243 AI-Any Input?

[PathFinder]

Ordered the dies and rented the reamers, so it's happening. Will post some pictures and updates when the tools show up.

 

[pods8 (Rugged Stitching)]

You gonna give it a tweaked name like 243Aish?

 

[Castle Rock]

Better to just strike it out if it’s going to be non standard

 

[pods8 (Rugged Stitching)]

Better to just strike it out if it’s going to be non standard

I was trying to be puny

 

[PathFinder]

You gonna give it a tweaked name like 243Aish?

Ha I should probably, it will depend on how much deeper the chamber ends up being. This chamber feels like it may be a hair on the short side, so the AI no-go may still no-go.
I'm going to leave the chamber markings so there's no issue checking into South Africa with some 243 win headstamped brass.

 

[Castle Rock]

Consider carefully before you use an Ackley head space gauge.
I made that mistake once on my first 22/250 Ackley and the chamber ended up much too long for the currently available brass.
I would use your die formed brass to set the headspace and you’ll never have that problem, either with brass or dies being incompatible

 

[satchamo]

I’m gonna sound stupid here but you’re telling me you can just get a 243ai reamer and just hand ream a 243 to an AI??

 

[HandgunHTR]

Ha I should probably, it will depend on how much deeper the chamber ends up being. This chamber feels like it may be a hair on the short side, so the AI no-go may still no-go.
I'm going to leave the chamber markings so there's no issue checking into South Africa with some 243 win headstamped brass.

Just an FYI, but the AI no-go is just a regular go-gauge for the standard cartridge.

The reason for that is so that you get a slight crush fit on the shoulders when shooting standard factory ammo in the AI chamber, thereby preventing case head separation.

Since your chamber is going to be long, the gauges for the AI won't do you any good.

 

[PathFinder]

Got the chamber and throat cut last night. Tried to go slow and steady, stopping frequently to blow out the chamber, clean the reamer, and apply more cutting oil. Using a drill for the chamber and throating by hand, the whole job took under 2 hours.
It doesn't seem like the chamber is particularly long. I just watched closely until the old shoulder disappeared. Some once fired 243 brass from another rifle became the gauge for the chamber. They closed really tight in the uncut chamber, and still have some resistance in the improved chamber.
The dies are a Redding 3 die competition set that includes a micrometer seater, micrometer neck sizer, and body die. This will require using both the neck and body dies for every firing, but the micrometer neck sizer is really handy for setting the false shoulder. I have 10 of the once fired 243 brass that were necked up to 6.5, then down again with a false shoulder. The other brass are Alpha 260 brass. The false shoulder on those is much more visible on the longer 260 Remington neck. I may try to fire form one with Titegroup to check the chamber, if not I'll be fire forming with bullets this weekend.

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[Castle Rock]

Good stuff, let us know how it shoots.
You will probably find that neck sizing is fine for many rounds until you need to use the body die

 

[TaperPin]

Cool project - I enjoy seeing folks doing fun DIY projects.

 

[PathFinder]

Good stuff, let us know how it shoots.
You will probably find that neck sizing is fine for many rounds until you need to use the body die

I have 60 rounds loaded up with 39.5 grains Hybrid 100V (had it laying around) and 105 hybrids. Looking at how far the shoulder needs to move, especially on the Alpha 260 brass, I think you're right about not needing the body die for a couple firings. I'm planning to move to H1000 and an improved load after the fire forming, but the powder charge might need to be increased after one firing with that load. My plan is to start with 48 grains of H1000 and either a 115 DTAC or 112 MB. This Alpha brass better last a long time once that's done.
Neck clearance is currently .004", hopefully that's sufficient. The free bore cut with the throater looks a little rough, but we'll see how it shoots.

 

[PathFinder]

Fire formed 110 brass with the load above on Saturday. Not quite sure what to think about how it shot. The first 10 with mixed head stamp brass were all over. The next 50 with 39.5 grains of H100V in Alpha brass sent almost every shot into 1.25". The last 50 were 2"+ with 40.5 grains, but the scope slipped in the rings and the front action screw was a little under 65 in/lb when I checked it.
Fire forming results were good. The first Winchester brass ruptured the shoulder, after that everything turned out nicely. The 39.5 load was adequate, 40.5 was a little hot. Shoulders appear to be fully formed. Chambering them again results in no resistance, but a mild click which is surprising. Ran them through the body die and the click is gone.
The Redding neck sizer was only able to size about half the neck, which was strange. Ended up sizing the necks in a 6UM die for now.
The chamber doesn't seem to be too long. I was a little worried about it being too long and necks ending up short, but they actually look longer than standard 243 necks.
Next step is load development with H1000. Probably going to try both 112 MB and 115 DTAC with 49-50 grains of powder.

Formed Alpha case next to once fired Federal .243 case. The formed neck is at least as long as the standard. Lots of volume to be gained in the 243

Formed Alpha brass vs before forming.

The group .5 mil below the dot are the last 50 Alpha brass with 40.5 H100V. It seemed like something went a little weird here, the scope had slipped in the Sportsmatch rings and the front action screw had dropped to around 55 in/lb from 65.

The first 50 Alpha brass with 39.5 H100V/105 Berger Hybrid. This was going fairly quick and cooling every 10 rounds.

First 10 with the Alpha brass

L-R: Formed Winchester or Federal brass, very 1st Winchester brass that blew out, formed Alpha brass

 

[BigDog00]

Any velocity data?

 

[PathFinder]

Any velocity data?

Not yet. I'll get some with the H1000 loads this weekend

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[wind gypsy]

Thanks for sharing, cool stuff.

I'm not familiar with the micrometer neck sizers but that sounds odd. When I've needed a little more neck sizing i've found the 20-some dollars it costs for a lee collet die to be a decent solution. I order an undersized mandrel though to get a little more neck tension.

 

[TxLite]

Using a drill for the chamber

Seems tough to keep it straight. I feel like I’d definitely mess this up