Extreme ES caused by barrel?

[Cookie114]

I've got a TC venture in 243 Win that is giving me fits with ES. Ive ran different powder/bullet/brass/primer combos but this particular rifle has ES of around 150fps(sometimes higher) regardless. Its shoots 1/2moa groups @100y but of course with those ES it would probably string at longer ranges. It will normally start out high and the velocity will decrease with every shot, not always but common. Same powder scale and same chronograph used with diffrent rifles that have low ES. Is there something with the chamber/barrel that could be causing this?

 

[dok7mm]

Possible the barrel is touching stock as it warms up. Something could be loose... Check action screws and scope mounts, then go from there.

 

[ShtrRdy]

When I see high ES I first think of something with the load. But it sounds like you assemble other accurate and low ES ammo.

Are you using new brass?

Would you mind telling us a little more about the components you're using?

 

[Cookie114]

When I see high ES I first think of something with the load. But it sounds like you assemble other accurate and low ES ammo.

Are you using new brass?

Would you mind telling us a little more about the components you're using?

Yes, this is the only rifle I have this issue with. Ive got Nosler brass and Remington brass both new and once fired. Ive ran H4350, superformance and R15 though it with the same results. I ran standard and Mag primers with superformance with no change. Maybe I should try neck sizing only a few pieces of once fired and see what happens🤷‍♂️. I normally bump .002 with a FL die on fired brass but I have a Lee Neck die laying around somewhere i could try.

 

[DJ Fergus]

There was a post a while back with this same sort of thing going on. Can I make a recommendation? Load up a round and shoot it off of a cold bore( 1st shot for that day), record your velocity. Put the rifle up. Go back the next day that you have a chance and fire a round that was loaded exactly as the previous. Record your velocity. Put the gun up for the day. Do these same steps a couple more times. See if your cold bore es across those 3 or 4 days is much less than shooting them all in one sitting. If it is, then that means for some reason your pressure is fluctuating or dropping off with successive shots in one days shooting session. Better yet, do you happen to remember the velocity of your 1st cold bore shot for the same load for 3 or more different days?

 

[ShtrRdy]

Which bullet and seating die are you using?

And you're seeing the large ES with both new brass and fired (in the same rifle) brass?

 

[Barehandlineman11]

I’ve seen this with nosler brass a few times

 

[DJ Fergus]

Yes, this is the only rifle I have this issue with. Ive got Nosler brass and Remington brass both new and once fired. Ive ran H4350, superformance and R15 though it with the same results. I ran standard and Mag primers with superformance with no change. Maybe I should try neck sizing only a few pieces of once fired and see what happens🤷‍♂️. I normally bump .002 with a FL die on fired brass but I have a Lee Neck die laying around somewhere i could try.

What bullet are you shooting?

 

[NATE40]

I've got a TC venture in 243 Win that is giving me fits with ES. Ive ran different powder/bullet/brass/primer combos but this particular rifle has ES of around 150fps(sometimes higher) regardless. Its shoots 1/2moa groups @100y but of course with those ES it would probably string at longer ranges. It will normally start out high and the velocity will decrease with every shot, not always but common. Same powder scale and same chronograph used with diffrent rifles that have low ES. Is there something with the chamber/barrel that could be causing this?

ES speed has much to do with bullet seating and neck tension
Keep your load!! But start at jam +20k then add 3k until you find 2 rifle nodes (tightest groups) together. Then choose a seating depth. Neck tension can play a part also . Less neck tension for long range. More neck tension for hunting just make sure you are getting the exact seating depth and neck tension so everything is the same

 

[whirlwindjml]

Do you trust your chronograph?

 

[Cookie114]

Which bullet and seating die are you using?

And you're seeing the large ES with both new brass and fired (in the same rifle) brass?

Rcbs. Yes both new and fired.

What bullet are you shooting?

Right now 75g hp and 85 sierra bthp but I've shot many through it.

ES speed has much to do with bullet seating and neck tension
Keep your load!! But start at jam +20k then add 3k until you find 2 rifle nodes (tightest groups) together. Then choose a seating depth. Neck tension can play a part also . Less neck tension for long range. More neck tension for hunting just make sure you are getting the exact seating depth and neck tension so everything is the same

This makes sense. Maybe I can get onto something

Do you trust your chronograph?

Yes

 

[aceball]

Chronograph issues. If it produces an honest 1/2" groups @ 100yrds then it's not the load or a barrel problem.

 

[Cookie114]

Chronograph issues. If it produces an honest 1/2" groups @ 100yrds then it's not the load or a barrel problem.

I wish that was it but hard to imagine that when I can shoot other rifles through it the same outing without issues. Unless the small 6mm bullet at those speeds are causing a chronograph issue? Like I said I hope your right. Guess I need to round up another graph to know for sure

 

[Tiny Tim]

Have you used a bore scope on it? How many rounds down the pipe? Have you noticed a great deal of fouling? How often do you clean it? If it progressively slows down shot after shot consistently, I'd look at the barrel.
@DJFergus has a great idea. If you find the barrel is extremely rough, you might consider JB bore Paste or fire lapping with David Tubbs kit. Maybe keep shooting it till it stabilizes, go home and without cleaning, shoot another day and ser if it still does the same thing with repeatable velocities. Just some suggestions