Grendel-like Belted Magnum Problem

[LRRPF52]

To follow up on what I was saying with Quick Load or the other internal theoretical ballistics model:

Here’s Hodgdon’s published data on the 90gr TNT on top of Benchmark, a compressed load, next to QL:

6.5 Grendel
Benchmark
2.200” COL
30.5gr compressed load
90gr TNT
47,000psi

It’s one of the lowest published chamber pressures for a max charge in 6.5 Grendel that I’m aware of. They couldn’t get anymore in the case basically even with a compressed load, at the short COL that is driven by such a short bullet.

An even lower one is this:

90gr TNT
8208XBR
31.0gr Compressed
2.220” COL
42,400psi

Enter those in and see what either of the internal engines kicks out for you.

QL shows 51,939psi for the 8208XBR load under 90gr TNT, which is 9,539psi higher than Hodgdon’s pressure test breech measured in the real world.

In GRT, it predicted:

Benchmark: 56,108 psi and 104.3% case fill. This is 9,108psi higher than Hodgdon’s real world numbers.
For 8208XBR: 52,674 psi and 103.5% case fill. This is 10,274psi higher than Hodgdon’s real world measurements.

 

[LRRPF52]

There's less capacity in a Lapua 6.5 Grendel case than a Hornady 6.5 Grendel case. It's as simple as that. All this gas block, dwell time, buffer weight, quick load supposition won't solve anything. You just can't run a Hornady brass charge weight in a Lapua case. Pure and simple. I've BTDT. And now the OP has too.

Opposite was true with regard to case capacity in all my measured samples, as well as others, but this could vary lot-to-lot. Lapua has more capacity every time I compared.

6.5 Grendel factory brass:

- Lapua 6.5 Grendel: 36.35 grain H2O
- Hornady 6.5 Grendel: 35 grain H2O

If you section the Hornady and Lapua, you’ll see that the Lapua cases are optimized for maximum capacity, and there is no way for the Hornady to increase the volume any more than that. Hornady brass has a larger radius at the web, which creates more mass to the brass/less volume.

If you take your data from Lapua brass and then try to use it in Hornady cases, you will increase pressure since volume has decreased.

We went through this study back when people were loading formed 7.62x39 brass, which has even less volume in every type I measured at least.

 

[Ledzep]

The issue is almost always from the head-web height and shape of the corner on the final draw punch on the Lapua cases. The picture of the three cases cross-section shows what's up. If you overlay them into chambers-- even properly cut ones, because at first glance a year or two ago I believed this issue to be because of excessive chamber chamfer-- there is a longer stretch of unsupported thinner web on the Lapua cases-- this is what balloons out during firing and forms the "belt".

As far as I am aware, no other mfg has this issue. Starline, Hornady, etc.. have either a larger radius, taller web-head height, and/or thicker web that holds up better, especially in AR's. You can form the same belt with other mfg brass, and even seen it in 5.56, but those instances are from excessive chamber pressure and are usually accompanied with broken parts in short order.

 

[357Max]

OP was 6 ARC formed from Lapua 6.5 Grendel.

I just measured capacity for 5 of each. Fire formed 1 x fired formed Lapua & 1 x fired factory Hornady 6 ARC.

Hornady 6 ARC

1. 34.8gr (115 dry/149.8 wet)
2. 34.9gr (115.3 dry/150.2 wet)
3. 35gr (114.9 dry/149.9 wet)
4. 34.9gr (115.1 dry/150 wet)
5. 35gr (114.7 dry/149.7 wet)
   • 34.92 avg

Lapua 6.5 formed to 6 ARC

1. 34.6gr (116.2 dry/150.8 wet)
2. 34.8gr (115.3 dry/150.1 wet)
3. 34.8gr (115.7 dry/150.5 wet)
4. 34.7gr (115.9 dry/150.6 wet)
5. 34.8gr (115.4 dry/150.2 wet)
   • 34.74 avg

@Ledzep - This is factory loaded Hornady 108 from an Odin Barrel. 6 of 50 look like the one on the left. The Rainier hasn't done this.

