Sizing brass for a black rifle (6.5 Grendel)?

[crimsoncomet]

Here I am again asking sizing questions. Thanks to all who helped me set my FL sizing dies up to bump the shoulders on the bolt action brass .001" to .002". Now I am on to sizing 6.5 grendel brass. I have about 200 pieces of Lapua brass thats needs to be sized and trimmed. I am using a redding type S FL die with no expander.

First off, I will say that I have had issues with this rifle since I have had it. Many of the loads I have tried working up in it (except some anemic varget loads) has shown ejector swipes. Some of them have shown ejector swipes and sooty necks. The ones that I have worked up safely, are tack drivers in the LW barrel. I have tried many powders and bullets. I believe it was over gassing with the long 24" barrel prematurely opening the bolt. So, I put the rifle in the gun safe until I was ready to tackle it again. Months later, I now I have a stiffer buffer spring and an adjustable gas block to tame the gas down. Anyone ever experienced over-gassing?

Here is what I need help with. I want to start testing again with the fired brass instead of diving into the rest of my new brass. I fired some lighter loads through the gun after the gas block install to check function. No sooty necks and no high pressure. I then used my hornady comparator to measure the length of the case from the base to the shoulder. What I am seeing is that the shoulder is being pushed forward .015". Is this normal in a gas rifle? I tried bumping the shoulder, .001" to .002" and check for chamber fit. No go, could barely get the bolt back open. I then started bumping the shoulder back more on several cases. I had one bumped back .001", .002", .003" and .005". The first two of course gave me hell getting the bolt back open. The .003" wasn't as bad but still stuck hard. The .005" fit good, and I felt a bit of stick when pulling the bolt back. I decided to stick with this. I feel like I am excessively sizing this brass. Do you guys normally see the shoulder pushed further forward on a gas rifle? Is this due to the bolt opening? If you all have any suggestions for sizing these high dollar cases, I would greatly appreciate it.

Thanks to everyone who has the patience to read through this.

 

[243winxb]

What I am seeing is that the shoulder is being pushed forward .015". Is this normal in a gas rifle?

Depends, are you starting with new factory sized brass that may be way undersize?

 

[crimsoncomet]

I am using new factory brass. But why do I have to push the shoulder back .005" to chamber?

 

[243winxb]

Some (M1 Garand) gas guns open a little to soon. The brass stretches more, becoming longer than the chamber. Test by turning off the gas if you can, then take measurement. Or just push the shoulder back on the fired brass by .005" , your good as long as it fits the chamber. Watch for case seperations.

 

[243winxb]

I am using a redding type S FL die with no expander.

The bushing may not size all the way to the shoulder/'neck junction. Some do, some dont. This will cause some drag on chambering after maybe 3 firings. But should never be a problem, as i have seen shoulders set back by .001" when the bolt slams closed on a long case.

 

[crimsoncomet]

Thanks 243. Ill size the brass back then. Maybe I'll just do a few to start load development. The bushing seems to be sizing the neck all the way back. I know the LW barrels chamber neck is .005" smaller than normal, so that could make it tight.

 

[243winxb]

I know the LW barrels chamber neck is .005" smaller than normal, so that could make it tight.

Make sure the loaded rounds neck diameter is not to large. There has to be clearence between the neck & chamber to let the brass expand to free the bullet on firing. As i am sure you know.

 

[Slamfire]

The .005" fit good, and I felt a bit of stick when pulling the bolt back.

The 6.5 Grendel has a very abrupt shoulder.

I have had issues trusting the measurements with my comparator and 7.5 Swiss brass, which also has an abrupt shoulder.

I tend to trust measurements made in a Wilson type cartridge headspace gage more than these comparators. The shoulder is being measured on a cut surface, at the correct angle, whereas where the conic section where the comparators touch is not calibrated to anything.

I would not push the shoulder back anymore than .005” from the fired location. Cases are only meant to stretch .006" (for most) once.

I wonder if there is a mismatch between the die internal shape and the chamber. You should not be experiencing an interference fit between a fully sized case and your chamber.

 

[longdayjake]

I own a grendel and I can say that it does require quite a bit of shoulder bump to get it to chamber. What you are experiencing is normal.

 

[crimsoncomet]

Longday and Slamfire, thanks for the advice. Slamfire I measures using my comparator and a Wilson case gauge. They both show the same thing. Te Hornady comparator shows that I am bumping the shoulder .005" and the wilson shows a .004" bump. .001" is within the accuracy of the calipers. Thanks for the advice though.

I did a test today. I loaded one round in a new case and fired it with the gas turned all the way off. New brass measures 3.198" to the shoulder.
Gas block closed measures 3.201"
Gas block opened measures 3.205"
So that make sense, since I am bumping the should .005" to get the round to chamber.

So it is stretching a bit more with the bolt opening. I'll just size it down and try to adjust the gas block down.

BTW 243. The chamber neck should be .295". My loaded round measures .2901"

 

[popper]

3.198" for 6.5 Grendel? The case isn't that long.

 

[crimsoncomet]

Sorry. I didn't subtract the comparator length.