Pilgrim
03-31-2006, 10:37 PM
I started having grouping problems with the double rifle a few weeks ago. After a few trips to the range with the rifle grouping rights and lefts into about an inch at 100 yds. (outstanding DR accuracy!), all of a sudden it starts "crossing" with the left barrel printing about 9" to the right of the right barrel. That's a no-no and usually indicates the velocity of the load is too fast. Well....it was the same load that grouped before, and the same load for which the rifle had been regulated. As near as I could recall everything else was the same (NOT). Three weeks of fooling around with loads, powders, bullets, method of holding the rifle & bench techniques (both very important with DRs - far more than with any other type rifle), I finally decided to go back to "zero". I took the scope off of the rifle, took a leather cartridge holder off of the buttstock, and shot the rifle with open sights and the same commercial ammo. It appeared to be shooting properly. So I put the scope back on, it still shot accurately with no crossing. It turns out that the accuracy problem was the leather cheek piece/cartridge holder I had added to the buttstock! That piece of leather can't weigh more than 4 oz. and caused a bullet spread of roughly 9" at 100 yds. Amazing. I had heard of such a small change causing enormous accuracy differences with DRs, but I really didn't believe it. Especially after having the buttstock cut off and a recoil pad put on, and then adding scope rings and a scope. I saw it with my own eyes, and it was my own rifle, with me behind the buttstock, and I'm not sure I believe it yet. But the leather cheek piece will stay off of that rifle for damn sure.
My Kimber .45 ACP Compact had been shooting OK, but accuracy was only so-so. Maybe 2" or so at 25 yards benchrest, no matter what handload I tried. One 225 gr. commercial cast bullet caused the groups to open up to 4" or so, but all of the 200 gr. SWC and 230 gr. RNFP CBs plunked into 2" to 2.5". I was also having intermittent feeding problems. OK accuracy wise , I guess, but not what I expected from the Kimber. The reliability issue was and is unacceptable. To add insult to injury, it also didn't shoot to point of aim (fixed 3-dot tritium sights) at 25 yards. It was about 2" low and 2" left. I tried seating the bullets out/in, roll crimp vs. taper crimp, different bullets, different powders, different primers, etc. Nothing seemed to change the accuracy or POI. The problem I was having seating bullets out was bugging me in particular as the chamber should have accepted the rounds, but wouldn't. Well, I finally figured out that the taper crimp die really wasn't crimping the case. The die was leaving a slight bell that couldn't be seen or felt. I guess the chamber must have a slight taper from base to case mouth, and the case "bell" that was remaining after bullet seating wouldn't let the cases chamber properly. I had to push the case quite a bit farther into the crimp die than I had expected to get the "bell" completely removed. Problem solved and the groups tightened up to ~1" to 1 1/2" with both 200 and 230 gr CBs. So far the feeding problem appears to bgone as well. Even better, the point of impact moved to point of aim with both loads (200 SWC @ 910 fps & 230 RNFP @ 860 fps) with the same powders and amount of powder as before. That was the first time I had seen point of impact shift that much with just OAL length change. Velocity didn't change at all per my chronograph.
Last Sat. at our monthly BR match, I shot like crap. The 100 yard scores were about my average, but how I got those wasn't (2 really bad targets out of 5 total). The 200 yard scores were beyond bad. Worse, the "bad" shots were way bad and beyond anything I would expect from parallax, or bad technique. Usually I can call them, or the impact is PDQ to where I expected it to be, but not in some cases Sat. I was using a new barrel, new scope, and new cases. All three had checked out at the home range, but something was really wrong last Sat. I even swapped scopes mid match and resighted in etc. It wasn't the scope. I noted that a few cases chambered harder than the rest (half dozen or so out of 150 cases used). It could only have been case neck wall thickness, but that didn't make any sense as I don't change the setting on the neck reamer, and 140 or so other cases were OK out of the new batch, and the old cases were OK with the same neck reamer setting. What gives? I came home and checked all 150 cases, and sure enough there were some dozen or so that were either thicker than I wanted or were "off standard" with respect to the other cases. I recut about 75 of the cases to remove all of the neck variations I could, but how did it happen in the first place? I usually target .001 or so neck clearance. What I think happened was some of the cases were prepped when the weather was really cold (freezing) vs. 40's and 50's when the other cases were prepped. My shop is unheated. The mandrel over which the case necks are turned must have been .0005" to .001" or so smaller in diameter due to the temperature, which resulted in cases that were .005 to .001" thicker in the neck that the other cases. I went back to the local range yesterday to check the cases after reworking them and all seems OK, but...time will tell. Next match is about a month away. Any cases that "throw" a shot will simply be thrown away after the next match unless I know why the shot went astray.