 

[Ledzep]

Yeah it's fairly common to get a body swell to match the chamber. I can't see it in your picture is it leaving a ridge that you can catch going from front to back?

 

[LRRPF52]

Have you actually fired the same load in Hornady and Lapua 6.5 Grendel brass?

Yes. When I loaded Hornady brass with 31.5gr CFE223 under 123gr A-MAX, it will cause non-optimal performance of the gas system, especially in 18” MLGS .076” ported rifle.

My fired cases seem to have closer capacities though, but it’s been a while since I measured all that. When I mass-produce a load, I stick to the specific case types to avoid that issue. If the load calls for Lapua brass, I’ll use that case/powder/primer/bullet/COL combo.

I have been able to interchange 31.2gr of CFE223 though between Lapua and Hornady cases, all other components the same. That’s my main go-to load. I’m not chasing x count, just shooting 1-3 MOA steel usually.

If a 10rd group cuts a ragged hole with one flier opening it to 1.2” at 100yds, I don’t really care. I typically alternate between factory ammo when it’s lower priced, and then hand-load when prices increase seasonally. I’ll probably go to all hand loads now though.

 

[357Max]

Yeah it's fairly common to get a body swell to match the chamber. I can't see it in your picture is it leaving a ridge that you can catch going from front to back?

You can't really catch it with your fingernail like a step, but can feel it and measure it. It looks like Odin does a double angle chamfer and the step appears to line up with the steeper/deeper chamfer.

 

[r.tenorio671]

OP was 6 ARC formed from Lapua 6.5 Grendel.

I just measured capacity for 5 of each. Fire formed 1 x fired formed Lapua & 1 x fired factory Hornady 6 ARC.

Hornady 6 ARC

1. 34.8gr (115 dry/149.8 wet)
2. 34.9gr (115.3 dry/150.2 wet)
3. 35gr (114.9 dry/149.9 wet)
4. 34.9gr (115.1 dry/150 wet)
5. 35gr (114.7 dry/149.7 wet)
   • 34.92 avg

Lapua 6.5 formed to 6 ARC

1. 34.6gr (116.2 dry/150.8 wet)
2. 34.8gr (115.3 dry/150.1 wet)
3. 34.8gr (115.7 dry/150.5 wet)
4. 34.7gr (115.9 dry/150.6 wet)
5. 34.8gr (115.4 dry/150.2 wet)
   • 34.74 avg

@Ledzep - This is factory loaded Hornady 108 from an Odin Barrel. 6 of 50 look like the one on the left. The Rainier hasn't done this.
View attachment 7832558

....after the reports of folks issues experienced with the ODIN +2 gas system tubes, wondering it more of these "belted" related reports are going to start showing up as more folks get out & shoot more entering into the spring & summer days...

....postings referring to the amount of chamber "chamfer" and resultant case support is logical, especially when combined with a high charge weight.

 

[LRRPF52]

I shoot 30.3gr of TAC in a 6.5 Grendel bolt gun in Hornady brass. Lapua will not tolerate that. I have to drop it to 29gr.

You are the only person that maintains Lapua brass has more case capacity than Hornady.

Example 1

Example 2

Example 3

Example 4 in Hornady’s favor by .1gr

I noticed that once they were fire-formed, they were so close as not to matter.

The batch of brass I measured at least 10 years ago had less H2O capacity than my Lapua brass had before fire-forming. I haven’t owned any unfired Hornady brass for a long time now, so it could be due to that.

To undermine my own measurements, the Accurate Shooter article is from 2012, so there’s that, but it was .1gr in favor of the Hornady brass.

That’s why I said I was going off the top of my head, but I wasn’t alone in my measurements. This seems to be more of a lot-to-lot thing, though Lapua has been consistent.

I started with Lapua brass pre-plastic blue cases, when they were still in glossy cardstock boxes, as well as with several boxes of AA Factory ammo that was AA head-stamped (by Lapua for AA) before they went to Hornady.

