Designated cast AR15

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Geargnasher posted this 24 July 2018

If you want it to cycle popgun loads with fast powder you need a very short gas system, i.e. port close to chamber to tap pressure earlier in the cycle before it drops off and to increase dwell time as much as possible. SP1 barrels are rifle barrels, having rifle-length gas systems. The retro-AR craze soaked up most if that kind of parts, so you may have to do or have done some modifications. If you want a 20" rifle with delta ring and standard handguard, you can have one made with a pistol-length gas system and low-profile gas block concealed under the hand guard and still install a "dummy" front sight gas block with the front handguard escutcheon tack welded or retained with a screw through the gas tube hole. Doing that will require custom gas block journals unless you can find a premade barrel like that, similar to the dissipator concept but in rifle length. Such a system will be insanely over-gassed for full power 5.56 loads and you will need to find an EFFECTIVE adjustable gas block (such as the ones thar vent excess gas rather than restrict it) and make a way to access it without removing the handguards.

Or you could just build a standard rifle and use enough IMR 3031 to make it run with your cast bullets.

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shastaboat posted this 24 July 2018

OK, so the trick would be to secure a barrel with a short gas tube set up (pistol-length) with a low profile adjustable gas block. I have absolutely no use for a military style dummy front sight and when scoped the only thing they are good for is hanging a rifle on a nail. Along with the low profile gas block I would be using a free floating smooth forearm. I will have to contact Green Mountain or another company to see if they would make me up a special 20" barrel with a pistol length gas port and preferably no chrome lining. I want to continue using my load of 10 gr of 2400.

Because I said so!

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Geargnasher posted this 24 July 2018

If you don't care about it looking a certain way, then yes, a short-for-barrel gas system (pistol-length on a 20" rifle barrel) is an easy solution, just install the barrel with a FF handguard of your choice and be done. You will still likely have to enlarge the gas port to work with your loads because 5.56 pistol gas ports designed for full power ammo are tiny.

I recommend a venting-type adjustable gas block with multiple/variable settings, not a "Off/On/Suppressed" type or one that uses a pointed screw like a carburetor jet across the port...those leak so much gas around the threads that even fully "off" they will push enough gas through to cycle....and probably break stuff with full power ammo and the port size/location it will take to run your load. Several companies make gas blocks which are adjustable from the front, very convenient.

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shastaboat posted this 24 July 2018

Now I only need to find a source of a barrel as I specified with a 7.5" gas port. I can open the port easy enough and install the adjustable gas port. No one catalogs such an barrel and I've sent out inquiries to several of the AR15 barrel manufacturers. Do you have any suggestion regarding what company may be able to facilitate my needs? I have no intent to shoot full power loads in this rifle build but a properly designed gas port would be in order.

Because I said so!

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Geargnasher posted this 25 July 2018

I don't think 7.5" is going to do it. See the other thread, I'll see what I can come up with using modeling first.

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Geargnasher posted this 26 July 2018

Looks like 20K peak pressure....at 2" of bullet travel. That means that you'll have about the same peak pressure at standard pistol port placement that a 20" barrel will have at standard rifle gas port location. So standard pistol-length gas system, start with a .08-something" port diameter and plan to enlarge it to .093 to .096" before it will lock the bolt back on the last round every time, even when dirty.

Carbine gas system is a no-go, port pressure will be around 12K psi and I don't think you can realistically make a large enough port hole in a .22 barrel to make it work. My Blackouts with carbine gas systems and 16.25" barrels require a minimum port presssure of 5.5K psi to function with subsonic ammunition....using a .120" port hole.

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shastaboat posted this 26 July 2018

So do you think a 7.5" will work or not? Is that the standard pistol gas spacing?

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Geargnasher posted this 26 July 2018

So some research on standard port placements and review what I wrote above. Understand that "bullet travel" is just that, from where the base of the bullet is located in the barrel before firing. Standard port distance is measured from the breech face, same as barrel length, so you will need to factor in the difference for proper port placement.

