Increased Pressure in "older loads"

[Ronin]

I'm unsure as wether this or handloading is the correct place for this so apologies if its wrong.

 

The other day I was out with my 6.5x284 and my 308 testing at 400yards. I took the 284 along as a comparison rifle as I know it shoots very well (when I do my bit)

 

Now I usually have 140g SST, 142 SMK and 140 bergers in my MTM case for the "what if" situations one sometimes come across.

 

I tend to have a supply of loaded 142SMK and 140SST's, the Bergers I load for "extended range" as and when I need them. I had 9 cases loaded with 49g of H4350, this gives a very predictable velocity of 2900fps with ES in SINGLE figures, no primer cratering, easy extraction etc etc etc. (usually)

 

Temp was about 15 degrees at the range, which is 1200ft above sea level, iv'e shot literally hundreds of rounds using this bullet powder combination and I expected a 2inch group at the POA.

 

Now I set up with the 308 (AI AW) and fired two strings of ten at the target, changing to the "284" to use as a "control"

 

I fired the first shot, it felt different, more recoil, opened the bolt (which was sticky) and examnined the primer (cratered), no impression of the ejector on the case head, so although I knew I was experiencing "some excess" pressure, I continued with the shot string.

 

 

Now on examining the target all shots went left and high (the wind was blowing ave 12.4 mph and i'd ajusted the scope using Exbal, which I know is bob on with this load.

 

The rounds were obviously going slightly faster than usualy and I can only attribute this to being "stored" for almost three months longer than normal for me.

 

 

Anyone else found similar phenomenon with their homeloads?

[Redfox]

I have had this on a number of occasions. I suspect that it is a combination of factors. The bullets tend to become stuck in the case mouth ( slight corrosion maybe) depending on where stored I have also noticed the Acetone has evaporated from the powder as well. This because our home loads are not crimped and sealed like factory ammo. The powder may be drier ? with this missing and burn faster, the possibilities are many.

I now make ammo only as I need it and for accuracy events always make it in the 2-4 days before I'm going to use it.

An interesting thing to get tp the bottom of for us, I had a favourite load in the 22-250 do exactly the same as yours after about 6-7 months and had no explanation for it, I stripped the rounds left and they were well within what they should have been but definitely hot ones.

Redfox

[Ronin]

Thanks Redfox

 

as you know i'm pretty particular when loading, all cases were turned exactly the same, primers seated same depth, powder trickled to exactly same weights, bullets seated to exactly same depth, I am at a loss to explain this really.

 

One would have thought neck tension is not too high as I use bushing dies that only resize by .002" over diameter of fired case. There is no excess lubricant in the cases - because I dont use it with titanium nitride coated bushings and as far as chemical "corrosion / weld" bettween bullet and case mouth well there isn't any evidence of this in the cases. Accuracy was as expected as well (except for one which was probably down to me)

 

Interesting, but alarming for those using hotter loads - not that this load is, but it certainly turned into one unexpectedly.

[Andrew]

Sometimes non-ball powders will break down from a number of things. If carried around a bit it can happen -especially in loads that are less than 100% density. If you change the shape of the powder kernel, you change the burning rate. Just a thought...~Andrew

[ejg223]

To rule out the slip stick or corrosion between

bullet and case, could you reseat one or two a tiny bit deeper

just before going out. Or pull a head off weigh the charge again

to see drying loss and maybe reload a new case with same type

head and old powder.

 

edi

[Stonewall]

Possibly a change in the neck tension of the loaded rounds caused this. I remember reading that the AMT at Fort Benning loaded .300 Win Mag just before shooting the rounds in matches to avoid this problem .

 

Glenn

[Redfox]

I have done the pulling and weighing and could find no significant weight change, the change would be in the burning rate rather than anything else. I have found that after a period the bullet is definitely "stuck " more firmly in the case, this coud be due to acids from your skin when handling the componenets or the action of the vapour from the powder, a tightening of the grip by the neck which was expanded by the bullet on insertion, storage conditions, the list is long, but the fact remains that rounds do change with time after reloading at home. As already mentioned, factory ammo is crimped and sealed at both ends to minimise change and failure with the end user, we dont do that so it must be one of the variables to consider.

It is an interesting subject and one we can debate a lot more yet, for sure.

I had an instance a year or two back that really made me think. I had gone to have a practice and zero check with the 22-250. It was an average day , not particularly hot or anything, I had about twenty rounds of ammo which was at least 5-6 months old and about 7 new rounds, made the day before. I fired the seven as a 3-4 round group, zero was ok and group ok as well. I then started on the twenty old ones and the first round was a touch higher but I assumed that was me.

The next round the bolt was hard to open and case extraction tight, b**dy hell I thought, must have been an overload ( never had one before by the way) so I chambered a new round and this was much the same, must have made a mess of the weighing I thought, so packed up and went home.

I stripped the other loads and two were less than a quarter of a grain light, the rest pretty much on the dot. The bullets were slightly discoloured at the neck area but only normal copper tarnish not been wet or anything severe like that. I re-neck sized the cases reloaded them with the same powder and inserted the bullets, I had to add a couple of grains of powder but it was from the same tub that they were loaded from originally.

Went back to the field, set up and fired all 18 rounds, reasonably good groups,tiny change in point of impact from the new rounds earlier but not enough to bother and most significantly no overpressure signs at all ( the primers were flattened on the two stingers fired earlier by the way), so I am still looking for a clear answer but I now make ammo just before I need it and dont keep boxes of made up ammo anymore for longer than a couple of weeks or so.

I asked both Hodgdon and Nosler ( I used their bullets then, now on Vmax) for any comments or observations on why they thought this might have occurred, they never replied!

Redfox

[Guest northernchris]

Redfox

 

It would be interesting to try some Nosler/CT lubinox coated bullets to see if that helps.

 

Chris

[Redfox]

You could be right there Chris, it usually drops the pressure and they certainly shouldnt be tight in the case neck even after time.

Redfox

[Stonewall]

A very interesting complicated subject. I once loaded a batch of .243 leaving some of old RCBS case lub inside the neck. That lot shot quite accurately for that year.But when I fired off the remaing rounds of that original lot next spring for brass I got a few flyers until I seated those rounds a couple thou more .

 

The subject on neck tension -"cold welding" comes up quite often on Br.com. Look at the post by Kevin M near the bottom of the page . http://www.benchrest.com/forums/showthread...6615&page=3

 

Glenn

[Redfox]

Good link Stonewall, I have looked at using tungsten dioxide instead of moly, as it has better lube properties without the sulphuric acid drawbacks, better pressure and temperature characteristics and doesn't seem to foul up the barrel like moly either, have you used it either as TD orDanzac?

Redfox

[Stonewall]

Not yet but I have purchased some .6 micron tungsten dioxide recently for possible use in some .308 sub sonic loads. I thought of using this for long term loaded ammunition . At this point I have preped brass and load most ammunition just before shooting.

 

I wonder what would happen if you polished the inside of the neck with Flitz first before loading the bullet ?

 

Glenn