Keith Glasscock
Gold $$ Contributor
I developed a problem during a match today. I have never seen one like this, so I'm looking for ideas as to what to check next.
The barrel is a Krieger in 308 Win chambered with a custom reamer. It shoots the 200 grain hybrid quite well. I have ~1300 rounds through the barrel total, and it was cleaned last Thursday including a quick (light) scrub of Jb bore paste (I do this every 200-300 rounds) and a full treatment of copper cleaner and powder solvent (the Jb was actually done between powder and copper solvents). This is my normal cleaning regimen and it gets the barrel clean. On Friday, I fired 6 fouler rounds.
The barrel was off ~200 rounds ago for a re-crown, and my gunsmith gave the throat area and crown a borescope look and chamber cast while it was apart. At that time, I had very light fire cracking and a perfectly clean bore.
The load is one I have used for nearly the entire life of the barrel. It shoots good, solid groups at 2650 fps. I have never had any pressure signs with this load (until now), and it has fired the batch of brass in question at least 2 times prior. The powder is Varget, and even though it is supposed to be temp stable, I remove loaded rounds if they stay in the chamber more than 15 seconds. I've actually tested to see if heat-soaking caused problems or pressure with no problems encountered, but I've developed the habit of not firing rounds that have been cooking in the chamber.
Here is what happened: I was shooting a 2 day F/TR match and the rifle shot well the first day, except the vertical zero moved up ~3/4 - 1 MOA on the second relay of the day. Accuracy remained through that and the third relay without any problems or pressure signs. I even fired the third relay very fast due to conditions without any problem (and I got the barrel quite warm - a normal thing for me - in the process). Yesterday, I fired a total of 71 rounds (5 sighters+ 20, 2+20, 2+20)
This morning (I don't clean between days - never have), I got to the line and the rifle started doing its thing. The POI was still ~ 3/4 MOA higher than my normal 1k come-up despite being a little cooler outside (mid 60's this morning). After 4 sighters and ~ 9 rounds of competition, I started to notice slowly increasing bolt lift. By 15 competition rounds, the bolt lift was getting downright heavy, and the 19th and 20th rounds had gas escaping around the primer. (found that after the last shot). Looking at the cases in order of firing, the primers started out nice and round, then got flatter, then I started seeing some shininess to the case head, then shiny ejector marks, then blown primers.
I put that rifle away and borrowed a friend's rifle (what a great friend Bill is!) to shoot my last relay. Now that I'm home, I've been working to find the cause of the problem. Even though I loaded all of the rounds in question in one session, I disassembled some to check charges. They all were within one granule of each other and weighed exactly what they should have. I whipped out the scale check weights, and, the scale is the same as it should be. I checked the seating depth - dead on. I checked the loaded round neck diameter - .0025 to .003 less than the chamber neck. I pulled the barrel and gave it a look - looks good fromt eh chamber end. I ran a single patch of carbon cleaner - smooth, but obviously a bit dirty. I then ran a chamber cast - dimensions are right on (neck diameter and length, freebore diameter and length), BTW, nothing came out with the cast (no carbon or anything).
Now, I'm thinking of imposing on another friend to get it borescoped. My thought is a carbon ring somewhere in that barrel. If that isn't it, what have I missed?
Forgot: All of the ammo for both days were loaded at the same time, all the powder came out of the same 8# jug, all the bullets are the same lot, and were sorted by weight and base-ogive, and all of the primers were from sequential slips of Tula large rifle primers from a single 1k box. The brass was weight sorted and fully tortured including machine annealing every use. All of the cases fired yesterday and today were from the same weight group (0.5 grains) and had performed well together in previous uses. All of these components have been used by me for several hundred rounds without any lot changes, etc..
Thanks in advance,
Keith
The barrel is a Krieger in 308 Win chambered with a custom reamer. It shoots the 200 grain hybrid quite well. I have ~1300 rounds through the barrel total, and it was cleaned last Thursday including a quick (light) scrub of Jb bore paste (I do this every 200-300 rounds) and a full treatment of copper cleaner and powder solvent (the Jb was actually done between powder and copper solvents). This is my normal cleaning regimen and it gets the barrel clean. On Friday, I fired 6 fouler rounds.
The barrel was off ~200 rounds ago for a re-crown, and my gunsmith gave the throat area and crown a borescope look and chamber cast while it was apart. At that time, I had very light fire cracking and a perfectly clean bore.
The load is one I have used for nearly the entire life of the barrel. It shoots good, solid groups at 2650 fps. I have never had any pressure signs with this load (until now), and it has fired the batch of brass in question at least 2 times prior. The powder is Varget, and even though it is supposed to be temp stable, I remove loaded rounds if they stay in the chamber more than 15 seconds. I've actually tested to see if heat-soaking caused problems or pressure with no problems encountered, but I've developed the habit of not firing rounds that have been cooking in the chamber.
Here is what happened: I was shooting a 2 day F/TR match and the rifle shot well the first day, except the vertical zero moved up ~3/4 - 1 MOA on the second relay of the day. Accuracy remained through that and the third relay without any problems or pressure signs. I even fired the third relay very fast due to conditions without any problem (and I got the barrel quite warm - a normal thing for me - in the process). Yesterday, I fired a total of 71 rounds (5 sighters+ 20, 2+20, 2+20)
This morning (I don't clean between days - never have), I got to the line and the rifle started doing its thing. The POI was still ~ 3/4 MOA higher than my normal 1k come-up despite being a little cooler outside (mid 60's this morning). After 4 sighters and ~ 9 rounds of competition, I started to notice slowly increasing bolt lift. By 15 competition rounds, the bolt lift was getting downright heavy, and the 19th and 20th rounds had gas escaping around the primer. (found that after the last shot). Looking at the cases in order of firing, the primers started out nice and round, then got flatter, then I started seeing some shininess to the case head, then shiny ejector marks, then blown primers.
I put that rifle away and borrowed a friend's rifle (what a great friend Bill is!) to shoot my last relay. Now that I'm home, I've been working to find the cause of the problem. Even though I loaded all of the rounds in question in one session, I disassembled some to check charges. They all were within one granule of each other and weighed exactly what they should have. I whipped out the scale check weights, and, the scale is the same as it should be. I checked the seating depth - dead on. I checked the loaded round neck diameter - .0025 to .003 less than the chamber neck. I pulled the barrel and gave it a look - looks good fromt eh chamber end. I ran a single patch of carbon cleaner - smooth, but obviously a bit dirty. I then ran a chamber cast - dimensions are right on (neck diameter and length, freebore diameter and length), BTW, nothing came out with the cast (no carbon or anything).
Now, I'm thinking of imposing on another friend to get it borescoped. My thought is a carbon ring somewhere in that barrel. If that isn't it, what have I missed?
Forgot: All of the ammo for both days were loaded at the same time, all the powder came out of the same 8# jug, all the bullets are the same lot, and were sorted by weight and base-ogive, and all of the primers were from sequential slips of Tula large rifle primers from a single 1k box. The brass was weight sorted and fully tortured including machine annealing every use. All of the cases fired yesterday and today were from the same weight group (0.5 grains) and had performed well together in previous uses. All of these components have been used by me for several hundred rounds without any lot changes, etc..
Thanks in advance,
Keith
almost the exact same thing. I cleaned the throat really good as well as the rest of it. Never did it again. Im very intrested to hear other peoples thoughts as well as I never did figure it out.
