200XTP vs 200XPB PT 50Cal Discussion

[ET]

Keeping the discussion of my PT threads seperate from my original trace seems to be the perfered format.
So I started this dicussion thread and included the trace and stats here also for quick reference.



Ed

[tar12]

ooops! I accidently locked the discussion.. Sorry Ed! ;D

[Dave W]

Thanks for the trace Ed. I would have like to have seen more velocity with the light bullet to see if the secondary spikes occur in the .50 like the .45.

Just a thought and probably all wet but has anybody given a thought to maybe the reason or part of the reason for the secondary spikes is due to the smooth barrels and light bullets in the customs just don't offer enough resistance?

[ET]

Jul 10, 2011 21:02:48 GMT -5 Dave W said:

Thanks for the trace Ed. I would have like to have seen more velocity with the light bullet to see if the secondary spikes occur in the .50 like the .45.

Just a thought and probably all wet but has anybody given a thought to maybe the reason or part of the reason for the secondary spikes is due to the smooth barrels and light bullets in the customs just don't offer enough resistance?

DaveW

There will eventually be traces with more velocity as I too want to see what develops.
That is an interesting thought about bore roughness playing a role for secondary spikes?

When I return to the 200gr bullet testing I will up the 4759 load for single powder but also want to try putting H4198 at the tail end of the burn to see if the rate of pressure decline can be extended. This should add more velocity without having to increase peak pressure say with a single powder burn.

For now I want to just cover some basic loads before digging deeper into powder burn reactions. The fun is yet to come. ;D

Ed

[mike3132]

I'm surprised you are not experiencing sabot failure with these light weight bullets. Are you recovering the sabots to see how they held up? In the past we've found lighter bullets tend to misfire or blow sabots because of the short length of the bullets wont allow the sabot to seal. I have a feeling the xpb are doing that now since the don't obturate like the lead core xtp and that is the reason you don't see them on target. Mike

[ET]

Mike3132

In this instance I didn’t check the spent sabots but have in the past with no signs of sabot issues. The XPB’S are knurled to a diameter of .455” from their original diameter of .451” and are slightly tighter fit than the 200XTP’s.
I too feel that in some way it’s obturation related for the lighter copper bullet but plan to continue with the 200XTP to get the velocity closer to 2500fps. Hopefully by then I can get some 200FTX’s into the game as well.

Using 4759 I have never had an ignition issue with 200gr bullets and the traces show no pressure curve issues that I recognize as something is amiss. If anything the traces show unlocked potential that hasn’t been reached yet IMO.
Eventually when I get back to trying the 200XPB’s I plan to try a washer under the heavy knurled bullet and also try a few with what I like to call tail feather knurling suggested by Greenhorn. Also annealing hasn’t been tried yet.

As much as I would like to jump back on this right away the 250SST traces are scheduled next. As they say “Everything in its own good time”.


Ed

[GMB54-120]

Not quite what i guessed in terms of fps. I agree that the bearing length may be part of reason. A tighter sabot might help and compare loading pressures?

IMO the 200gr FTX will likely increase "issues". The bearing surface is about the same as the 225gr FTX but the jacket is much tougher. Testing them against a Barnes 451-200gr which is longer might be worthwhile. Its bearing surface is longer than both but even harder to obturate.

I would love to get the 200gr FTX shooting well but ive never been able to achieve my goals with them. I still have a small supply of them. hopefully someone finds the right combination to get them to shoot as well as the 225gr.

[ET]

Gmb54-120

Arrangements have been made to acquire some 200FTX .452” bullets in the near future.
From the pressure trace results so far there is plenty of room to safely boost the velocity with more pressure. More pressure should provide a better kick to that bullets butt.
At this point in time the 200FTX appears to be my best candidate to get a 200gr bullet to work decently in a 50Cal. With the PT unit that has the OBT feature should help me narrow down the best load possible.

I will eventually find out what promise the 200FTX holds.
They may not produce the groups that the 225FTX does but if they can produce MOA I’ll take it.



Ed