Pressure Problems

[MGS]

Hi guys,I hope someone can help.
Loading 260 (Barnard, Kreiger in Mastin) with 42.5gns 2209, Fed primers behind 139 Scenars. Temps in my basement usually around 15 - 16 C at time of loading. Problem is range temps can be anything from 16 - 18 up to mid 30's. At these temps primers blow and cases are ## after 2 firings.
I am guessing, but in Aus (I am in NZ) do you have similar ranges between loading and range use? And if so, how do you avoid primers & cases failing?


TIA

Maurice

[John Smith]

If you are using .308 cases necked down or .243 cases necked up they will show pressure signs earlier than .260 Remington cases. Having said that, the bore diameter, neck clearance and the possibility of fouling in your barrel can cause increased pressure. Other areas to look at are scales accuracy and seating depth. If a large proportion of the projectile is in the case it will cause a pressure spike. The bottom of the boatail should not intrude past the shoulder of the case. The preferred option would be the bottom of the boatail level with the bottom of the neck.
John

[AlanF]

...Temps in my basement usually around 15 - 16 C at time of loading. Problem is range temps can be anything from 16 - 18 up to mid 30's...

Maurice,

Are you saying you have a place to test fire at 15 - 16C and there are consistently no pressure problems? With 2209 it would surprise me if there was a big difference - the ADI powders are renowned for their tolerance of a wide range of temperatures.

If you've only tested it at higher temperatures, you may simply be using too high a powder charge for your particular setup. And you could look at the things John has mentioned. To use the 139 Scenars, you would need a longer throat than the standard .260 - otherwise you'll be seating inside the neck-shoulder junction as John warns against.

Do you have access to a chronograph? The velocity could be a clue to what is going on.

Alan

[pjifl]

First thing I would be checking is the neck clearance. Measure the necks of the loaded rounds - do you know the reamer neck size ??? Occasionally you will get brass with thicker neck thickness which puts a minimum neck chamber on the edge.
Also check case length - make sure they are not crimping.

Second thing - get some measurents of velocity.

Peter Smith.

[MGS]

Thanks for the replies.
John, "shoulder" of boat tail is at junction of case neck/case shoulder. Lapua is approx .012 into lands.
Alan, load is chron'd at 2880 - consistently. Chamber neck is .297, OD of loaded round is .294. Case is Lapua .308 n/down and turned. Yes, all initial testing for load dev was at range at 15 - 16 C (early am to get still condtns) with no problems.

A friend had an identical rifle made by the same smith at the same time, and he is also having the same load problems. One of the reasons 2209 was used is for the reputed temp insensitivty.

As I have been involved in BR with some success for several years, I am confident that loading etc techniques are not at fault.
Frustrating thing is that accuracy is .5in at 200yds with primers blowing, but picking primers out of the action aint fun.

Again, thanks for the replies.

Maurice

[AlanF]

Maurice,

Try keeping your ammo cool in a chilly bin, but not too cool or you may get condensation forming on it. Then bring it out at the last minute before shooting. BTW 2880fps is reasonably high for 139gn in a 260. So I think you must be running so close to the edge, that even a minor pressure increase is enough to start popping primers. Have you tried different primers?

Alan

[a.JR]

e]

[John Smith]

You might have a fast batch of 2209. My rifle at your load only delivers 2700 from a 28" kreiger in a Nessika. I have found that with the 260 Remington cases you can consistantly use at least one grain of powder more than 308 or 243 necked cases. I have also found that if you want good case life with a 140gn bullet, 2800 is a realistic maximum velocity.
John

[Ken L]

Your problem may be that you are seating into the lands with a load that is above the 42 gn max set by ADI for a 140 gn pill.

Try a loading with 0.025" jump and see if that makes a difference.

[pjifl]

Investigate the neck some more but the following may be interesting.

I run a 6.5 x 55 with an increase in shoulder angle and it is extremely sensitive to bore tightness. I think the case shape helps make it quite sensitive.

I believe Kreiger is very consistent - but know that when moving from one rather tight bore barrel to another, load changed dramatically.

In one, 43 grains of 2209 hammered cases - in the other I can run 45.5 - even 46 grain. Same batch of powder. Same reamer. Same cases. Same projectiles. This would be close to a dangerous load in the other barrel.

With the tight bore I went to 2217 powder (not ideal in some ways but it shot well) - this in the other bore will not even reach required velocity.

I think both bore tightness - and a slightly smaller land width - is the cause of my difference. But shoot extremely well.

Maybe this is all irrelevant but just on the off chance I will mention that 2209 seems too fast in some 6.5's

Peter Smith.

[AlanF]

...I believe Kreiger is very consistent...

I don't Peter. I ordered two 6.5mm 8 twist barrels together, although I can't give a figure, one is much tighter than the other - the looser one shoots better with what I've tried to date. The reason I am sure about the difference is that I made a lead plug for one of them, and it is sloppy in the other one.

Alan

[pjifl]

Very interesting, Alan.

I have no experience of Kreiger personally - only what I hear from others.

At the moment my preferred barrel is Maddco. But that could change.

We tend to buy barrels on the evidence of how they once performed - which may or may not be a good predictor of the future.

My motto now is - never take anything for granted.

Like dont assume Lapua brass and projectiles are always consistent !!!

Peter Smith.

[MGS]

Thanks to all those above.

As best I can I have checked for donut, but can not find anything.

As point of interest, when developing the load above I ran up to 44 gns of 2209 at 2962 fps, with ES 92, SD 32.7 and no problems, but accuracy was markedly better at 42.5 - ES19, SD 6.8, so thats what I settled on. Barrel is 30"

As both of us (ref above) have had the same pressure problems, it seems a little unlikely that we both have tight barrels, but who knows. We dont have means of checking.

At this Sat shoot I will try the cooly bin and post results.

Maurice

[AlanF]

Make sure to keep all ammo at the same temp if you're doing this i.e. don't mix cool with warm, and keep the batches in the same conditions as they warm up when removed from the bin (they used to be called "Chilly Bins" when I left NZ about 30 years ago ).

Alan

[MGS]

Alan, chilly bins are bigger and for the important stuff, like beer.
But I will try to keep ammo all the same as far as temps go.

To those who Emailed me, I have checked head space. Go gauge is fine, No Go is definitely no go.

Hopefully a fine and warm Sat to check results.

Maurice