Tony Z

[270]

I read with interest that you thought that 2208 was inconsistant in your 6BR, Was that to do with accuracy?, it seems to be flavour of the month on 6mm BR, did any other powders stand out?
The reason I ask is because some of my loads recently show a lot of vertical stringing at 100m eg .1 moa wide and .6 moa tall.
Any one else got any ideas?

[Ackley Improved]

Mate

Check your setup... vertical like that from a 6mmBR is pretty uncommon I would say... I do not know if it is a handling issue/bag issue... but your saying 0.1"X 0.6" from a 6mmbr...

2208 is a great powder for a 6mmBR.. so is RL-15......

If you cant get your rifle to shoot with 2208 being a 6mmBR and heavy projectiels.. something else is going on.

Cheers
AI

[Tony Z]

270, this is one area i did a lot of long range work in and i am assuming since you are using 2208 you are talking of a long range rifle. If you are using it with lighter pills more suited to short range, then 2206 or BM2 are far better choices.
But let's assume it is for LR.
Early on in the barrels life, or possibly with a particular batch of 2208, this particular 6BR shot very well. At some point, or a possible change of burning rate of another batch, the rifle showed a lot of vertical at all ranges. After checking everything i found that the powder for some reason was no longer giving acceptable accuracy. Even after sourcing some of the original batch of 2208, things were not all that different. The bullets, 107 SMKs at that time were the original long version and were the same batch all the way through. So bullets were out. Other barrels of which this rifle had many, shot fine. So it eventually came down to the one barrel having problems. With our temperature ranges and high ambient heat i had long experienced severe ejector marks on just one or two cases during a string. No real order, first or last or somewhere in between. The loads would range anywhere from 30 to 32 grains of 2208 depending at what time of year it was and always with 205Ms as the primer. This pressure spiking that i was having was a definite ignition problem and i had to this point just lived with it.
In other cartridges i had worked with, any such spiking would have meant a change to another powder. The problem with the 6BR was that the worthwhile options were few. So after some thought i decided to try 2209 and CCI 450 mag primers. I started with 33 grains and kept going until i could get no more in without the bullet backing out from the compressed charge. At 34.5 grains i found the bullets would just stay put with the 2 thou under neck tension i was using. That was the limit i could go to. Pressure was never a problem and in my experience it would be virtually impossible to harm a case or rifle with a case full of 2209 and a 107 grain bullet. The limiting factor is volume, you just cannot get enough in the case and seat a pill over it for it to become dangerous.

The real point is that every load shot extremely well and all vertical had gone. But the LR test is the only one worth knowing and later that year i used that 6 BR to take out the short, middle and long yardages at the annual FClass match here. The important part is that at 900m the vertical spread was less than half a minute and that load was used in that barrel and others since until they were shot out. I have never gone back to 2208 and never deviated from the 34.5 grains of 2209 and bullet jumped about 10 thou in any subsequent barrel.
There have been a few others that have gone to the load i have used and all have found it to be very good. Whether they still use it i don't know.

Now this is one very important point when it comes to 6 BRs. This cartridge is very hard on crowns, just like a 243. If you have just a vertical issue, the crown may not be the problem, but if the group as a whole is really bad, check the crown. If the barrel is between 800 to 1200 rounds old, recrown it anyway as it probably has a worn crown and rods do wear the six o'clock zone and a bullet flung from there will show vertical even if the rest go pure. Our long range HGs and LGs are all recrowned at 400 rounds. 99% of the time with accuracy issues, i can retrace a lot of them back to the crown. Anyone who knows my work knows very well that i spend as much time, if not more, in setting up and cutting crowns than what i do in chambering. An ugly chamber can still perform well if the crown is good, but if the crown is ugly, the perfect chamber is a wasted effort as is any carefully prepared ammunition put through it.

If you have checked everything like bedding, tried another scope etc, my money will be on the crown if the barrel is not too old. The stuff above written about the 2209 load is worth considering as i have never been able to out perform it with 2208. But it has to be the CCI 450 mag primer as anything else just does not get you the velocity.

Jethro Bodine.

ps. After just glancing at you post again, i clearly recollect having virtually identical group patterns of straight lines up the target. Check the crown first then try 2209.

[GriMo]

I dont currently have a 6BR (its on the agenda, just a while off) but that has to be one of the most informative and beneficial posts i have read.

Cheers for that, much food for thought in the future.

[270]

Thanks for such a detailed reply, yes, the groups have gone from round to vertical strings in a matter of a couple of hundred rounds. Will get it recrowned.
The issue of pressure spikes (ejector marks) in the odd random case is all too familiar as well. I'll give the 2209 a run.
The generosity with which you share hard earned information is a credit to you.

[Curtley78]

.... some of my loads recently show a lot of vertical stringing at 100m eg .1 moa wide and .6 moa tall. Any one else got any ideas?

A change in temperature and atmospheric pressure will have an impact upon the burning rate of powder and upon the movement inside a rifle scope.

It is known fact that a mechanical time piece will lose time during cooler periods and gain time during the warmer. It is to do with metal contracting and expanding, this was countered in 1725 with the innovation of Grahams 'dead beat' clock, however any instrument with such meticulous mechanics such as rifle scopes will be prone to such minute malfunction.

Last week at the small bore club on my second last target I accidentally bumped my rifle (having slid my hand under ever so carefully to prevent a spent case from falling on the ground) my rifle keeled over in its front rest, the scope came into contact with the front rest and not thinking I realigned and squeezed off the next shot.

The shot fell into the seven ring, although I had initially thought that the contact between the Scope and the front rest was nothing to be concerned over it was enough to release the internal springs that are responsible for elevation and windage.

That cost me a perfect score last week but I'm fortunate that it occurred during a training night and not during a comp.

I also receive verticle if the rifle is not sitting level in the rest and is pointed slightly upwards or if there is a slight breeze coming from behind-at any time that could be an eighth of an inch.

Given that we are now moving back into the cooler seasons no doubt everyone will need to adjust their optics to compensate for the change of weather, last year I adjusted an inch and a half from the previous winter league and for a distance of no more then 50 meters.

[Simpson]

but that has to be one of the most informative and beneficial posts i have read.

Cheers for that, much food for thought in the future.

Exactly what I was thinking as well!

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