Heavy Bolt Lift in New Chamber

[Rset]

Need some suggestions.
Just replaced the barrel on my 6 dasher. New Reamer, 7.5 twist Brux, 30" finish length, Panda Action.
New reamer is .272 neck, .2438, 134 lead, .4720 @ .200. No print for my old chamber.
Sent a sized dummy round to JGS for some additional information when specifying the reamer.
Was shooting 32.5 gr Varget in old barrel @ 3030 fps in 8 twist 28".
Stepped down load with new barrel but getting heavy bolt lift at even 31.7gr @ 2886 - 2902 fps. Leaves slight ejector mark on fired Alpha cases, but this is not new. Also happened on old barrel where there were no issues with Lapua at higher loads and same point of impact.
SO, Is this just an issue with a new barrel or are there things I should be looking at to get this resolved. I assume the barrel will speed up with additional rounds fired (only 86 down the tube) but the heavy lift and low speeds is a concern.

 

[hogpatrol]

Are you using new brass in the new barrel or brass shot in another barrel?

 

[Rset]

Are you using new brass in the new barrel or brass shot in another barrel?

Brass shot in old barrel. 2 firings. Full length re-sized

 

[Thud]

New Barrel New Brass said many times here.
Saves you from Headaches.

 

[Rset]

New Barrel New Brass said many times here.
Saves you from Headaches.

Very true. Just looking for other possible issues before replacing all brass with new. Would hate to move to new brass and then still have the same issue.

 

[gunsandgunsmithing]

IME, ejector marks are an indication of one or both of two things...too much pressure and/or too much headspace.

Does the heavy bolt lift start at the first movement of the bolt handle or just near the top?
If it starts at first movement, it's either too much pressure or shoulders not bumped enough, which can show up on bolt closure before firing.

Old brass can cause issues but your reamer dimensions are rather generous for Lapua brass...Not sure about alpha but most new brass is well below that.

If the old chamber was the least bit bigger than the new one, try new brass. Try new anyway but if it only happens on old brass, there's you problem, in all liklihood.

 

[JMayo]

I had this with new barrel, old brass, prolly 6 shootings.
I bumped the shoulders a little more and it stopped.

I was told datum line might be enlarged and fl die wouldn't get to it...
Not the issue on mine though.

 

[Rset]

IME, ejector marks are an indication of one or both of two things...too much pressure and/or too much headspace.

Does the heavy bolt lift start at the first movement of the bolt handle or just near the top?
If it starts at first movement, it's either too much pressure or shoulders not bumped enough, which can show up on bolt closure before firing.

Old brass can cause issues but your reamer dimensions are rather generous for Lapua brass...Not sure about alpha but most new brass is well below that.

If the old chamber was the least bit bigger than the new one, try new brass. Try new anyway but if it only happens on old brass, there's you problem, in all liklihood.

Hard lift is from the start and when prevalent, fired cases are also hard to chamber and also have heavy lift. Loaded cases chamber and extract easily. .002 setback on headspace. Have had case head marks on Alpha Brass before with no other issues. Never saw it as a pressure problem. May need to start with new brass, but trying to solve without it if possible.

 

[Rset]

I had this with new barrel, old brass, prolly 6 shootings.
I bumped the shoulders a little more and it stopped.

I was told datum line might be enlarged and fl die wouldn't get to it...
Not the issue on mine though.

Additional shoulder bump is is order on the next session. at .002 now, will increase a little more and see if it helps. Wasn't too worried about the sizing at the .200 line since I specified a generous chamber when I ordered the reamer.

 

[gunsandgunsmithing]

Hard lift is from the start and when prevalent, fired cases are also hard to chamber and also have heavy lift. Loaded cases chamber and extract easily. .002 setback on headspace. Have had case head marks on Alpha Brass before with no other issues. Never saw it as a pressure problem. May need to start with new brass, but trying to solve without it if possible.