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shastaboat posted this 26 July 2018

Other than building a custom barrel with a odd for barrel length port distance, I would want to use common manufactured parts including gas tube and adjustable gas block. The port size can easily be altered and opened up as necessary

.

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Ken Campbell Iowa posted this 26 July 2018

just a thought about " main ... buffer .... recoil ... " springs.

( from recent mental games about using lighter springs in my Astra 400 in order to shoot functioning light plinking loads ) ...

the lightest spring you can use is one that from full open still reliably strips a new cartrtridge from the magazine, then pushes it into chamber and locks the " bolt " .... thus that is the limit of spring rate, not the maximum rate that will allow the bolt to fully retract.

since test springs are not always available, i was going to add several shorter springs of the required rate from a ( Lee? ) commercial spring supplier . note that adding springs reduces the combined rate. ( due to the longer torsion bar ) .

thanks guys for the interesting thread ..... i like stories about making things work that didn't ... kinda like marco polo crossing the alps ... ( g ) .

BTW i have heard pretty good things about green mountain barrels .... over-achievers they seem to be ...

ken

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shastaboat posted this 26 July 2018

Hi Ken,

Green Mountain barrels are excellent barrels and I have used several in conventional rifle builds. However they won't change or alter their standard designs for less than a 100 piece order. They do make a 20", 1 in 12" twist AR barrel but will not change the gas port location. Therefore I will have to find a decent machinist that is capable of building an AR15 barrel to my specifications from a rifled blank. I am not capable.

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shastaboat posted this 26 July 2018

I just ordered a custom AR15 barrel from McGowen barrels to my specs with the pistol length gas port. Under $300.00. 10 week delivery time. I may have to drill out the gas port hole as discussed to get it to cycle. Also ordered a low profile adjustable gas port and pistol length gas tube from Brownells. I'm going to rebarrel one of my AR's that has a lighter bolt group. (non m-16) It also sports a 2 lb Jard trigger and floating forearm. I may install a longer free-floating forearm in the future.

Because I said so!

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Geargnasher posted this 27 July 2018

Perfect. Standard pistol length, about 4" iirc from the breech face, will tap into that 20kpsi peak and should work very well for you. The only issue I could forsee is case rim damage from unlocking so soon, while the chamber pressure us still high, but at 20k the obturation of the case in the chamber won't take much force to break.

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shastaboat posted this 27 July 2018

I'm not sure what size gas port hole will be drilled but the adjustable gas block should give me the ability to adjust the weapon to full cycle at the least needed gas. And if the gas is insufficient I can always open the port size. We'll see. I received an email from McGowen regarding the unusual specs of my barrel order. I advised them what I am attempting to do. I'll see if I get any feedback. It should work.

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shastaboat posted this 14 September 2018

After waiting about 7 weeks my custom McGowan AR15 barrel was delivered last Wednesday. I had to wait until Friday to receive my slick sided upper to install the 20", 1 in 12" twist .223 Wilde chambered, pistol ported barrel. A quick install with an adjustable gas block and rifle length floating forearm and test fire was giving me 50% cycling. With a weighted carbine buffer and full power spring and the gas port shut down all the way, full power jacketed rounds cycled as normal. I was headed out on Saturday for a few days of Nevada Desert camping so I took my tools and a few parts with me. When I got camp set up I installed a buffer with no weights and a recoil spring that I had cut down 2". YAHOO! the AR functioned 100% and was printing less than 1" groups at 100 yards. I decided not to clean the barrel until accuracy subsided. After about 100 rounds and a 15 mph crosswind I think it's time to clean out any fowling. I could drill out the gas port but since I was successful in the cycling and accuracy goals, I'm going to leave it alone. With the adjustable gas block and a full power spring and fully weighted carbine buffer I can make it a jacketed firing AR.

