Shooting the AR15 22LR Conversion Kits

[TD1886]

Larry Gibson give your opinion on the questions I have asked please.
I wanted to discuss the 7 twist and these conversions. Let's say you have a velocity of a 22LR bullet using that kit from a 20 inch barrel of 1250 fps. That would be 128,571 rpm. What is your opinion that destroys the accuracy in the 7 twist, the incompadible diameter of the 22LR bullet to the .224 groove, the rpm of the bullet, or the fast twist is somehow ruining the very soft bullet to cause it be inaccurate. I also thought that some people get half decent accuracy with cast bullets, but they are usually longer, not as soft as the 22LR, and they fit the bore/groove much better. What do you think is the problem? Thanks in advance

[TD1886]

Larry wanted me to start a new thread on this in another thread I asked him about it, so I'm waiting for him to catch up.

[Larry Gibson]

Many irons in the fire here at home. My thoughts;

Using the M261 in 20" ARs with 7 and 12" twists; The difference between the two barrels given the use of the same 22LR ammunition at 1250 fps is substantial. While the 12,571 RPM with the 7" twist may seem sublime yet it still falls within the RPM Threshold range of 120 - 140,000 RPM. With the 12" twist AR the RPM is 75,000, substantially lower and well below the RPM Threshold range.

Additionally, a 22LR round in the M261 will have a 1.7" +/- free bore jump before it hits/engages the lead in the chamber throat. Obviously, the sharper angle of the 7" twist leade probably causes more damage to the bullet than will the shallower angle of the 12" twist. More damage to the bullet equates to more adverse effect the centrafugal force has on the bullet during flight. I'll leave it to the math garu's to figure out how much more effect the 42% more RPM may have on the centrafugal force.

As most all of the 22LR bullets I have measured run .224 - .225+ I find that not to be "incompatible" with a .224 groove barrel. Several builds of dedicated 22LR uppers I've seen built with 14" twist .224 CF barrels shoot as well as any with .222 barrels.

Back before the SF company I was full time with turned in our M16A1s (12" twist barrels) for M16A2s (7" twist barrels) we used our 50' indoor range using the M251s in the M16A1s for practice and alternate qualifications. We quickly found with the M16A2s and even a civilian 7" twist Colt H-Bars that it was difficult for Soldiers who fired expert with the M16A1s to fire a qualifying score on the same 50' target(s). We were able to retain two M16A1s in the SF company for use with the M261 22LR device for further qualifications on the indoor range at the armory. Also, given the inaccuracy with the then standard 7" twist M16A2s and M4s Big Army ceased use of the M261 devices.

Further testing at 50 yards with M16A2s and H-Bars with 7" twists further demonstrated the inaccuracy. However, using the Aguila heavier bulleted (60 gr?) subsonic 22 LR did give reasonable accuracy at 50 yards out of a 7" twist H-Bar and out of my 9" twist Colt Competition H-Bar.

[TD1886]

That's interesting. I too would figure that steeper 7 twist angle would do some damage to the soft 22LR bullet. I've love to know if the bullet didn't have that long jump to the rifling what it may have changed.

I had one of the Colt conversions. Is that same as the M261 and if so who did the Army purchase theirs from, was it Colt.

I remember shooting PMC HV 22LR ammo from mine and although not as accurate as a dedicated 22LR rifle. As I noted it was minute of squirrel easily at 25 yards. I can't remember if I shot it further. It was more of a novelty thing then a necessity. The PMC was a little bit fatter then the other 22LR ammo I had at that time. It was also copper coated, but that is such a thin coating I doubt it contributed to much.

As an aside I just recently bought some Speer 70 grain semi point bullets. Those are pretty old and Speer still makes them. I won't lie I'm not a Speer bullet fan. The only one I like way back is when that made a 150 some grain bullet in .313 diamter for the 7.65 Argentine. I believe they were the only company that produced a .313 bullet. Most were .312 or .311. It shot very well. Back to the Speer 70 grain semi point. I thought I'd shoot them from my old HBAR which had become pretty much a safe queen. I drug it out and while looking at it I though how old the style back then appeared compared to the new AR's. The lower receiver is so flat looking minus the protective ridges around the magazine release button. You know what I mean. I loaded those up with various powder burn rates and duty suprised when the old girl was wanting to shoot between 3/8's to just under 3/4 inch groups at 100 yards, velocity running 2900 fps to just making 3000 fps which is decent for that weight bullet. Not bad at all for an old 7 twist.

