7mm PRC Brass Headspace Measurement

[tdogg]

Can anyone post up the fired case headspace measurement for their 7mm PRC. I am seeing signs of pressure with factory Hornady ELD Match 180gr. I can't find anything wrong with the chamber but I lost about 6 pieces (out of 40) of brass due to overpressure breaking in my new rifle (Christensen Arms Ridgline FFT).

My fired cases measure 1.891 inches using the 0.420 inch comparator.

Thanks in advance.

Cheers,
Toby

 

[47WillysGuy]

 

[DaveTooley]

Hornady ammunition is known to be on the upper limits of pressure.
When you say "lost" what do you mean?

 

[tdogg]

Primer pockets blown out measured with a go/no go tool. I haven't mic'd the case heads but the primer pockets are trashed. Had heavy bolt lift and obviously should have stopped shooting.

Normally I'd wouldn't shoot factory ammo but you can't find 7mm PRC brass anywhere.

I have the Sammi specs but was not sure how much the brass would spring back post firing. I was hoping to crowd source headspace measurements to see if my rifles chamber was short (my fired cases are shorter than spec). I obviously don't have headspace gages to inspect this rifle.

Cheers,
Toby

 

[K22]

Actually, the term "fired case headspace" is a misnomer which I myself has used. What you are really measuring is a "datum line" point on the case. This measurement is used as a reference point to compare with the sized case to determine the amount of shoulder set back. In other words, these measurements are not universally absolute; only relative for the comparator / caliper used and rifle in which the case was fired.

First thing I would check is the rifle chamber headspace with go / non go gauges. A local gun smith for a nominal fee should be able to check this easily and quickly. The problem might be that since this a relatively new caliber, some gunsmiths may not have those gauges for that caliber. Call first.

Having factory ammo create that condition is troublesome. I wouldn't shoot anymore of that brand until I determine the root cause of the problem.

Also, a call to the rifle manufacturer might be worthwhile. In my opinion, this condition requires inspection by a professional to determine the root cause.

 

[tdogg]

Well whatever you want to call it, I would like to get fired brass measurements to compare. I understand it isn't going to match my rifle but if I get enough responses that their measurements are 0.005-0.010 inches (exaggeration) longer, I may wonder if my headspace on my rifle isn't set properly.

I would just purchase the go headspace gage and inspect it myself, rather than take it to a gunsmith. If I do suspect anything is wrong with the rifle I'd probably just send it back for warranty.

Cheers,
Toby

 

[JB10]

I would bet its a rifle issue. I saw same results with my 6.5 prc CA mesa. If you did not pay attention to the brass ( as a reloader does) might not have cought issue.

 

[M-61]

Well whatever you want to call it,

Wow. Not a nice response to someone who took the time to try to explain your problem and the correct nomenclature.

 

[tdogg]

No mal intent intended. I just don't think if I called it fired case datum line, anyone would know what data I'm after. After all this is the headspace dimension on the chamber and what they use to make go/no go gages.

Do you have a 7mm PRC fired case datum line measurement to contribute to my request for data?

Cheers,
Toby

 

[tdogg]

Well just to close out this thread since it was derailed.

I ordered both Go and Nogo headspace gages from Manson. It doesn't have a headspace issue. I can feel the gage with two layers of scotch tape so it is near the middle of the go/nogo range.

The factory Hornady Match 180 ELD OAL is not seated into the lands (about .075 off).

I pulled down the last box of the Match ammo and the average charge was about 72gr of what looks to be Staball HD. The bulk density was very near it but not exactly it so I can't be sure. If it is Staball HD about 3 gr over published max load based on Hodgdon's website. I dropped the charge down to 69gr and shot them without issue with mostly sub moa accuracy.

Now that I have about 55 pieces of brass, I will proceed with load development.

Cheers,
Toby

 

[SeabeeKen]

How hot was it outside when you shot the loads? Noticed you are in AZ. Hornady often uses powders that are not available to handloaders.

 

[Kermit in Va.]

A friend had the same problem

 

[tdogg]

I'm at 7200 ft elevation. It's been really mild here and when I shot these it was in the 60's.

Yeah it looks very similar to staball hd but obviously it could be any number of ways different.

Staball hd on left, unknown pull down on right:


Cheers,
Toby

 

[yooper24]

Hey all, new guy here looking for reloading info for a CA MESA 7 prc. I had same issues doing the suggested break in. About 30 out of 40 rnds of 175 eldx had ejector marks and some very stiff bolt lift. From what I see on threads, seems to be both the rifle and ammo. Although, I have been reloading the fired brass with h4831sc and 168 Barnes lrx and have had no trouble. My fired brass is approximately same after firing but longer after resize, can’t get a shoulder bump bc they already seem short.

 

[Coyotefurharvester]

Tdogg, since you pulled down a new rd. Knock out the primer and use the spent primer method to check bolt face to cartridge base clearance. If not excessive, than you will need to determine how much jump the factory ammo bullet has in your rifles chamber.

 

[tdogg]

Well just to close out this thread again. Sorry Yooper, I don't get on this forum often!

I purchased Go/NoGo gauges and the rifle is within spec.

There are two variants of 7PRC Hornady Match 180gr ammo out there (not sure about the eldx). One with ball powder that is at or exceeding SAAMI pressure and one that uses stick powder that is lower pressure. Hornady sent me a box of the stick powder variant but I haven't shot it yet (don't plan on it).

I found a hard carbon ring right at the case mouth that took some time to remove until I tried CLR. I now use CLR prior to scrub the chamber prior to cleaning the bore. The hard carbon ring starts to form within 20rds or so. I'm not sure what round count starts to show signs of pressure. I've been keeping the chamber clean.

So my issue was both ammo and gun related. I picked up some ADG brass and have a new cleaning regimen to keep the hard carbon at bay. Still trying to hone in a load for elk season.

Cheers,
Toby