20 Vartarg bullet seating depth issue?

[shaun1826]

I’ve just started making up dummy rounds to find my Jam length in a new 20 VT build. The reamer was spec’d to have a 0.010 freebore. I set the bullets long and kept using trial and error chambering the dummy rounds until I had no resistance closing the bolt. Then I loaded another dummy round .020 longer, chambered the round and let the chamber seat the bullet to find the Jam length. So I feel very confident that these seating depths as shown in the pictures are at the Jam length. I even loaded +.005 longer than this jam length and got a 0.005 bullet setback when chambering. And loaded -0.002 less than the Jam length and got no resistance or set back.

So what I’m finding is the bullets have to be loaded much longer than I expected in order to reach the Jam. Has anyone ran across this with their 20 VT? With the 40 grain Bibs, I’ll have to have a 0.100 jump in order to get 0.120 of the bearing surface in the neck. I’m not as worried about the 40 vmax, but even it only has about 0.1035 bearing surface in the neck loaded to Jam.

Thoughts?

 

[Hotshot]

Why do you think that you should jam them?

 

[shaun1826]

I won’t load to Jam, just finding the length that I will start working back from. I usually jump 0.020 off the jam length to do load development.

 

[rickiesrevenge]

This is why lots of people recommend 0fb reamers for 17s and 20s. But you'll be ok jumping them.

 

[Rick300]

I had the same issue with the 40 BIBs. Still shot great though.

 

[shaun1826]

I had the same issue with the 40 BIBs. Still shot great though.

Thank you. This was the confirmation I was looking for. My first thought was something was off with my reamer, but maybe thats just how the Bibs are. So I’m guessing you had at least 0.100 jump with the Bibs? Do you know about how much bullet bearing surface you had in the neck?

 

[Rick300]

I haven't shot them for a while but if I remember correctly I was at .080 jump and shot in the .3's

 

[Gabe22BR]

I shoot the 32 Vmax-.025” jump
Plenty to hold the bullet

 

[L.Sherm]

This is why lots of people recommend 0fb reamers for 17s and 20s. But you'll be ok jumping them.

Don't understand why anybody wants any freebore in a 20 cal. Even with .050 in my 20BRA and the 55's i could get away with atleast .025 instead of .050

 

[TheCZKid]

Find out how your chamber is reamed, to verify (1) how long can your case be in overall length - meaning you might be able to have a longer neck on your cases with no issue, thus adding more bearing surface on the seated bullets, and (2) how much freebore you actually have.

I'm somewhat new to 20 Vartarg, but a friend with a few Coopers has .080" jump with Nosler 32 BT, and has no problem staying in the 2's for groups. You might be just fine with more jump, testing recommended.

 

[shaun1826]

This is my reamer print.

 

[L.Sherm]

View attachment 1416676
This is my reamer print.

Looks like yours is set up for Lapua brass

 

[RGRobinett]

Find out how your chamber is reamed, to verify (1) how long can your case be in overall length - meaning you might be able to have a longer neck on your cases with no issue, thus adding more bearing surface on the seated bullets, and (2) how much freebore you actually have.

I'm somewhat new to 20 Vartarg, but a friend with a few Coopers has .080" jump with Nosler 32 BT, and has no problem staying in the 2's for groups. You might be just fine with more jump, testing recommended.

Without intent to either argue, or, punish, I submit the following, hoping that someone will find it instructive and helpful prior to ordering their own reamer(s). Know and understand the tolerances.

This, I forgot to bring into our conversation, and is a good point. The LAPUA [.221 FireBall] brass in my stash is 1.195" long, while the Nosler is 1.391" long. Of course, these dimensions do no "improve" your situation, but they do highlight why it is important to know and understand [reamer] tolerances: for a new reamer, I always measure the actual OAL when head-spaced on a "just closes" 'GO" gauge.

Back to the tolerances: angularity is +/- 1/4 degree (15 Min.), so, a particular reamer, spece'd at 1.5 Deg., would still be within tolerance anywhere between 1.25 deg., and 1.75 Deg., or, 30 minutes!! A sppecified 1.75 Deg., and a 1.5Deg. could be exactly the same, or, the latter could be steeper than the former, or, they could be a whopping 3/4 deg apart . . . and still be within manufactures specs.

This only highlights why, unless the chambers are cut using the same reamer, discussing/comparing "seating-depth" is useless - "it is what it is". Not to argue, but rather to illustrate: note, the attached Henriksen .204 RUGER reamer print, featuring .060" free-bore. The accompanying pic, displays a 40 Gr. BIB BT next a loaded round, which features a 40 GR. BIB BT seated [presumably] 0.010" short of kissing a NEW leade, via the .204 RUGER Henriksen reamer.

Admitting that comparing from the me'plat is, not a good practice - the comparison should be based upon the distance from the seater-stem:nose contact point (visible on the M-C seated bullet nose), to the shankgive tangent point of the - i snapped this pic for illustration.
Bottom line: we gotta/otta know what we have . . . This stuff can, "drive ya crazy" . . .RG

 

[AlNyhus]

shaun1826: Have you checked your chamber length with a chamber length gauge? -Al

 

[shaun1826]

shaun1826: Have you checked your chamber length with a chamber length gauge? -Al

I have not. That is a good suggestion. I’ll have to order a 20 cal.

 

[AlNyhus]

I have not. That is a good suggestion. I’ll have to order a 20 cal.

While it won't change the geometry, you may find some extra neck length to work with.

I'd also suggest that you find the 'touch point' by moving the bullet back until the rifling marks just disappear. The 'T.P.' is all we really need to know for a particular bullet, anyway. Try that and see what the difference is, ok?

Good shootin' -Al

 

[Coyotefurharvester]

I run the BIB bullet in a 20p and 204r, both magazine fed. Both jumping more than RG's photos show. For me they have been very tolerant of jump.

 

[HillbillyLongRifle]

I run the Bib 40s in several of my rifles. 20 Vartarg, 20 TACs, and 20 PPCs! They shoot very well with zero freebore or .075 freebore. They also kill Coyotes like Lightning! Dont worry about the jump but i do prefer my zero freebores in the 20 calibers!

 

[shaun1826]

Preliminary 5 shot group seating depth test after running a ladder test.

 

[Coyotefurharvester]

Are those lengths with some sort of body or block on the caliper jaws? I thought a 20vt was shorter, like 1.825 with a vmax bullet(coal).