One of my good friends may donate me one of those old Colt conversion and I'll thoroughly test especially now that I know much more about what is going on. The one thing I definitely want to try is my 22LR bullet swage to see if the increase bullet diameter makes much difference. I'll swage them up till they barely fit, much more fatter then the fat factory one you may fine.

Thanks for replying.

[Moleman-]

Neat, I picked up one of the M261 kits back in the early 90's and occasionally plink with it usually with a 20" 1:14" mystery unmarked heavy barrel. Does fine on cans and steel targets. Never shot it for groups using 22lr though. What would cause the flat tension spring to fail? I'm using standard velocity rem or federal ammo. The original went flat pretty quick so I got a replacement. That one broke pretty quick. 3rd one seems to be fine now for 15-20 years or so. Figured I was doing something wrong. If it kept breaking them I was looking at modifying it to use a coil spring.

[TD1886]

Here's something y'all may or may not know. There is a device called a Bore Buddy that pushes your conversion unit deeper in the chamber of your rifle and takes the fore and aft play out of and supposedly making it more accurate. I haven't tried that, but if I get another conversion unit I'll make one and see if there is a difference. Here's the link and scroll down to 22LR AR Buffer pressure plug:

https://borebuddy.com/

[Larry Gibson]

Neat, I picked up one of the M261 kits back in the early 90's and occasionally plink with it usually with a 20" 1:14" mystery unmarked heavy barrel. Does fine on cans and steel targets. Never shot it for groups using 22lr though. What would cause the flat tension spring to fail? I'm using standard velocity rem or federal ammo. The original went flat pretty quick so I got a replacement. That one broke pretty quick. 3rd one seems to be fine now for 15-20 years or so. Figured I was doing something wrong. If it kept breaking them I was looking at modifying it to use a coil spring.

Interesting, I never saw a broken one. Actually, never saw any parts breakage on the devices. Shouldn't be too hard to fabricate a spring if it does happen.

[Larry Gibson]

Here's something y'all may or may not know. There is a device called a Bore Buddy that pushes your conversion unit deeper in the chamber of your rifle and takes the fore and aft play out of and supposedly making it more accurate. I haven't tried that, but if I get another conversion unit I'll make one and see if there is a difference. Here's the link and scroll down to 22LR AR Buffer pressure plug:

https://borebuddy.com/

The M261 is better designed and made than all of the commercial devices I've so far seen, including the CMMG device as shown in that site's video's. All of the problems [chamber part needing pushed forward, sloppiness of fit and gas blow back through the charger handle slot] are already addressed and are non-problems with the M261.

I would point out that at the closer ranges the use of 22LR devices in faster twist ARs the accuracy is certainly acceptable for the type of shooting demonstrated in that site's videos. However, the level of accuracy needed for 50' alternate qualification courses is just not there with 7" twist barrels as it is with 12" twist barrels. Nor did I find the accuracy to be there for small game/vermin at 50 yards as it is with the 12" twist ARs.

[Larry Gibson]

I bellieve the M261 devices were manufactured by SACO Defense, if memory serves me correctly. The Colt devices were different. The Air Force ones may have been the Colt device but it's been numerous years since I've used either the Air Force or Colt devices. They took a special magazine also. The M261 magazine inserts can be used in 20 or 30 round AR magazines and are easy to insert and take out w/o disassembly of the magazine.

Quality commercial jacketed bullets shoot fine through 7, 8 and 9" twist ARs. Never said they didn't, Not sure of the why for this "apples to oranges" comparison of quality jacketed bullets to 22LR ammunition in AR/M16s when it's not relevant?

[TD1886]

I bellieve the M261 devices were manufactured by SACO Defense, if memory serves me correctly. The Colt devices were different. The Air Force ones may have been the Colt device but it's been numerous years since I've used either the Air Force or Colt devices. They took a special magazine also. The M261 magazine inserts can be used in 20 or 30 round AR magazines and are easy to insert and take out w/o disassembly of the magazine.

Quality commercial jacketed bullets shoot fine through 7, 8 and 9" twist ARs. Never said they didn't, Not sure of the why for this "apples to oranges" comparison of quality jacketed bullets to 22LR ammunition in AR/M16s when it's not relevant?