The barrel cost me $290.00 which was a bit high but that's the price of experimentation. This AR is going to be my spring ground squirrel primary weapon and it will be nice to run with a 30 round mag instead of continual loading of a 4 round bolt mag.

I just wish that a barrel manufacturer would see fit to make a 100+ order to these specs so others can do the same build with a bit less cost. I figure at 69 years old, I can't take my money to the grave so I might as well spend it now.

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delmarskid posted this 14 September 2018

Cool beans! I'm glad you could pull it off.

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Scearcy posted this 14 September 2018

It would be outstanding if you would do a short How To article for The Fouling Shot. I am one of the unwashed masses who doesn't own an AR but would gladly buy one if I could make it run on cast. The challenge is that most of us don't speak the lingo but there is significant interest in doing what you did. Good show!

Jim

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shastaboat posted this 14 September 2018

Well Jim, other than a basic AR15 build the changes are quite easy. I've pretty well covered it here.

Custom 1 in 12" twist barrel with pistol porting; adjustable gas block, lightened buffer; 2" cut off a standard recoil spring.

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Ken Campbell Iowa posted this 14 September 2018

hi shastabout ... congrats on new toy .... the price on that special barrel was pretty decent ... have to remember those guys .... .... i am not clear on a couple things ...

are you going to shoot cast in your rig ?? ....

with your mj loads, are you loading them down

... or does the adjustable gas valve cover that situation .

thanks and keep us informed of your further adventures.

ken

to make you feel better, i once ( once ! ) had a special barrel made by wilson ...$700 ....... it was unuseable ... big at both ends ( except maybe a foot in the middle ).... makes for great stories though ...

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shastaboat posted this 15 September 2018

To answer the above questions. I will be shooting cast bullets in this AR pretty much exclusively. If I choose to shoot jacketed bullets at full power I will have to change out the light weight buffer to a normal carbine buffer and I will have to install a normal recoil spring. The adjustable gas port will be used in both cast and jacketed. Basically the Upper cost me $400.00 to build and the other modified buffer and cut down recoil spring I already had.

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Scearcy posted this 15 September 2018

Good morning Shastaboat

If you had chosen the NOE 70 gr bullet rather than the 55 gr Lee would you think pistol porting would still be correct or would a carbine system be suitable. The twist rate would need to change of course.

Jim

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shastaboat posted this 15 September 2018

Jim, I have a problem with long skinny cast bullets which tend to bend when sizing/lubing and may not stabilize in slower twist barrels. Case in point is the 6.5x55 Swede. If I was going to use the NOE 70 gr bullet I would try it first in a 1 in 9" twist barrel at 2000 fps to see if it will stabilize and shoot accurately. I can only assume that you want to use this bullet for shooting hogs or something or maybe going suppressed and subsonic. You really have to determine what you want to do with a cast AR bullet first. If you want to send me some of your 70 gr cast bullets, I can try them in a 1 in 9" twist upper carbine barrel to see how they shoot, cycle and whether they require a low load of 4895 or if 2400 would work. I suspect 4895 would be required at 2000 fps.

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Scearcy posted this 15 September 2018

Shastaboat

The NOE 70 gr is a flexible and relatively easy to deal with design. I have seen it used in both 9" and 8" twist and it performs well most of the time. It also does not require special consideration in powder choice. The CBA has a very well known member who shoots Titegroup in his 223 as a match load with these and even heavier bullets. My question really concerned the timing of the pressure curve with a heavier projectile.

Jim

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shastaboat posted this 15 September 2018

I built my Designated cast AR with the pistol porting because I wanted to use my load of 10 gr of 2400 and the Lee Bullet because it shot so well in my bolt guns and did a fine job on ground squirrels and jack rabbits. I tried that load in a 1 in 9" carbine and it would not cycle so I never bothered to test the accuracy in the Carbine AR. Both my bolt guns have 1 in 12" twist. Others have gone a different route. I succeeded in building an AR that will cycle and shoot as accurate as my bolt guns with the same ammo.

