Neck Tension and Pressure Signs

[Bo Ployhar]

We don't clean our barrels until they stop shooting good, but cleaning the chamber properly, and often is a must IMO. As stated above 45 cal pistol jag and 1 or 2 patches on it (what ever it takes for a tight fit), and some rubbing alcohol makes quick work of it. Usually just a few wet patches till clean followed by a dry patch.

I had a batch of new 308 brass that did this a few years back. Some weird polish residue left on the brass. You couldn't wipe it off, but within 10-15 rounds after cleaning the pressure signs where back.

Also make sure you are keeping your lugs greased, doesn't take long to fuck up an action with dry lugs and lots of bolt thrust!

 

[918v]

If your coal is 2.820” then you can’t be .025” off the lands.

 

[OREGUN]

If your coal is 2.820” then you can’t be .025” off the lands.

If it was a factory chambered R700, you wouldnt be anywhere near them

 

[Timo Turl]

Is your factory ammo also using large rifle primers like your handloads ?

 

[918v]

I did a ladder this morning from 41.4-42.7grs in FC brass that weighed 171-172grs, about 3-4grs heavier than Peterson. You have major issues with your stuff. 41.4grs made 2650 FPS in my 24” barrel. No heavy bolt lift at any point, even at max. And FC brass is soft. I did get an ejector mark on top but this gun makes ejector marks earlier than other guns cuz the hole has rough edges.

So it’s not a characteristic of the powder in heavy brass. It’s got to be something in your equipment.

 

[Ratchet 94]

I've been struggling in my 6.5-CM loads with pressure signs (heavy bolt, extractor swipe marks, etc.) in loads that absolutely should "not" be delivering them. I'm talking about velocities that are hundreds of fps slower (2400-ish) than factory ammo (2700-ish) ... that by the way ... shoots with no pressure signs whatsoever. I was at a match this weekend whining about this, and an experienced shooter (that won the match) told me to loosen my neck tension and see if that helped. I'd never thought about that, but it does make sense that if the bullet is too tight in the case mouth, it could build up internal pressure that causes pressure signs but doesn't translate into higher projectile velocity. I size necks with a bushing tie, and then expand prior to seating with a L.E.Wilson Mandrel Die ... but that die is specifically and only equipped with a generic 6.5 mandrel. Assuming it's money well-spent, I've ordered the 21st Century die and mandrel kit to give me the ability to precision size my case mouths (the kit has a range of mandrel sizes over and under the standard) ... and see if I can solve this problem.

Anybody here agree ... that excess neck tension can cause pressure signs with low velocities? Just curious what the heavy-hitters here think about that. And ... am I on the right track with the 21st Century mandrel kit? Thanks! This whole journey is about continuous improvement ... at least that's what I keep telling myself.

I had Lapua brass that the head was not flat , causing heavy lifts every now and then on light loads as I was working up loads. Would scrap brass around primer but not show any other sign of pressure. Filed case heads flat with a smooth file and problem was gone and has not returned. Acted like a hit load but no ejector marks , no flattened primer. Intermittent heavy bolt lift was the symptoms.

 

[ReaperDriver]

I've been struggling in my 6.5-CM loads with pressure signs (heavy bolt, extractor swipe marks, etc.) in loads that absolutely should "not" be delivering them. I'm talking about velocities that are hundreds of fps slower (2400-ish) than factory ammo (2700-ish) ... that by the way ... shoots with no pressure signs whatsoever. I was at a match this weekend whining about this, and an experienced shooter (that won the match) told me to loosen my neck tension and see if that helped. I'd never thought about that, but it does make sense that if the bullet is too tight in the case mouth, it could build up internal pressure that causes pressure signs but doesn't translate into higher projectile velocity. I size necks with a bushing tie, and then expand prior to seating with a L.E.Wilson Mandrel Die ... but that die is specifically and only equipped with a generic 6.5 mandrel. Assuming it's money well-spent, I've ordered the 21st Century die and mandrel kit to give me the ability to precision size my case mouths (the kit has a range of mandrel sizes over and under the standard) ... and see if I can solve this problem.

