Diagnose my heavy bolt lift

[-Time-]

So I went to shoot my 300wm over the weekend, I had 20 rounds left from a previous loading, and loaded up the last 11 from my batch of 3x fires brass. I shot all 31 rounds over the weekend, and 9 of the rounds fired had heavy bolt lifts, and clear ejector marks.

I’m running 77gr H1000, under a 225gr ELD-M, in Norma brass, .030 off the lands. Loaded with FL Redding dies, and a chargemaster 1500, same way I’ve been doing it since I first got the rifle. Its an R700 LR in an AICS 2.0 chassis.

What could’ve caused 8 random rounds to be higher pressure? Was the RCBS just throwing off? Can carbon rings cause random higher presssure rousnds? The barrel has 322 rounds though it. I’ve measured basically every case dimension imaginable between the over and non over pressure rounds, and they spec the same. I’m truly stumped on this one. Do I need to just load up some more and see if maybe it was just me off somehow?

 

[davere]

Had you just cleaned the rifle?

 

[MtnCreek]

Test fit a bullet into the fired cases to see if they slide in freely.

FWIW, 77gr H1000/Norma/225gr sounds stout.

 

[TXBear]

What was the temp the last time you shot? The temp this time? I agree w/ MtnCreek, that load is rather on the stout end of the measure and a bit of temp difference could have been enough to push it over the pressure limits.

 

[-Time-]

Had you just cleaned the rifle?

I had not, I cleaned before I shot it, and run a bore snake through the barrel once after a range trip

Test fit a bullet into the fired cases to see if they slide in freely.

FWIW, 77gr H1000/Norma/225gr sounds stout.

The over pressure cases do seem a little more snug.

77gr is stout for sure, but I did this load development over the summer, in 75-80* weather, and I’ve been using this load the entire time. I didn’t get pressure signs until 79gr on my ladder test. These 8 rounds have very clear ejector marks. two rounds total (one over pressure and one not) were discarded for primer leakage as well. Dunno if that provides any insight.

What was the temp the last time you shot? The temp this time? I agree w/ MtnCreek, that load is rather on the stout end of the measure and a bit of temp difference could have been enough to push it over the pressure limits.

load was worked up in 75-82* weather, and it’s been ~50* the last 3 times I’ve been out, but I haven’t seen anything overpressure until now.

 

[davere]

I had not, I cleaned before I shot it, and run a bore snake through the barrel once after a range trip

My thought was that if you'd cleaned it before the most recent trip, you may have left some stuff in the chamber (cleaning solvent, etc), and you're seeing bolt thrust? (don't ask me how I know... ha ha)

 

[MtnCreek]

Sounds like something kept these from releasing the bullet as easily as the others. Cases too long? Fouling in neck area? How freely does a bullet slide into a fired case that didn’t show over pressure?

 

[Tnc]

Any chance you were free recoiling at all? I had factory ammo give me heavy bolt lift after free recoiling. Just a shot in the dark.

 

[-Time-]

Sounds like something kept these from releasing the bullet as easily as the others. Cases too long? Fouling in neck area? How freely does a bullet slide into a fired case that didn’t show over pressure?

One over pressure cause actually doesn’t fit a bullet, but I’m assuming it got dinged up somehow. The difference is very minute, I measured them and it was something like .309-.3095” for the over pressure case, .310-.3105” for a non pressure case. I could see carbon build up or something causing it but I measured all of the cases to ~2.613” oal, and I believe the max for 300wm is 2.620”. Is .007” of carbon build up possible in such few rounds?

 

[-Time-]

Any chance you were free recoiling at all? I had factory ammo give me heavy bolt lift after free recoiling. Just a shot in the dark.

I was not. That seems like a really “interesting” problem to try and diagnose though!

 

[texas_vet00]

Tagged... Same issue on brand new Bighorn TL3... Not trying to steal OP's topic of course...

 

[MtnCreek]

One over pressure cause actually doesn’t fit a bullet, but I’m assuming it got dinged up somehow. The difference is very minute, I measured them and it was something like .309-.3095” for the over pressure case, .310-.3105” for a non pressure case. I could see carbon build up or something causing it but I measured all of the cases to ~2.613” oal, and I believe the max for 300wm is 2.620”. Is .007” of carbon build up possible in such few rounds?

