COAL shorter than load data suggests....

[bullpen7979]

I was getting a seating depth worked out for my .308 casts today. When I closed the bolt with the 170 and 180 grain lead slugs with gas checks, I determined that 2.64 was the length of the cartridges as they came out of the chamber.

So, setting that back a few thousandths, I get (duh) 2.60". That's pretty short, and I had a hard time (read "could not") find load data to support this COAL.

Currently, IMR 4895 is one of the two powders I have listed as acceptable in this cartridge. It seems that it is one of the better choices for reduced loads.

The closest load data I could find was on Lyman 49th, on page 222 I think, where 4895 was spec'd out at a starting load of 33.x grains and 2.675".

I see where 4895 can have the starting loads cut by 60% for reduced recoil. Is that where you would start? Or would it be more like 25 ish?

I know enough not to presume things like this are a simple mathmatical ratio, and that things like chamber pressure increase in a logarithmic rather than a linear way.

I guess I'm trying to tap into the collective wisdom here. I would assume, given a slightly smaller coal than specified, that cutting the beginning powder charge by 40%....but I'd rather ask for guidance and not be sorry than not ask and have something bad come my way. This year's had enough bad stuff for two lifetimes already.

Thanks fellers. (and ladies too)

Regards,

Bull

[Hick]

I've had several similar cases where I was trying cast bullets in my 30-30 that were not really designed for 30-30. Could not go with the COL that made sense, and did not have good COL data. Realizing that shorter means more pressure, I went to starting load and started there-- carefully. Caution is the word-- but the difference between 2.65 and 2.5 is not a big percentage of case volume-- so I would just start low. YMMV

[runfiverun]

start at 28 and move ahead I bet 29-30 is gonna be your happy spot.
keep the powder against the primer or against the boolit.
4895 does best with a filler to avoid velocity variations so tipping the barrel before each shot will pay off with tighter groups.

notice I didn't address the oal question?
your working around it by using good loading practices and starting low and working up.
oh.... if the nose is engraving the rifling at the longer oal I'd leave it out there.

[TXGunNut]

If I'm using a Lyman mould/boolits I'll take a look at their COAL number, otherwise I try to figure out what the rifle wants. I think you're on the right track.

[Victor N TN]

If the shorter OAL shoots accurately and functions well, personally I would leave it alone. Some bullet / load combinations shoot well at longer, shorter or almost any length. Figure out what you want it to do first. Just keep your eyes open for high pressure signs on the primer. If you have a chronograph, use it and take a lot of notes. If it isn't handy to keep the target, draw it out in your notebook.

Good luck.
Victor

[robg]

As long as they fit in the magazine and chamber I seat my loads as long as I can without going into the lands.

[bullpen7979]

Ok, thanks guys. --

Just want to make sure I'm reading this right....I thought if the slug runs into the lands that that was something that could induce high pressures, and that you want the slug to have a bit of "jump" to it. I thought I remember seeing a few thousandths or so being the optimum. I know every gun is different but do you guys have a standard setback distance that you like to use?

Robg, sounds like we are approaching things the same basic way.

[gitano]

"Shorter means higher pressure" - Nope. DEEPER seating with the same bullet and powder means higher pressure. "Shorter" in and of itself is not related to pressure.

"In the lands" - I don't shoot a lot of cast bullets, but those that shoot the most precisely, AND ALL I HAVE EVER HEARD/READ is that putting CAST BULLETS into the lands "a little bit" - I don't know exactly what "a little bit" is - produces the best "accuracy" (precision).

On the other hand - loading jacketed bullets into the lands is in almost ALL circumstances not a good idea. A jacketed bullet in the lands will jack up pressure IMMENSELY! As a general rule, putting jacketed bullets into the lands is a bad idea.

As for "How far off the lands?" - for cast bullets, I haven't a clue. As I said, most of the experienced shooters I know say put the bullet into the land "a little bit". For jacketed bullets from rifles, the sweet spot seems to be from about .030" to about 0.070" off the lands, but it can range from 0 to 0.150" off. I have read that Barnes bullets "like to jump". I have no recent experience with Barnes bullets.

Paul

[DonMountain]

If the cartridge will work through the action ok, I set my boolets so when smoked with a match, I can see the rifling just touch the boolet surface when loaded. That way I can extract the cartridge if I decide not to take the shot. Of course this is more important when hunting than when target shooting. But I feel it is generally a safety issue to be able to extract the cartridge without leaving the boolet in the barrel.

[DougGuy]

My .308 *really* shrunk groups when I seated out .025" shy of the lands as opposed to seating in the cannelure.

