Bullet Seating Depth

[frittsk]

Update - Loaded up some ammo at 2.285 COAL. This put me at about 0.020" jump-to-lands. Unfortunately, this did not improve my patterns much. I also worked up 5 loads shooting a 120 gr Nosler BT and CFE 223 with an average velocity of 2401 fps. Loads ranged from 30.0gr of powder to 32.0gr. All loads shot similar groups (around 2" at 100 yds) with velocities ranging from 2401 fps to 2565 fps. I bought my upper assembly from SSK. It is a production grade 20" barrel with a 1:8 twist. I am beginning to think that I am doing the best I can with this barrel. I have a 223 with a 20" Shilen match grade barrel that I consistently shoot groups less that 1 inch.

What do you all think? Is it the barrel or do I need to experiment with other powders and bullets?

[Blute308]

Buy a box of factory Hornady 123gr ammo and fire four five shot groups.

If you are still getting 2" groups and you have checked all the other possibilities (loose scope mount, etc.) give JD Jones (SSk Industries) a call. He is proud of his stuff (Read expensive) so I'm betting he will make it right.

[LRRPF52]

I would pull the barrel and check to see if your receiver face is true before shooting anything else.

Use a receiver lapping tool to check it.

[Blute308]

If you had built the upper yourself I would agree with the advice stated above (Pull the barrel and check the receiver).

However, you stated you bought a complete upper from SSK. Once you start taking things apart, any warrantee or obligation on the manufacturers part usually becomes void. If it is defective, you need to give them the opportunity to make it right.

If it's a barrel problem, you can't correct the issue yourself. If it's a receiver problem, you shouldn't have to correct the issue yourself. You paid good money for your upper, make them give you a good product.

Good Luck

[frittsk]

I have shot several boxes of Hornady A Max rounds and they don't group as well as my loads.

I did e-mail JD and he put it on the barrel being a production barrel and not a match grade barrel. He did seem interested and wants to hear back from me once I have tried a couple more loads.

[frittsk]

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!

[rabiddawg]

Are you sure you scope is in good shape? I ask because I have had to send a few of mine back to the factory for a "tune up".

It can be very frustrating trying to dial in a load with a scope that is all over the place.

[frittsk]

Well, I can't be sure. I bought a new Nikon P223 4-12 and installed it on this rifle. Good thought! I can take the P223 off my 223 that I know is shooting straight and give it a try.

[frittsk]

Rabiddawg,

I tried the scope idea. After shooting my 223 and having a couple groups at .5" and the widest just under an inch, I switched the scope to the Grendel and shot a 2.5" group. Scope works fine. This is frustrating because of the $$$ I have in this rifle and reading all the posts about how accurate this caliber is (why I chose a Grendel), mine isn't what I expected. I just wish I knew where to start. I'm thinking I need a different barrel, but not sure. I've notice something else that I am not sure is related or if it is even an issue. After firing a few rounds there are brass deposits on the bolt face. Anybody have a comment on this?

[IMG][/IMG]

[frittsk]

Here is a better photo:

[IMG][/IMG]

[LRRPF52]

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?

[frittsk]

Bolt face depth is 0.139. I haven't done any research on bolt face depth. What should it be? Are there some threads that would cover this?

[LRRPF52]

The dimensions that AA uses is .136" -.003" allowable, not any deeper than .136". What method did you use to measure your depth?

I use the slide from my calipers as a protrusion gauge. Some machinists could chime in with a better method, but this is what I have available, and gives me readings that make sense on both Grendel and 5.56 bolts:

[frittsk]

LRRPF52,

That is exactly how I measured mine. Do you think that extra 0.003" could be causing any issues>

[LRRPF52]

Take several measurements to confirm what your bolt face depth is. Excessive head space can stretch the case around the web to the point that you get case head separation, and my friend's factory Remington 700 .300 Win Mag has crazy excessive head space. No matter what load you use, the primers look like hats, they are so flat.

If SSK chambered your barrel with that bolt, it might be fine for the combination.

[WildBill3/75]

LRRPF52---that is also how I measured my bolt.

[2ndAmendment]

I have since adjusted my C.O.A.L and am currently about 0.017" of my lands (my initial cartridge was 0.065" and still produced sub MOA groups). I used the el cheapo method to determine COAL and came up with 2.242" using the 120gn Nosler Ballistic Tip. This length made me pretty happy since my magazine maxed out at 2.300". I seated a bullet in a sized case starting at 2.242" and chambered it. It got stuck in the lands and required a little help to remove. I continued to seat the bullet deeper in 0.005" +/- increments until it chambered and ejected easily. I then colored the bullet with a marker and chambered/ejected then inspected. I found slight markings around the circumference of the bullet. The cartridge seemed to chamber/eject fine but I felt like I needed a reference. So I grabbed a Hornady 123 AMAX factory load, colored the bullet and ran it through the action. Don't worry, the muzzle was pointed in a safe direction the entire time and I obeyed all safe gun handling rules. Upon ejection I noted similar markings on the factory bullet. At this point I'm feeling confident with this seating depth and plan on working up a load using the 8208. I'm open to suggestions/comments/concerns/criticism so let it rip.

Marty

[NugginFutz]

I have since adjusted my C.O.A.L and am currently about 0.017" of my lands (my initial cartridge was 0.065" and still produced sub MOA groups). I used the el cheapo method to determine COAL and came up with 2.242" using the 120gn Nosler Ballistic Tip. This length made me pretty happy since my magazine maxed out at 2.300". I seated a bullet in a sized case starting at 2.242" and chambered it. It got stuck in the lands and required a little help to remove. I continued to seat the bullet deeper in 0.005" +/- increments until it chambered and ejected easily. I then colored the bullet with a marker and chambered/ejected then inspected. I found slight markings around the circumference of the bullet. The cartridge seemed to chamber/eject fine but I felt like I needed a reference. So I grabbed a Hornady 123 AMAX factory load, colored the bullet and ran it through the action. Don't worry, the muzzle was pointed in a safe direction the entire time and I obeyed all safe gun handling rules. Upon ejection I noted similar markings on the factory bullet. At this point I'm feeling confident with this seating depth and plan on working up a load using the 8208. I'm open to suggestions/comments/concerns/criticism so let it rip.

Marty

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...

[2ndAmendment]

Thanks for the tip!

[customcutter]

Remember to set your caliper base on a flat surface and reset the zero. Zero may not be in the fully closed position, when using it as a depth gauge.

dmsims21 posted that observation in the Welcome Forum a couple of days ago.