Your measurements don’t make sense to me. A bullet measures .308; your fired case neck dia should measure .32X to .33X.

No fired case should fit a bullet snug. It should slide in freely. Although exceptions exist that don’t apply here.

Carbon fouling could further constrict the case neck, causing it to hold the bullet more than slightly thinner neck cases on firing, causing more initial pressure. It could also pinch the mouth on slightly longer cases.

I think something is preventing consistent bullet release.

 

[-Time-]

Your measurements don’t make sense to me. A bullet measures .308; your fired case neck dia should measure .32X to .33X.

No fired case should fit a bullet snug. It should slide in freely. Although exceptions exist that don’t apply here.

Carbon fouling could further constrict the case neck, causing it to hold the bullet more than slightly thinner neck cases on firing, causing more initial pressure. It could also pinch the mouth on slightly longer cases.

I think something is preventing consistent bullet release.

I was measuring ID, my bad. OD for both over pressure and non are .340 on the nose.

I also realized I measured oal of the cases on the primer, the actual oal of the cases are 2.608 for both over and under pressure.

Here’s pics of both case heads

And a pic of the chamber if anything obvious jumps out at you

 

[-Time-]

Tagged... Same issue on brand new Bighorn TL3... Not trying to steal OP's topic of course...

Feel free to add whatever, even if it’s only a slightly similar issue any insight would be awesome. I’m hvaing my mind blown right now, by every metric I can compare these cases by they should be the same, yet they’re obviously not.

I have ~70 cases that are in the same position these cases were in before I fired, 2.605 oal before being sized, .340 neck OD, same web diameter, etc. I think I’m just gonna have to load them up for this weekend and see what happens, maybe my sizing die got wonky on the last few last sizing session or the RCBS is throwing off or something. If the problem persists I’ll be looking at cutting the cases back a little to test for a carbon ring, or maybe try to scrub the chamber and see what comes out.

This is probably the most frustrating issue I’ve seen with guns so far.

Do you think a case not getting its shoulder bumped enough could’ve caused more pressure? If my sizing die was sizing for cases with a specific amount of lube, and a few cases had less it would stand to reason they may not get bumped as much, and higher pressure would be caused because the case doesn’t have as much room to expand, but that wouldn’t show up when measuring the brass because the brass expands to chamber size either way, correct me if I’m wrong.

 

[texas_vet00]

No issues looking at brass... No primer issues... Nada. Yes, I did the lube thing of course. I spent several beers dry running the bolt... Same lift issue.

That all said, I had a guy mention that it might be a trigger issue. I am not a gunsmith at all so wtf but a data point nonetheless...

Factory Lapua 6.5x47 ammo for the record...

 

[Darkphage]

I think its your shoulder. Take a shot casing that was sticky on bolt opening, put it back in the rifle, close the bolt and feel the pressure, then start by bumping back your shoulder .002". Try it in again, see if the bolt stick is gone (I'm betting it will be), if not give it another .002". Some brass stretched more than others.

Thanks,

Dark

 

[mdmp5]

With my 6.5x47, I worked up a load of 36gr of 4895, 2750fps and it was totally fine. As I shot the rifle more, I noticed that same load started giving heavy bolt lift and some ejector marks. However, I don’t see it today.

I noticed you are working with a fairly new barrel. There is a phenomenon where a new barrel picks up speed after a little while. I’m not certain where exactly that point is, but it is probably in the low hundreds.

 

[RampedRaptor]

Did any of the cases have a small amount of case lube on them?

New lot of powder?

 

[MtnCreek]

Sorry, your measurements would have made more sense to me if I hadn't had a teaglass full of whisky...

It's hard to get id by measuring the id with a caliper, at least for me. IMHO, best method is to measure od and deduct case thickness.

Both over pressure and non over pressure cases measured 0.340. The over pressure case had a smaller id by 0.001. I'm betting if you measure a sized, loaded neck it's going to measure just a touch under .340 or right at it. Allowing for very little tollerance in bullet release. Small varriance in case thickness and just a little fouling can then take you from fine to over pressure.

