Looking for the weakest load that will cycle an AR15

For my action rifle competitions I was thinking about coming up with really mild loads to reduce recoil and staying on target. The farthest we shoot is like 75 yards usually no more than 50 yards. I whipped up a couple test rounds today and tried them at the range: 55 grain bullets over 5 grains of Trail Boss. Well, they fired, and were surely sub sonic but they turned my AR into a single shot rifle. Anybody already fooled around with my idea?

There are two things to account for here. Accuracy and light recoil. The light recoil will come at a cost of poor accuracy I bet. Now the slower the propellant you use (low velocity but still listed to use in the 223 safely) the lower the FELT recoil. The faster the propellant the sharper the FELT recoil. With a 55 grain bullet the slow propellants would be Varget, H 4895, and BLC-2. The fast ones would be IMR 4198, H322, and 2015. Also a heavier bullet with a slower propellant will yield a softer felt recoil. At least to me they do anyway.:) Now if the starting loads DO cycle the action and are accurate then you can try a load that is a bit lighter but I am betting most starting loads will be poor choices to begin with.

Chamber pressure is not what cycles the action of an AR or any other gas operated action.
What cycles the action is port pressure.

Port pressure is the gasses that travel down the bore and enter the gas port in the barrel. Fast powders burn to quickly and do not produce enough gasses or "port pressure" to cycle the action, but they can and will most certainly produce enough chamber pressure to blow your rifle up.

Just because the action did not cycle is NO indication that chamber pressures are low.

Chamber pressure is not what cycles the action of an AR or any other gas operated action.


Just because the action did not cycle is NO indication that chamber pressures are low.
The Trail Boss load came directly from a guy at IMR. It is also on the Hodgon website so it's proven and safe,

13.8 of 2400 cycles my mini-14 and is just under max of 14 for a 55g jacketed. very accurate at close range too.

Published Hercules data and in the Lee book. Not a low pressure round as Lee shows 14.0 @ 49,900psi, oal 2.215

W/e your regular load is, try reducing it 20-25%. Load up a ladder, going down by 1 grain at a time. Out to 75 yards in fast action shooting, I'd be surprised if you noticed a difference in accuracy.

With a 55 grain bullet the fast propellants would be Varget, H 4895, and BLC-2. The slower ones would be IMR 4198, H322, and 2015.You have the fast and slow powders reversed.

OP, if you're really serious about this, you can spend a good amount of money to tune your AR to require the least amount of gas port pressure in order to cycle. You'll end up with an adjustable gas block, a JP Rifles lightened bolt carrier and either a lightweight buffer and reduced power spring or one of JP's new captured spring and buffer assemblies in a reduced weight form. The next result of this is a finely tuned rifle specifically dialed in to shoot a very light, very specific load. If you move away from that load, you'll find yourself having to mess with the adjustment on the gas block getting it reliable again. You'd have to do this every time you changed ammo, so this would not be the rifle I'd keep around to defend the family. Once the rifle is tuned, you start working up, or down rather, a light load to cycle the rifle and give you acceptable accuracy. Powder choice becomes pretty important because you'll need a consistent burn with what will likely be a reduced load. Going to one of the 3-gun forums will give you some ideas about what works and what doesn't in that regard.

Actual recoil energy is what causes muzzle climb so the character of the recoil isn't that important. .22lr recoil is very sharp, but it is very low energy. Bullet weight and velocity are the two ammo considerations for recoil. A lighter bullet will reduce recoil. A slower bullet will as well. Going with a powder that is really too slow for the particular bullet will give you a reduced velocity while possibly still generating enough gas volume to sustain port pressure and cycle the action. However, if you go too slow on the powder, you'll end up with burn consistency and thus accuracy problems. The one nice thing about using a slow powder with a light bullet is that you are working in a range where it becomes essentially impossible to get enough powder in the case to reach dangerous pressures. Guys have had reasonably good luck using Varget with 50-55gn bullets. Velocity is down compared to the same bullet with something like Benchmark or RL10x or 2015 but so are pressures and Varget burn more consistently at reduced pressures than many other powders in its burn rate range.

The two simplest solutions would be either a muzzle brake or a dedicated .22lr upper receiver (if your competition allows it). I'd go with a good brake first and then decide if I needed more recoil reduction from there.

@helotaxi

so does a 55 gr. bullet over 20 grains of varget sound like something that might work? this is almost 3 grains below the listed starting load. still safe?

Adjustable gas block, as said above, sounds like a good idea.

The count,

I have done what you are trying, and my powder choice for the "bare minimum" load was varget.

When you're getting down this low, components and your rifle will play a part in your results. The 20 grain load of Varget for me did not work. Would not cycle the bolt on a Sabre Def. Or a Daniel Def. AR. I was not hellbent on this project enough to swap parts to allow low recoil loads. It was more of a powder economy thing to see how many rounds I could get out of a lb...

