Sizing die adjustment

[Sebrock]

that would depend on the chamber wouldnt it?

exactly - I had an oversized 6.5 creedmoor chamber and it took the Lapua brass five firings before I had to bump the shoulder. Until then all I did was size the body. Too big for my own taste, so I my next build was only .002 more than the go gauge and would grow to the chamber much quicker.

 

[BoydAllen]

IMO you want to know what the datum to head measurement is of a fired case is, preferably one that is tight and set your bump in relation to that. I have seen cases where the die was too large for the chamber and by the time the fellow got the feel that he wanted, he had bumped the shoulder back too far. If you find yourself in that situation, you need a different die. One of the common mistakes that reloaders can make is to bump the shoulder of a once fired case. It usually takes more than one firing to bring a case to the point where it has reached its maximum datum to head dimension so bumping the shoulder of a once fired case just adds additional clearance that serves no purpose. For that situation, I recommend adjusting the die so that the sized datum to head dimension is the same as the once fired case, and then try it in the rifle. Usually that works just fine. Be sure to wipe all the lube off of any case you chamber and reapply it if you need to size it a little more. When measuring a fired case you need to either remove the fired primer first, or use your primer seating tool to seat the fired primer deep in the pocket so that it will not influence the measurement. For factory chambers and off the shelf dies, one does not usually run into the mismatch that I mentioned, but for custom chambers it can happen, I have seen it.

 

[Sebrock]

IMO you want to know what the datum to head measurement is of a fired case is, preferably one that is tight and set your bump in relation to that. I have seen cases where the die was too large for the chamber and by the time the fellow got the feel that he wanted, he had bumped the shoulder back too far. If you find yourself in that situation, you need a different die. One of the common mistakes that reloaders can make is to bump the shoulder of a once fired case. It usually takes more than one firing to bring a case to the point where it has reached its maximum datum to head dimension so bumping the shoulder of a once fired case just adds additional clearance that serves no purpose. For that situation, I recommend adjusting the die so that the sized datum to head dimension is the same as the once fired case, and then try it in the rifle. Usually that works just fine. Be sure to wipe all the lube off of any case you chamber and reapply it if you need to size it a little more. When measuring a fired case you need to either remove the fired primer first, or use your primer seating tool to seat the fired primer deep in the pocket so that it will not influence the measurement. For factory chambers and off the shelf dies, one does not usually run into the mismatch that I mentioned, but for custom chambers it can happen, I have seen it.

I agree with the method you describe 100%. I have learned that lesson the hard way - first sizing brass that didn't need to be sized and then using dies that were too long. However, I believe he wanted to know how to set the bump without measuring since he doesnt have a comparator. Thats why I suggested that first he makes sure that the case will no longer chamber and then potentially make very minute adjustments on the die until he moves the shoulder enough to chamber the round - crude but better than nothing. Personally I would invest in a pair of calipers and a comparator with the proper datum line because how you are suggesting will save him a ton of grief.

 

[BoydAllen]

I agree with the method you describe 100%. I have learned that lesson the hard way - first sizing brass that didn't need to be sized and then using dies that were too long. However, I believe he wanted to know how to set the bump without measuring since he doesnt have a comparator. Thats why I suggested that first he makes sure that the case will no longer chamber and then potentially make very minute adjustments on the die until he moves the shoulder enough to chamber the round - crude but better than nothing. Personally I would invest in a pair of calipers and a comparator with the proper datum line because how you are suggesting will save him a ton of grief.

One thing that I forgot to mention and something that many apparently fail to check, is the amount that a die reduces the body diameter of a fired case. I do that by carefully (takes some practice using the tips of caliper jaws) measuring the before and after sizing diameter of the shoulder, and at the base )use the wider part of the jaws) , slightly above the extractor groove, at the point of maximum diameter. If a die reduces a case's body diameter then adjustment by feel, carefully done, is probably OK in a pinch, but you can never really know how much you are bumping the shoulder without measuring. This becomes more important for people who shoot a lot, whose cases see a lot of firings. For a guy that just loads to hunt game, not as much. For that, I suggest removing the sriker assembly from the bolt and testing each round in the rifle for fit so that you do not get a surprise on a hunt.

 

[divingin]

i see— looking at that gauge a little more i guess the marks are .001 and it shows nogo at
.010. it would be interesting to me what it shows a nogo gauge measurement. that wouldnt really matter to me though. this gage may be more consistent than i am with calipers- that would be its value to me.

It looks a lot quicker and easier than assembling the normal caliper mounted gauge every time you want to measure a case. Plus less of the spinning/wiggling to get the smallest measurement. I'm going to have to put that on my short list.

 

[JFrank]

The goal is to chamber freely before and after ignition.