Consistency of COL and 357 mag cases

[jal5]

I have read a lot about COL and understand the relationship to pressure, and ability to cycle the rounds, etc. However in loading 357 mag for revolver, how does consistency of COL in a batch of finished rounds affect accuracy?

IIRC the manual shows max. COL as 1.590 for the bullets I was loading and 1.570 in the example gun. I was getting 1.587-1.590 in that batch. Does that .003 make any real difference? I can never get them exactly consistent either, but I don't resize pistol cases. How important is this for overall accuracy? My usual reloads are within .003-.006 range in COL.

So how picky do I need to be about COL in developing a load and in my general reloading procedures for pistol ammo used for target or hunting?

thanks,
Joe

[SL1]

For on thing, you don't have the option of seating close to the rifling like you do in a rifle and may be able to do in an autoloader or single-shot. So, that accuracy issue isn't applicable in the revolver.

And, the COL is measured to the nose of your bullet, so the variation MIGHT be in the nose shape, especially if it is exposed lead. If your seating stem is not exactly fitted to the bullet's nose shape, the nose will crush a little as they are pushed into the cases, and the amount of crush can easily be several thousandths.

The thing that will matter some in your revolver is the consistency of your crimp. Unless the issue that is affetng your COL is also affecting your crimp, I wouldn't worry about it.

You COULD test it by sorting your loaded rounds for length and seeing if the long ones shoot different sized groups compared to the short ones, or if there is an apparent POI shift between the groups.

SL1

SL1

[jal5]

I wondered about the nose getting slightly crunched by the seater since I am using lead bullets swc. I didn't think about separating out according to length, that would be an easy trial. Thanks.

The crimp is another issue, generally these will crimp the same look and feel as it crimps but occasionally some seem to crimp tighter, I think the longer cases?

Joe

[SL1]

If your CASE lengths are different, that will affect the crimp, which can affect accuracy in a variety of ways. But, that can happen whether or not your COLs are the same.

SL1

[islander]

A few thousandths COL variation isn't an issue as far as accuracy especially in revolvers. Wouldn't affect velocity/accuracy any more or less than the slight variations in your powder charge, or crimps. As long as the COL is within the load's specific minimum COL and the caliber's maximum COL, for safety.

[Stick_man]

Overall case length could be an issue with different calibers, depending on where they headspace. Rimmed handgun cases (ie .38/357, .45LC, .44Mag, etc) headspace off of the base. Other calibers (ie 9mm, .40S&W, and most rifles) headspace off of either the shoulder or case mouth. With the straight walled rimmed case of the .357, the overall CASE length shouldn't make any difference, even in pressures as long as the overall CARTRIDGE length is the same.

I know several people that never trim .38 or .357mag brass, even after shooting them 7 or 8 times. Never had a problem with them. They just shoot them until the brass splits or cracks.

If I were loading for max accuracy (competition shooting), I would carefully measure and trim to uniformity of length along with other case prep that helps with consistent pressures. Since I don't shoot competition, I don't trim my .38 or .357mag brass.

Happy shooting!

[Unclenick]

Islander,

(I see you edited while I was composing, so maybe you caught this already?) COL's and all other cartridge dimensions are maximums with a +0, -nnn tolerance. It is chamber dimensions that are minimums, with a +nnn, -0 tolerance. The SAAMI specifications are written that way so the largest cartridge made that meets the specification will fit the smallest chamber made that meets the specification. Also the smallest magazine, where that is applicable.


Jal5,

My first question is why you are not resizing cases? That reduces the grip on the bullet which reduces ignition consistency and accuracy, especially with slower burning powders used in full power loads. Very light target loads can be an exception both because the powder is fast and because the brass often springs back below bullet diameter after experiencing their relatively modest pressures. But full power hunting loads usually will expand the brass some. It depends on your chamber dimensions. Generally, you want as much grip on the bullet as you can get for full power loads to prevent inertial bullet pulling during recoil.

That said, perhaps you've got another reason for doing it? Just curious?

To address your original question, no, .003" difference won't matter to a revolver load in the least. I defy anyone to measure the effect on paper. But you do want your cases the same length for crimp consistency which improves ignition pressure consistency. Again, this is especially the case with slower powders like H110/296 or 2400.

[Sevens]

What I've found with my revolver rounds (for me, it's .38, .357 and .44 Mag) that all the bullets I use have cannelures/crimp grooves whether I'm loading cast lead or jacketed. So I tend to let that crimp groove or cannelure decide the COAL of my loaded rounds with that bullet.

I don't let load data determine my COAL for revolver rounds... I let the specific bullet determine it.

