284 Shehane woes

[lrgoodger]

First the good news. The new Krieger barrel was chambered with the same reamer that did my first two Bartlein 5R barrels. Both Bartlein barrels had reamer chatter and fired cases had five evenly spaced 'lobes'. The cases fired in the fired Krieger are perfectly round. I won't get into this any further since it has already been beat to death on these forums.

The current issue with the new barrel (I saw it with the Bartleins as well) is first time fired cases are not opening all the way at the mouth. I can push a bullet back in the case by hand, but it takes a lot of force (8 'pounds' on the K&M press gauge). Once the pressure ring is inside the mouth, the bullet slides in freely. I don't think this is a good situation. The necks seem to be opening enough to release the bullets cleanly and brass springback is re-closing the neck right at the tip about a half thou, but I still don't like it.

Necks were turned to .013" wall thickness (loaded rounds measured .310) and fired in a .313 neck chamber. Rounds were loaded with 52.0 - 53.5 grains H4350 and 180 grain JLKs.

Here is what I have checked;

1. No carbon ring. The barrel only has 43 rounds on it and it was squeaky clean when I fireformed the last 25 rounds.
2. Chamber length measures 2.171". Fired cases measure 2.160 - 2.166 (I wanted to get them formed before I trimmed).
3. The reamer measures .313 on the neck cutters right out to the tips. At first I thought the reamer neck might be tapered too much and was too tight at the tip. It is tapered, but only .314 to .313.

I am at a loss as to what is causing this. I did trim cases back to 2.151" with the Lapua brass in the bartlein barrels and that alleviated the problem. I don't like having 20 thou space off the tip of the neck in the chamber because it makes more room for the infamous carbon ring, but if I can't pin this down that is what I may have to do again with this new Norma brass.

Anyone have any ideas?

 

[Scott Harris]

.003 clearance between the loaded round and chamber neck is insufficient in my opinion. Also, measure your fired brass neck diameter....might be less than you assume it is. I think .004" clearance is the minimum you should have on 7mm and 30 cal cartridges. We use a .310 loaded round and a .317 chamber for our Shehane.

PS. what's wrong with .020+ clearance between the end of the neck and chamber? I think generous clearance is better than tight clearance with respect to both neck diameter and end of neck clearance.

 

[bsumoba]

^ +1

I run a .317 neck with a .312 loaded round.

Also, if this is once fired brass, you might want to fire it one or two more times. I noticed the same thing as you, but after two-three firings, the bullet goes straight through and if anything, hits the donut region. I load the bullet above the donut region so that is not so much of an issue for me

 

[lrgoodger]

I forgot to mention the fired brass neck diameter. It measures .312 except right at the tip where it is tight. It measures .310 at the tip. I can't figure what's causing it to do that.

Rather than get the chamber neck cut bigger, I'll just turn the necks down another thou on the brass. That might alleviate the problem but still doesn't tell me what's causing it. I'm the kind of guy who likes to pin down the exact cause when it HAS to be a physical dimension, somewhere, somehow.

The fact that trimming the neck back 20 thou solves the problem seems to indicate that the 3 thou clearance is not an issue anywhere except right at the tip of the neck, but you are right that more clearance would certainly make the problem go away. I've read a number of posts from 284 Shehane users who say they run .310 loaded with a .313 neck. I can't figure why that's not working in my gun.

Hmmmm. Bsumoba is running 5 thou clearance and seeing the same issue on the first firing. I wonder if blowing the case walls out 10 thou on that first firing is absorbing enough of the pressure to cause a wimpy neck expansion right at the tip once the bullet gets released?

 

[expiper]

OP...how do the groups on the target measure,,,that may tell you more than all the fuss about the belled case mouth,,,Roger

 

[lrgoodger]

OP...how do the groups on the target measure,,,that may tell you more than all the fuss about the belled case mouth,,,Roger

My worry was that insufficient bullet release was AFFECTING the groups. I don't put much stock in groups that are shot while blowing out the case walls. I have not seen the match performance while doing so that others speak of.

 

[bsumoba]

OP...how do the groups on the target measure,,,that may tell you more than all the fuss about the belled case mouth,,,Roger

I have not seen the match performance while doing so that others speak of.

I have excellent groupings and can actually score decent while fireforming if I can read the wind correctly. Every so often, I will get a weird shot that deviates from the norm, but I don't fret about it too much. I actually shoot 3x600 local matches with fireform loads quite a bit. That's how I fireform my brass and it works really well. 54gr of H4831SC does well for me.

I don't worry about dimensions really until about the 2nd firing. Then, I know it is fully formed to my chamber with a full power load and not a fireform load. I usually do not see a nice, sharp shoulder until after the 2nd firing anyway.

 

[dbramley]

Pin gauge the neck diameter in the barrel. Of the 10 reamers I have bought only 2 came to me with same specs as the print.

 

[Jay Christopherson]

+1 to dbramley

I know a shooter that was having issues with his 6.5-284, similar-ish to you. He eventually tracked it down to the end of the case being "crimped" on bolt close by the end of the chamber. He was 100% certain that he was trimming back to leave clearance (and I believed him), based on the reamer print. At the end of the day, he decided to verify and found that the reamer print for case length did not match what the reamer was actually cutting.

Trust, but verify. It would not surprise me if the case length on your reamer did not match the print (being shorter) and the ends of your cases are being pseudo-crimped on bolt close.

 

[lrgoodger]

Jay,

Too short a chamber was my first suspicion. As my original post says, I actually measured the chamber length and did not merely go by the print. The measurements tell me this is not the problem.

I turned down the next 25 Norma cases an additional thousandth and a half and loaded them up using the load that grouped best on the first 25. My results were much better this time (as the attached target attests) with a bullet slipping in without resistance on about four of them after firing. The others still had resistance but it was less than before. After trimming them all to the shortest length (the new cases vary by 7 thou), I suspect the situation will improve further.

These are the best five shot groups I have ever gotten from a 284 Shehane barrel while fireforming brass. These 300 yard groups are showing real promise. After a couple of fouler groups they came together pretty well with groups 2 & 3 having one flyer (which doesn't surprise me considering the horrible runout on the first loadings) and the last group is under 1/4 MOA. Hopefully it will do even better with fireformed brass and a final accuracy workup.

My thanks to everyone for their input.

PS - ES spreads were terrible. I'm looking into a new firing spring for the BAT. It has over 7000 rounds on it and I hear a new spring can help ES.

 

[Jay Christopherson]

Sorry, I didn't read your original post close enough. :-[

 

[noload]

My 284S has a .314 nk. my fired necks are .313. Loaded necks are .310-.3095. I couldn't understand why my necks at the mouth were .001 under chamber nk size. I just chalked it up to spring back, my gun will group well and I'm probably at the minimal neck clearance required for the 284She.

 

[bsumoba]

My 284S has a .314 nk. my fired necks are .313. Loaded necks are .310-.3095. I couldn't understand why my necks at the mouth were .001 under chamber nk size. I just chalked it up to spring back, my gun will group well and I'm probably at the minimal neck clearance required for the 284She.

yup...it is springback

 

[tac284]

I'm curious, how do you clean your brass and what tool do you use to chamfer the inside of your necks?

 

[lrgoodger]

I'm curious, how do you clean your brass and what tool do you use to chamfer the inside of your necks?

This was brand new Norma brass. I neck turn it new but I don't trim or chamfer it until after it is fireformed. I need to change that order because I don't get an even cut into the shoulder with different case lengths.