Some cases hard to chamber, most aren't- what's going on?

[mattri]

6mm BR.

New, unfired cases chambered easily. All new cases were trimmed for uniformity and chamfered before loading.

After initial firing cases were sized with Redding die to resize neck and bump the shoulder .002", cases were sized, trimmed and chamfered.

On 2nd firing I noticed that the vast majority of cases chambered properly, but a few seemed "tight", the bolt closed ok but seemed to have an undue amount of friction.

It was only on a few cases, thought maybe it was me. Fired all cases and formed/trimmed/chamfered again.

This time I seemed to notice some slight extraction marks on a few cases, just a hint of a rubbed look. Load is well below max, only saw this on a few cases.

Sized/trimmed/chamfered again, rechecked all measurements- COL, length to shoulder, inner and outer neck diameter, body diameter, rim thickness- everything matched.

Chambered all the empty cases, a few were definitely tight. Triple checked measurements, then completely blacked out a couple of cases that chambered well, and a couple that were tight.

After extraction the only difference I could see was an extraction rub on the ones that were tight. If the overall length and length to shoulder bump are the same, where is this coming from?

 

[Terry]

Contact issues with brass comes from two areas, the shoulder and the base. When we bump the shoulder all of the pieces do not respond the same. Some don't take the bump as well. We can sort them into groups or bump them all just a little more.

If the base expands it can be resized with a 45ACP die or a .308 Small Base die.

 

[SmokinJoe]

Also, if you are getting an inconsistent bump, annealing usually fixes that problem. If the base is swelling, the load may be a little too stout, or sometimes the chamber/brass dimensional interaction isn't working just right. In that case you may want to polish the back of the chamber out a little, maybe a thousandth & try it again.

 

[LHSmith]

After initial firing cases were sized with Redding die to resize neck

Neck sizing strikes again. Neck sizing will work if you play with loads that you see listed as "starting loads" in the reload manuals and never venture from there. But how many on this site are satisfied in squib load land....especially with a 6 BR. All reloading die manufacturers should be banned from producing NS dies, and forced to exchange existing neck dies for FL sizing dies.
Bold close hard on chambering = more bump / bolt opens hard at top of lift = case head expansion

 

[mattri]

If the shoulders aren't being bumped back the same wouldn't that show up in the measurement?

 

[fguffey]

Measurements: There is no shortage of barrels around here. When out and looking for parts I find take off barrels complete with chambers. I think nothing of purchasing a worn out barrel? for the chamber. I have new barrels with chambers, a chamber is a gage. Chamber gages are available, to me chamber gages are tight Wilson case gages.

I do not use my thumb to measure case head protrusion, it is possible for the person that cuts the chamber to make a chamber gage with the same case head protrusion.

F. Guffey

 

[LHSmith]

Calipers are accurate to +/- 0.001" in skilled hands ....no matter what the resolution printed on them.

 

[Eddie Harren]

+1 on LHSmith

 

[Ledd Slinger]

are you getting this issue while chambering empty cases? If loaded rounds and seating bullets close to lands, check bullet base to ogive length. Perhaps some bullets are jamming when others are not.

Could have some thick rims that are out of spec on some of the cases as well. When the bolt cams over, the thick rims may be making it hard for the extractor to get over the rim. Just some thoughts...

 

[mattri]

Yes empty cases, possible on the rims but those measure the same too, very strange.

 

[Ledd Slinger]

Are you sure you measured the thickness? Not much play between the bolt face and extractor claw. If they are a couple thou thick, you could try trimming you ejector spring to get less outward force on the case making it a bit to make it easier for the extractor to grab the rim.

What about rim width? excessive width on a rim can cause trouble for an extractor as well.

 

[Ledd Slinger]

If possible, posting pictures of the extraction marks on the cases in question would definitely help address the situation.

You are talking about "extractor" marks and not "ejector" marks correct?

 

[mattri]

Correct, the ejector has been removed. I'll try to post a pic later.

 

[dcali]

I've found that once fired brass won't always size consistently. It could be as simple as some of your cases are a bit longer than others. In my experience, it takes a couple firings to be able to consistently bump the shoulder within .001". I'm not entirely sure why that is, as it seems like the first firing of the brass is when it's softest, but it's what I've observed at times.

 

[6BRinNZ]

Mattri - the cases that are tight to chamber are they longest base to datum? Talking in terms of thousandths or smaller you will be getting slightly varied dimensions. Even if you have extremely hot loads not every case will expand and contract to exactly the same dimension and neither will it size to exactly the same - even slightly longer dwell times when FLS will alter the dimension.

What I suggest in order to try and understand further where the issue lies;

1./ Measure newly fired cases base to datum and find the longest
2./ Remove the firing pin from the bolt (and ejector) and chamber the longest case with the firing pin removed. If the bolt closes with the tiniest amount of resistance then this is most likely the longest dimension you can have. Prove this by finding a case that is shorter - base to datum and repeating. You should find the bolt closes with no resistance. If its very short the bolt will simply fall closed.
3./ If point 2 works out - then when you size cases you need to measure them to ensure non are longer than the recorded longest length and ideally are no longer than the next longest length where the bolt closes easily with no firing pin or extractor

If the bolt closes easily on all fired cases then most likely another .001" or so can be tolerated in base to datum. i.e. if you FLS there would be no need to push the shoulder back just yet.

If you have a FLS you can artificially create a longer base to datum on a fired case by not screwing it (the FLS die) down enough - basically the body gets sized a little and this pushes the shoulder forward .001" or so, these cases will often show up with a small amount of resistance in the test with firing pin and extractor moved. This can give you an idea of max base to datum measurement. I don't recommend this as a practice but can be useful to figure things out without firing off cases.

Good luck.

 

[mattri]

Base to datum is the same on cases that chamber easily and ones that are tight.

Ejector has been removed previously.

 

[fguffey]

New, unfired cases chambered easily. All new cases were trimmed for uniformity and chamfered before loading.

I have new unfired cases that will chamber. To determine why a case will not chamber all I am required to do is compare the case that will not chamber to the case that will. Then there is the chamber gage, something like a portable chamber.

There are tools that do not exist in reloading.

F. Guffey

 

[Erik Cortina]

Take a piece of brass that chambers tight and run it through a F/L size die. Start with die backed out. If brass still tight, turn die down a little more and try again. Repeat this process until brass chambers in your gun with no resistance. Run all your other brass through same die which is now set up. F/L size after every firing from now on.

 

[fguffey]

Start with die backed out.

I do that, I have one chamber that is long from the shoulder to the bolt face. It is .002" longer than a field reject chamber, instead of 30/06 cases I use 280 Remington cases, I adjust the die off the shell holder .014". I am the fan of cutting down on all that case travel. My cases are .014" longer than a minimum length/full length sized case and the chamber is .011" longer than a go-gage length chamber.

I know that scares most but the case head protrusion is less than the case head protrusion on a Mauser by at least .020". I do not use tired and shot out cases when forming.

F. Guffey

 

[mattri]

Thanks for all the replies.

I understand the thinking behind the "run it through a full length sizer" argument but this does not answer the basic question- where/what is the difference?

If sizing now is producing cases that have the same OAL, same neck ID and OD, same shoulder bump, same body diameter, same rim thickness etc, than what will running them through a full length sizer do?

When run through the full length sizer, theoretically the cases will be sized correctly and fit better correct?

Where is the difference? What measurement will be different?