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Nesikachad - a question?

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Unread 02-20-2009, 01:50 AM
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Location: Blackfoot, Idaho
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Nesikachad - a question?

Bob modifies the fire control so that the action no longer climbs the helical ramps in the receiver when the action goes into battery.

What the heck are "helical ramps"????

I didn't want to hijack the other thread........
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Unread 02-20-2009, 12:00 PM
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Re: Nesikachad - a question?

Bob is probably doing the same thing I'm doing with my "smooth action" fire control.

It's a neat "trick" to make a Remmy feel good.

Picture a spiral staircase, now picture two of them that begin exactly 180 degrees apart from one another.

That's your helical ramp.

If you pull a barrel from a bolt action receiver you'll see it right away. You have two flats that are the lug surfaces that the bolt lugs register on when the gun is in battery. The helical ramps are two inclined planes and they serve two purposes:

1. Camming action when the gun goes into battery

2. Clearance so that when the primary extraction cam on the back end of the receiver contacts the bolt handle to yank the case out of the chamber, the lugs on the bolt don't hit anything.

When you have a receiver that is "cock on opening" only (what it sounds like Bob is doing) the helical ramps just become clearance for extraction. They aren't pulling the bolt forward as it rotates into battery. Nesika actions are built this way.

Picture the cocking piece that attaches to the back of the firing pin. It has an angled piece that lays up against the sear of the trigger. If you lift the bolt you cock this piece to the rear and after it climbs the little cam in the back of the bolt it registers on a little divit machined right after the transition from ramp to flat. Now as you go to close the bolt it the angled part of the cocking piece contacts the sear of the trigger. It can't go anywhere. You continue to rotate the bolt and the lugs on the bolt contact the two helical ramps in the receiver. Just like any other ramp they start to climb up it. Something has to give and in this case it's the striker spring. It compresses more until it reaches the maximum amount and that is when the bolt lugs transition from the helical ramps to the lug flats on the receiver.

Now the action is in battery and ready to fire.

Make sense? A little more info than you probably wanted but what the hell? I'm bored right now. (Sand storms outside so what else am I going to do?)

Hope this helped.

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Unread 02-20-2009, 02:11 PM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
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Re: Nesikachad - a question?

Thanks for the reply and the detail.

That must be what "timing" is all about.

It's interesting to know that stuff.

"BoB" is the fictional fella in one of your recent post where you also explained something very well.

Hmmmmmm, keep the sand outta them skivies.
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