loss of fps/accuracy with same load ?

[fisherman983]

got a question about something I ran into with my rifle. when I had it built last year, my load was a solid 1/4 - 1/2 moa shooter. with 140 bergers it was pushing them at 3265 fps. now that my gun has about 400 rounds down the pipe, accuracy has gone down hill, closer to 1/2 - 3/4 moa and velocity has dropped down to 3125. brass is Remington brand, but the powder and bullets im using now at different lots than when the original load was developed. using R33 for powder and the rifle is chambered in 264 win mag. McMillan a3 stock, bartlein 3b @26" Remington action trued up with jewel trigger.

what would cause a change this drastic?

 

[FEENIX]

got a question about something I ran into with my rifle. when I had it built last year, my load was a solid 1/4 - 1/2 moa shooter. with 140 bergers it was pushing them at 3265 fps. now that my gun has about 400 rounds down the pipe, accuracy has gone down hill, closer to 1/2 - 3/4 moa and velocity has dropped down to 3125. brass is Remington brand, but the powder and bullets im using now at different lots than when the original load was developed. using R33 for powder and the rifle is chambered in 264 win mag. McMillan a3 stock, bartlein 3b @26" Remington action trued up with jewel trigger.

what would cause a change this drastic?

That's one and probably the primary reason.

 

[ShtrRdy]

The energy in various lots of powder can create very different pressures.

 

[gohring3006]

That's one and probably the primary reason.

This is my view as well... I just experienced this with 30-06 and IMR 4350. The bullets were the same but I switched lots of powder and I lost accuracy. Velocity was slower by 50ish fps.

 

[fisherman983]

wow, im very surprised that a powder lot change would change my load so much. im wondering if increasing my powder charge would get me my accuracy and speed back?

my next question is this, for the "package" rifles that guarantee 1/2 moa such as MOA and gunwerks rifles that have their own ammo that can be provided how do they account for things such as powder and bullet lot changes in their ammo lines?

 

[Bbear]

Have had the same thing happen whenever I change lots of powder. Hence the reason I buy powder in 8 lb canisters.
Each time you change a component, be it the case, primer, powder, bullet, sizing die, COALTL, even if it is just a different lot or, you just didn't hold your mouth right when you loaded the 'new' stuff, you should re-work your load.

Since you chanced both your bullet lot AND your powder lot, I'd say you need to re-work your load.
Maybe this lot of powder needs an extra grain or grain and a half to reach previous speeds? Maybe this lot of bullets needs more powder to reach the velocity/pressure combination in your rifle? Only way to tell is to re-work it and see where you reach the accuracy you had, if this set of changes will permit it.

 

[TH]

The same thing happened to me and I ended up having to replace my barrel because it was shot out. I was really surprised because I had less than 500 rounds down the Tube. You might want to buy a bore scope and check out the lands and groves. I was really surprised what I saw....

 

[Mikecr]

I agree with all so far and add that group shooting(if that's what you mean) is not what anyone should do with such an overbore cartridge.
It's barrel life already sucks enough otherwise.

 

[fisherman983]

I agree with all so far and add that group shooting(if that's what you mean) is not what anyone should do with such an overbore cartridge.
It's barrel life already sucks enough otherwise.

I don't usually shoot groups with my rifle, I happened to be testing because I was doing some practice at long range, and my accuracy just wasn't what I thought it should be and I wanted to verify that everything was solid at 100 yards. then wanted to recheck my fps as well......its an enlightening experience, and I will start by buying 8 lb jugs with any custom build I do from now on. after this bear season, im going to have my gunsmith add a different pic rail for my atlas, add another flush cup and do a bore scope while hes got it.

 

[ShtrRdy]

wow, im very surprised that a powder lot change would change my load so much. im wondering if increasing my powder charge would get me my accuracy and speed back?

my next question is this, for the "package" rifles that guarantee 1/2 moa such as MOA and gunwerks rifles that have their own ammo that can be provided how do they account for things such as powder and bullet lot changes in their ammo lines?

I would think they have to tune there load to match the design point they're looking for. This would most likely be done by the powder charge they use for a given group of components.

 

[RT2506]

Yep could be different lots of components but very well could be your lands are eroding and you need to "chase the lands" by seating the bullet a little longer than you now do to get the same jump to the lands.

 

[Dgd6mm]

The burn rate on the lots of powder are different. I had this happen with H1000. You never read of it speeding up, it is always slowing down. You probably have some throat erosion also.

 

[johnnyk]

Just experienced it with my 6.5-284. Been shooting 59gns Retumbo with 140gn A-Max for a while. Velocity averages 3030fps and accuracy was .25 MOA. Switched to the new 140gn ELD-M and noticied the bullet length was a little different. With only changes being bullet, I started load development at 57.0 and proceeded upwards. After verifying the load, I stopped at 58.0gn - velocity and accuracy were identical to original A-Max load. JohnnyK.

 

[elkaholic]

Different lots of powder can definitely cause this, but I think it is more likely, in this case, that you have throat erosion which will definitely lower velocity AND potentially accuracy as well. You might try different powder that you have data for and see if you have the same problem.....Rich