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Hot load question

Namekagon

Oracle of the Hide
Full Member
Minuteman
Mar 22, 2018
823
1,618
Wausau, WI
So today I went out to confirm dope on a known load before a match next weekend. Shooting 6XC, 107 smk's over 39 gr H4350, gives me about 3,000 fps based on ballistic trajectory, and some limited chronograph work. 24" barrel, suppressed.

This is a load I've shot probably 600 rounds of in this barrel with no problems and excellent precision. I've never considered this load terribly hot. But today on the last five rounds on the longest string of fire, about 12-15 rounds at around 1 round per minute, I started noticing a bit of bolt resistance on opening and had ejector swipes on the brass. Fired about 20 total rounds today, and 3 as a zero check the day before, with no signs of pressure.

My assumption of the cause of this is, I started a new canister of powder yesterday, so I'm thinking this lot must be a touch hotter, but maybe it doesn't show up until the rifle is hot for some reason?? It didn't happen when I checked zero with 3 rounds or when I shot 5 rounds at 500. The pressure signs I was seeing weren't bad enough to make me worry about shooting the rounds today, but enough that I'd worry about what I'd get firing 10 rounds in 90 seconds on a stage.

So here is the problem...I think I need to drop my charge a touch, but I won't have an opportunity to do any more dope checking before the match. Targets will be out to 1000+. If I drop the charge by 0.1 gr, will that be enough to likely fix the pressure issue? Pretty sure I could drop a tenth and my dope wouldn't change enough to notice in a match setting.

In this situation, what's the minimum I can reduce the charge by and have confidence I made a difference in pressure?
 
It is due for a cleaning, I had considered that as a possibility. 120 rounds since last cleaning. Also thought that, with a total round count approaching 700, might have a carbon ring forming. I tend to clean with a very light touch, maybe I need to give it a good one.
 
Teslong borescopes are cheap. Will show you immediately if you have carbon.

Or push a tight patch through. If it’s tight in the throat and then eases up after a few inches, carbon.
 
So a follow-up on this, want to see what you guys think.

So I cleaned the barrel. I can't feel or see any evidence of a carbon problem. The barrel cleaned up quickly like it always does. I used Butch's Bore Shine on it, then the next day cleaned it again with Hoppe's Copper Solvent, which produced no further fouling on the patches. So, I assume barrel was clean.

After cleaning, took another 5 old hunting rounds and shot them fast to foul/heat up barrel. Then shot two groups with a different lot of H4350 and my old load of 39gr. BUT...I used three cases of my match brass for one group, and 3 newer cases for the other. I had minor ejector marks on the match brass, none on the newer cases. And I also had ejector marks on some of the hunting loads, which were loaded into match brass also. Chrony said the hunting rounds were going around 2960 fps, test match loads were right around 3000, where they have always been. With 107's, there is no way these loads should have pressure issues. Primers aren't flattened in the least.

I think the issue is not that my loads are too hot, but the brass might be the problem. The match brass has 7-8 firings on it. I mark each case with the number for every load, and it seems the 7's are showing more ejector marks more often than the 7's, but the 7's have it as well. I've been watching for signs of case head separation, but none yet. Some of the primer pockets are looser than Id like, but still functional.

So, has anyone ever had brass start to show ejector marks towards the end of its life? I thought I'd get 10 loads out of them, but now thinking I might use them for this match and then scrap them and move on to next batch.
 
Brass tends to show ejector marks at the beginning of it’s life, less so toward the end because the case head gets harder due to the repeated pounding against the breechface.

re cleaning: How do you clean? Do you use a brush? Plastic or bronze? Just because you don’t see any copper doesn’t mean it’s clean.
 
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Borescope is the only way to know how clean it is.

Patches will come out clean and the barrel can still be pretty dirty.
 
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Brass tends to show ejector marks at the beginning of it’s life, less so toward the end because the case head gets harder due to the repeated pounding against the breechface.

re cleaning: How do you clean? Do you use a brush? Plastic or bronze? Just because you don’t see any copper doesn’t mean it’s clean.

I soak patches in butch’s and soak the barrel. Then I’ll push a nylon brush through a couple times and leave it sit for 15 minutes. Then I’ll run a few patches wrapped around a .22 nylon brush through, and follow with patches on a Eyelet jag until they come clean. If I was still getting fouling on the patches, I might do more brushing with a wet brush, but this barrel has always cleaned up extremely quickly compared to my factory barrels.
 
Nylon does not clean carbon it rides on top. Get a bronze brush and run it only in one direction. It will cut through the carbon down to the metal. Also, once you’re 90% there, use sweets 762 or Barnes cr10 to get the last of the copper. It will also raise more carbon.
 
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There is always putting a no go gauge on it to make sure it doesn't close.
 
Was the new jug of powder a different lot vs the original jug?

I'm guessing the new lot is a touch hotter than the previous one.

Chrony the loads again and see how it stacks up.
 
Was the new jug of powder a different lot vs the original jug?

I'm guessing the new lot is a touch hotter than the previous one.

Chrony the loads again and see how it stacks up.

I suspected that also, so I got ahold of a different lot that was older from my old man, because he bought some at the same time as myself so It was likely a lot that I had used previously with success. Went back to the 39 gr load that was creating pressure signs, and tested/chrony-ed. Got right at 3,000 fps with 107 SMKs, which is where it always has been. But even with this, I get some light ejector marks now, where I never did before. Not enough to cause bolt lift resistance, but enough to see the mark. Not every shot marks the brass, I'd say it shows up on half of them. I even tried some slower hunting loads I have that push 105 VLD's at around 2950, and those were marking as well. I settled for a low node on that load for accuracy. Only 38.5gr H4350. This can't be too hot.

My brass is getting old, thought maybe brass is flowing into the ejector, but lacks the elasticity to spring back? Others say older brass should be less likely to mark up due to hardening.

Also, as suggested above, I re-cleaned the rifle with a bronze brush, instead of nylon. I can definitely tell that was more effective, as I did get more fouling out. I'm done with nylon i guess. I have always cleaned with a very light touch, maybe I need to get after it a little. We'll see what happens at the match I guess.

I'm a little stumped as to how pressure can be higher, but velocity be the same. And 3000 fps with a 107gr in 6XC, to me anyway, doesnt suggest pushing too hard. I had no problems in any weather for 700 rounds with this load.

Checked headspace with No-Go, the rifle is good. Checked case headspace, and setback was bigger than I expected at 0.006". I think this is becasue the die was setup on newer brass to give 0.003", and the older brass isn't springing back at all. So its more than I intended, but not unsafe, and still longer than virgin norma by .001-.002". I know .003" is more than I need, but this is mostly a field rifle that I hunt with, not a custom match rifle. I shoot 1-2 matches a year just for practice.