Blowback Around Case

[crazydaysorg]

I'm loading 30-30 with 28.5gr IMR-3031 with 150gr RN.

I took a bunch out to shoot and wound up with some wavy blowback lines around the top of the case. They don't go the entire length of the case, just the top half inch or so.

When I've loaded some light recoil rounds I don't recall the wavy lines or using factory rounds.

Is this normal? Indicative of the brass hardening too much? Or the chamber maybe having corrosion and not creating a good seal? Or something else I haven't even considered?

 

[egg250]

I get similar results with light loads in my .303 British SMLE, using IMR4064 and IMR4895. I've not noted any adverse effects. Seems that heavier loads don't have this issue for me.

 

[rcmodel]

Normal with a very light load.

28.5gr IMR-3031 with 150gr RN.

You are using less then the suggested starting load according to Hodgdon/IMR data.

150 grain Sierra FN
Start load = 28.7
MAX Load = 30.5.

The 30-30 is a relatively low pressure round, even with a Max load.

It is also normally heavly crimped for use in a lever-action tube magazine.

So, with a sub standard powder charge like yours, not enough pressure soon enough to complety iron the crimp out.

Power gas gets it's nose under the tent at the crimp before it opens completly, if at all.

rc

 

[crazydaysorg]

rcmodel, the Lyman 49 says 28.5gr for a jacketed RN, so I was using that as the load. And everything I read here says to not trust the internet for load data. However, when I did go to the IMR/Hodgdon site I see it does list your numbers.

So, should I not trust Lyman 49 for accurate numbers?

I'll try the IMR suggested load tomorrow and report results (or visit the hospital). ;-)

 

[rcmodel]

So, should I not trust Lyman 49 for accurate numbers?

Yes, you can trust it.

Hodgdon/Alliant is using a Sierra Bullet.
Lyman #49 is using a Hornady bullet.

That is enough to get varing data.

I don't know what bullet you are using.

But it really doesn't matter.

30-30 Starting loads, whatever they might be, don't develop enough pressure to expand the case neck & seal the chamber.

rc

 

[helotaxi]

That and 0.2gn is less than 1% of the powder charge and differences in crimp or neck tension will make a bigger difference in pressure than that tiny powder change.

Nothing magic or inviolable about book starting loads 99% of the time. Most are either a certain % reduction in the max charge or max velocity. With some powders and cartridges, going lower might cause some issues, but those are certainly the exceptions, not the rule.

 

[crazydaysorg]

All digits and eyeballs accounted for:

Without being able to find exact information on IMR (powder) or the Nosler site (http://www.nosler.com/bullets/combined-technology.aspx 30-30 150gr RN), I used what seemed closest and went up to 30.5gr. Once I was over 30gr I noticed the blowback wasn't there anymore. So, that seems to be a magic number.

 

[brickeyee]

So, that seems to be a magic number.

It will also vary as the brass work hardens.

 

[GP100man]

That was gonna be my question ,how many times has this brass bee loaded ???

As it work hardens it`ll need more & more pressure to seal off .

A lite annealin would probably tell the tale .

A good crimp is a must in a tube feed rifle & to get things started .

 

[MEHavey]

The OP's load is fine. No problems other than it only develops 28,000psi (or about 2/3rds of normal Max).
However that won't (isn't) sealing the neck walls to the chamber upon ignition.

Three options:

1. Do nothing. (It isn't anything of particular consequence.)
2. Load hotter ~ 35,000psi (31gr IMR3031 would do it)
3. Anneal the necks to soften them up and permit pressure sealing.

Unless you are a died-in-the-wool/gotta-have-clean-cases OCD victim... I'd go Curtain #1.

 

[gamestalker]

I see the same thing when my brass has been reloaded multiple times, thus work hardening of the necks follows. So long as it isn't getting back any further down the neck or to the shoulder, either anneal, increase the load a tad, increase your crimp slightly, or just live with the minimal sooty look that it creates. Me, I just live with the sooty looking brass as long as the load is performing well. 90+ % of the soot will tumble off anyway, no harm no foul.

GS