Should I be concerned?

[VarmLR]

Yesterday, I took some loads which I was developing for 600 and 1000 yards to the range to test.

 

Here's a photo of three fired cases which were new Lapua .308 cases:

 

 

 

 

The top two cases are:

 

 

One was taken from a load comprising 44.5 grains N140 over a 155 grain #2155 SMK using CCI large rifle primers, bullet seated to 2.800";

 

Middle one was from 42.4 grains N140 over a 190gr SMK seated at 2.865"

 

The bottom one was from a load comprising 43.8 grains N140 over a 155smk.

 

None of these loads are particularly what I'd have previously considered as "hot".

 

Whilst the 190 load is above that stated in the Lyman load manual (42gr) and from Sierra 5th (41.3gr) it is within Vhit's recommended 42.9. the big difference is all of those loads are for a smaller COAL, typically 2.795" which I considered way too compressed with the 190SMK unless loading to around 41 grains.

 

My rifle is a T3 heavy barrel (24 inch) and the mark's on two of the cases are from the rounded pin located just within the bolt face (not the extractor claw).

 

There were no other signs of over-pressure such as significantly notable increase in noise or recoil, the primers look about the same as the lower loads...you can see that they clearly have defined shoulders remaining and haven't flattened much, although I appreciate this isn't always reliable.

 

My gut instinct is that any such marks can only be due to pressure, so I ought really to back-off a little. I know plenty of people who use higher charges of N140 for both these bullets safely. The 42.4 grains also got me just over 2500 fps for the 190 so I was going to try that at Bisley in preference to my 155 loads, to see how I got on.

 

I could go to N150 but i doubt I'd get any better velocities in my barrel.

 

Rather than re-assurance, I was hoping from a little collective wisdom. Having no extractor (gap) marks reassures me a little so these pin marks are a little strange as I've never had them previously on any loads. I once had extractor marks on a very hot N140 load but these pin marks were just not evident then, plus primers were very obviously pan-caked on those occasions.

 

Incidentally, the 42.4 load produced virtually a one hole group at 100 yds with the 190's.

[duey]

Those loading don't sound to be hot to me but each rifle is different

 

It could be that the new brass is undersized enough ( as lapua can be ) that the case isn't grabbing the chamber fully and therefore you get an increase in rear movement of the case into the bolt face, hope that makes sense

 

 

But it could be high pressure

 

I swapped N140 to N150 in 308 using 165gr SGK and got the same velocity without the pressure signs similar to what your getting so may be worth a go with 150

 

Duey

[That bald headed Geordie]

Another cause could be a wet chamber. I have had this happen to me before as I had forgotten to wipe out the chamber from a previous soaking. The case upon firing could not grip the chamber walls and was pushed back to the bolt face causing the same indicator you had noticed.

However, if you suspect a hot load then did you have hard bolt lift as that is another sign.

[VarmLR]

Hi Duey

 

I would do if it wasn't for the fact that I'm only trying 190's and wouldn't normally shoot many of them, hence would like to keep the n140 as I use it for other loads. I did check the new brass and it gave about a 2 thou headspace gap in my chamber so that sounds ok to me although admittedly not the zero gap of fire-formed. Perhaps I just ought to try the same loads fire-formed and see what I get?

[VarmLR]

Another cause could be a wet chamber. I have had this happen to me before as I had forgotten to wipe out the chamber from a previous soaking. The case upon firing could not grip the chamber walls and was pushed back to the bolt face causing the same indicator you had noticed.

However, if you suspect a hot load then did you have hard bolt lift as that is another sign.

 

No heavy bolt lift but now you come to mention it, I did put an oil soaked rag down the barrel after the last cleaning, and forgot to dry-patch prior to shooting so this may well be a contributing factor. Good shout.

[gbal]

Paul, " gut instinct speak with straight tongue'-plunger marks are one sign of the pressure needle flickring into the red.

What plenty people do varies,but no handloader can measure pressure,so there really is no reliable,nor need there be visible symptoms (though if there are, back off). And of course,a warmer day might just be enough to add in stiff bolt etc -see below.

Using s mall primer Palma brass is less likely to show symptoms-not the same as there being no pressure,and not everyone states which brass....

" Vihtavuori is conservative" some say.... hmmmm.....too many interactions going on to be definitive..