Other stuff like the above also happened with revolvers during the past few weeks, but you get the idea. All new stuff for me, and two of 'em in particular are outside of my experience (DR and case neck differences) and outside the experience of others with whom I discussed the problems. Oh well, we just keep learning...FWIW, Pilgrim
My Kimber .45 ACP Compact had been shooting OK, but accuracy was only so-so. Maybe 2" or so at 25 yards benchrest, no matter what handload I tried. One 225 gr. commercial cast bullet caused the groups to open up to 4" or so, but all of the 200 gr. SWC and 230 gr. RNFP CBs plunked into 2" to 2.5". I was also having intermittent feeding problems. OK accuracy wise , I guess, but not what I expected from the Kimber. The reliability issue was and is unacceptable. To add insult to injury, it also didn't shoot to point of aim (fixed 3-dot tritium sights) at 25 yards. It was about 2" low and 2" left. I tried seating the bullets out/in, roll crimp vs. taper crimp, different bullets, different powders, different primers, etc. Nothing seemed to change the accuracy or POI. The problem I was having seating bullets out was bugging me in particular as the chamber should have accepted the rounds, but wouldn't. Well, I finally figured out that the taper crimp die really wasn't crimping the case. The die was leaving a slight bell that couldn't be seen or felt. I guess the chamber must have a slight taper from base to case mouth, and the case "bell" that was remaining after bullet seating wouldn't let the cases chamber properly. I had to push the case quite a bit farther into the crimp die than I had expected to get the "bell" completely removed. Problem solved and the groups tightened up to ~1" to 1 1/2" with both 200 and 230 gr CBs. So far the feeding problem appears to bgone as well. Even better, the point of impact moved to point of aim with both loads (200 SWC @ 910 fps & 230 RNFP @ 860 fps) with the same powders and amount of powder as before. That was the first time I had seen point of impact shift that much with just OAL length change. Velocity didn't change at all per my chronograph.
Last Sat. at our monthly BR match, I shot like crap. The 100 yard scores were about my average, but how I got those wasn't (2 really bad targets out of 5 total). The 200 yard scores were beyond bad. Worse, the "bad" shots were way bad and beyond anything I would expect from parallax, or bad technique. Usually I can call them, or the impact is PDQ to where I expected it to be, but not in some cases Sat. I was using a new barrel, new scope, and new cases. All three had checked out at the home range, but something was really wrong last Sat. I even swapped scopes mid match and resighted in etc. It wasn't the scope. I noted that a few cases chambered harder than the rest (half dozen or so out of 150 cases used). It could only have been case neck wall thickness, but that didn't make any sense as I don't change the setting on the neck reamer, and 140 or so other cases were OK out of the new batch, and the old cases were OK with the same neck reamer setting. What gives? I came home and checked all 150 cases, and sure enough there were some dozen or so that were either thicker than I wanted or were "off standard" with respect to the other cases. I recut about 75 of the cases to remove all of the neck variations I could, but how did it happen in the first place? I usually target .001 or so neck clearance. What I think happened was some of the cases were prepped when the weather was really cold (freezing) vs. 40's and 50's when the other cases were prepped. My shop is unheated. The mandrel over which the case necks are turned must have been .0005" to .001" or so smaller in diameter due to the temperature, which resulted in cases that were .005 to .001" thicker in the neck that the other cases. I went back to the local range yesterday to check the cases after reworking them and all seems OK, but...time will tell. Next match is about a month away. Any cases that "throw" a shot will simply be thrown away after the next match unless I know why the shot went astray.
Other stuff like the above also happened with revolvers during the past few weeks, but you get the idea. All new stuff for me, and two of 'em in particular are outside of my experience (DR and case neck differences) and outside the experience of others with whom I discussed the problems. Oh well, we just keep learning...FWIW, Pilgrim