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Scearcy posted this 15 September 2018

Shastaboat

Thank you, I understand. I like the slightly heavier bullet. My hope is to do the build with a non custom barrel if possible. While I have not yet done my homework, perhaps a 9" twist barrel with carbine length gas port will be an easier item to find. I have a friend with a copy of Quickload. I will get him to do some modeling with different powders.

Your process of working through the issues is very helpful.

Jim

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shastaboat posted this 15 September 2018

Jim, If the 70 gr bullets will stabilize and shoot accurately in a 1 in 9" twist barrel, I am sure that a carbine length system can be made to work with the appropriate powders. That said, Green Mountain Barrels makes carbine length barrels in 1 in 7"; 1 in 8"; and I think 1 in 9". All of these same twist barrels are available from other sources as well at less cost than Green Mountain. My 1 in 9" barrel is quite accurate with 55 gr jacketed bullets at full power. Others have used the 69 gr jacketed bullets with good results in a 1 in 9" barrel. I have another low cost build, total $310.00 cost build including the lower receiver with 1 in 8" that would be fine with heavy jacketed bullets. The trend for builds with 1 in 7" twist for heavier than 70 gr bullets is foolish to me. Maybe they would be a good hog gun. I really don't know. I would be glad to test try some 70 gr cast bullets in the 1 in 9" upper to see how they perform. Are you just wanting to shoot targets or what? My experience with fast twist barrels in cast as previously stated in 6.5x55 required me to drop velocity to approx 1700 fps using WW to stableize. We both know that a drop in velocity equals a drop in pressure. An AR requires pressure to function. It becomes counter productive. We also know that a slower twist with the appropriate weight bullet that will stabilize in that slower twist generally are more accurate with cast bullets.

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John Alexander posted this 15 September 2018

Just as a point of information the the 70 grain NOE bullet will stabilize in 1 in 10.5" or quicker twist -- from actual experience.

John

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Scearcy posted this 15 September 2018

Shastaboat

Probably just punching paper which might include some of our local CBA matches. We do shoot 200 yards in these matches so the extra weight helps a little. Mostly I would just like to get an AR going with cast for my own education.

Jim

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shastaboat posted this 16 September 2018

Just as a point of information the the 70 grain NOE bullet will stabilize in 1 in 10.5" or quicker twist -- from actual experience.

John

Does that mean a 1 in 12" twist will not stabilize them? Also at what velocity can they be driven in a 1 in 9" or 1 in 8" barrel for accuracy?

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John Alexander posted this 16 September 2018

Shastaboat,

I was never able to get them to stabilize in a 12" twist and know other that couldn't. Maybe some have at higher velocity.

I don't know at what velocity they can be driven with practical accuracy. Accuracy always fell off for me well before 2,000 so I quit. Depends on what level of accuracy you are satisfied with.

John

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358156hp posted this 16 September 2018

I'm accumulating a 225 mould and tooling (Star Die) for a similar project. After reading Ed Harris' article on cast in the 223 I decided to pursue a more beaten path, and have ordered a 62 gr NOE mould, and of course a .225 sizing die for my Star. I could have gone heavier on bullet weight, but my slowest twist barrel is a 1-10, and that may not even see cast. My carbine barrels are 1-9, and this should work out fine until my goals end up better defined. I will use conventional lubing for this project, at least to start out with, I have some lingering misgivings about powdercoating such small, lightweight bullets.

http://www.hensleygibbs.com/edharris/articles/Cast%20In%20an%20AR.htmhttp://www.hensleygibbs.com/edharris/articles/Cast%20In%20an%20AR.htm

http://noebulletmolds.com/NV/product_info.php?cPath=24_110&products_id=361

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shastaboat posted this 16 September 2018

I'm shooting the Lee C225-55-RF bullets, Sage aluminum checs, cast in straight WW, sized .225 and lubed with my 50% beeswax/50% Lithium based hi speed wheel bearing grease to 2000 fps. Both my bolt guns will shoot to less than 1/2" at 100 yards if I am very critical with casting, culling, weighing. etc...If I'm not as critical with them and cast and load for volume then my groups expand to 1" at 100 yards. So far I've been able to equal the accuracy with the AR. All three are 1 in 12" twist. The other day I was shooting in a 15 mph cross wind and accuracy spread out to 3-4 inches with a horizontal spread. Go figure!...lol...