 

GIven your 190 load was accurate at 100,dropping back to 42 grains is unlikely to increase dispersion,nor is 50+ fps less velocity going to have much impact compared to wind reading error anyhow...but note vertical on target-that is load related (velocity consistency).

 

For what it's worth (a lot to me,but rifles vary), here is my 308 Rem VSSF data,carefully developed/checked by a trusted reloader for 1000y comp use:

 

Sierra 190 HPMK molycoated 43.6 Viht N 140 mv at 65f was 2558 fps;at 35f it was 2531fps

 

Lapua 185 scenar molycoated 43.4g N140 and mv at 42f 2595 fps under 40F,use 44g 140

 

Note moly bullets mean a small powder increase and I was using considerably more powder (of that batch )for just a little more fps (50fps);no pressure signs, but developed as optimal load....this simply confirms individual rifle/conditions/powder batch/reloading variation- bullet seating, tension....etc and you can only be driven safely by what your rifle tells you,via the fired brass.

 

g

[VarmLR]

Paul, " gut instinct speak with straight tongue'-plunger marks are one sign of the pressure needle flickring into the red.

What plenty people do varies,but no handloader can measure pressure,so there really is no reliable,nor need there be visible symptoms (though if there are, back off). And of course,a warmer day might just be enough to add in stiff bolt etc -see below.

Using s mall primer Palma brass is less likely to show symptoms-not the same as there being no pressure,and not everyone states which brass....

" Vihtavuori is conservative" some say.... hmmmm.....too many interactions going on to be definitive..

 

GIven your 190 load was accurate at 100,dropping back to 42 grains is unlikely to increase dispersion,nor is 50+ fps less velocity going to have much impact compared to wind reading error anyhow...but note vertical on target-that is load related (velocity consistency).

 

For what it's worth (a lot to me,but rifles vary), here is my 308 Rem VSSF data,carefully developed/checked by a trusted reloader for 1000y comp use:

 

Sierra 190 HPMK molycoated 43.6 Viht N 140 mv at 65f was 2558 fps;at 35f it was 2531fps

 

Lapua 185 scenar molycoated 43.4g N140 and mv at 42f 2595 fps under 40F,use 44g 140

 

Note moly bullets mean a small powder adjust;and I was using considerably more powder for just a little more fps (50fps);no pressure signs, but developed as optimal load....this simply confirms individual rifle/conditions/powder batch/reloading variation- bullet seating, tension....etc and you can only be driven safely by what your rifle tells you,via the fired brass.

 

g

 

 

Thanks George. What was your seating depth for the 190's? I suspect that published loads using mag-feed lengths will show pressure signs much sooner hence because I was unsure about how safe it was to push to 42.4, I increased length to 2.865 and loaded singly. Incidentally, I got the same marks at a 42 grain load but little difference in POI, although group was not as tight.

[gbal]

Thanks George. What was your seating depth for the 190's? I suspect that published loads using mag-feed lengths will show pressure signs much sooner hence because I was unsure about how safe it was to push to 42.4, I increased length to 2.865 and loaded singly. Incidentally, I got the same marks at a 42 grain load but little difference in POI, although group was not as tight.

COL for bullet jam with StoneyPoint comparitor with the 190 Sierra was 3.353; single load for 1000 comp.

[GeorgeB]

If there were traces of oil left in the chamber, that would considerably increase the pressure on the bolt face due to the brass not gripping the chamber wall.

 

N150 might not give you much increase in velocity, but it should avoid the pressure spike you are getting with N140. As soon as N150 came on the market all the MR shooters switched to it for that reason.

[VarmLR]

...double post

[VarmLR]

I may just switch to N150 George as according to Vhit, it gives higher velocities in the 155gr and 150gr bullets too. I'll reserve the 140 for my 223 loads where pressures are sensible. Using a fired case, and also checking the seating depth with a less than satisfactory Frankfurt Arsenal COAL length tool, my chamber gives a depth from bolt face to lands with the 190SMK as 2.895 inches. I could load closer to the lands to avoid compressed loads.

[GeorgeB]

If you are compressing your 190/N140 loads that would also be contributing to the pressure problem.

[Brillo]

Like you mention, those loads aren't hot and there's no sign of cratering. GeorgeB may be on the right track.