 

[LRRPF52]

You can't really catch it with your fingernail like a step, but can feel it and measure it. It looks like Odin does a double angle chamfer and the step appears to line up with the steeper/deeper chamfer.
View attachment 7832976

This makes me pull up Bill’s post from Page 1:

Statically, the breach has to be machined correctly. The case must remain supported to a point behind the start of the case web, seen as where the case walls begin to thicken into the case head proper. This was achieved by reducing the 120 feed cone diameter on the barrel which was in turn made possible as the round would lift higher on the feed ramps.

 

[Ledzep]

It's not an internal volume thing, it's unsupported side-wall. Unfortunately I've misplaced or deleted my drawings that had the Lapua and Hornady cross sectioned brass in a SAAMI chamber in an AR-15, but the Lapua case relies too heavily on the hoop strength of unsupported side wall in an AR-15 with the .136" bolt face. The design on the Hornady and Starline cases has web material further forward and shortens or eliminates the "bridge" between web and supported side wall. It really just depends on how the chamfer/radius interacts with the given case. If it's tight, Lapua users often get away with it, but if it's on the loose end of still being "correct", the Lapua cases will form the belt. It's not excessive pressure, it's marginal sidewall support.

Again, you can get the same results (belted case) even with 5.56 but those DO require excessive pressure, but the way the webs lay out on pretty much everything else eliminates or drastically reduces the chances of it happening.

There's nothing necessarily inherently "wrong" with the Lapua case design-- it just doesn't mesh well with the AR-15 chamber and the .136" deep bolt face on the Grendel bolt.

 

[jb313]

Just a quick thought, dont laugh

After firing cases a few times and then running them through a full size die, i was worried about the constant stretching and weakening of the brass, like maybe pushing the shoulder back too far and then it expanding when fired,
I devised this simple tool, run it down the case wall inside, if you feel a ridge near the base its possible you are starting to get case head separation,

 

[LRRPF52]

It's not an internal volume thing, it's unsupported side-wall. Unfortunately I've misplaced or deleted my drawings that had the Lapua and Hornady cross sectioned brass in a SAAMI chamber in an AR-15, but the Lapua case relies too heavily on the hoop strength of unsupported side wall in an AR-15 with the .136" bolt face. The design on the Hornady and Starline cases has web material further forward and shortens or eliminates the "bridge" between web and supported side wall. It really just depends on how the chamfer/radius interacts with the given case. If it's tight, Lapua users often get away with it, but if it's on the loose end of still being "correct", the Lapua cases will form the belt. It's not excessive pressure, it's marginal sidewall support.

Again, you can get the same results (belted case) even with 5.56 but those DO require excessive pressure, but the way the webs lay out on pretty much everything else eliminates or drastically reduces the chances of it happening.

There's nothing necessarily inherently "wrong" with the Lapua case design-- it just doesn't mesh well with the AR-15 chamber and the .136" deep bolt face on the Grendel bolt.

I’ll mention again that I think it has more to do with gas system length and port diameter than anything else.

You can push higher charge weights with a 20” RLGS in Grendel than you can with a 28” RLGS. The 28” RLGS was notorious for causing the belted cases with hand loads, not because they aren’t supported in the chamber, but due to residual plug dwell pressure during extraction.

Same with suppressors.

With 6mm and .224” Grendel variants, reducing the bore volume only makes this worse, so the port should be moved as far forward as possible to allow port pressure and mass-flow to be regulated into the happy window of the cyclic rate operation, not near the edge.

Also, if the feed cone is cut too deep, that will make the problem show up or appear when it shouldn’t.

Going down to a different bore diameter basically creates a different rifle from an engineering perspective, and trying to use the proven staple datum for certain critical locations of things like gas ports doesn’t transfer over automatically.

 

[357Max]

This makes me pull up Bill’s post from Page 1:

Yeah I'm pretty disapointed with the big chamfer on the Odin.

I'm going to need a bigger lathe to start rolling my own.

As for gas system length, I don't think I'll have any issue with a + 2 RL on a 22" Edit: Gas port on this is .086
This Rainier has a fairly modest radius chamfer, so should be good there as well.

You should check current brass if you're going to opine on a current problem. Look at the OPs situation. Same load works fine in Hornady brass but blows the unsupported web out in Lapua brass. The only solution is to run a lower charge. Pretty simple.

