Seating Depth or Powder?

[GAR700]

Hi all,
Perhaps some of you can help me out with a question I have...

I am trying to work up a load for my Marlin XS7 .243 with 85 grain Barnes TSX's, Reloader 19, Winchester cases, and Federal large rifle primers. My question is regarding the "order of operations" when working up a new rifle load.
I have read some information that says the best way to go about it is to start at minimum load and work up groups varying only seating depth. Then, once you have settled on the seating depth your rifle likes, you should try varying the amount of powder.
It seems to me that all you change when varying seating depth is pressure and that varying the amount of powder would do the same thing.
So, my question is, should I vary the seating depth while using the minimum load or should I vary the amount of powder and then change the seating depth to fine-tune the load.
Sorry for the confusing question...

GAR

[oneoldsap]

I work up to the powder charge that shows the most potential , then adjust seating depth to optimum for that bullet and load . Then make sure they will cycle through the magazine , if that is a consideration . Make only one change at a time !

[farmerboy]

Have'nt heard it in that order. Usually it's the other way around but I'm sure if you ask you'll hear multiple ways. Make about 5 rounds with starting charge and increase powder 1 tenth grain and make 5 more. Do this to max charge but you may not get to test all because your particular gun may max out with pressures before you actually get to Max published loads. Anyways let say you have around 15 different batches. Shoot each batch at its own target and label with a pen/marker before shooting and label each batch of ammo. Shoot slowly and dont heat barrel too much or they will give false groups due to the heat. After you get your results find the groupings that perform best to you. If you want to continue with length do the same and see if it improves or not. I have an 06 that really doesnt help nor hurt so I stay with the best charge that gave me the best groups. Some guns I hear it does change but for me I just go with powder charges.

[Jim243]

There are a number of ways you can do this, so any choice would be what you are most comfortable doing. Here is what I do:

The first thing when loading for a NEW bullet that I have not used, is to determine the OAL of the chamber and throat of the rifle I am loading for.
To do this I use a Hornady Lock-N-Load curved O.A.L. gauge and the LNL 243 modified case (sold seperately). Placing the bullet in the modified case on the LNL gauge I can get the MAX OAL that this rifle will accept with THIS bullet. Due to design differences from mfg to mfg each different bullet will have different MAX OALs. I then subtract 0.020 from the results and that is what I use for my starting OAL.(a 0.020 jump to rifling seems to work best).

I will then go to my load manuals (BOOKS, buy them, a cheap investment) and see what is recommended for the weight and type bullet I will be using.
They will seldom have the same exact bullet listed unless you are using the manual from the bullet mfg.

I will then pick a powder that will fill the case about 80% to 90% of the case by volume. I then set my powder measure to 0.5 grains less than the MAX load in the manual. This gives me additional insurance that I will not go over MAX and that I have some room to make adjustments if I need to on the next load. I generally find that I do not have to adjust the load and have excelent ammo for that rifle.

If you get unacceptable results with that load, you will need to pick a different powder NOT adjust your settings. Not all powders will work well in all calibers. For 243 I use H4895, but I only use 105 grain Hornady A-Max in my rifle. If you use a lighter(shorter) bullet a different powder might work better like H335.

Just how I do it.

Have fun and stay safe.
Jim

[briandg]

Just FYI, an accepted load for .243 Win is imr 4350. I've read hundreds of times that it was the best accuracy, and it gives good velocity and pressure.

I use 4350 and 100 grain sierra PSP.

[Unclenick]

Changing seating depth does change pressure and barrel time. But so does changing powder charge. I have an example of pressure change with seating depth and a fixed powder charge for a round nose bullet in the .30-06, below.

One reason to adjust seating depth first with a low charge is that best accuracy loads are frequently right up near maximum pressure. Indeed, having groups start to open up more than usual as you increase charge is one of the many pressure signs. So, if you establish the peak accuracy powder charge at near maximum pressure first, then move the bullet where it increases pressure further, you can easily miss the best seating depth because the pressure-induced inaccuracy exceeds the improvement made by getting the seating depth right.

There is one obvious exception to the above, and that is doing a best accuracy load workup with the bullet jamming the lands. That is the highest pressure condition, so if you establish a load that is safe for that condition, it will be safe at all other practical seating depths. So you could start with that and tweak seating depths safely from there, if you choose to?

[GAR700]

Thanks for the input.
I have loaded for this rifle before. I have just never considered varying the seating depth. I just free floated the barrel to see if I could get better accuracy. It shot about 1.5 inch 4 shot groups before. Now I am going to work up a new load (same components) and see if I can make it shoot. This is simply a preference question. I will probably work up a load based on the Barnes Manual (which I have) and then adjust the seating depth.
Jim243. why would you NOT adjust your settings? I realize that many rifles like the bullet seated close to the lands, but if I have learned anything from my reloading experience, it is that all rifles are unique.
briandg. I have used imr 4350 in my other rifles but I do not like the way it meters. Do they make a short cut version?
Thanks
GAR

[GAR700]

Unclenick,
Thanks for the info. That almost perfectly answered my question.
Hopefully, this will save me some head scratching later on down the line.

