6.5CM, RS62, overpressure signs.

[MikeJ]

Good day to all. I acquired a Bergara BMP in 6.5CM a year ago and have been enjoying shooting and reloading for it. Range access is limited to 200 yards, but best 5-shot groups of 0.5MOA were achieved using 139g Lapua Scenar, Petersen LP brass and either 40,6 or 42,5g RS62. I have thus been using the lower charge, which gives around 2610fps. The higher charge gives 2750fps. However, with the higher charge, there is some flattening of the primers (not to the extent that the shoulder is squared off though) and a barely discernible ejector mark on the case head (although no sign of "swiping" or sticky bolt lift. The higher loads were behaving fine at Bisley 1,000 yards, but should I be concerned at the faint ejector marks? 

42.5gr RS62 doesn't appear to be a hot load - I have read all Laurie's articles and the various posts on here but was wondering (a) whether the faint ejector marks should be cause for concern and (b) whether others using the same combination might offer some observations?

Thanks for any thoughts...……..

[Brillo]

It sounds like the cases are not expanding and gripping the chamber wall quickly enough, so they are pushed back against the bolt face as the powder ignites. From my own experience this gives similar symptoms to over pressure signs.

2750 fps is modest for the 139 Scenars, especially as some push them successfully at +2900 fps. 

My own CM likes 142 gr SMKs at 2850.

I suggest increasing the charge weight and you’ll find those pressure signs disappear.

[MikeJ]

Thanks Brillo - I hadn't thought of that. I had come to a conclusion that 2750fps was a decent speed for the Scenars (it's certainly accurate at that speed) and higher loads didn't seem to improve matters. I shall try some further loads and maybe see you at Severnside again!

[DaveT]

The symptoms that Brillo describes can also come from not cleaning lube off of your brass properly or having the chamber contaminated with lube.

Worth a check.

[MikeJ]

Thanks Dave. These were once-fired and neck-sized; no lube involved. I also shot the lighter loads at Bisley and they seemed unaffected, but I will give the chamber a brushing just in case.

[Catch-22]

Dave, are the cases sooty at all? If so it is usually a symptom that shows with lower velocity charges where the case hasn’t fully expanded to seal the chamber, which allows soot to cover the case.

[MikeJ]

No, not at all sooty. It's the higher load which was the potential "issue", not the lower load. I'll load up some new, unfired and see how that looks after it's been shot. Not the weather for it today though!

Something strange though - have just cleaned and resized the cases with the slight marks and found that the primers slip in with very little effort, so I'll dump them. I'm absolutely sure that I loaded with 42.5gr RS62; the only difference to the other, lighter loads was COAL of 2.825" rather than my usual 2.800". 

I must have learned something from this, but I'm not sure what 😞

Thanks,

Mike.

[DaveT]

Loose primer pockets are a pretty good sign of pressure excesses or brass which is getting on a bit re to many firings.

I have not used Peterson brass but it looks good on inspection....  how many times fired.....just the once?

[DaveT]

You don't mention load length or neck tension.

Brass from the box can have too tight a neck (Lapua certainly does) which increases initial pressure.

Loading way too deep or too close / into the rifle can raise pressures.

I have no RS load data to hand re powder charges but you say that you have researched so I am assuming your high charge us within reasonable limits.?

[DaveT]

If 42 and a bit grains is causing ejector marks and loosening primer pockets then hot load or not its too much for your specific rifle.

[DaveT]

One last comment..... its unusual with this size of case to find accuracy nodes a whole 2 grains apart.... at least in my experience.

I suspect that you have another good grouping load to be found right in between the two charges you mention.

[DaveT]

Just noted your load length of 2.825....  are you on the rifling by any chance?

[One on top of two]

6 hours ago, Brillo said:

It sounds like the cases are not expanding and gripping the chamber wall quickly enough, so they are pushed back against the bolt face as the powder ignites. From my own experience this gives similar symptoms to over pressure signs.

2750 fps is modest for the 139 Scenars, especially as some push them successfully at +2900 fps. 

My own CM likes 142 gr SMKs at 2850.

I suggest increasing the charge weight and you’ll find those pressure signs disappear.

Top post , and bang on the money 👍

[MikeJ]

DaveT - thanks very much for your observations. Cases were 2x fired (not 1xF as I mentioned at the beginning). As for the nodes, I have checked my notes and found the two loads mentioned at the start were those which gave me 1/2" groups of five shots at 100 yards so I stuck with them. I'll start again and work through to see whether anything has changed. As for COAL, I took the 2.825" to be the "official" maximum length, which with the Scenars I doubt would be jammed into the lands. I will, however, make further measurements as this is the only thing that has significantly changed. Previous loads were all at 2.800" with this bullet. RS load data availability is very limited, and I hope that I have been erring on the side of caution. I've no means of measuring neck tension other than by measuring the neck i.d. and subtracting it from the bullet diameter, but there was nothing unusual encountered during the loading process. I'm beginning to think that the issue may just be with the OAL of the cartridge.

Brillo, 1/2/2, thank you both for your comments too.

kind regards

Mike.

[baldie]

First thing to do, is junk that brass. I wasted an entire day trying to work up a load in my new AXMC creed barrel.

Couldn't get anything below 1 1/2". Never, in the years i've been building creed moors have I seen that happen.

Peterson brass looks good, but it appears to me , to be fairly thick walled.

I resized the brass and tried again, the groups came down to about an inch. Nowhere near good enough.

