stonehog Wrote:More testing today - different powder (SW Match Rifle) but same 123 ELD-M bullets. I did two 5-round group/es tests and lo and behold I got a ringed Starline (new) on one of the cases in the second groups. At that point, I lost trust on this barrel. I'm going to contact Odin Works and see if I can send it to them for evaluation. BTW, when the gas block was off, I measured the gas port at around .076-.080? Hard to get an accurate measurement with my old RCBS caliper. Again - I closed the gas on this barrel and slowly (? turn) opened until I got a lock on last round. I feel like the gas is controlled, and this was with the Monster bolt and H3 buffer. Fun stuff. I think I'm going to order a 16" monster barrel in the mean time...
.076 is too large for CLGS 12 6.5 Grendel suppressed.
.076 is too large for 10.3 5.56 NATO suppressed.
I think the SOCOM spec for 10.3 guns is .070/.071 since they are pretty much run suppressed all the time.
Even with my Faxon group buy barrels ported at .068, they need to be choked fully with the Bootleg carriers suppressed.
One thing I did notice was that the 12 with .068 port, unsuppressed, with Maxim PDW tiny 2.9oz buffer and short/stiffer spring, would not cycle factory 90gr TNT 100%, with the Bootleg carrier on the fully-open position (no choke).
As soon as I attached the Ultra 5 suppressor, it cycled like a raped ape with factory 90gr TNT, as if they were all designed to work optimally with each other in that configuration.
Its asking a lot to run a wide range of factory ammunition weights and powder combos, especially tiny, short bullets that need to be punted out with fast-burning powders and still have enough port pressure to reliably cycle the action, then load up 120-129gr with medium-slow powders and hit the port with anything close to that pressure and gas flow rate.
To graph it out, it would look like this:
Light, short bullets like 85gr Sierra and 90gr TNT, fast powder..............larger port, lighter buffer, moderate spring weight
Long, high SD bullets like 123gr ELD-M, 123gr SMK, 123gr Scenar, medium-slow powder.........smaller port, H or H2 buffer, standard or heavier spring
Add a suppressor and you might need to buffer and spring-up a bit even behind the 90gr TNT.
There are a lot of factors in this, as the above assumes a Mil-Std spec M16 carrier with correct 3-bore inner diameters, correct upper receiver ID and coating, gas tube seal to the block, actual Mil-Std action spring, correct bolt, etc.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
As another point of reference, my PSA Grendel upper w/ 12" SS barrel has a 0.070" gas port. I have an H2 buffer and a Superlative Arms adjustable, bleed-off capable, clamp-on gas block. It runs well at 1 turn open suppressed w/ TBAC 30 Cal Ultra 7, and 1.5 turns open unsuppressed, both with supersonic loads and conventional restrictive side of the gas block. Subsonics run well at 1.5 turns open.
I just got word back from Odin. They received my barrel/bolt and checked it out. Headspaced just fine, but said there was some wear on the back of the bolt lugs from the action with the light buffer. They also said the chamfer may have been a contributing factor. They are sending out a new barrel with a different chamfer. All in all, I'm pretty impressed with their customer service - they seemed thoughtful, and even checked out this thread. I'll let you know when it's back and I've had a chance to fire some downrange.
10-28-2022, 02:30 AM (This post was last modified: 10-28-2022, 03:04 AM by Sovereign77.)
Had the bulge problem post sizing at case web (posted with pics on accurate shooter) with stuff fired through a midway Shilen w/matched bolt. It had a different chamber feed cone that may have exacerbated the problem. Headspaced fine with gauges, but that meant the cartridge was unsupported that much more and barrel bolt combo was bad. I measured bolt face depth and it was over spec (0.138 vs 0.133-0.136) have checked every dimension since even on matched bolts and have a stable of solid Grendel bolts that I can use to get the best fit. Most bolts I have seen since have all defaulted to the 0.133 lower spec limit. Havent seen the problem since on Lapua brass.
At the time you believed it was your Hornady die oversizing the case, and once you changed to a Redding body die it was fine. Do you still think this was the cause/solution?