GAR

[farmerboy]

UncleNick, That graph is really impressive but how can you actually tell if you are at 58,OOO or at 65'OOO psi when shooting different rounds? Just Wandering.

[Unclenick]

Exact pressures are impossible to determine because modeling shows a chamber actually has complex pressure gradients and there is combustion turbulence and other complicating factors are involved. However, you can get an indirect indication that's close enough for most general purposes (say, within 5% or 10%) and that will show relative pressure changes for a given powder pretty well by use of strain gauges attached to the outside of the chamber portion of the gun. This actually measures the hoop strain of the steel, but steel within its elastic limits stretches pretty linearly with pressure, even if there are dynamic considerations at work that skew it some. The instrumentation basically turns the gun into a roughly calibrated electronic pressure scale, and you get a reading based on how much the metal was stressed by the pressure it contained.

RSI makes such an instrument available.

[farmerboy]

Uhhhhh OK. Thanks had to ask anyhow

[James R. Burke]

Just myself I find the correct c.o.l. for that bullet first. Then on here or reading etc. I try to find a few powders that are a good match for it, and also try to have a manual for that bullet. I start at the min working up watching the groups, and for signs of presure. If I see any signs of presure thats it back it off, and decide if those groups are any good. If not on to a differnt powder. I try to use powders that give me a good fill also. I am also watching that crony. Most the time my first few fouling shots are through the crony. So just myself I get the c.o.l. right for the bullet I will be using first. Then I start at the min work up watching for presure, and group size, and checking the crony. Like I said that is just me.

[Nnobby45]

Not just about pressure, it's also accuracy. You have enough variables to experiment with by changing powders, powder charges, primers, different case brands, and so forth without adding seating depth to all the other variables.

Temperature also plays a part in pressure. Develop a hot load in winter, shoot the load in summer (maybe when the suns has been cooking your cases) and you could have problems.

Remove the seating depth pressure variable and you don't have to worry about it. Admittedly, larger cases with more capacity are less affected by seating depth changes, and none are affected by changing in 20 or 30 thousandths increments when probing for the best accuracy.

NOTE: The way experienced handloaders do it is start very close to, or even touching, the lands. If the load is safe there, pressure decreases as you seat the bullet farther from the lands (deeper in the case) when working up the load. It isn't until you seat the base of the bullet down into the case and changes the powder capacity that seating depth starts to raise pressures.

Confusing, isn't it? Closer to the lands equals more pressure. And seating the bullet deeper does too.

Welcome to hand loading.



Once you have different loads developed, you can also fool around with depth from one load to another to varify that proper seating depth is universal to all your loads.



When loading 6mm ICL, (a wildcat cartridge) I found out that depth did affect pressure enough to cause problems, since I had to seat the bullet deep enough for the ammo to feed thru the short action I had it built on. Get the seating depth and the pressures associated with it from the start and work
from there.

Best tip for a young handloader: KEEP NOTES!

[Jim243]

Welcome to hand loading.

(LOL) Well said.

Jim243. why would you NOT adjust your settings?

I would not change the OAL from 0.020 under max for the barrel YOU are using, because, you must maintain a constent to judge if the other changes (powder level (+or-) or type of powder) have any effect on reducing your groups. Each barrel is cut differently even from the same mfg from barrel to barrel, most tooling gets duller with each barrel cut and will give different results. If you are using someone else's data from their barrel (test or real) the results will be correct for their barrel only. Loading data is only a recommendation from the test data they have obtained. (may or may not be correct for your gun) that is why everone says start low and work your way up. A change in .2 grains of powder will have more effect on pressure than a change of 0.02 in OAL. Therefore, finding the correct powder level is more important than finding the best OAL. Once you have the best powder and powder level then you can play with OAL to bring you 0.4 inch groups down to 0.1 inch groups.(if your rifle will shoot that close a group).

Jim

[farmerboy]

Excellent way to put it Jim243. I do EXACTLY the same and this way has always proved to be the best for me anyhow...It's so nice sometimes to just to hear/read it put so simple, straight forward and to the point than to hear it with all the mumbo jumbo confusing way that sometimes dont dont add up to a hill of beans (IMO)

[GAR700]

Thanks Jim
I appreciate you clearing that up for me. You answered my question the first time, just not in a way that I understood... I will work on this a little and see what i can come up with.

GAR