Gear's 190x

[btroj]

Hey Gear, how is that 190X working for you in the 30xcb?

I got good results at low velocity but as the pressure and velocity build accuracy starts to fall off.

I have pretty well decided that it fits too well and the fit of the 30 Sil is better as pressure and velocity build.

[geargnasher]

Let's call it a successful experiment in that it proved a theory of mine. Unfortunately, what it proved was that my theory was not the best approach.

As an overview, I concluded that it shot worse at high velocity (2400 fps) in my XCB than either the 185G or the Mihec .30 Silhouette when cast of the same alloy and shot with the same load. It shot second best with a softer alloy at lower velocity, with the 185G coming out on top. I still haven't put the 190X through my .308, but I suspect it will actually do pretty well in that one.

Conclusions? The "Morse Taper Fit" technique only works at standard cast bullet velocities. When you push past that, a whole new method of fit must be used, because the bullets are not strong enough to engrave without some base deformation due to neck tolerance when they have a large amount of contact area. Giving a MTF bullet a head start (jump) helps immensely with accuracy, but it is not the best design for proper centering and alignment at during high-velocity launch. I know one thing for certain now: If you want to achieve HV accuracy, you're going to need to take an approach that is 180 degrees from conventional "wisdom". Those three bullets and and some experimentation with the most oft-overlooked and misunderstood thing (something 357 Maximum mentioned a lot, among others) has been teaching me just what does and doesn't get us accuracy past a certain point. Barrel twist has little to do with it, though slowing it down can let you push the 1.5-2 MOA accuracy window up a little bit using conventional techniques and loading philosophies. If you want sub-moa at truly high velocity, slow twists won't do it, you have to throw out the baby with the bath water and start over with a completely different approach at the loading bench. The "secret"? DYNAMIC FIT.

Look for a new design soon, more like the 185G but with some slight changes to the nose and a crimp groove so I can use them in my tube-fed rifles.

Gear

[btroj]

Ah yes, dynamic fit. The importance of understanding what happens when our relatively soft bullet gets hit from behind with a big hammer of pressure.

I have had far better luck with the 30 sil as pressure and velocity goes up. I still think my alloy is too hard for the pressures I'm getting. I need to max out the case capacity with RE 19 and see what happens. My loads are only in the 42K PSI range so i have lots of room to go up. The 3/1 alloy is just too hard at those pressures.

I need to also look at more loads with 4350 to see if they shoot better at similar charges as RE 19. Pressure should be rising faster and that should help overcome the overly hard alloy. Only one way to know, right?

[popper]

Link to original thread, please?

[geargnasher]

I never could get 4350 to shoot well in either my .308 or XCB with WD 50/50. I tried and tried with three different bullets. Must be a mismatch somewhere. It's like right at the point the powder started working the alloy was fading out. 2400 fps with two rifles, one with a ten and one with a 12 twist. My alloy tested in the 19-21 bhn range depending on which bullet and batch was used.

When I switched to H-414 things started coming together, but below the failure point of the alloy. There was a sweet spot right under 2400 fps in both guns with both the 185G and .30 sil. Push it up a bit and the powder is still working fine but hitting the bullets too fast. I think a heat-treat to 25-27 bhn with the same mix will get the half-MOA point up to 2600 or so, I just haven't gotten around to it yet.

I've shot a lot of scattergun groups with my XCB, and some stellar ones, too. Like any other decent rifle, feed it what it likes and it will shoot, feed it what it doesn't like and it flings.

Gear

[btroj]

Link to original thread, please?

What original thread? There really isn't one. This is the Accurate 31-190x

[btroj]

Alloy strength and pressure curve must be matched pretty closely I think. Your heat treat could be all it takes.
I can water drop my range scrap and get 24 BHN. I do know it doesn't matter what temp I heat treat to, it all comes out the same. Yep, 375 or 440 degrees it gives the same BHN. I think it is the low tin that does this. I bet adding tin would give a variation in hardness based on heat temp but would also lower the hardness I acheive.

Tin is a double edged sword.

[geargnasher]

I started a thread on this forum about this bullet design back in the spring, but it ran its course. I also started an XCB thread in special projects, but I am leaving it to the gunsmith and cartridge developers.

Now that tin thing is interesting. Where have I come across this before..... I think I can bump my 50/50 with a better quench because it contains at least 1% tin. Otherwise I'll have to switch to my 3/2 alloy with next to no tin but a bit more antimony. People always wonder how consistent BHN can be achieved via water-quenching, well, low tin content is a big part of it. Then there's arsenic and sulfur to study, I still want to find out how much heat treatability an alloy just having lead, antimony, and trace arsenic has vs. one that has some tin in it, too.

I don't know how to make this bullet shoot very well at HV. I think I know why I am having trouble, and that "why" has moved me away from the design. Not saying it can't be made to shoot in the XCB, but I'm out of ideas and am ready to move on to a shape that I know works an just focus on alloy for a while until I get to my next goal, 2500 fps with a 180-190 grain bullet and still maintain MOA or better to 500 yards.

