Barnes TTSX seating and pressure

[Bullshot]

Newbie question regarding principle of seating depth / pressure applied to Barnes TTSX.

All else being equal, would there be much difference in pressure from a TTSX seated just off the lands, base of bullet above the bottom of neck to one seated way off the lands and deep in the neck with base below the neck, assuming uncompressed load.

2nd question, between an uncompressed 99% load and a mildly compressed say 101% load, is there typically any pressure spike or would it be expected to follow a more linear rise commensurate with just the extra powder (assuming you are safely working up).

Just trying to better understand what these factors (seat depth and compression) independently introduce to the equation of safe reloading since a few of my reloads are hovering in the max book area (w/uncompressed powder and middle of the road seating) and I am wanting to tinker more with seating and that last .25- 1 grain of powder to finalize a recipe.

 

[VikingsGuy]

Newbie question regarding principle of seating depth / pressure applied to Barnes TTSX.

All else being equal, would there be much difference in pressure from a TTSX seated just off the lands, base of bullet above the bottom of neck to one seated way off the lands and deep in the neck with base below the neck, assuming uncompressed load.

2nd question, between an uncompressed 99% load and a mildly compressed say 101% load, is there typically any pressure spike or would it be expected to follow a more linear rise commensurate with just the extra powder (assuming you are safely working up).

Just trying to better understand what these factors (seat depth and compression) introduce to the equation of safe reloading.

For hunting I am not convinced chasing lands is worth the effort. Just sticking to 0.050 per Barnes recommendations has given me all the accuracy I will ever need from a hunting bullet.

Pressure spikes near the higher end are very much chamber specific. Work up to initial signs and then fall back a bit - % of theoretical load isn't needed but don't go above recommended max unless your are quite experienced. Also the %s only accurate to that degree if you are water weighing case volumes and size sorting. All also not useful for hunting rounds in my opinion.

 

[Bullshot]

For hunting I am not convinced chasing lands is worth the effort. Just sticking to 0.050 per Barnes recommendations has given me all the accuracy I will ever need from a hunting bullet.

Pressure spikes near the higher end are very much chamber specific. Work up to initial signs and then fall back a bit - % of theoretical load isn't needed but don't go above recommended max unless your are quite experienced. Also the %s only accurate to that degree if you are water weighing case volumes and size sorting. All also not useful for hunting rounds in my opinion.

Very good points, these are hunting rounds, not benchrest. I am not carefully sorting cases by volume, just by weight, and therefore will not be trying to stretch beyond max load in any case, but some max’s are listed as compressed. And in my rifle, I have to seat way out to be around .05.

Based on pic below, I guess my real question is, at same charge, which of these two rounds would be expected to be highest pressure. Long one is clear but just shy of lands. Short one is very lightly compressed.

 

[VikingsGuy]

Very good points, these are hunting rounds, not benchrest. I am not carefully sorting cases by volume, just by weight, and therefore will not be trying to stretch beyond max load in any case, but some max’s are listed as compressed. And in my rifle, I have to seat way out to be around .05.

Without case volume work (case water weighing) the theoretical 98% vs 102% difference is speculative and will not consistently predict "compressed" rounds. In theory compressed loads are more consistent, but depending on the specific rifle chamber, the specific powder, specific brass, etc, this isn't always the case. I recommend not worrying too much about theoreticals and go straight to working up a "velocity ladder" from midpoint to max (or as close to max as your rifle allows before showing pressure sign and then select the best node with a bias towards larger charge weights.

Somewhere on this form I give a brief description of my use of the velocity ladder approach and link to some decent resources if you want to do a little searching around.

Trying different powders, different bullets, and various charge weights will get you 98% of the hunting accuracy needed. Neck tension, seating depth, etc is hard to get good statistics to support even in bench shooting scenarios and are not worth the bother for most of us. But as simply a hobby, can be fun to mess around with at 1000yd at a target.

 

[VikingsGuy]

Based on pic below, I guess my real question is, at same charge, which of these two rounds would be expected to be highest pressure. Long one is clear but just shy of lands. Short one is very lightly compressed.View attachment 337424

Too many vairables to "predict". There are generalities, but in a given rifle chamber pressure is not linear. I suggest don't worry about it and set depth at 0.050" off the lands and do your charge ladder. With that picture my first question is not about compressed charge or not but if that lower one is just too long for your chamber, remember monos need some "jump" you do not want to push them right up near the lands. That can create pressure spikes and sketchy precision.