[35remington]

Given we are not talking a 9mm with Bullseye powder here, seating depth does not play the pressure increasing role it does in handguns. Primer ignition and bullet engraving and peak pressure are not concurrent events. Cast bullets engrave relatively easily to boot. This is not a grave concern to be avoided.

Seating deeper increases jump to rifling. With slow rifle powders there is relatively little to be concerned about compared to seating longer in the same chamber. Differences are hard to find on a chronograph, which means pressure differences are insignificant as well.

In many instances I have loaded jacketed bullets into the lands to judge the effect. Again, the chrono couldn't tell the difference. No velocity increase means a pressure increase is also absent.

[B. Lumpkin]

I always start rifle load development with bolt actions with the bullet "Jammed" into the lands. Once I've built an accurate load that way, I will adjust seating depth back. Sometimes the groups shrink, sometimes they grow. I have many saved targets that show it. As the throat wears, you end up chasing the lands if the bullet liked to be jammed.

[gitano]

Seating deeper increases jump to rifling. With slow rifle powders there is relatively little to be concerned about compared to seating longer in the same chamber. Differences are hard to find on a chronograph, which means pressure differences are insignificant as well. Actually, muzzle velocity is not a function of peak pressure - which is what were are talking about here - it is a function of the area under the pressure vs time curve. Two VERY different peak pressures can yield essentially the same muzzle velocities. Muzzle velocity is NOT an indicator of pressure. Seating deeper increases peak pressure. I agree that this path to increased pressure is rarely an "issue", but it most certainly does increase peak pressure.

In many instances I have loaded jacketed bullets into the lands to judge the effect. Again, the chrono couldn't tell the difference. No velocity increase means a pressure increase is also absent.
Here, I could not disagree more vigorously. And before I continue let me qualify my following statements. 1) Almost everyone that knows me thinks I "play on the edge" more than most. 2) I loathe "Chicken Littles" for whom the sky is ALWAYS falling, and 3) Handloading is one of the safest "hobbies" in the WORLD. That said, THERE IS NO ASPECT OF HANDLOADING THAT I WOULD CAUTION SOMEONE MORE SERIOUSLY ABOUT THAN LOADING JACKETED BULLETS INTO THE LANDS. I have been reloading for 50 years. I make my own rifles - not "assemble" them - make them. I have made "special" firearms for the DoD under contract. I swage my own bullets because I can't get what I want. I spent a couple of years developing duplex and triplex loads for .22 caliber bullets to be used in .30 caliber sabots. I was able to exceed 4700 f/s but only with triplex loads. I do A LOT of "experimenting". I have pressure MEASURING equipment to evaluate my loads and produce pressure time curves. In other words, I plow my own furrow and am not "shy" about reloading practices. However, in 50 years of reloading, no single kind of reloading error or experiment has caused more stuck bolts, blown primer pockets, and separated heads than loading jacketed bullets into the lands. A friend of mine did that with a beautiful custom 6.5x57 and destroyed the rifle. It didn't come apart, but only for the grace of God. SO... Reload as you wish. So will I. Advise as you wish. As will I.

Paul....

[35remington]

We are using the same powder, just seating the bullets differently. Pressure increases of a high level will realize noticeably increased velocity.....because the "area under the curve" increases greatly when peak pressure increases greatly. It has to...the pressure is higher, area under the curve greater. Your premise that much higher pressure will result in no velocity change is quite invalid. Again, it's the same powder. When it does something differently, different things happen over the chronograph. High pressure doesn't hide its effects when the same powder is used.

There's no need to go into great detail about other things that don't have a bearing on the subject. Not sure that going on about triplex loads has any bearing on this particular point.

Seating deeper does not necessarily increase pressure for the reasons I detailed in my first post. There is every reason to understand that seating deeper causes little problems in rifle cartridges under many if not most conditions. Exceptions exist, but often have to do with long bearing surface bullets crammed into short throated rifles as compared to bullets of entirely different shorter bearing type of lower loading density. Then apples and oranges are being compared.

And the the universal warning that seating into the lands with jacketed bullets is utterly deadly, as you suggest, is contradicted by those of us who regularly do so under controlled, incrementally tested conditions. Look up who regularly shoots jacketed bullets seated into the lands. Quite common in some circles. In some cases, like in my short throated Marlin 35's and the 220 Speer, for example, little jump is possible even crimped in the cannelure. Seating into the lands has little detrimental effect or velocity increase. I have numerous other examples, enough such that I view universal warnings against the practice with well justified suspicion.

I am not suggesting it as a matter of course as seating into the lands does not produce functional ammo that can be ejected. But cautioning against doing so with cast bullets as being certain to cause a wrecked rifle or high pressure is most certainly going overboard in most cases, and very often with jacketed as well. Reread my previous post as the valid reasoning still applies.

