Berger Bullet Seating - accuracy problems????

[sevenmil]

I am an F Standard shooter with just under 2 years experience - I have been shooting reasonably well (won a few badges at various OPMS in A Grade). Whilst I still have a lot more to learn, I have been shooting reasonably well and only just missed out coming 2nd in our club championship by one point last year.

Of recent time however my scores have dropped off a fair amount and this coincided with starting with a new batch of 308 Berger projectiles (155.5gn batch No. 6190). This particular batch BTO measurement were 14-15 thou different to last batch which shot brilliantly (batch 3883) - I didn't adjust my seating die when I went to this new batch, so I have been jamming them slightly into the lands more than the last batch.

Last week at a 600m match my group opened up dramatically (went from X's to 5 and back to Xs with elevation shots) - there wasn't that much wind, maybe 1 moa, so the only thing I could think was that there might be pressure variations given this new batch are 14-15 thou different).

Have any of you had similar experiences with different seating levels ?

[Brad Y]

When ever you change batches of projectiles, you will need to re confirm seating depth, possibly velocity and definitely accuracy. Sometimes you will strike it lucky and just be able to continue on when you left off, but other times you can get caught out with bearing surface length changes and diameter diferences. I got caught out horribly with some 6mm hybrids. The good thing is you generally wont make the same mistake twice

[Longranger]

New batch number means retesting. A bit of a pain but unavoidable. Generally, while there are often differences between lot numbers, they are usually fairly consistent within that lot.

Buying in large quantities saves load development work.

[saum2]

You have answered your own question, there is 14-15 thou difference in seating depth and it WILL make a difference compared to your previous seating depth and scores.
As Brad Y suggested, remeasure using the new projectiles and seat them to the same seating depth as the old batch, a pity you don't have one projectile left of the old batch to measure throat erosion as this could also be a factor with seating depth. You have to find the sweet spot with the new batch.

[sevenmil]

Thanks guys - I thought that's what you were going to say. Intrinsically I thought that was the case, of course I had to confirm this the hard way at the NSW Queens recently…… Dropped 9 points on the first day with that new batch and was fighting over the next few days to recover, but no luck. I thought something was wrong on the first day at 300m. The shots I was pulling felt good and I normally get possibles at 300m, sometimes dropping a point in bad wind, but that first day I dropped 5 points at 300m which didn't make sense as the wind wasn't that bad. Then dropped another 4 points at 600m again, wind not too bad.

I should have known, but at the time of loading I didn't have time to test the new batch and thought it probably wouldn't make that much different as the last few different batches all shot well without adjusting depth.

You are right though, I won't make that mistake again!

Thanks for your feedback, really appreciate it….

[aaronraad]

Of recent time however my scores have dropped off a fair amount and this coincided with starting with a new batch of 308 Berger projectiles (155.5gn batch No. 6190). This particular batch BTO measurement were 14-15 thou different to last batch which shot brilliantly (batch 3883) - I didn't adjust my seating die when I went to this new batch, so I have been jamming them slightly into the lands more than the last batch.

I'm thinking that if you haven't necessarily adjusted your seating die then you haven't necessarily adjusted your seating depth either...unless 1) there has been a dramatic change in the ogive profile between batches???

If you set-up for a jump previously, you should still get a jump again. I could see some issues with a double ogive design if your seating die picks up right on the interface between the two ogives but a single ogive should be relatively consistent even if the ogive length does change...unless 2) your seating die is pushing off the meplat instead of the ogive nearer the shank???

So if all of a sudden if you're noticing a jam scenario there is more than likely something else going on.

Check if there is a change in boat-tail length, but this is not likely. A change in ogive length (for the same profile) will also be evidenced by a change in the meplat OD, so it's easier for comparison. The most likely place for a change to take place is in the bearing surface length.

I've read of one instance where a 0.009" variance in bearing surface resulted in 1 MOA of vertical at 1000y, but haven't found any other work on the subject to date. Accuracy wasn't affected, just point of impact in this case.

If your powder charge is close to 'compressed', you may have been getting a false seating depth measurement from your original load. Projectile can spring back off the powder if the right neck tension is in play and still feel like there was no tension when closing the bolt and not leave any visual rifling marks on the projectiles surface.

Hope the answer is simple anyway.

