Leading issue...primer cause. (not cb related, revolver related)

[Shome10x]

I've a S&W M14 that I use in competition. In pursuing a competitive 148 HBWC swaged load, I ran into some leading issues in the throats. The load shot fine, but would lead with several powders, sometimes severely. Different parameters in development resulted in the same result. I determined that the "fit" was fine but still couldn't explain it... until this week.

The scenario is that I kept everything the same, except for the primers. I used Rem 1 1/2s extensively in the load development. New brass came loaded with and I had plenty of stock. I noticed the velocity spread was a little large, but lessened when loads approached the max. Actually they were the best when at max. Spreads were <40 fps and sds in the single digits. Fine, but I didn't want a max load for competition.

Then a theory about the throat leading came to me...I needed to try a different primer for "reduced" loads. I loaded 100 rounds with Win sp primers and the leading in the throats went away. (Edit: adjusted to same velocity) Cleanest I'd ever seen this revolver.

So... I know mine, but do you have any theories why the leading went away? I'll present mine after some discussion. I think the key is the 148 hbwc and this situation is really a non issue with other boolits.

Thoughts?

[Shome10x]

Some clarification: The bullet was a purchased HBWC, "dry lube". I tried other hbwc's, with the same initial results. End result was with same bullet.

[44man]

Primers are one of the most important things I test looking for accuracy. But there are nuances you did not find or tell, some related to mainspring tension, cup hardness, primer pressure, ignition flame, etc. You have just touched on the edge.
To say a primer stopped leading is not enough.

[Shome10x]

Apparently I'm not good at giving out details. Oh well... I'll have fun burning powder. If someone has a similar issue and I could help, pm me.

[wv109323]

It could be several things. The roughness or diameter of the forcing cones. The diameter of the bullets may allow the rounds to "droop" and not be aligned with the bore. Bullets could be sized down when seated in the case.

[Rattlesnake Charlie]

The only thing the OP changed was the primer, and the leading problem went away.

FOCUS!

I don't have the answer, but sure want to find out what it is.

[dverna]

The Remington primer did not develop sufficient initial pressure to expand the HB

[runfiverun]

in the smaller cases the primer will drive the boolit forward and ignite the powder at the same time.
without the powder you can drive a boolit into the barrel.
changing primers changes the ignition timing and thus where the peak pressure is in relation to where the boolit is at that point in time.
drive it more forward or less forward before peak pressure and you change the static fitment. [not initial mechanical fitment]

it's a trick we use in cast shooting in rifles too, only we do it with jump/alloy hardness and powder speed. [the initial engraving pressure influences the pressure climb]

[Treeman]

One could theorize that a more brisant primer was melting traces of lead from the deep-seated hollowbase bullet and depositing it in the throat. A different primer had no such effect. My understanding is that Remington 1 1/2s are a pretty mild primer so I am more inclined to think that things worked as others have postulated-To whit: a hotter primer upped pressures enough at the right time to obdurate the bullet base so that blow by and gas cutting didn't occur.

[Shome10x]

Runfiverun,

Your theory matches mine. In this case, the issue is exaggerated by the hbwc. I don't think there was enough expansion of the skirt in the case. Once the pressure was moved earlier in the curve, the leading in the throat vanished.

The issue was the Rem primer. One of my favorites because of its brisance, it had too much initial energy. It drove the hbwc too far before "complete" ignition. Gas cutting and mechanical erosion seemed to be taking place. I sure wish I had the means to view the pressure curve.

So for full power loads, I'll stick with the rem primer. But for reduced loads, I'll use a mild primer. One thing I did finding interesting, of the primers tested CCI standards were the mildest. (Per Chrono). I was expecting the Feds to be the mildest. BTW, Rem primers are not for +p loads. Cup is too thin and will pierce. Been there...

Thanks for the comments.

[44man]

I used CCI primers for years and years with no problems. But I went to Fed with IHMSA. It is said the cup is thinner but up to the 500 S&W, I don't see it. I even went well over 55,000 in .454's with them. I have used Rem primers too along with WW. But accuracy can change with the primer. I refuse to use a mag primer in the .44, just a Fed 150. I talked to federal and they do not use a mag primer in the .44 factory loads.
Leading is not an issue that I found with primers but I will not discount it. Boolit movement before ignition has been my findings so there might be something there.

[243winxb]

After the leading, the barrel was cleaned good. Next test, no leading. Bullet lube is not compatible.

In other words, clean out the barrel before changing lube/bullets.

[44man]

I have had leading. Worst was Alox or TL of any kind. Soft boolits are nasty. I don't clean barrels for 5 years or more now. I cleaned my .45 after 6 years to try some jacketed. I got no lead at all. None of my guns have lead in the bores with Felix lube. Put mule snot on and expect anything is funny.

[243winxb]

The 5.56 mm primer study showed that the firing of the primer burns about 1/3 of the powder at firing.

The rest of the powder is pushed against the base of the bullet, as it burns.

Maybe a stronger primer places the powder in the Hollow Base of the 148 gr??

Good to know that a primer may make the difference.

I loaded 100 rounds with Win sp primers and the leading in the throats went away. (Edit: adjusted to same velocity)

Meaning? Added more or less powder?