Lapua is avg .18 gr less capacity than Hornady.
I'll be shooting both brass options this coming weekend with the same charge weights and see how they compare. Hope to not trash any Lapua brass, but I need to look for upper end loads. Will update this thread.

I'd really like to see north of 2775 for the 100 gr TGK @.515 G1. They don't touch lands til 2.333 so I'm hoping I can find something under 2.290 that will shoot. Anyone have a suggestion for TGK jump window?

 

[Ledzep]

But it's both isn't it. If you get belts, your only option is to back the charge weight down or get a new barrel. I've gotten them using Hornady brass in 22 Grendel when I was exploring top end charges. They came with ejector swipe and torn rims. Just like the OPs

You can back charge weight (pressure) down until it doesn't happen anymore, but my suspicion is that in most situations with Lapua cases, that resulting chamber pressure will be significantly below 52,000psi SAAMI MAP. That's anecdotally from me judging the MV from people who've had the issue and loosely relating MV to peak pressure-- which without any test equipment might as well be a Picasso painting... so take it for what it's worth.

I'd wager your 22 Grendel was running at higher pressure than a lot of the folks who are having belted Lapua issues. And the guys that pull this belted shit off with 5.56 are hitting the high scores for chamber pressure.

 

[bill alexander]

The Grendel chamber geometry and bolt was designed in concert with the Lapua case. The chamber "if" correctly dimensioned and with the correct feed cone geometry will allow chamber pressures well in excess of 68k psi without the case deforming. Obviously this is for Proof loadings only and should NOT be used as the basis of any load development. It will damage the rifle! The absolute maximum is 51,800 psi and MAOP pressures are held around 50k psi. Pushing loads to 52kpsi allows zero envelope for pressure excursions, which will and do happen even with the most carefully assembled loads.

Stretching of the case above the web results from either an incorrectly machined barrel or excess residual bore pressure as the case is extracted. I do not have direct experience of the 6mm ARC but simple expansion ratio calculations indicate the timing will need attention. This is not just the size and position of the gas port in the barrel but also the reciprocating mass which includes the impulse from the fire control group.

Regardless, the 6mm ARC is an exceptionally well designed cartridge with an excellent balance between case volume and primer flash volume, which is something that is frequently missed. It benefits from some excellent powders and projectiles.

 

[r.tenorio671]

The Grendel chamber geometry and bolt was designed in concert with the Lapua case. The chamber "if" correctly dimensioned and with the correct feed cone geometry will allow chamber pressures well in excess of 68k psi without the case deforming. Obviously this is for Proof loadings only and should NOT be used as the basis of any load development. It will damage the rifle! The absolute maximum is 51,800 psi and MAOP pressures are held around 50k psi. Pushing loads to 52kpsi allows zero envelope for pressure excursions, which will and do happen even with the most carefully assembled loads.

Stretching of the case above the web results from either an incorrectly machined barrel or excess residual bore pressure as the case is extracted. I do not have direct experience of the 6mm ARC but simple expansion ratio calculations indicate the timing will need attention. This is not just the size and position of the gas port in the barrel but also the reciprocating mass which includes the impulse from the fire control group.

Regardless, the 6mm ARC is an exceptionally well designed cartridge with an excellent balance between case volume and primer flash volume, which is something that is frequently missed. It benefits from some excellent powders and projectiles.

...some REALLY good info being passed on here, Thank You Mr. Alexander!

 

[357Max]

but also the reciprocating mass which includes the impulse from the fire control group.

Bill - I'd be great if you could expound on this a little farther.

I'm curious if something like the Hiperfire with it's toggle system would delay bolt movement sim to a heavier buffer.
Those springs hold the hammer forward with more force than a std FC.

 

[TonyTheTiger]

I'm curious if something like the Hiperfire with it's toggle system would delay bolt movement sim to a heavier buffer.
Those springs hold the hammer forward with more force than a std FC.

I wondered the exact same thing when I read his post.

 

[r.tenorio671]

I wondered the exact same thing when I read his post.

