 Dolomite_Supafly 
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Joined: Jun 2006  TN, USA
 Posts: 1984 Feedback: 100% (4) |
Posted: 6/14/2012 4:09:07 PM
THE IMAGE ABOVE IS A PAID ADVERTISEMENT I always thought it was because the rimfire bullet was smaller than the bore. Well I measured a handfull of rimfire bullets today and they all measured at least .2245". Some even measured .226". I used an old AR barrel to make a rimfire barrel and suprizingly it shot just as well as the rimfire barrel it replaced. So I knew the .224 bore wasn't an issue. Well I decided to push a rimfire bullet down the smooth bore of my conversion. The bullet started out as .225" and on the other end it was .221". I suspect this is the reason why the conversions do not shoot as well as the barrels are capable of. I spent about 30 minutes opening up the freebore of the conversion so the 22 bullets would drop out at .223-.224 if they are larger than that to begin with. I chucked the chamber insert into my lathe then used a 5.7mm drill bit to open it uo then followed it up with a file as it spun. Then I began with 600 grit sand paper, then 1000 and then 2000. The I shot some groups at 25 yards and with Winchester Subsonics, which started out at .224", the holes were touching. With the SSS, which started out at .225", the group was even smaller. Is it as accurate as my match chambered 22? No, but the groups were probably cut in half from what they were before I opened up the freebore. I can honestly say that this made a noticeable improvement in my conversion. I do have a dedicated that will shoot circles around the conversion and I use it 99% of the time. Dolomite |
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Circuits
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Joined: Jan 2001 CO, USA
Posts: 6068 Feedback: 100% (21) Link To This Post |
Posted: 6/14/2012 5:38:43 PM
[Last Edit: 6/14/2012 5:38:55 PM by Circuits]
Neat, thanks for sharing! pixplz
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ColonelHurtz
Horror and moral terror are your friends.
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Joined: Apr 2007  KHM
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Posted: 6/14/2012 7:22:39 PM
Then there's that pesky twist rate.
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Posted: 6/14/2012 7:49:07 PM
Twist rate tighter than desirable, free bore in the adapter, lack of total seal at the chamber region causing variable gas pressure, blowback mode of operation - it's a wonder they're as accurate as they are.
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Posted: 6/14/2012 8:44:24 PM
Originally Posted By SecondAmend:
Twist rate tighter than desirable, free bore in the adapter, lack of total seal at the chamber region causing variable gas pressure, blowback mode of operation - it's a wonder they're as accurate as they are. THIS |
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forever4
Firearms aficionado
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Joined: Nov 2008 KY, USA
Posts: 3103 Feedback: 100% (27) Link To This Post |
Posted: 6/14/2012 9:49:44 PM
Originally Posted By SecondAmend:
Twist rate tighter than desirable, free bore in the adapter, lack of total seal at the chamber region causing variable gas pressure, blowback mode of operation - it's a wonder they're as accurate as they are. Thank you for saving me the time of typing that. Personally I love the conversions as they let me practice with my existing rifles on the cheap. Also, my rifles have been acceptably accurate for 25-50 yard range practice. I have dedicated target rifles that I shoot for tight groups, my .22 ARs are just for fun. They are plenty accurate enough to take care of those zombie tin cans and other aggressive targets of that size and nature. That pop can doesn't care where on the can you hit, the result is the same. |
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Posted: 6/14/2012 9:59:13 PM
I do not think the bore diameter or the twist rate has as much of an impact on accuracy unless it is something excessive like 7 twist or you are shooting shorts.
I used a 9 twist center fire barrel to make a barrel to shoot SSS rounds. Surprisingly subsonic 40 grain bullets shot better that the SSS rounds in that barrel. And as I said most of the rounds I put a micrometer to were over .224. The Winchester subsonic 40 grain bullets measured .2245" and the SSS measured close to .2260". Now the bulk Winchester did measure .221". Remington subsonics measured .224" if I remember correctly. And all of the bullets that measured at least .224" shot better while those that didn't showed no improvement. Dolomite |
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Posted: 6/14/2012 10:02:12 PM
Also, this was just a test to see if it helps. I rarely use this kit because I have a dedicated. Most time this kit gets used by friends at the range.
Maybe tomorrow I will do a apples to apples comparison. I have a spare chamber insert that has not been modified. Dolomite |
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Redtazdog
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Joined: Dec 2002 WA, USA
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Posted: 6/14/2012 10:19:58 PM
Originally Posted By Dolomite_Supafly:
Also, this was just a test to see if it helps. I rarely use this kit because I have a dedicated. Most time this kit gets used by friends at the range. Maybe tomorrow I will do a apples to apples comparison. I have a spare chamber insert that has not been modified. Dolomite What chamber inserts are you using as the spikes are different than the cmmg that are different than the ciener. Several years back I found that simple scotch tape around the chamber adapter improved accuracy as it holds the adapter in the chamber snug and made a better fit in some barrels, soon after I cut Oring grooves as they lasted more than a few hundred rounds. The tape is a good cheap test 
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Posted: 6/14/2012 11:01:07 PM
It is a Ciener conversion but I also had a friend with a CMMG conversion that slugged his chamber insert. He said he got the same exact numbers I did. He is in the process of using some sandpaper and a drill to do the same as I did.
Dolomite |
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