The CMMG units in my opinion are junk. Thus why I haven't bought one. Waiting to see if my friend is going let me have the old Colt one. Today I located my 22LR bullet swage die so I'm all set to thoroughly test one again should I get one.

I only mentioned the jacketed Speer is because I never liked Speer bullet so never tried them. I was surprised they shot so good out of the old 7 twist HBAR. Remember that HBAR was old school, not free float forearml, match trigger, etc. Not a flattop either for lower scope mounting. Those free float forearms definitely increase the accuracy of an AR in my opinion.

[M-Tecs]

I bellieve the M261 devices were manufactured by SACO Defense, if memory serves me correctly. The Colt devices were different. The Air Force ones may have been the Colt device but it's been numerous years since I've used either the Air Force or Colt devices. They took a special magazine also. The M261 magazine inserts can be used in 20 or 30 round AR magazines and are easy to insert and take out w/o disassembly of the magazine.

I have three of the AF versions with 6 mags. They do take the mags pictured here plus more info and history below. The chamber inserts are rifled.

https://www.gunsinternational.com/gu...n_id=100489855

https://forums.g503.com/viewtopic.php?t=308557

https://www.rimfirecentral.com/threa...-unit.1223349/

https://www.bing.com/images/search?q...hacc=0&first=1

[Larry Gibson]

"Remember that HBAR was old school, not free float forearml, match trigger, etc. Not a flattop either for lower scope mounting."

Not sure where you got all that from.

The HBAR configuration matches that of the M16A2 thus it is still usable for NRA HP Service Rifle matches. The Colt HBAR I purchased in the early '90s (pre-ban) is a flat top and has worn a scope off and on since back then. I also put a float tube inside the handguards [available even back then] which free floats the barrel inside the forearm. The trigger from Colt breaks very crisply right at 4 1/4 lb, the legal lowest trigger pull for HP Competition.

When new it would hold moa for 22 shots at 200 yards [well within the X ring] with Federal 69 gr MKs. Now after numerous thousands of rounds it still holds MOA with 22 shots at 200 yards with the 69 MKs and Hornady 75 gr match bullets. That was not from a benchrest either but from a prone unsupported position w/sling. Now, since I no longer shoot HP Competition, I have replaced the fore end with a heavier aluminum tube fore end. I many use it now in suppressed mode when calling coyotes. A 55 gr Sierra Blitz King over H335 at 3100 fps still holding moa does the trick.



To get back to the topic of this thread, here is the set up for use in my shooter AR15 w/12" twist milspec barrel. Been shooting this set up since '06 and it ain't broke so no need to fix it.



Now, as to all the "improvements" in Leggo built ARs, I constantly see many show up at the range with ARs all "tricked out".



Sorry, but that's not for this "old school" guy...........

[TD1886]

"Remember that HBAR was old school, not free float forearml, match trigger, etc. Not a flattop either for lower scope mounting."

Not sure where you got all that from.

The HBAR configuration matches that of the M16A2 thus it is still usable for NRA HP Service Rifle matches. The Colt HBAR I purchased in the early '90s (pre-ban) is a flat top and has worn a scope off and on since back then. I also put a float tube inside the handguards [available even back then] which free floats the barrel inside the forearm. The trigger from Colt breaks very crisply right at 4 1/4 lb, the legal lowest trigger pull for HP Competition.

When new it would hold moa for 22 shots at 200 yards [well within the X ring] with Federal 69 gr MKs. Now after numerous thousands of rounds it still holds MOA with 22 shots at 200 yards with the 69 MKs and Hornady 75 gr match bullets. That was not from a benchrest either but from a prone unsupported position w/sling. Now, since I no longer shoot HP Competition, I have replaced the fore end with a heavier aluminum tube fore end. I many use it now in suppressed mode when calling coyotes. A 55 gr Sierra Blitz King over H335 at 3100 fps still holding moa does the trick.



To get back to the topic of this thread, here is the set up for use in my shooter AR15 w/12" twist milspec barrel. Been shooting this set up since '06 and it ain't broke so no need to fix it.



Now, as to all the "improvements" in Leggo built ARs, I constantly see many show up at the range with ARs all "tricked out".



Sorry, but that's not for this "old school" guy...........

Yup, everything but the kitchen sink on AR's today.

