.243 Ackley fire forming case shoulders vs pressure signs

Tictac

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Sep 1, 2018
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#1
Hi all,

I could do with a bit of advice. I am struggling to get a decent shoulder on the fired cases in my .243 AI. Am I expecting too much? At standard .243 Winchester max load (41.9) the shoulders are very round .

I have now worked up to 43.8 grains under an 87g Berger. I'm getting light extractor marks only visible with close examination under magnification from 43.2 but at 43.8 I have a more obvious mark which I'm not comfortable with, a half moon shiny patch. I have a very angular shoulder at this level, no primer issues. Maybe bolt is a little heavier but not sure yet if there is much in it - I've only fired one case at this level. Does 43.8 sound too hot against book .243 win 41.9?

The chamber is cut tight, I can feel the empty case as I close the bolt, bumping the new case indicates I have .004 crush. I have sectioned a case and web looks good.

Barnard SM action
Bartlein 24" 1 in 8 barrel .274 neck cases turned to .2706
BR2 primers
Lapua brass
IMR 4350
.040 off the lands

I am happy my rounds are consistantly loaded but I do get the odd case that forms ok'ish shoulders at book max which is odd ???? I'm cleaning every 5 and the odd one that looks promising is at the end of the 5 shot string, maybe the extra pressure from a bit of fouling?

Not intersted in other forms of fire forming like COW.

Grateful for any pointers.

Paul
 
Last edited:

Holland375

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Oct 25, 2018
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#2
Cases need 2 to 3 firings to get to complete form to your chamber. Sometimes a change in powder burning rate can help. Some brass brands are harder than others and might take more firings and a charge used for fire forming will produce less velocity than that same charge when used after fired form. I would not fireform with charges that give you pressure signs, again the max charge for a normal 243 should be good for initial fireforming for the first 2 or even 3 firings.
Hopefully I didn't make it more confusing.
 

MarinePMI

Battery Operated Grunt
Jun 3, 2010
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#3
You could also back the charge down a bit, and seat the bullets long (into the lands). This will cause an early pressure spike, which should form the shoulders more fully, without going over pressure limits (since the spike is early, and evens out as the powder burns/expands down the length of the barrel). This is a method many wildcatters have been doing for years when they are radically changing a case's dimensions.

I'm not really sure that AI'nig a .243 gets you much improvement, but that is another discussion, and really boils down to personal preference (some folks just want one, and that's cool).
 

MarinePMI

Battery Operated Grunt
Jun 3, 2010
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#4
An after thought...is this once fired brass? Even if it's virgin brass, annealing the neck/shoulder will also allow a better fireforming. This is required for many wildcat cartridges that work harden the case in the forming process (which the AI doesn't have), but is worth considering. I've seen many brands of virgin brass that were not really annealed very well, so it could be a solution in your incomplete fire forming.
 

Holland375

New Hide Member
Oct 25, 2018
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#5
An after thought...is this once fired brass? Even if it's virgin brass, annealing the neck/shoulder will also allow a better fireforming. This is required for many wildcat cartridges that work harden the case in the forming process (which the AI doesn't have), but is worth considering. I've seen many brands of virgin brass that were not really annealed very well, so it could be a solution in your incomplete fire forming.
110% agreed with MarinePMI, that should have been included in my response, seat them against the lands and back of on the charge. Anyway you will be checking at the same time if your bullets like to be jammed or not and annealing is a most if it is not virgin brass.
 

Tictac

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Sep 1, 2018
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#6
Thanks all for the input.
It's virgin brass. I expanded it, neck turned, chamfered and loaded. I think neck tension was on the loose side so have dropped the charge back to the point I was seeing pressure signs and sized new virgin cases after turning with a .267 bushing giving me just over .003 grip. I'm hoping this extra initial spike will help much like being into the lands? I do not have an annealer yet, Im in the uk and getting an AMP is like hens teeth! It is head spaced off the neck shoulder junction, so the case is not moving forward. It's odd that I did get a few cases at lower loads that had a half decent shoulder. I don't want to be into the lands as it's going to leave only 3mm or so of the bullet in the case and I need to be able to eject an unfired case without dumping the powder. If it takes a couple of firings and I'm safe then thats fine. I'll see how the next batch perform.....
 
Jul 1, 2014
282
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Charlotte NC
#7
Get a battery powered drill and mount a 12mm socket to it. Set a small propane type burner up and make sure it is secure and can’t turn over. Get it to burn nice and blue and clean. Drop a case into the the socket, start the drill spinning, and insert the case into the flame near the shoulder area. Keep it in the flame for approximately four seconds. You may have to adjust this time a little, but not by much. This should give you a nice anneal. It is not as nice of a set up as a machine, and you have to actually manually do it, but it works pretty good, and will help get you by until you can pick up a machine. Good luck with your project! Hope this helps.
 
Oct 24, 2007
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#9
I’m going to take a wild guess. You might have lube in your chamber. That could be what’s giving you ejector marks before there is too much pressure. I form a fair number of improved rounds and don’t have to jam any of them but there are a couple that shoot better that way
 

Tictac

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Sep 1, 2018
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#10
Nope, no lube in chamber. Progressive marks as powder increases from just above book max in virgin brass. I've had some form no problem at 42.5. The ones that have partially formed I've reloaded with the same load and they will not form any further, very round shoulders. I'm going to try annealing as I can only think the brass is not consistent as everything else is.