For the prudent handloader willing to work up from below, rather than just changing something with an already super max load, try the loadings with varied seating depth and see for yourself. No need for me to expect anyone to take my word for it.

Seems like you've painted yourself into a corner.....deep seating causes high pressure.....seating into the lands (seating shallow) causes high pressure. I'll let the OP determine the truth of the matter, suggesting the use of mild loads to give a margin of error if that gives prudent procedure. Better to find your own truth than take someone else's word for it.

My prediction is he will discover the sky isn't falling. If too deep causes high pressure, and too shallow causes high pressure, heaven forbid he doesn't get the seating depth perfect on the first try or the gun will explode. Bullets, especially cast bullets, are far more forgiving than that.

[35remington]

For the OP, cast bullets engrave easily. The primer alone can seat the bullet well into the barrel. As I said, unless you're shooting very fast powder, peak pressure occurs when the bullet is some distance down the barrel, not concurrently with engraving.

In a considerable amount of testing there is often little velocity difference with varied seating depth....believe me, I've shot a great many cast bullets with everything from jump to crammed. This cannot and does not mean that great differences in pressure are therefore hiding unseen and undiscovered when velocity changes hardly at all. It means that great differences in pressure do not exist. Previous reasoning still applies.

Please by all means discover this for yourself. If levers pop open and bolts stick you can blame me, but that ain't gonna happen.

And think about this for a minute.....given how little clue most handloaders have about seating depth, the premise that a perfectly safe load can be turned into an utter rifle wrecker (presuming you are following loading manual suggestions in the first place) by adjusting seating depth a little one way or another would suggest that blown up rifles would be much more common than they actually are, would it not? For cast bullets in rifles, especially, we're spilling too much ink on the topic here.

[NavyVet1959]

What matters is the distance between the base of the bullet and the inner web of the base of the cartridge. This is the area where the powder resides and where gas expansion can occur before the bullet starts moving. Two bullets that weigh the same can have different lengths due to a difference in nose profiles.

Let's say that you want a 200 gr bullet with a diameter of 0.308". Let's use 2796.3197 gr/cu-in as the density of the alloy. I'll also ignore the lube grooves to make it simpler.

Let's assume a 0.6" long base for the bullet. This works out to be 125.0056 gr. That means that we have 74.9944 gr left to put into the nose of the bullet.

Let's make the nose a truncated cone with a nose diameter of 0.2". That means that the nose would have a length of 0.521423262", making the total length 1.121423262".

Now, let's make the nose a truncated cone, but with a bit more pointy of a design and with a nose diameter of 0.1". That means that the nose would need to be 0.755107469" long, making the total length 1.355107469".

The same thing would be happening if we were using bullet profiles with a curved noses that were not the same. Every curved bullet profile can be approximated by a series of truncated cones.

So, you have two bullets that differ by 0.233684207", but if you seat their bases to the same distance from the inner web of the cartridge, then they should have the same pressure with a particular powder charge.

Here's a drawing to illustrate what I'm talking about:



Both of these bullets weigh the same and have the same bearing surface. If you seat based on the same OAL though, the top one is going to have less pressure than the bottom one. If you seat based on the distance from the base of the bullet to the inner web area, then they will have the same pressure.

[35remington]

Smallish differences in seating depth of the type mentioned here using the same bullet mean relatively little to remaining case volume in bottlenecked cases of noticeably larger diameter than the bullet like a .308. Throw in slowish powder and the effect is hard to prove as substantive.

[gitano]

35remington - It'd be really nice if you 1) wouldn't put words in my mouth, and 2) read what I wrote instead addressing points as if I made them when I said no such thing.

Paul

[35remington]

I did address your points, most particularly the "area under the curve" claim. The point I am making in opposition to yours was that greatly higher pressure means more area under the curve and thus more velocity.

You did say that muzzle velocity is not an indicator of peak pressure. With the same powder it most certainly is. Particularly with no change in charge weight. The idea that no significant change in velocity means no significant change in pressure under these conditions is entirely valid.

Since pressure is the only thing that drives the bullet, and the same powder is being used, you may want to try to explain how pressure can greatly increase yet not show up on the chronograph. While you are at it, load the 308 and 30-30 with the same powder to two different pressure levels and tell me a velocity increase won't show up on the chronograph there either.

I am challenging that idea because it does not fit reality, not just to be contentious. For whatever it is worth.

As for the rest, I invited the OP to determine it for himself as to the effects of seating depth. Given the above is factual, he will be in a better place to evaluate seating depth changes and their actual value.