You mention earlier using a pressure trace to confirm pressure readings were within safe limits. How did you attach the trace to your AR? Did you drill into a receiver and barrel nut or did you attach it further down the barrel?
Out of interest how long is the barrel and gas port?
10-28-2022, 02:03 PM (This post was last modified: 10-28-2022, 05:18 PM by Sovereign77.)
Resolution is a bit lower (approximate resolution is 733 psi), as the strain gage is mounted over the bore forward of case mouth, but used factory loadings to establish max pressure limits (used Federal GM 130gr factory load as max). If I were to get it over the case body resolution would be much better. I now believe the primary root cause is the feeding cone/bolt interaction, causing excess unsupported space near case head. I do think hornady case web helps mitigate the issue, but doesnt change the OOS bolt condition. It's worth noting that the case head dimensions of virgin hornady (and found in the hornady manual) are different (.438") than other brass manufacturers. Lapua (new brass), I've found is right around .440". I find that factory loads or reloads, the case head expands initially, but in properly machined barrels is limited and springback threshold is maintained.
I havent seen the bulge since but thats because Ive used different barrels with personally matched bolts. Going to contact Shilen and discuss.
Ive wired up several barrels and have achieved similar responses. Interestingly, in my 24 brnls barrel, CFE223 started showing secondary pressure waves with 123gr bullets in cold weather only but thats a discussion for another day.
So many new MSR cartridges and barrel suppliers and unspecified feeding cone designs ..An idea is a chamber support gage, similar idea to those used in gunsmithing of 1911s to ensure any barrel feed ramp work would not lead to unsafe conditions or bulged cases thoughts? Could be used to confirm support.
Sovereign77 Wrote:Resolution is a bit lower (approximate resolution is 733 psi), as the strain gage is mounted over the bore forward of case mouth, but used factory loadings to establish max pressure limits (used Federal GM 130gr factory load as max). If I were to get it over the case body resolution would be much better. I now believe the primary root cause is the feeding cone/bolt interaction, causing excess unsupported space near case head. I do think hornady case web helps mitigate the issue, but doesnt change the OOS bolt condition. It's worth noting that the case head dimensions of virgin hornady (and found in the hornady manual) are different (.438") than other brass manufacturers. Lapua (new brass), I've found is right around .440". I find that factory loads or reloads, the case head expands initially, but in properly machined barrels is limited and springback threshold is maintained.
I havent seen the bulge since but thats because Ive used different barrels with personally matched bolts. Going to contact Shilen and discuss.
Ive wired up several barrels and have achieved similar responses. Interestingly, in my 24 brnls barrel, CFE223 started showing secondary pressure waves with 123gr bullets in cold weather only but thats a discussion for another day.
Bill A. found that changing to higher quality strain gauges eliminated the phenomenon of what appeared to be secondary pressure spikes, if I recall the discussion correctly.
Its been about 7 years or so, so maybe JASmith can pipe in on that.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
10-28-2022, 07:00 PM (This post was last modified: 10-28-2022, 09:04 PM by Sovereign77.)
LRRPF52 Wrote:Bill A. found that changing to higher quality strain gauges eliminated the phenomenon of what appeared to be secondary pressure spikes, if I recall the discussion correctly.
Its been about 7 years or so, so maybe JASmith can pipe in on that.
The gages are from Micro Measurements, if there is a better gage, I'd love to know
God didn't give us a spirit of fear but of power, love, and self-control. 2 Timothy 1:7
It also may have been a strain gage at the edge of operational performance due to less than ideal application and adhesion. Lately I've been using wax paper to make sure good pressure without getting stuck to the gage. We'll see. I will likely repeat this work in a new barrel to confirm; I'd love to see different data as CFE223 would be a great powder to play with and push velocity safely, a bit. Lots of information and debate floating around on secondary pressure spikes. Unclear if it's real, however I could turn it on and off by using different powder or temperature. Faster powders didn't create the issue observed originally. If there is in-fact a better strain gage to use which eliminates this "noise" I would love to switch to the improved unit. Thanks for sharing the knowledge.