Gear

[btroj]

I need to add a small amount of tin to my range scrap and see how this all changes. Right now it is 1.8% Sb and .25% Sn. Bet if I went to 1% Sn the temp at quench would dictate the end hardness.
That can be good or bad. It is bad if water dropping as it could give variations in hardness based on time from pour to quench. It could be good if using an oven for heat treat as it would alloy a single alloy to be adjusted in hardness just by changing oven temp.
I prefer to keep it simple right now so I am using a 3% Sb 1% Sn alloy. Haven't done the testing to see how temp at quench alters hardness, if it does at all.

So many things to be looked into. Hardness testing alloys handled different ways takes lots of time. No way to speed up waiting a month, is there?

I do like how the 190X casts. Easy to get lots of good bullets. I also use it for alloy testing as it has a nice flat nose that is easy to get the Cabin Tree indent point centered on.

[btroj]

Sure was a pain doing all the alloy testing but I'm glad I was told to do it. Taught me a bunch and made me realize that not all I was told was always true.

Thanks to the guy who told me I needed to do the testing even if I did hate being told.

[geargnasher]

How do you like that rebated, Hornady check shank? The 185G has a similar once and shoots very well under the right conditions, so I'm pretty confident that any "weakness" of the design is not affecting accuracy.

Gear

[btroj]

It take a Gator check fine? It is sort of a pain in sorting, I find it makes it a bit harder to tell if the base was really well filled out. I like the round lube groove, no sharp edges to give fillout problems and it drops easy too. I am seriously thinking of using it in Dad's 06 for deer this year. Should be quite good at 2200 fps or so. I rarely shoot over 50 yards so that would be plenty fast even though I know I can get "deer accuracy" at 2400 pretty easily.

I am sold on Tom's moulds. I wish he could make a smaller diameter meplat but the quality and time to deliver is awsome.

[geargnasher]

I'm not sold on the radiused lube groove for HV shooting, I'm not sure it allows the metal in front of it to displace rearward as uniformly as a "Keith style" lube groove does, particularly during some slight misalignment situations which will always exist prior to it being fully engraved. I haven't proved that it doesn't work, either, but it is a variable that will take two more mould designs to eliminate. I may change just the nose of the 190X, or I may change just the nose on the 185G with the deeper, more square lube groove. Working on it.

Gear

[btroj]

A deeper square lube groove? Like the 30 sil? I know someone who REALLY likes that lube groove design, it appears on lots of bullets. Maybe he knows something? Whatever you do go with a single groove, I think they are the only way to go on a 30 cal bullet like this. What sort of weight?

The rounded groove does cast easier but in the end it is the target that matters. I don't like moulds that don't like to drop bullets but seeing them go into small groups eases the pain.

Won't matter too much either way, Tom will make em fall right out.

[RickinTN]

Following closely here guys! I'm not as deep into as you all are, yet!. I had Tom do a similar bullet for me which matches the taper of the leade in my long freebore 30-06. It is the 31-185R. Gotta love Tom's molds. I've only had the mold a couple of weeks so not much testing so far. I have gotten good accuracy at around 1,600 fps, which is no trick but with the only load I tried to push it just a little, to what should be around 2,100 fps accuracy went out the window. My velocity goals aren't as high as yours as I would be happy in the 2,400 or so fps range. The "taper fitting" or "pre-slumped" design, in my mind anyway should work well and I hope we all prove that it does. I am working with a copper enhanced alloy and have tried it air cooled and heat treated, but neither actually aged very long obviously. My bullet does have a single deeper square lube groove. It is actually based off of the 31-180R that Tom did for me several months ago and has been a good bullet so far. I was thinking the modifications would make it a better bullet.
Thanks to all of you for your work as I find it beneficial and trying to follow along.
Rick

PS Good to see you posting again Gear!

[btroj]

Man does that 185R look similar to the 190X. In an 06 it should be good in the 2100 fps range. Really good.

[RickinTN]

It is certainly influenced by the 190X. The throat and leade of my rifle are apparently a little different than most? I have over .200" freeebore. After almost a gazillion measurements to be sure of the taper and then Tom doing his magic with the mold (my first brass mold by the way, and I love it! Thanks Tim for the suggestion) the taper matches the leade taper of my rifle perfectly. I do have very high hopes for it and I think letting the alloys age for a bit should do better.
Take care,
Rick

[btroj]

Don't be afraid to let it jump a bit to the lands. Sometimes that makes a difference, the rifle will let you know what it wants.

[geargnasher]

Taper and "pre-slumped designs" don't work as well as some of us had hoped when you start really pushing the velocity. In fact, Btroj and I are discovering for ourselves that "pre slump" is not at all what we need to happen. If you're hanging around the 1600-2K fps area, matching those tapers and making sure the bullet is centered in the throat when fired can deliver extraordinary accuracy. Not the only way, but a good way.

Gear

[btroj]

I do hate to say that we were told so, but we were. Dang I hate saying that.
It was sure worth trying and it taught us a bunch. Learning by trying different things is the only way to go. We, or you, had an idea and we ran with it.
I still need to push mine harder and see what happens. With a couple bullets and numerous alloys it sure does take a heap of range time for testing. I can remember tellig someone it would take maybe 1500 rounds to really see what is gonna work, I think that may be a little short.