AR15

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  • Last Post 01 February 2016
shastaboat posted this 26 January 2016

I've been trying to get my M4 16” AR to function with cast.  I have tried 18 gr of H4895 with a 55 gr LEE cast GC bullet that is chronoeing at on 1625 fps.  I was told that this load would function other AR's.  I've also tried the same bullet with 15 gr of 2400 and it will not function with that load either.  I didn't chrono the 2400 load but It feels just a bit hotter.

I've even taken a standard carbine buffer and removed 2 of the 3 weights and even cut 1.5” from a spare main spring.  I installed a 1.5” portion of a Mauser firing pin spring to keep the single buffer weight in place.  Now the buffer retainer and retainer spring are popping out when the action is cycled even though the bolt is fully cycleing. 

I have a brand new buffer and a brand new main spring I can install back to stock but I was wondering if anyone had tried similar modifications and were you successful?

Because I said so!

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Ken Campbell Iowa posted this 26 January 2016

cutting a spring actually stiffens it .... so you you really need a lighter spring of the same length .

i know nothing at all about that system, but can you open the gas port/valve ??

ken

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TomG posted this 26 January 2016

I have a DPMS M3 carbine in 9” twist. The gas port hole is 8” in front of the bolt face. It runs real well on 15 grs. of Rel. 7.  I'm getting 2000 fps. from this load and it is accurate averaging 1.25” groups at 100 yds..

I use the RCBS 55 gr bullet and it feeds perfectly. These are cast of WW's + tin and heat treated to 30 BHN.

My brother had a S&W cabine with a 7 twist and my load wouldn't quite work the action. What he did was to drill out the gas port hole a little larger. He then installed an adjustable gas block so he could dial down the gas pressure when shooting full house loads. This bullet and load also shot accurately in his gun.

I would not recommend cutting the springs down as you will change the timing of the gun considerably. Best thing to do is run stock springs and weights and open the gas port.

What works the action is the gas pressure at the point where the bullet passes the gas port and afterwards. Rel. 15 provides the pressure peak at the correct time to work the action with the gas port 8 in. in front of the bolt face.

I developed this load using the program called Quick Load which gives the chamber pressure curve in relation to bullet travel. It also predicts % of powder burned which is important to stop the gun from gunking up prematurely.  Others have copied this load and it worked for them. I would think that having the gas port further down the barrel would be an advantage when using cast bullets with lighter loads.

If you cut down on the weight of the recoiling parts or the spirng you can get in a situation where the bolt unlocks too soon and there is still pressure in the chamber. This is hard on the extractor etc.. 

If you drill the gas port out, go slow. I would only go one number drill size at a time as a small dia. increase can increase the pressure considerably.

The neat thing of this load is that the gun is on at 50 yds. and on again at 100 yds. Sometimes you're the windshield, and sometimes you're the bug!! Just got lucky on that one. 

Tom G.

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onondaga posted this 27 January 2016

http://castbulletassoc.org/view_user.php?id=3261>shastaboat

It sounds like you stopped at 18 gr H4895..   why? Didn't it cycle your rifle?

That is about a 2500 fps load by software and you chrono at 1625. Regardless, if your rifle wont cycle with 18 grains, up the charge. You can safely go to the same MAX as a jacketed bullet at 26 gr H4895. So, going up is not a pressure safety problem.

Try attacking the problem backwards. 25.0 gr is Hodgdon Start. reduce to the lowest charge below START that will function reliably. Then, evaluate accuracy. Just don't go below 1/2 case full per Hodgdon notes.

You don't need special buffering in an AR for cast. The lowest load that functions with H4895 is a good rule of thumb.

Gary

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shastaboat posted this 27 January 2016

Gary. I just used your suggested 18 gr of 4895 load. I certainly can increase it. I don't know why a stiff load of 2400 won't work. I guess I'm gonna have to do some load development. I really don't want to drill the gas port or change to an adjustable gas system. I'll install a new mil spec spring and buffer and get it running again with jacketed and then go from there.

Because I said so!

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shastaboat posted this 27 January 2016

Tom G, That will be my last resort. Thanks.

Because I said so!

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358156hp posted this 28 January 2016

I don't think 2400 produces enough gas volume to cycle the action reliably. Reloader 7 seems to be the hot ticket for 55 gr cast, as mentioned earlier. Don't load for velocity, load for accuracy and reliable functioning. Both are completely possible.

