S121 and tumbling cast bullets

[oafpatroll]

Hoping for some magic trickery that can be offered by the more knowledgeable than me.

I have reloaded cast and then later powdercoated cast bullets with the same MS200 recipe for many years. It gave me a comfortable 6 or 7 margin over SADPA factor regardless of season and performed well in my pistols.

When the great Somchem propellant drought hit I eked out my stocks of MS and was into an inherited tin of MP when a batch of S121 became available. Fearing that the end was nigh I bought as much of it as i could squeeze on my card and felt poorer but smugger.

Having never used the stuff I was struck by two things when I started load dev. One was how filthy it is and the other that any load that would make factor with a 130gr cast and PC bullet would have a reasonable chance of factoring tumbling.

The bullets are sized .367 for barrels that slugged out between .365.355 and .366 .356 and I have them running 150fps down from where the same range scrap alloy worked perfectly fine with both MS and MP and in rifle bullets up to 2000fps.

Can anyone suggest a potential route to happiness? I have loads of 121 and can't stomach the idea of busting out the card again to buy something else.
My deeply amateur assumption is that the faster burning MS creates a pressure spike that overcomes   

[BBCT]

Sorry, but I have to fact check you here - I know it's not answering your question.

Bullet size: You say they are sized .367 with a bore size of .365/.366, but do you perhaps mean .357 with bore size of .356?

There are probably people out there looking for S121. I know guys that swear by it. Maybe you can find somebody that is willing and able to swap MS or MP for S121?

Where are you?

[janfred]

How do you know you are at the max load for S121?

[oafpatroll]

Bullet size: You say they are sized .367 with a bore size of .365/.366, but do you perhaps mean .357 with bore size of .356?

Where are you?

Thanks for spotting the dumb in the dimensions. Correct, sized .357 for bores of .355/.356

I'm in the North of JHB.

[oafpatroll]

How do you know you are at the max load for S121?

It's not near max. I realise that typing while pissed is stupid. On rereading what i wrote I can barely make sense of it. Corrected below.

"Having never used the stuff I was struck by two things when I started load dev. One was how filthy it is and the other that any load that would make factor with a 130gr cast and PC bullet would have a reasonable chance of factoring tumbling."

The loads are on the lower end of the scale and as I reduced charge the incidence of tumbling reduced. Can't go much lower if at all without risking not factoring.

 

[Treeman]

I never found anything special in anyway about 121, except that it coats my skin and I can taste it when using.
You say that tumbling was reduced as you reduced charge ? I thought, have experienced the opposite. When we were doing reduced and subsonic loads, tumbling came with lower than XYZ speeds.

Regarding posting while pissed.
Problem with having a few drinks while on the net is that time flies when you enjoying yourself, time x drinks = a bit pissed. A bit pissed makes all the world clearer and the mind faster than the fingers. That's where the problems start.

...................... but I think i talk to a amateur when it comes to this shit

[janfred]

I'd go as far to say that S121 might not be the problem.

Have you changed anything in your process since the last time you used MS/MP powder, i.e. alloy, powder coating, sizing, etc.?

[NoStepOnSnek88]

@oafpatroll,

Greetings 

A little over a year ago I believe, I was shooting an IPSC club match, and long story short there was a gentleman that changed over from the Frontier CMJ's to Silver Rapids, he had issues with tumbling bullets. One of the regular shooters and a person with decades more experience than me asked to see a few of his rounds, he looked at them and suggested that he believed that he had over crimped / or the crimping was too aggressive on the Silver Rapids he was using.
Anyways, just thought I would mention it, hopefully, you do get it sorted out soon enough.

[oafpatroll]

@oafpatroll,

Greetings 

A little over a year ago I believe, I was shooting an IPSC club match, and long story short there was a gentleman that changed over from the Frontier CMJ's to Silver Rapids, he had issues with tumbling bullets. One of the regular shooters and a person with decades more experience than me asked to see a few of his rounds, he looked at them and suggested that he believed that he had over crimped / or the crimping was too aggressive on the Silver Rapids he was using.
Anyways, just thought I would mention it, hopefully, you do get it sorted out soon enough.

Howzit and thanks snek. Problem for me is that the only thing that's changed is the propellant so while it could be a crimp thing it's unlikely as the die setup is completely unchanged. I actually had a 'transitional' batch that was about 3/4 MS and 1/4 just above start load of 121.

[oafpatroll]

I'd go as far to say that S121 might not be the problem.

Have you changed anything in your process since the last time you used MS/MP powder, i.e. alloy, powder coating, sizing, etc.?

Absolutely nothing else has changed. Bullets are from a batch of 5k I made early this year and were cast from range scrap that was melted, cleaned and ingoted in one go. Press and dies were unchanged and as mentioned above the changeover in propellant happened in the middle of a batch. None of the MS rounds showed keyholing while around 1 in 4 of the first batch of 121 rounds did.