[ecomeat]

Sevenmil,
Can you get someone in your area with a Borescope to have a quick look in front of your chamber, to rule out carbon fouling being a problem (any fouling for that matter !!)
I scoped two x 308's over the QRA Queens, and both had a "significant issue " with carbon fouling. One of those shooters applied an abrasive paste carefully, and did a great job of getting the carbon out. A couple of weeks later he won a Range at Goondiwindi OPM.....which wouldn't have been at all likely going on the way it shot at Belmont.
I haven't see the other one since, but it's owner has a strong reputation for performing well in TR normally. Seeing the Carbon baked in multiple layers in the throat of his barrel, it's no wonder he had a fairly ordinary QRA Queens.
Without a Borescope to verify your cleaning process and results, you are simply guessing, in my opinion. Especially so with carbon.
How many shots down this tube, Sevenmil ? Has anyone ever looked down it with a Borescope ? Have you used JBs, or Iosso paste , or KG2 or similar in it ? How many shots ago ?
Matt P has one

[ecomeat]

Another thought......the new bullets measured 0.014"-0.015" longer base to Ogive.
If you are measuring your loaded round length with a Comparator, on a decent caliper, after seating with the identical seating die setting, in my opinion, unless you have got a really odd batch, it should show that you are seating 0.014" further into the case (so less room in there = more pressure = higher velocity = maybe too fast and off the node), and NOT that you are jamming 0.014" further into the lands.
Or are you actually saying that the "Cartridge base to Ogive" of a loaded round.....measured with a decent micrometer and a 7mm Comparator........is 0.014" longer with the new batch of bullets ?
My shitty old Sinclair "Nut" actually measures 0.277 for the 7mm hole, so seeing as Bartleins are 0.278, and Maddco, Brux and others are 0.277" Bore measurement, it should be giving me quite accurate cartridge overall length (to the Ogive) measurements.
I am keen to hear a bit more about your measuring.

[plumbs7]

As always , there's plenty of good advice above ! So I don't know if mine will be much help!
The cause of vertical are many ! Just make sure ur not cooking the round in the chamber before u pull the shot . This quite noticeable at 600 yds and on! Could be crook powder ? Could be some round not jammed then some soft jammed giving different pressures !
Regards Graham.

[plumbs7]

Check extreme spreads on a chrony to make sure !

[Barry Davies]

Just for the record. I have ( currently ) two batches of Berger 155.5's with 56 thou difference in base to ogive measurement. This 56 thou is all in the parallel length. If you seat with the same jump you have 56 thou more projectile in the case ( equating to 56 thou less case capacity)
Differences such as this require a serious look at load, for obvious reasons, which in turn invariably requires a retune to return accuracy.
It seems to be a problem that all manufacturers cannot overcome, and is really a pain.
For what it's worth I find Sierra's have the least variation and don't require any major retune -- maybe a few thou on seating depth or a few degrees turn of the tuner.

[bartman007]

It may not be the change in projectile either

If after some more load development things don't come good, get your armourer to check/renew the crown. It may have been damaged during cleaning. Anyway, for a few bucks it is worth getting renewed.

[sevenmil]

Hi guys - thank you all for your feedback, all valuable information. Just to rule out some of the variables, my crown is fine, the powder (2208) is a fairly new 4kg batch, but there could be fouling going on. I have only put about 1400-1500 rounds through the barrel, but I have got into a habit of not cleaning the barrel for up to 4, 5 or 6 matches - it didn't seem to affect accuracy, in fact I thought the gun liked being a little dirty, so maybe I overdid it. I might ask Matt P to use his borescope to have a look.

In regard to the projectiles, there was definitely a difference in ogive shape. The best shooting batch were actually longer and the ogive was more tapered compared to the new batch which appeared smaller and fatter - when I first cycled tested a dummy round, the new projectiles grabbed a bit, so I back of about 1 thou, but I don't think this was enough. After measuring 14-15 thou difference, I have now back off my die by this amount, so I'll see how they fly this Saturday.

Bloody target shooting, its as bad as golf !

[DannyS]

In my barrels, I have found that the 155.5s like to jump rather that being jammed, they also appear to be very tolerant of the amount of jump. Very quick to dismiss, suggestions such as re-crowning, but you do have a fairly high round count. So many variables in this sport at times. Don't automatically blame a batch change of projectiles.

Cheers
Danny

[ecomeat]

?.......... but there could be fouling going on. I have only put about 1400-1500 rounds through the barrel, but I have got into a habit of not cleaning the barrel for up to 4, 5 or 6 matches - it didn't seem to affect accuracy, in fact I thought the gun liked being a little dirty, so maybe I overdid it. I might ask Matt P to use his borescope to have a look.

My money is on the Carbon ......multiple layers of it hard baked on with copper in between like a special lasagne !!