Using LC brass, Win primers, 55 grain Hdy FMJ and Varget my "bare minimum" load that worked in both rifles ended up being 22.5 grains.

20 grains gave me unacceptable groups at 100 yards. When I got to the 21.7 to 22 grain mark the bolt cycled but about 1/3 of my brass was getting chewed up from cycling issues.

Good luck with whichever route you take!

The count,

I have done what you are trying, and my powder choice for the "bare minimum" load was varget.

When you're getting down this low, components and your rifle will play a part in your results. The 20 grain load of Varget for me did not work. Would not cycle the bolt on a Sabre Def. Or a Daniel Def. AR. I was not hellbent on this project enough to swap parts to allow low recoil loads. It was more of a powder economy thing to see how many rounds I could get out of a lb...

Using LC brass, Win primers, 55 grain Hdy FMJ and Varget my "bare minimum" load that worked in both rifles ended up being 22.5 grains.

20 grains gave me unacceptable groups at 100 yards. When I got to the 21.7 to 22 grain mark the bolt cycled but about 1/3 of my brass was getting chewed up from cycling issues.

Good luck with whichever route you take!
Thanks, will try 23 gr. of target. That should cycle for sure as its the starting load per the Hodgon website. I already 'upgraded' my AR with several goodies so buying new parts to just lighten the weight is not in the cards for me either.

It was more of a powder economy thing to see how many rounds I could get out of a lb...
Varget wouldn't be my top choice for economy...

I've found a 55 gr cast boolit over 19 grains of H335 cycles my MSAR on the high gas setting. Shoots pretty good, too. Yeah, I'm cheating on two fronts.:)

I agree gloob. H335 would be a better choice if you were going strictly by grains. Varget was just my powder choice at the time. My logic was this is the one powder I thought was the most stable (out of my choices on hand) and actually makes claims to not be temp sensitive. Between the fact of having loads that weren't listed anywhere and hearing negative stories resulting from going too low almost as much as overcharges, I wanted to play it safe.

I'm curious what kind of cast are you using?

Why do you want to do this?

.223 out of any AR is already soft in terms of felt recoil. You're going to stick a bullet in the bore.

I see the answer to be real simple. From your load data select the starting charge. then Reduce by a grain until it doesn't cycle. Then increase one grain and test. No adjustments to the rifle are needed.

The Trail Boss load came directly from a guy at IMR. It is also on the Hodgon website so it's proven and safe

I'm sure it did and if it's from Hodgdon I'm sure it's safe.

My point is that TB is a fast powder and does not produce enough gas(port pressure) to cycle the action of a semi-auto.

Increasing the powder charge will increase "Chamber" pressure but it will not increase "port" pressure. Meaning the rifle will blow up before TB will cycle the action.

@BOVICE

Maybe you don't know what action rifle shooting is. There are several stages where you often have to move around and sometimes double tap or triple tap targets. The whole thing is timed and scored for accuracy. Every second you can shave off by staying on target (hence looking for lowest recoil and muzzle climb) makes a big difference.

Increasing the powder charge will increase "Chamber" pressure but it will not increase "port" pressure. Meaning the rifle will blow up before TB will cycle the action.

Can't really happen with Trail Boss because you can fill up the case to where the bullet ends and this will be the max load and still safe.

You might try SR 4759 or AA 5744.


Sounds like an interesting test. I have some test .223 cases all primed and ready, as well as some of both of those powders.


Yea, hard to blow anything up with Trail Boss.

I don't think that you can get enough Trail Boss in the case to kaboom an AR. That's the point of Trail Boss and jacketed bullets in rifle cartridges. You can't likely get enough in the case to cycle an AR either.

I still highly recommend starting with a muzzle brake.

I still highly recommend starting with a muzzle brake.
Just received a YHM muzzle break today and already installed it. Will whip up some rounds with Varget and H335 as recommended above and see what happens. Will post my finding here in a couple days.

Can't really happen with Trail Boss because you can fill up the case to where the bullet ends and this will be the max load and still safe.

Not what I said!

I said, you will never get a fast powder like TB to cycle the action. Increasing the charge will only increase the chamber pressure and not increase the port pressure. You will blow the rifle up before you will get fast powders like TB to cycle the action. Meaning it can't be done.

Like others have said, I would find a good, yes I read that you have one but the key word is good, muzzle brake first, then focus on working up your load. I own and use a Yankee Hill Phantom 5M1 (aggressive end) muzzle brake\compensator, and I love it. Felt recoil is pretty low, and it's easy for me to shoot 5-10 rounds on target. I could probably do a whole magazine dump if I had a better trigger, but for now the basic trigger from my LPK will do. The concussive blast is probably the worst I've felt from any brake.

