6CM clickers

BBob

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That measurement can only be accurately take with a ball mic, at exactly .2" above the case head, so it's a little harder to diagnose based on dimensions and specs.
People conflating case head measurements and measurements at the .200” line, two different things with two different purposes. You need a blade mic for measuring the case head (just above extractor groove) but not the .200” line (but you could use one here if you wanted to). Measuring the case head is a hit or miss proposition to attempt to judge pressure/over-pressure. Measuring at the .200” line is used as an attempt to decipher brass, chamber, size die fit.
 
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solarshooter

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I have pretty new Mitutoyo 8" calipers with certs, they seem to be very accurate and repeatable, but don't capture the 4th digit beyond 0.0005" increments. I was measuring with the calipers parallel with the central axis of the case, such that I grab the widest point, and it seemed very repeatable. I was mostly checking for major red flags of 0.001-0.003" order variations. But maybe it's much more sensitive than that? And like I said, I was not able to measure the dimension at the 0.200" line precisely, I'd like to hear some techniques for doing that if anyone has one.
 
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I loaded up 10ea at 40.0gr and 41.0gr and shot them yesterday with the Lab Radar running. Avg MV may have increased a bit since the first test (45 shots ago), but considering the initial test was only 3 shots, I don't think it's a statistically significant delta. I got maybe 3/10 clickers at 40.0, and 2/10 at 41.0. The 43.0 load may have been exacerbating this issue, but considering that I was still getting clickers at nearly 2gr below book max I don't think that fully explains it. I will say, I didn't have any extreme stuck bolt issues that required smacking open like I did at 43.0.

Measuring the fired brass, I see base diameters from 0.470" to 0.471". There is no correlation between base diameter and clickers. However, when I was measuring the bases, I noticed that some cases showed wear marks from the resizing die going much lower on the case than others. So it could be that the height of the max diameter is significantly different case to case just depending on what chamber it was initially fired in, rather than the overall max diameter itself. I was not able to directly correlate this to the clickers I experienced in test either.

150 pieces of new ADG 6CM are on the way thanks to @762 ULTRAMAGA, so I'll test with those at 40.0gr to start and see if that cures the issue.

Repeating myself.
when you consider said data is usually based on hornady brass with 6%+ more h20 capacity than the brass you’re using. Meaning 40.0 would probably be about max if they would have used the same brass as you. Really you’re closer to 3 grains over max.
Not saying powder charge is the sole problem but you are still referencing book max (with hornady brass) as if it's applicable to ADG/Gunwerks brass and it isn't. 40.0 grains is about 4% less than 41.7 book max listed in a couple locations and last i calc'd it ADG brass is about 6% less capacity than Hornady. I'd venture to guess your "Almost 2 grains under max" is close to the same or maybe higher pressure than was used to select a book max with Hornady brass.

This is standard language from ADG for many of their cartridges:
ADG manufactured brass is optimized not only for consistency in performance, but also for durability. One of the ways we accomplished this is by optimizing the material in specific areas to strengthen it. With the optimized material geometry, our brass will generally have a different case volume than most other manufacturer’s brass and therefore will require a different charge weight to achieve the same pressures and velocities. We recommend using a reputable load data source and working up from their recommended minimum starting loads.

We recommend reducing any existing charge weights by 10% and re-developing your specific load when replacing any component in a load recipe with a new component (brass, projectile, primer, or powder type). Failure to reduce charge weights established using other manufacturers brass may result in higher pressures and velocities while using ADG brass and may result in unsafe pressure levels.
 
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solarshooter

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Repeating myself.

Not saying powder charge is the sole problem but you are still referencing book max (with hornady brass) as if it's applicable to ADG/Gunwerks brass and it isn't. 40.0 grains is about 4% less than 41.7 book max listed in a couple locations and last i calc'd it ADG brass is about 6% less capacity than Hornady. I'd venture to guess your "Almost 2 grains under max" is close to the same or maybe higher pressure than was used to select a book max with Hornady brass.

This is standard language from ADG for many of their cartridges:
I see I see. I can try even lower and see if that resolves it.

I have experience with ADG brass in other cartridges and I haven't encountered this before, maybe the effect is just bigger on 6CM in particular. In fact, with many different makes of brass and cartridges, I've pretty much universally found that any published book maxes are below where I begin to encounter pressure signs via testing.

