7 PRC Resizing

[JM151]

I went to the range first thing this morning only to chamber a round and not fit. Ok cool tried 5 more and not even close to fitting. Ended up packing up and driving a hour back home.

I’m confused what’s going on here. I was sure my headspace was correct by doing the feel method. I have a BAT vesper action and removed the firing assembly and ejector from bolt. Came up with 1.897 would not fit. 1.8965 had some minor resistance and 1.896 was better. My .002 bump was determined to be 1.894.

Had loaded 20 rounds to test of 1x fired brass and shoulder bumped to 1.894. None would fit. Got back home and tried to bump them back to 1.892 still would not fit. I tried multiple out of this batch and none would fit. I stopped here.

I basically have 2 boxes from ADG that I have kept separate, both being 1x fired. From the other box I have resized all pieces with a goal of 1.894 and loaded up and shot 25 last week. I still have 25 of this box that is sized but shoulder bump ranges from 1.896 to 1.892 as I was trying to dial in my sizing die. To verify I don’t have an issue with my sizing die, i took the two that measured 1.896 and just seated a bullet in them. They both fit. Ok so now I wanted to test if something was going on with my sizing die. I took the remaining pieces and ran them through the sizing die and got them all to 1.894. Seated a bullet in a few and they all fit. This confirms I don’t have an issue with my sizing die. I take the other box and run them through die again to go from 1.894 to 1.892 and they will not fit in chamber.

I have eliminated any issues with sizing die and seating die. The only difference is two different boxes but they have the same lot number. What is going on? I’m tempted to throw away the box I can’t get to fit.

 

[JM151]

I took multiple measurements between ones that fit and don’t…..and they are the same.

 

[A382DWDZQ]

Your cases that don’t fit probably are not the same size as the ones that do, somewhere. Measure every aspect of one of each and find out where they are different. Neck diameter, loaded and unloaded (dummy rounds), body diameter, and base diameter, and full length of the case. Put the bullet comparator on the two dummy rounds, one from each box, and confirm the CBTO matches. Cover the one that does not fit in black sharpie and try and load it. See where the points of contact are. If you have a case gauge, plunk one of each in there and see if they are both showing the same length.

 

[JM151]

@A382DWDZQ I’m not finding any difference. I’ll have to try the sharpie.

 

[wapitibob]

Either the body dia is too large, shoulder is hitting the chamber, case length is long and hitting the end of the chamber, or the bullet is hitting the lands. Pull the bullet and eliminate each variable, one at a time.

 

[A382DWDZQ]

Just to confirm, with a sized case from each box, with no bullet, one will fit and one will not?

Also, can you describe how you are measuring your shoulder bump? Are you using a comparator or case gauge? What brand?

 

[A382DWDZQ]

Reason I ask is because SAAMI spec shows 1.904”-1.897” on the datum at 0.420” diameter, for the cartridge (1.900”-1.910” for the chamber). I’m guessing the comparator is 0.400” ID, which would be even further down the length of the case towards the neck. If the 0.400” point on the shoulder is 1.892”, then the datum is going to be 1.909”, which is just under the 1.910” max for the cartridge. 1.896” would be ~1.913”. Check my math, I could have this wrong, but seems like either the measurement is suspect or something is up with the chamber. If the chamber is at all tighter than max spec then .001” difference in the sizing would definitely affect it, and without a high grade comparator, I think that could occur pretty easily. A quick thing to try would be to just do a generous bump back with one of those that doesn’t fit. Could be that the two boxes have a slightly different shoulder profile.

 

[JM151]

Just to confirm, with a sized case from each box, with no bullet, one will fit and one will not?

Also, can you describe how you are measuring your shoulder bump? Are you using a comparator or case gauge? What brand?

That’s interesting part as well. They will all fit without the bullet. I have all the bullets .020” off the lands, so I shouldn’t be impacting anything. When I seat the bullet they will no longer fit from one but then will fit from the other box.

I’m using a Hornady comparator .420 insert.