Would anyone be able to offer me some advice? I have a Sako 75 stainless synthetic rifle which is chambered for 6.5 x 55 and have just started reloading, I am using a recipe that shoots fantastically in my friends Sako 75 Hunter, but for some reason will go overpressure in my gun. When you chrono the loads they shoot about 150 fps faster out of my gun. I have tried it with a spotless barell dirty barell and all give the same result. I find that if I only shoot 5 rounds from a cold barell the bolt will lift easily but anymore and it starts to be a bugger to open. Any advice why this might be happening when the guns are from the same manufacturer out of the same factory? I have thought about dropping the powder load by 1 grain to reduce the pressure but just wondered if anyone had any simillar experiences and why it happens.
Thanks

If I were a gambling man I'd bet it's a seating depth issue with the bullets. If your gun has a shorter throat maybe the bullets are jammed into the rifling which would raise pressures.


Eric

Different chamber geometery, different throat size, different free bore, different bore diameter, difference in bore roughness/smoothness, possible temp change between when cartridges were fired.
Even though both rifles are of the same manufacture no two rifles are them same. They likely were built on different days and the chambers/bore cut with different reamers. This is a good example of why one should start low and work up a load. The manuals don`t do any more then report on one set of components, in one test bed. The chanches are your rifle will follow their result closely but there is no garantee.

Thanks for the good advice, I've already checked the seating depth, it is currently set about 0.005" off the lands so that should be alright, I imagine it would be something to do with the bore and how it was cut. I think I'll start near the begining and build the load up again checking with various powder weights etc.

I would say that you have a tighter barrel then your friend.

That will give you higher V:s and pressure problems as the barrel heats up and gets dirty.

In true a pseudoproblem, adjust accordingly and go shoot.

Best regards Chris

quote:

Originally posted by Millwall Paul:
...I've already checked the seating depth, it is currently set about 0.005" off the lands so that should be alright...

You already got good advice with regards to working up a load in your particular rifle, as opposed to using a load which is deemed safe in a different gun.

I wanted to address the comment about seating depth you made. Attention: it is quite common for big game bullets to vary .005" (and more) over the ogive. If you choose a seating depth nominally .005" off the lands, depending on how much your bullets vary, you may sometimes be off and sometimes in the lands. That is almost guaranteed to create varying pressures, with potential varying POI.

IMHO, unless you want to seat into the lands, I rarely use seating depths as low as .005" off the lands, except for small caliber, match bullets. Larger caliber and in particular hunting bullets, I choose a seating depth no closer than .010" off the lands to be sure to be off lands with all bullets.

YMMV.

- mike

It maybe the same Gun ,but the barrel may have been forged on a differnt mandrel.Smaller size chamber or bore and pressures rise.Kenny Jarret does this(Small chambers and tight bores) to increase muzzle vel.on some of his rifles.He wrote an article in The Precision Shooter about this. OB

Thanks again for the advice I'm going to start developing the loads about 1.5 grains lower and then go up in about .5 grain steps. Shoot groups of 3 of each and see how they go.

Thanks