Seating Depth Question

[Wrbjr]

Lee 175 grain TC .40 mold.

I have loaded this round to an OAL of 1.125 and put it through the chronograph and settled on a load with Blue Dot achieving approx 1100 fps. Quite accurate and I am happy. http://i1275.photobucket.com/albums/y441/bryan578/police001_zpsc049486d.jpg (http://s1275.photobucket.com/user/bryan578/media/police001_zpsc049486d.jpg.html)

However... I am going to start coating this boolit with Hi Tek and will for my own peace of mind re do the range tests again to see if there are any significant changes vs Alox.

Should I seat this boolit to 1.1 which brings the crown to the brass line... and reduce the powder charge of course to compensate for the deeper depth?
http://i1275.photobucket.com/albums/y441/bryan578/hottop004_zps6d21983a.jpg (http://s1275.photobucket.com/user/bryan578/media/hottop004_zps6d21983a.jpg.html)
Is there any real advantage to one depth or the other? This boolit cycles and functions flawlessly at 1.125... and I assume it will at 1.1 as well. Interested in some input here to one scenario or the other.

[tazman]

If it works flawlessly at the longer seating depth, I wouldn't change it. Coating it with pc will not change anything significantly as far as feeding.
I always prefer to err on the side of reducing pressure whenever I can.

[rsrocket1]

Depends on your gun. I seat my 401-175-TC's to 1.115 (like your bottom picture on the fridge) because I load my bullets as cast without sizing anymore, just tumble lubed in 45/45/10. They drop at 0.4025" to 0.403". When I seat the bullet to 1.130" (like the ones in your magazine, the bullets will not pass the plunk test in my M&P 40 barrel and if I press the cartridge in then push it back out with a dowel, the exposed lead above the rim is bare and shiny. This happened even if I sized the boolits to 0.401"

I compensated by dropping the max charge down from 6.0 grains to 5.5 grains and everything worked out well. I lost about 40 fps, but the paper targets didn't complain so neither did I. I have since dropped down to 5.0g as the standard load simply because I can get more shots out of a pound of powder that way. Oddly enough, the powder measure setting is the same for 4g Red Dot which is the ideal charge for that powder so now I can switch between powders and not adjust the powder measure settings, just do a couple of check drops and weighings.

With your Blue Dot loads, I would start by dropping the charge by 10% and testing the load out. With the smaller internal volume, you will have a higher Pmax so you will need to drop the charge which will also drop your MV a bit.

The good thing is that regardless of the bullet thickness, you won't run into any bullets getting stuck in the throat and preventing the slide to lock into firing position so long as your loaded rounds pass the plunk test.

OTOH, if your sized bullets already work fine and you are sizing after PC'ing, you are good to go with the longer lengths.

[Wrbjr]

Depends on your gun. I seat my 401-175-TC's to 1.115 (like your bottom picture on the fridge) because I load my bullets as cast without sizing anymore, just tumble lubed in 45/45/10. They drop at 0.4025" to 0.403". When I seat the bullet to 1.130" (like the ones in your magazine, the bullets will not pass the plunk test in my M&P 40 barrel and if I press the cartridge in then push it back out with a dowel, the exposed lead above the rim is bare and shiny. This happened even if I sized the boolits to 0.401"


I compensated by dropping the max charge down from 6.0 grains to 5.5 grains and everything worked out well. I lost about 40 fps, but the paper targets didn't complain so neither did I. I have since dropped down to 5.0g as the standard load simply because I can get more shots out of a pound of powder that way. Oddly enough, the powder measure setting is the same for 4g Red Dot which is the ideal charge for that powder so now I can switch between powders and not adjust the powder measure settings, just do a couple of check drops and weighings.

With your Blue Dot loads, I would start by dropping the charge by 10% and testing the load out. With the smaller internal volume, you will have a higher Pmax so you will need to drop the charge which will also drop your MV a bit.

The good thing is that regardless of the bullet thickness, you won't run into any bullets getting stuck in the throat and preventing the slide to lock into firing position so long as your loaded rounds pass the plunk test.

OTOH, if your sized bullets already work fine and you are sizing after PC'ing, you are good to go with the longer lengths.

I use 45/45/10 as well. I am going to use Hi Tek chemical coating, not the Powder Coat process so the added thickness is virtually negligible from what I am told. If this process works as well as others report I will forgo the Alox for a bit to experiment.

My Springfield XDm40 does not have the problem of headspacing you are experiencing. I assume this is what you are referring to as the plunk test. The rounds come out without any additional marking or shiny areas. They definitely "plunk" against the case mouth.

I did put a micrometer on the boolits and they measure out pre sized at .4025 to .403. I find it interesting you are not sizing at all... that makes sense really. Anyway... this particular pistol just seems to eat anything I put in it. As to the longer depths... more powder... deeper depths... less powder... so maybe the only real difference is less driving bands being used at 1.25. Probably not even a factor anyway.

What weight are your's dropping at? I find mine to range from 176 up to 180 for the most part. I'm sure the alloy counts toward the weights... mine is approx a #2 alloy.

[Wrbjr]

If it works flawlessly at the longer seating depth, I wouldn't change it. Coating it with pc will not change anything significantly as far as feeding.
I always prefer to err on the side of reducing pressure whenever I can.

My thinking is that even if I seat the round deeper to 1.1... the powder is reduced, so not much changes really? But I am tempted to stay at 1.25 because I know it works well and the pistol functions beautifully with this load and boolit.

[tazman]

But I am tempted to stay at 1.25 because I know it works well and the pistol functions beautifully with this load and boolit.

If it isn't broken, don't fix it.

[rsrocket1]

What weight are your's dropping at? I find mine to range from 176 up to 180 for the most part. I'm sure the alloy counts toward the weights... mine is approx a #2 alloy.

Yes, my 401-175-TC's typically drop closer to 180 than 175.