I'd clean the neck area of the chamber well. I'd also trim back all cases to 2.610, to eliminate any incostancies between lengths. I'd back off the charge weigth by a few grains and fire from the clean/dry chamber. Measure/record neck od before and after firing. If you're only seeing a couple thou difference in od, you're dealing with cases that fit too snug in the chamber.

 

[mdmp5]

Best method to measure internal diameter is with a pin gauge. Too much room for error any other way

 

[-Time-]

I think its your shoulder. Take a shot casing that was sticky on bolt opening, put it back in the rifle, close the bolt and feel the pressure, then start by bumping back your shoulder .002". Try it in again, see if the bolt stick is gone (I'm betting it will be), if not give it another .002". Some brass stretched more than others.

Thanks,

Dark

That’s what I’m banking on. When I load up this next batch I’ll measure them all and make sure they’re bumped back .002” it’s what I have done previously and I’ve had no issues so I’m gonna assume some brass just didn’t happen to get bumped.

Did any of the cases have a small amount of case lube on them?

New lot of powder?

Same 8lb of powder. They did have a little lube in the neck. I wiped most of it off the outside but it’s not out of the realm of possibility for me to have missed some. Using the home brew lanolin/alcohol mixture for lube.

 

[-Time-]

Sorry, your measurements would have made more sense to me if I hadn't had a teaglass full of whisky...

It's hard to get id by measuring the id with a caliper, at least for me. IMHO, best method is to measure od and deduct case thickness.

Both over pressure and non over pressure cases measured 0.340. The over pressure case had a smaller id by 0.001. I'm betting if you measure a sized, loaded neck it's going to measure just a touch under .340 or right at it. Allowing for very little tollerance in bullet release. Small varriance in case thickness and just a little fouling can then take you from fine to over pressure.

I'd clean the neck area of the chamber well. I'd also trim back all cases to 2.610, to eliminate any incostancies between lengths. I'd back off the charge weigth by a few grains and fire from the clean/dry chamber. Measure/record neck od before and after firing. If you're only seeing a couple thou difference in od, you're dealing with cases that fit too snug in the chamber.

Duely noted about measuring neck ID.
These next cases are 2.605 before sizing so I should be good on OAL.

What do you recommend to clean the neck/chamber area? I’m struggling to even find a 300wm chamber brush.

 

[supercorndogs]

That’s what I’m banking on. When I load up this next batch I’ll measure them all and make sure they’re bumped back .002” it’s what I have done previously and I’ve had no issues so I’m gonna assume some brass just didn’t happen to get bumped.

I thought about the shoulder bump, but if you bump the shoulder too much it should headspace off the belt like it was designed to, rather than off the shoulder like we size them to.

 

[MtnCreek]

Duely noted about measuring neck ID.
These next cases are 2.605 before sizing so I should be good on OAL.

What do you recommend to clean the neck/chamber area? I’m struggling to even find a 300wm chamber brush.

A tighter than bore patch on a pierce jag or a loop jag with cut up teeshirt. If you use a loop, run it through the bore, run the patch material through, pull it back part way into the chamber, then back into the neck area. That should tighten it up and leave material between the loop and barrel metal.

 

[RampedRaptor]

The home brew lube can be quite slippery and if you missed some by accident that could be to blame for a false positive in the pressure arena.

Easiest test would be to clean your chamber real well like described above and then load a ladder up and shoot them. If a inconvenience, you wouldn't even have to shoot them at long distance as you are more interested in the pressure at this point.

Don't forget to wipe all the lube off the next rounds. Making the home lube less viscous makes it easier to clean up also.

 

[-Time-]

I thought about the shoulder bump, but if you bump the shoulder too much it should headspace off the belt like it was designed to, rather than off the shoulder like we size them to.

My thought was not that the case was getting bumped too much, but rather just enough for me to not notice it was right when loading, and the inability for the brass to expand much was increasing pressures, but maybe I’m incorrect about that. I have noticed the home brew case lube is very finicky on sizing depending on how wet the lube is, so I believe it possible I could have the die set to be sizing off of somewhat wet cases, and a drier case would not be sized as much. I have ruled that possibility out with this last batch.