You may find that your first (few) muzzle brake(s) won't do the trick. I also suggest looking into a PSW FSC556. It may seem a bit pricey at $100, but I have used one under full-auto fire quite a few times and experienced almost no muzzle climb.

Since this is the reloading forum after all, I admire your search for finding a low-power load that will cycle reliably. I'm not so sure using a stock set-up, you'll be able to find one that's low enough to make a difference. My suggestion would be to look into lightening some parts if you really were dead-set on a light load, but you may run into timing issues. It's a delicate balance.. For instance, if you opened your gas port, got a lighter bolt, lighter spring, and lighter buffer you may be able to shoot light loads, but running a full-power load would most likely be hell on your rifle.

Depending on your budget, and I'm not sure what kind of set-up you have, there's a myriad of things you could do to improve your times before even working on a load. Making sure your rifle is balanced would be my first step; rear-heavy is going to increase felt recoil, front-heavy is going to make it harder to swing around and get on target.

I'm curious what kind of cast are you using?
Lee "Bator" 6-cavity mold, 2-3 parts lino to 1 part wheel weights, Hornady checks, Lee .225 sizer. Tumble lubed in a very light coating of liquid alox. Cases are flared with a kiss from my 7mm-08 sizing die. Seated with a good roll crimp right behind the first driving band to safeguard against setback.

You might try SR 4759 or AA 5744.
I loaded up those eight .223 test cases I had sized and primed already.

I used some Winchester 55 Gr FMJ-BT bullets loaded to an average 2.225 OAL.


I loaded 4 with 17.5 Grs of SR 4759. (Right at 100% load density)

They gave an average 2708 FPS, cycled the action, & tossed the brass at about 12:25 on the clock and around 6 to 7 feet away.

I loaded 4 with 18.5 Grs of AA 5744. (100% load density is about 23.5 Grs)

They gave an average 2605 FPS, cycled the action, & tossed the brass at about 12:15 on the clock and around 5 to 6 feet away.

I was using PSA upper with a Spikes ST-T2 buffer.

Recoil was mild. Obviously you can go lighter than this. How much is the question. A standard buffer would help as well.


Edit: I forgot to mention this is a mid-length upper.

I loaded 4 with 18.5 Grs of AA 5744. (100% load density is about 23.5 Grs)
They gave an average 2605 FPS, cycled the action, & tossed the brass at about 12:15 on the clock and around 5 to 6 feet away.
I was using PSA upper with a Spikes ST-T2 buffer.
Recoil was mild. Obviously you can go lighter than this. How much is the question. A standard buffer would help as well.

Edit: I forgot to mention this is a mid-length upper.

Interesting stuff, thanks...The How Low can You Go quest continues.... :-)

The test brass will be ready to load soon. Perhaps I will load four each with 17.5 & 18.0 Grs of AA 5744 and try them. I have a standard weight buffer I could use as well. IMR 4895 is probably worth trying.

How about Blue Dot ?

I loaded 4 more each with 18.0 Grs and 17.5 Grs of AA 5744.

18.0 Grs averaged 2525 with an ES of 38 and an SD of 15. It cycled the action fine, and tossed brass at about 12:25 on the clock and around 6 feet away.

The 17.5 Gr load was a problem. The first two shots were 2478 & 2473 and cycled the action, but the third shot was 2428 and short stroked. The fourth shot was 1638 and it did not feel like the bolt moved. Don't know though.

It would appear that about 18.0 Grs of AA 5744 is as low as it needs to go with a 55 Gr FMJ-BT bullet before things get erratic.

jibjab

How about Blue Dot ?

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.

With 33 gr Vmax bullets, no amount of Blue Dot will cycle any of my AR15s.

That goes all the way up to 18 gr 4200 fps that destroys the brass.

http://i757.photobucket.com/albums/xx220/ClarkM/AR15BlueDot18Gr33VmaxDSCF0027-2.jpg

Try H4895

18 grs cycles my 6.8 with 130 gr cast....

You can load 60% down from max...i.e ..@ 14.5 gr for the 223

http://www.hodgdon.com/PDF/H4895%20Reduced%20Rifle%20Loads.pdf

23 of h4895 for 165 cast in 308 carbine works.

Back from the range... what worked was 20 grains of H335 under a 55 grain bullet. The new muzzle break makes a big difference. The weaker load helps but its not a HUGE difference compared to a regular load of 24 grains. Nothing like a 1200 ft/sec load out of a bolt action, thats for sure. Anyway, with the muzzle break and the weaker load there is a tiny edge, which is good.

Be sure to inspect/clean your gas port after you shoot a hundred or so to gauge the fouling. My reduced charge H335 loads require more frequent cleaning. You wouldn't want to have a surprise in the middle of a match.