Replicated the loads with small primer lapua brass, and bingo ! It shoots .2" regularly, and probably the most accurate barrel in creedmoor I've ever had. Its a cut rifled Sassen.

The peterson primer pockets were loose after the first firing, never again.

Try Vhit 160, its a very good powder with 140/142 bullets. Mine is doing 2875 with a 142 SMK.

[No i deer]

22 hours ago, Brillo said:

It sounds like the cases are not expanding and gripping the chamber wall quickly enough, so they are pushed back against the bolt face as the powder ignites. From my own experience this gives similar symptoms to over pressure signs.

2750 fps is modest for the 139 Scenars, especially as some push them successfully at +2900 fps. 

My own CM likes 142 gr SMKs at 2850.

I suggest increasing the charge weight and you’ll find those pressure signs disappear.

I'm not really sure how that works Mark if there's only 2 to 3 thousanths head space. I guess the ejector is pushing the case into the front of the chamber so there's that miniscule movement backwards that causes witness marks.??

How does this work with a non ejector bolt then..

You set your head spacing up and the cartridge is free to move back and forth in the chamber with the bolt closed as there's no ejector to push the cartridge forward...???

 

[DaveT]

Brillo is refering to the case neck expanding to grip the chamber and then the case stretching back under restraint rather than slamming back under pressure if the front end does not grip.

[No i deer]

I understand that Dave but how can you prove the theory that the case moving backward 2 thousanths does this...

[MikeJ]

8 hours ago, baldie said:

First thing to do, is junk that brass. I wasted an entire day trying to work up a load in my new AXMC creed barrel.

Couldn't get anything below 1 1/2". Never, in the years i've been building creed moors have I seen that happen.

Peterson brass looks good, but it appears to me , to be fairly thick walled.

I resized the brass and tried again, the groups came down to about an inch. Nowhere near good enough.

Replicated the loads with small primer lapua brass, and bingo ! It shoots .2" regularly, and probably the most accurate barrel in creedmoor I've ever had. Its a cut rifled Sassen.

The peterson primer pockets were loose after the first firing, never again.

Try Vhit 160, its a very good powder with 140/142 bullets. Mine is doing 2875 with a 142 SMK.

Thanks David. A while ago I weighed my once-fired brass with the following results:

Peterson 175gr, Sellier & Bellot 165gr and Hornady 155gr each having water capacities of 3.35cc, 3.38cc and 3.45cc respectively. Your conclusion that the Peterson brass is thick-walled thus seems sound. The primer pockets are still tight in the Peterson cases which had the lower powder charge.

On the matter of my COAL of 2.825" for the 42.5gr RS62 loads, I have measured a round with the bullet set against the rifling and that gives a COAL of 2.910", so from this I would assume (perhaps wrongly - always happy to be educated, please!) that there would have been a good 75 thou' jump to the lands.

Perhaps the difference in case capacity between, say, the Peterson and Hornady brass, of 0.1cc is enough to cause 42.5gr RS62 to go over pressure (although I used a long drop tube and there was no "crunching" when I seated the bullet.

I'll give N160 a try (I had been thinking N150 but will take your advice).

[baldie]

Folk do use 150 with 140 grain bullets, I've always thought it a little fast, unless you have a short barrel. I've long used 150 with 123 grain bullets in the creed however.

160 works very well with the heavier bullets. Its the go to favourite in the 260 rem with heavies, the creed is not a lot different.

[DaveT]

+1 on Daves post if it helps.....although I use the N5 series equivalents

[MikeJ]

Thanks both! N160 is on the list - I'll be trying it out soon!

[geek]

1 hour ago, baldie said:

Folk do use 150 with 140 grain bullets, I've always thought it a little fast, unless you have a short barrel. I've long used 150 with 123 grain bullets in the creed however.

160 works very well with the heavier bullets. Its the go to favourite in the 260 rem with heavies, the creed is not a lot different.

I use N160 (41.5) using Lapua 139s, in my (son shoots) Ruger PR (24" barrel). Getting approx. 2614 ft/s and no problem operating the electronic targets at 1000 yards. Yes, I could load no powder, but haven't felt the need.

For reference using N160:

41.0 - 2574 ft/s

40.5 - 2554 ft/s

[markymark]

Hi guys. Hope I don’t mean to hijack the post. I’ll soon be working up a load for my Creedmoor’s in both 130 & 140gr. 
 

I’ve previously worked up RS62 42.5gr with 139gr to good effect. 
 

I was going to use RS62 because I have it in stock. However I have one barrel at 26” and one barrel at 18”. I assumed I would hopefully work up a load that would work on both. Accepting a lower velocity on the 18”. Not being a huge reloader I’m never sure which powders compliment what application. Fast vs slow burn rates. 
 

I’m toying with the idea / hoping it might work having one bullet / one load for all applications (across two rifles). Bullet being Sierra 130 GMK not being the best BC but good enough and can use for range and hunting. (Potentially also Sierra 140 SP)
 

Baldie mentioned N150 is better for shorter barrels. 

Do you think RS62 is realistic for my application or should I use two powders and two loads to get the best out of each rifle / application. Such as N150 / N160 or anything else for that matter. 

[geek]

5 minutes ago, markymark said:

Baldie mentioned N150 is better for shorter barrels. 

When changing powders to Vihtavuori for the 6.5CM, I was advised by someone who has forgotten more than I know to use N160 for 139s, but N150 for 123s.