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Posted: 3/14/2026 3:20:47 PM EDT
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I am trying to build out a 20in A2 .22 with irons. It is my understanding that using lead .22 bullets in chrome lined barrels is a bad idea. If I used copper coated/ plated would that be remedied? 1/12s are available but they all seem to be chrome lined now. Nitride barrels are available and cheap, but they are all 1/7, which isn't desirable either as I understand it. In an ideal world, I would pick up a 1/12 HBAR, unlined, but that is a unicorn apparently??? Any thoughts appreciated. |
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Since it sounds like your assembling an upper, why not go dedicated? Yeah it will cost a little more but if accuracy is at all your end goal, Dedicated is the way. Dedicated tends to be a little more reliabe. Not that chamber adaptors aren't reliable, they certainly can be. Accuracy will always be in favor of dedicated... Right to bear makes a 20" barrel(out of stock at the moment) and it has a shoulder for an FSB if you want full A2. Either pin or use a set screw FSB. If it were me, if I had a 20" upper I would drop in a conversion. Building an upper, Dedicated all the way cost be dammed 
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Originally Posted By shultz: Since it sounds like your assembling an upper, why not go dedicated? Yeah it will cost a little more but if accuracy is at all your end goal, Dedicated is the way. Dedicated tends to be a little more reliabe. Not that chamber adaptors aren't reliable, they certainly can be. Accuracy will always be in favor of dedicated... Right to bear makes a 20" barrel(out of stock at the moment) and it has a shoulder for an FSB if you want full A2. Either pin or use a set screw FSB. If it were me, if I had a 20" upper I would drop in a conversion. Building an upper, Dedicated all the way cost be dammed I get it. The idea is mostly starting from how cheap you can get some 20in AR uppers now from PSA. But then I dig into it and it becomes another more expensive project. How bad it is it to use 1/7 barrels? |
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Originally Posted By RedFox1911: I get it. The idea is mostly starting from how cheap you can get some 20in AR uppers now from PSA. But then I dig into it and it becomes another more expensive project. How bad it is it to use 1/7 barrels?  between the fast twist rate and over sized bore as long as you dont expect much past min of steel out to 50 you'll be happy.
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I should have added to above... With a dedicated barrel, expect typical off the shelf 22lr accuracy shooting less expensive ammo. It likely won't be as accurate as say a bergara, CZ ect shooting SK, lapua, ELEY ammo but in line with say a 10/22/typical 22lr auto... You can certainly get more accurate buying a much more expensive dedicated barrel and shooting better quality/consistent ammo. |
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The A1 in the picture is an upper I got on the EE here many years ago. It's a 1x12. I got it so long ago that Ciener 22lr conversion kits were the only real game in town. I put a KNS .052 sight pin on with the round ball on top. It is ridiculously fun. Put the ball on the target and shoot.  Edit 100 yards believe it or not 
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I was born in Birkenhead and I was poor , I was dressed from the local army and navy store and I can tell you its no fun going to school dressed as a Japanese admiral-UKjohn
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I was issued an M16-A1 20” 1:12 twist when my Agency started issuing 5.56 rifles and carbines to Patrol Officers. I shot some 22 LR with a conversion kit a couple times to compare it to my 1:9 twist Olympic arms 5.56 1:9 twixt CMV upper. I only had iron sights for the M16-A1 and my shooting was done at 35 to 50 yards. There wasn’t much difference in overall accuracy between the 1:12 twist chrome lined 20” barrel and the 16” 1:9 twist CMV barrel. The particular ammunition used made a more significant difference than the difference in 1:12 & 1:9 twist. Typically shooting .223 22LR through a fast twist .224 barrel produced fliers from rimfire bullets. Some ammo like CCI standard velocity shot pretty good but you still get fliers which will ruin a small group. For shooting steel plates, CQB drills the 22 LR conversion produce acceptable results. For shooting small groups on paper targets the fast twist barrels produce fliers which will ruin a small group. You get fliers with a lot of rimfire ammo but the fast twist 5.56 barrels produced more dispersion than typically seen with 22 LR barrels with 1:16 twist. I conducted a short test comparing 22 conversion kits in AR-15’s to dedicated 22 LR barrel AR-15’s. You can still look at this test on rimfirecentral.com. I posted the test on ARF.com but it has been archived. https://www.rimfirecentral.com/threads/ar-15-22-rimfire-conversion-test.754849/?post_id=7117985#post-7117985 |
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I’ve shot a lot of 22 LR with conversion kits in CMV, Chrome lined, Nitride and stainless steel Wylde 5.56/223 AR-15 barrels. If you don’t clean or shoot a few centerfire rounds through 5.56 barrels lead will accumulate in the gas port and gas tube. Lead from shooting rimfire ammo tends to accumulate on flash hiders and compensators. When a Friend and I were shooting 22 LR with Ciener conversion kits we cleaned the barrels with a bore snake and fired a few centerfire rounds in the 5.56 barrel to keep the gas system clear. The biggest hazard IMHO in shooting rimfire ammo in a centerfire barrel is a rimfire out of battery and lodging a bullet in the barrel and firing another round. Shooting 22 LR is filthy and once dedicated 22 LR barrels started becoming available I prefer having dedicated upper/lower 22 LR AR-15’s. Shooting 22 LR in a centerfire 5.56/223 barrels does provide cheaper trigger time for close range shooting. My Friend shot a lot of rimfire 22 LR in a Colt Competition H-Bar 1:9 twist. He’d dial up his rear fixed sight to where it was zeroed at 35 yards. With my 16” AR-15 1:9 twist barrels I used a 100 yard zero with 55 grain centerfire ammo. I had no trouble shooting steel plates out to 50 + yards with 22 LR conversion. With a 50 yard combat zero on a 5.56 AR-15 you’d be surprised how close the point of aim/point of impact will be with rimfire. Not near as much as you’d think at 50 yards and in. Green Mountain sell a Chrome Lined CMV 20” barrels in 1:14 & 1:12 twist. CMMG has manufactured 20” 22 LR barrels but I haven’t seen a 20” CMMG or Right to Bear 22 LR barrel in about five years. BoreBuddy was selling a 22 LR barrel to give a 20” AR-15 length appearance. Rimfire barrels sit deeper in the upper receiver by 1”-1.5” so a 21” rimfire will be close to a 20” AR-15 5.56. https://www.gmriflebarrel.com/military-barrels/ar-15-/-m16-/-m4-rifle-barrels Here is a link to Borebuddy 21” 22 LR barrel. This barrel or a BB upper is probably the best option for a dedicated 22 LR upper with CMMG pattern bolt. RRA sell dedicated 22 LR uppers with 20” barrels. https://borebuddy.com/product/borebuddy-apogee-match/ https://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_ID=1972 |
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Here's a 20" dedicated RTB barrel with A2 upper receiver and Lyman Globe sight on a Lipski base. Very fun to shoot offhand. https://imgur.com/mkfJbQH Here's the same Barrel with Lyman sights front and rear. This also has a Catch22 bolt hold-open which works very well with S&W mags. https://imgur.com/a/7VQSR4n |
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Originally Posted By RedFox1911: I get it. The idea is mostly starting from how cheap you can get some 20in AR uppers now from PSA. But then I dig into it and it becomes another more expensive project. How bad it is it to use 1/7 barrels? I don't notice any differences as most of the .22lr rifle work is within 50 yds practice for me. I compared the drop in conversion bolt with my 16" carbine to a 16" dedicated Spikes upper, of course the dedicated upper is more accurate than the conversion bolt but that's irrelevant at 25-50 yds when I'm shooting steel plates. |
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