Can anyone explain this? Possibly neck tension issue?

[JWFilips]

Had a chance to try out some of my boolits from the MiHec 358156 HP mould. Nothing too scientific since I knew the weather was cold and did not have time to work up new loads.
I loaded up 24 rounds in relatively new Starline brass (Shot 2 times) and 24 rounds in older Federal brass ( shot numerous times)

boolits weighed on average 151.5 gr (with the range from 151.3 to 151.8 grain) these were the plain base penta HPs & fired in my S&W Pre-27 (circa 1953 .357 mag) Boolits sized .359" and Ben's red Lube. Load was 13 grains 2400 ( a proven good load in a 158 gr SWC) All loads crimped the same

I use a custom neck expander for cast:
The first thing I noted was the Federal brass had more resistance to the expander then did the Starline. The boolits seated with more resistance in the Federal brass ( to the point that I made note that I felt that the boolit may have been swaged smaller in the loading of those cases)
I started to suspect the Federal cases may have started to become hardened from numerous firing vs the quite new Starline brass

Two targets were shot from a stable rest at 20 yds The two groups were almost identical except the Federal brass loaded boolits printed 2" lower!
Could this possibly be a neck tension issue? and if so why does one print lower then the other?
Thanks

[country gent]

There could be several things causing this issue. One is brass hardness, a harder springier case will shrink back more than a softer case with less "memory". A thicker case will act the same. A neckwall thickness of .010 will act "softer than a neck wall thickness of .011 will. Both will end up close to sme ID after trip over the expander but .011 will be "harder" to pull over the expander. Cases fired many times may have a diffrent Hardness from others but also cases from diffrent manufacturers may have slightly diffrent hardness out of the box brand new never fired. Comparing starline to federal to winchester to remington may all show diffrent results. The Heavier tension may have resulted in slightly diffrent velocities ( improved ignition better combustion) resulting in diffrent harmonics. Velocity increases affect point of impact point of aim changes alot also.

[JWFilips]

The Heavier tension may have resulted in slightly diffrent velocities ( improved ignition better combustion) resulting in diffrent harmonics. Velocity increases affect point of impact point of aim changes alot also.

So Then: Higher velocity would show as a lower impact point at 20 yds (?) I think what you have stated may be the issue here.
Poses a good case for sorting cases by headstamp and age!

[RickinTN]

I fully agree with Country gent's post above and I'll add one more strong possibility. Check the internal volume of the two cases and compare. In handgun cartridges a small difference in seating depth can make a considerable difference in pressure and velocity. In this case if your Federal cases are smaller volume-wise they would give similar results to seating a bullet deeper resulting in a smaller combustion chamber. Your results sound like they are at least consistantly different.
Good Luck,
Rick

[CastingFool]

When I was reading the post, the first thought that came to mind was wall thickness is probably different, since you have two different brand of cases. Country Gent did an excellent job of explaining the various issues.

[dubber123]

I fully agree with Country gent's post above and I'll add one more strong possibility. Check the internal volume of the two cases and compare. In handgun cartridges a small difference in seating depth can make a considerable difference in pressure and velocity. In this case if your Federal cases are smaller volume-wise they would give similar results to seating a bullet deeper resulting in a smaller combustion chamber. Your results sound like they are at least consistantly different.
Good Luck,
Rick

In my .45 LC, Federal brass will match the velocity of Remington brass with a 1.5 gr. LOWER powder charge. Significantly smaller internal volume in my case.

[TXGunNut]

Couple of other things to consider: revisit your thoughts about the Federal cases possibly swaging the boolits down a little and causing poor boolit to bore fit. You also said the crimps were the same, does that mean you used the same setting? Different brands of cases are often differents lengths so a crimp die set to the same height will give less crimp on a shorter case and vice versa. I never trim .38 cases but I've been known to measure them. Just for grins I'd pull a boolit from each type of case to check your earlier line of thinking. I'd also consider a chrono session if you have one available. 2" @ 20 yds is a significant difference when the only variable is the case.

[JWFilips]

You also said the crimps were the same, does that mean you used the same setting? Different brands of cases are often differents lengths so a crimp die set to the same height will give less crimp on a shorter case and vice versa.

Crimp Setting were different for the two types of cases.....the reason I said crimp was the same is because the way I use my crimp die ( not sure if this is a scientific method either) : after all my boolits are seated I back the seater button out , bring the ram & cartridge up and screw the crimp die body down until I feel a firm resistance on the case mouth then lower the cartridge out of the die....then by using an index mark ( I have made on all my crimp dies) I turn the die in 1/4 + 1/8 turn more That usually gives me a good crimp on all my .38 Spec and .357 mag loads. I will re-set this for each batch of different brass. I too, don't usually trim my .38 Spec and .357 Mag brass however I do measure the lengths and put them in to like batches for case lengths and also head stamps...so I do have a loading method ( albeit some what anal one )
I did recheck my group centers this morning and the Federal brass did print at the least 1 3/4" lower

Another test I did last night was to grab another batch of Federal & Starline brass size it and expand it
Again no problems with the realativly new Starline brass however the multi-shot Federal cases behave differently to the expanding ..some were as smooth as the Starline however many of them required more fore to expand the cases and even withdrawing the expander button required more pressure
Might I deduce that those cases may be getting too hard & time for culling? I have used the Federals the most over the past 2 years and have added to them when new range brass was collected so I do have a mix of ages in there.

[Pepe Ray]

Let me introduce another possible variable. Oh,Oh!!
Friction between the boolet and the case wall, aside from tension.
The kind of friction caused by grit or carbon.

Although I've normally cleaned my cases via the corn cob or Walnut shell media in vibrator, it only recently got my attention that there was a better way.
I purchased several hundred cases from a fellow member and was shocked when I saw the apparantly NEW cases that I received from him.
WRONG!!
They had been cleaned w/Stainless Steel media in a tumbler and soap bath. There was NO residue in the primer pocket nor the interior of the case. The friction coefficient had to be as a new case.
At my age I'm not about to embark on a new experiment that could take months of conserted concentration. But I am convinced it would be a worthy project for some young pioneer.
Meanwhile I'm going to go with my new theory and include case wall shine as a sorting criteria.
FWIW
Pepe Ray

[JSnover]

Could be both; harder or thicker brass. Clean them and weigh them.

[detox]

I have also noticed inconsistant neck tension while expanding....my lot of Winchester brass is the worst....Starline is a little better. I would cull those that have too much tension...then anneal later down the road.

Remington brass is softer and has very consistant neck tension...all feel the same when expanding...Remington 357 is very hard to find as of now.

[popper]

Only a chrony trip will tell if it is a brass problem. I've played with 2400 in a 30/30; it seems to have an unusual burn characteristic. I had to stuff the case with filler, almost compressing the powder to get decent results. That said, I am guessing at case volume and crimp.