I've mentioned this before on another post and on another forum where a similar query was posted.

 

Some time ago in my glorious Sako TRG days I tried some H4895 loads and observed the same signs you have posted. I queried it on UKV and the consensus was that the case wasn't obdurating (expanding to grip the the chamber wall). I increased the charge by 1 full grain and the pressure signs disappeared.

 

It might be worth doing some more load development from your end point. Just a thought.....

[VarmLR]

I did try lighter loads Brillo, in fact starting at 41 grains. It was only when I went to 42 grains that the marks became apparent. Ditto with the 155SMK loads. Fine up until about 44 grains after which the same marks started to appear on the cases. It's really odd this one, as with some 5-fired cases, I had no visible signs on the cases at all. This has only happened with the new cases.

 

My money's on a combination of factors...I certainly need to clean the chamber properly with a meths or IPA soaked mop. Normally, the bore-guide just goes in (shooting shed aluminium one), Wipeout is patch applied and left for an hour before patching out followed by an oil soaked rag on the jag pushed through.

 

I have been careful every time that a full case is reached that I extend the seating length (ie reduce seating depth) so as to avoid compressing charges.

 

For my 155 loads, full case appears to be around 44 grains at 2.800, with slightly compressed loads by 44.5 grains.

[baldie]

Clean the chamber and bore. the ejector marks are not excessive powder/pressure signs, but lack of chamber wall grip.

 

Barrels don't need oiling unless your cabinet is damp/ chrome moly barrel.

 

An oiled bore is dangerous in a rifle, and can be catastrophic in a shotgun.

[VarmLR]

Clean the chamber and bore. the ejector marks are not excessive powder/pressure signs, but lack of chamber wall grip.

 

Barrels don't need oiling unless your cabinet is damp/ chrome moly barrel.

 

An oiled bore is dangerous in a rifle, and can be catastrophic in a shotgun.

 

Good advice baldie and advice I will act on. Old habits die hard. I normally dry patch all my firearms before firing and have always lightly oiled all my barrels after use and cleaning, a practice I'll now stop.

[VarmLR]

Chamber and bore cleaned through with a meths-soaked mop followed by dry patches. Put a torch onto the chamber and looks very clean except for very slight score marks left by brass cases. Will re-shoot the problem loads and see how it performs. Cleaned the bolt for good measure, paying close attention to bolt face.

[Brillo]

I did try lighter loads Brillo, in fact starting at 41 grains. It was only when I went to 42 grains that the marks became apparent. Ditto with the 155SMK loads. Fine up until about 44 grains after which the same marks started to appear on the cases. It's really odd this one, as with some 5-fired cases, I had no visible signs on the cases at all. This has only happened with the new cases.

 

My money's on a combination of factors...I certainly need to clean the chamber properly with a meths or IPA soaked mop. Normally, the bore-guide just goes in (shooting shed aluminium one), Wipeout is patch applied and left for an hour before patching out followed by an oil soaked rag on the jag pushed through.

 

I have been careful every time that a full case is reached that I extend the seating length (ie reduce seating depth) so as to avoid compressing charges.

 

For my 155 loads, full case appears to be around 44 grains at 2.800, with slightly compressed loads by 44.5 grains.

I meant higher to get the case to expand and grip the chamber wall as Dave mentioned. In the case of my TRG I saw what looked like pressure signs with X grains of powder as prescribed in one reloading manual. When I increased it to X+1 grains, which was OK in a a different manual, those signs disappeared.

[VarmLR]

Noted Brillo, but I'd like to re-fire the loads now that the chamber has been thoroughly cleaned back. I've shot the 44gr loads previously without any pressure signs in warmer weather too, so after what Baldie and others have said, my money at the minute is that there was a slight oil film in the chamber causing the problems. If cleaning has't solved it, I'll then carefully increase loads and look for other pressure signs as the loads increase. One thing at a time though. Thanks to you and everyone else who has offered a view and advice.

[VarmLR]

Armed with squeaky clean chambers, put a few rounds downrange today using the same loads. No repeat of the pressure signs, so I've put it down to slight traces of oil in the chamber....lesson learnt!. Also had more consistent groups from the 190s which proved to be very accurate at 600.