hi folks, new member here. I have a question for the collective. I have been reloading for a couple years now and up until a couple weeks ago I haven't had any problems I couldn't find an answer to. Either in a reloading manual, in a forum, or even youtube. I recently bought a Thompson Center Venture bolt action .223 for target shooting. I put some of my ammo reloaded for my AR through it and it showed signs of over pressure. All my load data shows 25-27gn BL(C)2 for a 60 gn jacketed bullet, I am running 25.8gn. My AR loves this load. The primers were flattened and cratered in the bolt gun. The chrono showed 2934 fps avg. That is a 200 fps faster than my AR shoots these loads. I measured the fired cases to datum to get closer resize length thinking the cases were blowing back in the chamber. I reset the sizing die to press the shoulder back .003 from fired size. (It was pushing it back .011). I also measured the distance to the lands to make sure I wasn't jamming the bullet in. I now have about .001-.002 jump. The accuracy of this load is ~1 MOA @ 100 yds in this rifle. The primers are no longer flattened and I've never seen bolt face marks on the case head, but the primers are still cratered. Is it possible there's enough room around the firing pin to allow material to flow in making it appear as a craters edge? The bolt opens with the same resistance as with out a round chambered and the primers press out and in with good resistance. I am using assorted brass, Winchester SR primers. BL(C)2 powder and VMaxx 60 gn bullets. The rifle has a 22in barrel with 1:12 twist. I have pics, but can't see how to post them.

A picture is worth a thousand words.

OK, maybe I cans see how to post images. The top left was the first shot today in a clean barrel.

If you did NOT work up for that rifle, then the problem cannot be varified.
If you work up, flattening will increase as pressure rises. If the cratering also suddenly appears in the string, then it is pressure caused. If cratering occurs with start loads, as it does in my Rem 700 VSSF II in 22-250, then it's the bolt face/firing pin hole clearance.

Thanks for the reply.I feel kinda dumb now that I didn't figure that variable.I will start over with this rifle and work up from there. If it doesn't rain tomorrow I should be able to get more results to compare. Thanks again.

Apart from starting with lower charge, I would stop at the max velocity in the manual for the load - bullet / powder / case combination.

It worries me that you are using assorted cases as that is a BIG variable for pressures, velocity & accuracy.

I would separate the cases by make & weigh them in lots. Even if I was using a box of 100 cases with 5 brands, I would load them in 5 separate lots - with individually tweaked powder charges.

Your primers look ok but I am not sure of the lighting & shadows. They do not look like 200 fps over max primers & the fact that reseating primers is firm with resistance raises a bunch of questions.

I do not mean to offend you or discredit you. I am just saying the info does not add up for me - round (not flattened) primers, new primers reseat with resistance, good accuracy, no change in bolt resistance, but 200 fps above max velocity with mixed cases !!!!!????? Normal thumb rule is pressure goes up at double the rate (or more as it is exponential) to powder charge & velocity.

Finally - with such little lead / seating depth as you mentioned, I would drop the velocity / charge. I do not seat max loads closer than 0.030 from lands. With monometal bullets I seat them 0.050 off lands.

Be safe & have fun!

Sounds like you are a good student of the craft. Welcome to AR.

I agree with all previous posts, esp. Naki's about distance to the lands. Two thousandths leaves no room for error, variables.

I'm not as experienced as some others here. The indentations don't look horrible to me. That said, back down .008" +/- on seating. And yes, separate your brass. There are lots of variables there.

Where y'all from?

Welcome

By the load manual and available online load data, I am at just below half way between min and max charge (25-27gn). The data also tells me I am at the lower end of the velocity (2948-3137fps). I have tried setting the bullets back .008 from lands and the accuracy went out the window with no change in how the primers are looking. The velocity for that set was 2911fps. I am going to go back to basics and work this load up from min charge. When I worked up this load for my AR I sorted my brass by weight and head stamp. I don't know why this didn't occur to me for this rifle. Thanks folks! An outside perspective is what I needed.

quote:

Is it possible there's enough room around the firing pin to allow material to flow in making it appear as a craters edge?

Yes, its possible. Remington had a few rifles like that, by design.

