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measuring jam and jump?

 
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  #1  
Old 10-05-2011, 11:38 PM
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measuring jam and jump?

i am new to this and i am am wondering how you measure your jam and jump off the lands and what tools i will require. Thanks Tyler
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Old 10-06-2011, 05:57 AM
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Location: N.T. Australia
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Re: measuring jam and jump?

Hi Tyler,

May I suggest you take a look at this nice little tool:

Hornady Manufacturing Company :: Reloading :: Metallic Reloading :: Tools & Gauges :: Lock-N-Load Gauges-Formerly Stoney Point :: OAL Gauges & Modified Cases :: OAL Gauges :: Lock-N-LoadŽ OAL Gauge Straight 1Each



It has special brass cases you screw onto the tool and take measurements from it:



I think you will find this will help you a lot if you are not fully experienced.

Cheers.

Quote:
Originally Posted by 3rivers View Post
i am new to this and i am am wondering how you measure your jam and jump off the lands and what tools i will require. Thanks Tyler
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Old 10-06-2011, 07:05 AM
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Re: measuring jam and jump?

Good timing!

Go here: When a jump is jam! Or not?
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Old 10-06-2011, 12:52 PM
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Re: measuring jam and jump?

Thank you guys very much this should help.
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Old 10-06-2011, 10:11 PM
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Location: Sioux Lookout, Ontario
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Re: measuring jam and jump?

I take a fired case, pop out the primer, cut a slit in the neck and insert a bullet so that the bullet can be pushed in and out of the case. Now I insert the case, close the bolt slowly, then extract the case being careful and guiding with a finger so that the bullet does not drag along the side of the action. Then I measure the overall legnth and do this about 10 times to get an average.

Some say that doing this will actually jam the bullet a small amount, and they are probably right. But I find that by doing this, the amount the bullet is jamed is very small, maybe 1-3 thou. Either way, it gives you a base line which is what you want. Use this base line as your "distance to lands" and start seating there as your working up your load. Since you are working up your load you will see pressure signs sooner when a bullet is jamed into the lands versus jumping to the lands, and once you find your best powder weight, you will most likly be moving your bullet further away from the lands to get the tightest group.

The bullet I use to find the "distance to lands" never gets loaded into a live cartridge. I save this bullet and use it with the case with the slit in the neck to set up my seating die. I basicially put the bullet and case into the press, seat the bullet, measure, adjust the bullet seating die, pull bullet out of case a bit, seat again untill I get the desired depth I want. You want to keep this bullet seperate because the legnth of bullets even from the same box will be different which will give you different COAL's. Clear as mud?
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