kBob
Member
Those of you who follow me on rimfire central can stop reading as this is a cut and paste.....
Some years ago I bought from Olympic Arms a .2LR conversion unit that replaces the Bolt Carrier Group and magazine of an AR15 to allow the use of relatively inexpensive .22LR in an AR and allow the use of an AR where back stop and safety fan issues would prevent the firing of Centre fire cartridges.
When it first came in I was excited having used the COBRay units the US ARMY had with the M16A1 and, despite warnings to the contary, never had issues with.
The Olympic unit had only a single stout leg on the side opposite the ejection port and the actual chamber adaptor has only one connection point, to that leg, via a roll pin and so flops about when not in the rifle.
Well despite trying multiple brands of ammo, various lube stratagies and holding my mouth just right I could not get more than three or four rounds to fire before a jam. In a fit of disappointment I put the thing away for a year or two.
When next it came out I made a more careful study of what was happening. First the Black Dog M261 magazine was letting rounds go awfully high and (viola!) nearly every HP brand ended up saying hello to the top edge of the chamber in loading and thus soon one would stop to talk to the breech face. Digging out now ONLY my Round nose solids I got the thing to work....... for 5 to seven rounds.
Now I was noticing sometimes it stopped with a round in the chamber after the hammer had dropped. After looking things over I found that each of the unfired rounds had barely been kissed by the firing pin. Having taken the thing apart multiple times I knew there was a firing pin spring to help prevent slam fires and when I checked it .....man was that a hard and heavy spring. I looked in my "Box O' Stuff" out in the shop and found a spring about the same shape and sized that seemed less powerful by about 50 percent. I hand cycled magazine or two of ammo through the action and inspected the ammo to see that the new spring was still doing its job..... but not with as much resistance to the hammer blow. Back out to the back stop and yea verily the thing worked better.....not much better but now instead of a stoppage every 5 to 7 rounds, it was a stoppage every 7 or eight rounds
AAAARRRRGGGHH!
It went back into storage.
This week end I was reading about someone doing a "Fluff and Buff" on a completely different type of firearm and thought, "maybe I just need to polish that puppy up. Well a little time with some black "crocus cloth" and the rail and bolt and spring guide all felt and looked smoother.
I was playing with the device after polishing and noticed something.
Remember I said the actual chamber piece sort of flops around on a roll pin?
Well the clearance between the edge of that part and the bolt face as it passes is very near or less than ZERO. Just a gagillanth of a degree misalignment.....like say when a blow back operated adapter is bouncing on the front of a AR buffer.....and when the bolt goes forward it runs its sharp and square 90 degree edge up against a similar sharp 90 degree edge on the chamber adaptor facing it.
I used a hand file to round off the edge of the chamber adapter at that point and barely broke the similar edge on the bolt.
Just fired 15 rounds of .22LR RN 40 grain HV without even a suggestion of a hiccup.
Wish me luck!
I just thought there might be others that bought these when they were initially offered that might have had similar bad experiences that might wish to know what I have been doing.
-kBob
Some years ago I bought from Olympic Arms a .2LR conversion unit that replaces the Bolt Carrier Group and magazine of an AR15 to allow the use of relatively inexpensive .22LR in an AR and allow the use of an AR where back stop and safety fan issues would prevent the firing of Centre fire cartridges.
When it first came in I was excited having used the COBRay units the US ARMY had with the M16A1 and, despite warnings to the contary, never had issues with.
The Olympic unit had only a single stout leg on the side opposite the ejection port and the actual chamber adaptor has only one connection point, to that leg, via a roll pin and so flops about when not in the rifle.
Well despite trying multiple brands of ammo, various lube stratagies and holding my mouth just right I could not get more than three or four rounds to fire before a jam. In a fit of disappointment I put the thing away for a year or two.
When next it came out I made a more careful study of what was happening. First the Black Dog M261 magazine was letting rounds go awfully high and (viola!) nearly every HP brand ended up saying hello to the top edge of the chamber in loading and thus soon one would stop to talk to the breech face. Digging out now ONLY my Round nose solids I got the thing to work....... for 5 to seven rounds.
Now I was noticing sometimes it stopped with a round in the chamber after the hammer had dropped. After looking things over I found that each of the unfired rounds had barely been kissed by the firing pin. Having taken the thing apart multiple times I knew there was a firing pin spring to help prevent slam fires and when I checked it .....man was that a hard and heavy spring. I looked in my "Box O' Stuff" out in the shop and found a spring about the same shape and sized that seemed less powerful by about 50 percent. I hand cycled magazine or two of ammo through the action and inspected the ammo to see that the new spring was still doing its job..... but not with as much resistance to the hammer blow. Back out to the back stop and yea verily the thing worked better.....not much better but now instead of a stoppage every 5 to 7 rounds, it was a stoppage every 7 or eight rounds
AAAARRRRGGGHH!
It went back into storage.
This week end I was reading about someone doing a "Fluff and Buff" on a completely different type of firearm and thought, "maybe I just need to polish that puppy up. Well a little time with some black "crocus cloth" and the rail and bolt and spring guide all felt and looked smoother.
I was playing with the device after polishing and noticed something.
Remember I said the actual chamber piece sort of flops around on a roll pin?
Well the clearance between the edge of that part and the bolt face as it passes is very near or less than ZERO. Just a gagillanth of a degree misalignment.....like say when a blow back operated adapter is bouncing on the front of a AR buffer.....and when the bolt goes forward it runs its sharp and square 90 degree edge up against a similar sharp 90 degree edge on the chamber adaptor facing it.
I used a hand file to round off the edge of the chamber adapter at that point and barely broke the similar edge on the bolt.
Just fired 15 rounds of .22LR RN 40 grain HV without even a suggestion of a hiccup.
Wish me luck!
I just thought there might be others that bought these when they were initially offered that might have had similar bad experiences that might wish to know what I have been doing.
-kBob
