300 BLK primers cratering :(

[Sgt_Jamez]

I had my first range day with my newly assembled 300 BLK rifle and I saw primer craters on both of the loads I tested.

Rifle Info:
New CMMG 16" bbl on an Aeroprecision Upper/Lower
Standard Spring
Spikes Heavy Buffer (ST-T2?)
SI Defense BCG
Timney Trigger
UBR stock

Loads derived from QL:
Winchester .223 Brass, run through Forster die w internals removed to form shoulder, chopped, chamfered, full-length sized, trimmed to 1.365"

Hornady 150gr FMJ-BT
2.065" OAL (based on advice for ogive to clear PMag rib)
W296 Charge Range 14.8gr-16.6gr (based on a 10% redux of max calculated by QL)

I don't have the load info in front of my for the Hornady 110gr round nose but I saw the same cratering on even the lowest charge. The velocity was a tad higher than QL predicted but only by about 50fps.

What could be causing this high pressure? Would a new, rough chamber be gripping the brass too much or maybe for too long?

Is my QL load data somehow way off? For the 150gr load, predicted velocity is 1984fps. My measured velocity was something like 2030fps.

I didnt see any case head marks. Just cratering. The case sides did show marks that I am assuming were imprinted from the chamber walls.

Thoughts? I'd hate to have to back off from the low end charge just get the pressure down. Thanks Hiders!!

14.9gr W296 - QL Predicted 1797fps, Chrono'd at 1856fps

15.5gr W296

16.6gr W296

 

[The Mechanic]

Re: 300 BLK primers cratering

Can you get a pic up? I really don't think it is a rough chamber. Since you say you have QL you may want to get the case volume on a fired case. It is easy to do. Tumble the brass real clean with the primer still in place, weigh the case empty and then very carefully fill the case with water and reweigh. The difference is your water weight and just punch that number into QL and you may find the pressure problem or maybe just a matter of a soft primer, oversized FP hole, or maybe even a powder problem.

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

I used either CCI400s or BR4s. I will do the case volume check and try to get a pic up maybe tonight. What powder problem would you mean?

Do you use Magnum primers for this application?

 

[The Mechanic]

Re: 300 BLK primers cratering

I do not shoot this round but when I saw your data I thought you may have been shooting suppressed. Also it was my understanding the recommended powder was H110 or Vit N110

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

Mech - I don't have a supressor and H110 is very near to W296. Never used N110. But QL gave me a charge for W296 which I reduced by 10% to get my starting charge.

 

[The Mechanic]

Re: 300 BLK primers cratering

I found the load data thread on it. You may want to repost on that thread. Still like to see a couple of pic's
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2085833

 

[former naval person]

Re: 300 BLK primers cratering

I'd bet that the cases as formed before firing are just a bit short in headspacing. That will give you the same case/primer read as excess pressure. Try the same load in the now fire formed cases (take care not to bump the shoulder back too much...easy to do with such a minimal shoulder. This is where a headspace gauge will be most helpful. JMHO

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

Pics added.

Is there a chamber gage available for the 300 BLK?

I have a set of shoulder bump gages but I am not near my reloading stuff now. Will the .308 collar from the Hornady set work?

 

[The Mechanic]

Re: 300 BLK primers cratering

IMHO they don't look that bad. Seems a little bit of flow into the firing pin hole but the primer is not "that" flat. Here is a good pic of what some should look like. Copied from web site. Best pics I could search up.
http://www.larrywillis.com/pressure_signs.html

1. Very mild load (this is too mild).
2. Mild load.
3. This is an ideal load (could go just a bit hotter).
4. Absolute Maximum load (approach this pressure very carefully).

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

So you'd consider these safe loads?

 

[The Mechanic]

Re: 300 BLK primers cratering

I am going to go out on a limb and say yes. Get some additional opinions from some of the guys that are shooting them but I think it looks good.
See how the corners of the primer has a nice rounded edge? Usually you will get a little more flattening that will give it a more square edge.

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

Ok thanks for the advice!

 

[bricktop]

Re: 300 BLK primers cratering

Since the primers are round at the edge, it kind of just looks like your bolt face firing pin hole is too big. I've seen that before. Take your bolt out and with the firing pin in the "fired" position, take a picture.

 

[tansinator]

Re: 300 BLK primers cratering

Send to Gre-tan to get a bushing for the firing pin hole. Or you could just shoot it as is. My 223 ackley looks just like that.

Eddie

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

So here's a closeup of the boltface with firing pin extended.

Good to go still?

 

[bricktop]

Re: 300 BLK primers cratering

Hmmm, that looks good (I've seen much worse). Is that with the CCI 400s? If you aren't already, I'd use ones with a thicker cup. Not so much an issue with large rifle ones, but small rifle primers can have thin primer cups. It might not be too long till you pierce one, and start welding your bolt face.

http://www.jamescalhoon.com/primers_and_pressure.php

 

[Sgt_Jamez]

Re: 300 BLK primers cratering

I've used both CCI 400s and BR4s and have had the craters.

Anyone using CCI 450s with the BLK? Seems to make sense with the use of W296 ball powder.

Also, I am thinking to bump the shoulders less. My plan is to back the die out a bit until a sized case is too long to chamber. Then work the die in until a case just fits. My question then is once I have the "just chambers" shoulder length, I assume I need to go a tad shorter still right? 2 thou? 3?

 

[The Mechanic]

Re: 300 BLK primers cratering

Maybe give these a try.
http://www.cci-ammunition.com/products/primers/primers.aspx?id=30

 

[Austan]

Re: 300 BLK primers cratering

The first primers I used in load testing for the 300blk were wolf srm's. They showed no pressure signs with all my testing (test for speed and bringing the load down to subsonic). The last batch I loaded with cci 400's and they have cratering just like yours. Not from pressure but softness of the primers. You could try wolfs or the mil type that Mechanic posted, or just use what you've been using. Doesn't look to be too much pressure.

 

[wphoto]

Re: 300 BLK primers cratering

In our testing yesterday, we also found the CCI400's to be a bit soft for the supersonic loads in this caliber.

Our focus yesterday was on the Hornady 110 Vmax's with H110 loads. We used once fired Twin Cities (late 60's era) brass formed with Dillon 1200b and CH4d trim die on a 1050. All below test loads were dispensed with a Chargemaster and seated with the Forster 300BLK seater. 2.088 COAL.

18.5gr of H110 showed average velocities of 2041 with CCI400 and 2069 with Rem 7 1/2's

19.0gr of H110 showed average velocities of 2083 with CCI400 and 2125 with Rem 7 1/2's

At this load we decided that the CCI400's were showing increased signs of pressure and chose to continue the increased load testing with the Rem 7 1/2's only.

19.5gr: Av. 2141
20.0gr: Av. 2174
20.6gr: Av. 2201
21.1gr: Av. 2233
21.6gr: Av. 2272 Here the Rem 7 1/2's looked the same as the CCI400 did at 19gr.

20.1gr: was the sweet spot with this setup with an Av. 2181

Testing rig:
Noveske 8" SS Barrel
H2 Buffer with std. carbine spring
Scar-H SD Suppressor.


We will try some CCI450's in the near future.

 

[Austan]

Re: 300 BLK primers cratering

I settled on a load and tried both today for grins (and to see what the POI shift is between them).

CCI 400's on the left (5 rows wide on bottom)and Wolf SRM's on the right (2 rows on bottom). You can see the cratering with the CCI 400's and none with the harder Wolf primer.