Odd pressure issue

[Mr_Logic]

Right folks, an odd one I could do with hand solving!

On the 223, I made a load to shoot yesterday which I'd tested the week before and was all good (albeit only 5 rounds)

It is 25.5 N540 behind 80 A max seated 5 thou off at 1.965 to the ogive. Brass PPU (although properly worked on!) and primer Rem 7 1/2.

Most of the firings are correct - they give a still-rounded primer and no problems with extract. My other half was shooting the 223, and was fine for a while, and then was getting the case stuck at extract - good whack on the bolt solved all but not right. We also saw some over pressure signs with gas escape round the primer.

I shot it later in the day, and I had the odd one. The only thing I noticed was that if I took longer than a couple of seconds on the shot, I was getting more of a problem.

The new batch was accidentally made to 1.956 (teach me for doing the loading late in the day!) but initially still shot fine. I did have one that was tough to extract, but the rest were OK. I fired a 2+15, and overall had 3 dodgy ones. The results on target were good - barring a flyer (not an over-pressure shot) I had everything in a .5MOA elevation spread roughly at 1100 yards.

My reloading practice is to use the Chargemaster for each charge, seat the bullet straight after I charge the case. I am confident there is very limited variance in charge weights - being 223 I already watch it like a hawk.

The normal case and the over-pressure version are very different. I am not seeing a tiny variance by the looks of the back of the fired case. I am struggling to explain why the odd one is going so nuts.

Answers on a postcard, or even just back in-thread, please :)

[Steve E]

What was the outside air temp when you were shooting?
This weekend has been unduly hot at +30C down at Bisley and this can quite easily increase pressures. Combine high temperatures with a hot barrel and loads that are close to max can easily go over pressure or show signs thereof.A load that works well in moderate ambient air temps (less than +25c) may well be over pressure when the temps rise 28-30C.
With temps that we have just had I keep my ammunition in a coolbag/box and keep it in the shade as much as possible. I am loading back up ammunition for this weekends shooting and I am backing my .308 loads off by 1 1/2 grains, just in case the temps stay high. Don't want popping primers in the Welsh Open.

Steve

[ovenpaa]

I shot it later in the day, and I had the odd one. The only thing I noticed was that if I took longer than a couple of seconds on the shot, I was getting more of a problem.

I had this Saturday due to heat, if the round was chambered for more than 2-3 seconds it would string vertically on the target so I would suggest the barrel and chamber was getting very warm.

.5MOA at 1100 is good, how MOA did you need to get to the target?

[Mr_Logic]

35MOA with the 1.956, and the 1.965 did seem to be a smidge lower, but equally consistent - I had to switch over mid string.

T'other half put the rifle in slip all day and it was much more insulating than we thought - when I checked the rifle was still hot from earlier so I am sure that would have contributed.

I guess the only reason why it's the odd one is that some are left in-chamber longer than others.

I tested the original ones last week and it was about 24 degrees, so not that different really.

[ovenpaa]

I was seeing a good 3/4MOA and more of elevation climb if I left a round chambered too long Saturday, would put the afternoon temperature at around the 29/30C mark. Is the 25.5 grains of N540 is a typo or are you seating them incredibly long, the Ogive length is not a good indicator as the majority of comparators are just drilled so tend to vary somewhat.

[Mr_Logic]

I'll have to check it, around about 2.5" or so I think though

[essexboy]

As we know each other and I know you are of sound mind etc,I still think you have a pressure spike problem, them N5 powders are known for it when loading at the top end, if your using the load manual for sierra bullets (80g) you may find you are over pressure, I know quick load gives different pressures for both bullets with the same powder load. When I fire up my main pc I'll check for you, unless ovenpaa answers first.

Steve

[dromia]

As Essexboy has pointed out you are over the maximum load in the Vihtavuori published data for an 80gn bullet by 1.8gns.

That is a 7% overload.

I suggest that you stick to published data and read the "Checking for signs of pressure" sticky at the top of this forum.

Primers are not reliable indicators of pressure and a stuck bolt says to me that that load it over the top in the danger zone and should not be used again.

What was your starting load and what increments did you use to work up to the load described in your post and what published data did you use as a basis for the load?

[dromia]

BTW the Vihtavuori data also states that the N540 data was with a test barrel with a long throat so the bullet was seated further out so your load could be well over the top.

With these fiddly little rounds the room for error is small and small differences at the handloading bench can make a big difference in the chamber.

[Mr_Logic]

The published data in question is from Sierra, and has been incredibly reliable. Shooting 223 at 1000+ yards requires it to be run hot, it doesn't work otherwise.

The point of my post was that the majority of rounds were absolutely fine, like the ones I used when originally testing the load. I can only work on the basis that longer strings and a hotter day (albeit only slightly) caused this one.