Considering 357 mag, 125 grain bullets, and Titegroup powder.

Why does their max data say 41,200 CUP for XTP rounds, but only 22,800 CUP for lead rounds? Just looking for a simple explaination.
Mike

Their choice of where to stop on lead rounds. No other explanation.
Try Lyman's for a different opinion.
At any rate, if you just want to go faster, pick a slower powder. I use Titegroup by the carton for 9mm and .40 competition loads, but is is a poor choice for trying to go fast in .357.

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Science plus Art

It probably applies to Hornadys lead bullets which are swaged.If you loaded them to the same pressures ,they wouldn't grip the rifling being very soft.If you want to load cast lead check out Lyman's manuals

Mike,

You need to keep in mind, that as pressure increases, so does velocity. Once lead bullets start passing 1000 fps, the tendency is that lead bullets can start to lead the barrel. Any powder producer realizes that they have no control over the type or hardness of the lead bullets, so they err on the side of safety and make the assumption that the lead bullet is a soft swaged bullet.

As you increase the hardness of the bullet, you can increase the velocity, gradually. I have never seen a manufacturer of powder alone provide recipes for swaged and hardcast bullets.

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Judge control not gun control!

Thank you. Beginning to be clearer now.

They stop at 22,000 with lead because soft lead bullets pushed too fast leave streaks of lead in the barrel. As long as you're willing to clean you can bump up the velocity using jacketed bullet data without any safety issues using cast bullets. Also, while velocity is a factor, most leading with cast bullets at magnum velocities is not really caused by the bullet traveling too fast down the bore, but by gases escaping past the bullet between it and the inside of the bore. The gas melts the lead and as the bullet travels through leaves streaks of lead in the bore. Much of the bore leading can be minimized by using bullets sized .001" over the bore size. ie in a .357" bore, load .358" cast bullets. Gas checked bullets pretty much eliminate leading by stopping the gas cutting.
Your choice of Titegroup for loading low pressure cast loads in the .357 is a good one though. It is a fairly fast burning powder and is great for low velocity loads in the .357 and 38spl. If you want to go fast with those 125 gr XTP's go with 2400 powder. For magnum loads with heavier jacketed bullets like 158 gr.and up. Go with H110 or W296. The 110 and 296 powders are virtually identical, but they need a magnum primer, especially in cold temps.

Actually, Horandy swaged lead bullet are 95/5 to 94/6 alloy and NOT that soft--certainly not for any TiteGroup velocities.
TiteGroup throws out pressure spikes. The MAX load is probably the highest load that did not have pressure spikes that exceeded SAAMI pressure limits. Now that we have pressure vs. time traces and can SEE any spikes, a LOT of load data has been reduced.
Clays also throws pressure spikes at times and you might find it having a rather low max for the same reason.
Next, TiteGroup does not always "play nice" with lead bullets. It burns very hot and at least one coated bullet manufacturer warns users NOT to use TiteGroup and save themselves problems.
Call Hodgdon and ask.
I shoot 140gn Hornady swaged .358" "cowboy" bullets in HOT .38 Super loads (PF 175+) and get no leading. Bullets are plenty hard enough.

I traded some Trail Boss for some Titegroup with a friend. He had never loaded Trail Boss nor I the Titegroup.
The bullet I loaded was 125 gr Hi Tek coated, BH=12, from Missouri co. The primers were cci small pistol. I loaded 50 each of 5 grain, and 5.5 grain. Those shot well so I loaded 50 of 6 grain. The latter shot well but was noticibly louder with a sharper crack. The recoil was not quite that of Federal 158 gr JSP factory loads. The 6 grain load was knocking bigger chunks off the rotted log.

Primers fared well for all three as did the brass. No leading at all for any of the loads. I would not go higher than 6 grain and see no reason why I would want more than 5.5 grain. Accuracy seemed ok for all three but a rotten log was my target.

Mike

You'll find most lead data stops at around 1200 fps or so. That's regarded as the upper limit of velocity for a lead bullet, after which you get leading.

Lead can be loaded faster, with a little experimentation. Another option is to use a gas-checked bullet (denoted with a "GC"--such as LRNFP-GC). However, gas checks are expensive. They're only economical if you desire the terminal ballistics of lead, as in a hunting bullet.

It's cheaper to switch to a plated or jacketed bullet if you're doing target work. Or simply accept the speed limit.

In the case of the .357, I would suggest switching from a 125-grain LRN to a 158-grain LSWC. They'll deliver more of the full-power experience while being less expensive than jacketed bullets (though not as cheap as 125s). 158 LSWCs and 148 WCs are really the .38/.357 standard, anyway. 125s are sort of an economy choice.

There are heavier bullets available (up to 200 grains or so) but data becomes less and less available.