Advice please pressure problems.

[Mark S in NM]

Sako TRG in 260 Rem, Lapua 260 brass, Wolf primers, 43.2, H4350, 139 Scenar. All brass same lot as were bullets and primers. All brass 4+ fired trimmed to min length. 0.003" chamber clearance. Powder charges weighed 3 different scales. Yesterday 99F 1/2 of loads showed big over pressure, heavy bolt lift, ejector imprints on brass the other half none of the above, perfectly normal. All were ran over chrono and I fired 3 groups of 15 in each string. Ave. 2865 FPS, SD 6. None were exposed to sun and all aprox same temp when fired. I'm at a loss here any help appreciated.

 

[watercam]

As it seems you were very careful with charge weights and you have fired this load 4 times already in all the cases I suspect something to do with the brass. Do bullets all seat with the same 'feel' on the press? Possible there is a donut of brass making its way up from the base of the neck due to lengthening.
Were there major ambient temperature increases lately?
Is the chamber clean?
Any build up of fouling in the throat area?
Other than powder charge weights varying, I am at a loss as well.

 

[bowslngr]

Is it possible that your OAL put the ogive right at the lands, on average? If so, minor differences in bullets result in some being jammed slightly and some falling just short. Those that were jammed result in much higher pressure.

 

[Shynloco]

Mark,
What I'm gonna say is purely a guess (because I don't load for a 260 or use H4350) or perhaps ideas to prompt some thought. In looking up the Hodgdon recommendations for H4350 in 260 Rem, the spread shows 39 - 42 grs and thats for a 140 gr bullet as your 139 Scenars are not even listed. And I noted that your shooting temps were at 99 degrees and some powders don't care for that much heat. In my experiences there are several powders that shoot great in 68 degree temps, but act up in 95+ degree temps. If you rely on velocity results alone, that conclusion (IMHO) can lead to issues. It strikes me that you need to find the threashold for your particular rifle and bullet seating depths that in SOME calibers, lead to pressure issues when the bullet is seated into the lands. That observation is NOT a constant so you need to find out where your works and see if there any difference in pressure by moving say .10 out of the land if you are in. Personally, what I would do, is to drop your powder load by at least 1 gr and see if the pressure issues go away. If so, start working back up to find the "sweet load." I do shoot a 6.5/140 - 142 Bergers and sometimes wish I'd gone with a 260 instead only because that is a very neat caliber in my opinion. Keep at it. Sometimes it just takes time and determination.

 

[bheadboy]

I agree with the two above postings, 99f is pushing the temp even with Hodgden temp stable powders then combine that with the fact that very high BC bullets can have a significant base to ojive length (measure some), and you can get a jam with slight bullet differences, remember the throat is tapered, as the bullets are tapered thus you are matching two tapered faces, a slight change in one will cause a contact that is not expected,

combine that with temp and pressure can go up a lot, one thing also, how long did the pressure rounds sit in the chamber before firing, as the chamber heats up on a 15 round run, you can cause major heat upin the powder/primer wiht the bolt closed on a chamber round particularly if the round sits there 1-3 minutes, remember brass is a very good heat conductor.

Bob

 

[Mark S in NM]

Thanks all, has me baffled but your suggestions give me a place to go. I just finished checking for donut with a look and a pass through with a K&M after sizing with a particularly beat up piece of brass. I'm 0.030" off lands but will check again. I did note some cases chambered a bit harder but did no think to separate at range but I just bumped shoulder back on a few I didn't fire yesterday and now they chamber with just a hint of drag on bolt close but that should not have any affect other than hard closing correct? Powder is same lot I have been using all summer @ 100 degrees I did have same problems at 43.8 and up with Scenar but with all loads not just half so figured no problem @ 43.2 The only thing different was new lot of Scenars and I did not check against old lot. Thinking now I DID seat bullet in 0.020" future than last loads which were 0.010" off lands but that produced no problems in testing. Testing showed that was optimal length and no problem while testing then with same powder charge. I looked at log book and that testing was done at 96 degree's. What also has me baffled is the great SD #'s. I didn't think 2865 was pushing to hard, hard yes but not over the top. Obviously I need to start with a lower charge and go from there. There is a node 42.8-43.5 and know the upper part isn't going to fly. As far as length of time in chamber I would say no more that 5-6 seconds . Shy, the data I have indicates 142 SMK with H 4350 41.5-44.5 for 260 granted no Scenar. Neck tension was 0.002 and all felt good seating.

