Standard deviatio 95 fps

[Fran49829]

My HW30 began shooting erratically and has a sd of 95 fps over 10 rounds ( 520 to 615).  I pulled the main spring and it looks fine.  The lockup seems good.  Any ideas?
Fran

[eeler1]

Thats an extreme spread all right.  So, not the spring.  Was there a pattern to the fps?  Like started at 615 and dropped continuously to 520?  I suspect the piston seal is the culprit, in any case.

[Yogi]

As mentioned, check the piston seal.  Then check the breech seal.  Put a piece of TP over the barrel lock-up and see if it moves.
Otherwise, inconsistent lubrication.

-Y

FWIW-always check your stock screws.

[Mark 611]

Let's ask a few questions first, did you buy the gun new? if so, how many shots have you put through it? and lastly has the gun ever been opened up?

[MDriskill]

What you describe is "extreme deviation" of the velocity over the shot string. "Standard deviation" is a different bit of mathematical chicanery that analyzes consistency over the string.

Now - with my annoying trivial pedantry out of the way - the usual suspects have been well covered above. But I would also ask what pellets you are using (any gun likes some better than others of course). An odd spike from a diesel, odd drop from a peewee pellets, etc., are not unusual; but if it's gone from "mostly high" to "mostly low" then yeah something is off.

[Fran49829]

I have more information.  Nine shots  609,601,608,569,615,591,525,620,622,=597  ES=97.  Toilet paper moved  but could have just been recoil, I changed the breech seal but it didn't help .  Gun was bought new, first time opened, dry fired once recently.  1000 shots or more.  Barrel is aligned a little to the left.  Barrel has droop. 
If I remove the piston what would I be looking for on the seal.  The gun has always had a slight smell of burning oil.  Pellet choice does not help problem.  Am now using FTT 8.64gr that fit the bore snug.
Fran

[Madd Hatter]

I have more information.  Nine shots  609,601,608,569,615,591,525,620,622,=597  ES=97.  Toilet paper moved  but could have just been recoil, I changed the breech seal but it didn't help .  Gun was bought new, first time opened, dry fired once recently.  1000 shots or more.  Barrel is aligned a little to the left.  Barrel has droop. 
If I remove the piston what would I be looking for on the seal.  The gun has always had a slight smell of burning oil.  Pellet choice does not help problem.  Am now using FTT 8.64gr that fit the bore snug.
Fran

That looks to me IMHO that the skirts have some damage on the low velocity shots.

[Deerstalker]

New HW95L damaged piston seal which was caused by dieseling as the rifle was over oiled/greased at the Weihrauch factory.  FPS varied & dropped just like your chrono readings. 

[Duckfish]

I have more information.  Nine shots  609,601,608,569,615,591,525,620,622,=597  ES=97.  Toilet paper moved  but could have just been recoil, I changed the breech seal but it didn't help .  Gun was bought new, first time opened, dry fired once recently.  1000 shots or more.  Barrel is aligned a little to the left.  Barrel has droop. 
If I remove the piston what would I be looking for on the seal.  The gun has always had a slight smell of burning oil.  Pellet choice does not help problem.  Am now using FTT 8.64gr that fit the bore snug.
Fran

Start with the easy stuff first.

Did you clean the barrel?  Patch worm and Ballistol till the patches come out clean.

[Mark 611]

I'm going to agree with Dave, JMO as well, which is why I always preach to open the gun up after test firing it, step#1 always is to clean the barrel first! step#2 shoot it for accuracy, usually less than 50 shots! if all is well? take it apart and clean out all of the factory lubes!!! Period!!! Step#3 deburr it! step#4 check piston seal fit and for damage!!! if all is well? step#5 re lube it with the correct lubes in the right places and use them sparingly!!! step#6 put it all back together! Now this is how I do it, I also tighten up the spring guide to spring fit, I also add a top hat or at least a DELRIN washer between the open spring end and the top of the piston! I will shoot this type of home tune as long as the spring noise is gone and the rifle behaves like it should? if not I will do a full-blown tune with and ARH spring kit and a new piston seal! IMO you need to just buy all new parts like I just described and start fresh with a tune up!!! YMMV

[Fran49829]

Thank you for all your help, i really mean that.  I did sand down my breech seal which helped with barrel droop and lock up.  My groups are better but not good enough running 1/2" at 20 yards.  It used to shoot around 1/4" at 20 yards.  I like to shoot pencils, matchsticks and flies at 20 yards.  I ordered a ARH tune kit and will see if that will help.  Thanks again for your help.
Fran

[Fran49829]

HW30S is fixed.  Piston seal and to much lube were probably the main culprits.  I installed a ARH Deluxe HW30 kit with Hornet seal and a homemade  piston sleeve and my velocity for AA 8.4 gr averaged 622 fps with an extreme spread of 10fps.  A different tin averaged 617 fps with ES of 9fps.  So I am happy with the velocity, (no more 95fps ES).  The accuracy is back to normal at 20 yds, can hit 1/4” spinners most of the time, same with pencils.  Thanks for your help.

[Mark 611]

Good to hear!

[EMrider]

HW30S is fixed.  Piston seal and to much lube were probably the main culprits.  I installed a ARH Deluxe HW30 kit with Hornet seal and a homemade  piston sleeve and my velocity for AA 8.4 gr averaged 622 fps with an extreme spread of 10fps.  A different tin averaged 617 fps with ES of 9fps.  So I am happy with the velocity, (no more 95fps ES).  The accuracy is back to normal at 20 yds, can hit 1/4” spinners most of the time, same with pencils.  Thanks for your help.

That is good news, congrats.  I have an ARK kit on the workbench waiting to go into of my R7s too.  The gun is shooting about 6.4fpe and I think it is time for a refresh.
R

 

[Fran49829]

I checked  my HW30S velocity again after the ARH deluxe  kit, and piston sleeve,  AA 7.33 646 fps, and AA8.4 584 fps.  The AA 7.33 are more accurate. Maybe my first velocities were wrong.  Does the ARH deluxe kit normally reduce velocity?  I am not complaining as the rifle is scary accurate for me.

[splitbeing]

The smoother shot cycle of ARH springs sometimes comes with less velocity than OEM as they break in. Totally worth it. If its accurate and tight ES and you like shooting it, don't change a thing.

[Mark 611]

The new piston seal is probably bedding into the tube and has a better fit, called break-in, a lot of times the velocity increases, YMMV