Bullet Seating Depth

[frittsk]

I took multiple measurements in different locations on the bolt face and it is 0.136". I must have been in a hurry yesterday. I did pull my barrel and the extension is extremely loose in the receiver. The end of the barrel will move a total of 3/16"+ back and forth and up and down. Everything I've read indicates that I should bed the extension. I thought I would true the receiver while I have it apart, but Brownells' lapping tool is on backorder. Maybe after I get these things done, my groups will tighten up even though I have a very deep chamber. Wish me luck!

[frittsk]

Extractor lip is probably sharp, and could use some fine tuning. The small deposits of brass are usually from a sharp extractor. A sharp ejector can do it too, so I always like to radius that part.

If you just have a production barrel with no real accuracy potential better than what you're getting, then you need a better barrel. Lilja has drop-in Grendel barrels now as a normal option.

What's your bolt face depth BTW?

LRRPF52,

I have radiused the ejector and the extractor does look a little sharp to me. How would you recommend that I smooth it out?

[LRRPF52]

Just carefully take take the sharp corners off with a fine file, or even a cotton buffing wheel with polishing compound. Don't go hog wild, just lightly take off those sharp edges, and you will be in better shape as far as treatment of your case rims goes.

If you look at the extractor geometry, and understand how it is basically a claw that pulls the case out by the rim, as long as you don't compromise it's ability to firmly grasp the rim, it will be GTG.

Here's a great article on related AR15 tunings: http://bulletin.accurateshooter.com/tag/ar15/

[frittsk]

Thanks again LRRPF52! Great article! I've seen this one before and this is what I followed to bevel the ejector. I will do a little work on the extractor next. It does leave a small scratch on the side of the rim and I'm sure its a little too sharp. I love this stuff. Almost as much fun working on the rifle as shooting it. As I mentioned before, I'm probably knowledgeable enough to be dangerous, but if you don't try, you don't learn.

[warthog]

Marty - If you feel compelled to put a live round in the chamber for such a test, it is a simple matter to remove the firing pin from the bolt. Makes a ND / AD a statistical impossibility. Just for future reference...

In removing your bolt for chamber testing, do all the other components remain in the bolt other than the firing pin?

[45r]

Taking the firing pin out can bind things up and make it hard to get your BCG out.

[JASmith]

Just curious if anyone can enlighten me on why the seating depth on this rifle would be so deep. I have done more measuring and it is difficult to come up with consistently accurate measurements. But at oal of 2.285 I am still close the .030" from the lands give or take a few thousandths. Seems like there must be an issue with the barrel extension. Just looking for some advise from those who are more familiar with this than I am.

Thanks!

Is your chamber a SAAMI Grendel chamber or the .264 LBC? In the current context, the important difference is the throat configuration. The LBC will allow some short-nosed bullets to be seated at magazine length without jamming the lands.

The same is true of longer nosed bullets like the AMAX & SST. These, however, won't touch the throat until they seated out further than normal. The added jump is one possible explanation for the accuracy challenge you describe. Other explanations, many of which have already been posed in this thread could also account for the challenge.

LRRPF52 mentioned shooting positions and styles.

The comment raises the question: "How does your accuracy with the Grendel compare to the other rifles you shoot?"

[frittsk]

JASMITH,

The rifle came from SSK and they tell me they use a SAAMI spec cutter. I have noticed a difference in the seating depth between bullets. I had been using 120gr Nosler BT. I had also measured depth with 123 gr Hornady SST and it was about the same as the Noslers. I just picked up some 120gr Hornady Amax and they get me quite a bit closer to the lands. I haven't had a chance to shoot them yet, but hope that helps. The one thing that gave me the most improvement in accuracy so far has been bedding the barrel. As far as my other rifles, I consistently shoot between 1/2" and 3/4" groups with my 223. It does have a Shilen match grade barrel and I would expect it to be a little more accurate. I will keep at it and hopefully tighten things up some more. Thanks for the thoughts.

[JASmith]

You are welcome!

Your experience with the .223 suggests that shooting skills are not an issue (unless the kick from a .243 Winchester bothers you! -- LOL !! --).

Have you tried swapping scopes? I once got better accuracy with a .270 Winchester using open -- not peep -- sights (1.5" 3-shot group at 100 yards) than with a 9-power scope (4 to 6 inch groups). That and the zero being different every time i went to the range suggested a scope swap was in order.

Once that is ruled out, then the troubleshooting outlined earlier can proceed with greater confidence.

PS I doubt the barrel extension is the source of your ability to seat the bullets way out there. The cartridge must headspace on the shoulder of the chamber. It is the distance between that point and where the throat constricts enough to engage the bullet that sets your allowable COL.

[frittsk]

JASMITH,

I did switch out the scope from my 223 with no improvement. I think I am getting closer and am anxious to shoot the A-Max rounds. After I bedded the barrel I actually shot one 1/2" group, but most groups were a little over an inch, which isn't bad considering the grade of my barrel. I think I'm going to be able to save it.