My cast shooting is aimed at shooting either for pests, varmints or game. I've never competed in a match but might if I had someone to coach me through the process just for fun.

I really think going heavy may not be the way to go in .223/5.56. By going heavy you then may require a faster twist barrel and consequently may have to reduce velocity under 2000 fps. I started shooting cast in .223/5.56 when 22RF ammo went out of site cost wise. My cost per cast .226/5.56 round is under 7 cents per round. I would say my cast rounds pretty much exceed what you can do with a .22K Hornet.

I may someday cast some harder bullets and alloy them with 10% linotype. If I was match shooting this may be the way to go and boost velocities to 2400 fps. However in my past experience I've always attained the best accuracy at around 2000 fps except for that 6.5x55 fast twist military barrel. I built a 6.5x55AI with a 1 in 9" twist that may be accurate up to 2000 fps. Just never shot cast in it yet. If I do I'll use the 266455 bullet.

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John Alexander posted this 17 September 2018

You mention that you might be interested in competing in a match. I am sure that any CBA match there would be shooters to help you out and I encourage you to give it a try with either your ARs or bolt guns.

There are two classes for factory rifles and two for custom rifles and with the accuracy you cite in your above post you would have probably won in any of them at the CBA nationals just finished a week ago.

I think it would be good for CBA shooters to see that an AR can compete and it might encourage others to give them a try.

John

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shastaboat posted this 17 September 2018

You mention that you might be interested in competing in a match. I am sure that any CBA match there would be shooters to help you out and I encourage you to give it a try with either your ARs or bolt guns.

There are two classes for factory rifles and two for custom rifles and with the accuracy you cite in your above post you would have probably won in any of them at the CBA nationals just finished a week ago.

I think it would be good for CBA shooters to see that an AR can compete and it might encourage others to give them a try.

John

John,

If you can encourage any Cast Bullet Assc competitor in the Reno, NV area to contact me and we'll see if my participation is possible. I know that they have a few shoots in Nevada. The nearest sanctioned range from me is almost 2 hours away by paved road and only an hour by dirt road. I think the Spring shoot is either in Winnemucca or Elko, Nevada which is quite a distance. We'll see. Thanks, Brent

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John Alexander posted this 18 September 2018

I know our matches are few and far between in many parts of the country. You might try a few postal matches to show the flag for the AR folks.

John

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shastaboat posted this 18 September 2018

I wouldn't know where to start. I have communicated with an individual in Gardnerville, NV that shoots with the Modesto CA club that I will contact to see if he would be able to coach me through the process. I know he shoots in the desert down there too. It's about 1.5 hrs drive. Another thing I'll do sometime this week on a windless day is to go out and set up on my BLM range and take some pics. I have target stand bases set in concrete at 25, 50 and 100 yards. I'll take a pic of my best target and post it here.

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shastaboat posted this 07 May 2019

April 2019 update!

So I took this "Designated Cast Bullet AR15" to shoot squirrels a couple of weeks ago. I had already turned the barrel down to .600" straight contour in front of the .750" gas port to the muzzle and re-parkerized it. I had not replaced the round floating forearm since building the rifle and also had the carbine adjustable stock on it. I wasn't happy with feel of the rifle and frankly the round floating forearm wasn't very stable so I ended up shooting my Browning A-bolt the entire week of squirrel shooting.