This has worked for me and since I don't deviate from it, I don't know how shorter or longer COAL affects accuracy in revolver rounds.

[islander]

UncleNick yes indeed I didn't like my original post as it was not completely correct, manuals do list maximum COL as this is critical to avoid bullets jamming on the rifling and the dangerous pressures that can result. Lee's Modern Reloading specifically states the OAL's (same as COL) are a minimum and he puts the fear of God in you about how pressures can build up drastically with shorter OAL's especially in handgun calibers -his load data lists "Min. OAL", while the caliber drawings specify the equally critical maximum OAL. All my other manuals similarly identify a caliber maximum and what I am "assuming" is a specific load minimum COL/OAL. Please advise if I am misinterpreting any of this.

[wncchester]

"My usual reloads are within .003-.006 range in COL."

That's precise enough.

[jal5]

thanks for all the explanations.

Unclenick- I am resizing cases but not trimming 38/357s, my fingers type faster than the brain engages at times!

My technique has been to not trim these straight walled cases and to use the cannelure as the crimp point. But using LSWC bullets and the rounded type seater plug I don't think I am getting uniformity in overall cartridge length. The crimps seem pretty much uniform with the exception being if the case is shorter compared to the others yet within tolerable limits, the crimp is a little different a lighter type crimp I think. Like SL1 pointed out.

On 9mm reloading I tend to be much more precise about length of case because of how the round headspaces, and critical issues of volume being full of powder and pressure.

[TEDDY]

I shot compitition with 38 spec and 45 acp and never checked he OAL length.
I am with SEVENS how do you load if you dont use the crimp groove.I never trimmed,and my cases are 30 ys old.I never had a failure to feed or jam.in the
auto.the mod 52 does.but never the 1911s.to much nit picking will ruin your pleasure.and nit picking it is. shoot them and thats how you find things out.
we dont have your loads or gun so all we can do is SPECULATE.

[Unclenick]

jal5,

The trimming is just about getting uniform crimp, precisely to avoid the situation you describe where a short case makes a light crimp. This is something that only matters with roll crimps in revolver loads that either have enough recoil to back bullets out until they protrude from the cylinder and jam the gun, or with magnum loads of the hard-to-ignite slower powders, and H110/296 powder, in particular gives irregular performance if you ignore this.

For target loads, you really don't need to worry about it. I often just use a taper crimp on wadcutter loads in my .38 and .357 and .44 revolvers. There isn't enough recoil to back the bullets out, and the taper crimp gives longer case life where you can use it.


Islander,

You're correct that a minimum COL is sometimes given for a specific bullet. That doesn't change the SAAMI COL which is a maximum. That minimum that is specific to the bullet still needs to fall within the SAAMI maximum if you are going to insure the round will chamber in all guns and fit all magazines designed for it.

I think the best way to clarify the matter would be for the manuals to specify a maximum seating depth for all bullets of a given weight and construction (i.e., lead or jacketed) rather than separate COLs for each bullet. Seating depth determines how much volume the powder starts burning in, and that is the major factor in determining peak pressure. Seating depth is easily figured. Sum the case and bullet lengths and subtract the COL of a published good load, and you've got it. You can then take any other same-construction, same-weight bullet and give it that same seating depth with that same load, regardless of the resulting COL (except where the resulting COL would jam you into the rifling, which raises pressure). My old Hornady Second Edition loading manual used seating depth rather than COL and I wish they would return to it or add it in, because it is more useful information in many cases.


Teddy,

Trimming case length for case stretch is different from uniforming case length for uniform roll crimp tension. Almost no cartridge fired below about 30,000 psi will stretch. It doesn't see enough pressure to stick the brass to the chamber wall, which is required for stretching the head back to the breech and forming a pressure ring. At .45 ACP and .38 Special pressures it just doesn't happen. Indeed, those cases often shorten with each load cycle because the pressure backs them up like a piston in the chamber, then seals the chamber walls by expanding them which shortens and fattens them. Resizing tends to squirt the length back forward, but it never quite returns all the way to what it was before the last loading cycle. Instead, a tiny portion of the brass gets massaged back toward the head during sizing and stays there.

I once tracked a batch of a 1000 Winchester cases I used with light Bullseye loads in 2700 matches through 50 reloading cycles, applying the calipers to a dozen of the them every 10 reloadings or so. They actually shortened an average of half a thousandth per load cycle, and were 0.025" short by the time I retired the ones that hadn't been sacrificed to the range gods. The nice thing about taper crimping those was that the taper is gradual enough to deal with mixed brass lengths and keep functioning after all that.

[jal5]

Thanks to all who replied for the clarification !