At this point, pending a major barrel speedup, I'd probably want to switch to a slower powder if 40.0 is still too hot. Maybe H4831SC or something like that. There's a lot of room in the case with 40.0 and it's barely over 2700fps. I've seen much higher MV numbers almost universally in searching the internet for this cartridge/bullet/barrel combo. It starts to really hurt the wind number of the gun, like make it a 5mph vs 7mph gun, which is why I care.
 

Harvey_NW

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I have pretty new Mitutoyo 8" calipers with certs, they seem to be very accurate and repeatable, but don't capture the 4th digit beyond 0.0005" increments. I was measuring with the calipers parallel with the central axis of the case, such that I grab the widest point, and it seemed very repeatable. I was mostly checking for major red flags of 0.001-0.003" order variations. But maybe it's much more sensitive than that? And like I said, I was not able to measure the dimension at the 0.200" line precisely, I'd like to hear some techniques for doing that if anyone has one.
A precise .2" spacer, or whatever offset needed for the contact points of the measuring tool to be at .2". I was just noting this measurement because it can help diagnose an issue, like if your sizing die is sizing it down far enough for proper clearance, or if the tail end of your chamber is under spec from something like a worn reamer, which I've personally experienced. But it has to be taken with the proper tools and at the spec'd locations, or it could be wrong. Like when people measure headspace with comparator inserts that have a tiny chamfer on the inside of the mouth, that changes the contact point a couple thou. But sometimes (like in my case) even with calipers a fired case was .002" under SAAMI min spec as close as I could get on the .2" line, so the issue was obvious.
 
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People conflating case head measurements and measurements at the .200” line, two different things with two different purposes. You need a blade mic for measuring the case head (just above extractor groove) but not the .200” line
Just file a touch off either side of the rim if you only have a standard mic, it won’t affect function of the cases
 

Lawnboi

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I didn’t see it mentioned but is it possible you have a .236 bore? That would also do it.


The easy way to see if it’s a you problem or a barrel problem is to spend a few bucks on some Hornady match and see what it does.

Book max is going to be ~3000 fps for a 24”. Subtract 25 an inch and that’s what I would plan on reasonably after speed up.

To give you an idea, my current load in this last 6 creed im shooting alpha brass, 105 hybrid with 39.5 of h4350. That load is coming out at 2950, after speeding up from 2800 on the first 20 shots.
 
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solarshooter

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I didn’t see it mentioned but is it possible you have a .236 bore? That would also do it.


The easy way to see if it’s a you problem or a barrel problem is to spend a few bucks on some Hornady match and see what it does.

Book max is going to be ~3000 fps for a 24”. Subtract 25 an inch and that’s what I would plan on reasonably after speed up.

To give you an idea, my current load in this last 6 creed im shooting alpha brass, 105 hybrid with 39.5 of h4350. That load is coming out at 2950, after speeding up from 2800 on the first 20 shots.
Someone did mention the narrow bore, but I'm not sure how to measure that precisely (ball gauge maybe?), nor what I would do with that information (I'm still going to try and optimize the load for the barrel). It's a Bartlein that I bought off Bugholes, no mention of bore diameter one way or another. I also don't quite see what the box ammo would do to illuminate the issue, since I wouldn't know what the equivalent powder charge is...

I just received the 150pcs of new adg, so I'll start even lower, say 38.0, and check if that combo solves the clickers. If so, I'll load the lot and go practice until it's all fireformed, which would put me at 215rds down the tube. Hopefully whatever speedup that might happen has happened by that point, and then I'll start over with a pressure test and maybe switching powders to try and optimize it.

If that doesn't solve the clicker issue, I'd say the first two possible causes on the original list have been eliminated (load too hot, once fired brass). At that point I'll be getting back in touch with UM to see what their advice is as far as dies or messing with the chamber.
 

Lawnboi

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Probably not a tight bore from bartlein if you didn’t order it that way specifically.

H4831sc can definetly be a little easier going but I havnt had issues with h4350 either.

