Therealkoop Posted January 21, 2015 Share Posted January 21, 2015 What dictates the minimum charge for a rifle cartridge? Lets talk about .223 specifically. 40g ballistic tip vs 55g FMJ with H335. The minimum for a 40g in Hornady's manual is 24.3g, and 20.8g for a 55g. Most of what Ive read seems to state that minimums are based on case capacity, however the capacity for a 40g vs 55g doesn't seem too much different. especially if you load the 40g shorter than the 55. So why is the minimum so much lower with the 55g? Link to comment Share on other sites More sharing options...
jkrispies Posted January 21, 2015 Share Posted January 21, 2015 As I understand it, "minimum charges" are typically just 10% less than the maximum charge. "10%" is pretty much just an arbitrary number that's been picked somewhere along the line and made the standard. So, to answer your question, the minimum charge is derived from the maximum charge. Now, lots of people can start replying how and why I'm wrong... Link to comment Share on other sites More sharing options...
MustangGreg66 Posted January 21, 2015 Share Posted January 21, 2015 Interesting topic. Obviously when you start getting too little powder you can stick a rifle bullet in the barrel, the same as a pistol. Far before that, you'll run out of gas to run a semi-auto (AR). I imagine (thinking out loud) that with a very small powder charge, you could run into inconsistencies from powder position within the case. A friend of mine has done some research into it in pistol calibers and found it to be a factor in certain powders/primers in his revolvers. The first round, having the powder positioned more towards the back of the bullet, would go off with a bit more authority than subsequent rounds, and no, it wasn't the bullets working forward from recoil. OAL was the same after 1-2 firings of neighboring cartridges in the cylinder. I used to do some varmint hunting and remember reading some articles on 223 VS 218 Bee. One guy was loading the 223 down to ~2000fps velocities but he wasn't just downloading 223 powders, he actually used Blue Dot. I shot some in a 14" Thompson Contender and the powder gave a good blast when loaded to higher velocities and a nice pop when loaded lower. Link to comment Share on other sites More sharing options...
Flatland Shooter Posted January 21, 2015 Share Posted January 21, 2015 Rather than just use a 90% of the maximum charge for a minimum charge, how do we go about developing a safe minimum load? What should we watch for when trying to get really low powder charges? If it cycles the gun, is reasonably accurate and gives decent chronograph data, can i call it good or is there something else out there I need to be concerned with? I currently run a sweet load right at 80% of the loading manual's maximum that meets all of the above criteria, but if there is a problem with it, I'd really like to know. Thanks. Bill Link to comment Share on other sites More sharing options...
jkrispies Posted January 21, 2015 Share Posted January 21, 2015 (edited) Flatland Shooter, I don't know how to figure that out. However, there's a well documented phenomena where a too low charge can initially cause a bullet to stick in a barrel, immediately folllowed by an overpressure caused by the continuing expansion of gas having nowhere to go, and a kaboom. Sounds very hocus-pocus to me, but I've read about it in several places, and they were reputable sources. I'll let somebody else test the theory! MustangGreg66, other folks have tested the theory with the position of the powder in a case. It's been done mostly with .38spl target loads. Somebody else could remember the load I'm sure, which uses a ridiculously small charge of Bullseye and something like a 148gr wadcuttter. I've shot them, still have a few in my garage right now, actually, and they're very accurate and softer than a .22lr when shot through a heavy revolver. Anyway, with that load, the old advice is to tip the muzzle up before firing each round to get the powder to settle back against the primer. I think with a load like this you may not necessarilly get an inconsistent velocity (maybe so?) but there could be something approximating a hang fire if it takes an extra millisecond or whatever for the primer charge to make it across the case to the powder if it is settled at the front. EDIT TO ADD: Flatland, without intending to give advice that might blow up your gun--use at your own risk!--when the powder charge gets too low, you'll probably start seeing inconsistent velocity. If your current load is consistent on the chronograph, I wouldn't be overly concerned. Edited January 21, 2015 by jkrispies Link to comment Share on other sites More sharing options...