I still don't see your problem. Actually, you do not have one, seems to me. Your primers will look a lot different if you really do get to high pressures; look for some pics of them. Or if they get loose, you need to back off. Until then, drive on.

I've never seen any company countersink the firing pin hole before. Looks like a Rem. Bolt.

My Weatherby Vanguard in 204 Ruger would produce primers like that until I had the gunsmith fix it. The firing pin hole was oversized.

Cratering is about the least reliable for all the reasons the above posters mentioned.

Bolt-lift (really drags). or flattened primers (yours are far from flattened) and or ejector marks are way more reliable for me....and always use a chronograph if you want to tickle maximum for your rifle otherwise you'll have no idea where you are.

Like others have said also, don't assume anything. Always work up your loads.

Also like others have said. 1 or 2 thousandths isn't far enough away from the lands for a hunting/plinking rifle. Bench Rest... maybe and I have a couple friends who allow their bolt-cam to seat the bullets into the case and into the lands but this is very VERY specialized.

10 to 50 thousandths is about the best range for most applications.... and 10 is pretty damn close to touching. I usually hover around 20 thousandths average across the board.

Zeke

The crater is caused by your bolt. It is odd to see a countersink where you'd want to have support for the primer. I reread your post, I had said that the primers weren't flattened then saw you. Hanged the sizing. I'd guess that the flattening you were seeing was from the primer hitting the bolt face then the case pressing back on to the primer. Changing the case sizing got rid of that. Have you been setting back the shoulders too far for the Thompson and the AR, or is the Thompson chamber that long?

The velocity difference could just from the difference in actions and barrels.

quote:

Originally posted by dpcd:
I still don't see your problem. Actually, you do not have one, seems to me. Your primers will look a lot different if you really do get to high pressures; look for some pics of them. Or if they get loose, you need to back off. Until then, drive on.

IMHO U got no problem with high pressure. roger

what was the supposed advantage of counter sinking the firing pin hole?

Jerry Stiller wrote a very concise article, in Precision Shooting, concerning primer cratering and/or blanking. It was some years ago.

Good reading.

Kevin

Reply from Remington to me. "The cratering you are experiencing is from a design* in the bolt face, it does not effect any thing in a negative way it is a worry to some because it makes it difficult to read your primers for reloaders. With this said Remington will replace your bolt, follow the instuctions on the web-site for sending your whole gun to us for repair" Read this online " normal on guns manufactured between 2008 and 2010."

May not be related but, did you have the cratered primers before you set the the shoulder of the cases back. Tell me again why you thought you needed to set the case shoulder back more.

I didn't want to set the shoulder back more, I wanted to set it back less so I would get less movement inside the chamber and I wasn't over working the brass. My resizing die (Lee full length resizing)was set at mfg recommended set point and cartridges cycled through my AR worked fine. My AR is chambered in 5.56, but I use .223 load data for reloading. I had time today to go out and try some worked up loads. Starting with min charge going up .2gn each set to my current charge of 25.8. I also tried moving the projectile back .015 and .020 off the rifling in each set. The cratering was still apparent in all charge rates and distance to rifling, tho the craters were slightly more pronounced with each increase in charges. The low charge gave the worst accuracy regardless of set back. I got vertical stringing in the next up charge, and horizontal stringing in the 3rd charge set. Again regardless of set back. My best group was with the 25.8gn charge and .020 distance to rifling. This group measured .585 @ 100yds

Have you tried a different primer or a magnum primer. Some (mag) have thicker cups.

This article may shed some light on cratering.
http://www.accurateshooter.com...d-pressure-analysis/

The 5.56 chamber is different than a .223 chamber. The 5.56 has a longer throat as well as a different angle on the rifling where it gets reamed out for the throat.
I don't recall the numbers right off.
This allows the 5.56 to operate at lower pressures with the same load.
Being as you have not been loading very long you might not realize that no two guns are the same. One may like one bullet over another, One can work with more powder than another.
Your rifles are not even the same chambering. So how can you expect them to both like one loading.
Any rifle, even in the same chambering should be approached as an individual. Start the load development low and work up.
Leo