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Hammerhead
Reply with quote  #1 
Hey Guys,
I have a reamer from PTG and a go gauge for the same.
It is a 22-6mm. I have done one chamber with it with no problems on fire forming brass.
My question is I have read on here before that you need to leave the chamber a little short for a crush on the brass for fire forming, how much?
I have done a search and can't seem to find it here.
Anyone care to help me out on this one?

Thanks,
Tim
eskimo1
Reply with quote  #2 
Never done a AI but a couple of ppc chambers. What i do is that i use a case for a gauge and cut the chamber until i get a crush fit on the case. A couple of thousands crush should do it. You feel the crush when closing the bolt on the action.
WayneShaw
Reply with quote  #3 
An AI go-gauge is .004" shorter than the parent case go-gauge, IIRC.
Hammerhead
Reply with quote  #4 
WayneShaw,
I did use a AI go gauge and the bolt was stiff to close on the first chamber.
Am I good to go?

Tim
Preacher
Reply with quote  #5 
It shouldn't take a lot of pressure to close the bolt on a ackley chamber, but you should be able to feel it with the firing pin assembly out of the bolt.
You need to have that contact, but no more than that...
Ackman
Reply with quote  #6 
You want to feel pressure when the bolt closes. And really, on these things the amount of crush is up to you. Measure headspace on the brass you'll be using if you have a way to do it. You can make a gauge using about a 1" piece of barrel cut-off..... run the reamer in just enough for a neck and shoulder. Cut a lengthwise pie shaped window and you can also use it to see brass neck length in relation to the chamber.

As an example with some .243 brass. I measured a couple dozen each of Win., PMC, and Lapua cases.....from casehead/boltface to neck-shoulder junction. Each headstamp varied by .004"-.005" shortest case to longest. And the shortest of one headstamp was .009" less than the longest of another headstamp. I don't know where those measurements fall in relation to a go-gauge, but that's a pretty big gap. My .243AI chambers are set with up to .015" crush on Win. brass and it works beautifully.

The number that gets thrown around is .004" crush. But if that's off a headspace gauge and since brass can vary quite a bit, it could easily not be enough. You can use however much you want. It's between you and the gun. Crush is just the neck/shoulder radius of a new unformed case hitting that corner of the chamber. With even .015" crush - which sounds like a lot - bolt pressure isn't real heavy. Keep lube on the lugs and things will be fine.
tightneck
Reply with quote  #7 
Quote:
Originally Posted by Hammerhead
WayneShaw,
I did use a AI go gauge and the bolt was stiff to close on the first chamber.
Am I good to go?

Tim


yes
WayneShaw
Reply with quote  #8 
Ackman, you are correct in saying the crush is a variable. Brass thickness can directly play a part in the bolt feel. The -.004" measurement is an average I suppose that works most of the time.

But .004" isn't much with a brass case. I think the whole idea of Ackey's was to be able to run his reamer into an existing chamber and blow out a case. If that is true, you will never get a -.004" gauge to work. The best you can do is get the shoulder/neck junction "point" as one, no more, no less.

To use a -.004" go gauge on an existing chamber, you need to set the shoulder back some, re-time the barrel if it has sights, etc. That wasn't the original intent.

There are ways around all this .004" thing. What you really need is a way to keep the brass fully seated against the boltface while fireforming. You can jam a bullet real hard and fire it (with a lot of neck tension), or you could expand the neck up one caliber, then resize it back only enough to get your crush bolt close back.

That .004" long brass will never give any trouble, as long as you properly adjust your sizing die afterward. After all, the difference between a go and no-go is what .004 or .006?
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