....I would think that Hiperfire engineered the spring rate to avoid inducing too much "drag" on the bolt carrier's motion that potentially could adversely affect overall reliability or decrease the triggers design objective of improved trigger pull weight and resultant increased rates of fire. In my minds eye, the amount of resistance it provides to the BCG's initial movement would be negligible and counter-intuitive to it's deign objective. IMHO, a "heavier (std M4)" BCG, heavier buffer and higher spring rated buffer spring, individually or in combination, would be the proper areas to address delaying bolt unlock timing if gas adjustment wasn't available or possible.

 

[357Max]

IMHO, a "heavier (std M4)" BCG, heavier buffer and higher spring rated buffer spring, individually or in combination, would be the proper areas to address delaying bolt unlock timing if gas adjustment wasn't available or possible.

The above part I agree with, assuming you have an appropriate length gas system to start with.

Everything else is mostly wrong. The easiest way to explain the Hiperfire toggle system would be to think in terms of a compound bow.
Here is a quote from Hiperfire that captures the concept.

"When the hammer is manually cocked, one can feel that the initial force
required to start cocking is very high. As the hammer lies down, or as the toggle
springs go over-center, that force drops off dramatically. This new feeling is like
drawing a compound archery bow."

The above = the initial force to move the BCG is very high & hence my question.

If you care to more fully understand what that toggle system does then read these first White Paper. The second is on their sear geometry which doesn't apply to this thread, but enlightening.

https://www.hiperfire.com/hprtch/01_HIPERTECH_Cam-Over_Toggle_Engine.pdf

https://www.hiperfire.com/hprtch/02_HIPERTECH_Radical_Sear_Mechanics.pdf

Mr Alexander mentioned the impulse from the fire control group & that is the first time I've seen that mentioned as a consideration with regards to bolt unlock timing. It makes complete sense though. Not night and day changes but it is a piece of the whole pie.

I've got 1 Hiperfire in a 16" mid gas with a non adj gas block (223W). It started life ejecting @ 1:00. With a std full mass carrier, Vltor A5 spring/buffer, & the Hiperfire it is now ejecting @ 3:00 and eaten everything I've tried feeding it. It's like Mikey.

 

[357Max]

I need to append my earlier post now that I have more info. The picture I posted showing what looks like the start of a belt on the factory ammo out of the Odin barrel. It's not what it appears. All of the Hornady brass I have here are below Saami @ the .200 line. The cases that measure .438 resulted in the step/belted appearance. The cases that measure .439 have no step. Cant say for sure that's what caused it, but seems likely.
Saami is .441 @ .200 line.

Lapua Grendel brass are all consitantly .4406 +-.0002

So what looks like a belt is actually backwards. The supported section of case expanded to the chamber. The unsupported section shows no permanent expansion at all? This has me scratching my head. It must just spring back in the unsupported area

Hornady brass matches Hornady FL sizer dies.
Lapua brass matches LE Wilson FL sizer die.

In the below pictures: Left brass is Hornady that showed the step next to a formed Lapua. Both are once fired & both sized with the LE Wilson FL die.
Same shoulder bump for both (.003). You can see how far down the sizer reaches on the Lapua. Hornady is still .003 under sammi & smaller than the die @ the lower portion. You can still feel the step.

Hornady below the step/unsupported area & at the step resized area.

Lapua below the step/unsupported area & at the step resized area.

 

[bill alexander]

I must apologize for the delayed response. Work, is at times, most inconvenient.

To reply to the question regarding the impulse from the fire control group. To be clear this has little to do with the springs which add only a minor preload. The main input is from the moment of inertia of the hammer itself which is simply the force required to accelerate the mass of the hammer around it's axle. It is possible to take advantage of this by increasing the weight of the hammer or moving the center of gravity of the hammer away from the pivot.

As always there is no free lunch and using this approach will cause a more pronounced jump in the rifle as the firing pin is impacted, which is detrimental to accuracy, as is the long lock time.

 

[357Max]

Update to post #57

Measured capacity for 5 of each. Fire formed 1 x fired formed Lapua & 1 x fired factory Hornady 6 ARC.