A very accomplished IPSC shooter i know mentioned having had a similar issue with 121 when running cast bullets and he said he thought it was pressure peak related.

[223]

9mm P cast bullets that tumble when loaded with S121 or similar (H TiteGroup, IMR Target, Lovex S022, VV N320 etc.) fast-burning powder is not uncommon at all.  I have experienced it as well.

The reason for the tumbling is pressure.  To make minor PF the load with almost any bullet weight runs close to max pressure (35000PSI).  This pressure exceeds the tensile strength of the cast lead bullet, thus deforming it and causing it to strip in the rifling.

Frontier CMJ's have a relatively thick and hard copper jacket, which can handle these high pressures much better.

When shooting cast lead, whether powder coated or wax lubed, the slower powders (MP200, S221, Lovex D036, D037.1, VV 3N37, 3N38, Alliant Unique etc) work much better, since they operate around 25000PSI with minor PF loads.  This is acceptable with +/-25BHN bullets.

I also suspect that the lower operating pressures help to reduce pistol wear, which is especially important on pistols with a weaker action like the Beretta 92 and derivatives. (I have broken the locking block on my Taurus PT92 already. This is pretty common.)

I also think that the faster powders and resulting high pressures cause cases to bulge and primer pockets to stretch, resulting in cases to be scrapped much earlier than with the slower powders.

The reason for the popularity of the fast powders is the lower powder cost per shot, compared to the slower powders.  If you add the cost of case wear, the saving vanishes.

In low pressure cartridges like 9mm Short, 38 Spl and 45 Auto, S121 and similar fast powders seem to work very well.  Their max pressures are around 18000 - 21000 PSI which is well below what cast bullets can tolerate. (Edit: Most common loads in these calibers develop pressures well below max, even when loaded with S121.)

Cast bullet hardness also needs to be addressed.  Not all bullets and alloys are equally hard.  To get to 25BHN (Brinell Hardness Number) you need to have enough Antimony in the mix and quench harden the bullets from the mould (and again from the PC oven).  Since Antimony is somewhat costly, many casters cast bullets that are just not hard enough for high pressures.  Than may well be true for commercial casters too.  To measure is to know.

Powder coating (PC) is normally harder than lead, so a generous layer of thermoplastic coating can help to strengthen the bullet surface and prevent stripping to some degree.

Another important parameter to consider is bullet to bore fit.  Ideally, a cast bullet should be at least 0.001" (0.025mm) bigger than the groove diameter of the barrel.  Since PC is somewhat "springy", most casters use bullets that are 0.002" (0.05mm) larger than barrel groove diameter.  Do get your barrel measured (slugged) to determine the actual size.  I have seen several 9mmP pistols with groove diameters as large as 0.359", in fact, I own one of them.  Standard is 0.355" to 0.356".

If the bullet does not fit snug in the barrel, some hot gasses will escape (blow by) past the bullet and cause flame cutting of the bullet's bearing surface. This causes leading, stripping and tumbling.

Do it right and you will enjoy many years of accurate shooting at a moderate cost.

[oafpatroll]

@223, you have it covered. A competitive and very high volume IPSC shooter I know said exactly the same thing about the pressure characteristics of S121.

The bullets are sized a thou over slugged bore dimension and worked perfectly well, even at substantially higher velocities, for years with MS200. They are cast from range scrap and quenched from the mold and the PC oven. Given that i make them in large batches and shoot them out FIFO thay are probably as hard as they can get given the alloy. There were zero changes to anything other than the propellant and as i mentioned above it was actually changed out part way through a batch so the difference was really obvious.

Will try and swap my remaining stock of S121 out for something else more suitable.     

[Treeman]

223 answered this question with this "The reason for the tumbling is pressure.  To make minor PF the load with almost any bullet weight runs close to max pressure (35000PSI).  This pressure exceeds the tensile strength of the cast lead bullet, thus deforming it and causing it to strip in the rifling.

Frontier CMJ's have a relatively thick and hard copper jacket, which can handle these high pressures much better

This was discussed on GS a few years back.

I had a tumbling PC bullet problem with my .357 Ruger B/H - coincidently the barrel was fouling rather quickly as well. I do believe my coating was thin and also a bit hit and miss in places.
I once cast a batch of bullets and for some reason loaded up without powder coating, can not recall the road to the uncoated loads, but they were there. They also tumbled and also left samples down barrel. One fact stood out and that was the 121, tried it because it was more available and cheaper  than S265.
One of those things that I figured out later, after stopping the combo. I figured the bullet was obturation pressured against barrel and smeared off causing stability issues down barrel.