Home Forums Reloading Big Game Rifles Chronograph re MAX LOADS...

Hey All...Have read everywhere to use a Chronograph to stay out our trouble re MAX LOADS...ok...the loading books usually use 24-26" bbls...most loading data is based on these longer 22-24" bbls....
sooooooo...you work up to a max load re the books...of course your velocity is nowhere near what the book says ...maybe you bbl is most likely shorter than the "book"......soooooo...how do you know if you are at max pressure and or velocity for the set of components you are using....??????? I am referring to the AR type of hunting weapons...most have 16-18" bbls....yes...yours may have a 22 to 24" bbl....there are many bolt action rifles with 16 to 20" bbls..... same set of circumstances applies....using your chronograph will show you nowhere near what the "books" say.... soooooo.. what is the rule of thumb..(???) to "predict" when you are at max velocity or pressure even when you are using your chrono..??????
Pete

All of my load books for non magnum cartridges are with 24" barrels. Some magnum data is from 24" barrels, some 26". You just have to look. I don't currently own anything with a 24" barrel, but those that I did were within 10 fps of what the book said they should be.

Most of my rifles are 22", but some as short as 18". I work up the load with the 22" barrels and usually find my speeds with a max load are within 50 fps of what the book says they should be with a 24" barrel. That is about what I expect with a 308 class cartridge from a 2" shorter barrel. I then shoot them in the shorter barrels just to see what I'm getting. My 18" 308 BTW is about 50 fps slower than the 22" rifle.

There just isn't nearly as much loss from shorter barrels as a lot of people think. Based on what I've seen these are the numbers I expect with barrels between 20" up to 26". As you go longer the differences are smaller. Get below 20" and you see greater differences.

30-30 class cartridges: 5-10 fps slower/inch
308 class cartridges: 10-20 fps slower/ inch
30-06 class cartridges: 15-25 fps slower/inch
30 caliber and under magnums: 25-35 fps slower/inch
magnums over 30 caliber will be in about the same class as 30-06

Loading for short-barrel AR type rifles is a pain because loading data is all over the place for barrels of substantially varying lengths and with varying twist rates. For almost any loads approaching max in any gun, I find that the chronograph tells the tale when doing a load workup. There usually comes a point where increased powder results in ever diminishing increases in velocity, or even decreases, and the extreme spreads and standard deviations start rising. I back off at that point, then test the more consistent loads for accuracy even if the velocity is not the highest. Of course, you also need to look for standard pressure signs like flattening primers, ejector marks, extraction, etc.

With a chrono you know when you are near max. You will usually see deviations in velocity sometimes large increases in vel with only an incremental increase in charge or as stated above little or no increase with more charge. A chrono is just one more tool to use to keep you out of trouble and you have to learn how to interpret the results.

Quick Load will let you model muzzle velocity as a function of barrel length.

It’s always been my belief 20/25 fps per inch of barrel for rifles.
Here is a good article. I’m sure every rifle and different cartridges will produce different results but it’s a ballpark figure.
https://rifleshooter.com/2014/12/30...arrel-length-versus-velocity-28-to-16-5/

Others have said what I look for either spikes or flat lines in velocity. My question is how much velocity do you loose with gas auto's? Is it even a factor?

I look for the velocity spread between load increments to decrease and then suddenly increase quite a bit. With most of the powders I use that will happen when you are near max pressure and start to see the evidence in the primers.

IMO, a gas gun will have similar/same velocity to a bolt gun of same barrel length, within the margin of error of a large sample. Might be a little lower over all but statistically and real life insignificant.

I've chrono'd the same load out of my 16" 1:9 twist, 18" 1:8 twist and 20" 1:7 twist ARs and the average drop is about 25 fps per inch, about 50 fps between each.

Learn to read pressure signs and put the chronograph away till you have the load you want. Then chronograph the load. Be terrible if the chronograph just happened to give the wrong reading now and then and you blew up your rifle!

Pray tell, which of the widely debunked pressure signs is it that you stake your fingers and eyesight on?

Widely debunked pressure signs!?!? What, you're going to try to tell me that when my magical invisible pegacorn Princess GummiBerryDrop tells me to pour more powder into a case it ISN'T SAFE?!?! That's just ignorant. 500 fps over book maximum for a 38 special is totally fine if the Princess says so!

you shouldn't be relying on a chrony for telling you what your max loads should be...

all it is, is a radar unit so to speak...

once you reach a max load, all it does it tell you what the Velocity is of your max load...

doing otherwise, is a good way to blow up a rifle action.. and potentially hurt yourself.

Some rifles get to max pressure before you get to max powder. Its nice to have chrono readings to sort that out.

Velocity = pressure.

So, how are you determining what your max load is?

Traditional method, start low and work up your load... once I hit pressure signs, or a full case, I usually back it off
and then pick whatever was the most accurate load tested.. then chronograph it to see what the velocity is..

as Smokepole eluded to....there are rifles that will not take certain "max loads" listed in load manuals...

I have a batch of 223s....and I don't assume a load that is good in one of them, is good in another one...

Like what I have been playing with for this varmint season...

a Rem VLS will pop primers, on loads that function just fine and are the most accurate in a Ruger VT.

each rifle is an entity onto itself...

I heard that somewhere...

It also works in reverse. I had a 7 WSM that I found a really accurate load for with 160's. Chronoed it and saw that it was shooting at 7-08 speeds.

I will research several printed/published load manuals to find what powder/bullet/case I will be loading and from that I have a minimum and maximum powder charge and what those charges will produce as velocity.

I always load with a chronograph. It tells me when something is not tracking with what I expect base on the data research. During the workup I am little to not at all concerned about variance and SD and do not in fact usually even tell the Chrony to do the calc. If I get the kind of accuracy I am looking for and haven't hit a book listed max I am done, at least with most rifles. With a rifle I am specific about velocity goals for I will keep pushing it up and looking for classic pressure signs while I am looking for a good node further up. Sometimes you get that node at or closely above a book listed max. Sometimes you don't. If I don't I move on to the next candidate powder and repeat.

Once I have a good load I will then start to wring it out. Look for a "window" to center the charge in, look for average and SD velocity as well as how wide ES is. After that I may test it against temperature. All the while running each shot across the chronograph.watching for irregularity. By the time I get done I have a very good idea of how close to Max I am with that particular rifle and load.

IMO there is nothing a chrony will tell you about max without that kind of testing, at least nothing I would care to hang my hat on.

Sure it will. If you load up just a few rounds at or near the max book load and get over the velocity listed for those charge weights, your chronograph is telling you to back off because powder charge does not = pressure, velocity = pressure and it doesn't take extensive testing to reach that conclusion.

I've had rifles like that, and it didn't take more than a few rounds at higher than expected velocities to tell me something was up.

Having chronographed thousands of rounds from many different cartridges, I nearly always come up well short in terms of velocity compared to what most manuals say. Years ago I had a Remington 700VLS 22/250 with a 26" bbl and when using Varget with a 50gn bullet I remember that Nosler manual saying I'd get xyz velocity, but my rifle produced velocity 200fps less despite having a barrel two inches longer. Go figure !