jkrispies Posted January 21, 2015 Share Posted January 21, 2015 Lord only knows why I'm about to transcribe the following, but... from Understanding Firearm Ballistics page 41 by Robert A. Rinker addresses both of the issues raised above: "As related by an expert wintess from H. P. White Laboratory, the theory stated that when a cartridge is loaded so that the powder charge leaves a lot of space in the cavity between the primer and the base of the bullet, the primer flash can cross the open space while the powder is laying on the bottom... This flash may move the bullet out of the case but it will have insufficient energy to properly engage the rifling. This will take place a short instant before the powder is ignited and creates the main gas expanding force. More force is then required to move the bullet than is normal and excessive pressure is exerted on the cartridge's base and breech mechanism of the gun... "Another theory that is about the same maintains that the powder may partially ignite and create a 'slow burn.' This propels the powder to the front where it presses abainst the bullet and can create a pressure wave caused by runaway burning. "Norma, the Swedish ammunition manufacturer, cautions about the hazards of light loads that fill cases only about one third of their volume. They warn that the primer may flash along the surface of the powder and only ignite part of it. This will press the bullet into the rifling where it may stop. A microsecond or two later, when the balance of the powder ignites, it will not be able to move the lodged bullet and will create extra high pressure. Remember that the bullet plugs the barrel so the gas does not have its normal means of escape. Also, if the gun survives this shot... the barrel will be plugged when the next shot is fired... "It is interesting that tests by the Frankfort Arsenal show changing the powder position in an unfilled case has a big effect on performance. With .30 caliber M72 Match Ammo, the shift from forward to rearward powder position can alter the strike point 2 or 3 inches at 300 yards and at 1,000 yards from 16 to 30 inches... "Whether the powder is positioned forward, rearward, or level is not as imperative as for it to be the same for each shot... [M]any target and bench-rest shooters raise the barrel to position the c harge to the rear or a side to side shake to level it before each shot." Link to comment Share on other sites More sharing options...
Flatland Shooter Posted January 21, 2015 Share Posted January 21, 2015 Interesting stuff John. Thank you. Bill Link to comment Share on other sites More sharing options...
Therealkoop Posted January 21, 2015 Author Share Posted January 21, 2015 Haha thanks for the info. Much more than I expected to hear back. The biggest concern I see from most searches is from dual or irregular flame front, similar to knock in an engine or pre ignition, causing pressure spikes. This doesnt seem to always apply though such as in my previous example. The case capacity is close enough to the same that there shouldnt be risk of "knock". The idea of max pressure/charge - 10% seems logical looking at data. Link to comment Share on other sites More sharing options...
thermobollocks Posted January 21, 2015 Share Posted January 21, 2015 MustangGreg66, other folks have tested the theory with the position of the powder in a case. It's been done mostly with .38spl target loads. Somebody else could remember the load I'm sure, which uses a ridiculously small charge of Bullseye and something like a 148gr wadcuttter. ... I think with a load like this you may not necessarilly get an inconsistent velocity (maybe so?) but there could be something approximating a hang fire if it takes an extra millisecond or whatever for the primer charge to make it across the case to the powder if it is settled at the front. 2.7 grains canonically The other thing to consider with the wadcutter is that since it's seated alll the way down, there's way less free space in the case, so even though 2.7 sounds hilariously light, there's not nearly as much free space as with, say, 3.5 grains of Bullseye and the 158 SWC. With handgun ammo, what also contributes to potential hang firing is the kind of powder. Bullseye excels in the .38 special because it is fast burning and generally insensitive to free space. Not all fast burning powders are like this. I had some dubious Accurate #2 loads where even with near max charges, I would get ratty sulfur colored leftovers, and tilting the revolver back or forward to settle the powder would produce a frightening difference. Pellet gun vs. normal gun performance. Link to comment Share on other sites More sharing options...
LikesToShoot Posted January 29, 2015 Share Posted January 29, 2015 What dictates the minimum charge for a rifle cartridge? Lets talk about .223 specifically. 40g ballistic tip vs 55g FMJ with H335. The minimum for a 40g in Hornady's manual is 24.3g, and 20.8g for a 55g. Most of what Ive read seems to state that minimums are based on case capacity, however the capacity for a 40g vs 55g doesn't seem too much different. especially if you load the 40g shorter than the 55. So why is the minimum so much lower with the 55g? I don't know where the minimum charges come from but I'm not believing the case capacity aspect. Look at 55gr .223 using Titegroup, the charge is only 3.1gr and it's rated at 1064 FPS and 4000 CUP per Hodgdon load data. http://www.hodgdonreloading.com/data/rifle When I searched .223 and Titegroup I found many had tried this load and the bullet left the barrel OK but obviously there wasn't enough pressure to cycle the bolt. Regarding the question "So why is the minimum so much lower with the 55g?" It's pretty typical for the heavier bullet to use less powder to get similar "pressures". Punch in 38spl, 125gr HDY, 140gr HDY and 170gr SIE and Titegroup, this clearly shows the heavier bullet using progressively less powder charges. The COL were 1.455", 1.455" and 1.450" respectively. Charges 4.4 - 4.6gr, 3.9 - 4.2gr and 3.0 - 3.6gr respectively. Pressures were 12.8 - 15.6K, 13.1 - 15.8K and 11.1 - 16K. Of course the velocities fell dramatically 953 - 1010 FPS, 864 - 919 FPS and 635 -764 FPS. Unlike our vehicles that use more fuel for more weight to get up a hill, heavier bullets need less powder to get to the same "pressures". Link to comment Share on other sites More sharing options...
