accuracy change due to GC thickness?

[RU shooter]

I've been narrowing down some hunting loads for my 35 Rem. using A 200 gr saeco #351 plain base bullet with Pats plain base GC's installed . I upped the powder charge one grain for my newest load test I'm using Russian 4895(pulled 54R powder) around 36-37 gr. accuracy has been very good so far using both .004 can checks and .008 litho plate at the 36 gr load. Today I tried 37 grs and it shot great with the .004 thick can material actually the best groupings I've gotten to date with it . Three 5 rd groups were all between 1.5-2" at 100 yds using an old weaver K2.5 . Now the odd thing is the results using the .008 which all shot well before ,This time they really opened up each of the three ,5 rd. groups were 4-6"....? I was actually thinking that I would get the opposite results that the half as thick alum. can chex would fail as pressures went up or is it possible that something else is going on here. The only variable was the chex thickness between the two loadings. Any ideas?

Thanks,Tim

[runfiverun]

you might be getting some spring back to the check and it isn't as tight as you think.
the only other thing i can cone up with is it's displacing more material.
it may be a combination of the two.

[1Shirt]

Have always wondered about this, and think it deserves much more attention and revies. Would like to see a lot more postings on the subject as more people try various thicknesses with Pats checks.
1Shirt!:coffee:

[JeffinNZ]

What was the 8 thou material? I have tried deod/hairspray can material lately and it does not shoot well. Too soft I believe.

[RU shooter]

Jeff, It was litho plate material

[Bret4207]

I have seen .0015 difference in patch material make an enormous differnece in ML. No reason to think GC thickness couldn't make an equal difference. Determining just how and why...that's the tircky part.

[JeffinNZ]

Jeff, It was litho plate material

Gotcha.

I like my checks to be a few thou over diameter prior to running through the sizer. The .22's are a good .230, the .303's are .317 inch. At very minimum they should form to final sizing to file the void of groove/shank but RU, you know that already.

Strange old business.

[Larry Gibson]

I've tried .006, .008, .010, .012, .014 and .015" thicknesses of various material for GCs. My tests in .30/.31 cal cartridges conclude less than .010 thickness will result in flyers which I conjecture may be caused by the GCs coming off in flight or more likely the undersize (GC shank diameter + 2xGC thickness equals less than groove diameter of barrel) are allowing gas blowby, especially in exit from the muzzle. JeffinNZ is correct.

I make my aluminum .30/.31/.32/.35 GC out of .014 aluminum flashing now for normal velocity loads (upwards of 2000 fps). For my HV loads above 2000 fps I use brass shim of .015 thickness. The accuracy with both equals that of Hornady GCs.

Larry Gibson

[RU shooter]

Jeff and Larry, Yes I agree completely with both of you as its been my findings also on regular GC's. But the issue here is different as its a plain base bullet and a plain base GC in question. Maybe the .008 matl. is too soft ?or as another posted it displaced more material at the bullet base when sized on? I still dont know But as a plug for Pats PB chexs I'm really happy with the results .

[btroj]

Is the thicker material making it harder to size the bullet and seat the check? Is the bullet being deformed when searing the check? Is the check going on totally square?
So many factors could be causing the thicker material to give larger groups. If you are happy with the thinner materials results then stick with it.

[JeffinNZ]

Oh I see. Right. Different kettle of fish.

I would think that if you applying a check to a PB then the thinnest possible material would be best. Just think; the boolit metal has to displace somewhere and the smaller the somewhere the better.

[Larry Gibson]

Is the thicker material making it harder to size the bullet and seat the check? Is the bullet being deformed when searing the check? Is the check going on totally square?
So many factors could be causing the thicker material to give larger groups. If you are happy with the thinner materials results then stick with it.

+1 on those potential problems/variables, especially keeping the base square with the axis of the bullet.

Larry Gibson