6.5 Grendal brass observations.

[sovereign77]

I run MSR type Grendel rifles and have tested many different barrels and brass. I've seen quite a few instances of folks getting a (post resizing) ring around the base of the case head. I had a similar experience. I've confirmed that this is not case head separation, as I measure and track shoulder bump on all my rifles. You can see the bulge from the resized Lapua brass to the right and was used in the shilen barrel. I scratched my head and started down the rabbit hole. I've had experience with Saturn, Shilen, and unknown source with complete upper from Atheris Rifle. I found that the Shilen breech cut was was the most drastic of them all and provided perhaps the least case support of all of the rifle barrels. (all barrel/bolts have been go/nogo/field gauge checked upon installation. All had proper headspacing. I use a pressure trace with barrel testing and observed no differences in pressures significant enough to account for the bulging.

Lapua Bulge

Shilen breach cut inside extension. Not radius'd like majority of my other barrels.

Hornady Brass post sizing, Also shot from the Shilen barrel. Same shoulder bump no "step" or sizing ring like Lapua above.

The next thing I wanted to look at was the brass. The hornady brass case head (new brass) measured .437 diameter just above case head, whereas the Lapua fresh brass measured .440 just above the case head. When I opened up the two different cases, there was a big difference in how much additional support the hornady case heads had (likely more important for autoloaders). See the image to the right on a dimensional comparison of Lapua (0.1675) vs Hornady (0.208).

I picked up some starline brass to try as well due to shortages. So far with my radius'd barrels no shoulder like experienced with the Lapua example above. But we'll see on repeated reloads how it goes. I figured I would share my experience and diagnostics with everyone. I will post an update with further inspections and data.

Keep Shoot'n

 

[Bill K]

Now that is interesting.

 

[AM_ARixon]

You may want to measure diameter at the base of the chamber. Could be that when the chamber was cut the reamer was not run in true to bore so it would open that base diameter up. This would let the brass expand greater than CIP spec and the ring would form due to die sizing it back down.

Looking at the web thickness isnt the whole story, we have closely examined all the different brass manufacturers heads and what you will find is that the hardness and grain structure of Lapua is completely different than hornday or all other brass types. The Lapua hardness is greater and the grain structure is much tighter, providing far superior head strength.

 

[sovereign77]

After examining the Starline brass, the internal dimensions/geometry is similar to the Lapua brass. What's interesting is that

You may want to measure diameter at the base of the chamber. Could be that when the chamber was cut the reamer was not run in true to bore so it would open that base diameter up. This would let the brass expand greater than CIP spec and the ring would form due to die sizing it back down.

Looking at the web thickness isnt the whole story, we have closely examined all the different brass manufacturers heads and what you will find is that the hardness and grain structure of Lapua is completely different than hornday or all other brass types. The Lapua hardness is greater and the grain structure is much tighter, providing far superior head strength.

Thanks for the feedback. I have some pin gauges on the way to check. Fired and Sized Lapua base diameters were .443 at the ring. Max chamber diameter near case head is .4451 per SAAMI spec. I am also using Hornady dies and am curious if they are manufactured to represent "small base" type. I have reading body die and Lee collet neck sizer headed this way. I use this combo for bolt rifle and I get very little TIR. I will see if I can get a little less sizing. Just measured the chamber opening in the Shilen barrel, it is .443 +/- half thou. We'll see how the other barrels fair when the pins arrive, as I can't remove the barrels to get a caliper in there.

 

[AM_ARixon]

Great way to check using pin gauges! Good question on the hornady dies, can pin the die to get that diameter too. It may be hard to get a good feel with the barrel in place, but should provide some feedback if it is way oversized for some reason.

 

[S3silver]

That's how my Hornady brass looks like also after full length sizing.

 

[sovereign77]

After getting some pin gauges I don't really see a difference in barrel chamber cut opening diameter. I am going to repeat this process with my resizing dies (hornady compared to Redding body die). We'll see if the hornady die (current in use) is behaving like small base.