God didn't give us a spirit of fear but of power, love, and self-control. 2 Timothy 1:7
10-31-2022, 01:04 PM (This post was last modified: 10-31-2022, 01:20 PM by Sovereign77.)
Klem Wrote:Sovereign,
Have just read your thread on the other forum.
At the time you believed it was your Hornady die oversizing the case, and once you changed to a Redding body die it was fine. Do you still think this was the cause/solution?
You mention earlier using a pressure trace to confirm pressure readings were within safe limits. How did you attach the trace to your AR? Did you drill into a receiver and barrel nut or did you attach it further down the barrel?
Out of interest how long is the barrel and gas port?
Klem
Hey Klem,
I re-examined my hornady vs redding body (which I now use) and the hornady design is highly chamfered and does leave more of the case (especially near web) untouched.
[ATTACH=CONFIG]19258[/ATTACH]
So, I'm back to sizing die is part of the problem, too. Using hornady cases, the casehead grows (which every factory cartridge case I've fired in Grendel does, in all barrels) but it starts from such a narrow case head that this chamfer is not a problem. When you have case heads that start at .440 and grow from there it's a problem, combine that with a poor chamber feed cone and deep bolt, and you have a recipe for more growth than wanted.
God didn't give us a spirit of fear but of power, love, and self-control. 2 Timothy 1:7
Im into my load development for my AR15 6mm ARC Bartlien 26 7.25 twist by Paul Craddock.
Im resizing 6.5 Grendel using L E Wilson bushing FL die. I also anneal my brass.
Here is what Ive observed.
SAAMI specs cartridge .4410 @ .200 from base and .4315 @ 1.00 from base
specs chamber .4426 @ .200 from base and .4325 @ 1.00 from base.
Hornady 108 match ammo
cartridge .4350 @ .200 from base and .4275 @ 1.00 from base.
Fired brass
cartridge .4425 @ .200 from base and .4320 @ 1.00 from base.
Resized with L E Wilson die
cartridge .4350 @ .200 from base and .4250 @ 1.00 from base
Measurements taken with Mitutoyo CD-6" ASX to the best of my ability.
Question is, is this die re-sizing the body too much? I am getting the shoulder bump I need and use Short Action headspace comparator with datum B .350 insert.
Shouldn't, ideally, resizing be the same as SAAMI cartridge spec. It seems that the difference from fired brass and resized brass of .0075 is a lot. I know ammo manufactures need to have adequate clearance for all platforms but Im looking to load for my specific rifle. My concern is over-working the body during sizing. This leaves a noticeable ring about .200" from base. I just checked my 223 to compare. It resizes the body by about .002 to 0025" with no noticeable ring.
John Whidden suggest about .002-.0025 with about .0001 spring back. I ordered a custom die from Whidden, 8 weeks to go.
12-11-2022, 11:24 PM (This post was last modified: 12-12-2022, 04:55 AM by Klem.)
Phil,
Those specs appear to be fine, and your bump is safe - but not optimum.
SAAMI permits a maximum case stretch of 0.0171" for the 6ARC. This from the deepest acceptable chamber (1.2001"), firing the shortest acceptable cartridge (1.183"). If you had such a chamber and then bumped the spent cases back to SAAMI they wouldn't last long. But after first firing, then bumping only .003-.004" for a gas gun, or even less for a bolt gun, they would be fine. Using recommended bumps as a benchmark you can adjust the bump to whatever is the most reliable in your gun, for longest case life. Whatever you end with will be close to the recommended bumps for gas and bolt guns.
In your case you are currently bumping .0075" so can improve case life by unscrewing the sizing die slightly to halve that. Given the die is slightly tapered, backing it out will also help with the axial squeeze that you are concerned about. After lessening the bump to .003" can you post a photo of what rings (if any) you are now getting.
I don't know how I missed your post earlier. Holidays got in the way?
The .0075 was the change in body diameter @ .200 from base. I was bumping the shoulder .003.
Waiting on Whidden die before I resize any more cases.