 

[-Time-]

I went round by round and made sure every case was sized, and all of the lube was wiped off. RCBS chargemaster is throwing accurately as well. I’m taking it out Saturday, and I’m going to bring cleaning stuff, but I want to drop a couple rounds before cleaning, to cross off variables for the future, since I have no way to easily check if the neck area is dirty. Although a bore scope is on my list. Also bringing the magnetospeed to see if the velocity has changed at all. Anything I’m missing?

 

[RampedRaptor]

Sounds good. Did you test some of the round to make sure they chamber smoothly before you make the drive to the range ?

 

[-Time-]

Sounds good. Did you test some of the round to make sure they chamber smoothly before you make the drive to the range ?

Yes, and I tried bumping the brass from the batch that were over pressure. the over pressure rounds are harder to chamber than the non, even after bumping. It seems to be around the belt, but unfortunately the Larry Willis collet die I have doesn’t work with my forester coax.

 

[digrazir]

I would try some factory rounds to see if they chamber and shoot. If the factory rounds chamber and shoot you know it is your reloads. If the same issues continue it is the rifle. ?Ray

 

[Tnc]

Really. At least that’s the only thing I can come up with. Nothing else changed. Hasn’t done it since however

 

[-Time-]

Well I chrono’d the loads today. They’re running ~2866, about 70fps faster than it used to be. I didn’t get a really heavy bolt lift, but ejector marks were still present on most of the brass. I cleaned the chamber, to no effect.

I’m truly at a loss for why this load shoots 70fps faster when in 3x fired brass. I have some new brass on the way to a ladder test in.

My only ideas at this point are, I have a chamber that’s cut .010 short in the neck area, the area around the belt expanding increases pressure, or there’s something else dimensionally different with the brass to throw it off, or I got an off box of Hornady bullets.

 

[SPAK]

Make sure you can depress your ejector and there isn’t any crud under it keeping it from depressing.

Are your rounds closing easily or with crush fit?

How many rounds on barrel?

 

[MtnCreek]

Expanded heads will cause difficult extraction, but won’t cause extrusion into the ejector hole. If bullets won’t slide freely into fired necks, the case necks are too long or too thick. I believe you said some were +0.0015 after firing. That’s not enough.

 

[-Time-]

Make sure you can depress your ejector and there isn’t any crud under it keeping it from depressing.

Are your rounds closing easily or with crush fit?

How many rounds on barrel?

About 350 on the barrel. Rounds close easy and the ejector is clean.

Expanded heads will cause difficult extraction, but won’t cause extrusion into the ejector hole. If bullets won’t slide freely into fired necks, the case necks are too long or too thick. I believe you said some were +0.0015 after firing. That’s not enough.

Bullets will slide freely into fired cases, I think earlier ones didn’t slide freely because they got dinged up, I made sure to catch all of this brass.

You’re right the brass OAL isn’t moving much at all, maybe +0.002-0.0015. Do you think this is the cause of my problem, and what do you think is causing it?

 

[SPAK]

Good info. Id check for a carbon ring in the throat. Clean the barrel really well. Look for threads on how to clean up a carbon ring.

I have had some barrels exhibit pressure signs with subsequent firings due to carbon fouling.....

Sometimes normal cleaning methods are not enough to get rid of the carbon ring buildup and you need to address it specifically. Even with only 350rnds on the tube.

At this point in order to take care of all your variables you need a clean barrel to start.....

 

[-Time-]

Good info. Id check for a carbon ring in the throat. Clean the barrel really well. Look for threads on how to clean up a carbon ring.

I have had some barrels exhibit pressure signs with subsequent firings due to carbon fouling.....

Sometimes normal cleaning methods are not enough to get rid of the carbon ring buildup and you need to address it specifically. Even with only 350rnds on the tube.

At this point in order to take care of all your variables you need a clean barrel to start.....

I bit the bullet on a Lyman borescope, so we’ll know for sure soon.

Anyone tried cutting brass just below max to eliminate carbon ring build up, or is it in vain?