I ended up shooting about 1200 rounds for the week and figure about 50% hits out to 300+ yards. 100% at 50; 80% at 100; 50% at 150-200; and about 20% at over 200 yards. Average was about 50%. This gives me a kill rate at about 600 squirrels in 5 days of shooting. 2 days were raining and overcast...no squirrels to speak of...

When I got home I ordered and A1A2 solid stock and a streamlined light weight forearm with a flat base that is only 1.5" diameter. (removed the 2.0" round one...it's for sale). Because the A1/A2 stock tube is longer than the carbine length stock tube I decided to use an stock carbine length spring and the weightless carbine buffer I used before. They worked flawlessly with 100% reliability, extraction and bolt hold open on the last round. The lightweight streamlined gas port is adjusted fully open without enlarging the gas hole in the custom pistol ported 7.5" ported, 20" McGowan bbl.

Today, I went out to my BLM private range to test and sight in a bit more. Wind was gusting at 12-15 mph from about 1:00 o'clock. Not prime shooting! I'm extremely excited about the potential of the rifle now. I will post a pic of the rifle and 2 targets I shot today. 50 yards and 100 yards. Not stellar because of the wind but the potential is there. The rifle is much more stable and comfortable now. I do see me shooting more rounds than my bolt guns with reloads after 20-30 rounds instead of every 4 rounds or between each shot.

I'll be using this AR when I go back on my next squirrel shoot in late June after the first alfalfa cutting/baling. I figure to clean the carbon fouling after every 100 rounds or as needed when accuracy falls off. That's what I do with my bolt rifles. No leading in any of them.

Now to get back to casting, sizing/lubing, brass prep and loading. Thank God I'm using a LEE Pro1000.

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shastaboat posted this 08 May 2019

Not sure why my post from yesterday posted in two spots.

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M3 Mitch posted this 08 May 2019

I'm a bit late posting this, but, it might have been a good idea to have built this upper on a slightly shortened, or at least with the shoulder set back, case, to preclude anyone putting military ball ammo in it while it's set up for cast only. Just a thought. More for anyone else who might decide to give this a try.

It's always great to read on here where people are doing stuff that the unwashed majority would have said can't be done!

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shastaboat posted this 08 May 2019

I'm not in habit of leaving my weapons around where just anyone can get a hold of them. And I can shoot jacketed mil spec or commercial ammo in this by installing a standard rifle spring and buffer and adjusting the gas block to a more closed position.

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M3 Mitch posted this 11 May 2019

I'm not in habit of leaving my weapons around where just anyone can get a hold of them. And I can shoot jacketed mil spec or commercial ammo in this by installing a standard rifle spring and buffer and adjusting the gas block to a more closed position.

I don't leave my weapons around or loan them out either, but, keep in mind they "outlive" us. Just sayin'. Not a big deal, but the general principle started I think with the .357 Magnum, to do something with the "hot" ammo so it won't get into gats that are not appropriate for it.

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shastaboat posted this 11 May 2019

The whole point about this post was to build an AR15 platform rifle that I can shoot the same cast ammo in that I use in my bolt guns. Most of us know the limitations of velocity, alloy, lube and powders that consistently provide good to excellent results in cast bullet shooting. Also the individuals who actually have experience with AR platform rifles and other semi auto rifles know the difficulty of shooting cast in a semi auto to insure functionality and accuracy. Unique to an AR platform is the breaching and bolt system with a multi lug rotating bolt face and corresponding breech face. In addition this build will shoot jacketed full power ammo if two buffer parts are changed. So I promise on my deathbed to convert this weapon to shoot full power ammo before I die. As my 32 year old son is my sole beneficiary of my trust/estate and is aware of the many wildcat rifles as well as specialty arms and is quite aware of AR platform rifle designs and including this special build, I think I am safe in believing that no ill results will ever come of this "DESIGNATED CAST AR15". Maybe I should just paint the muzzle "Pink".

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