My pre ban HBAR made in early 80 wears a Japan rubber armored 3x9 Tasco and uses the COLT Marine A.R.M.S. mount on the carry handle and it's been on their since the 80'. Never taken off, transported in truck all around the country, dropped numerous time, and still ticking today. If you have a good barrel a free float tube and match trigger are the best improvement to an "old school" AR15.

I think I may have located one of the M261 conversion kits. You know how the M261 part that inserts in the chamber doesn't have the case neck section and CMMG does. Well those old Colt conversion are like the M261 in that respect. I've read where the elimination of that neck help keep from gumming the throat up. Don't know why CMMG insists on still using it and you can imagine how thin the metal is being it fits in the chamber neck area and a 22LR bullet has to pass through it.

[Larry Gibson]

Back in the '90s the issue 22LR ammo was Winchester white box match. The bullets had a generous coating of wax lube on them. One time we fired over 1k rounds through each of the two M16A1s on the armory indoor range. After about 500 rounds each the rifles began to malfunction once in a while. We found the failure to feed were caused by not making sure the mag insert was seated correctly in the magazine after loading. Failure to fully chamber malfunction was caused by the buildup of the wax lube and the normal powder fouling associated with 22LR blow back systems. A liberal application of BreakFree or LSA kept them running. I also found using copper plated 22LR ammunition greatly reduced the fouling problem. That's why I prefer the copper plated ammunition for the M261 device.

The M261 mag inserts in milsurp 20 and 30 round mags will also lock the bolt back after the last round is fired. Not sure any more about the magazines for the other devices.

[TD1886]

Larry I think another company that may have made those M261 kits was MAC Atchisson

[Larry Gibson]

The MAC Atchisson device evolved into the Atchison/Ceiner device for civilian sales. The M261 was designed by John Foote. This article is an interesting read on the 22LR devices for the M16 rifles; https://smallarmsreview.com/full-aut...-the-m16-rifle

A small excerpt from that article;

"John Foote, another former employee of the Military Armament Corporation, had also designed and built a .22 caliber conversion kit for the AR-15 and M16 rifle.His design competed with Atchisson’s for adoption by the U.S. Army. After the usual extensive testing and government red tape, Mr. Foote’s conversion unit won the competition and was adopted by the Army as the .22 Caliber Adapter, M261. The M261conversion was blow-back operated, with a 10-round magazine designed to fit inside a standard 20-round M16 magazine. The first production run was subcontracted out to Okay Industries, of New Britain, Connecticut. A second contract was awarded to Maremont of Saco, Maine. Mr. Foote later formed his own company, the U.S. Armament Corporation. Mr. Foote eventually sold the company and the rights to the M261 .22 caliber conversion kit."

It seems initially the M261s were manufactured by Okay Industries. There were 130,00 - 150,000 +/- of them manufactured and I do not know the breakdown of how many by which firm.

[TD1886]

The MAC Atchisson device evolved into the Atchison/Ceiner device for civilian sales. The M261 was designed by John Foote. This article is an interesting read on the 22LR devices for the M16 rifles; https://smallarmsreview.com/full-aut...-the-m16-rifle

A small excerpt from that article;

"John Foote, another former employee of the Military Armament Corporation, had also designed and built a .22 caliber conversion kit for the AR-15 and M16 rifle.His design competed with Atchisson’s for adoption by the U.S. Army. After the usual extensive testing and government red tape, Mr. Foote’s conversion unit won the competition and was adopted by the Army as the .22 Caliber Adapter, M261. The M261conversion was blow-back operated, with a 10-round magazine designed to fit inside a standard 20-round M16 magazine. The first production run was subcontracted out to Okay Industries, of New Britain, Connecticut. A second contract was awarded to Maremont of Saco, Maine. Mr. Foote later formed his own company, the U.S. Armament Corporation. Mr. Foote eventually sold the company and the rights to the M261 .22 caliber conversion kit."

It seems initially the M261s were manufactured by Okay Industries. There were 130,00 - 150,000 +/- of them manufactured and I do not know the breakdown of how many by which firm.

Thanks for the link.

[TD1886]

Larry I can't get that link to open in two browsers.

[Larry Gibson]

Opens right up for me.

Google "Full Auto Rimfire Conversions for the M16 Rifle" and the article site will come up.

[TD1886]

Opens right up for me.

Google "Full Auto Rimfire Conversions for the M16 Rifle" and the article site will come up.

Thanks