Anybody here agree ... that excess neck tension can cause pressure signs with low velocities? Just curious what the heavy-hitters here think about that. And ... am I on the right track with the 21st Century mandrel kit? Thanks! This whole journey is about continuous improvement ... at least that's what I keep telling myself.

I know this is an older thread, so apologies if this has already been addressed..... but I ran into the exact same thing recently while doing load development for a .260 gas gun. I was getting pressure signs for no reason on what should have been light loads. Flattened primers, swipe, Ejector hole imprints, etc but at normal velocities using Lapua brass.

After much head scratching, we eliminated it to neck thickness / tight match chamber. The tell-tell sign was that you could not slide a bullet into a fired case mouth. In a normal chamber, the neck obviously opens up to the dimensions of the chamber and you should be able to slide a bullet into the mouth with minor resistance. We also measured the fired case necks and they just barely more than a loaded neck measurement. So we neck turned all the brass to shave a very small amount off and then retried them. Viola, no pressure and the accuracy improved significantly. It was not so much the Lapua brass was too thick, it was the chamber was cut to very min spec and there was no room for the brass to expand and release the bullet during ignition - thereby causing pressure to spike. Hope this helps.

 

[OREGUN]

I do remember some old time Benchrest shooters I used to shoot with talking about going through a phase where they were all convinced that the tightest possible neck would be the best. As it turns out they all found out that’s not in fact the case. You do need some space for the brass to expand and release the bullet. What I didn’t remember about that conversation with them was talking about overpressure or pressure signs but it makes sense. I just assumed they meant their accuracy suffered.

 

[918v]

In some applications you can get away with a tight neck. In others you can’t.

 

[SoYoCo]

Rusty

I've been struggling in my 6.5-CM loads with pressure signs (heavy bolt, extractor swipe marks, etc.) in loads that absolutely should "not" be delivering them. I'm talking about velocities that are hundreds of fps slower (2400-ish) than factory ammo (2700-ish) ... that by the way ... shoots with no pressure signs whatsoever. I was at a match this weekend whining about this, and an experienced shooter (that won the match) told me to loosen my neck tension and see if that helped. I'd never thought about that, but it does make sense that if the bullet is too tight in the case mouth, it could build up internal pressure that causes pressure signs but doesn't translate into higher projectile velocity. I size necks with a bushing tie, and then expand prior to seating with a L.E.Wilson Mandrel Die ... but that die is specifically and only equipped with a generic 6.5 mandrel. Assuming it's money well-spent, I've ordered the 21st Century die and mandrel kit to give me the ability to precision size my case mouths (the kit has a range of mandrel sizes over and under the standard) ... and see if I can solve this problem.

Anybody here agree ... that excess neck tension can cause pressure signs with low velocities? Just curious what the heavy-hitters here think about that. And ... am I on the right track with the 21st Century mandrel kit? Thanks! This whole journey is about continuous improvement ... at least that's what I keep telling myself.

Sorry to dig up this old thread, but I’m currently experiencing this same issue. Rusty, any chance you found a remedy

 

[rustyinbend]

Rusty

Sorry to dig up this old thread, but I’m currently experiencing this same issue. Rusty, any chance you found a remedy

Wow ... that was a long time ago. I no longer have that issue in anything I'm reloading. I can't say or remember exactly what solved this specific problem, but here is what I do/use that works for me.

I "think" it was finding the right combination of neck bushing (to shrink) and mandrel (to expand). I did a LOT of experimentation around that time with the whole "bushing-down / mandrel-up" thing.

Equipment is AMP Annealer, Redding FL Bushing die, Imperial Sizing Wax (outside), NeoLube #2 (inside), 21-C Mandrel Set, LE Wilson Inline die, and AMP Press for bullet seating.

Hope that helps. Sorry ... I'm too old to remember where I put my reading glasses 10 minutes ago ... so remembering something I tweaked 5 years ago is pretty much impossible.

 

[SoYoCo]

Wow ... that was a long time ago. I no longer have that issue in anything I'm reloading. I can't say or remember exactly what solved this specific problem, but here is what I do/use that works for me.

View attachment 8651761
I "think" it was finding the right combination of neck bushing (to shrink) and mandrel (to expand). I did a LOT of experimentation around that time with the whole "bushing-down / mandrel-up" thing.