Factory ammo would just confirm that everything is normal, if you got stiff bolt or clickers with factory ammo, or velocity was outrageously different from what’s expected it could quickly tell you something is off without burning expensive brass. Usually in a 6 creed even if I’m going to I’ll run a box of factory through it just to confirm function before loading expensive brass.

Let us know how the new brass goes.
 

eoperator

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Like wind gypsy said I think you are over pressure. My 6cm maxes out at 38.5g h4350/108eh with peterson brass, nosler data lists 39.5g as max.
N555 would likely get another 100fps.
 
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Like wind gypsy said I think you are over pressure. My 6cm maxes out at 38.5g h4350/108eh with peterson brass, nosler data lists 39.5g as max.
N555 would likely get another 100fps.
Which brings up another point - if @solar shooter wants to squeeze the most velocity out of his short barrel, he’d probably be well served to use brass with more capacity. I think 243/260 cases get something like an 8% capacity increase when ackley improved? 223AI is 7-8% over standard 223? That should be a fair illustration that a 6% difference between different head stamps makes a difference.
 
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Terrapin

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Brass shot in an over size chamber, then full length resized & shot in a standard chamber can cause clickers. (I’ve seen this with range pickup AR10 brass)

A rough chamber can cause clickers as the brass expands into grooves and chatter marks then breaks loose during primary extraction.

Incorrect timing on the bolt can also cause clickers by starting primary extraction too late in the cycle. Seen this on “blueprinted” rem 700 actions.

Usually it’s caused by me trying to get just a little bit more velocity out of a gun. Some barrels are just slow.


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I have experience with ADG brass in other cartridges and I haven't encountered this before, maybe the effect is just bigger on 6CM in particular. In fact, with many different makes of brass and cartridges, I've pretty much universally found that any published book maxes are below where I begin to encounter pressure signs via testing.

It definitely varies by cartridge. I found in 6.5 and 7 SAUM i was pretty dang close to norma and R-P capacities with ADG. Enough that I got the same velocities with 0.5 grain or less variance in charges of H1000 and that's a small overall % change when you're talking charges in the 60+ grains vs 40 grains. Smaller the cartridge, smaller the variance has to be to be noticeable.
 
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solarshooter

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Great useful input from everyone, thank you all. Considering I just bought even more ADG, I'm not planning to switch brass, but again, there's a lot of room in the case, so that tells me I should be running a slower powder if I'm hitting pressure at 40 or below. I'll back it way off for the next test, maybe down to 36 or something, to make sure I have some headroom.
 

bpctcb

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This is your answer. Send the barrel back and have UM open up the back end. Easy peasy. I can do it in 15 minutes. If they won't do it find someone that will.
How do you open up the back end in 15 minutes?
Do you have a custom reamer or ???

BP
 
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It literally only takes a few seconds once you have the barrel off to use a bit of 600 grit paper wrapped around a dowel . You’re only doing the back 3/8 inch of the chamber and only taking a couple thousand of an inch off of it.
Edited to add that this is done in a lathe
 

BBob

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How do you open up the back end in 15 minutes?
Do you have a custom reamer or ???

BP
As said above. Barrel in the lathe. Split dowel with sand paper. I use multiple pin gauges to quickly check for size as I’m doing it. No dinking with gages and micrometers that way. I will final check with a gage and mic. In the case of a PRC with a SAAMI chamber I’d run a reamer in with a larger back end. I’d choose this method because I have a PRC reamer witha larger back end in hand. The reamer solution can also be done without removing the barrel with the reamer run through the action with a T-Handle extension.
 

SouthPaw

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The reamer solution can also be done without removing the barrel with the reamer run through the action with a T-Handle extension.
Random question as I don't know much about gunsmithing/chambering: can a freebore reamer be used through the action without removing the barrel? Curious if extending freebore is an involved activity or simple.
 

Carl Ross

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Random question as I don't know much about gunsmithing/chambering: can a freebore reamer be used through the action without removing the barrel? Curious if extending freebore is an involved activity or simple.

Not a 'smith, but I wouldn't want anyone cutting a throat on a rifle of mine without dialing in the barrel to be concentric to the bore. Seems way easier to do so with the action off. If I already have a gun otherwise disassembled pulling the action off the barrel takes maybe 2 minutes.

The rear end of the chamber is different.
 
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