 

[AJ]

260 Lapua Brass has a thicker wall in the neck area. I have two friends that had to either turn there necks or have there chamber ( neck ) reamed out for the Lapua brass to work in their rifles. This could be the issue.
AJ

 

[Flouncer]

wiht the bolt closed on a chamber round particularly if the round sits there 1-3 minutes, remember brass is a very good heat conductor.

Never thought about that. Very good point. I learn something almost every time I am on this board. 8)

 

[Mark S in NM]

Fired brass measures 0.003" larger than loaded round if add 0.001" spring back that should not be the problem.

 

[338Lapua]

You could try running some Remington 260 brass through it with the same load.

 

[jonbearman]

Sounds like your brass should be annealed to let your die do its job. If some chamber snug out of the lot,that is a sure sign your fairly healthy loads tend to work harden quicker especially if it has extra wall thickness. I would anneal irregardless to a good feel the press gives you. Remember the press has great mechanical advantage and after I anneal it feels like the bullet is falling in ,yet I cant budge it with my fingers. I have also noted that h4350 gets alittle weird at high ambient temps. Some guys keep their loads in a cooler with an ice pack to keep them cool for competition on hotter than frying pan temps,LOL I hope this helps.

 

[Mark S in NM]

Jon the brass had been annealed one session prior to last outing so that is not an issue. I just finished loading dropped the powder a grain and worked back up to 42.8 in .2 grain increment's and will give those a go. My new goal 2800 + or - a few and good ES/SD. I prefer to keep other 'must haves' in my cooler not ammo.

 

[Essential]

Sorry to hear you are having problems with the new TRG, last I knew you were still waiting for it to show up. Let me know if I can help in any way I will be testing some 215gr and 230gr Berger Hybrids over the next couple of days if you want to meet up at the range. Two heads are better than one they say and at the very least you could get some time behind my AICS, too see if you like it. Good luck, Nick F

 

[scott_at_vortex]

What is your annealing process? When I read your OP this was the first thing that came to mind- I wondered if you maybe over annealed and got the brass hot enough to soften up some of the case heads. If your velocities were the same on the over pressure looking cases then this would even further support this.

Anyways, just a thought. I could be way off here.


Scott

 

[Mark S in NM]

Hi Nick, not a problem with the rifle it's a SUPER shooter. I was playing with loads and ran into the pressure problem and I think I found the cause. More than a little embarrassing but I mixed necked down and turned Lapua 308 with Lapua 260 and just enough difference in case capacity to cause problems near max :-[. I will be paying more attention from now on and dropping load down a bit. We need to hook up and shoot a few advise when your heading out. Thanks all for the input. Mark S

 

[Essential]

Hey Mark, PM sent

 

[Mark S in NM]

Update I feel is important. I found the culprit that is a FOR SURE the cause of my problem. While getting ready to pull down the loads I noted some SLIGHTLY greasy cases and on this batch I had switched from RCBS lube with wipe pad that I have used forever to Imperial sizing wax. On a hunch I cleaned some of greasy cases with lacquer left some greasy and headed to the range. Sure enough no problem with the lacquer wiped case's and original high pressure signs with the ones not wiped down well. While at the range I wiped some greasy cases that I had not at home and end of pressure problem. Lesson learned, a simple dry rag wipe down that worked with the RCBS lube will not work at least for me with the Imperial squeaky is clean imperative. The problem cases were not at all lube soaked just a bit slick. Live and learn. :-[

 

[PREMOD70]

Glad to read that you found the problem but I wish to ask what is the .003 case clearance your OP states, is that the headspace measurement and also are you now using laquer thinner as a cleaner for your cases.

 

[Mark S in NM]

The 0.003" I refer to is the amount a loaded round measured at the neck has to expand before contacting the chamber wall at the neck, it has to have clearance for the bullet to release. Lacquer thinner was handy and is cheap so will continue to use.

 

[DOGCAPPER]

I had a temperature pressure problem in Wyo shooting a 223. Bullets began blowing up in a puff of blue smoke..They were sittinng in direct sun and were too hot to hold in the hand...Poured water on them and set in the shade while I cleaned the rifle.. Problem went away...LT