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TomG posted this 28 January 2016

At first thought I figured that 2400 powder would peak and drop off too quickly and not provide enough port pressure to work the action.  I just ran in through my Quick Load program and it looks like it will work somewhere around 11 grains. It shows around 13,500 PSI at the port and pretty good remaining pressure after the bullet passes the gas port. Percent powder burned is estimated at 99% which should burn clean. What works the direct impingment action is the pressure available after the bullet passes the port. The energy available is basicaly in proportion to the area under the pressure curve. Thus you need a burning rate that has a pressure curve that doesn't peak too quickly and retains pressure sufficient to work the action but still burns clean. Not an easy feat. 

I've found that my gun will cycle with what is estimated to be 12,500 psi at the port. If you choose a powder that is too slow, the percent powder burned is very low and the gun's gas system and bolt get gunked up pretty quick. I've never had mine gunk up till it quit as I clean it often but I did get a lot so soft carbon and some granuals in the action with too slow a powder or too little peak pressure.

If you have a fast twist like 9 or faster, it will take a very hard lead bullet to follow the lands. I heat treated them to 30 bhn and found that they would do 2100 fps. and still be accurate. Over that and the accuracy went away as the bullets couldn't take the fast twist.

It's too bad more folks don't experiment with this gun with lead bullets. I once posted a question in the forum on AR 15.com and asked if anyone had shot lead bullets in an AR 15. I got several responses from guys who were keyboard experts with no experience shooting a lead bullet in this rifle. They all said it wouldn't work and would lead up the gas system. A new old wives tail was started that had no basis in actual experience or fact. I didn't ask any of them if they ever shot a lead bullet in an AR. I didn't need to.  I've shot thousands in mine and never got any lead in the barrel or the gas system.

I did find some videos on You Tube where a couple guys shot lead in AR's. They were happy if they could hit a pie plate at 20 yds. That's what they used for accuracy testing out in the woods in the  back yard with and old flat screen TV for a backstop.  I guess if it hit sideways it was still OK. 

 I've not tried this load and have no knowledge if this low loading density could cause detonation in this cartridge. If you try it you do so at your own risk.

TomG

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shastaboat posted this 28 January 2016

TomG. Thanks. I didn't get any range time today. Will probably go out and try tomorrow.

Because I said so!

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shastaboat posted this 29 January 2016

Today's range session. Used shortened spring and modified light buffer. 15 gr of 2400 unlocked the bolt but failed to completely eject case. Bolt retracted about 1” and then reclosed. Neither 18 gr of 4895 no 12 gr of Blue Dot unlocked the action. Next range session wil be with 16 gr of 2400. I'd like to see if I can get the AR to function with less than 2000 fps cast bullet. 2400 fired case was clean. 4895 fired case was showing powder fouling.

Because I said so!

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shastaboat posted this 29 January 2016

Well, 16 gr of 2400 didn't work with the light buffer and cut down spring. I didn't chronograph the load but the muzzle blast report was again heavier than the 18 gr of 4895. I then installed a stock recoil spring and buffer and fired one round of jacketed ammo. Rifle functioned fine. Back to the drawing board.

My original goal here was to develop some cast ammo that would function in the AR, chrono between 1800 and 2000 fps and shoot 1 MOA or better in my 2 bolt guns and the AR. A secondary goal was to use less powder to accomplish the first goal by using a slower pistol/shotgun powder. I believe the second goal may not be attainable without a custom lighter weight full length recoil spring and an appropriate buffer.

Shooting jacketed ammo then would require a switch back to a stock buffer spring and buffer. Not a problem in the field. Takes about 30 seconds.

I'm going back to Gary's suggestion and will do a ladder test with 4895 to see if I can get the AR to function with the 55 gr cast GC bullets. Feeding is fine. At the 18 gr of 4895 load, not enough pressure was generated to expand the case neck to keep powder fouling off the case. I'm afraid that if I have to exceed 2000 fps the hardness of my bullets would have to be higher than 18 BHN.

I'm just not ready to modify the gas port and install an adjustable gas block.

Fun stuff.

Because I said so!

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shastaboat posted this 31 January 2016

With stock buffer and spring, I still cant get the gun to function with up to 22 gr of 4895. No success with 4227, 2400 etc...Guess I'm gonna have to consider the adjustable gas block and drilling out the gas hole.

Because I said so!

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TomG posted this 31 January 2016

Before you do anything further, I would check out the gas system. Sounds like you may have a plugged up or damaged gas tube or something else going on. Sometimes the gas hole inside the barrel will have a burr protruding into the barrel. This will strip jacket material or lead off and can fill up the bleed hole. I once saw one with my borescope that had a nasty burr from improperly drilling the bleed hole. It was a gun that a customer brought in that had copper all over the bleed hole and extending a half inch forward of the hole. This gun functioned but accuracy was in the toilette.

