New AR 6.5 Grendel Problems

[John from MD]

Headspace comparators are great tools for those looking to build the most precise ammunition.

 

[gungate]

Here is a video of the chamber. No obvious issues that I can see.

 

[DavidA]

That's a case gauge, not a headspace comparator.

New Starline Grendel brass is sized at the factory but it can have dings/etc, especially in the neck, from shipping/handling since it left the factory. I usual run it through my full length sizing die which is set to move the shoulder of fired cases back a few thousandths (.003"). It doesn't do any shoulder bumping on new brass, but it does straighten out the necks.

When you chambered rounds made with new brass, it is likely that the force of chambering was enough to overcome whatever was causing it to hang up in the case gauge.

The unsized/not adequately sized previously fired reload looks looks like it is near the SAAMI max chamber headspace dimension. So that's roughly what your chamber dimension is, except your chamber is slightly less because when the bolt on a semiauto unlocks there is still some pressure in the chamber, so the brass is expanded slightly longer than the chamber. Thus the need to "bump the shoulder back" at least a few thousandths for a semiauto to cycle reliably.

When you resized in accordance with the die setup instructions, you ended up near the SAAMI minimum.

So if you don't use a headspace comparator to set up your sizing die, your brass will get stretched from about SAAMI min to about SAAMI max (i.e. about 10 thousandths) every cycle. With a headspace comparator you can set it up so you are only moving the shoulder back a few thousandths from it's fired dimension every cycle. This can help extend brass life. However, these rounds may not chamber in someone else's rifle that has a shorter chamber.

Below is a picture of a headspace comparator. It is used with your calipers to make comparison measurements between fired and unfired brass headspace. Because the point where the comparator inset touches the shoulder is likely NOT exactly where official headspace is measured for a given cartridge, the actual numbers are meaningless except as a comparison. Popular headspace comparator kits are made by Hornady and Sinclair. Each kit has inserts that cover most bottleneck cartridges that are typically reloaded.
View attachment 442614

You can use a next size up standard comparator and it will give you a decent reading that can be used as well. Basically measuring the distance at a given part of the shoulder.

I can tell you one thing though , for me at least virgin new , or fired brass I always resize. That way brass is always pretty dam consistent, both shoulder and the case overall length. Plus as pointed out new brass can have dinged necks.

I Don’t think I have ever trimmed new brass but I always check.


Sent from my iPhone using Tapatalk

 

[gungate]

Wow just today I got an email back from my initial question about this issue. BCA simply sent me an RMA. No discussion, no advice, no questions, just an RMA to return it. I am really disappointed in their (lack of) customer service.

 

[KRC]

I responded to your barrel post before I read this thread.

Small base die (as per erwos post #27), combined with a set of Redding Competition Shellholders to set proper shoulder length, (as per Growler215 post #40 <nice post!).