it the case here? The same thing happened with every load I’ve tried allo the way up to 43 grains of powder.

Should I be worried? And what could be the cause or solution?

Thanks a lot!

Ed.
 
I'm still putting my money on too light a load for the application.
You may find another accuracy node above 43 grains of Varget
as well. I would be working up carefully.
Have you annealed your brass? Hard necks can fail to seal well.
Dave.
 
Thanks for the quick reply!

It’s true that I’ve stop at 43 grains before seeing any slight pressure sign. So it’s possible to go hotter, I was just being careful as there is a really little data with 243AI and varget. On other forums I’ve seen people talking about it but it was always between 39gr and 43gr.

I did not annealed yet, I have not invested on that yet, I’m mostly an hunter, i dont shoot enough I would say haha. But the brass I use right now are browning, 1 shot for fire forming and 2 shot as 243ai. Only 3 shot total. I used Fl sizing die and collet neck sizing die.
 
I don’t have access to a chronograph right now, but my plan was to borrow one at some point to have proper the ballistic charts.
 
Smudging would indicate lower pressures; probably lower velocities as well. Sort of defeats the purpose of an AI.
 
42 gr of Varget behind a 70 gr bullet is a max load in the 6mm Rem, which a 243 AI is very, very close to in case capacity. I think a chronograph would be a very helpful tool for you. If you are going to increase your load go carefully. Perhaps a slightly faster powder would help you. I will dig through my old load books, I had a 243 AI at one time (still have the barrel, used the receiver for something else). I seem to recall Win 760 as working well. - dan
 
That’s why I was a bit scared of going on higher charges without investigating more. I just cleaned the chamber, can’t be more clean now, so I hope that previous deposits were preventing the case to seal properly. Maybe that will solve the problem. If not, a chronograph will help me for sure. I will re check the neck sizing, just to make sure it’s to the chamber specs.

I hope I will be able to stick with varget, powder is hard to find haha. And I have good amount. But I’m super interested by your datas, it you find them at some point.
 
Not .243AI, but when I was developing loads for my .260, Varget produced superb accuracy - but I was getting pressure signs before I could get the velocity I needed for long range. Slower powders resulted in accuracy and velocity. Velocity was significantly higher than with Varget.
That is why I asked if you had a chronograph. I suspect that the same sort of thing might be happening.
 
Thanks, I will look for one asap. If I look at the scarce data there is with the varget, the speed should be around 3500 fps maybe more. It depends on a lot of factor. So yeah, chronograph!

I’ve stop before the pressure signs, as I’m suppaused to be close of max load, I wanted to investigate before going to far.
 
Edouard M. said:
Thanks, I will look for one asap. If I look at the scarce data there is with the varget, the speed should be around 3500 fps maybe more. It depends on a lot of factor. So yeah, chronograph!

I’ve stop before the pressure signs, as I’m suppaused to be close of max load, I wanted to investigate before going to far.
Click to expand...

Both 4064 and Win 748 are slightly faster, and both have given me good accuracy in similar sized cases. - dan
 
Edouard M. said:
Hi!

I’m not using this forum really often, but I thought that I would give it a try on that topic.

So basically, I’m currently developping a load recipe for my .243AI.
I’m using varget powder, as it is super weather stable. And I have a good amount on hands. I’m using Berger 69gr high bc FB bullets. The rifle like them!

I started using 40 grains of varget and working my way up. The most accurate load was with 42 grains. I was quite impressed with the .719" 3 shot group at 200y. I’ve continued to work my way up but the groups started to open slowly. Stopped at 43gr.

Everything is great with that load but one thing. The case gets partly covered with fouling. Well over the shoulder. I understand that it’s usually a light load symptom, or bad combinaison of slow powder and light bullet. But is it the case here? The same thing happened with every load I’ve tried allo the way up to 43 grains of powder.

Should I be worried? And what could be the cause or solution?

Thanks a lot!

Ed.
Click to expand...

I fully understand your cautious approach and agree with it.

It's difficult to give you an answer to your query without knowing the type of receiver you're rifle is using, so we can make some assumptions concerning strength.

Assuming it's a relatively modern, strong action, the first thing I would do with your present load is use a MAGNUM primer, such as the excellent CCI250, which will likely very slightly increase pressures and might be enough to seal the case against the chamber during firing.

IMHO, Varget is OK, if that's all you have on hand or have a large quantity of it, but it isn't ideal for the application as it's a bit to fast and has a short pressure curve, compared to slower powders such as IMR4350.

I tried several different powders in both the 6mm Remington as well as the 243WSSM, whose case capacity is just about identical to that of your 243AI.

I used magnum primers for more initial pressure to seal the case necks against the chamber but there was always a bit of black smudge, which never went onto the shoulders or sidewall, once a good load was developed. A combination of CCI250 primers, IMR 4350 powder and Lapua brass worked very well in the WSSM and still works well in the 6mmRem.

Varget actually gave me erratic velocities and pressures in both cases, which resulted in hohum accuracy, from rifles that are easily capable of 1/2 moa if I do my part.
 
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Hi!

So I did my homeworks, I bought a chronograph and did some testing. Everyone was right saying that 42gr was probably a light load for my rifle. Effectively, i’ve started back at 43gr where i’ve stopped earlier. I was doing 2 shots for every load, moving with .3 grains increments. Starting to see some light faint cratering at 46gr.

So my new load for this rifle is 45.7gr of varget propelling a Berger 69gr fb bullet. Browning brass with CCI BR2 primers. Grouping at around .4 moa. 3720 fps at muzzle, highest speed was 3724 and the lowest was 3713. Quite steady. I’m starting to like that rifle a lot. We will see how it will work in a hunting situation haha.

The fouling problem on the case is solved, case stays clean, only the neck is dirty.

Thanks a lot for your tips!







tiriaq said:
Not .243AI, but when I was developing loads for my .260, Varget produced superb accuracy - but I was getting pressure signs before I could get the velocity I needed for long range. Slower powders resulted in accuracy and velocity. Velocity was significantly higher than with Varget.
That is why I asked if you had a chronograph. I suspect that the same sort of thing might be happening.
Click to expand...
 
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