(also, I have several loads where the COAL is well shorter than would be required to get to 0.050" off the lands due to magazine length limitations - and via charge ladder got great shooting rounds anyway)

 

[D4570]

Most of the time you shouldn't load any barn. copper bullets up to the lands. They need a
Jump" to shoot well and keep the presser. Their website says something like .005 off.

 

[VikingsGuy]

Most of the time you shouldn't load any barn. copper bullets up to the lands. They need a
Jump" to shoot well and keep the presser. Their website says something like .005 off.

I am pretty sure you mean 0.050" -- but as with all numbers used in re-loading every user needs to verify every number themselves against trusted sources - Internet forums are good for general discussion, but a reloader should never take simply on faith the numbers posted by other users.

 

[golfer]

Very good points, these are hunting rounds, not benchrest. I am not carefully sorting cases by volume, just by weight, and therefore will not be trying to stretch beyond max load in any case, but some max’s are listed as compressed. And in my rifle, I have to seat way out to be around .05.

Based on pic below, I guess my real question is, at same charge, which of these two rounds would be expected to be highest pressure. Long one is clear but just shy of lands. Short one is very lightly compressed.View attachment 337424

I’m guessing the top one in the photo will produce less velocity. Just going off of what I’ve seen.

 

[Caseknife]

Very good points, these are hunting rounds, not benchrest. I am not carefully sorting cases by volume, just by weight, and therefore will not be trying to stretch beyond max load in any case, but some max’s are listed as compressed. And in my rifle, I have to seat way out to be around .05.

Based on pic below, I guess my real question is, at same charge, which of these two rounds would be expected to be highest pressure. Long one is clear but just shy of lands. Short one is very lightly compressed.View attachment 337424

Theoretically based on the two rounds pictured, the lower one would have lower pressure IF it is still at least .050" off the lands. That is a big if! I load monos exclusively and have had compressed loads that show pressure signs that I have seated the bullets .025" deeper and the pressure signs disappear. That amount of volume change in the case will not increase the pressure as much as the longer distance from the lands decreases the pressure, if that makes sense.

 

[D4570]

I am pretty sure you mean 0.050" -- but as with all numbers used in re-loading every user needs to verify every number themselves against trusted sources - Internet forums are good for general discussion, but a reloader should never take simply on faith the numbers posted by other users.

YUP your right

 

[Wind Gypsy]

Here's a graph ive seen in the past that illustrates relationship between seating depth and pressure. I'm sure it varies based on other variables but I found it to be a useful illustration. I'd guess that the 150 grain bullet and 53 gr 4064 are not fighting too hard for volume in the case with this example but don't know that to be true.



I wouldn't be surprised if the lowest pressure seating depth for the combo in the OP was somewhere between the two options but neither of them seem optimal. As others have said, I'd jump em 0.050" or a bit more and roll on.

 

[Bullshot]

Been thinking about this some more all day and appreciate the comments. I decided, even though they are not actually jammed, they look too long and to not even bother with testing them but to seat the long rounds one band deeper and then compare to the shorties. Then test in between as well. All of my rounds will end up much deeper than .05. I will probably end up with basically a book max but uncompressed load with a longer COAL than book but a good bit farther from the lands than .05.

Now I am wondering if my rifling is really eroded (its a used rifle) or if it was cut with an overly generous distance to the lands.

 

[cahunter805]

What brand of rifle and cartridge is it? Also that long loaded bullet might not even fit your magazine length.
I would load them either .050 off or if that won’t fit I would load them to magazine length minus .010 to ensure they feed well.
Also just because a load is compressed doesn’t mean it is over pressured. Slower powders fill the case more.

 

[VikingsGuy]

Been thinking about this some more all day and appreciate the comments. I decided, even though they are not actually jammed, they look too long and to not even bother with testing them but to seat the long rounds one band deeper and then compare to the shorties. Then test in between as well. All of my rounds will end up much deeper than .05. I will probably end up with basically a book max but uncompressed load with a longer COAL than book but a good bit farther from the lands than .05.

Now I am wondering if my rifling is really eroded (its a used rifle) or if it was cut with an overly generous distance to the lands.

With hunting rifles I usually find magazine length to be more of a length limiter than lands.