Weirdly one of my guns hates .177 JSB exacts...

[Shed tuner]

Just on the chrono, I've a mk2 TX that slightly favours lighter pellets, but gives good, consistent power with all of the following:

RWS Superdome
H&N FTT
JSB Exact Express
Defiant 7.5
BSE elite (just happened to have some )

...but is 2FP down with JSB exacts

Which is a shame 'cos they are a great pellet - but clearly not in this gun !

(And for the "just shoot it" brigade, yes, the exacts are not half as good in terms of accuracy either - expresses on the other hand are mustard)

Weird !

[secretagentmole]

But what head size did you try? It might be it needs to be a different head size or batch to get the power back up. I gave up with JSB pellets a long time ago!

[Dodger21]

Jon
Is that 2ft/lbs down with one particular size of pellet?
I.E 4.51 to 4.53 or have you tried several sizes, poor fitting pellets either way will show lower power.

Not trying to be clever here just interested.

[chrisbaker42]

My hw100 has a problem with JSB Eacts but only 4.51's, it loves 4.52's.

4.52's give sub 5p sized groups all the time, 4.51's are anything up to two inches apart.

[RobF]

Post 38 on this thread may prove of interest

http://www.shooting-the-breeze.com/f...ad.php?t=25906

fwiw, i've got 2 batches of express that give a guestimated 30mm drop at 55 yds difference. I'm not entirely too sure the flatter one isn't gaining 1 ft-lb at the muzzle either. (in the springer).

the joke is the flatter pellet is shocking to group in my pcps, but really good in my springer. Same head size, which as someone else seems to think (by that old fashioned thing of actually measuring things, is a nonsense)

[Shed tuner]

very interesting that STB thread...tried another batch of 4.52s... better but still 1 FP down on everything else. Group better though.

Even just that difference between batches (supposedly same head size ) is pretty scary !

[RobF]

very interesting that STB thread...tried another batch of 4.52s... better but still 1 FP down on everything else. Group better though.

Even just that difference between batches (supposedly same head size ) is pretty scary !

Yep.

People used to look at me oddly when I said I rezero'd when I changed batch... imagine what it's like at 55 yds...

[Shed tuner]

Yep.

People used to look at me oddly when I said I rezero'd when I changed batch... imagine what it's like at 55 yds...

Yeah, I'm testing at 28 and it's 3/4" !!!

[RobF]

Yeah, I'm testing at 28 and it's 3/4" !!!

Yep.

Once you see the effect revealed clearly, it does throw into sharp relief a lot of other theories about things happening to pellets doesn't it... we've kind of assumed one tin, headsize, hell even shape, should produce the pretty much same trajectory down range... but it don't.

It opens a right can of worms when you see significant changes in trajectory depending on batch don't it...

Question... comparisons made over time... all used the same batch? The correct answer in my opinion should leave you with a little sick feeling

[Amac]

I love it when I find a gun that prefers anything other than JSB. I have a Daystate that doesn't like them at all in the mags. Superdomes work best!

Andy

[thevoid]

I can draw quite a few parallels with your results, in my little old HW50 I too find 8.44 exacts to be down on power, for instance I can get 8.64 FTT shooting 775fps where the exacts are around 720!
Best groups for me were FTT (back a few years ago where the QC was much better than now) supremely efficient and the shot cycle is superb.
Now I shoot exact RS, I still hanker for FTT but I cant be arsed to size them
superdomes, I've yet to find a springer that superdomes feel nice with. the shot cycle seems almost percussive, even if they group they just feel horrible

[Shed tuner]

So wanted to keep this general first to gather experiences without derailing the thread, but know seems a good time to add some further info...

The barrel previously worked great with Exacts - it's a TX mk2, and both before and after with the usual short stroking, HW seal etc it shot very well with them.

However when I put the 23mm powerplant into the gun, the significant degredation in performance with (just) them occurred. A fwe hours ago I managed some further testing outside and noticed another effect; even with pellets it likes, it is very sensitive to slight deformities in the pellet skirts causing minor fliers (say 1/4" from the main group). Right now I'm thinking that my new powerplant is somehow lacking in supplying an air blast to the back of the pellet strong enough to expand it / seal it / push out any deformities.

I'm going to try some thinner skirted AA fields and see if this improves things. I may also try tweaking the powerplant (more piston weight, for example) to try to give higher pressures...

I'm also going to swap this power plant into a mk3 TX (that also loves Exacts), to see if the same effect occurs, or if it a unique combination of barrel / lead in and powerplant.

Finally, a comment on superdomes from Paul's post - they are pretty tight, so will sap a bit of power on most springers, and cause piston bounce (nasty cycle, feels slammy), unless either i) you have a large / loose bore / lead in ii) you have a gun that is tending to slam.

Weirdly however, they shoot fairly well in this gun, and it has neither of those characteristics - maybe it's because the 23mm is much more resistant to piston bounce...?

Rgds - JB

[TonyL]

Crikey, Jon.

Post 12 gives some serious food for thought and ought to, rightly, be a thread starter in its own right.

Going to have to log off very soon, but I can see this being very absorbing and it'll be more than a little interesting to see if it's the barrel or small bore powerplant.

[RobF]

Jon, make sure you test with another batch.

That was my point. Drawing conclusions when you haven't been using the same batch or haven't used more than one is futile. The batches can throw poi changes and flyers at short range and it can be down to that solely rather than the power plant. This I know by testing several with the same power plants.

[Steyr]

Why is it Weird. You have been around long enough to know barrels are individual. And that even head size or batch/Die number can make a big difference.