As I mentioned over in Miscellanea (under ‘target shooting results’), I started out shooting groups of 0.84″ to 1.23″ at 30 yards. And I was half-way impressed but not all that sure how to interpret the results.
Well, things got worse. My average group became around 1.23″ and some patterns were so ugly it hurt to look at them. I knew I could shoot better than that. And heck, using a shooting rest, I was actually even cheating. (Apologies to bench rest shooters out there, I still feel kinda funny using a shooting rest. It’s growing on me, though.)
As you might imagine, I got very concerned. Maybe even agitated. I scoured the ‘net for information on what might be going on. There’s a lot of fluff information out there, but after lots of reading it began to look like I needed a re-chamber job.
So I called the local gunsmith, and told him what was going on. He agreed the shooting results were awful, but in spite of his years of re-chambering, never heard of anyone getting better groups on paper as a result. His suggestion: check the crown. He’d seen that make a real difference.
So, I checked the crown, which on this rifle isn’t all that simple. First, off comes the compensator, then the jam nut, and then the muzzle adapter.
There, in all its glory, was the crown. I was looking for a nice star-burst pattern of blow-by around the exit hole, and there it was. But it wasn’t the dark-gray carbon I was looking for, it was this dark brown-looking crap.
Oh well. Time for a cleaning while I think of something. I must’ve cleaned on that barrel for half an hour. Oil it, run the mop through, run the brush through, run the mop through, run a patch through. Make an ugly face at the patch and do it all over again. Never in my life had I ever dealt with such a dirty, awful barrel. (By the way, the gun oil I use is 1/2 air compressor oil and 1/2 brake fluid.)
After taking the gun halfway apart and cleaning the heck out of it, it was time for a serious test. Could dirt be the issue? Lug out the shooting rest and the targets.
I shot the first five rounds with the take-down screw a bit loose, and the barrel band off. Got a slightly decent group. Tightened down the take-down screw and, Shazam! A group averaging 0.7735.
I put the barrel band back on, and my group widened out again.
So I thought I’d play a bit with the notion of vibration-damping bedding. I got an old automobile inner tube, which is butyl rubber 0.085″ thick. I cut a piece of it to match the flat inner part of the stock that surrounds the take-down screw, where it faces against the bottom of the receiver. This has the effect of raising the receiver in the stock, and raising the barrel as well. Underneath the barrel, in the barrel channel, I put a strip of butyl rubber 0.25″ wide and 3″ long. Then I tightened it all back together.
My group got smaller again. I was onto something with this vibration damping.
I put the barrel band back on tight (it wouldn’t go all the way back on) and got pretty much the same improved results, though about 1/2″ lower. With adjustable rear sights, that’s a simple fix.
Then I put the muzzle adapter back on. Pretty much no difference.
Then I put the compensator back on, and, Shazam! A group of 0.5795″. A new personal record, and I’m finally feeling I can actually shoot with this rifle. And meanwhile, I learned a few things.
1. Just because the bore looks clean, bright and shiny, doesn’t mean it’s clean. I got my 22″ barrel used, and it looked clean, so I installed it. It was dirty. And my groups were getting progressively worse, because the dirt was collecting dirt. That’s how dirty it was. A good cleaning shrank my groups by a whole one-half inch.
2. The idea of using a vibration-absorbing material for bedding the rifle has real merit. I have a draft article on that from researching the topic, and now I’m going to do it. Watch this space.
3. It took a lot of reading and research for me to get sold on the benefits of a compensator/muzzle brake and how it should function, which you can find here. Even so, I didn’t have personal experience and real numbers to go with that. Now I do. They work. But there’s a caveat: I’ve stuck with designs that have large exit ports (JP and GRG), to rush that 44 cubic inches of raging propellant gas away from the bullet in a hurry. There’s other designs out there with bunches of smaller holes, and I have my doubts about how well they work.
So, there it is. I’ll be shooting more for fun off and on, and gearing up for the bedding project.