Graham Smith Posted January 29, 2015 Share Posted January 29, 2015 (edited) Now, lots of people can start replying how and why I'm wrong... Not wrong but perhaps incomplete? I've seen some recommended charges from some sources that are typically more conservative on the bottom end than others. The brass itself can influence this to some degree. I've seen a number of people state that Lake City brass tends to be thicker and has a smaller capacity which can result in higher pressure. This statement is usually accompanied by a recommendation to use an 85% load rather than 90% of max. So perhaps that's what these lower number represent. From what I have personally seen, many Max recommendations tend to be rather low as well, which leads me to think that perhaps there's quite a bit of CYA in all of the numbers. Edited January 29, 2015 by Graham Smith Link to comment Share on other sites More sharing options...
Steve RA Posted January 29, 2015 Share Posted January 29, 2015 True, if you compare loads from manuals from the 40s and 50s to late model manuals there is usually a noticeable reduction in the maximum loads listed. Either the quality of the powder has increased quite a bit or the CYA has. Link to comment Share on other sites More sharing options...
dauntedfuture Posted January 31, 2015 Share Posted January 31, 2015 24.3-20.8=3.5 3.5 / 20.8 = 16.8% charge weight variation so that is significant. (55-40) / 40 = 37.5% heavier bullet which is significant. The reason that you are not seeing such reductions is that H335 is a medium to slow-ish powder in .223 and you will usually run out of case capacity before you get to high pressures. I don't know at what point of reduction from max you will run into an under -pressure / explosion combination from flash-over or what ever. I suspect, but don't know, that I think what happens is that the primer pops, the bullet lodges in the bore without sealing the case and the powder burns with too low of pressure to seal the case and the gas blows out around the case and back into your face as the with the bullet stuck in the bore, you have essentially created a much larger capacity case. What I do KNOW is that without enough powder you can and will have inconsistent velocity and pressure, your rifle might not cycle and the bullet could get stuck in the bore. I suspect that what causes more issues is that you get a bullet stuck in the bore and then try to fire another one behind and the rifle explodes. Some powders like 4895 specifically say that they work well with reduced loads, which are less then starting load, loads. I understand that people have had good luck with very log charges of AA1680 but I have never tried any and you cant find it now. Link to comment Share on other sites More sharing options...
LikesToShoot Posted February 3, 2015 Share Posted February 3, 2015 I started single stage reloading for handguns back in the late '80's. About nine years ago I did some Bench rest and silhouette reloading with the .308 for a short time before switching to progressive handgun reloading to feed the need of IDPA, Steel Challenge and USPSA. Now I've started reloading for the .223 and have some Varget and H4895 to work with. I found a good deal on some Hornaday 55g FMJ BT and decided to finish off the 1/3# of H4895 for local in-door three gun winter matches. A powder puff load of 20.4gr at 2.220" seems to work very well in my AR. Next I'll try to work up some Varget loads for real rifle distance shooting until I can find some of the more favored .223 powder. I guess I have about 5# of Varget to work with. While looking at the Hodgdons website I seen their Titegroup and Clays loads listed. Since I had a Dillon powder measure full of Clays from a recent pistol loading session I went ahead and loaded ten rounds of 55gr HDY FMJ BT .223 with 3.2gr Clays at 2.206" just for fun. As expected this was super soft, not very loud, didn't move the bolt and exited my 18" barrel with no problems. (Hodgdon lists their test barrel at 24") I don't see any use for this in semi auto but for a bolt gun it may have a use somewhere. Link to comment Share on other sites More sharing options...
Guy Neill Posted February 3, 2015 Share Posted February 3, 2015 The primary reason much of the newer data is lower than older has to do with improvements in pressure measuring technology. The older copper crusher method only gave a point pressure indication. The piezoelectric transducers used now give information for the entire pressure event. Any CYA is in the SAAMI specs - at least for the manuals I worked on. I took pressures as close to the specified limit as I could without going over for load data I tested for the manuals. Guy Link to comment Share on other sites More sharing options...
9146gt Posted February 3, 2015 Share Posted February 3, 2015 Guy,who and how do they calibrate the piezoelectric transducers ? Tom Link to comment Share on other sites More sharing options...
Guy Neill Posted February 3, 2015 Share Posted February 3, 2015 They have a separate fixture that they can apply pressure to the transducer with, combined with a gauge, if I recall correctly. SAAMI also has special lots of reference ammunition that each SAAMI member will fire samples for a general comparison of the various pressure guns. Guy Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now