Equipment is AMP Annealer, Redding FL Bushing die, Imperial Sizing Wax (outside), NeoLube #2 (inside), 21-C Mandrel Set, LE Wilson Inline die, and AMP Press for bullet seating.

Hope that helps. Sorry ... I'm too old to remember where I put my reading glasses 10 minutes ago ... so remembering something I tweaked 5 years ago is pretty much impossible.

No worries buddy, thanks for sending the info over. I’m running type S dies and a .262 mandrel with 140’s over H4350. I get pressure after a few shots but I can run factory rounds after reloads with no pressure signs. It’s a real head scratcher.

 

[KnowNothing256]

No worries buddy, thanks for sending the info over. I’m running type S dies and a .262 mandrel with 140’s over H4350. I get pressure after a few shots but I can run factory rounds after reloads with no pressure signs. It’s a real head scratcher.

What’s your process for removing lube after sizing?

If there’s any residual lube, the case can fail to stick to the chamber wall properly, and it will slam backwards against the bolt face and give false pressure signs. This would make sense for your description, where it happens after a few rounds; the lubrication builds up on the chamber wall and eventually the cases start slipping.

Try wiping off the outside of a mag’s worth of loaded rounds with alcohol, then run them through the gun and see if it improves. If you see any visible discoloration on the rag or towel you use to wipe the rounds down, that’s another sign of this issue.

 

[SoYoCo]

I’ll give that a whirl, I’ve been using a rag to wipe down the cases after sizing. I’ll be more diligent the next round of testing to make sure that isn’t a underlying factor.

 

[rustyinbend]

No worries buddy, thanks for sending the info over. I’m running type S dies and a .262 mandrel with 140’s over H4350. I get pressure after a few shots but I can run factory rounds after reloads with no pressure signs. It’s a real head scratcher.

One thing to note from around this time, was that I had literally no idea what my seating force was. On a regular press with a normal bullet seating die, it's quite impossible to "sense" or "feel" seating force accurately. I suspected this might be a problem, so I got an Arbor Press with a dial measure and LE Wilson Inline dies, and learned that my seating force was off-the-charts high. I never suspected that, given the ease with which I was seating bullets on my single stage press. The adjustments necessary to bring my seating force to sanity were huge. I eventually got an AMP Press, and knowing my exact seating force, and working backwards from that to the right bushing-mandrel combination, has resulted in pressure signs only when expected, like at the high end of a charge ladder test. Bottom line ... I'm a "true believer" in using a tool (like the AMP Press) to take the guesses out of proper seating force. If I had to vote my tools "off the island" ... my AMP Press would be the last to go. Just picking seating force by "neck-diameter" and "press feel" ... well ... Iet's just say I've found a better path.

 

[SoYoCo]

I have double checked my fired brass and loaded rounds. Looks like I’m getting .003 of neck expansion, I’m assuming that is plenty to get a clean bullet release each shot. It almost seems as though my brass isn’t getting a good seal in the chamber. Im running Redding bushing FL size dies and a 21-C .262 mandrel to bring the necks back out.

 

[918v]

One thing to note from around this time, was that I had literally no idea what my seating force was. On a regular press with a normal bullet seating die, it's quite impossible to "sense" or "feel" seating force accurately. I suspected this might be a problem, so I got an Arbor Press with a dial measure and LE Wilson Inline dies, and learned that my seating force was off-the-charts high. I never suspected that, given the ease with which I was seating bullets on my single stage press. The adjustments necessary to bring my seating force to sanity were huge. I eventually got an AMP Press, and knowing my exact seating force, and working backwards from that to the right bushing-mandrel combination, has resulted in pressure signs only when expected, like at the high end of a charge ladder test. Bottom line ... I'm a "true believer" in using a tool (like the AMP Press) to take the guesses out of proper seating force. If I had to vote my tools "off the island" ... my AMP Press would be the last to go. Just picking seating force by "neck-diameter" and "press feel" ... well ... Iet's just say I've found a better path.

So what seating pressure are you running currently?

 

[SoYoCo]

So what seating pressure are you running currently?