Hornady 6 ARC

1. 34.8gr (115 dry/149.8 wet)
2. 34.9gr (115.3 dry/150.2 wet)
3. 35gr (114.9 dry/149.9 wet)
4. 34.9gr (115.1 dry/150 wet)
5. 35gr (114.7 dry/149.7 wet)
   • 34.92 avg

Lapua 6.5 formed to 6 ARC

1. 34.6gr (116.2 dry/150.8 wet)
2. 34.8gr (115.3 dry/150.1 wet)
3. 34.8gr (115.7 dry/150.5 wet)
4. 34.7gr (115.9 dry/150.6 wet)
5. 34.8gr (115.4 dry/150.2 wet)
   • 34.74 avg

So Lapua has .18 gr less capacity than Hornady.

I've got some interesting data comparing Lapua to Hornady & it's not what I expected.

Sorry @Ledzep - I'm not burning down all my supplies for statistically significant data, but I think this trend is relevant.

Loaded a ladder as follows to test for pressure with Lever and the Sierra 100gr TGK

All rounds loaded to 2.280 coal. All loaded in once fired brass, annealed, LE Wilson FL bushing sized, .2405 mandrel, CCI #41 primer, & Lever.

29.3 x 3 Lapua = 2729avg Hornady = 2733avg
29.6 x 3 Lapua = 2748 Hornady = 2760
29.9 x 3 Lapua = 2779 Hornady = 2784
30.2 x 3 Lapua = 2831 Hornady = 2835

Seems a little strange that the Lapua shot a little slower considering it's got less capacity?
There are 2 other differences besides capacity.

• Lapua has a larger loaded neck diameter @ .2705 vs Hornady @ .2685
• Lapua has a smaller flash hole.

I'm thinking it might be the small flash hole that's knocking a few fps off the Lapua????

On another note. The hottest loads still did not blow the base of the Hornady brass out to saami. It still measures small at the .200 line.
I think I still have a little head room with the Lever.
So far I'm happy with 2830 on the TGK's & 2730 with the Berger 109's All primers felt good coming out.

Here's brass from the hottest loads.

PVA 100gr Seneca's loaded with 30.3 Lever @ 2.410 & single loaded. These jokers have such a long BT they would fly well backwards (they might have been). I'm betting the BT is enough to screw with internal combustion. Hell they're 60fps slower than the TGK's with .1 more gr Lever.

This was the only load that Lapua had a slight speed edge of 3 fps

30.3 x 3 Lapua = 2773 avg Hornady = 2770 avg

I'd love to hear some thoughts on how the hell these unstable PVA's aren't throwing a shotgun pattern??

The larger necks on the Lapua rained supreme with these unstable PVA's. The Hornady x 3 PVA made 1 round hole & 2 triangles for a 1.8" group

That's 3 from the Lapua brass on the right. about .375" & I posted a pic of another Lapua PVA 1 triangle group up thread.
Berger 109's on left @ 2700 & 2.290 coal.

 

[Aaron.From.Winchester]

@357Max So you don’t believe the issue was caused by the Odin barrel? I have everything but the barrel for my 6mm ARC build and was gonna go with an Odin. But not if it’s belting the cases.

 

[357Max]

@357Max So you don’t believe the issue was caused by the Odin barrel? I have everything but the barrel for my 6mm ARC build and was gonna go with an Odin. But not if it’s belting the cases.

The belt is not what it first appeared in my case. I’m blaming that on the Hornady Brass that’s -.003 smaller than Saami at the .200 line. At first I thought it was the Odin barrel since the Rainier didn’t do it. After measuring all my fired cases from each barrel evidence points to case size.

The Odin does have a deeper chamfer then the Rainier, but unless you push pressures well past 52k I doubt you’d see any problems.

I’d bet the upper charge wt of my last load pushed a little past 52k and it didn’t even blow the Hornady bases out to Saami. FL sizer still doesn’t touch the bottom 1/4” of case.

If you go with Odin I’d get the 21”. It was easy to get reliable function with the +2 gas. It also comes with the better adj gas block. The gas tube it comes with is offset & should be straight. I straightened mine.

 

[MidsouthHunter]

Reviving this thread as I’m having issues. @357Max got me here.

