Long throat question

[bkondeff]

New 7mm toy arrived and was all set to play with berger seating depth.

I have 180VLD, 168VLD, and 168 Hybrids. Due to 24" barrel, figure I should start with 168's.

When I go to see how far to touch the lands I see that I can't get more than .11" contact on bearing surface of bullet. Given the neck on the 7mm is only .26" long when trimmed, this means to get 100% contact, I will have .15" of jump.

I guess I will give it a try, but can't imagine I would expect to get lucky with this much jump. Thought I would post this before I chase my tail, in case someone had any ideas on what I should expect, or how to attack load development knowing this is the case.

 

[Edd]

I just had a 30 caliber barrel chambered for a .250" bullet jump. When I start load development, I don't intend to give any consideration to how close the bullet is to the lands.

 

[bkondeff]

Turns out it wasn't ridiculously long throated. The neck is tighter than my factory rifles and I can't get the Comparator Gauge with it's expanded neck to seat into chamber, which grossly misread the seating length of bullet.

So, how do you all use a gauge with a tight neck?

 

[.284]

Never ran into that yet. Any chance it's the shoulder of the modified case? Do you have a full length bushing die or body die to bump it before trying any thing else?

If not I guess you'll have to neck turn the modified case but I suspect you may need to size it down a bit so that it's tight on the turning mandrel? Try to fit it on the mandrel first to see if there is too much slop because it may become a little tight to push the bullet up into the lands afterwards unless you have a way to slightly expand it a again. Or inside neck turn it afterwards.

Other option would be to neck turn a case fairly thin, then load and fire it and thread it for the oal gauge.

Or load a bunch of dummies up at progressively longer oal's and measure them before and after chambering to see when closing the bolt pushes the bullet back into the case.

You could also carefully measure the difference in length between a cleaning rod that touches a closed bolt face and one that touches a jammed bullet but this would be my last choice as it's not generally very precise and would not give distance to the lands from the ogive. You would have to measure oal from the tip which is not the right way to measure seating depth.

That must be an awfully tight neck though?

 

[JeffVN]

+1 you need a tight neck modified case to use on your comparitor gauge. I make my own. I turn down one of the cases (2 or 3 thou smaller than the neck), shoot it, drill it out in 3 steps, then tap it with the proper thread and bingo tight neck comparitor gauge. You need to go back to the smith who built the rifle and find out the neck dimensions on your chamber, so you know what dimensions you need to put on your comparitor modified case.

JeffVN

 

[Wedgy]

Tap size to make your own is 5/16-36

good enough for doing brass
5 16 36 UNF HSS Plug Right Hand Tap 5 16 36 | eBay

 

[Engineering101]

Bergers pretty universally shoot good within 0.010" of the lands. I don't mess with any other seating depths unless they won't shoot there. Off hand I can't remember any situation where they didn't. Seems to me you could go with the 180 VLD which may let you get near the lands.

Since someone mentioned using the lands to seat a bullet to find the max COAL for that bullet I'll mention a refinement to that technique. Do the same thing but split the neck of the case with a hacksaw so you can adjust the seating depth with your hand. When chambered, the bullet will get pushed into the case by the rifling to the precise length of max COAL for that bullet. You can then pull the bullet by hand and use it for a different bullet. To get consistent results, you may have to play with the neck tension by resizing again to tighten or by bending the bullet to loosen. I have one of these cases made for every bullet I load. You can also use this case to set the bullet seater for the desired seating depth.

 

[barefooter56]

New 7mm toy arrived and was all set to play with berger seating depth.

I have 180VLD, 168VLD, and 168 Hybrids. Due to 24" barrel, figure I should start with 168's.

When I go to see how far to touch the lands I see that I can't get more than .11" contact on bearing surface of bullet. Given the neck on the 7mm is only .26" long when trimmed, this means to get 100% contact, I will have .15" of jump.

I guess I will give it a try, but can't imagine I would expect to get lucky with this much jump. Thought I would post this before I chase my tail, in case someone had any ideas on what I should expect, or how to attack load development knowing this is the case.

bkondeff,
Take a look at the "VLDs,making them shoot article in the tech string under the information tab on the main page. You will be surprised at how far we have jumped the VLD bullet to get it to shoot. On the Hybrid bullet the jump and being able to seat the bullet to magazine length should not be an issue. Our Hybrid bullets ( CLASSIC HUNTER) are very tolerant of jump due the combination secant (VLD) and Tangent( standard bullets) ogive design of the nose of the bullet. If you have any questions you can contact us here in this string or at [email protected]. Thanks for using our bullets!