IMR SR 4756 in 10mm-OLA moves

[warren5421]

I am using Dillon 550B & SDB, both set up for 10mm. I weigh each charge, IMR SR 4756 @ 7.9 gr in new Star Line brass, 200 gr XTP's, COLA 1.250". I have several 100 XTP's, so far the gun likes the load so I don't want to change if I have enough 4756 powder to load these XTP's. The XTP's are all the same lot number. Cases are all trimed to the same length give or take .001. Bullet setting stem is locked so it isn't moving. Any ideas on what to do as my OAL keeps changing as much as .050. I have changed the bullet stems to try a different contour no help!

 

[LeverGunFan]

I am using Dillon 550B & SDB, both set up for 10mm. I weigh each charge, IMR SR 4756 @ 7.9 gr in new Star Line brass, 200 gr XTP's, COLA 1.250". I have several 100 XTP's, so far the gun likes the load so I don't want to change if I have enough 4756 powder to load these XTP's. The XTP's are all the same lot number. Cases are all trimed to the same length give or take .001. Bullet setting stem is locked so it isn't moving. Any ideas on what to do as my OAL keeps changing as much as .050. I have changed the bullet stems to try a different contour no help!

When you say the OAL varies as much as .050 inch, is that +/- 0.050 (OAL of 1.200 to 1.300) or a total of 0.050 inch (OAL of 1.225 to 1.275)? As you probably know the seating stem contacts the bullet on the ogive, not the end, so the OAL length will vary based on the consistentcy of the shape of the hollow point. Measure the length of a few XTPs and see how consistent the length is. How consistent can you measure OAL with calipers? Usually there is some variation in individual technique that introduces a few thousandths error in measuring, can you get repeat readings within a thousandth or so? Is there anything on the press that might prevent a full up stroke on the seating die? If the OAL length is usually longer than spec, perhaps you are not getting the bullet fully seated. Is the bullet entering the case straight and not cocked to the side? These are just a few thoughts off the top of my head....

 

[warren5421]

I measured the length of 2 dozen of the XTP's, all are within .001 of each other. Fixed a jig and measured the ogive, they are not constant, varying just enough to catch the seating die in different area of the ogive.

 

[LeverGunFan]

Maybe you could replace the seating stem with a flat plug that would seat the bullet by the nose, not the ogive. That would tighten up the OAL length variation, given that the XTPs are of uniform length.

 

[warren5421]

Changed the seating plug and started getting good constant readings. Had to mill new plug as didn't want to grind one down then need it.