I’m seeing this issue once attempting to re-size my brass. Out of 50 cases, 22 had formed a belt and were unusable as posted below

Measured the inside of my Hornady match bushing die, .440. I haven’t had this issue until recently. I’m interested in the timing issue mentioned above. My pressures are fine (105BTHP, 29.7 LVR, CBTO 1.698”, COAL 2.200” — basically rebuilt factory BLACK ammo)

20” proof RLGS +1”
JP bolt
OSS Helix 7.62
Have tried both Armaspec SRS H and standard rifle buffer/spring

I am getting short stroke (2 every 10) and bad ejection (530-6). Was issuing adjustable gas block but switch to standard.

Basically how will I be able to slow my unlocking down while getting proper ejection/chambering?

 

[hlee]

Reviving this thread as I’m having issues. @357Max got me here.

I’m seeing this issue once attempting to re-size my brass. Out of 50 cases, 22 had formed a belt and were unusable as posted below View attachment 7860054

Measured the inside of my Hornady match bushing die, .440. I haven’t had this issue until recently. I’m interested in the timing issue mentioned above. My pressures are fine (105BTHP, 29.7 LVR, CBTO 1.698”, COAL 2.200” — basically rebuilt factory BLACK ammo)

20” proof RLGS +1”
JP bolt
OSS Helix 7.62
Have tried both Armaspec SRS H and standard rifle buffer/spring

I am getting short stroke (2 every 10) and bad ejection (530-6). Was issuing adjustable gas block but switch to standard.

Basically how will I be able to slow my unlocking down while getting proper ejection/chambering?

Are you seeing a “belt,” or a ring from the die on the case at the extremes of what it can size? Have you tried to find a thin spot from the inside of the case (bent paper clip test). Or, have you cut a case open to inspect that area? Your photo is a bit blurry on my phone, however, I see a ‘ring’ but not the belt as posted previously. This may sound semantic, but I’ve seen a ring in sized brass that was not the result of excessive case stretch; merely the ‘normal’ function of a sizing die. No thinning of the brass observed from sectioning a case.

 

[Evintos]

I am getting short stroke (2 every 10) and bad ejection (530-6). Was issuing adjustable gas block but switch to standard.

Basically how will I be able to slow my unlocking down while getting proper ejection/chambering?

If you're basically stuck between mass selections (H2 = short stroke, H1 slightly over gassed, with optimal gassing somewhere in between) and you don't want to use an adjustable gas block, the tuning option left available would be increase spring strength rate and/or customize a buffer utilizing a combo of tungsten and aluminum pucks (in this case, it should be 2 tungsten and 1 aluminum puck to get in between H1 and H2 weights).

 

[MidsouthHunter]

Are you seeing a “belt,” or a ring from the die on the case at the extremes of what it can size? Have you tried to find a thin spot from the inside of the case (bent paper clip test). Or, have you cut a case open to inspect that area? Your photo is a bit blurry on my phone, however, I see a ‘ring’ but not the belt as posted previously. This may sound semantic, but I’ve seen a ring in sized brass that was not the result of excessive case stretch; merely the ‘normal’ function of a sizing die. No thinning of the brass observed from sectioning a case.

Okay more like a ring. I’m currently in the midst of a test. 4 cases of 1x factory ammo and 4 cases of 2x reloads. So far, no rings from the sizing operation.

 

[MidsouthHunter]

If you're basically stuck between mass selections (H2 = short stroke, H1 slightly over gassed, with optimal gassing somewhere in between) and you don't want to use an adjustable gas block, the tuning option left available would be increase spring strength rate and/or customize a buffer utilizing a combo of tungsten and aluminum pucks (in this case, it should be 2 tungsten and 1 aluminum puck to get in between H1 and H2 weights).

Next, from sized cases aforementioned, buffer spring test. I feel with the RLGS +1” from proof, I should be okay with standard GB and just adjusting buffer weight/spring. My 22” Shaw which had a RLGS benefitted from the ADJGB

 

[MidsouthHunter]

Okay more like a ring. I’m currently in the midst of a test. 4 cases of 1x factory ammo and 4 cases of 2x reloads. So far, no rings from the sizing operation.

