Scott S
February 22, 2001, 10:15
A week or so ago I posted a message regarding a recent range trip where I experienced several failures to feed Hirtenberger with my DSA standard length. Extraction and ejection worked, but the bolt would stop after stripping a cartridge about halfway out of the mag. This failure to feed occurred after firing shots and after dropping the bolt using the release. Called DSA and spoke to their 'smith. Said that I should adjust my gas setting, and that a slightly more vigorous cycle might be all that was needed (same comment I got from Gary J.). Haven't been to the range to test the gas adjustment fix.
However, that fix doesn't address the feed problem when dropping the bolt using the bolt release tab/button (Norman74 and Mt Guerrilla also reported this problem). Looked at this problem last night. Every time I inserted a full mag and hit the bolt release, the bolt would fail to completely strip the round from the mag. Tip of cartridge would go into the chamber a quarter to half inch, but the rim/head would still be in the mag. With a mag of less than 10 rounds, dropping the bolt chambered the round every time. So, it seemed that full mag tension against something caused enough friction to prevent complete feeding. Looking closely at the action as I cycled it slowly with my hand on the charging handle, I could see that the shoulder of each cartridge was scraping on the edge of the receiver feed rails. This scraping left a mark that looked like the cartridge had been rubbed with the edge of a piece of 120 grit sandpaper. Just one small spot on the feed rails caused this scraping. Look from underneath the rifle through the mag well into the action. At the back of the mag well the receiver feed rails are parallel to each other. Going forward, they diverge. They then converge and finally become parallel again. The *very* shallow angle where the convergence ends and the front parallel part begins is where the rounds were hanging. When you insert a mag with rounds in it, the body of the cartridge just behind the shoulder touches this point on the receiver. Shining a flashlight into the mag well I could see a thin layer of brass on the rails at this point. This edge was sharp enough to dig into the case shoulder, slowing the bolt just enough to stop it on full to nearly full mags.
In lieu of running several hundred rounds through the gun to help polish this sharp edge, I opted to go the Dremel route. Used a little, hard rubber-tipped bit impregnated with a fine abrasive to ever-so-slightly break the bottom edge of the rails at this point. I also polished the inner rail surfaces and lower rail surfaces for a quarter inch in each direction--just enough to remove the parkerizing. I went very slowly, checking my progress very often. Screw this up and you're hosed.
Now, when I insert a full mag and drop the bolt using the release, the cartridge slides home without a hitch. And the cartridge doesn't have the small scrap on the shoulder--just a tiny polished-looking mark in the same location.
FWIW,
Scott
[ September 10, 2001: Message edited by: gary.jeter ]
However, that fix doesn't address the feed problem when dropping the bolt using the bolt release tab/button (Norman74 and Mt Guerrilla also reported this problem). Looked at this problem last night. Every time I inserted a full mag and hit the bolt release, the bolt would fail to completely strip the round from the mag. Tip of cartridge would go into the chamber a quarter to half inch, but the rim/head would still be in the mag. With a mag of less than 10 rounds, dropping the bolt chambered the round every time. So, it seemed that full mag tension against something caused enough friction to prevent complete feeding. Looking closely at the action as I cycled it slowly with my hand on the charging handle, I could see that the shoulder of each cartridge was scraping on the edge of the receiver feed rails. This scraping left a mark that looked like the cartridge had been rubbed with the edge of a piece of 120 grit sandpaper. Just one small spot on the feed rails caused this scraping. Look from underneath the rifle through the mag well into the action. At the back of the mag well the receiver feed rails are parallel to each other. Going forward, they diverge. They then converge and finally become parallel again. The *very* shallow angle where the convergence ends and the front parallel part begins is where the rounds were hanging. When you insert a mag with rounds in it, the body of the cartridge just behind the shoulder touches this point on the receiver. Shining a flashlight into the mag well I could see a thin layer of brass on the rails at this point. This edge was sharp enough to dig into the case shoulder, slowing the bolt just enough to stop it on full to nearly full mags.
In lieu of running several hundred rounds through the gun to help polish this sharp edge, I opted to go the Dremel route. Used a little, hard rubber-tipped bit impregnated with a fine abrasive to ever-so-slightly break the bottom edge of the rails at this point. I also polished the inner rail surfaces and lower rail surfaces for a quarter inch in each direction--just enough to remove the parkerizing. I went very slowly, checking my progress very often. Screw this up and you're hosed.
Now, when I insert a full mag and drop the bolt using the release, the cartridge slides home without a hitch. And the cartridge doesn't have the small scrap on the shoulder--just a tiny polished-looking mark in the same location.
FWIW,
Scott
[ September 10, 2001: Message edited by: gary.jeter ]