 

[msalm]

on the AR platform, it’s better to use a type I bolt vs the Type II. The type I has .010” less depth on the bolt face and the chamber is correspondingly deeper supporting more of the case. .125” vs .135+”. I measured some new Grendel bolts recently and they were closer to .140” depth. I chamber my own AR barrels so can do so, but a type II chamber could be reamed deeper and use a type I bolt (7.62x39 bolt). Also I minimize the chamfer and radius on the breech and have never seen the kind of expansion ring posted often in the net with these chambers.

 

[mac86951]

Interesting, I'm tagging in on this one.

Checking my Grendel brass just now and I'm seeing a line similar, though about half again the distance to the case head from your picture. I've a few ARs and a bolt gun for comparison, I can see how one AR would be more prevalent over another due to tolerances of bolt thickness, Barrel Extension and chamber for each unique headspace, but I wouldn't expect that much difference, unless as mentioned a Type I vs. Type II bolt. I was reading that AA used a different face depth to differentiate from 7.62x39 bolts which weren't always treated to provide the strength needed for the Grendel.

Anyway, I'm using Hornady, Lapua, Lapua(AA), and reformed 7.62 brass and other than some light markings I'm not getting a significant donut there, which makes me wonder: What brand sizing die are you using? Initially I had big troubles with brass cases stuck in the chamber for an AA barrel when using a Redding sizing die. LE Wilson case gauge showed me that I wasn't sizing enough, and a near turn and a half past "touching" was needed to get cases to fit the case gauge. Changing to a thinner shell holder, or in my case acquisition of Hornady dies resolved my problem.

-Mac

 

[Laurie]

No such issues with a Howa Mini 6.5G bolt-gun, Lapua brass and sizing with Forster standard 'BR' dies.

What I did find is that Lapua is very 'short' for my chamber to the point where a near excess headspace condition exists. So the first firing is producing a fair bit of fireforming and a risk of case-body stretch. The chamber is known to be within CIP spec tolerances (passed UK proof test).

 

[sovereign77]

After all of my research, I have come to the conclusion that my hornady dies were oversizing the brass and did not size down the case as far as another die. I use a Redding body die for my .308 rounds and picked one up for the grendel. I took the same cases and re-processed using the new die and it all but eliminated the ring at the bottom because it sized farther down. I will use the Redding die from here on out.

 

[mac86951]

After all of my research, I have come to the conclusion that my hornady dies were oversizing the brass and did not size down the case as far as another die. I use a Redding body die for my .308 rounds and picked one up for the grendel. I took the same cases and re-processed using the new die and it all but eliminated the ring at the bottom because it sized farther down. I will use the Redding die from here on out.

Thanks for posting your finding!

-Mac

 

[SG4247]

No such issues with a Howa Mini 6.5G bolt-gun, Lapua brass and sizing with Forster standard 'BR' dies.

What I did find is that Lapua is very 'short' for my chamber to the point where a near excess headspace condition exists. So the first firing is producing a fair bit of fireforming and a risk of case-body stretch. The chamber is known to be within CIP spec tolerances (passed UK proof test).

I chamber my Grendels (and variants) short for this very reason. Lapua Grendel brass can be .008” under. I haven't seen any case rings or bulges with the type 2 bolt in roughly 25-30 bbls that I have personally shot and reloaded brass for. I have Redding dies. Lapua and AA brass.

 

[Laurie]

Lapua Grendel brass can be .008” under.

Yes, that's what I've found. The condition gave some strange primer and false pressure indications on first firings in the Howa depending on powder. 8208 XBR light to modest charges fully fireformed cases and produced moderately hard extraction because of inadequate headspace, ie case-head to shoulder jammed hard in the chamber producing fairly hard bolt-lift offset by primers suggesting low pressures; Ramshot TAC only half fireformed giving easy extraction, but flattened primers suggesting high pressures or excess headspace. It was the latter examples that pointed me to examine case length / shoulder position comparing fired v new brass.

 

[Sniper338]

Ive ran the AA lapua brass for YEARS in my grendel. I have no reason to try anything else at all. I start culling brass around 15 to 16 reloads due to loose primer pockets, most go over 20 firings on each piece. Never had issues with splits, they go due to primer pockets getting too loose.

Anneal every firing.

 

[WEL]

I have not seen this issue using Lapua with a type 1 bolt in my rifle. Fyi using Hornady dies also.

 

[DLT]

My hornady brass looks just like that, huge swell at the bottom. Starline not so bad