Previous sized with “ring”

Recently sized 2x fired with no ring.

 

[MidsouthHunter]

Okay so testing complete. I think a solution has been found FOR MY SCENARIO. This may not work for you but hey, information is the power to problem solving.

Scroll to the end for the answer, I’ll post for SA the whole “test”

1x fired Hornady factory brass (4ct)
2x fired competition load (2ct)

I had been having issues with a brass “ring” during the sizing operation. Used a Hornady custom die and even worse with Hornady match grade bushing die.

1.189” fired to the shoulder
1.187” sized to the shoulder

This was prevalent in almost 50% of cases in my match grade dies after I got a case stuck in my custom die because I used the wrong shell holder. (Dumb)

So I was looking and I don’t think my press was giving me the results that I wanted. I was using my fathers hand down Lyman from most likely the 80s, which I have used for 25 years. Everytime I cammed over, the turret portion have just the slightest play.

My shell holder would not make contact with my sizing die. This doesn’t necessarily explain the excess amount/tolerance in the case above the case head, but I’ll get to why I think it was different now.

So I purchased a Hornady Lock and Load single press from Academy and tried again. All my same reloading process minus the press change. So I loaded up 6 rounds and set to test fire

1 STUMP WAS HARMED IN THIS TEST. IF YOU HAVE A THING AGAINST SHOOTING STUMPS, PLEASE CONTACT YOUR LOCAL ARBORIST.

I used a charge master 1500 with 29.7 grs LVR, Hornady 105BTHP, CCI41, Hornady 6ARC BRASS (1x fired and 2x fired), COAL 2.200, CBTO 1.700. .268 neck tension.

MOST IMPORTANT: shoulder bump was normally from 1.187” down to 1.185.5-xx86. The stiffness from the press allowed me more shoulder bump and also more consistent. In my opinion, this lead to better lock from the bolt.

Set up out of a 20” PROOF RLGS+1”, JP bolt, Armaspec H1 SRS, standard GB, OSS 7.62 can.

MagnetoSpeed v3 chrony.

Cycle was flawless, not a single double feed, short stroke, or other malfunction. Ejection pattern was perfect as well, 3-4 O’clock.

Chrono graph numbers tightened up from yesterdays range session. The barrel is still under 100 rounds but these are promising

So now the real test for the original issue of brass rings on resized cases was to be tested. The ejection and feeding seemed to be fixed, at least for now.

Slight marks on brass but nothing alarming.
Lost 1 of the 2x fired pieces.
Got the kids looking now to earn some ice cream.

So same cleaning and hit with some imperial sizing wax case lube and ran through the press. Now this is 2x fired and 3x fired.

perfect. No issues at all. Brass sized clean and shoulder bump was just as consistent as before. So the answer?

I say the press. It’s rigidity allowed better and more consistent sizing. Which once fired, was more consistent going in and coming out. Leading to more reliable feeding and re-sizing once fired.

I got it, gas guns are inherently difficult. They either run flawless with everything or can be a picky bitch. More moving pieces, parts, gas, blah blah blah. I love my gasser in 6ARC. It’s a whole mess of fun to shoot. I would recommend it to anybody.

learning was going on and this post is hopefully to help others. Find a problem, fix it, spread the word. In my Shaw, with my Lyman press I was unable to get brass to bump enough to chamber because it was cut a little tight. (After about 30 it loosened up and no issue). I had play in my shell holder and actually placed 2x pieces of scotch tape on the case head to make it tighter in the shell holder to get it sized. Not ideal but hey it worked. But for this problem, Mine was a simple change of press.

 

[Constructor]

If you aren't sure if it's a timing/port size problem or a pressure problem or difference in brass thickness or case capacity shut the gas off and shoot it. If you get the same bulge you know it's not timing or port size. I ruptured a 6mmAR/Grendel case in 2007 using Lapua brass, IME the Lapua is thinner, at least down near the web.

 

[KnightOfNee]

Don't fire anymore, check your headspace with a go and no go gauge, that brass bulge looks scary, same thing with all the extra dirty burnt powder on the brass.