Hard from the start is likely too much pressure unless the old chamber was long and the brass has developed a memory..It does that. But since you said it is hard to chamber, I'd question you are actually getting .002 setback, where it matters. Mark up a case with a magic marker, especially from the shoulder/body junction to the case mouth. Chamber it several times and inspect for ink rubbed off. That'll tell you where the interference is coming from upon bolt closure.

 

[Rset]

Hard from the start is likely too much pressure unless the old chamber was long and the brass has developed a memory..It does that. But since you said it is hard to chamber, I'd question you are actually getting .002 setback, where it matters. Mark up a case with a magic marker, especially from the shoulder/body junction to the case mouth. Chamber it several times and inspect for ink rubbed off. That'll tell you where the interference is coming from upon bolt closure.

Sized loaded cases experience no issues and chamber / extract without restriction. Fired cases measure nearly identical to those from old chamber (+.0005). Cases have also been annealed after every firing. Only the fired cases are hard to chamber. It certainly sounds like pressure, but the velocity is not where it should be for a dasher running at pressure.

 

[gunsandgunsmithing]

Sized loaded cases experience no issues and chamber / extract without restriction. Fired cases measure nearly identical to those from old chamber (+.0005). Cases have also been annealed after every firing. Only the fired cases are hard to chamber. It certainly sounds like pressure, but the velocity is not where it should be for a dasher running at pressure.

Sounds like all that's left is to fire a new piece and see if the problem still exists. I'm betting not. A half thou is a lot of difference if you're measuring at the .200 line.

 

[Rset]

Sounds like all that's left is to fire a new piece and see if the problem still exists. I'm betting not. A half thou is a lot of difference if you're measuring at the .200 line.

half a thou is headspace. No tight chambering with sized cases, but fired cases are hard both in and out. With . 4720 at the .200 line I have plenty of room to work with. Will try bumping the old cases back a little more to see if it changes anything, but think I will also have to buy some new brass to try. Was hoping someone had a solution that I had not thought of yet. Still concerned with the pressure signs given the low velocities.

 

[hammerjack]

See if a bullet will slip into fired case could be the problem.

 

[jackieschmidt]

Just a thought, but did you polish the chamber like many do. To smooth as finish will not allow the case to grip the chamber walls increasing bolt lift Because of action stretch at high end loads. I leave my chambers in the finish the reamer leaves, as I believe this aids in primary extraction when shooting in the upper load window.

But that would not necessarily explain the mark on the case head, which is a very good indicator that you are reaching the limit of pressure.

 

[JFrank]

half a thou is headspace. No tight chambering with sized cases, but fired cases are hard both in and out. With . 4720 at the .200 line I have plenty of room to work with. Will try bumping the old cases back a little more to see if it changes anything, but think I will also have to buy some new brass to try. Was hoping someone had a solution that I had not thought of yet. Still concerned with the pressure signs given the low velocities.

Just knock them back another thousand or so until they chamber. It is what it is.

 

[Rset]

See if a bullet will slip into fired case could be the problem.

Neck expands as expected.

 

[Rset]

Just a thought, but did you polish the chamber like many do. To smooth as finish will not allow the case to grip the chamber walls increasing bolt lift Because of action stretch at high end loads. I leave my chambers in the finish the reamer leaves, as I believe this aids in primary extraction when shooting in the upper load window.

But that would not necessarily explain the mark on the case head, which is a very good indicator that you are reaching the limit of pressure.

Chamber was left as the reamer created it. No additional polishing was performed.
Slight mark on the case head would be a concern, except I have seen this happen on Alpha cases in the past that were well withing pressure limits. Have also heard from others indicating the same. May be a slightly softer base material than with Lapua? I really don't know.

 

[Rset]

Just knock them back another thousand or so until they chamber. It is what it is.

un-fired cases chamber easily at .002 bump. Only after firing are the cases hard to chamber.
I will do that just to see, but my thought was that the case would still expand to the chamber when fired. Was told that sometimes giving them a little more room solves the issue so I am going to bump them back a couple more and see what happens. If that doesn't work, looks like I start with some new brass.

 

[MGYSGT]

Check trim to length after full length resize.