I’m using a Redding competition seater. No way of knowing unfortunately

 

[918v]

I’m using a Redding competition seater. No way of knowing unfortunately

R u getting a ring around the seater stem contact point?

 

[ReaperDriver]

Rusty

Sorry to dig up this old thread, but I’m currently experiencing this same issue. Rusty, any chance you found a remedy

I had all the same issues.... I was blowing primers and getting swipe at loads that had previously shot well and were definitely not super hot. My eventual remedy was two-fold. I found the necks in my Lapua brass were a bit tight in my match chamber (drop in Proof barrel for an AI-AT). So I turned the necks of all my 6CM lapua brass.

I also attacked my carbon ring with CLR as nothing else I tried touched it. I did CLR for about 15-20 min max on a soaked patch in just the chamber and then thoroughly cleaned any CLR out.

Both of those together seemed to do the trick. The rifle shoots the same loads now with no signs of pressure and is still a hammer. I was banging a 1300 yd plate with it just a few days ago.

to edit: I also went back and rechecked my headspace and realized I was probably bumping the shoulders back a bit much. I went from about 3-4 thou down to about 1 thou. I bump them just enough so that the case chambers easily but no more.

 

[SoYoCo]

R u getting a ring around the seater stem contact point?

I was, but it went away when I changed to the VLD stem

 

[SoYoCo]

I had all the same issues.... I was blowing primers and getting swipe at loads that had previously shot well and were definitely not super hot. My eventual remedy was two-fold. I found the necks in my Lapua brass were a bit tight in my match chamber (drop in Proof barrel for an AI-AT). So I turned the necks of all my 6CM lapua brass.

I also attacked my carbon ring with CLR as nothing else I tried touched it. I did CLR for about 15-20 min max on a soaked patch in just the chamber and then thoroughly cleaned any CLR out.

Both of those together seemed to do the trick. The rifle shoots the same loads now with no signs of pressure and is still a hammer. I was banging a 1300 yd plate with it just a few days ago.

to edit: I also went back and rechecked my headspace and realized I was probably bumping the shoulders back a bit much. I went from about 3-4 thou down to about 1 thou. I bump them just enough so that the case chambers easily but no more.

I’m sure it’s not a carbon ring, bar Md new Bartlien with 20 rounds on it when the issue started … I’ll double check headspace and strip the bolt

 

[SoYoCo]

I’m sure it’s not a carbon ring, bar Md new Bartlien with 20 rounds on it when the issue started … I’ll stop the bolt and double check headspace on my fired brass

 

[918v]

I was, but it went away when I changed to the VLD stem

But if it’s a seating pressure issue, as in the OP’s case, then you just masked instead of curing the problem.

 

[SoYoCo]

But if it’s a seating pressure issue, as in the OP’s case, then you just masked instead of curing the problem.

I see what you’re saying. I can try a larger mandrel. I assumed that the .262 would hold my tension around .002-.003

 

[918v]

I see what you’re saying. I can try a larger mandrel. I assumed that the .262 would hold my tension around .002-.003

Tension is one factor. Then there’s friction. Is the neck annealed? Did you use dry lube prior to seating? Also, some bullets seat harder than others. You have to factor all of that in.

 

[SoYoCo]

Tension is one factor. Then there’s friction. Is the neck annealed? Did you use dry lube prior to seating? Also, some bullets seat harder than others. You have to factor all of that in.

It’s once fired brass, alpha and Hornady headstamps. I have not annealed it. I do use moly lube when I mandrel and do not brush the necks. They have the leftover moly and carbon inside of them.

 

[SoYoCo]

Do you think running the expander ball as a test may help short term? I could always measure the expander if it the loads don’t produce pressure.

 

[918v]

Do you think running the expander ball as a test may help short term? I could always measure the expander if it the loads don’t produce pressure.

Is the expander ball .263”? That would certainly lower seating pressure. Dry lube would help too.

 

[pabrousseau]

What do the primers look like on your fired high pressure loads?

 

[pabrousseau]

Pictures.

 

[SoYoCo]

Is the expander ball .263”? That would certainly lower seating pressure. Dry lube would help too.

I’ll have to measure it when I get home.

Pictures.

ill get some posted up when I get home tomorrow