couple questions about jam to jump

[Link]

This is in my 30 br 18t, 118 gr Bibs. I am doing load workup to see if I can get it more accurate. After doing a ladder I want to do AOL. I really don't want to jam but start with lil square rifling marks on the ogive and work out, my question is how far to work out and at what increments .005? Do you think I would miss something if I don't try jam ? thanks Link

 

[Toby Bradshaw]

This is in my 30 br 18t, 118 gr Bibs. I am doing load workup to see if I can get it more accurate. After doing a ladder I want to do AOL. I really don't want to jam but start with lil square rifling marks on the ogive and work out, my question is how far to work out and at what increments .005? Do you think I would miss something if I don't try jam ? thanks Link

I'm not sure why you don't want to start at the jam length. But at any rate, my 30BR shoots best 0.012"-0.015" off the jam using a bushing 0.003" smaller than the loaded round diameter, and moving seating depth in increments of 0.005" is fine.

 

[Zero333]

I have no experience with the 30br nor the 118bib's, but you can usually be in the lands a little with out the bullet being jammed.

I have and had plenty of barrels where I needed to go 0.025"+ into the lands to feel the bullet jamming.

I've found you can easily find a node jumping the bullet, but if jumping the bullet doesn't give you satisfactory results you can start playing with the COAL in the lands.

Sometimes I take a middle of the road charge weight and do the COAL test first. This way I'm not gonna find myself over pressure if the best accuracy is found near or at max charge weight and then I begin the OAL testing.

I've also tested charge weight before OAL but had the bullets in the lands 0.007", then once I had my optimal charge weight I had no problems playing around with the OAL in the lands.

I hope someone with the 30br and 118bib's chimes in and gives you more relevant experience for your scenario.

 

[T-shooter]

I went from .005" to .030" in .005" increments and the rifle liked .025" so I quit" Shot 5 each as a test round robin. Look to see if and when the groups tighten up. Two things are happening. Less jump can cause more pressure especially if it's jammed but the farther you seat the bullet out, case volume will increase and relieve it to some degree. Watch your brass and for any pressure signs. Be safe!

 

[vahena]

I can only tell you what works for me, I am no expert by any means but I called Randy Robinett which in my option is like the godfather of the 30 Br. He told me to load almost to the top of the case about 1/8" below for me that is 34.8 of H4198 and somewhere around .015 jam.
I first started at 33.0 grs and worked up from there, then I did a seating test and found that a hard jam {bolt seated jam} worked the best in my rifle. You would thing that would be overpresure but bolt lift and primers are as they should be and confirmed by Randy. she shoots the same exact 5 shot grouping everytime in a 3 clover leaf and that drives me crazy but I cant seem to change it as I have tried everything from powder charge to seating. Although my 5 shot groups at 100 yds. are from .110 to .204 always within that area and as Randy says, I would be happy with that and I am but I want them all in one hole...LOL...
My best advice is to call Randy Robinett he is a great guy. Good luck

 

[Toby Bradshaw]

You could try a charge/seating depth test of the sort that Tony Boyer uses. Here's one for my 30BR (115gr Berger FBs -- saving my BIBs for matches!). On each target below you can see the charge weight in gr of H4198, and seating depth in the length of the Wilson seater stem. 1.737" is the jam length with a bushing 0.003" smaller than the loaded round diameter. The Wilson stem is 1.754" when the bullet is just touching the lands. 100yd, 3-shot groups.

 

[Link]

Thanks for the replies.
One reason for me wanting to jump is my rifle has a long throat when I jam there is less than .050 of bullet shank in the neck. I have tried 34.8 touching and I have to work my brass to much. After a few firings I get hard bolt lift and run the case through a 306 sizing die to cure it.
So I would rather shoot the bottom node.
thanks again Link

 

[dkhunt14]

Thanks for the replies.
One reason for me wanting to jump is my rifle has a long throat when I jam there is less than .050 of bullet shank in the neck. I have tried 34.8 touching and I have to work my brass to much. After a few firings I get hard bolt lift and run the case through a 306 sizing die to cure it.
So I would rather shoot the bottom node.
thanks again Link

If the bolt lift just gets tight at the top alias bolt click. I bet your Reamer doesn't match your die. The die is either too big or the Reamer is too small. Matt

 

[Link]

If the bolt lift just gets tight at the top alias bolt click. I bet your Reamer doesn't match your die. The die is either too big or the Reamer is too small. Matt

Yes I should have had it re chambered when I found it was off.

 

[.22gongzilla]

I'm not familiar with the 'bibs' profile but jamming hard with any degree of consistency requires consistent neck tension, I found that out. In lieu of jamming these days I just use neck tension that's tight enough for a good smooch on the lands when the rounds are chambered.