Shrinkage difference between PA66 GF50 & PA66 GF30

This is an interesting question, because the lineal mold shrinkage is characteristic percent shrinkage of a plastic between melt processing and the final cooled article. Specifying materials of low shrinkage will make it easier to avoid problems of warpage and to increase dimensional precision of injection moldings. Mineral or glass filled plastics have lower shrinkage and are often specified to reduce molding problems.

Also it depends on several factors.

1. You can work with the same mold, but you need to consider what happening with the cavity surface, due to a great friction inside if try a 50% of G.F., your mold must be have a surface treatments, or special finishing protection, also some time is better use special oil.
2. If the sink marks is continuously you can try to improve some special test runs into the injection molding machine process, I recommend you try with 3-4 different profiles at the second pressure in order to led the flow front advance and fill the cavities more properly.
3. The data of the material that you are using is around of: Linear mold shrink for PA66+30GF 0.2-0.6%
   Melt temperature 428-579 °F
   Mold temp. 104-140°F
   Linear mold shrink for PA66+50GF 0.09-0.11%
   Melt temperature 455-590 °F
   Mold temp. 104-140°F
   

Well at this point maybe is better to invite at your material representative or require the complete process data to run most properly, if you want to run some trial there is no problem, also verify the tonnage of your press in order to compare the weight of you parts, maybe if you try to test the next press it will be better, don’t forget, write a notes and compare pressure, weights, temperature and make measurements in some special diameters or bosses in order to evaluate your sink marks tuning.

So you need to take care also of the weather humidity and try to simulate first, and have a good test, maybe later you can share us which test or procedure was better to improve your shrinkage.

Assuming using the same mold to mold part individually with material PA66 GF50 and PA66 GF30, meaning runner/gate/cooling systems are kept same, the part's finished dimensions are still dependent on part design and process conditions. However, it's not suggested to obtain qualified dimensions by adjusting process conditions. The most direct way is (1) using the optimized process conditions of each material to mold the part individually, (2) Inspecting/recording all dimensions of part made by each material then compare them to dimension specifications one by one, and (3.1) designing exchangeable core/cavity components of mold so that they are assembled to handle significant dimension change caused by different shrinkage of PA66 50GF and PA30GF, and get all dimensions qualified. Or (3.2) If lucky enough, all finished dimensions might still be in spec and accepted without consistency concern. Then it's not necessary to design any exchangeable core/cavity component of mold.