You need to pull the gas block and the gas tube and see if they are clean and unrestricted. It could be a crushed gas tube but it sounds like you aren't getting enough gas to the gas key on the bolt. Check for binds and witness marks that show unusual drag on the reciprocating parts.

Punch out the gas port with a drill bit. This is a good time to gauge the size of the hole. You can try different sized fractional and numbered drills in the hole till one fits.  Make sure that the hole in the gas block lines up with the bleed hole in the barrel. If it doesn't gas flow will be restricted.

Only after checking out the entire gas system would I consider modifying the gun. Keep up posted.

Tom Gray

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shastaboat posted this 31 January 2016

Tom, My AR has at least 1000 Jacketed rounds through it. Before I do anything I will pull the gas port, barrel and inspect. It's snowing out so maybe today will be a good day to pull the barrel and do a thourough cleaning of the gas system. I have a brand new barrel that has about a 1/16 gas port hole. Just wondering what your's measures?

Because I said so!

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TRKakaCatWhisperer posted this 31 January 2016

What is the distance between the gas port and the end of the barrel?

If it is too short, the time of the pressure applied to the port will be reduced.

Therefore, an alternative is to look to see how much a different flash-hider would affect that pressure level.

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TRKakaCatWhisperer posted this 31 January 2016

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shastaboat posted this 31 January 2016

My barrel is a standard 1 in 9 mil spec M4 barrel with gas port approx 7.25” from the receiver. Measures approx 8 9/16 from the muzzle with no flash hider. or muzzle break. I've installed a knurled, thread cover. I do not believe a muzzle break will change the gas port pressure whether installed or not.

I stripped and inspected the barrel and measured the gas port. The gas block may have been positioned a bit close to the receiver but the gas port is concave dished about .030-.040 into the barrel. The actual gas port hole measures over .080 and opens up on the concave to .125 which matched the gas block. I was very careful to reinstall the gas block directly over the cas port. I'll go check function again with the 22 gr of 4895 and see if it will function. Another issue is that I am not crimping the cast loads and may have to crimp to increase pressure to function. I “know” this may affect accuracy so I'm trying one thing at a time. I'll load a few with a heavy crimp and see if the weapon will cycle.

Because I said so!

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shastaboat posted this 31 January 2016

OK, a quick trip out to BLM in the snow. Gas port lined up correctly. 15 gr of 2400 cycled but no lock back. 21 gr of 4895 cycled but no lock back. 22 gr of 4895 still no lock back. 20 gr of 4198 clcled but no lock back. Fired a 55 gr jacketed with 25.5 gr of H335 cycled but no lock back. The new DPMS buffer may be the cause. I can live with the failure to lock back.

I'm going to load 20 or more with 15 gr of 2400 and do some accuracy and more function tests when the weather clears and my BLM dries out.

The crimp made no difference. Both crimped and uncrimped functioned.

Because I said so!

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TomG posted this 31 January 2016

Brent,

Sounds like it was the gas block not aligned with the gas hole.  I hope you poked out the gas tube to make sure it was clear.

It appears to be acting normally now.  Too bad you don't have some Reloader 7 to try. It has the best pressure curve of all the powders I checked for cast in an AR.

I can't remember what the gas port hole measured in my gun. It's a DPMS and I did measure it a couple of years ago. I writ it down but I'm  currently wintering in Tucson so I don't have access to my notes.

The harder you can make your bullets the faster and harder you can run them. That's why I heat treated mine.  A 9” twist is plenty so velocity is probably not a problem.

For best accuracy I would suggest slugging your chamber throat. Mine was huge with a NATO chamber in it. Size your bullets to one thou. less than the throat. This will help keep them straight as they enter the barrel and seal off the young gas better. All that will help keep the lube from blowing off the bullet before it gets in the bore.  You might try shooting some as-cast and not sized.

That cold weather you have now will be here tomorrow. Highs will be in the high 40's and low 50's for a few days. It was 81 yesterday and tee short weather today.

Keep us posted

Tom

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shastaboat posted this 01 February 2016

I'm sizing .225. As for accuracy the ones I fired in my Browning A-Bolt were quite accurate. The first test showed the AR will do just fine. Now that I've got it cycleing I'll be testing for accuracy. I've been shooting cast rifle for 40 years so I understand the intricities. Getting better than 1” was the most difficult with my 6.5x55 but eventually I accomplished that. So far the .223 has been a breeze. I'm really looking at 15 gr of 2400 as it showed a lot of promise when I first tried it in the Browning and also in the AR even though it wasn't cycleing before. We'll see. Thanks for your assistance.

Because I said so!

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